JUM@P '13: Joint Users' Meeting at PSI 2013

Europe/Zurich
Paul Scherrer Institut, Villigen, Switzerland

Paul Scherrer Institut, Villigen, Switzerland

Description
Bi-annual user meeting of the PSI large scale user facilities: SLS, SINQ and SMuS
    • 9:30 AM 10:30 AM
      Registration WHGA - Foyer

      WHGA - Foyer

      Paul Scherrer Institut, Villigen, Switzerland

    • 10:30 AM 12:15 PM
      Plenary session: chair: J. Mesot WHGA/001

      WHGA/001

      Paul Scherrer Institut, Villigen, Switzerland

      • 10:30 AM
        Welcome 15m
        Speaker: Prof. Joel F. Mesot (Paul Scherrer Institut)
      • 10:45 AM
        How Large Research Facilities Can Contribute in Solving Challenges in Energy Research 30m
        Strong efforts in both industry and academia are directed towards energy research, i.e. the generation of energy from new and clean sources as well as generally working towards more sustainable and environmentally friendly processes, in a wide range of applications. New and more knowledge is required on all levels, i.e. fundamental insights in materials and mechanisms as well as societal impact issues. In this lecture we will look at a few different challenges in energy related research at a fundamental level; understanding and improving catalytic processes, new renewable energy processes and battery research. The use of large scale facilities in this field of research can provide unique insights compared to lab-based facilities, e.g. fast detailed structural and electronic information on materials and reactions, while they are functioning. The additional insights obtained using novel technique developments like increased temporal, spatial and energy resolution will be emphasised.
        Speaker: Prof. Moniek Tromp (Technische Universität München, Catalysis Research Center, Chemistry, Characterisation in Catalysis)
      • 11:15 AM
        NIT-2Py 30m
        We present thermodynamic and magnetic properties, as well as muSR spectroscopy results of a new organic magnet which is built from molecules in the nitronyl nitroxide family of free radicals. NIT-2Py exhibits a complex magnetic phase diagram at low temperatures and high magnetic fields. Susceptibility measurements at high temperatures show the paramagnetism of a free spin 1/2 with antiferromagnetic interactions. We saw the onset of bulk magnetic order at 1.3 K, as determined from specific heat Cp measurements. This anomaly in Cp is suppressed by magnetic fields above 3 T. In this field range, the sharp peak in Cp is replaced by a Schottky anomaly pointing to collective switching of all magnetic moments between two distinct levels. At a higher fields of 5 T, we observed a second sharp anomaly indicating a second magnetic phase. Magnetisation curves measured below the ordering temperature show magnetization plateau at half of the saturation value of 1 μB/molecule. In combination with the specific heat results, this behaviour suggests a new quantum spin ground state in NIT-2Py. In order to get a better understanding of the magnetic interactions between the molecules, we carried out electronic structure calculations. MuSR measurements show oscillations in the longitudinal signal in zero field indicative of an internal field below the phase transition. The temperature dependance of this internal field follows a mean field behaviour. This oscillation fits to a two frequencies model indicating two distinct muon sites. Applications of longitudinal fields up to 2 T did not show any longitudinal signal, typical in a Ising system without hard magnetic axes.
        Speaker: Prof. Andrea Bianchi (Université de Montréal)
      • 11:45 AM
        LCLS – The first four years and a look at the future 30m
        With ultrashort and ultrabright x-ray pulses X-ray Free electron lasers provide revolutionary unique new capabilities to study a wide range of phenomena. The Linac Coherent Light Source (LCLS) at SLAC has been the first of such machines delivering x-rays to users in the 280 eV to 11 keV range. LCLS is just about to finish the first four years of operations and we will review some of the most exciting highlights, upgrades as well as some lessons learned. We will also present the planned new capacity and capability as we are moving forward with LCLS II.
        Speaker: Prof. Uwe Bergmann (SLAC National Accelerator Laboratory)
    • 12:15 PM 2:15 PM
      Poster session I and lunch WSLA - Foyer

      WSLA - Foyer

      Paul Scherrer Institut, Villigen, Switzerland

      • 12:15 PM
        4D imaging at TOMCAT 2h
        We present the latest development in 4D microtomography. With a dedicated fast tomographic endstation at the TOMCAT beamline a full set of tomographic images can now be acquired in a fraction of a second with voxel sizes of 1-11 micrometers [1]. The large field of view ensures that statistically relevant volumes can be analyzed [2]. Tomograms at 20 Hz frequency can be achieved. In addition to attenuation contrast, advanced processing of the datasets results in retrieving the phase shift of the X-rays interacting with the sample. In this way the 3D volume reconstructions of noisy projections (exposure time as short as 100 microseconds) show high contrast to noise ratio and can be segmented and labeled to form an input to the quantitative analysis toolbox that was developed for large time series of tomographic datasets (4D data) [3]. To overcome the usual problem of limited collection time of fast tomographic datasets, a detector capable of continuous recording at 8 GB/s was developed. The exploration of the dynamics of many new systems becomes possible with the new data acquisition capabilities.
        Speaker: Rajmund Mokso (Paul Scherrer Institut)
      • 12:15 PM
        A device for immunotheraphy against Alzhaimer's disease : the challenge of measuring amyloid β plaques at TOMCAT beamline 2h
        Alzheimer's disease (AD) is a devastating neurodegenerative disorder causing the most prevalent form of dementia. AD is characterized by a prominent accumulation of protein aggregates in affected regions of the brain called amyloid β plaques (Aβ) that are used as markers for defining and monitoring the pathology. An active role of Aβ on the AD progress was proposed in the past suggesting the clearing of the Aβ as a possible cure for AD. Recently, controversial results have indicated that the Aβ role is predominant in the early stage of the disease. Therefore further studies are necessary toward a definitive AD cure. In the framework of the Commission for Technology and Innovation (CTI), a team composed by researchers from EPFL, Roche and PSI is developing an encapsulated cell device for the passive immunization against Aβ focused on the early clearing of the Aβ. Measuring small changes of Aβ accumulation is a further challenge within the project. At the moment, x-ray differential phase contrast is the only way to measure Aβ at high resolution (5-20 μm) in 3D with high sensitivity. Using the grating interferometer setup developed and available at the TOMCAT beamline it is possible to investigate and disclose the proposed therapy efficacy. In this contribution the capability of the TOMCAT beamline together with the project status and the first results will be presented.
        Speaker: Dr Alberto Astolfo (PSI)
      • 12:15 PM
        Combined XAS-DRIFT cell for the analysis of functional materials 2h
        A spectroscopic cell has been commissioned and tested on solid catalysts at beamline SuperXAS that enables combination of quickEXAFS and DRIFT measurements in a novel geometry in a single experiment. Pt/Al2O3, Pd/Al2O3 and Pd/CZ were tested under pulsed conditions, CO vs. O2. Beside obtaining high quality EXAFS data, IR spectra of adsorbed species both on the support and on the metal nano-particles were obtained in the synchronous measurements, this potentially allowing for the direct comparison with structural information from EXAFS analysis. Further combination with a modulated excitation approach that is achieved by the pulsed experimental conditions enabled to massively enhance the sensitivity of quickEXAFS. Contributions related to adsorbed species, such as Pt-CO, Pt-H and Pd-CO could be isolated in the time-resolved quickEXAFS data.
        Speaker: Dr Davide Ferri (PSI)
      • 12:15 PM
        Controlling satiety v by tailored interfaces 2h
        The overall focus of this study is to utilize food structuring and breakdown pathways to reduce obesity. Fat based emulsions are considered to be a suitable model system not only due to the high acceptance by consumers. Moreover, the textural mouth feeling of fat activates neuronal responses, which implement a short-term control of appetite and eating.
        Speaker: Thomas Geue (Paul Scherrer Institut)
      • 12:15 PM
        Density Profile of Water Confined by Two Ion-exchanged Mica Surfaces 2h
        Two surfaces in contact are found in everyday life. For hydrophilic surfaces in contact, the natural presence of a confined layer of water in the narrow gap between them has important implications for geochemical and biological processes such as swelling of clays and diffusion of water through nanopores [1]. Numerous surface force experiments have been performed on such systems [2]. However, force studies do not provide information on the molecular structure of the confined water. We have adapted a surface force apparatus (SFA) [3] to be used as confinement device X-ray reflectivity (XRR) experiments conducted at the cSAXS (XSA12) beamline of the Swiss Light Source at PSI. A pair of cylinder-shaped muscovite mica membranes were made to approach each other until a flat contact area was formed. We have then performed XRR experiments from the contact area as a function of the momentum transfer q ranging from 0 to 3.5 Å-1. Model dependent fits [4] to the measured reflectivity I(q) allowed us to determine the minimum gap distance and the electron density profile along the confinement direction [5]. After a first set of experiments on water confined between freshly cleave mica membranes, in order to shed light on the effect of the surface ions on the structure of the confined fluid, we exchanged the natural layer of K+ ions present on cleaved mica surfaces with monovalent Rb+ or divalent Sr2+ ions. The ion-exchanged membranes were brought into contact in a nitrogen environment with controlled relative humidity (RH). XRR measurements were then made at 0 and 60 % RH. We observed layered electron density profiles within the gap with the period of layering equal to the hydration shell of the cations. We also determined quantitatively the minimum gap distance between the mica surfaces under the influence of different surface ions (1.82 nm for Rb-exchanged mica at 0% RH and 2.04 nm for Sr-exchanged mica at 0% RH), which increases for higher RHs. References 1. Israelachvili, J.N., Intermolecular and surface forces: revised third edition. 2011: Academic press. 2. Pashley, R., DLVO and hydration forces between mica surfaces in Li+, Na+, K+, and Cs+ electrolyte solutions: A correlation of double-layer and hydration forces with surface cation exchange properties. Journal of Colloid and Interface Science, 1981. 83(2): p. 531-546. 3. Perret, E., et al., Molecular liquid under nanometre confinement: density profiles underlying oscillatory forces. Journal of Physics: Condensed Matter, 2010. 22(23): p. 235102. 4. Perret, E., et al., X-ray reflectivity theory for determining the density profile of a liquid under nanometre confinement. Journal of synchrotron radiation, 2010. 17(4): p. 465-472. 5. Chodankar, S., et al., Density profile of water in nanoslit. EPL (Europhysics Letters), 2012. 99(2): p. 26001.
        Speaker: Mr Shirish Chodankar (Paul Scherrer Institut)
      • 12:15 PM
        Distinction of liquid water and ice based on dual spectrum neutron imaging 2h
        Polymer electrolyte fuel cells (PEFCs) have attracted much attention during the last decade, because of extremely low emissions at very high power densities. However, before its commercialization, PEFC have to prove its durability at ambient conditions, particularly during operation at subfreezing temperatures. As the freezing mechanism inside PEFCs is not fully understood in literature, imaging methods have to be improved to enhance the understanding. In this poster, we would like to present a visualisation method to identify phase transitions of water based on dual spectrum neutron imaging. The attenuation of neutrons passing through a specimen is strongly dependent on the energy spectrum of the beamline. It has been shown [1,2] that the attenuation of water increases with decreasing neutron energy and differences between the frozen and liquid aggregate state can be measured at very low neutron-energy. Unfortunately, in this energy region, the flux is rather low at the cold neutron imaging beamline, ICON [3], of the Paul Scherrer Institut and no significant deviations between liquid and solid phase can be distinguished with the full beam spectrum. Introducing a polycrystalline beryllium filter inside the neutron beam, the low energy part of the spectrum is emphasized and phase transitions between liquid water and ice are more distinctive. As the water distribution may change over time, consecutive images are captured with and without filter (dual spectrum). In the first part, we would like to present results based on a cylindrical water column. Those measurements provide reference values for the attenuation coefficient at different aggregate states. As expected, due to the decreasing attenuation of water with increasing energy [1,2], differences between the liquid and frozen aggregate state were identified. Despite the fact that the change in attenuation between the aggregate states is only 1.8%, phase transitions were clearly identified based on dual spectrum neutron imaging. Subsequently, this imaging setup has been applied to a fuel cell. Surprisingly, the measured ratios of attenuation (with and without filter) were not consistent with the reference water column measurements. Nevertheless, phase transitions between liquid water and ice in the fuel cell can still be identified with this method. [1] L. Torres, J.R. Granada, J.J. Blostein, Nucl. Instrum. Meth. B 251, 304 (2006) [2] L. Josic, E.H. Lehmann, D. Mannes, N. Kardjilov, A. Hilger, Nucl. Instrum. Meth. A 670, 68 (2012) [3] A.P. Kaestner, S. Hartmann, G. Kühne, G. Frei, C. Grünzweig, L. Josic, F. Schmid, E.H. Lehmann, Nucl. Instr. Meth. A 659, 387 (2011) [4] Y. Ishikawa, H. Hamada, M. Uehara, M. Shiozawa, J. Power Sources 179, 547 (2008) [5] P. Oberholzer, P. Boillat, R. Siegrist, R. Perego, A. Kaestner, E. Lehmann, G.G. Scherer, A. Wokaun, J. Electrochem. Soc. 159, B235 (2012)
        Speaker: Mr Johannes Biesdorf (Paul Scherrer Institute)
      • 12:15 PM
        Estimation of the Number of Acini during Postnatal Rat Lung Development 2h
        Rationale: The pulmonary airways are subdivided into conducting and gas-exchanging airways. The small tree of gas-exchanging airways, which is fed by the most distal conducting airway, represents an acinus. Until now a so called dissector (five consecutive sections) was used to count lung acini. We developed a faster method and determined the number of acini throughout rat lung development. Methods: Right middle rat lung lobes were obtained (postnatal days 4-60), stained with heavy metals or critical point dried, and scanned at TOMCAT beamline or with a micro CT (Skyscan 1172), respectively. The acini were counted in the re¬sulting 3D-stacks of images by scrolling through them and counting every acinus per lobe using morphological criteria (thickness of epithelium and appearance of alveoli) for the detection of the transitory bronchioles (entrance of an acinus). Results: Our method appeared to be reliable and relatively fast. Between postnatal days 4-60 the number of acini per lung stayed constant (5747 +/-518, p < 0.1). A mean airspace acinar volume of 0.053, 0.142, 0.270, 0.302, and 0.910 µl were estimated at postnatal days 4, 10, 21, 36, and 60, respectively. Conclusion: We conclude that the acini are laid down latest at the end of the saccular stage (before postnatal day 4) and that the developmental increase of the lung volume is achieved by an increase of the acinar volume and not by an increase of the number of acini.
        Speakers: Dr David Haberthür (TOMCAT, Swiss Light Source, Paul Scherrer Institut) , Mr Sébastien Barré (Institute of Anatomy, Bern)
      • 12:15 PM
        Form factor of pNIPAM microgels in overpacked states 2h
        We study the form factor of soft, thermoresponsive microgels based on poly(N- isopropylacrylamide) at high effective volume fractions, where the particles must shrink or overlap to fit into the available space. Small-angle neutron scattering with contrast matching techniques is used to determine the particle form factor. The apparent particle size is found to be constant up to a volume fraction roughly between random close packing and space filling. Beyond this point, the particle size decreases with increasing particle concentration; this decrease approximately cor- responds to what is expected in the absence of microgel interpenetration. Noteworthy, we do not observe a glass transition, as the suspensions remain liquid-like even above space filling. In addition, shear thinning profiles do not map onto hard sphere behavior, confirming that particle softness is responsible for our observations.
        Speaker: Dr Urs Gasser Gasser (Laboratory for Neutron Scattering, Paul Scherrer Institut)
      • 12:15 PM
        Hygro-mechanical behaviour of wood investigated by Synchrotron radiation X-ray Tomographic Microscope. 2h
        Wood exposed to air at different relative humidities (RH) swells and shrinks due to moisture content changes. High-resolution phase-contrast X-Ray Tomography at the TOMCAT beamline of the Swiss Light Source, PSI Villigen, is well suited to capturing micro and nano structures of wood and is used to investigate the hygro-mechanical properties of spruce wood (Picea Abies) at cellular and sub-cellular scales. In our previous work, we investigated affine deformations to quantify the global strains along the three orthotropic directions of wood (tangential, radial and longitudinal) but we could not detect local deformations. For this reason, we are currently working on a method to detect and quantify these local deformations using a non-rigid registration model. This type of registration employs a Free-Form Deformation (FFD) model based on B-splines. With the FFD model, an object is deformed by manipulating an underlying mesh of control points in order to produce a transformation which allows the contribution of the local deformations to the global strains to be quantified. In particular, we observed that: - The anisotropy of swelling increases with increasing wood porosity, with a tangential/radial swelling ratio between 1 and 3.2 for porosities between 45% and 78%. - The swelling anisotropy in low porosity wood could be due to the restraining behavior of rays, which seem to be the cause of local deformations at the cell wall level. - Local deformations occur at the transition zone between high porosity and low porosity layers in wood, with higher influence in the more porous layer. - The B-spline algorithm recovers both large deformations occurring at the wood edges during free swelling/shrinkage and the collapse of the wood cells due to swelling under mechanical restraint. - The refined B-spline grid identified localized strains at the cell corners and close to some ultrastructure features of the wood cell wall, named bordered pits.
        Speaker: Mrs Alessandra Patera (EMPA/ETH)
      • 12:15 PM
        In-vivo study of lung physiology with sub-second X-ray tomographic microscopy 2h
        Lung failure represents the leading cause of morbidity and mortality worldwide and is the fourth leading cause of death in Switzerland [1,2]. Despite the fact that recent decades have brought forth a huge clinical progress in treating lung injuries, including e.g. the immediate postnatal treatment of very preterm infants, two hypotheses on the structural alterations in the gas-exchange area during breathing are still under debate: a heterogeneous distention pattern of different lung areas and a homogeneous cyclic opening-and-collapse of all alveoli. Current techniques for performing lung imaging with small animal models at synchrotrons [3,4], however, were unsuccessful in answering these questions either by only applying 2D imaging or due to insufficient temporal and/or spatial resolution. We present our recently developed protocol for 3D in-vivo lung imaging, realized by a new ultra-fast endstation with a novel data acquisition and post-processing paradigm [6]. Results from pilot experiments conducted at the TOMCAT beamline with ex-vivo mouse samples, where tomograms are acquired only in the fraction of a second, are presented. We describe our approach to image formation and biological interpretation therein, aiming at optimal image quality in terms of contrast, resolution and deposited radiation dose. Finally, the first biological application of the technique is demonstrated, namely the study of tissue overextension in ventilated lungs as a possible cause to various lung disfunctions such as the ventilator-induced lung injury (VILI). [1] B.R. Celli, W. MacNee, A. Agusti et al. (ATS/ERS Task Force), Eur. Respir. J. 23 , 932–946 (2004). [2] Statistik Schweiz, “Sterblichkeit, Todesursachen”, http://www.bfs.admin.ch/ . [3] R. A. Lewis, N. Yagi, M. J. Kitchen et al., Phys. Med. Biol. 50 , 5031 (2005). [4] S. Bayat, L. Porra, H. Suhonen et al., Eur. J. Radiol. 68 , S78 (2008). [5] K. Mader, R. Mokso, C. Raufaste et al., Colloid. Surface A 415 , 230 (2012). [6] G. Lovric, S.F. Barré, J.C. Schittny et al., J. Appl. Crystallogr. 46 (4), 1 (2013).
        Speaker: Goran Lovric (Paul Scherrer Institute)
      • 12:15 PM
        Localization and Quantification of Phosphoric Acid in HT-PEFCs by X-Ray Tomographic Microscopy 2h
        Localization and Quantification of Phosphoric Acid in HT-PEFCs by X-Ray Tomographic Microscopy Sebastian H. Eberhardt, F. Marone, Felix N. Büchi, Thomas J. Schmidt Paul Scherrer Institute CH-5232 Villigen PSI Tel.: +41-56-310-2541 sebastian.eberhardt@psi.ch Abstract High temperature polymer electrolyte fuel cells (HT-PEFCs) exhibit an increased CO-tolerance of up to 2% in the anode feed [1] due to faster CO-oxidation kinetics at operating temperatures of 160-190°C. The high CO tolerance, compared to low temperature PEFCs, is a significant system advantage of HT-PEFCs allowing to use H2 rich reformate gas without expensive clean-up. This gives rise to a thermodynamically favorable process of combined heat and power applications. In order to sustain the high temperatures specially designed membranes based on a polybenzimidazole backbone doped with phosphoric acid (PA) as an electrolyte [2] are used. Acid evaporation and redistribution is exclusive to HT-PEFCs and its in-situ characterization is of importance to better understand the underlying mechanisms. Therefore, x-ray tomographic microscopy (XTM) has been applied to visualize the acid inventory and movement in the GDL for correlation with performance. The ability to quantify the amount of phosphoric acid as well as to distinguish between different concentrations are key factors for evaluating performance degradation. XTM imaging is conducted at the TOMCAT beamline of the Swiss Light Source. Segmentation strategies of gray scale images and first results of PA calibration experiments will be presented. [1] T.J. Schmidt, et al. (2006) Durability and reliability in high temperature reformed hydrogen PEFCs ECS Transactions, 3, 861-869. [2] T.J. Schmidt, (2009) High Temperature Polymer Electrolyte Fuel Cells: Durability Insights in Polymer Electrolyte Fuel Cell Durability, F.N. Büchi, M. Inaba, T.J. Schmidt (eds) (pp. 199-221). Springer, New York. Financial support from BASF SE is greatly acknowledged.
        Speaker: Mr Sebastian Eberhardt (PSI Electrochemistry Laboratory)
      • 12:15 PM
        Micron Resolution Imaging with MÖNCH 2h
        MÖNCH is a charge integrating readout ASIC (Application Specific Integrated Circuit) prototype for 25 micron pixel pitch silicon sensors developed at PSI, which allows new imaging applications in the field of micron resolution and spectral imaging. It is a fully functional, small scale prototype of 4x4mm2, containing an array of 160x160 pixels with a low power consumption of 3-5 μW/pixel. The small pixel size of this system leads to charge sharing between pixels, which can be used to gain additional information about photon absorption position and photon energy. To capture these information high frame rates and therefore high data rates are needed. We show the design of the read out system, which is capable of online pre-compression of the data to allow continuous storage. We present results of experiments with a comparable strip detector (adapted GOTTHARD system) showing that with the aid of single photon interpolation algorithms micron resolution is achievable. We will also show the energy discrimination capabilities of such a system. Additionally, we present measurements with a resolution phantom and the MÖNCH pixel detector to further investigate the imaging capabilities concerning total exposure time.
        Speaker: Mr Sebastian Cartier (Paul Scherrer Institute)
      • 12:15 PM
        Nano-tomography at the cSAXS beamline 2h
        Imaging specimens in three-dimensions with a resolution of 100 nm or below is not an easy task, especially when representative volume elements of several tens of micrometers are required. In general, hard x-rays in the multi-keV range are needed in order to reach a depth of focus larger than the entire specimen. However, the fabrication of efficient x-ray lenses at these energies is a challenging task. In addition, the absorption contrast at these high energies is in most cases very weak, making phase contrast imaging methods essential. One of the proposed methods to overcome this issue is ptychography, which uses coherent diffraction patterns recorded in the far field in order to reconstruct the complex-valued transmissivity of the specimen. Thereby, it can provide both absorption and phase contrast images with high resolution, which is not limited by any magnifying lens [1]. At the cSAXS beamline we routinely use this technique in combination with tomography to obtain three-dimensional density maps of specimens which are several tens of micrometers in size. Here we present the ptychographic tomography technique in detail and our latest developments in image processing and tomography reconstruction. We further report on the status of the OMNY project [3], which will provide an instrument for imaging specimens at cryogenic temperatures with a resolution down to about 10 nm in three dimensions. [1] H. M. L. Faulkner and J. M. Rodenburg, Phys. Rev. Lett 93 (2004) 023903. [2] M. Dierolf et al., Nature 467 (2010) 436-439. [3] M. Holler et al., Rev. Sci. Instrum. 83 (2012) 073703.
        Speaker: Dr Manuel Guizar-Sicairos (Paul Scherrer Institut)
      • 12:15 PM
        Numerical simulation of phase-sensitive X-ray imaging by combining wave-optics and Monte Carlo methods 2h
        The high sensitivity towards electron density variations makes phase-sensitive X-ray imaging well suited for the imaging of soft tissue matter. A recently established phase-sensitive imaging method is grating interferometry (GI) which has the advantage of producing three complementary types of contrast: absorption, phase and dark-field [1]. However there are still open questions about the image formation process, for example details of the dark-field contrast formation process are not yet fully understood. We present a numerical simulations framework for the investigation of these contrast mechanisms. Since for a realistic simulation of phase-sensitive X-ray imaging both particle- and wave-like properties of X-rays have to be taken into account, we developed a framework that combines Monte Carlo (MC) methods with wave-optics. The framework was validated through comparisons between simulations and measurements obtained at TOMCAT beamline [2]. The results show that the combination of MC with wave-optics was successful and the comparisons showed good agreement between simulations and experimental results, establishing the framework as a reliable method for modelling GI. The simulation framework can now be used for detailed investigations of the phase contrast formation process and is, due to the inclusion of refraction as well as Compton and Rayleigh scattering, particularly suited to study the scattering contribution of such processes. References [1] T. Weitkamp et al, Opt. Express 2005; 13(16):6296 [2] S. McDonald et al, J. Synchrotron Rad. 2009 16, 562
        Speaker: Silvia Peter (Paul Scherrer Institut)
      • 12:15 PM
        OmmatiDiag - A mosaiced detector for the GlobalDiagnostiX radiology project 2h
        Approximately 4 billion people, about two-thirds of the world population do not have access to diagnostic imaging. First world countries try to solve this problem by donating old radiological equipment to hospitals in need. But, according to the WHO, about 70% of the more complex devices do not function when they reach their destination in developing countries [1]. As part of the GlobalDiagnostiX alliance, we are challenging existing systems for generating and detecting x-rays for the medical domain. A mosaiced setup of independent detector modules (each containing optics and a CMOS detector, thus an independent eye, much like the *Ommati*dias in insect eyes) images a scintillator converting the incoming x-rays to visible light. Image merging and processing will result in a standard-compliant *Diag*nostic image. The performant, modular, cost-efficient and standard-compliant x-ray imaging device based on frugal engineering approaches is an integral part of the GlobalDiagnostiX radiology device. The combined effort of the alliance will culminate in an appropriate diagnostic x-ray imaging system, which is adapted to the context of resource-poor settings and can be sold to district hospitals in developing countries for an affordable price. [1] First WHO Global Forum on Medical Devices: context, outcomes, and future actions. http://www.who.int/medical_devices/gfmd_report_final.pdf
        Speaker: Dr David Haberthür (TOMCAT, Swiss Light Source, Paul Scherrer Institut)
      • 12:15 PM
        Phase contrast mammography: A novel tool for breast cancer screening and diagnosis 2h
        Phase contrast mammography using grating interferometer is a promising alternative to current mammography. Preserving the conventional absorption contrast, this novel technology also yields differential phase contrast and small-angle scattering contrast simultaneously. Our research team imaged mastectomy breast samples from 33 patients using this technology and a multicenter, international reader study is performed aiming at the evaluation of its clinical relevance. The results show that phase contrast mammography images have a better image quality with respect to sharpness (p<0.001), lesions delineation (p<0.001), visibility of microcalcifications (p<0.001) and additional clinically relevant information (p<0.001), resulting in a general improvement in image quality. Additionally, by combining the three complementary signals, quantitative information can be obtained to further improve screening and diagnosis. We proposed a method which is able to discern microcalcification types noninvasively as well as a method for quantitative volumetric breast density estimation. The first one provides a possible way to discern the benign and malignant breast lesions in the imaging stage thereby reducing unnecessary biopsy rate and the second yields more accurate estimation about breast density, which is a strong indicator of breast cancer risk, overcoming the subjectivity of the methods in daily routines.
        Speaker: Dr Zhentian Wang (PSI)
      • 12:15 PM
        Phase-contrast imaging at 100 keV on a conventional X-ray tube 2h
        This projects demonstrates a Talbot-Lau interferometer with edge-on illumination [1] on a conventional high-energy source. The edge-on configuration can achieve the large aspect ratio needed to stop the high-energy radiation in the absorption gratings. The fabrication of such gratings for a conventional face-on geometry would not be possible with the current technology. An analysis of the performance of the system and images acquired at a tube voltage of 160 kVp and an interferometer design energy of 100 keV are shown, thus bringing the technique in the range of medical computed tomography as well as material science and security applications.
        Speaker: Matteo Abis
      • 12:15 PM
        Proton dynamics of triethylammonium triflate probed by neutrons 2h
        Protic ionic liquids are an important group of molten salts, which can form a hydrogen-bond network with proton-donor and proton-acceptor sites. The knowledge about their proton transport properties is crucial for a variety of electrochemical applications. Neutron scattering techniques are sensitive to the presence of hydrogen atoms and thus can provide useful information about proton dynamics in a sample. Here we report both elastic scans measurements and QENS-experiments on a protic ionic liquid (triethylammonium triflate, [NH(C2H5)3][CF3SO3]) performed on the IN10 and IN5 spectrometers at ILL and FOCUS at SINQ on different time-scales by choosing the corresponding linewidth of the resolution function. The temperature range considered during the experiments (2-440 K) encompasses the regions where the sample undergoes several phase transitions with the corresponding changes in the global and localized dynamics of the cation. At higher temperatures all the following types of motions contribute to the quasielastic broadening: long-range ion diffusion, diffusion in a cage formed by the neighboring particles, ethyl groups librations, etc.; they are gradually switched off with the temperature decrease. In order to separate the motions of the cation as a whole and localized dynamics of the side chains a sample with the deuterated ethyl-groups was investigated as well.
        Speaker: Ms Tatsiana Burankova (Saarland University, Paul Scherrer Institut)
      • 12:15 PM
        Ptychographic X-ray nanotomography: a new insight into the most primitive vertebrate skeleton 2h
        Conodonts are an extinct group animal that have been suggested as the first vertebrates to possess a mineralized skeleton manifest as an oropharyngeal feeding apparatus. As such, the conodont skeleton is of great significance because of the insights it provides concerning about the biology and function of the most primitive vertebrate skeleton. However, the origin of this skeleton, the histological and developmental differences between the different groups of conodonts (proto-, para- and euconodonts), even their relationship with the rest of the vertebrates, remain controversial. It has been argued that the most primitive vertebrate skeleton occurs in the extinct euconodonts. However, the origin of the euconodont skeleton, and its relationship to the proto- and paraconodonts, remain under debate. Morphological, histological and stratigraphical data indicate that euconodonts evolved from paraconodonts, while the relationship with protoconodonts is unclear. A nanoscale characterization of the skeletal tissues in these groups will settle debate and finally resolve this 150 years old scientific controversy. The preliminary results using ptychographic nanotomography on the cSAXS beamline confirm the potential of this technique to characterize fully the nanostructure of the conodont tissues. To reach our goals we scanned different regions of interest within 5 specimens of the earliest representatives of conodonts: Phakelodus (a protoconodont), Furnishina (a paraconodont), Procondontus and Teriodontus (euconodont), as well as chaetognaths spines of Sagitta sp. (a proposed relative of the protoconodonts). The nanometrical resolution, with a voxel size of 0.0438 microns, showed subtle detail in the Calcium Phosphate material from which the elements are comprised, facilitating the recognition of significant small vacuities, growth lines, and tissue layers of differing density. These preliminary result from ptychographic nanotomography permit a detailed characterisation of the physical structure of proto-, para- and euconodont elements which will help us to test the hypothesis of relationships between paraconodonts and euconodonts, and the homology or analogy of conodont and vertebrate skeletal tissues, providing a direct insight into the evolutionary origin of the vertebrate skeleton.
        Speakers: Dr Carlos Martínez Pérez (University of Bristol, School of Earth Sciences) , Dr Manuel Guizar-Sicairos (Paul Scherrer Institut)
      • 12:15 PM
        Quantitative assessment of bone’s ultrastructural orientation by a novel 3D scanning SAXS method 2h
        The arrangement and orientation of the ultrastructure plays an important role in the mechanical properties of inhomogeneous and anisotropic materials, such as polymers, wood, or bone. In this study, a novel method is presented, which allows deriving the three-dimensional (3D) orientation of the material’s ultrastructure in a quantitative and spatially resolved manner. The proposed 3D scanning small-angle X-ray scattering (3D scanning SAXS) method was applied to a section of a human vertebral trabecular bone specimen. A micro-focus X-ray beam was used to raster scan the sample for different rotation angles that covered almost the full 360o range, excluding a small angular range, where the bone section was practically parallel to the X-ray beam. A mathematical framework was developed to describe the relation between the two-dimensional (2D) information regarding bone’s ultrastructural orientation, which is retrieved from the X-ray diffraction patterns for the different rotation angles, and the local 3D orientation of the bone ultrastructure. This allowed deriving the local 3D orientation of the bone ultrastructure with high certainty, by fitting the theoretical model to the experimental data (mean and median coefficient of determination equal to 0.94 and 0.99, respectively). The bone’s ultrastructural orientation has been visualized by a 3D orientation map using vector fields, which revealed links between trabecular bone microarchitecture and local ultrastructure. Moreover, the 3D orientation maps may help to quantify and understand structure-function relationships linking bone ultrastructure and bone mechanics. Finally, the proposed 3D scanning SAXS method can also be used in other research fields such as material science, to derive the 3D orientation of ultrastructural material components on a local level.
        Speaker: Mr Marios Georgiadis (ETH Zurich)
      • 12:15 PM
        Quantitative Interpretation of Ultra-Small Angle X-Ray Scattering in Grating Interferometry 2h
        Grating interferometry (GI) is a well established phase sensitive X-ray imaging technique providing access to three complementary contrasts: absorption, differential phase and dark-field. It was recently demonstrated that the local unresolved distributions of scattering angles of the sample can be retrieved with an appropriate deconvolution procedure [1]. The three first moments of the retrieved scattering distributions correspond to the traditional contrasts, hence this method can also be considered as an alternative analysis procedure. Moreover, the retrieval of the scattering distributions allows higher moment analysis and therefore access to a large number of possibly complementary contrasts. However, the quantitative interpretation of the obtained scattering distributions remains an open question. The purpose of this work was to establish a connection between the retrieved scattering distributions and the physical subpixel structure of the sample. This was achieved by performing a correlation analysis between the retrieved signal and the known underlying structure of artificial samples. It was furthermore demonstrated that the higher moment contrasts can provide additional information about the subpixel structure of the sample. Finally, the possibility of using the new analysis method as an alternative to the standard procedure was investigated. A thorough comparison indicated that the new approach preformed better in terms of CNR for both differential-phase contrast and dark-field imaging. [1] P. Modregger, F. Scattarella, B.R. Pinzer, C. David, R. Bellotti, and M. Stampanoni, Phys. Rev. Lett. 108, 048101 (2012).
        Speaker: Matias Kagias (Paul Scherrer Institut)
      • 12:15 PM
        Reconstruction algorithms for under-constrained tomographic datasets 2h
        This project is aimed at developing reconstruction algorithms optimized for tomographic datasets consisting of a low number of projections. In the tomographic imaging, this kind of situation occurs, for example, when the speed of the scan or the dose delivered to the biological specimens is a major concern. Conventional tomographic methods, like the filtered back projection (FBP) or algebraic techniques (ART, SIRT, SART), do not represent the ideal solutions to guarantee clean and faithful reconstructions of the image from a limited number of noisy projections. Our research is, now, dealing with the implementations of an iterative method, called Equally Sloped Tomography, and of an iterative version of GRIDREC, which represents an in-house developed Fourier method. These two iterative techniques are particularly suited to perform reconstructions starting from under-constrained tomographic datasets, since they facilitate the inclusion of a priori knowledge of the sample as well as of denoising routines to keep noise under control. A particular focus lies on in-vivo applications, where dose minimization to the specimen is mandatory, but image quality should be only marginally compromised.
        Speaker: Filippo Arcadu (Paul Scherrer Institut)
      • 12:15 PM
        Separation of collective and single-particle dynamics in a pyridinium-based Ionic liquid by means of polarized neutrons 2h
        The analysis of QENS-data measured on hydrogen-rich organic samples is usually started with the assumption that the incoherent signal from hydrogen determines the total scattering intensity, while the coherent contribution is considered to be negligible. On the other hand the static structure factor of many ionic liquids features so-called pre-peaks in the Q-range accessible normally by QENS; and thus this assumption for such kinds of samples is questionable. Here we report experiments on separation of collective and single-particle contributions of the total scattering intensity of [BuPy][Tf2N] (1-butylpyridinum bis(trifluoromethylsulfonyl)imide). The intensity of the coherent part, which describes collective dynamics, follows the static structure factor of the totally deuterated sample measured on the diffractometer HRPT at the Swiss spallation source SINQ. The quasielastic broadening of the coherent contribution corresponds to a slow collective motion on the timescale of several picoseconds. The incoherent intensity decreases monotonously with Q and can be characterized by two processes: a slow motion (of the whole cation), which is diffusive in nature and faster localized dynamics, associated with chain and ring librations.
        Speaker: Ms Tatsiana Burankova (Saarland University, Paul Scherrer Institut)
      • 12:15 PM
        Setup for time-resolved XAS experiments with microsecond resolution. Application to hydrogen-evolving photocatalysts 2h
        A new setup for time-resolved X-ray absorption measurements in the microsecond time range has been developed at SuperXAS beamline of SLS. It consists of the nanosecond laser (~1W average power, 447 nm or 671 nm wavelength, 5-50 kHz repetition rate), detection system based on avalanche photo diodes that is optimized to measure signals of dilute samples (with concentration ~1mM) and data acquisition system that allows to record a full kinetic information (arrival time of all fluorescent X-ray photons relative to the laser pulse). The method has been applied to investigate intermediate state of multicomponent photocatalytic system that evolves hydrogen. Transient spectra corresponding to the intermediate states of Co-based catalyst cobaloxime has been recoded and formation of Co(I) intermediate has been observed. We have not observed any signatures of the second reaction pathway proposed in the literature that corresponds to the Co(II) oxidation. The structure of Co(I) intermediate has been clarified on the basis of combination of transient XANES fitting and DFT calculations.
        Speaker: Grigory Smolentsev (Paul Scherrer Institut)
      • 12:15 PM
        Study of Ion Beam Mixing of Te/In and Se/in systems by Cascade Collisional Mixing Model 2h
        Ion Beam Mixing at room temperature of Te/In and Se/In bilayer systems induced by 400 KeV Ar+ ions from Jordan Van De Graaff Accelerator with fluences ranging from 1.11x10^14 - 7x10^15 ions/cm2 for Te/In system and 1.35x10^14 - 2.3x10^16 ions/cm2 for Se/In system. The systems are studied by means of AC electrical resistivity measurement, which shows higher mixing efficiency of Se/In system than Te/In system, and by 2 MeV He+ backscattering spectrometry, which shows the width of intermixed layers are 100 nm and 50 nm for Se/In and Te/In respectively. Ion Beam Mixing for these systems are studied theoretically by cascade collisional mixing "Haff and Switkowski" model , the nuclear stopping powers are calculated by TRIM computer code. The diffusion rate is calculated for the systems Te/In and Se/In, which showed that the diffusion rate and mixed layer for the system Se/In is greater than that of Te/In, which agree with experimental results. The theoretical study is a tool and indication to determine the efficiency of mixing between upper and lower layers before preparation and irradiation of samples, which provide the effort and money.
        Speaker: Dr Buthaina Al-Qaisi (Iraqi)
      • 12:15 PM
        Temperature-controlled flow-through cells for combined UV-Vis/SAXS measurements 2h
        New flow-through cells for simultaneous UV-Vis/SAXS measurements of liquid samples are designed. For concentration or pH-dependent experiments, multiple sample solutions can be injected. A quick and precise temperature control of the sample in the range from 0 to 80 °C is foreseen. The cell will be compatible with an on-axis microscope, facilitating precise sample positioning and for observing bubble formation. SAXS can be measured through virtually scatterless windows. UV-Vis spectra can be collected along the flow channel. The pathlength of can be varied according to the absorption by the sample. The design aims at enabling reliable user-friendly measurements both in static and in continuous-flow mode, even for low scattering liquid samples. Millisecond time resolution can be realized fast readout of X ray and UV-Vis detectors. Faster dynamics can be investigated as a function of sample delay. The combined spectroscopic and SAXS approach will be offered to users at the cSAXS beamline at the Swiss Light Source and shall be applied in investigations, for which only minute sample volumes are available, and for characterizing dynamical processes in biological and soft-matter systems.
        Speaker: Mr Jun Han (Postdoc)
      • 12:15 PM
        The new x-ray phase contrast endstation at TOMCAT 2h
        Grating interferometry (GI) constitutes a recently established phase contrast x-ray imaging technique that provides a particular high sensitivity towards density variations in the sample. For this reason, GI is especially suitable for imaging subtle differences in soft tissues, which resulted in an ever increasing interest from the biomedical researchers. Until recently, the experimental implementation of GI at TOMCAT was shared with different setups. Now, TOMCAT offers an endstation that is dedicated to phase-sensitive x-ray imaging with GI. The new setup offers significant advantages to the user community. First, the setup time is severely reduced allowing for a more effective use of beamtime. Second, the longer source to sample distance implies a high sensitivity and a larger the field of view. Third, the new design allows for more flexibility with respect to changing imaging parameters. In addition to the new experimental setup, the analysis pipeline was considerably optimized regarding reconstruction time (200s for a 2000x1000x1200 pixel data set) as well as artifact reduction. We will show the significant improvements of imaging conditions as well as experimental examples from our users and collaborators such as visualising amyloid plaque deposition in the mouse brain, monitoring of tissue degradation in an artificial heart valve and imaging arteriosclerosis in mouse models.
        Speaker: Dr Peter Modregger (Swiss Light Source, Paul Scherrer Institut, Switzerland)
      • 12:15 PM
        Time-resolved (4D) in situ x-ray tomographic microscopy at TOMCAT: Understanding the dynamics of materials during elevated temperature processes 2h
        Non-destructive synchrotron-based x-ray tomographic microscopy is ideal for studying various materials systems in three and four dimensions, and the TOMCAT beamline of the Swiss Light Source is one of the premier beamlines in the world for such experiments. Spatial resolution ranges from 1-10 µm with fields-of-view from 1-22 mm, and temporal resolution is as fast as 0.1 s for full 3D data acquisition. Contrast varies from standard absorption, typically used in metal and composite systems, to propagation- and gratings-based phase contrast, predominantly used for biological and other traditionally low-contrast materials. The efficient image-processing pipeline provides a full 3D reconstruction within seconds, making visualization close to real time. To exploit these state-of-the-art capabilities, a dedicated laser-based heating system has been developed to explore the dynamics of materials at elevated temperatures. I will summarize these capabilities at TOMCAT and provide examples of its versatility and suitability for various materials systems. This will include a specific focus on understanding recent novel results in 4D directional solidification of dendritic microstructures in metals systems and mimicking volcanic processes in geomaterials.
        Speaker: Julie Louise Fife (Paul Scherrer Institut)
      • 12:15 PM
        Transient formation of bcc crystals in suspensions of pNIPAM-based microgels 2h
        We present a small angle X-ray scattering study of crystals formed by temperature-sensitive, swollen microgel particles consisting of poly(N-isopropylacrylamide) co-polymerized with acrylic acid and 5 mol% of cross-linker. As for hard spheres, the random hexagonal close packed structure is predominant during crystal growth and slowly transforms towards the face-centered cubic structure. However, a transient phase of body-centered cubic crystal is observed in an intermediate range of effective volume fractions. We estimate that the studied suspensions are close to a transition from fcc to bcc structure that can be understood by the tendency of the system to maximize excluded volume and minimize the contact area between the particles.
        Speaker: Dr Urs Gasser Gasser (Laboratory for Neutron Scattering, Paul Scherrer Institut)
      • 12:15 PM
        Ultrafast pump-probe X-ray spectroscopy and scattering at SwissFEL 2h
        With their unique combination of high per-pulse X-ray flux and femtosecond pulse durations, hard X-ray free electron lasers are an almost ideal source for time-resolved structural experiments. The SwissFEL, which is currently under construction at PSI, will be capable of generating femtosecond hard x-rays pulses in the photon energy range of 2-12 keV, with a planned emphasis on performing femtosecond pump-probe measurements. SwissFEL will take advantage of the significant local expertise at PSI in time-resolved X-ray measurements, X-ray spectrometer development, X-ray detector development and energy research. Experimental Station A (ESA) of the SwissFEL will focus on probing the ultrafast dynamics of systems in solution using a combination of X-ray spectroscopy and scattering. The primary goal of ESA will to enable users to perform X-ray absorption (XAS) and emission (XES/RIXS) spectroscopy pump-probe experiments with a focus on the 2-5 keV energy range with <50 fs time resolution (FWHM) using a range of excitation wavelengths (UV to IR). ESA will also be capable of using advanced methods for the injection of aerosol particles and sub-micron protein crystals. This poster will provide an overview of the techniques we expect to have available at ESA and will present a prototypical ‘ESA experiment’ which uses a combination of femtosecond X-ray diffraction, scattering, and spectroscopy to investigate the electronic and structural dynamics in photoexcited titania (TiO2) on the very shortest of timescales.
        Speaker: Dr Christopher Milne (Paul Scherrer Institut)
      • 12:15 PM
        Unraveling biological and physical processes with 3D imaging and quantification 2h
        3D tomography has enabled the probing and imaging of biological processes at previously unachievable temporal and spatial resolutions[1]. At these scales, many types of samples have tens of thousands of substructures with complicated patterns of spatial positioning, orientation, and shape. An examination of these structures provides insight into the underlying processes which drive growth, development, and mechanical behavior. In bone tissues the network of small cells called osteocytes, reflect the development course of the bone with more and less organized regions corresponding to newer and older bone respectively [2]. Furthermore as the primary mechanosensors of the bone their spatial positioning and distribution is a proxy for the mechanical sensitivity of the bone tissue. On a finer scale, small processes running in tunnels called canaliculi connect the osteocytes together and enable communication, nutrition, and waste removal. The connectivity of the network, while studied on the scale of dozens of cells, is crucial for understanding pathologies in bone which are known to occur when the intercellular signaling is suppressed. Recent improvements in flux and image quality have allowed even these nanometer scale structures to be visualized in the context of the entire bone. At the TOMCAT beamline, we have developed a scalable framework [3] for characterizing these complicated structures and reliably condensing millions of voxels into useful quantitative results. Utilizing the cluster computing resources at PSI, the tools developed, while not yet real-time, enable rapid data exploration and preliminary analysis within the timeframe of a beamtime. The framework is easily adaptable to a wide variety of sample types and analyses ranging from egg-shells to ice-cream and even rheological characterizations of foam and volcanic rock. [1] Mokso R, Marone F, Stampanoni M. Real-Time Tomography at the Swiss Light Source. AIP Conf. Proc. SRI2009, 2009. [2] Mader K., Schneider P., Müller R., Stampanoni M. 2013. A Quantitative Framework for the 3D Characterization of the Osteocyte Lacunar System, Bone (Accepted) [3] Mader K, Mokso R, Raufaste C. Quantitative 3D Characterization of Cellular Materials: Segmentation and Morphology of Foam. Colloids and Surfaces A: … 2012;415:230–238. doi:10.1016/j.colsurfa.2012.09.007
        Speaker: Mr Kevin Mader (Paul Scherrer Institute)
      • 12:15 PM
        Visualization and stereological characterization of individual rat lung acini by high-resolution X-ray tomographic microscopy 2h
        The difficulty of characterizing individual respiratory functional units of the lung from two-dimensional physical sections leads to a limited knowledge about biological parameters like volume and surface of these so-called acini. The three-dimensional architecture of the acini has a strong influence on ventilation and particle deposition. We developed a method to semi-automatically extract individual acini from rat lungs lungs imaged by high-resolution synchrotron radiation based X-ray tomographic microscopy [1] and estimated their volume, surface area and number of alveoli. 43 Rat acini were isolated by semiautomatically closing the airways at the transition from conducting to gas-exchanging airways. We estimated a mean internal acinar volume of 1.148 cubic mm, a mean acinar surface area of 73.9 square mm, and a mean of 8470 alveoli per acinus. Assuming that the acini are similarly sized throughout different regions of the lung, we calculated that a rat lung contains 5470 ± 833 acini. The proposed method allows for the non-destructive and semi-automatic extraction of individual acini. Either manual stereological or automatic analysis make our approach well suited for the fast and reliable characterization of a large number of individual acini in healthy, diseased, or transgenic lungs of different species, including humans. [1] David Haberthür et al. http://doi.org/amg
        Speaker: Dr David Haberthür (TOMCAT, Swiss Light Source, Paul Scherrer Institut)
      • 12:15 PM
        X-ray phase contrast tomography of Ice Cream 2h
        Food microstructure is one of the most important parameter when it comes to sensorial perception of food. Accordingly, changes of the microstructure over time typically lead to a loss in product quality. The mechanisms behind these changes are not yet completely understood, mostly due to a lack of experimental methods to directly observe the structural modifications. We are using synchrotron tomographic microscopy at the TOMCAT beamline at the Swiss Light Source to follow the evolution of ice cream microstructure at constant temperatures. The benefits of using x-ray tomography for time lapse studies on ice cream samples enriched with a contrast agent have been shown before (1). Propagation based phase contrast imaging (PCI) at a synchrotron allows us now to differentiate - without the addition of contrast agents and at a fifteenfold higher resolution - between sucrose solution and ice crystals. This method preserves the original chemistry in our samples, and with scan times on the order of several minutes we can investigate the dynamics of coarsening. We present first results regarding the structural characterization and evolution of ice cream obtained with PCI under constant thermal boundary conditions. The four-dimensional data sets provide unique insight into the physical processes that lead to coarsening and quality degradation, making it possible to develop new strategies to avoid these effects in food. (1) Pinzer, B. R., Medebach, A., Limbach, H. J., Dubois, C., Stampanoni, M., & Schneebeli, M. (2012). 3D-characterization of three-phase systems using X-ray tomography: tracking the microstructural evolution in ice cream. Soft Matter, 8(17), 4584-4594. The Royal Society of Chemistry. doi:10.1039/C2SM00034B
        Speaker: Annabelle Medebach (Paul Scherrer Institut)
      • 12:15 PM
        X-ray tomographic microscopy at TOMCAT: An overview and latest developments 2h
        The TOMCAT beamline at the Swiss Light Source has established itself as a cutting edge hard X-ray tomographic microscopy endstation for experiments on a large variety of samples, such as new materials, biomedical tissues and rare fossils. We present an overview of the hardware and techniques available to the user community. Absorption and phase contrast imaging with an isotropic voxel size ranging from 0.16 up to 14.8 microns (horizontal field of views from 0.41 mm up to 30 mm, respectively) is routinely performed with mono- (energy range of 8-50 keV) or polychromatic radiation. Phase contrast is obtained either with propagation-based techniques (simple edge-enhancement and/or using phase retrieval algorithms) or grating interferometry. Typical acquisition times are on the order of a few minutes. A sample exchanger and a package of automation tools are available for performing high throughput studies in a fully automatic manner. Custom devices for in-situ experiments can easily be installed on the sample stage. A cryo-chamber and a laser-based heating system are currently available for such experiments. In addition, novel cutting edge science is frequently performed thanks to the latest improvements in spatial and temporal resolutions. Nanostructures (100 nm) in micrometer-sized samples can be imaged using a full-field hard X-ray microscope, also providing phase contrast capabilities. Dynamic processes (e.g. evolution of liquid foams and physiology in small living animals) can be followed in 3D thanks to the recently commissioned ultra-fast tomographic endstation, which provides sub-second temporal resolution. Development of new strategies for efficient handling and fast post-processing of large amount of data (up to 8 GB/s) complement the hardware implementation. With an alternative tomographic reconstruction algorithm based on Fourier methods, a 18-fold performance improvement compared to standard Filtered Back-Projection has been achieved with negligible quality degradation. In addition, the entire post-processing pipeline concept is being revised to match the new challenging data rates and enable quasi-real time monitoring of the acquisition process in 3D. Finally semi-automatic quantification tools are also being developed and their potential has been demonstrated on a selection of diverse applications.
        Speaker: Dr Federica Marone (Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland)
    • 2:15 PM 6:15 PM
      Plenary session: chair: J.F. van der Veen, K.N. Clausen WHGA/001

      WHGA/001

      Paul Scherrer Institut, Villigen, Switzerland

      • 2:15 PM
        News from SLS 15m
        Speaker: Prof. J. Friso van der Veen
      • 2:30 PM
        PSI Thesis Medal Ceremony 15m
        Speaker: Prof. J. Friso van der Veen (Paul Scherrer Institut)
      • 2:45 PM
        Sensitive discrimination of multiple species in chemically heterogeneous systems by transition metal 2p3d RXES (Presentation by PSI Thesis Medal Winner) 30m
        Metals, metal oxides (as well as sulfides, carbides, etcetera) and metal complexes play a big role in nanotechnology and catalysis. In most reactions that make use of a metal catalyst, many different chemical forms of the metal entity exist and it is often unclear what the active site is that performs the catalytic conversion of reactants. In my thesis-work[1-5] I did not try to identify such active sites of a given catalyst, since I believe this would have been close to unfeasible at present. Rather, I demonstrated that 2p3d2p resonant X-ray emission spectroscopy (RXES), or resonant inelastic X-ray scattering (RIXS), is capable of discriminating more chemical species out of a heterogeneous mixture of compounds than 2p X-ray absorption spectroscopy (XAS) or, for example, lab-based ultraviolet-visible (UV/Vis) spectroscopy. All work was deliberately performed on cobalt compounds, since it is a relatively abundant and cheap transition metal and a general consensus exists that society should shift towards catalysis based on such abundant metals. Moreover, since the final state of a 2p3d2p experiment is close to the system ground state (the final state has a 3d hole) one measures essentially the valence electronic states that are important in chemistry i.e. states that occur a few electron volt above the highest occupied state. This work thus exhibits some of the rich information that metal 2p3d2p RXES contains about complex and relevant transition metal systems. All data were obtained at the ADRESS beamline of the Swiss Light Source (SLS). References: [1] M.M. van Schooneveld, 2p3d resonant X-ray emission spectroscopy of cobalt compounds, 2013. [2] M.M. van Schooneveld, R.W. Gosselink, T.M. Eggenhuisen, M. Al Samarai, C. Monney, K.J. Zhou, T. Schmitt, F.M.F. de Groot, Angewandte Chemie Int. Ed. 2013, 52, 1170. [3] M.M. van Schooneveld, R. Kurian, A. Juhin, K. Zhou, J. Schlappa, V.N. Strocov, T. Schmitt, F.M.F. de Groot, Journal of Physical Chemistry C 2012, 116, 15218-15230. [4] M.M. van Schooneveld, E. Suljoti, C. Campos-Cuerva, R.W. Gosselink, A.M.J. van der Eerden, J. Schlappa, K.J. Zhou, C. Monney, T. Schmitt, F.M.F. de Groot, Journal of Physical Chemistry Letters 2013, 4, 1161. [5] M.M. van Schooneveld, A. Juhin, C. Campos-Cuerva, T. Schmitt, F.M.F. de Groot, Jounral of Physical Chemistry C 2013, 117, 14398.
        Speaker: Dr Matti van Schooneveld (Max Planck Institute for Chemical Energy Conversion, Muelheim an der Ruhr, Germany)
      • 3:15 PM
        Bubble coalescence in magmas: Insight from in-situ high temperature tomography 30m
        The possibility of gas to be removed from magma during its rise to the surface decreases the probability of an explosive volcanic eruption to occur. In this respect, bubble coalescence and the achievement of a permeable network play a pivotal role in favoring magma degassing and limiting the explosivity of eruptions. Significant growth and interaction between bubbles occur in natural volcanic systems during ascent of the magma to the surface. To simulate bubble growth in the laboratory we forced gas exsolution by heating natural glassy magmas at atmospheric pressure. We performed real-time, 3D, and high temperature measurements of bubble nucleation and growth using laser-heated, synchrotron-based X-ray tomographic microscopy at the TOMCAT beamline of PSI. The experiments were performed from room temperature up to 1300 K on two different types of crystal-free rhyolitic samples: a vesicle-free and an obsidian containing pre-existing vesicles. We constrained in-situ the main textural variations (bubble volumes, size distributions, shapes, and bulk textures) during the nucleation and growth of bubbles in these highly viscous systems, and tracked the evolution of parameters such as viscosity and overpressure in the foaming samples, which are essential to retrieve information on the processes preceding an eruption from the interpretation of the textures observed in eruptive products. The microstructural features of the starting material, nominally the presence of initial vesicles, strongly influence the dynamics of bubble coalescence. The presence of bubbles in the starting material tends to limit coalescence therefore increasing the possibility of bubble overpressure to develop. A possible implication of these experiments is that volcanic systems where magma is volatile saturated already in the subvolcanic reservoir may have a higher tendency to feed explosive volcanic eruptions.
        Speaker: Prof. Peter Ulmer (Department of Earth Sciences / ETH Zurich)
      • 3:45 PM
        Coffee 30m
      • 4:15 PM
        News from the PSI Users Association 15m
        Speaker: Dr Sarah Dunsiger
      • 4:30 PM
        News from SINQ and SMuS 15m
        Speaker: Dr Kurt N. Clausen
      • 4:45 PM
        News from SwissFEL 15m
        Speaker: Dr Rafael Abela (PSI)
      • 5:00 PM
        Electric field control of skyrmions in the chiral-cubic insulator Cu2OSeO3 30m
        Skyrmions are topologically protected magnetic spin vortices that form a hexagonal 2D lattice arrangement in non-centrosymmetric magnets. Until last year, skyrmions had been observed only in metallic and semiconducting chiral-cubic B20 compounds where, in MnSi in particular, it was shown that skyrmions can also be manipulated by conduction electrons. The recent discovery of a skyrmion lattice (SkL) phase in the chiral-cubic insulator Cu2OSeO3 has generated excitement since it evidences skyrmion formation as a more general phenomenon to be expected in non-centrosymmetric systems. Since Cu2OSeO3 furthermore displays a magnetoelectric coupling, an important open question was to learn how and if the skyrmion lattice can be manipulated by applied electric fields. We report small-angle neutron scattering experiments that demonstrate the successful manipulation of skyrmions by applied electric fields in insulating Cu2OseO3. In an experimental geometry with μ0H||[1-10] and E||[111], we discover that the effect of applying an electric field is to controllably rotate the SkL around the magnetic field axis in a manner dependent on both the size and sign of the electric field. Our results provide the first evidence for a new manifestation of the electric field control of magnetism in insulators, and also show the electric field to be a new experimental parameter for studying the basic physics of skyrmions in chiral-cubic lattices.
        Speaker: Dr Jonathan White (Laboratory for Neutron Scattering, Paul Scherrer Institut)
    • 6:30 PM 9:00 PM
      Dinner 2h 30m OASE

      OASE

      Paul Scherrer Institut, Villigen, Switzerland

    • 9:00 AM 12:30 PM
      Functional Materials WHGA/001

      WHGA/001

      Paul Scherrer Institut, Villigen, Switzerland

      Organizers: Z. Salman, E. Morenzoni, C. Niedermayer

      • 9:30 AM
        Strain effects in correlated transition metal oxides from first principles 30m
        Transition metal oxides exhibit a wealth of fascinating and potentially useful properties, such as metal-insulator transitions, multiferroic behavior, or high-temperature superconductivity. The unique electronic structure of these materials generally leads to a very strong coupling between their structural, electronic, and magnetic properties. We are using first principles electronic structure calculations and combinations of such first principles calculations with model-based approaches to explore the unique properties of functional complex oxides. Here, I will address the question of whether epitaxial strain, which is present in most thin film samples as a result of the lattice mismatch between the thin film material and the substrate, is able to induce metal-insulator transitions in the prototypical correlated oxides LaTiO3 and SrVO3. Furthermore, I will demonstrate how Wannier functions can be used to connect the realistic electronic structure calculated from first principles to simplified models, which allow to better understand the interplay between spin, orbital, and lattice degrees of freedom in complex oxides.
        Speaker: Claude Ederer (ETH Zurich)
      • 10:00 AM
        Soft x-ray photoemission spectroscopy on buried interfaces 30m
        At the interface between complex oxides, unexpected electronic properties different from those of the constituent bulk materials can arise. A particularly interesting example is the appearance of 2-dimensional conductivity at the interface of the band insulators LaAlO3 (LAO) and SrTiO3 (STO) [1–3] above a critical LAO thickness of 4 unit cells (u.c.) [4]. A very recent related heterostructure is the diluted system of (LaAlO3)x(SrTiO3)1−x/SrTiO3 (LASTO:x/STO) which also shows interfacial conductivity above a certain critical LASTO thickness which scales inversely to the LAO content [5]. The interfaces of LaAlO3/SrTiO3 and (LaAlO3)x(SrTiO3)1−x/SrTiO3 heterostructures have been investigated by soft x-ray photoelectron spectroscopy for different layer thicknesses across the insulator-to-metal interface transition. The valence band and Fermi edge were probed using resonant photoemission across the Ti L2,3 absorption edge. We measured, for the first time to our knowledge, clear spectroscopic signatures of Ti3+ signal at the Fermi level in fully oxygenated samples of LAO/STO and the related system of mixed LASTO:0.5/STO. Our results show that Ti3+-related charge carriers are present in both systems, but only for conducting samples. No Fermi-edge signal could be detected for insulating samples below the critical thickness. Furthermore, the angular dependence of the Fermi intensity allows the determination of the spatial extent perpendicular to the interface of the conducting electron density. [1] A. Ohtomo and H. Y. Hwang, Nature 427, 423 (2004). [2] N. Reyren et al., Science 317, 1196 (2007). [3] A. D. Caviglia et al., Nature 456, 624 (2008). [4] S. Thiel et al., Science 313, 1942 (2006). [5] M. L. Reinle-Schmitt et al., Nat. Comm. 3, 932 (2012).
        Speaker: Dr Claudia Cancellieri (PSI, SLS, Villigen)
      • 10:30 AM
        Interplay between superconductivity and magnetism in La2-xSrxCuO4 / La0.67Ca0.33MnO3 heterostructures 15m
        We studied the interplay between superconductivity and magnetism in La2-xSrxCuO4 (LSCO)/La0.67Ca0.33MnO3 (LCMO) superlattices (SLs). By varying the Sr content and thus the hole doping in the cuprate layers, three SLs (x=0.0, 0.15 0.30) have been prepared using pulsed laser deposition. Upon Sr doping, the cuprate layers evolve from the insulating parent compound with an AF order of the Cu moments at x=0, over the high temperature superconducting state at x=0.15, to a metallic state where superconductivity is suppressed again at x=0.3. The quality of the samples has been characterized by in-situ Reflection high-energy electron diffraction and X-ray diffraction techniques. The polarized neutron reflectometry on these SLs reveals the existence of a so-called depleted layer with a strongly suppressed ferromagnetic Mn moment on the LCMO side of the interface with a thickness of about 10 Å . On the other hand, with X-ray magnetic circular dichroism measurements we observed an induced Cu moment on the LSCO side of the interface. With X-ray magnetic linear dichroism measurements we also observed the signature of an orbital reconstruction effect of the Cu states at the interfaces of these superlattices.
        Speaker: Mr Saikat Das (Department of Physics and Fribourg Center for Nanomaterials, University of Fribourg, Chemin du Musée 3, CH-1700 Fribourg, Switzerland)
      • 10:45 AM
        Coffee 20m
      • 11:05 AM
        Orthorhombic LuMnO3 thin films, a multifunctional multiferroic 30m
        Materials featuring the co-existence of coupled magnetic and ferroelectric order allow the switching of magnetic moments by an electric field and vice versa. Experimentally, only a few multiferroic materials are known to be ferromagnetic, with the large majority being antiferromagnetically ordered. We studied thin films of orthorhombic LuMnO3, a material which is known to exhibit magnetically-induced ferroelectricity with an E type antiferromagnetic groundstate. In single crystalline like thin films grown by pulsed laser deposition on YAlO3 substrates, we identify co existing and coupled ferromagnetic and antiferromagnetic orders. The ferromagnetism is located in a layer close to the substrate-film interface and extends over ~10 nm with a constant magnetic moment of ~1µB, subsequently falling off towards the film surface. This single phase material with coupled ferro-, antiferromagnetic orders thus represents an important step towards a future utilization of multiferroic materials in spintronic device with a built-in exchange bias.
        Speaker: Dr Christof Schneider (PSI)
      • 11:35 AM
        XMCD/XLD Study of the Magnetoelectric Coupling Mechanism in the Multiferroic Composite Co/PMN-PT(011) 15m
        Multiferroic composites are promising candidates amongst the strategies to achieve electric field control of magnetism. In compounds consisting of ferromagnetic and ferroelectric (FE) layers strain can couple the FE phase via the piezoelectric effect to the magnetic phase employing magnetostriction. [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x (PMN-PT) is a relaxor FE with strong piezoelectric properties near the morphotrophic phase boundary x=0.3 [1] - Wu et al. reported on a remanent in-plane FE polarization for PMN-PT (011) in addition to the two out-of- plane polarization directions [2]. The impact of the FE order of PMN-PT (011) on the electronic and atomic structure of a Co top layer is studied using X-ray magnetic circular dichroism (XMCD) and X-ray linear dichrosim (XLD) for Co and Ti respectively. We observe the development of a magnetic easy axis upon rotating the FE polarization to in-plane due to strain-mediated coupling (see Fig. 1, red curve). The data suggest an additional charge driven magnetoelectric coupling due to electron accumulation/depletion at the Co/PMN-PT interface(Fig. 1,green and blue curve). Moreover, the Ti data shows a change in the spectrum with applied voltage which is described with the help of multiplet calculations.
        Speaker: Ms Jakoba Heidler (Paul Scherrer Institut, SLS, SYN)
      • 11:50 AM
        Muon-spin Relaxation Studies of Diffusion Processes in Battery Materials 15m
        Solid state diffusion is a very complex mechanism and, up until recently, studies of such properties have mainly been conducted by macroscopic methods that do not yield true material properties. This has been a major problem for materials development regarding e.g. Li-ion batteries where the basic operational principle is based on diffusion of Li-ions. Although the microscopic diffusion coefficient of Li+ (DLi) in solids has been frequently evaluated by Li-NMR, difficulties arise for materials that contain magnetic ions. As a result, it is very difficult to correctly estimate DLi by Li-NMR for most battery materials, particularly for positive electrode materials. Since DLi is one of the primary parameters that govern the charge and discharge rate of a Li-ion batteries, such situation is very unsatisfactory. In order to rectify the shortcomings of NMR and electrochemical measurements, we have developed a novel method that utilizes the muon-spin relaxation (muSR) technique to probe the microscopic ion self-diffusion constant (Dion) in a straightforward manner. In this poster, we will give an introduction to the method itself [1-2] but also summary our muSR work on Li-diffusion in battery cathode materials [3-6]. Furthermore, we will show that the method is not limited to studying only Li-ion diffusion but can also be extended to other groups of compounds [7] and applications e.g. vacancy order formation in transition metal oxides. Finally, we will compare our method to other available microscopic techniques that are able to study ion diffusion in solids, e.g. quasi-elastic neutron scattering (QENS), as well as make an outlook towards future developments. REFERENCES (J. Sugiyama, M. Mansson et al.) [1] Phys. Rev. Lett. 103, 147601 (2009) [2] J. Phys.: Conf. 225, 012052 (2010) [3] Phys. Rev. B 79, 184411 (2009) [4] Phys. Rev. B 82, 224412 (2010) [5] Phys. Rev. B 84, 054430 (2011) [6] Phys. Rev. B 85, 054111 (2012) [7] Publication in progress (2013)
        Speaker: Dr Martin Mansson (Laboratory for Quantum Magnetism (LQM), EPF Lausanne)
    • 9:00 AM 12:30 PM
      Opportunities for Energy Research OSGA/E6 (PSI)

      OSGA/E6

      PSI

      Organizers: M. Nachtegaal, J.P. Embs, F. Marone

      • 9:30 AM
        CO2 capture - How can XAS help us? 30m
        Owing to the increasing concentration of CO2 in the atmosphere and the climate change associated with it, there is increasing pressure to reduce the anthropogenic emissions of CO2. CO2 capture and storage (CCS) is a mid-term solution to mitigate climate change. However, the currently technologically available CO2 capture technique, i.e. amine scrubbing has very high, potentially prohibitively high CO2 capture costs. Thus, the development of more efficient CO2 capture processes is imperative. Recently, CO2 capture via the reversible carbonation/calcination reaction of CaO and the so-called chemical looping combustion process has been proposed. A cornerstone of these two processes is the development of novel CaO and transition metal based materials which possess, respectively, a high and stable CO2 uptake capacity and stable redox characteristics. In addition, to model the CO2 capture processes a better understanding of the underlying reaction mechanisms is required. In this talk we present our preliminary results using X-ray absorption spectroscopy to elucidate reaction pathways during material synthesis and repeated redox cycles.
        Speaker: Prof. Christoph Müller (ETH Zürich)
      • 10:00 AM
        A clue for the actives sites of Cr-based ethylene polymerization catalysts ? 30m
        Transition metal catalysts play a central role in the formation of polyethylene (PE), a bulk commodity material made on over 80 million metric tons per year. The Phillips catalyst, which contains chromium dispersed on silica, was the first commercialized material that could produce PE industrially and accounts for 40 – 50 % of global high density PE. Despite 60 years of intensive research the active catalytic sites of the Phillips catalyst remains unknown, though X-ray Absorption Spectroscopy shows that Cr(II) species are formed, inferring that they are responsible for catalysis. We synthesized well-defined Cr sites on silica using Surface Organometallic Chemistry and tested these materials for ethylene polymerization. Comparison of the XAS features of this material revealed novel information about active sites. These well-defined Cr sites exhibit activities exceeding the Phillips catalyst, though the PE produced by these two materials is very similar indicating that the same active sites must be responsible for catalysis.
        Speaker: Mr Georges Siddiqi (ETH Zurich)
      • 10:30 AM
        The role of synchrotron and neutron sources in understanding the structure of materials for H2-storage and O-conducting materials for Solid Oxyde Fuel Cells operating at low temperature 30m
        Two classes of structurally complex materials will be discussed in this talk. The first concerns iso-structural UiO-66/67 [JACS, 2008, 130, 13850] metal-organic frameworks that showed some interest for H2 storage and some potentialities as porous scavengers for interim radioactive waste scavenger. UiO-66/67 exhibits a different degree of long- and short-range order that has been disclosed using combined XRPD EXAFS and DFT calculations [Chem. Mater, 2011, 23, 1700; PCCP, 2012, 14, 1614; PRB, 2012 86, 125429]. The second class of materials concerns mixed oxides SrMO2.5+x (M = Co or Fe) that can act as O-conducting materials for solid oxide fuel cells operating at low temperature. We followed by in situ neutron powder diffraction and EXAFS/XANES the electrochemical oxygen intercalation in the whole SrMO2.5+x --> SrMO3.0 solid state phase transition [JACS, 2006, 128, 13161; J. Phys. Chem. C, 2011, 115, 1311]. Inelastic neutron scattering highlighted that the low temperature oxygen condition mechanism inside these materials is phonon assisted [JACS, 2008, 130, 16080].
        Speaker: Prof. Carlo Lamberti (Department of Chemistry, Turin University)
      • 11:00 AM
        Coffee 20m
      • 11:20 AM
        Imaging Liquid Water in Polymer Electrolyte Fuel Cells by XTM 30m
        Polymer electrolyte fuel cells (PEFC) are electrochemical reactors, strongly governed by fluid mechanical processes. Heat, charge and multiphase mass transport on length scales from nanometers, up to meters are interlinked. Carbon fibre based gas diffusion layers (GDL) with a thickness in the order of 200 μm bridge the scale gap between the catalyst layer (sub-µm structures) and channel/rib domain of the flow field (mm to cm). The liquid water present in the pore network of the GDL can significantly influence the reactant gas transport and the related electrochemical losses (i.e. efficiency and/or power density of the PEFC). X-ray imaging is sensitive to water and carbon. The achievable spatial and temporal resolution of synchrotron based X-ray tomographic microscopy (XTM) is sufficient to image GDL and the contained water in-situ so single fibers and the droplets of condensed water are visible . The high beam intensity allows for performing tomographic scans in the order of 10 s. The images can be segmented into the three distinct phases of solid water and void and the transport properties of these structures may be determined [1,2]. [1] J. Eller, T. Rosen, F. Marone, M. Stampanoni, A. Wokaun, F. N. Büchi, J. Electrochem. Soc. 158 (2011) B963–B970. [2] T. Rosén, J. Eller, J. Kang, N. I. Prasianakis, J. Mantzaras, F.N. Büchi, J. Electrochem. Soc., 159 (2012) F536-F544
        Speaker: Felix Buechi (Paul Scherrer Institut)
      • 11:50 AM
        Synchrotron X-ray Tomographic Microscopy of Lithium Ion Batteries 30m
        Realization of high performance lithium ion batteries requires the development of roadmaps for achieving favorable porous electrode microstructure through the selection of active materials, additives, and electrode processing conditions. To develop such roadmaps, a clear understanding of battery microstructure is needed. We report the use of synchrotron radiation x-ray tomographic microscopy (SRXTM) to obtain statistically significant volume 3D reconstructions of lithium ion battery electrodes. We demonstrate the use of SRXTM to quantify directional tortuosity in lithium ion battery electrodes, determine its origins, and assess its impact on lithium ion battery (LIB) performance and safety. Finally, we show that SRXTM can be applied to operando investigations of porous electrodes during electrochemical operation.
        Speaker: Vanessa Wood (ETH Zurich)
    • 9:00 AM 12:40 PM
      Strongly Correlated Electron Systems: Novel Interaction Phenomena WWHB/106 (PSI)

      WWHB/106

      PSI

      Organizers: JH Dil, C. Rüegg

      • 9:30 AM
        Interaction Effects in Topological Materials 30m
        Topological Insulators are a new phase of electronic matter which realizes a non-quantum-Hall-like topological state in the bulk matter and unlike the quantum Hall liquids can be turned into superconductors at the bulk and/or at the interface. I will first review the basic concepts defining topological matter and experimental probes that reveal topological order. I will then present recent results demonstrating interaction effects in topological materials including superconductivity, magnetism and Kondo physics. Time permitting, I will also briefly present experimental results on a new class of topological insulators beyond the Kane-Mele Z2 theory and discuss interaction effects in them.
        Speaker: Prof. M. Zahid Hasan (Princeton University)
      • 10:00 AM
        Complex Spin Pattern at the Fermi Surface of a Strongly Spin-Orbit Coupled Atom Layer 30m
        The spin texture of the metallic two-dimensional electron system formed by Au on Ge(111)is revealed by fully three-dimensional spin-resolved photoemission, as well as by density functional calculations. The large hexagonal Fermi surface, generated by the Au atoms, shows a significant splitting due to spin-orbit interactions. The planar components of the spin exhibit a helical character, accompanied by a strong out of-plane spin component with alternating signs along the six Fermi surface sections. Moreover, in-plane spin rotations toward a radial direction are observed close to the hexagon corners. Such a threefold symmetric spin pattern is not described by the conventional Rashba model. Instead, it reveals an interplay with Dresselhaus-like spin-orbit effects as a result of the crystalline anisotropies.
        Speaker: Dr Joerg Schaefer (University of Wuerzburg, Department of Physics)
      • 10:30 AM
        SANS and muSR studies of the non-centrosymmetric superconductor BiPd 15m
        BiPd is a non-centrosymmetric superconductor with a monoclinic crystal structure, a Tc of 3.8 K, and an upper critical field Bc2 (T = 0) ~ 0.7 T. The initial motivation for investigating this compound was to search for signs of mixed singlet-triplet pairing, as is permitted in systems lacking inversion symmetry. However, recent measurements by TF muSR and SANS have shown that the most striking feature of BiPd seems to be extreme multi-band superconductivity. MuSR provides evidence of at least two components with very different critical fields and penetration depths. Flux lattice measurements by SANS confirm the existence of a phase with a critical field around 10 times lower than that identified by resistivity and magnetisation. We also find evidence of an intermediate mixed state, where Meissner and flux lattice phases coexist. In addition, I will present an improved method of SANS data treatment for flux lattice diffraction patterns, using Bayes’ theorem.
        Speaker: Dr Alexander Holmes (University of Birmingham)
      • 10:45 AM
        Separating the bulk and surface n- to p-type transition in the topological insulator GeBi_(4-x)Sb_xTe_7 15m
        We identify the multi-layered compound GeBi_(4-x)Sb_xTe_7 to be a topological insulator with a freestanding Dirac point, slightly above the valence band maximum, using angle-resolved photoemission spectroscopy (ARPES) measurements. The spin polarization satisfies the time reversal symmetry of the surface states, visible in spin-resolved ARPES. For increasing Sb content in GeBi_(4-x)Sb_xTe_7 we observe a transition from n- to p-type in bulk sensitive Seebeck coefficient measurements at a doping of x=0.6. In surface sensitive ARPES measurements a rigid band shift is observed with Sb doping, accompanied by a movement of the Dirac point towards the Fermi level. Between x=0.8 and x=1 the Fermi level crosses the band gap, changing the surface transport regime. This difference of the n- to p-type transition between the surface region and the bulk is caused by band bending effects which are also responsible for a non-coexistence of insulating phases in the bulk and in the near surface region.
        Speaker: Mr Stefan Muff (Paul Scherrer Institut)
      • 11:00 AM
        Coffee 20m
      • 11:20 AM
        Pulsed High Magnetic Fields for Synchrotron and Neutron Applications 30m
        Over the past years, numerous efforts have been performed to combine high magnetic fields with X-ray and neutron scattering experiments. This combination is of significant interest as it provides new opportunities for the study of magnetic materials. In this context, pulsed magnetic fields play a central role, operating in the 30-40 T range, high above superconducting magnets. In this talk I will review the various pulsed field magnet devices jointly developed by the LNCMI-Toulouse, the ESRF, the ILL and the CEA, Grenoble. These developments will be illustrated with some recent results.
        Speaker: Dr Fabienne DUC (Laboratoire National des Champs magnétiques Intenses)
      • 11:50 AM
        Magnetism of single impurities at surfaces 20m
        Artificial heterostructures consisting of thin films and small clusters down to single atoms, deposited in a controlled way on surfaces or embedded in a substrate are model systems to investigate the origin of the magnetic anisotropy energy (MAE) and magnetic interactions. In particular, we want to find which combination of magnetic atom and substrate results in the highest MAE. Good candidates are very small Co clusters on graphene and benzene. Recent theoretical calculations predicted an MAE of a few tens of meV for the Co monomer on graphene and even larger values of about 300 meV for the Co dimer adsorbed on benzene [1, 2]. However, these predictions are only for pure freestanding graphene, thus it is reasonable to imagine that the interaction of graphene with the supporting substrate is a key parameter. Graphene is strongly hybridized with the d valence bands of Ru(0001) and Rh(111) while the bonding is mostly of van der Waals character on Ir(111) and Pt(111) [3, 4]. In order to check these predictions, we deposited Co single atoms, dimers and larger clusters on Ru(0001) and Ir(111), used as model substrates for the case of strong and weak hybridized graphene, respectively. Strong differences are observed as a function of the cluster size and the degree of hybridization between graphene and substrate. The experiments has been performed at the at the X-Treme beam line of the Swiss Light Source. This beam line gives the unique opportunity of combining in a single UHV chamber a low temperature (2K) high magnetic field (7T) cryostat for XAS-XMD, a chamber for sample cleaning and in-situ MBE growth [5], and a variable temperature STM (scanning tunneling microscope) fundamental to check the quality of the in-situ grown graphene. [1] R. Xiao, D. Fritsch, M. D. Kuzmin, K. Koepernik, H. Eschrig, M. Richter, K. Vietze and G. Seifert. Phys. Rev. Lett. 103, 187201 (2009). [2] M. Sargolzaei and F. Gudarzi. J. Appl. Phys. 110, 064303 (2011). [3] A. B. Preobrajenski, M. L. Ng, A. S. Vinogradov and N. Martensson. Phys. Rev. B 78, 073401 (2008). [4] C. Busse, P. Lazic, R. Djemour, J. Coraux, T. Gerber, N. Atodiresei, V. Caciuc, R. Brako, A. T. N`Diaye, S. Blgel, J. Zegenhagen and T. Michely. Phys. Rev. Lett. 107, 036101 (2011). [5] C. Piamonteze, U. Flechsig, S. Rusponi, J. Dreiser, J. Heidler, M. Schmidt, R. Wetter, M. Calvi, T. Schmidt, H. Pruchova, J. Krempasky, C. Quitmann, H. Brune and F. Nolting. J. Synch. Rad. 19, 661 (2012).
        Speaker: Dr Stefano Rusponi (Institut of Condensed Matter Physics (IPMC) - Ecole Polytechnique Fédérale de Lausanne (EPFL))
      • 12:10 PM
        HAL - The new High-field And Low-temperature µSR facility at SµS 20m
        Since this year, the sample environment range for muon spin rotation/relaxation (µSR) at the Swiss Muon Source SµS is significantly extended by the installation of the new HAL (High-field And Low-temperature) instrument working at high magnetic fields up to 9.5 T and sample temperatures down to 20 mK, an hitherto unaccesible region in the B-T phase diagram of condensed matter research using muons as local field probes. The instrument presently is in the final commissioning phase. In this talk, an overview of the instrument parameters (sample environment, detectors, and beam line) will be presented and the performance will be illustrated by a few examples.
        Speaker: Robert Johann Scheuermann (Paul Scherrer Institut)
    • 12:30 PM 2:30 PM
      Poster session II and lunch WSLA - Foyer

      WSLA - Foyer

      Paul Scherrer Institut, Villigen, Switzerland

      • 12:30 PM
        Angle-resolved photoemission study of Fe-based high temperature superconductors 2h
        We use high-resolution angle resolved photoemission spectroscopy to study the electronic structure of Fe-based high temperature superconductors. We find that the substitution of Ru for Fe is isoelectronic, i. e., it does not change the carrier concentration. More interestingly, there are no measured significant changes in the shape of the Fermi surface (FS) or in the Fermi velocity over a wide range of Ru substitution (0 < x < 0.4).[1] This unusual behavior is in contrast with the case of Co substitution, where even small amount of Co induces large change not only in the size of the FS pockets but also in the FS topology, i. e., Lifshitz transition which is closely linked to the superconducting dome.[2] Given that the suppression of the anti-ferromagnetic and structural transition temperature is associated with the induction of the superconducting state, Ru substitution must achieve this via a mechanism that does not involve changes of the Fermi surface. We speculate that this mechanism relies on magnetic dilution that leads to the reduction of the effective Stoner enhancement. Furthermore, we reveal that the band structure of pure and Ru substituted BaFe2As2 changes significantly with sample temperature. The hole and electron pockets are well nested at low temperature, which likely drives the spin density wave and resulting anti-ferromagnetic order. The size of the hole pocket shrinks and the electron pocket expands upon warming, i. e. the nesting is degraded at higher temperatures. These results demonstrate that the temperature dependent nesting may play an important role in driving the anti-ferromagnetic/paramagnetic phase transition.[3] [1] R. S. Dhaka et al., Phys. Rev. Lett., 107, 267002 (2011). [2] Chang Liu et al., Nature Physics 6, 419 (2010); Phys. Rev. B, 84, 020509(R) (2011). [3] R. S. Dhaka et al., Phys. Rev. Lett., 110, 067002 (2013).
        Speaker: Dr R. S. Dhaka (Division of Materials Science and Engineering, The Ames Laboratory, US DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA; Present Address: Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland)
      • 12:30 PM
        Confined Electrolytes at the Nanoscale: an X-ray Reflectivity Study 2h
        When a liquid is confined within a nanometer-sized gap, interfacial and size effects confer to the system properties different from those observed in bulk fluids [1]. For electrolytes one expects that confinement influences the hydration of cations near the confining walls, in our study muscovite mica surfaces. Knowledge of the ordering behavior of the electrolyte’s hydration shells under confinement contributes to our understanding of, e.g., friction, and diffusion and corrosion phenomena in Nature and technology. . We have adapted a surface force apparatus (SFA) [2] to be used as confinement device in an X-ray reflectivity (XRR) experiment conducted at cSAXS (XSA12) beamline of the Swiss Light Source at PSI. Two cylinder-shaped muscovite mica membranes were made to approach each other and a flat contact area was formed in which droplets of RbCl, CsCl and BaCl2 solutions at different concentrations were confined. To achieve such confinement, we had to screen out the double layer repulsion and allow attraction between the mica membranes, working at concentrations with the Debye length λD<1 nm. We have performed XRR experiments from the contact area as a function of the momentum transfer q ranging from 0 to 7 Å-1. Model dependent fits to the measured reflectivity I(q) [3] allowed us to determine the minimum gap distance (1.84 nm for RbCl, 1.64 nm for CsCl and 3.21 nm for BaCl2) and the electron density profile along the confinement direction [4]. The profiles indicate an ordered layering of the liquid within the gap, with the layering being most pronounced for hydrated ions closest to the confining walls. A comparison between the structures of confined chlorides with different monovalent and divalent cations (Cs+, Rb+ and Ba2+) at different concentrations reveals ion specific features that can be related to ion size, valence and hydration energy. References [1] Israelachvili, J.N., Intermolecular and surface forces: revised third edition. 2011: Academic press. [2] Perret, E., et al., Molecular liquid under nanometre confinement: density profiles underlying oscillatory forces. Journal of Physics: Condensed Matter, 2010. 22(23): p. 235102. [3] Perret, E., et al., X-ray reflectivity theory for determining the density profile of a liquid under nanometre confinement. Journal of synchrotron radiation, 2010. 17(4): p. 465-472. [4] Chodankar, S., et al., Density profile of water in nanoslit. EPL (Europhysics Letters), 2012. 99(2): p. 26001.
        Speaker: Simone Liuzzi (Paul Scherrer Institut)
      • 12:30 PM
        Damage in cement-based materials by the Alkali-Aggregate Reaction: detection and characterization by X-ray Tomographic Microscopy 2h
        We investigated the usefulness of X-ray Tomographic Microscopy (XTM) as a tool for the detection and characterization, at multiple scales, of the damage produced by the Alkali-Aggregate Reaction (AAR) in cement-based materials. The goal of our broad experimental campaign was to assess the potentiality of XTM as a non-destructive technique complementary to other 2D microscopy methods that require invasive specimen preparation.
        Speaker: Dr Michele Griffa (EMPA, Swiss Federal Laboratories for Materials Science and Technology)
      • 12:30 PM
        Dynamic stabilization of nonequilibrium domain configurations in magnetic squares 2h
        We explore the linear and nonlinear dynamic regimes of micrometer-scale Ni81Fe19 squares. The response of the magnetisation under a continuous sinusoidal excitation is monitored by time-resolved scanning transmission x-ray microscopy. Non-equilibrium domain configurations are dynamically stabilized under increasing amplitude of the excitation field. On reducing this amplitude, the magnetisation returns to the equilibrium configuration. We have spatially resolved the transition between two stable magnetic configurations and present complementary micromagnetic simulations alongside the experimental data, which provide insight into the energy dissipation and spin wave contributions. Spin wave instabilities, which arise in the non-linear regime and play a role in the generation of non-equilibrium modes can ultimately lead to vortex core reversal.
        Speaker: Ms Stephanie Stevenson (Paul Scerrer Institut)
      • 12:30 PM
        Dynamics of Aqueous Ferrocyanide Solvent Interaction Revealed by High Repetition Rate Laser Pump / X-ray Probe Technique 2h
        Understanding the role of a solvent in influencing the rate and/or selectivity of a reaction is of great importance to chemistry. In general, solvent effects may be classified into two distinct groups; passive or active. Active solvents are directly involved during the course of the chemical reaction by forming a explicit interaction with the reacting species. In such cases, these interactions generally result in mechanistic changes and the formation of new reaction channels. A case in point, is the photochemistry of aqueous hexacyanoferrate (ferro- and ferricyanide) ions. Previous studies have determined the photochemical dynamics of aqueous ferrocyanide can be separated into photooxidation ([FeII(CN)6]4-* -> [FeIII(CN)6]3- + e-) and photoaquation ([FeII(CN)6]4-* -> [FeII(CN)5 H2O]3- + CN-) [1], however little is known about the dynamics of these processes or their geometric structure. While numerous time-resolved optical studies of the photooxidation process exist, getting information on the photoaquation dynamics proved difficult, as it is related to the population of intramolecular states with low extinction coefficients. In addition, while the relaxation pathway towards photooxidation or photoaquation strongly depends on the excitation wavelength, the photoaquation tends to be obscured by intramolecular MLCT and intermolecular CTTS transitions, making separate studies of photooxidation and photoaquation challenging. To shed light on the different dynamics, we used our recently developed high repetition rate laser pump / x-ray probe setup [2] at different laser excitation wavelengths while probing with x-rays at the Fe K-edge. Our transient x-ray spectra (pumped sample x-ray absorption spectrum minus unpumped sample x-ray absorption spectrum) upon 266 nm and 355 nm excitation show unique fingerprints for each pump wavelength, which can be directly linked to photooxidation and photoaquation respectively. While 266 nm excitation into a charge transfer to solvent state (CTTS) results in a characteristic edge shift of the excited state due to the oxidation state change of the metal, upon 355 nm excitation simulations of the photoaquated species are in good agreement with the experimental transient spectrum. This allows a differentiated view into the dynamics involved. [1] M. Shirom et al., J. Chem. Phys. 1971 55(7), 3372–3382 [2] F. Lima et al., Rev. Sci. Instrum. 2011, 82, 063111.
        Speaker: Jochen Rittmann (EPFL/PSI)
      • 12:30 PM
        Ground state ordering of artificial spin ice 2h
        Using electron beam lithography combined with appropriate imaging techniques, it became possible in recent years to design, pattern and imvestigate artificial spin ice systems, the 2-dimensional parallel to the pyrochlore spin ice, and which are considered to be ideal model systems to directly investigate the behavior of frustrated systems. In particular, using photoemission electron microscopy, it’s possible to visualize the moment configuration and eventual fluctuations in such a system. Thus far, the systems investigated were patterned films with Curie temperatures far above room temperature, so that these systems could only be manipulated by applying magnetic fields, whether achieving low energy states via demagnetization [1] or the observation of emergent magnetic monopoles upon field reversal [2]. Inspired by the recent work of Morgan et al. [3], we present a thermal ground state ordering in the artificial kagome spin ice building blocks, consisting of a finite number of hexagonal rings of nanomagnets, which occurs during the early stages of film deposition. In infinite arrays of the artificial kagome spin ice, while a unique ground state is not observed, the ice rule is obeyed at every vertex. A strong dependence of the ordering on the film thickness and coupling strength is observed. With heating experiments we were able to apply direct thermal annealing on the building blocks and observed high frequencies of ground states achieved. [1] E. Mengotti, L.J. Heyderman, A. Fraile Rodríguez, A. Bisig, L. Le Guyader, F. Nolting, and H.B. Braun, Phys. Rev. B 78, 144402 (2008) [2] E. Mengotti, L.J. Heyderman, A. Fraile Rodríguez, F. Nolting, Remo V. Hügli, and H.B. Braun, Nature Physics Vol. 7 NPHYS1794 (2011) [3] J. Morgan, A. Stein, S. Langridge, C.H. Marrows Nature Physics 7, 75-79 (2011)
        Speaker: Mr Alan Farhan (PSI)
      • 12:30 PM
        High-temperature precipitate microstructure and misfit in Inconel-type superalloy 2h
        Nickel base superalloys are a natural composites consisting of γ’ precipitates (L12) with an ordered structure coherently embedded in a γ solid solution (fcc) matrix. The critical parts of turbines made of Ni-based superalloy are subjected to cyclic elastic-plastic straining as a result of heating and cooling during start-up and shut-down periods. Consequently, low-cycle fatigue at operating temperatures (up to 900°C) is an important factor in the evaluation of the service life. The thermo-mechanical exposure during low-cycle fatigue is connected with a change of its microstructure, namely the size and distribution of precipitates. Moreover, an important parameter for the characterization of microstructural changes in nickel base superalloys is misfit - the relative difference between lattice parameters of γ matrix and γ´ precipitates. Nickel base superalloy IN738LC has been studied after low-cycle fatigue by small-angle neutron scattering (SANS) and neutron diffraction (ND) at SINQ (SANS-II and POLDI facilities). Samples subjected to high-temperature low-cycle fatigue were annealed at various temperatures to change the size and the distribution of precipitates. Ex- and in-situ SANS and high resolution TEM studies were performed. It was found that additional precipitates are produced either during slow cooling from high temperatures or after reheating above 570°C. Their size and distribution were evaluated. The precipitates arise regardless the application of the mechanical load. Nevertheless, these small precipitates influence low-cycle fatigue resistance. From the SANS data, it can be also deduced that the equilibrium volume fraction of γ’-precipitates at temperatures from room temperature to 825°C is significantly higher than 45%. The kinetics of formation of small and medium-size γ’ precipitates at 700 and 800°C was determined as well. Misfit in IN738LC superalloy was examined at POLDI TOF neutron diffractometer both ex-situ and in-situ at elevated temperatures. A careful out-of-furnace measurement yielded the lattice parameters of both γ and γ’ phases at room temperature (aγ= 3.58611(10) Å, aγ´= 3.58857(17) Å) as well as misfit (equal to 6.9(6)×10-4). The in-situ measurement at elevated temperatures determined the temperature dependence of lattice parameters of γ (up to 1120°C) and γ’ (up to 1000°C). Using these data, evolution of the misfit with temperature was calculated. The misfit decreases with increasing temperature until it reaches zero value at temperature around 800°C. Above 800°C, it becomes negative. The support by GACR project No. P204/11/1453 and NMI3-II EC infrastructural project No. 283883 are acknowledged.
        Speaker: Dr Pavel Strunz (Nuclear Physics Institute, CZ-25068 Rez near Prague)
      • 12:30 PM
        Highly time- and size-resolved measurements of trace elements in London during ClearfLo 2h
        The identification and quantification of particle sources has long proven challenging due to the complex composition of ambient aerosol. Measurements of trace elements provide uniquely source-specific information; e.g. barium and copper are emitted by traffic sources, while vanadium and nickel are linked to heavy oil combustion. The power of source apportionment by trace elemental analysis is greatly enhanced by simultaneous measurements of complementary aerosol species. Optimization of trace elemental data requires measurements with sufficient temporal resolution to distinguish sources with different characteristic diurnal patterns such as traffic and sea salt, while size-resolved measurements can help resolve different source classes with similar composition, e.g. iron from resuspension appears in PM10-2.5 while brake wear processes appear in PM1. Here we present highly time- and size-resolved measurements of trace elements as part of the ClearfLo (Clean Air for London) 2012 field campaign, a multinational collaborative effort to investigate boundary layer pollution in and around London, UK. Sampling was performed at several sites in and around London during two Intensive Observation Periods (IOPs) in 2012. During the winter IOP (11 Jan. to 8 Feb.) particulate matter was sampled at a site with heavy traffic (Marylebone Road, MR) and an urban background site (North Kensington, NK) in London, and at a rural site in Detling, southeast of London. Summer sampling took place at the two London sites from 18 July till 22 August, a period which included the Olympic Games. Rotating drum impactors (RDIs) collected particles in three size bins (PM10-2.5, PM2.5-1.0 and PM1.0-0.1) with a high time resolution of 2 h, instead of more common 24 h sampling times. The elemental composition of the samples was analysed by synchrotron radiation induced X-ray fluorescence spectrometry (SR-XRF) at the Swiss Light Source (SLS, Paul Scherrer Institute, CH) and at HASYLAB (Deutsches Elektronen-Synchrotron, DE). The RDI SR-XRF setup provides quantification of elements with atomic number 11 (sodium) to 82 (lead) with a detection limit on the order of a few pg. We will show median diurnal variations of selected elements in PM10-2.5 during the winter IOP. The rush hour peaks for iron and barium commonly observed in a street canyon with stop-and-go traffic. Ba is typically related to brake wear and elevated concentrations are thus likely at such a site. Elevated concentrations during daytime for mineral dust elements like aluminium and calcium occur from continuous resuspension at MR. NK shows lower levels due to dilution of air during transport from the traffic to the urban background site. Rather constant values were observed for e.g. sodium (Na) and magnesium (Mg). These sea salt elements are likely advected throughout the day, but the elevated values at MR indicate local emissions as well. Correlations with e.g. black carbon, nitrogen oxides and meteorological conditions will enhance the source separation of the trace elements. This work was funded by the ClearfLo project (NERC grant NE/H00324X/1), the SNF (grant 200021_132467 /1) and the European Community’s Seventh Framework Programme (FP7/2007-2013, grant n°312284).
        Speaker: Ms Suzanne Visser (MSc)
      • 12:30 PM
        Imaging the induced magnetic moment in spin-bearing molecules by means of X-ray Photo-Emission Electron Microscopy 2h
        The assembly of spin-bearing metal-organic molecules, as for instance metallo-porphyrins and –phthalocyanines, on ferromagnetic substrates has received significant attention during the last few years [1, 2, 3]. So far most of the studies have been carried out by spectroscopic techniques lacking of spatially resolved information. Here, we present the first spectro-microscopic investigation performed by X-ray PEEM on a model system [3] consisting of manganese(III) tetraphenylporphyrin chloride (MnTPPCl) molecules adsorbed on various surfaces like native Co, oxygen-covered Co, and a chromium wedge layer on Co[4]. Our results demonstrate that X-ray PEEM in combination with X-ray magnetic circular dichroism can be used to study the induced magnetic moments in a molecular monolayer of spin-bearing molecules with submicron spatial resolution. [1] H. Wende et al., Nat. Materials 6, 516 (2007) [2] C. Wäckerlin et al., Chem. Science 3, 3154, (2012) [3] A. Scheybal et al., Chem. Phys. Lett. 411, 214 (2005) [4] J. Girovsky et al., submitted (2013).
        Speaker: Mr Jan Girovsky (Laboratory for Micro and Nanotechnology, Paul Scherer Institute)
      • 12:30 PM
        In situ Materials Science with X-ray Ptychography 2h
        With the ability to control the structure of multiphase materials for applications on the nano- and mesoscale, methods for imaging these materials are becoming increasingly important. Especially techniques able to image sub-micron structures of functional materials in operando are in high demand, as these problems often fall outside the range of electron microscopy due to requirements of complex sample environments or less invasive sample preparation procedures. Ptychography is a technique for lensless imaging, implemented for X-rays over the last few years and still in rapid development[1, 2]. Relying on an iterative reconstruction algorithm to form real space images from a series of coherent small-angle scattering patterns, thus solving the “phase problem”, it yields quantitative images of both the absorption and phase shift induced by the object. The penetrating power of X-rays allows ptychography to work also in customized sample environments, such as high temperatures and specific gas atmospheres. Using tomography methods, ptychography can also provide three-dimensional images[3]. We discuss the potential of this new imaging technique for solving problems in materials science, especially related to structure investigations of highly inhomogenous materials with structures on length scales approaching 10 nm. Examples will be drawn from our recent work on hydration of isolated silk fibres, where we have used three dimensional quantitative imaging by X-ray ptychography to show that silk fibres swell anisotropically through absorption of water in the protein matrix when the surrounding atmosphere changes from low to high relative humidity, while the pore structure is left unchanged[4]. References [1] J. M. Rodenburg et al., Phys. Rev. Lett. 98, 034801 (2007) [2] P. Thibault et al., Science 321, 379–382 (2008) [3] M. Dierolf et al., Nature 467, 436–439 (2010) [4] M. Esmaeili et al., Macromolecules 46, 434–439 (2013)
        Speaker: Jostein Bø Fløystad (Norwegian University of Science and Technology)
      • 12:30 PM
        In-situ X-ray Absorption Spectroscopy to study the precipitation of CaCO3 2h
        Calcium carbonate has great scientific relevance in biomineralization and geosciences, forming enormous scales of biological (reefs and ocean sediments) and geological origin, which bind a huge amount of CO2 and affect the chemistry of ocean water[1] and, with it, Earth’s atmosphere and climate. CaCO3 provides a model system for nucleation and crystallization analysis of mineral for classical[2] and nonclassical crystallization[3] theory and has been studied for more than a century. Despite its relevance, the precipitation mechanism of calcium carbonate is still under intense research and specified complex crystal structures challenge the classical view on nucleation considering the formation of metastable ion clusters[4]. It is known that CaCO3 exists in at least six phases, of which three are anhydrous (calcite, aragonite and vaterite) and three are hydrated forms (monohydrate, hexahydrate and amorphous) and amorphous calcium carbonate (ACC) has been identified as a prenucleation-stage precursor in calcium carbonate mineralization[3]. There is growing evidence that different species of ACC, that is the amorphous phase shows, a specific short-range order, exists as a transient phase during calcium carbonate precipitation and this corresponds to the long-range order of the particular crystalline polymorph[3]. The life time of the transient species is temperature dependent. Micro X-ray Absorption Spectroscopy (μ-XAS) can probe the local structure around the Ca atom in both amorphous and crystalline materials, giving information on the type, number and distance of neighbouring atoms and can give important clues about the transient species that are formed during the reaction. Using Ca-K edge μ-XAS we investigate CaCO3 precipitation using a segmented-flow microfluidic cell[5] to study the reaction between CaCl2 and Na2CO3 to form carbonate, under specific conditions. Microfluidic systems have significant advantages in terms of speed, throughput, yield, selectivity and control when compared with macroscale devices. All the mentioned characteristics are facilitated by system downscaling and realted improvements in mass and thermal transfer. In addition, microfluidic systems have been shown to be crucial and highly effective when variables such as reagent concentration, temperature, and pH, have to be controlled with precision. For example, with a segmented flow microfluidic reactor picolitre-sized droplets (of variable chemical composition) at frequencies in excess of 100 Hz can be generated[5]. This allows thousands of individual reactions to be processed in very short times and the consequent transposition of the reaction time onto spatial coordinates enables the in-situ observation of the millisecond reaction. Nevertheless, manipulation and processing of samples with instantaneous volumes ranging from a few picolitres to hundreds of nanolitres provides a significant challenge for detection and identification and in many ways defines the principal limitations of current microfluidic systems. This will be overcome, in extension the already performed studies, combining a microfluidic device with synchrotron radiation. In particular at the PHOENIX beamline (SLS, Switzerland) analysis at low energy edges in diluted and micro-samples can be carried out thanks to its high photon flux, very fast detector and microfocussing beam. [1] R.E. Zeebee et al. Science 2008, 321, 51 [2] J.J. De Yoreo et al. Rev. Mineral. Geochem. 2003, 54, 57 [3] Y. Politti et al. Adv. Funct. Mat. 2006, 16, 1289. [4] J. Rigger et al. Faraday Discuss. 2007, 136, 265. [5] A. J. DeMello Nature 2006, 442, 394.
        Speaker: Dr Sonia Pin (Paul Scherrer Institut)
      • 12:30 PM
        In-situ X-ray Absorption Spectroscopy to study the Structure of Hydrothermal Aqueous Sulfate Solutions 2h
        Hydrothermal aqueous salt solution play an important role in geochemistry for the understanding of the ore deposit formation as well as in the supercritical water oxidation (SCWO) and the supercritical water gasification (SCWG), which use hot compressed water as a process medium. At the Paul Scherrer Institut a SCWG process was developed [1], which turns various kinds of wet biomass into synthetic natural gas. One big task in the SCWG and SCWO is the salt separation from the process stream to recover nutrients such as P, S, K and Na and to avoid problems such as blocking of the apparatus or poisoning of catalysts used in the SCWG. For optimizing such processes and understanding the solution chemistry, especially solubility of salts, a detailed knowledge on the phase behavior and microscopic structure of salt solutions is needed. Water changes its structure at elevated pressures and temperatures drastically, with strong impact on dissolved matter. Specifically, the solubility of salts in hydrothermal water may decrease strongly when approaching the conditions of the critical point of pure water (374°C, 22.1 MPa). Especially for sulfate solutions this behavior is known [2]. One possible effect is the formation of ion pairs under or close to supercritical conditions. Extended X-ray absorption fine structure (EXAFS) measurements can provide insight into the microscopic structure of solutions as they yield a direct measurement of atomic distances. Up to now the ion pair formation has been studied for systems containing ions with, on the energy scale, high absorption edges. Studies with the lowest energy were performed at the Ca-K-edge (4038.5 eV) [4]. Performing such measurements for light elements, such as sulfur or phosphorus is challenging, as the absorption edges are at low X-ray energies with intrinsically small penetration depth of a few tens of microns. Due to this small penetration depth the thickness of the X-ray windows and the path length in the fluid are critical issues. Here, we present a design of X-ray windows and a cell, which are suitable to perform measurements at the S-K-edge (2482 eV). The windows are 18 µm thick diamond membranes (Diamond Materials, Freiburg, Germany) which are supported by a diamond ring on a titanium holder. The free aperture is 100 µm. The path length in the solution can be adjusted to values between 25 and 240 µm using different spacers, which are also used for the axial alignment. The cell is sealed with copper O-rings and was designed for temperatures up to 400°C and pressures up to 300 bar. The solution is flushed through the cell using a high pressure syringe pump (ISCO). The pressure is controlled with a back pressure valve. At the PHOENIX beamline (Swiss Light Source, Switzerland) with its high photon flux and microfocussed beam at low energies it was possible to perform measurements of a K2SO4 solution (5% w/w) at a pressure of 300 bar up to a temperature of 297°C. [1] F. Vogel, Catalytic conversion of high-moisture biomass to synthetic natural gas in supercritical water. In: Handbook of Green Chemistry , P. Anastas (Series Editor), Volume 2 Heterogeneous Catalysis, R. Crabtree (Volume Editor), Wiley-VCH, Weinheim, chapter 12, 281-324, 2009. [2] V.M. Valyashko, Chapter 15 - Phase equilibria of water-salt systems at high temperatures and pressures. In: Aqueous Systems at Elevated Temperatures and Pressures, D. A. Palmer, R. Fernández-Prini, and A. H. Harvey (Editors), Academic Press, London, 597-641, 2004. [3] T.M. Seward et al., Geochim. Cosmochim. Acta, 63, 16, 2409-2418, 1999. [4] J. Fulton et al., Rev. Sci. Instrum., 75, 12, 5228-5231, 2004.
        Speakers: Mr Joachim Reimer (Paul Scherrer Institut) , Dr Sonia Pin (Paul Scherrer Institut)
      • 12:30 PM
        Investigating the Fate of Plutonium: Speciation of Plutonium during Diffusion in Opalinus Clay 2h
        With regard to the safe disposal of heat-generating radioactive waste in deep geological formations, detailed information on the interaction between the radiotoxic, long-lived radionuclides such as 239Pu (t1/2 = 24,110 a) and the host rock as important geological barrier are required. A combination of spa-tially-resolved synchrotron based microprobe techniques has been used to determine the chemical speciation of the redox-sensitive Pu migrating through heterogeneous Opalinus Clay (OPA, Mont Terri, Switzerland). Long-term diffusion experiments were conducted with the redox-sensitive Pu(V) species under aero-bic conditions. Spatially-resolved molecular-level investigations were performed at the microXAS Beamline of the Swiss Light Source (SLS, Paul Scherrer Institut, Villigen, Switzerland). First, micro-scopic chemical imaging by micro-X-ray fluorescence (μ-XRF) demonstrated the complex nature of the reactive transport pattern. A strong correlation between the distribution of Pu and the geochemical heterogeneity of the rock matrix (represented by major elements such as Ca, Mn, Fe, or Sr) was ob-served. The chemical speciation of the redox sensitive Pu along the migration pathway was deter-mined by micro-X-ray absorption fine structure spectroscopy (µ-XAFS). Generally, in all investigated diffusion (and in complementary sorption) samples, Pu LIII-edge µ-XANES spectra on Pu hot spots demonstrated that Pu(IV) is the dominating species on OPA. Accordingly, the highly soluble Pu(V) was reduced by components of the OPA rock materials and converted to the less mobile tetravalent oxidation state. For the first time, by means of µ-XRF, we succeeded to record a full 2D representation of a diffusion profile of Pu in a relevant geological medium. Moreover, in addition to the elemental distribution of Pu, fundamental chemical information could be obtained by µ-XANES. These spatially-resolved speciation measurements of Pu showed that Pu(V) was reduced progressively along its diffusion path to Pu(IV). To gain further information about the redox-reactive mineral component of the OPA rock, micro-X-ray diffraction (μ-XRD) measurements were employed in areas of interest. A correlation between Pu(IV) with the Fe(II)-bearing mineral siderite and the clay mineral illite was observed by µ-XRD. The combination of these spatially-resolved x-ray microprobe methods is a powerful tool to determine the transport mechanisms of actinides in heterogeneous systems. The obtained information is an essen-tial part of the evaluation of the long-term safety of a repository and increases also the confidence in clay rocks as option for the geological disposal of radioactive waste. This work was financially supported by the BMWi (contract no. 02E10981) and Actinet-I3 under con-tract no. 232631.
        Speaker: Dr Daniel Grolimund (Paul Scherrer Institute, Swiss Light Source)
      • 12:30 PM
        Investigation of Exchange Coupled Composites with Scanning Transmission X-ray Microscopy 2h
        Novel exchange coupled composites incorporating a hard and a soft magnetic layer have the potential for a number of applications including magnetic recording, sensors, MRAM and oscillators. We investigate the magnetic behaviour of ferromagnetic L10 FePt thin films exchange coupled to soft ferrimagnets, including FeGd and FeTb, using Scanning Transmission X-ray Microscopy (STXM), which allows us to probe each layer individually, and magnetic force microscopy (MFM). Using a luminescence detection scheme, we are able to determine the magnetic domain configuration using STXM. From MFM measurements we find a compositional dependence of the domain structure in the ferrimagnetic films.
        Speaker: Phillip Wohlhüter (Paul Scherrer Institut)
      • 12:30 PM
        Investigation of Ferromagnetic Semiconductors through Depth Resolved Spin Resonance Techniques 2h
        Ferromagnet-Semiconductor heterostructures show immense promise for device applications, in particular for the injection of polarised spins into a semiconducting substrate. More fundamentally, prototypical systems like the III-V semiconducting materials Ga1−xMnxAs/GaAs or EuO1-x/doped Si exhibit unusual long range indirect exchange interactions mediated by charge carriers in the semiconductor host. By contrast, the dominant mechanism of exchange in magnetic insulators is usually superexchange. Large changes in the electronic structure occur as the temperature is reduced through the Curie temperature, caused by an exchange splitting of the conduction band in the ferromagnetic state. This unusual interplay between magnetism and transport properties opens up interesting and potentially technologically useful possibilities of modulating magnetic behaviour by controlling the charge carrier properties and vice versa. Artificial heterostructures based on these ferromagnetic semiconductors may be produced in thin film form using nonequilibrium molecular beam epitaxy techniques. Investigations using local probes which are sensitive to magnetic structure on a nanometre depthscale are therefore invaluable. I will discuss our recent studies of the internal magnetic field distribution and spin fluctuations in these model materials for spintronic devices using depth resolved Low Energy μSR and β-detected Nuclear Magnetic Resonance, complementary spin resonance techniques.
        Speaker: Dr Sarah Dunsiger (Technical University of Munich)
      • 12:30 PM
        Liquid-jet XPS study on the air-aqueous interfacial composition of mixed sodium bromide/citric acid solutions 2h
        Bromide ions at the sea salt solution - air interface are implicated in ozone depleting reactions in marine environments. Driven by the relevance, we intend to use near ambient pressure X-ray photoelectron spectroscopy (NAPP) on a liquid microjet at the SIM Beamline in order to determine the surface concentration of bromide ions in mixed solutions containing bromide and citric acid to mimic the complex composition of natural sea water derived aqueous phases. The results show three exemplary scans of the region of about 160 eV photoelectron kinetic energy, excited at 229 eV photon energy. Br 3d (doublet due to spin orbit splitting) and Na 2s of sodium bromide have a binding energy of about 73 eV and 68 eV, respectively. We therefore used the presence of the small amount of second order light available at 458 eV to obtain C1s photoelectrons from citric acid around 170 eV kinetic energy. The three peaks in the C1s region are due to the occurrence of the carbon atom in different electronic configuration, i.e., three carboxyls, one alcohol and two methyl carbons in the citric acid molecule. Along the same line, we used third order light (687 eV) to observe O1s around 148 eV. Taking the spectra in this way allows to obtain directly an internal reference for the overlap between photon beam and the jet via the O1s or the C1s signals without the need to change the photon energy at the beamline in between. Furthermore, apparently Br 3d peaks were not clear from the interface for the conditions of low bromide and high citric acid concentrations in the solutions. At higher bromide concentrations, the bromide signal remained clearly visible in presence of 2.5 M citric acid.
        Speaker: Mr Ming-Tao Lee (PSI)
      • 12:30 PM
        Looking inside iron ore pellets 2h
        About 25 % of the world´s iron ore production of about 1,1 billion metric tons per years is traded as iron ore pellets. These spheres with diameter between 8 and 16 mm are made of iron oxide ore powder (100% - 150 µm), additives to adjust the chemical composition for the individual blast furnace operations and binders to control the compressive strength during the production process of pelletizing, drying and firing for final hardness (compressive strength of 2000 N). Sodium rich natural or activated bentonites are the most common binders used in a mass proportion of 0,7 to 1,5 % within a pellet. Due to their schist structure and chemical composition they are able to incorporate water in the structure causing swelling, followed by dissolution to a colloid gel of high viscosity depending on the amount of water added. According to the common theory of pelletizing the strength of a bentonite bonded humid pellet exceeds that of the simple water bonded due to the even distribution of the gel in the capillary system. This is in contradiction to the technical mixing process during pellet production providing neither sufficient homogenization nor residence time for the formation of the gel. Controlled drying experiments observed by neutron imaging at ICON/ PSI allowed to study the drying process by time resolved 2D radiography completed by neutron tomography of humid and dry pellets. Single humid pellets rolled under industrial conditions with and without bentonite were positioned into a specially designed climate chamber for constant temperature and moisture content and centered in the beam. The drying event was imaged for 2 hours at high resolution (25 x 25 mm frames) and 90 sec exposure time. Radiography allowed to record the drying process with time for selected points in the cross cut of the pellets. Tomography provides information about the allocation of the bentonite within the volume of the pellet.
        Speaker: Dr Boehm Andreas (Montanuniversitaet Leoben, mineral processing)
      • 12:30 PM
        Low temperature magnetic structure and lattice anomalies at the commensurate-incommensurate transition of multiferroic 2h
        Ferroelectric materials have been known since almost one century ago [1]. While their potential for applications was rapidly recognized, the possibility of combining ferroelectricity with magnetic order -preferably with ferromagnetism- has resulted in an enormous deal of interest during the last decade. Several new materials combining both types of order have been reported, although their promising multifunctionalities have been obscured by two facts: one one side, most of them are antiferromagnetic. On the other, their transition temperatures are too low for most practical applications (typically below 40K). The oxygen-defficient double perovskite YBaFeCuO5 constitutes a remarkable exception. Spontaneous electric polarization has been recently reported to exist below an unusually high temperature of TC ≈ 230K [2] coinciding with the occurrence of a commensurate - to - incommensurate reorientation of the Fe3+ and Cu2+ magnetic moments [3,4]. From a more fundamental point of view the observation of incommensurable magnetic order in a tetragonal material at such high temperatures is rather surprising. In particular, the nature of the relevant competing magnetic interactions and its possible link to low dimensionality or geometrical frustration is not understood at present. Although the existence of the spin reorientation in this material is know since 1995 [3] the low temperature magnetic structure has not yet been solved. Using neutron powder diffraction we have recently been able to propose a spiral model which satisfactorily describes the measured magnetic intensities below TC [4]. Also, investigation of the crystal structure showed the existence of small anomalies in the lattice parameters and some interatomic distances at TC. The relevance of these findings for the magnetoelectric coupling, the direction of the polarization, the modification of the different exchange paths in the structure and the stabilization of the incommensurate magnetic order below TC are discussed. [1] J. Valasek Physical Review 15, 537(1920) [2] B. Kundys et al., Appl. Phys. Lett. 94, 072506, (2009). [3] V. Caignaert et al., J. Solid State Chem. 114, 24, (1995). [4] M. Morin et al., in preparation
        Speaker: Mr Mickael Morin (Paul Scherrer Institut)
      • 12:30 PM
        Magnetic excitations in the Ising-chain material RbCoCl3 2h
        One of the simplest realizations of a quantum phase transition is the Ising model in a transverse magnetic field. The Co2+ ion is a good resource for anisotropic spins with Ising or XY interactions. Several families of cobalt halides and oxides have been classified as approximate realizations of the Ising chain model. The hexagonal perovskite family ACoX3 with A = Rb, Cs, Tl and X = Br, Cl is one class of potential Ising materials [1, 2, 3]. The material RbCoCl3 has been studied to a lesser extent. In RbCoCl3 the Co2+ ions have effective spin-½. Neutron powder diffraction data show that the ordered magnetic moments are aligned antiferromagnetically up-down the crystallographic c-axis with an amplitude modulation in the ab-plane. Two antiferromagnetic phase transitions at TN1 = 28 K and TN2 = 13 K were observed [4]. On the new thermal TAS EIGER at SINQ, the spectrometer IN22 at ILL and the LET ToFspectrometer at ISIS Ising-domain wall excitations were measured. These excitations show a cosinusoidal dispersion and sharpening and splitting at the successive magnetic transitions at TN1 and TN2. In the experiment on we observed how the excitations change with temperature. We were also able to observe the splitting of the modes in a very successful commissioning experiment on EIGER at PSI. We will present results and preliminary analysis of the LET, IN22 and EIGER data. References [1] S. Nagler et al., Phys. Rev. Lett. 49, 590 (1982). [2] J. Goff et al., Phys. Rev. B 52, 15992 (1995). [3] A. Oosawa et al., J. Phys. Soc. Jpn. 75, 015002 (2006). [4] N. Hänni et al., in preparation.
        Speaker: Ms Eva Hirtenlechner (Institut Laue Langevin, BP 156, 38042 Grenoble Cedex 9, France, Laboratory for Neutron Scattering, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland)
      • 12:30 PM
        Microscopic indicator for thermodynamic stability of hydrogen storage materials provided by muon-spin spectroscopy 2h
        In search of a high-capacity hydrogen storage system, we have investigated the thermodynamic properties of borohydrides [M(BH4)2]. Using muon-spin rotation and relaxation (muSR), we have acquired data for five different powder samples below ambient temperature. Zero-field muSR measurements indicate the formation of the H-muon-H system in LiBH4, NaBH4, KBH4, and Ca(BH4)2 but not in Mg(BH4)2. It is also found that the amplitude of the H-muon-H signal (A) varies with the electronegativity (chi) of Mn. Since the thermodynamic stability of M(BH4)n also depends on chi, the amplitude (A) is thought to be a microscopic indicator for the stability of the M(BH4)n unit. Consequently, we can present muSR as a novel tool for investigating similar hydrogen storage materials [1]. REFERENCES [1] J. Sugiyama, M. Mansson et al., Physical Review B, 81, 092103 (2010)
        Speaker: Dr Martin Mansson (Laboratory for Quantum Magnetism (LQM), EPF Lausanne)
      • 12:30 PM
        Ozonolysis of individual shikimic acid particles studied with in situ STXM/NEXAFS 2h
        Atmospheric aerosols are an important focus of environmental research due to their effect on climate and human health. Organic compounds account for a large fraction of total fine aerosol mass (up to 90%). Chemical and optical characteristics of particles can be altered by chemical ageing, which in turn affects their environmental impact. In this study we therefore investigated the changes in chemical composition and morphology of shikimic acid as an organic particle proxy [1] upon in situ exposure to ozone in presence of humidity. This was achieved by monitoring changes at the C-edge via scanning transmission X-ray microscopy (STXM) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Measurements were conducted at the PolLux beamline at Swiss Light Source. We used an environmental micro reactor [2,3], designed specifically for the end station, to enable the investigation in situ. We observed oxidation of shikimic acid particles in situ during exposure to ozone at different humidities, whereby humidity was found to be a critical factor controlling the rate of the reaction. [1] P.M. Medeiros et al. Environ. Sci. Technol. 42 (2008) [2] T. Huthwelker et al. Rev. Sci. Instrum. 81 (2010) [3] V. Zelenay et al. J. Aerosol Sci. 42 (2011)
        Speaker: Sarah Steimer (Paul Scherrer Institut)
      • 12:30 PM
        Probing active sites of Pt/CeO2 CO preferential oxidation catalysts using time-resolved x-ray absorption spectroscopy. 2h
        During production of hydrogen it is important to decrease CO traces down to 10 ppm level because these traces can poison catalysts used in hydrogen fuel cells. CO preferential oxidation (PROX) catalysts selectively oxidize CO to CO2 without oxidizing hydrogen. Platinum nanoparticles supported on ceria (CeO2) are promising candidates for such catalysts. Pt selectively adsorbs CO which is then oxidized by oxygen provided by CeO2 somewhere at the Pt-CeO2 interface. It is of interest to identify and characterize the active site in order to understand the reactivity and selectivity for improving future PROX catalysts. We probed the changes in oxidation state and coordination environment of Pt/CeO2 PROX catalysts using modulation excitation X-ray absorption spectroscopy at the Pt L3 edge during periodic switches between the typical PROX conditions (1%CO+1%O2+50%H2 in inert atmosphere) and oxygen free conditions (1%CO+50%H2 in inert atmosphere). The main goal is to see whether periodic changes in the atmosphere composition lead to periodic changes in the coverage of active Pt sites by CO and oxygen and to detect how fast this process happens in comparison to the changes in the oxidation state of the ceria support providing active oxygen for CO oxidation.
        Speaker: Rene Kopelent
      • 12:30 PM
        Probing correlated electron systems on the femtosecond timescale at SwissFEL's Experimental Station B 2h
        The SwissFEL hard X-ray free electron laser at PSI will produce femtosecond X-ray pulses from 2-12 keV at a repetition rate of 100 Hz and 10^11 to 10^12 photons per pulse. Experimental Station B at SwissFEL proposes to combine time-resolved laser spectroscopy methods and X-ray scattering techniques to study the dynamics of cooperative interactions in crystalline materials that exhibit long-range elecronic and magnetic order. One important class of these types of materials are strongly correlated electron systems ('quantum materials') that exhibit competition between lattice, charge, orbital and spin degrees of freedom. Such materials also show complex phase diagrams. We propose to install a dedicated instrument for X-ray pump-probe scattering and diffraction including polarization control and flexible sample environment. Photon-in/photon-out scattering experiments allow to directly correlate the electronic, magnetic and structural dynamics. The focus of the experimental station will be on performing pump-probe experiments on crystalline samples (thin films, bulk crystals) with excellent time resolution (<50 fs) and a variety of excitation sources, with an emphasis on sample excitation with THz fields. The techniques available will initially include grazing incidence X-ray diffraction and resonant X-ray diffraction with a variety of sample environments, including low temperatures (10K). The future plans of the instrument, including the ability to perform polarization analysis using phase retarders and inelastic X-ray scattering (RIXS) measurements, will also be presented.
        Speaker: Gerhard Ingold (Paul Scherrer Institut)
      • 12:30 PM
        Recombination dynamics of hemoproteins in physiological media investigated by picosecond X-ray absorption spectroscopy 2h
        Recombination dynamics of hemoproteins in physiological media investigated by picosecond X-ray absorption spectroscopy M. Silatani1, F.A. Lima1, J. Rittmann1, C.J. Milne2, T.J. Penfold1, 2, M.H. Rittmann-Frank1, M. Reinhard1, F.G. Santomauro1, M. Chergui1 1École Polytechnique Fédérale de Lausanne, SB, ISIC, LSU, CH-1015 Lausanne, Switzerland 2Paul Scherrer Institute, Swiss FEL, Villigen, Switzerland The small protein Myoglobin (Mb), consisting of a single polypeptide chain of 153 amino acid residues and a heme group, plays a central role in many biological processes by acting as a typical heme-based sensor for diatomic molecules either toxic (e.g. CN-) and/or crucial for survival (e.g. O2, NO). While modern crystallographic techniques make it possible to determine the global structure of the protein with almost atomic resolution, one would prefer to determine the structure of the protein in its physiologically relevant environment. In addition, the biological function and reactivity of Mb strongly depends on the electronic structure of the active site. For determining both the local geometric and the electronic structure around the active center, X-ray absorption spectroscopy (XAS) is ideal. In addition, real time changes of local geometrical and electronic structure in the early stages of a biological process in proteins can be described in detail via time-resolved X-ray Absorption Spectroscopy (XAS). Here we show our characterisation of the Fe K-edge X-ray absorption spectra of ligated (NO, O2, CN, CO) and unligated Mb (metMb, deoxyMb) [1, 2], Then using our high-repetition rate picosecond laser pump/X-ray probe setup [3] we follow the ligand recombination dynamics in MbNO under physiological conditions (pH=7, low concentration, continuously flowing of sample). Our results show, in agreement with literature that the transient spectrum of MbNO (pumped at the Q-band) consists of a long lived deligated structure identical to the deoxyMb ground state and an additional shorter-lived species. Slight deviations of the transient at 50 ps from the static difference spectrum of deoxyMb-MbNO in the post-edges features indicates the presence of NO in the vicinity of Fe. Likewise, minor deviations in the pre-edge region suggests the interaction between the NO ligand and the Fe center. Using multiple scattering, quantum chemistry and molecular dynamics simulations we are able to assign this transient species as a recombined MbNO, which is trapped in an excited spin state. These results confirm the time-resolved Raman experiments [4] and shine light on the structural and electronic dynamics, for which until now only recombination time scales are known [4, 5]. [1] F. Lima, PhD thesis, EPFL, 2011. [2] F. Lima et. al, PCCP., submitted. [3] F. Lima et. al, Rev. Sci. Instrum. 82, 063111, 2011. [4] S. Kruglik et. al, PNAS, 107(31):13678– 13683, Jan 2010. [5] D. Ionascu et. al, J. Ame. Chem. Soc., 127(48):16921–16934, 2005.
        Speaker: Ms Mahsa Silatani (EPFL)
      • 12:30 PM
        Selenium speciation in a spent UO2 fuel and in non-irradiated UO2 reference samples: a synchrotron-based (micro-)XRF / -XAS feasibility study 2h
        In the safety case for underground radioactive waste repositories, aqueous corrosion of the waste plays a central role, since it determines the source term of radionuclide release to the environment. The direct disposal of spent nuclear fuels is an option adopted in many countries, implying that radionuclide release studies from spent UO2 and mixed oxide fuels are critical for building confidence in the safety case. One of the major issues to be solved is the reliable determination of the «Instant Release Fraction» (IRF), i.e. the cumulative inventory fraction of potentially easily soluble nuclides (129I, 135Cs, 36Cl, 79Se, 14C), which will be released on contact with aqueous solutions penetrating a breached canister soon after failure of the waste overpack. Whereas I, Cs and Cl are soluble within the entire natural Eh range, C and particularly Se mobilization on contact with aqueous solution strongly depends on oxidation potential. Especially, under oxic conditions the easily soluble Se(IV) and Se(VI) form, whereas under reducing conditions the sparingly soluble and thus almost immobile Se(0) and Se(-II) are stabilized. In the present feasibility study, X-ray absorption spectroscopy (XAS) and X-ray fluorescence (XRF) investigations have been conducted at the Se K-edge, partly at micrometric beam resolution. The samples used were (i) a high burn-up (~ 79 GWd/t) UO2 spent fuel and (ii) several non-irradiated UO2 reference samples doped with Se in amounts covering the concentration ranges expected in spent fuel (~ 50 -150 ppm). Meaningful data were obtained in spite of the very low Se concentrations and the heavy sample matrix (UO2). For instance, the micro-XANES spectra obtained on particles of the irradiated sample -not larger than a few micrometers- consistently indicate the presence of mixed valence selenium (possibly Se(0) and Se(IV)). Moreover, acceptable and consistent bulk EXAFS data have been obtained for the UO2 reference sample doped with 100 ppm SeO2.
        Speaker: Dr Annick Froideval Zumbiehl (Paul Scherrer Institut)
      • 12:30 PM
        Single Domain Spin Manipulation by Electric Fields in Strain Coupled Artificial Multiferroic Nanostructures 2h
        The continuously increasing demand for data storage systems that exhibit both high-speed and low energy consumption has encouraged researchers to look for novel ways of manipulating and recording information. One promising and viable solution is to couple a magnetostrictive ferromagnet to a ferroelectric piezoelectric creating an artificial multiferroic, a material whose magnetization configuration can be manipulated by applying an electric field [1, 2]. In this work we demonstrate the first experimental evidence of an electric field-induced 90 uniform magnetization reorientation between two single domain states in 200×100 nm2 Ni nanoislands. Artificial magnetoelectric coupling is achieved depositing the Ni nanoellipses on a Pb(Mg0.66Nb0.33)O3-PbTiO3 (PMN-PT) ferroelectric single crystal [3]. Imaging of the magnetic domain configuration was obtained by photoemission electron microscopy (PEEM) using the X-ray magnetic circular dichroism (XMCD) effect at the Ni L3 edge. By applying an electric field that drives the polarization reversal of the ferroelectric, the magnetization in the nanoislands rotates uniformly from the in-plane easy axis defined by the shape anisotropy, to the perpendicular in-plane easy axis, defined by the converse magnetoelectric interaction. Our experimental findings correlate well with micromagnetic simulations and the observed electric field-induced magnetization reorientation can be explained by strain mediated magnetoelectric coupling which causes the magnetization to reorient as a result of the competition of shape anisotropy and magnetoelastic contributions induced by the ferroelectric distortions. We believe that our results constitute an important step not only towards the realization of magnetoelectric memory devices containing an artificial multiferroic film stack with low power consumption and high switching reliability but also for a greater understanding of the physics related to strain coupled nanostructured artificial multiferroics. [1] C. A. F. Vaz, J. Phys.: Condens. Matter 24 333201 (2012) [2] R. V. Chopdekar, et al., Phys. Rev. B 86 014408 (2012) [3] M. Buzzi, et al., Phys. Rev. Lett. 111 027204 (2013)
        Speaker: Mr Michele Buzzi (Paul Scherrer Institut)
      • 12:30 PM
        Size-dependent magnetization curves of individual iron nanoparticles at finite temperatures 2h
        Magnetic nanoparticles show a variety of novel magnetic phenomena when compared to the respective bulk materials, mostly due to the effect of the surface and interface on the magnetic interactions and to critical magnetic length scales such as domain wall width and exchange length. For instance the size may determine whether a particle is in a single domain state or whether it will show a non-collinear spin structure [1]. A related aspect concerns magnetic switching processes in a nanoparticle. For sufficiently small structures it is assumed that the magnetic reversal occurs as a coherent rotation of the atomic spins at T = 0 K. However, at finite temperatures thermal excitations may disturb the ferromagnetic spin order and thus lead to complex reversal modes [2]. These modes are not only relevant for the quasi-static properties of the particles, but also determine their dynamical response to external stimuli. We have used photoemission electron microscopy (PEEM) together with x-ray magnetic circular dichroism (XMCD) to detect the magnetization curves of individual Fe nanoparticles at room temperature, cf. Fig. 1. By varying the particle size we observe the transition from superparamagnetic fluctuations to stable ferromagnetic order at a particle size of about 12 nm. Applying a magnetic field allows us to record magnetization curves of the particles in both, the superparamagnetic and the ferromagnetic state, as well as in the transition regime. We compare these data with the predictions of conventional macro spin theory and discuss the role of thermal excitations and non-collinear spin structures on the magnetization reversal. references: [1] A. Fraile-Rodriguez et al., Phys. Rev. Lett. 104, 127201 (2010). [2] S. Krause et al., Phys. Rev. Lett. 103, 127202 (2009).
        Speaker: Ms Ana Maria Balan (Paul Scherrer Institut)
      • 12:30 PM
        Spreading and absorption of impinging droplet on porous stones 2h
        Wetting by wind-driven rain (WDR) refers to rain droplets carried by the wind and impinging on the building façade. WDR water is a main agent of deterioration of building materials, such as surface soiling, algae formation, salt damage and frost damage, which becomes an important issue when retrofitting old or historical buildings by adding insulation, planning energy efficient cities, and doing assessment of soiling of facades and leaching of harmful biocides and nanoparticles from buildings. The understanding of phenomena of single water droplet, such as spreading, splashing, bouncing, absorption, evaporation, film forming and run-off can lead to better estimation of WDR load on buildings within urban environments. We report on the wetting and absorbing dynamics of a 4.3 ul deionized water droplet impinging on porous building stones, Pietra Serena, Meule, and Savonnieres. This study examines the influence of materials and drop impact velocity on the spreading and absorbing characteristics from the measurement of contact diameter between droplet and stones and penetration depth of drop into materials. The movement of waterfront and variation of moisture contents into different porous stones were investigated using neutron radiography. We found that penetration depth of impinging droplet is function of impact velocity of droplet and main pore size of stones.
        Speaker: Dr Dominique Derome (Empa)
      • 12:30 PM
        State of chromium in chromia doped uranium dioxide fuels 2h
        Large grain uranium dioxide fuels, doped with different transition metal oxides as additives, are being used in light water reactors worldwide for energy production. Most of the doped UO2 have been produced in order to improve the fuel performance as compared to the standard UO2 ones. In this context, chromia (Cr2O3) has been used to fabricate successfully larger than standard UO2 grain structures. Therefore, it is of paramount importance to understand the role of chromium as a dopant in UO2 matrix and any apparent change of its state that may occur in chromia doped fuels as a result of irradiation effects. In this work the next neighbour atomic environment of chromium in Cr2O3-doped uranium dioxide has been investigated using advanced x-ray techniques, such as micro X-ray absorption fine structure (micro-XAFS) spectroscopy and micro X-ray fluorescence (micro-XRF). Characterization tests were performed at the micro-XAS beamline, SLS, Paul Scherrer Institute (PSI). The investigated fresh material was pure UO2 powder enriched up to 4.8% and sintered with 1600 ppm Cr2O3. Spent doped-fuel pellet was previously irradiated in two cycles in a commercial reactor with an average burn-up of about 40 MWdkg-1. The Cr K-edge XAFS spectra using micro-focused synchrotron light were measured for both fresh as well as irradiated UO2. Collected spectra were analyzed and quantified using the FEFF 8.40 code. To fit the theoretical spectra with experimental data, two types of different clusters were considered. In the first model substitution of U by Cr in UO2 has been done. In the second model molecular clusters of UCr2O6 have been considered. Thereafter, chromium next neighbor’s distances and other structural properties were determined. The results of the difference in chromium speciation between fresh and irradiated UO2 were discussed based on the comparison of quantitative structural parameters obtained from the investigated chromia-doped two fuel samples.
        Speaker: Mr Cyprian Mieszczynski (LNM, Paul Scherrer Institute)
      • 12:30 PM
        Sulfidation Kinetics of Silver Nanoparticles 2h
        Ag-NP released from consumer products to the environment may undergo transformations. Especially the sulfidation has been identified as one of the key transformation process, which strongly reduces the antimicrobial properties of Ag-NP. This is mainly due to the low solubility of Ag2S. Under aerobic conditions, bisulfide (HS-) is quickly oxidized and thus becomes unavailable for the sulfidation of Ag. Metal sulfides (MS), however, are relatively stable under aerobic conditions and may represent a reservoir of sulfide available for the sulfidation of Ag-NP even under aerobic conditions. ZnS and CuS are present in large quantities in wastewater. In aerobic surface waters, concentrations in the order of microgram / liter are reported, along with expected half-life times of the MS of approximately two weeks. The goal of this study was to determine the sulfidation rates of Ag-NP in the presence of MS in comparison to HS-. We reacted citrate-capped Ag-NP with a diameter of 10 and 100 nm (0.16 mM Ag) suspended in TRIS buffered (10 mM, pH = 7.5) aqueous media with different MS (weakly-crystalline and well-crystalline CuS and ZnS; 0.34 mM) in order to assess the dependence of the Ag sulfidation kinetics on the type and crystallinity of the MS. In addition, 40 nm and 100 nm Ag-NP were reacted with dissolved HS-. To determine the degree of Ag-NP sulfidation as a function of time, the solids were analyzed by Ag K-edge (25.514 keV) at the Dutch Belgian Beamline (Dubble, BM01B) at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) and at the SuperXAS beamline (X10DA) at the Swiss Light Source (SLS, Villigen, Switzerland). The sample spectra were analyzed by linear combination fitting (LCF) using crystalline Ag2S, poorly crystalline Ag-sulfide, and metallic Ag as references. The sulfidation rates of the Ag reacted with MS were additionally determined by measuring the increase of dissolved Cu or Zn after complexation with Zincon using UV-Vis analysis. For Ag-NP reacted with MS, the results from LCF analysis were generally in very good agreement with the expected degree of Ag-NP sulfidation derived from UV-Vis measurements. Attempts to quantify the metallic Ag fraction via UV-vis measurements were not successful due to strong interferences with the Ag2S and the sulfidation rates of Ag-NP reacted with HS- were exclusively determined by XAS analysis. Larger Ag-NP showed a slower reaction kinetics, but not to the degree expected on the basis of their external surface derived from transmission electron microscopy images. The Ag-NP were more rapidly sulfidized when reacted with weakly-crystalline MS than with crystalline MS, and CuS lead to faster sulfidation than ZnS. The sulfidation of Ag-NP reacted with HS- seemed to be diffusion limited and thus also exhibited a strong size-dependence. Our findings highlight that the Ag-NP sulfidation rates result from a complex interplay of Ag-NP size, oxidation kinetics of the Ag-NP, and dissolution kinetics of MS. The sulfidation rates directly affect the half-life of Ag-NP in aquatic systems and consequently their potential (eco)toxicological effects on the aquatic environment.
        Speaker: Mr Basilius Thalmann (Eawag)
      • 12:30 PM
        Sulfur Poisoning and On-Stream Regeneration of a Ru/C Catalyst for Hydrothermal Biomass Reforming 2h
        Introduction The catalytic supercritical water gasification (SCW-G) of wet biomass is a highly efficient way of producing methane-rich synthetic natural gas (SNG) from various types of biomass. However, catalyst deactivation due to poisoning and fouling (coking) severely limits the lifetime of catalysts used in this process, making the development of regeneration protocols imperative [1]. Particularly, catalyst poisoning mechanisms by sulfur, a major obstacle in catalytic biomass conversion, need to be understood in order to design sulfur resistant catalysts and regeneration procedures. Materials and Methods The dynamic structural changes of a Ru/C catalyst (2 wt% Ru nanoparticles on coconut carbon) during the conversion of biomass model compounds to methane in supercritical water (400°C, 24.5 MPa) were studied in a continuous flow reactor. The structural analysis via in-situ EXAFS was combined with electronic structure calculations and isotope labeling in order to establish structure-reactivity relationships for both active and sulfur poisoned catalysts. The efficiency of on-stream regeneration of poisoned/deactivated catalysts, achieved by an oxidative treatment, was studied with in-situ XANES and isotope labeling. Results from these methods are accompanied by analysis of catalyst samples via electron microscopy, chemisorption and physisorption as well as MS and GC analysis of product gas samples. Results and Discussion The active catalyst phase under supercritical conditions is metallic Ru0. Sulfur poisoning of the catalyst occurs due to surface adsorption of sulfur atoms instead of bulk sulfidation. For complete sulfur poisoning, a surface coverage of about 40% was determined experimentally by in-situ EXAFS, suggesting that only the active sites of the catalyst are blocked by sulfur whereas the less active parts of the Ru surface most likely remain free. Using a combination of DFT calculations and direct chemical probing via isotope labeling, the pathway of the methanation reaction under hydrothermal conditions was resolved. Under SCW conditions, methanation proceeds via direct hydrogenation of (hydro-) carbon adsorbates on the Ru surface instead of the classic methanation pathway via carbon monoxide and hydrogen. On an active catalyst, organic molecules are predominantly broken down and dehydrogenated to surface bound C* before full hydrogenation to methane occurs. Upon sulfur poisoning, stripping of hydrogen from the hydrocarbon adsorbates proceeds at a much lower rate and leads to the preferential formation of CH* instead of C*. The change in the free energies of the (hydro-) carbon adsorbates on an S-poisoned Ru surface explains both the lower overall activity as well as the change in composition of isotope-labeled methane. Through a liquid-phase oxidation of the S-poisoned catalyst at mild conditions, the original state of the catalyst was restored, both in terms of surface reaction pathways as well as catalyst structure. This treatment does not seem to lead to Ru particle sintering or corrosion of the carbon support. Our current efforts are concentrated on finding optimal regeneration conditions that guarantee long term stability of the catalyst. Significance This work not only offers for the first time a mechanistic insight into hydrothermal biomass conversion – a new and challenging process – but also opens new pathways for performing and studying chemistry under conditions that go beyond the capabilities of most spectroscopic techniques and analytical setups. The presented results will enable a better understanding of reactions and catalysts under hydrothermal conditions and offer an incentive for the further development of biomass-to-SNG conversion processes. References 1. Elliott, D.C. Biofuels, Bioprod. Bioref. 2, 254 (2008)
        Speaker: Mr Marian Dreher (Paul Scherrer Institute)
      • 12:30 PM
        Surface and Bulk Rashba Splittings In Noncentrosymmetric BiTeI 2h
        In systems lacking bulk inversion symmetry the Kramer‘s degeneracy can be lifted by spin-orbit interaction giving rise to Dresselhaus or Rashba effects. Materials in the class of layered bismuth tellurohalides, such as BiTeI, have a layered and noncentrosymmetric structure with a giant Rashba-type splitting of the bulk bands. We present direct measurements of the bulk band structure of BiTeI measured with soft x-ray angle-resolved photoemission (ARPES), revealing the three-dimensional Fermi surface. The observed spindle torus shape bears the potential for a topological transition in the bulk by doping. Moreover, the bulk electronic structure is clearly disentangled from the two-dimensional surface electronic structure by means of high-resolution and spin-resolved ARPES measurements in the ultra-violet regime.
        Speaker: Gabriel Landolt (Paul Scherrer Institut)
      • 12:30 PM
        Switching of magnetic domains reveals evidence for spatially inhomogeneous superconductivity 2h
        The interplay of spin and charge fluctuations can lead to quantum phases with exceptional electronic properties. A case in point is magnetically-driven superconductivity, where magnetic correlations fundamentally affect the underlying symmetry and generate new physical properties. The superconducting wave-function in most known magnetic superconductors does not break translational symmetry. However, it has been predicted that modulated triplet p-wave superconductivity occurs in singlet d-wave superconductors with spin-density wave (SDW) order. Here we report evidence for the presence of a spatially inhomogeneous p-wave Cooper pair-density wave (PDW) in CeCoIn5. We show that the SDW domains can be switched completely by a tiny change of the magnetic field direction, which is naturally explained by the presence of triplet superconductivity. Further, the Q-phase phase emerges in a common magneto-superconducting quantum critical point. The Q-phase of CeCoIn5 thus represents a generic example where spatially modulated superconductivity is associated with SDW order.
        Speaker: Mr Simon Gerber (Laboratory for Neutron Scattering, Paul Scherrer Institut)
      • 12:30 PM
        Three-dimensional Percolation Properties Simulation of a Barrier Marine Coating Based on Its Real Structure from Ptychographic X-ray Tomography 2h
        Artificially structured coatings are widely employed to minimize materials deterioration and corrosion, the annual direct cost of which is over 3% of the gross domestic product (GDP) for industrial countries. Manufacturing higher performance anticorrosive coatings is one of the most efficient approaches to reduce this loss. However, three-dimensional (3D) structure of coatings, which determines their performance, has not been investigated in detail. Here we present a quantitative nano-scale analysis of the 3D spatial structure of an anticorrosive aluminium epoxy barrier marine coating obtained by ptychographic X-ray computed tomography (PXCT) [1-3]. From the analysis, orientations, lengths and volumes of individual objects in the coating film were revealed. We then use finite element simulations to demonstrate how percolation through this actual 3D structure impedes ion diffusion in the composite materials. We found the aluminium flakes align within 15 degrees of the coating surface in the material, causing the perpendicular diffusion resistance of the coating to be substantially higher than the pure epoxy [1]. The work demonstrated an approach for validating mechanistic assumptions of materials and potentially provides a practical method to engineer the efficacy of anti-corrosion coatings by modelling electrochemical process in materials based on the actual 3D structures. (This abstract is based on the content from reference [1].) [1] Chen, B. et al. Three-Dimensional Structure Analysis and Percolation Properties of a Barrier Marine Coating. Sci. Rep. 3, 1177 (2013). [2] Dierolf, M. et al. Ptychographic X-ray computed tomography at the nanoscale. Nature 467, 436–439 (2010). [3] Guizar-Sicairos, M. et al. Phase tomography from x-ray coherent diffractive imaging projections. Opt. Express 19, 21345–21357 (2011).
        Speaker: Dr Bo Chen (London Centre for Nanotechnology, University College London)
    • 2:00 PM 10:30 PM
      ESUO Annual Meeting WBGB/019

      WBGB/019

      Paul Scherrer Institut, Villigen, Switzerland

      • 2:00 PM
        Welcome notes by PSI and ESUO 5m
        Speakers: Prof. Joel F Mesot (Paul Scherrer Institut) , Prof. Ullrich Pietsch (University of Siegen)
      • 2:05 PM
        Presentation of PSI incl news from SLS & SwissFEL 25m
        Speaker: Johannes Friso van der Veen (Paul Scherrer Institut)
      • 2:30 PM
        ESUO activity report 30m
        Speaker: Prof. Ullrich Pietsch (University of Siegen)
      • 3:00 PM
        Situation of national user organizations 1h
        Speaker: Prof. Ullrich Pietsch (University of Siegen)
      • 4:00 PM
        Coffee 20m
      • 4:20 PM
        Presentation and discussion on BioStruct-X 1h 30m
        Speakers: Dr Anastassis Perrakis (he Netherlands Cancer Institute (NKI)) , Dr Matthias Wilmanns (EMBL Hamburg)
      • 5:50 PM
        CALIPSO status and next steps 30m
        After signature of the Grant Agreement, CALIPSO (www.calipso.wayforlight.eu) project is running towards it first milestones. The wayforlight portal will develop into a single entry point for European users, starting with the publication of standardized beamline datasheets for all European facilities. Forthcoming issues are the implementation of some Umbrella (www.umbrellaid.org) tools, pilot access procedures and a roadmap towards a standardized proposal format. ESUO continuous feedback and cooperation are crucial for the benefit of European users and for the overall project success.
        Speaker: Dr Cecilia Blasetti (Elettra - Sincrotrone Trieste)
      • 6:20 PM
        Visit of SLS and SwissFEL injector test facility 1h 10m
        Speaker: PSI visitor service
      • 7:30 PM
        Social Dinner at PSI restaurant OASE with music show 2h 30m
      • 10:00 PM
        Bus transfer from PSI to hotels 'Rotes Haus' and 'Terminus' 30m
    • 2:30 PM 6:00 PM
      Functional Materials WHGA/001

      WHGA/001

      Paul Scherrer Institut, Villigen, Switzerland

      Organizers: Z. Salman, E. Morenzoni, C. Niedermayer

      • 2:30 PM
        Lithium Transport through Nanosized Amorphous Silicon Layers 30m
        The talk presents an approach to use neutron reflectometry (NR) to measure non-destructively lithium transport through nanometer thin layers of, e.g., relevant electrochemical materials. Such experiments are interesting for research on nanostructured electrode materials to understand and improve high energy density lithium batteries. Beside the important role of Li diffusion for the insertion and removal of Li at electrodes, the determination of the Li permeability through ultrathin films is also of interest. This is especially true for devices where selective diffusion of Li is required. The selective filtering of Li is especially important for lithium-air batteries, Li ion selective electrodes, and sensors [1]. The methodology is demonstrated for 10 nm thin amorphous silicon layers covered by solid Li tracer reservoirs [2]. A multilayer with a repetition of five [Si / natLiNbO3 / Si / 6LiNbO3] units is used for analysis. Two types of NR Bragg peaks are detectable. One type of Bragg peaks originates from LiNbO3/Si chemical contrast, the other one from 6Li/7Li isotope contrast. Diffusion annealing reduces the intensity of the Bragg peak resulting from the 6Li/7Li isotope contrast but not that from the LiNbO3/Si chemical contrast. This demonstrates that the Bragg peak decrease is a measure of the 6Li and 7Li transport through the Si layer. These results open the possibility to determine the rate determining step (diffusion controlled or interface reaction controlled) of the Li transport process and to quantify Li transport parameters (diffusivity and permeability) in nanometer thin layers as a function of (i) chemical composition, (ii) film structure (amorphous or nanocrystalline), (iii) confinement (thickness of the layer) and (iv) temperature (e.g. to determine activation energy). References: [1] T.T. Truong, Y. Qin, Y. Ren, Z. Chen, M.K. Chan, J.P. Greely, K. Amine, and Y. Sun, Single crystal silicon membranes with high lithium conductivity and application in lithium-air batteries, Adv. Mater. 2011, 23, 4947. [2] E. Hüger, L. Dörrer, J. Rahn, T. Panzner, J. Stahn, G. Lilienkamp, and H. Schmidt, Lithium-Transport through Nanosized Amorphous Silicon Layers, Nano Lett. 2013, 13, 1237.
        Speaker: Dr Erwin Hueger (TU-Clausthal)
      • 3:00 PM
        Using muons as microscopic spin probes for organic devices 30m
        One future avenue that may expand the rapidly growing spintronic technology is to take advantage of the long spin coherence time and of the flexibility of organic semiconductors [1]. However, advancements in understanding the behaviour of hybrid organic/inorganic spintronic devices have been slowed down by the lack of experimental techniques able to directly measure the polarization of injected carriers in operational devices. We show how it is possible to use low energy muon spin rotation (LEM) to obtain a direct and depth-resolved measurement of the spin polarization of the injected charge-carriers in a fully functional organic spin valve. Muons act as local magnetic probes, directly measuring the magnetic field distribution at the implanted site. By measuring the local magnetic field with current on and current off it is possible to extract the contribution of the spin-polarized current. Using different implantation energies finally allows to obtain the depth-resolution [2]. Using LEM we were able to prove, for example, that it is possible to control the spin polarization of extracted charge-carriers from an OSC by the inclusion of a thin interfacial layer of polar material [3]. References [1] I. Bergenti et al., Org. Electron. 5, 309 (2004) [2] A.J. Drew et al., Nature Mater. 8, 109 (2009) [3] L. Schulz et al., Nature Mater. 10, 39 (2010)
        Speaker: Dr Laura Nuccio (University of Fribourg)
      • 3:30 PM
        Single-Ion Magnets: Playing with Molecule-Substrate Interactions 15m
        Single-Ion Magnets (SIMs) [1-3] contain a single transition metal or rare-earth ion embedded in an organic ligand. In contrast to many other mononuclear molecular magnets, SIMs exhibit long magnetization relaxation times rendering them good candidates for future molecular spintronics or information processing applications. In order to exploit their properties they should be organized and addressable one-by-one [4], and one way to achieve this goal is to deposit submonolayers of SIMs on to surfaces. Interestingly, the properties of SIMs can be strongly modified upon adsorption on a surface with respect to the bulk crystalline phase because of molecule-substrate interactions [5]. It is thus important to understand how these interactions can be employed to control magnetic and structural properties of the SIMs. We will present our most recent experiments with respect to these goals. [1] Ishikawa, N.; Sugita, M.; Ishikawa, T.; Koshihara, S.-y.; Kaizu, Y. J. Am. Chem. Soc. 2003, 125, 8694. [2] AlDamen, M. A.; Clemente-Juan, J. M.; Coronado, E.; Marti-Gastaldo, C.; Gaita-Arino, A. J. Am. Chem. Soc. 2008, 130, 8874. [3] Westerström, R.; Dreiser, J.; Piamonteze, C.; Muntwiler, M.; Weyeneth, S.; Brune, H.; Rusponi, S.; Nolting, F.; Popov, A.; Yang, S.; Dunsch, L.; Greber, T. J. Am. Chem. Soc. 2012, 134, 9840. [4] Gatteschi, D.; Cornia, A.; Mannini, M.; Sessoli, R. Inorg. Chem. 2009, 48, 3408. [5] Domingo, N.; Bellido, E.; Ruiz-Molina, D. Chem. Soc. Rev. 2012, 41, 258, and references therein.
        Speaker: Dr Jan Gui-Hyon Dreiser (Ecole Polytechnique Federale de Lausanne and Paul Scherrer Institut)
      • 3:45 PM
        Coffee 20m
      • 4:05 PM
        Phase change in stacked chalcogenide layers 15m
        Phase change materials (PCM) are promising substitutes for existing flash memories which have almost reached their miniaturization limit. The PCM memory storage is based on modification of optical and electrical properties at the transition from an amorphous to a crystalline state. Here, we report on single and bi-layer thin films of GeTe, SnSe and GaSb prepared by pulsed laser deposition on glass substrates. GeTe has been chosen because is one of the fastest phase change material with the switching speed of less than 10 ns. SnSe is very similar with GeTe, it has the same average number of valence electrons and almost the same band gap. Unlike GeTe which crystalizes in the rombohedral structure, SnSe crystalizes in the orthorombic structure. On the other hand, in the amorphous phase, SnSe is highly resistive which results in a lower current necessary to reset the memory cell. The third material, GaSb, is characterized by a remarkably high thermal stability and it crystalizes in a cubic structure. The variation of single layer resistance as function of temperature was measured by four-probe method in inert atmosphere. The bi-layer samples were annealed at different temperatures below and above their transition temperature. All the films have been investigated by Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD). The EXAFS analysis at the Ga, Ge and Se K-edges reveals information about the changes in local atomic environments as a function of temperature. Complementary to EXAFS analysis, X-ray diffraction spectra of the as-deposited and annealed samples were recorded in transmission at 17 keV. At specific annealing temperatures, discrete changes in the atomic long range order of bi-layers were detected. In the case of GeTe/SnSe bilayers we observed that SnSe increases the crystallization temperaure of GeTe. The formation of SbSn alloys in GaSb/SnSe bilayers at high annealing temperatures was evidenced.
        Speaker: Alin Velea (Paul Scherrer Institut)
      • 4:20 PM
        Electronic structure of impurity systems by resonant soft-X-ray ARPES: Application to the diluted magnetic semiconductor GaMnAs 15m
        A fundamental benefit soft-X-ray ARPES (SX-ARPES) in the energy range around 1 keV is the photoelectron escape depth increasing by a factor of 3-5 compared to the conventional VUV-ARPES. Furthermore, this region covers the 2p and 3p core levels of the transition and rare earth metals, respectively, which brings another benefit of the elemental and valence-state specificity achieved through resonant photoemission. These spectroscopic properties of SX-ARPES, combined with advanced instrumentation since recently available at the ADRESS beamline of SLS, have enabled the move of this technique from bulk materials to buried heterostructures and impurities. We illustrate first applications of resonant SX-ARPES to impurity systems with the diluted magnetic semiconductor (Ga,Mn)As, which is considered as the paradigm spintronics material. Despite more than a decade of intense research and various theoretical approaches ranging the p-d exchange to double-exchange models, the mechanism of ferromagnetism in (Ga,Mn)As still remains obscured. Our resonant SX-ARPES experiments on the Mn 2p absorption edge have for the first time unambiguously identified the Mn 3d-derived impurity band (IB) inducing the ferromagnetism as located about 300 meV below the valence-band maximum and hybridized with the light-hole band of the host GaAs. These findings conclude the long disputed picture on the (Ga,Mn)As valence band structure. The non-dispersive character of the IB and its energy alignment relative to the GaAs bands unveil its origin as a split-off Mn-impurity state predicted by the Anderson model. Responsible for the ferromagnetism in (Ga,Mn)As is the transport of hole carriers in the IB. Our experiments are further extended to (InFe)As showing the ferromagnetism induced by doped electron carriers. These examples illustrate an enormous application potential of SX-ARPES to a wide range of functional materials from bulk systems to heterostructures and impurities. [1] M. Kobayashi et al, http://arxiv.org/abs/1302.0063
        Speaker: Dr Vladimir Strocov (Swiss Light Source, Paul Scherrer Insitute, Switzerland)
      • 4:35 PM
        Electron Dynamics in TiO2 Nanoparticles Study by High Repetition Rate Laser Pump / X-ray Probe Technique 15m
        Electron migration and surface trapping are crucial in applications such as photocatalysis and solar energy conversion. Indeed for the former, the migration of charge carriers to the surface, where they can react with species adsorbed onto it, is the most important step. To address the issue of charge migration, we performed ps time resolved X-ray absorption spectroscopy at the Ti K-edge on TiO2 anatase nanoparticles suspension, using our recently developed high repetition rate data acquisition scheme [1]. After exciting electrons across the band gap at 355 nm, the transient spectrum (excited – ground state sample) at 100 ps clearly shows a localization of the electron at reduced Ti3+ centres that are coordination-unsaturated (i.e. tetra- or pentacoordinated, as opposed to hexacoordinated for the bulk). These unsaturated coordination sites predominantly occur at the surface due to truncation effects [2]. We found that the reduced centres, generated within the 70 ps width of the probe pulse, decay typically on two time scales, which we attribute to tetra- and penta-coordinated sites that are promptly populated, as opposed to a cascade mechanism from shallow to deep traps [3]. Similar results were obtained upon injection of an electron into the conduction band from an adsorbed Ruthenium dye (N719, as in dye-sensitized solar cells) excited at 532 nm. This implies that whichever way the electron is delivered to the CB, its ultimate trapping sites are identical. [1] F. Lima et al., Rev. Sci. Instrum. 2011, 82, 063111. [2] P.K. Naicker et al., J. Phys. Chem. B, 2005, 109, 15243. [3] Y. Tamaki et al., J. Phys. Chem. C 2009, 113, 11741.
        Speaker: Mrs Mercedes Hannelore Rittmann-Frank (Laboratoire de Spectroscopie Ultrarapide, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland)
    • 2:30 PM 6:10 PM
      Opportunities for Energy Research OSGA/E6 (PSI)

      OSGA/E6

      PSI

      Organizers: M. Nachtegaal, J.P. Embs, F. Marone

      • 2:30 PM
        Solid State Ion-dynamics in Materials for Future Energy Devices 30m
        One of the most important scientific problems to solve for our modern society is how to convert and store clean energy. In order to accomplish a paradigm shift in this field we need to understand the fundamental dynamical processes that govern the transfer of energy on an atomic scale. For future energy devices like solid-state batteries (SSB) as well as solid-oxide fuel cells (SOFC) this means understanding and controlling the complex mechanisms of ion diffusion in solid matter. Only recently, developments of state-of-the-art large scale experimental facilities e.g. neutron/muon spallation sources as well as free electron lasers, have opened new possibilities for studying such intrinsic material properties in a straightforward manner. Layered transition metal oxides (TMOs) have been extensively studied both for their correlated electronic properties (frustrated magnetism and superconductivity) as well as for energy applications e.g. Li-ion batteries or thermoelectrics. Recently these two fields have been unified under the framework of the layered NaxCoO2 family where Na-ion vacancy order as well as dynamics has been shown to tailor low-temperature magnetic and thermoelectric properties. In addition, room-temperature sodium batteries are currently receiving considerable attention since the available lithium reserves of our planet are very limited. In many ways the NaxCoO2 compound is the Na-analog of the most common Li-ion battery electrode LixCoO2. Hence, understanding Na-ion diffusion mechanisms of NaxCoO2 would seem a logical first step. Consequently, we have conducted systematic studies of this compound using neutron powder diffraction (NPD) [1], quasi-elastic neutron scattering (QENS) [2] and muon spin relaxation/rotation ($\mu$SR) [3-4] as a function of temperature as well as Na-content (x) and pressure [5]. In this talk I will show how our use of neutron scattering and $\mu$SR has established a novel and detailed insight into the ion diffusion mechanisms in this group of compounds. Further, such knowledge now allows us to contemplate and actively consider future possibilities for tuning fundamental physical properties as well as solid state engineering of energy related materials with improved functional properties. REFERENCES [1] M. Medarde, M. Månsson et al., Physical Review Letters, 110, 266401 (2013) [2] F. Juranyi et al., publication in progress [3] J. Sugiyama, M. Månsson et al., Physical Review Letters, 103, 147601 (2009) [4] M. Månsson et al., Submitted for publication [5] Y. Sassa, M. Medarde, M. Månsson et al., publication in progress
        Speaker: Dr Martin Mansson (Laboratory for Quantum Magnetism (LQM), EPF Lausanne)
      • 3:00 PM
        Neutrons and the Prospects for a Sorption Based Hydrogen Storage System 30m
        The substantial effort by many groups around the world to solve the problem of storing large amounts of hydrogen in the fuel tank of a car, along with facile release of and recharging with H2 at near-ambient conditions, has not yet resulted in a practical system. One common approach has been to utilize adsorption of H2 in porous materials, which have favourable adsorption/desorption kinetics, but low capacities at desirable operating conditions because of weak hydrogen binding energies. Various strategies for strengthening the interactions of H2 in porous materials have been implemented by materials synthesis. These improvements can be understood at a molecular level with the use of inelastic neutron scattering (INS) spectroscopy of the hindered rotations of the hydrogen molecules adsorbed at various sites, particularly when combined with sophisticated computational studies. The results of our systematic studies on a large number of porous materials provide some of the necessary information and thereby give direction to efforts in the synthesis of new materials aimed at reaching the goal of a practical sorption based hydrogen storage material. The work reported herein is the outcome of a large number of collaborations with many investigators, particularly P. Georgiev, I. Matanović, M. Eddaoudi, M. Zaworotko, O. Yaghi, D. Antonelli, and their groups
        Speaker: Peter Georgiev (University of Sofia)
      • 3:30 PM
        Small-angle scattering studies of graft-copolymer electrolytes 30m
        The fuel cell, using a polymer electrolyte, is a clean and efficient electrochemical energy conversion device and is attractive for portable electronics, distributed power source, and electric vehicle applications. The limited lifetime and the high cost of commercially available electrolytes, however, block the large-scale commercialization. Radiation-grafted copolymers have attracted considerable attention owing to the cost-competitive and versatile synthesis. The current focus is on (a) improving the chemical stability, (b) obtaining mechanical integrity at high ionic content, and (c) sustaining ionic conductivity at low water content. The phase-separated structure of the polymer electrolyte is a key parameter for (b) and (c), and small-angle scattering is an outstanding technique to study structure on the relevant length-scales. Insights into the certain relationships between fuel-cell-relevant properties and electrolyte structure will be presented.
        Speaker: Dr Sandor Balog (Adolphe Merkle Institute, University of Fribourg)
      • 4:00 PM
        Coffee 20m
      • 4:20 PM
        Structural characterization of polymer solar cells, from high resolution to high through-put 30m
        The structure and architecture of polymer solar cells on scales from nm to mm have crucial impact for the device performance. With standard X-ray scattering techniques, we may determine donor and acceptor domain sizes in polymer solar cells, crystalline structure and characterize the dimensionality of the interface, but to quantify the capability of the nanostructure for separating electron-hole pairs and for transporting free charges, we need access to the 3D structure on the nm scale. X-ray ptychography has the potential to allow these investigations, and has the further advantage that it is a reasonably mild technique, due to the weak interaction of X-rays with the material, as compared to electron and soft X-ray transmission microscopy, where dose loads are much higher. We have carried out very promising studies at cSAXS, where we with reasonable ease approach a 100 nm spatial resolution, and with clear pathways for improving resolution. In a completely different type of experiment, synchrotron X-rays were used to probe active materials for polymer solar cells on flexible polyester foil. The active material was coated onto the flexible 130 micron thick polyester foil using roll-to-roll differentially pumped slot-die coating and presented variation in composition, thickness and additives. The coated foil was passed through the synchrotron X-ray beam on a small unit comprising unwinder and winder for the foil roll, an X-ray probe station and a barcode reader for sample registration. Foil lengths of 8 meters were probed and yielded X-ray scattering data for every ̴ 1 cm along the foil that presented linear variations in processing and coating parameters along the foil length. We demonstrate a synchrotron X-ray based characterization method that is compatible with roll-to-roll coating methods in terms of speed and that provides detailed information on morphology and the effect of processing parameters on the same scale and in the same volume as the manufacturing method. We found that X-ray characterization is possible at web speeds of up to 6 m min-1. We found a distinctive morphological effect of changing the donor/acceptor blend ratio and of introducing chloronaphthalene as a processing additive.
        Speaker: Dr Jens Wenzel Andreasen (Technical University of Denmark)
      • 4:50 PM
        Synchrotron x-ray and neutron imaging for the investigation of fuel cells 30m
        Tomography and radiography are non-destructive investigation methods that are successfully applied in various fields in materials science and fundamental research. Neutron and x-ray imaging can be used for investigation of polymer electrolyte membrane fuel cells (PEMFC) and their components on different length scales. X-ray imaging resolves inner sample details with micrometric spatial resolution. The ability of neutron radiation to penetrate thick layers of metals and being extremely sensitive to small amounts of hydrogenous materials at the same time allows for investigation of the water management in PEMFCs. In this way the information gained by complementary non-destructive investigation of samples by x-ray and neutron tomography is unique.
        Speaker: Dr Ingo Manke (HZB)
      • 5:20 PM
        Discussion 20m
    • 2:30 PM 6:00 PM
      Strongly Correlated Electron Systems: Novel Interaction Phenomena WWHB/106

      WWHB/106

      Paul Scherrer Institut, Villigen, Switzerland

      Organizers: JH Dil, C. Rüegg

      • 2:30 PM
        Flux line lattice studies of UPt3 using small-angle neutron scattering 30m
        The heavy-fermion material UPt3 can be considered as a paradigm for unconventional superconductivity. The Cooper pairs in this material are believed to form a triplet, introducing an addition degree of freedom and leading to the formation of three distinct superconducting phases. Despite intense studies the exact nature of the order parameter in this material have remained elusive. We have used small-angle neutron scattering (SANS) to study the vortex lattice (VL) in UPt3. The vortices reflect the properties of the host material and SANS can therefore be used as a bulk probe of the superconducting state. Measurements of the temperature dependent VL scattering allow a deconvolution of the contributions to the VL form factor from currents along the a∗ and c-axes, and gives direct information about the nodal structure of the order parameter. The results are consistent with a linear temperature dependence at low temperatures of the c-axis penetration depth and support the assignment of E2u symmetry to the superconducting state of UPt3. Studies with the fields along the crystalline c-axis show a rotation of the VL and a subtle dependence on magnetic field history. The results indicate a coupling between the VL orientation and the chirality of the superconducting state, differing between vortices with screening currents circulating with or against the chiral direction.
        Speaker: Prof. Morten Ring Eskildsen (University of Notre Dame)
      • 3:00 PM
        Amplitude-modulated magnetic order and persistent spin dynamics in frustrated multiferroic FeTe2O5Br 30m
        Exotic magnetic ground states are often induced by geometrical frustration, imposing unbalance into the system and thus making it highly susceptible to all kinds of perturbations. As a result, frustrated systems may develop incommensurate magnetic long-range orders (LRO), highly disordered static spin-glass phases or even dynamic spin-liquid states. Moreover, complex magnetic LRO can induce ordering of other degrees of freedom (e.g., electric polarization in multiferroics) or may even be accompanied by persistent spin dynamics (PSD). The two extraordinary phenomena are rare and still lack a comprehensive description. We focus on a layered FeTe¬2O5Br system, which below TN1=11K develops an amplitude-modulated incommensurate magnetic LRO [1], which is below the second transition, at TN2=10.5K, accompanied by electric polarization [1]. The incommensurate modulation appears to originate form surprisingly strong Fe-O-Te-O-Fe exchanges, forming a magnetic exchange network composed of Fe3+ (S=5/2) spin chains coupled by weaker frustrating interactions [2]. Here presented results [3,4] reveal that complex magnetic ordering has a weak perpendicular component, leading to an overall elliptical structure. Nevertheless, the amplitude modulation is preserved and is accompanied by spin fluctuations, persisting at lowest accessible temperatures, hereby offering a well-defined framework and a coherent explanation for the coexistence of LRO and PSD [4]. [1] M. Pregelj et al., PRL 103, 147202 (2009), M. Pregelj et al., PRB 82, 144438 (2010). [2] M. Pregelj et al., PRB 86, 054402 (2012). [3] M. Pregelj et al., PRB 87, 144408 (2013). [4] M. Pregelj et al., PRL 109, 227202 (2012)
        Speaker: Dr Matej Pregelj (Jožef Stefan Institute)
      • 3:30 PM
        Magnetic Order in the Quasi-One-Dimensional Ising System RbCoCl3 15m
        The magnetic order in RbCoCl3 was investigated in a series of neutron scattering experiments at SINQ, PSI, on powder and single-crystal samples between 1.5 K and 300 K. RbCoCl3 is a hexagonal perovskite of CsNiCl3 type structure. It crystallizes in space group P63/mmc with lattice parameters of a=7.0003(3) Å and c=5.9959(2) Å at room temperature. Upon cooling the octahedrally coordinated high-spin Co2+ ions show one-dimensional (1D) antiferromagnetic (AFM) interactions along the c-axis. At TN1=28 K 3D AFM order occurs with k=(1/3,1/3,1). The magnetic moments are aligned along the c-axis with μz=3.97(2) μB and an amplitude modulation in the ab-plane. A second magnetic phase transition is observed at TN2=13 K where the moments along the c-axis increase to μz=4.08(1) μB and two additional propagations k=(0,0,1) and k=(1/2,0,1) occur. The k-vectors were confirmed by single crystal neutron scattering. In agreement to the neutron scattering data, the magnetic susceptibility along the c-axis shows a broad maximum at 90 K due to 1D AFM interactions along the [CoCl6/2]- chains. The heat capacity shows a λ-anomaly at TN1 but no effect at TN2. Results from inelastic neutron scattering on RbCoCl3 will be presented separately.
        Speaker: Ms Nora Hänni (Universität Bern)
      • 3:45 PM
        Resonant Soft X-Ray Scattering On Artificial Spin Ice 15m
        Artificial spin ice comprises coupled dipolar magnetic nanoislands placed at the sites of a square or kagome planar lattice [1,2]. These particular geometries prevent the dipolar interactions to be simultaneously satisfied at the vertices where the islands meet, making the system magnetically frustrated. Microscopy techniques (magnetic force microscopy [3], photoelectron microscopy [4], Lorentz microscopy [5]) are usually employed to investigate such systems and to directly resolve the magnetic configuration of the islands. In contrast, scattering is a complementary method which provides information on magnetic correlations over length and time scales not accessible with microscopy [6]. In the present work, we employ soft x-ray resonant magnetic scattering with circularly-polarized light to study the organization of the magnetic configurations in artificial square spin ice. The scattering patterns are recorded by a CCD camera, providing an extended picture of the reciprocal space in two dimensions. By varying the applied magnetic field, we track the variations of the Bragg peaks intensity using the dichroic contrast. Pure magnetic Bragg peaks observed in as-grown samples indicate the presence of a long-range antiferromagnetic ordered phase [3], which is subsequently destroyed by orienting the magnetic moments with an applied field. Numerical simulations based on the kinematical approach can correctly reproduce the experimental scattering patterns, allowing us to estimate the number of reversed moments along the two directions of the square lattice. [1] A.S. Wills, R. Ballou and C. Lacroix, Physical Review B 66, 144407 (2002). [2] R.F, Wang et al., Nature 439, 303-306 (2006). [3] J.P. Morgan et al., Nature Physics 7, 75-79 (2011). [4] C. Phatak et al., Physical Review B 83, 174431 (2011). [5] E. Mengotti et al., Nature Physics 7, 68-74 (2011). [6] K. Chesnel et al., Physical Review B 66, 172404 (2002).
        Speaker: Dr Luca Anghinolfi (Paul Scherrer Institute)
      • 4:00 PM
        Coffee 20m
      • 4:20 PM
        Doping evolution of the magnetic excitations in the high-temperature superconducting cuprates 30m
        High resolution resonant inelastic x-ray scattering (RIXS) has recently emerged as a highly sensitive probe of magnetic excitations – it can even be used to measure magnetic excitations in isolated one-unit-cell-thick La2CuO4 layers [1]. This talk will describe how RIXS has provided new insights into the magnetic excitations in the high-temperature superconducting cuprates. Photoemission and scanning tunneling spectroscopy have given us exquisitely detailed picture of the electronic structure of Bi2Sr2CaCu2O8+delta, but little is known about its high-energy (>100 meV) magnetic response. Using RIXS we measure the magnetic response [2] and show that a phenomenological theory based on electron pockets can consistently describe the electronic and magnetic response of this cuprate [2, 3]. In the heavily overdoped cuprates such as La2-xSrxCuO4 (x>0.3) superconductivity disappears despite the high electronic density of states. We used RIXS to measure the magnetic excitations across the whole La2-xSrxCuO4 phase diagram. The magnons induced by local moment physics in La2CuO4 evolve smoothly into broadened paramagnons in the overdoped state where itinerant quasi-particles dominate most properties of the cuprates. The fact that paramagnons persist relatively unchanged as superconductivity disappears is very difficult to reconcile with theories that suggest these high-energy paramagnons seen by RIXS, rather than the lower energy magnetic excitation in other regions of the Brillouin zone, are causing superconducting pairing [4]. [1] M. P. M. Dean et al. Nature Materials 11, 850–854 (2012) [2] M. P. M. Dean et al. Phys. Rev. Lett. 110, 147001 (2013) [3] A. J. A. James, T. M. Rice and R. M. Konik, Phys. Rev. B 86, 100508(R) (2012) [4] M. P. M. Dean et al. arXiv:1303.5359 (2013) (in press at Nature Materials.)
        Speaker: Dr Mark Dean (Brookhaven National Laboratory)
      • 4:50 PM
        Ultrafast Studies of Laser Induced Dynamics in Charge and Orbital Ordered Manganites 15m
        Disentangling the coupled processes in the material class of strongly correlated electron materials offers great challenges due to their intricate balance of competing structural, magnetic and charge interactions. In order to advance the understanding of the underlying correlations in these materials our current efforts focus on the interaction of the atomic, electronic, and magnetic subsystems on their relevant time scales. In the atomic and molecular regime masses are so light and distances so short such that these time scales shift to the subpicosecond range. Here, we present our study of specific lattice modulations coupled to the melting of charge and orbital order in a manganite by means of femtosecond x-ray diffraction. More recently, by recording Bragg reflections sensitive to the charge, orbital and structural order on and off resonance at a free electron laser further progress is made to disentangle the interactions of the different ordering mechanisms.
        Speaker: Andrin Caviezel (Paul Scherrer Institut)
      • 5:05 PM
        Discussion 15m
    • 8:15 AM 2:30 PM
      ESUO Annual Meeting WBGB/019

      WBGB/019

      Paul Scherrer Institut, Villigen, Switzerland

      • 8:15 AM
        Bus transfer from hotels 'Rotes Haus' and 'Terminus' to PSI 45m
      • 9:00 AM
        Future of Transnational Access in 'Horizon 2020' 40m
        Speaker: Dr Jonas Oehler (EU Grants Access, ETH Zurich - University of Zurich)
      • 9:40 AM
        News from Umbrella 20m
        Speaker: Mirjam van Daalen (Paul Scherrer Institut)
      • 10:00 AM
        Coffee 30m
      • 10:30 AM
        Specialized user groups: status and next steps 1h
        Speaker: All
      • 11:30 AM
        ESUO website: status and next steps 15m
        Speaker: All
      • 11:45 AM
        aob 30m
        Speaker: All
      • 12:15 PM
        Lunch 1h 45m
      • 2:00 PM
        End of meeting (public transportation to Zurich airport) 30m