JUM@P '11: Joint Users' Meeting at PSI 2011

15 Sept 2011, 09:00 → 17 Sept 2011, 18:00 Europe/Zurich

Paul Scherrer Institut, Villigen, Switzerland

Thursday 15 September

Registration

Plenary session

1 Welcome

Speaker: Prof. Joel Mesot (Paul Scherrer Institut)

2 In situ structure-function studies of metal catalysts

The continuing search for more efficient processes for the manufacture of fuels, chemicals and materials is one of the more significant components in attaining a globally sustainable lifestyle. Whether it in atom-efficient syntheses, environmental protection, or transformations from alternative feedstocks, an understanding of the relationship between local structure around catalytic centres and the activity and selectivity provides the basis of catalyst design. By a combination of structure-sensitive spectroscopies (XAFS, IR, uv-visible) these centres can be probed under relevant conditions, the aim being to establish the primary reaction steps associated with a catalytic cycle. Using examples from oxide-supported metals, related to the automotive exhaust catalysts, and molecular catalysts for selective manufacture of linear alkenes, the strengths and weaknesses of in situ, steady-state, perturbed and photo-excited techniques to probe catalytic cycles will be discussed.

Speaker: Prof. John Evans (University of Southampton and Diamond Light Source, Oxfordshire, UK)

3 Tomographic insight into the evolutionary assembly of the vertebrate head

Most living vertebrates are jawed vertebrates (gnathostomes), and the living jawless vertebrates (cyclostomes) provide scarce information about the profound reorganization of the vertebrate head during the evolutionary origin of jaws. The extinct bony jawless vertebrates (ostracoderms) are regarded as precursors of jawed vertebrates, providing insight into this formative episode in vertebrate evolution. Using synchrotron radiation X-ray tomography, we describe the cranial anatomy of galeaspids, a 435–370 Ma ‘ostracoderm’ group from China and Vietnam. The paired nasal sacs of galeaspids are located anterolaterally in the braincase, and the hypophyseal duct opens anteriorly towards the oral cavity. These structures were thus already independent of each other, like in gnathostomes and unlike in cyclostomes and osteostracans and, therefore, have the condition that current developmental models regard as prerequisites for the development of jaws. Thus, reorganization of vertebrate head was not driven deterministically by the evolutionary origin of jaws but occurred stepwise, ultimately allowing the rostral growth of ectomesenchyme that now characterizes gnathostome head development.

Speaker: Prof. Philip Donoghue (University of Bristol, UK)

Poster session I and lunch

4 Sample Environment News

The sample environment team at PSI provides expertise and support for systems to manipulate the sample or its environment during experiments at large scale facilities. A variety of cryostats, furnaces and cryo-magnets enable experiments under extreme conditions. Over the past years we have extended the experimental possibilities substantially. We will present a selection of new setups which have been successfully used for neutron scattering experiments. This includes examples such as a new horizontal magnet of 6.8 T, electric fields at low and ultra low temperatures using voltages up to 6 kV and high currents at the mK temperature range.

Speaker: Dr Marek Bartkowiak (Paul Scherrer Institut)

5 First experiment at the new SINQ beamline BOA

The operation of the multi-purpose neutron beamline BOA (Beamline for neutron Optics and other Approaches) has started successfully in May 2011. BOA is a 18 m long instrument located at beam-channel 51 looking on the SINQ cold source and is actually a redesign of the former FUNSPIN beamline. The primary polarization element (polarizing bender) of FUNSPIN was kept because research with polarized neutrons is of key interest in the neutron scattering community. The position of BOA close to the cold source is crucial for the performance of the instrument: The measured polarized neutron flux is around 1x108 n / (cm2 s mA)-1. The secondary instrument consists of a highly flexible geometry. It is equipped with three rotating axes with flexible translation tables and aperture units. The maximum available free space is around 12 m, which allows new experiments presently not possible at SINQ. An area sensitive CCD camera system and optionally a He-3 neutron counter are available for data acquisition. The beam characterisation measurements have shown that BOA fulfils the performance predicted by extensive McStas/MCNPX simulations done in 2010. In a first experiment making use of the excellen

Speaker: Dr Uwe Filges (Paul Scherrer Institut)

6 Scanning small-angle X-ray scattering at the cSAXS beamline

Scanning small-angle X-ray scattering (SAXS) images the density and orientation of nanostructures. As a 2D imaging technique it can be applied to spatially resolved investigations on square centimeters large samples, i.e., information on nanoscale structures is imaged over comparatively large areas. In computed tomography mode 3D investigations are feasible as well. For each voxel the full SAXS pattern can be reconstructed. Therefore a rich set of information can be retrieved and several image representations result from a single SAXS scan. As an example scanning SAXS tomography data on rat brains are presented. We show the extraction of a scattering peak corresponding to myelin, the layered material that surrounds the axons of nerve cells. Demyelination is for example causing multiple sclerosis and we hope that scanning SAXS data can contribute to a deeper understanding of diseases.

Speaker: Dr Oliver Bunk (Paul Scherrer Institute, 5232 Villigen PSI, Switzerland)

7 Characterization of a 20 nm hard X-ray focus by ptychographic coherent diffractive imaging

Recent advances in the fabrication of diffractive X-ray optics have demonstrated hard X-rays focal spots below 30 nm. However, the characterization of these devices is not straightforward using conventional methods such as knife edge scans. Here, we have used ptychographic scanning coherent diffractive imaging to characterize a 20 nm-wide X-ray focus produced by Fresnel zone plate at a photon energy of 6.2 keV. A scanning transmission X-ray microscope was modified to perform the ptychographic scans on a test object. The ptychographic algorithms allowed the reconstruction of the image of the test object as well as the 3D reconstruction of a focused hard X-ray beam waist. The reconstructed wavefields confirm that the diffractive x-ray lenses were focusing the incoming radiation into spots as small as 20 nm. This method yields a full description of the focusing field at any propagation distance, including wavefront aberrations at the plane of the lens, and demonstrates its usefulness for metrology and alignment of nanofocusing X-ray optics. It is very robust against the longitudinal position of the sample, and requires no previous knowledge of the test object.

Speaker: Dr Ana Diaz (Paul Scherrer Institut)

8 Combining 3-D X-ray Velocimetry with ultra-fast tomography at TOMCAT

The capabilities of the ultra-fast tomography endstation at TOMCAT to visualise the 3-D structure of rapidly moving objects at high resolution, provide also the requirements for the accurate quantitative determination of motion. This is a very important ability in many areas of research, such as in the fields of materials and biomedical science. Whilst visible light velocimetry methods have long been used for the measurement of flow, X-ray velocimetry is a relatively new method. Its primary advantage is the penetrating power of X-rays which allows transmission through opaque samples, and also gives a measurement that is volumetric (rather than planar). Combining X-ray velocimetry with tomography is an even more recent advance. Fast image sequences may be obtained at multiple projection angles, and depending on the rate of movement, statistical cross-correlation analysis and/or more simple particle-tracking algorithms may be used to determine motion in 3-D. Here we present some examples, and the first results of such measurements newly incorporated into the TOMCAT beamline.

Speaker: Dr Sarah Irvine (University of Lausanne (UNIL) and the Paul Scherrer Institute (PSI))

9 4D microtomographic imaging with sub-second temporal resolution with hard X-rays.

A new fast tomographic data acquisition scheme [1] is being developed at the TOMCAT beamline. We acquire the full set of (600-1000) tomographic projections in typically 0.5 seconds with the voxel sizes ranging from 0.5 to 11 μm and a corresponding field of view from 0.7 to 22 mm. The acquisition of 4D series with high temporal and spatial resolution opens up the possibilities to observe dynamic phenomena at the microscale. A wide range of in-situ and in-vivo experiments will benefit from such unique capabilities. We will report the challenges and successes of 4D imaging. References [1] R. Mokso, F. Marone, D. Haberthuer, J. Schittny, G. Mikuljan, A. Isenegger, M. Stampanoni, AIP Conf. Proc. , XRM2010 (2011)

Speaker: Dr Rajmund Mokso (Paul Scherrer Institut)

10 Ultrafast Data Post Processing Pipeline for Real-Time Tomographic Imaging at TOMCAT

At the TOMCAT beamline at the Swiss Light Source, current efforts are focused on the development of a new endstation, devoted to tomographic microscopy with sub-second temporal resolution. Despite the continuous progress in computing technology, fast post processing of the large amount of data produced (up to 10 Gb/s) by this new endstation is, however, still difficult, if not impossible, with standard approaches. New solutions are mandatory to fully exploit advantages provided by this high acquisition speed. Our current scientific activities focus namely on the development of new strategies for efficient handling and fast post processing of large amount of data to complement the hardware implementation. Until recently most efforts were spent on tomographic reconstruction algorithms, in particular validating Fourier methods as alternatives to the standard Filtered Back-Projection approach. Currently, the rest of the post processing pipeline is also taken into account, with focus on an optimized data format permitting fast I/O, on rapid sinogram generation and the efficient usage of the available computational resources. Our latest solutions and performances will be presented.

Speaker: Prof. Marco Stampanoni (SYN-PSI and Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland)

11 X-ray tomographic microscopy at TOMCAT: an overview

During its first five years of life, 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. 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 0.37 up to 14.8 microns is routinely performed. Phase contrast is obtained either with simple edge-enhancement, propagation based techniques or grating interferometry. Typical acquisition times are in the order of few minutes. An automatic sample exchanger is available for high throughput studies. In addition, new cutting edge experiments are now possible thanks to the latest efforts towards improving spatial and temporal resolution. Nanostructures (100 nm) in micrometer size samples can be imaged using a full-field hard X-ray microscope. Dynamic processes can be followed in 3D for the first time thanks to the new ultrafast tomographic endstation offering sub-second temporal resolution. A laser-heated furnace, a cryo-chamber and a compression-tensile device are available for in-situ experiments.

Speaker: Prof. Marco Stampanoni (SYN-PSI and Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland)

12 Nanotomographic Imaging at TOMCAT

Synchrotron-based full-field tomographic microscopy established itself as a tool for non-invasive investigations. Many beamlines worldwide routinely achieve micrometer spatial resolution while the isotropic 100 nm barrier is reached and trespassed only by few instruments, mainly in the soft X-ray regime. We present an X-ray, full field microscope with tomographic capabilities operating at 10 keV and with a 3D isotropic resolution of 144 nm recently installed at the TOMCAT beamline of the Swiss Light Source. Custom optical components including a beamshaping condenser and phase-shifting dot arrays were used to obtain an ideal, aperture-matched sample illumination and very sensitive phase contrast imaging. The instrument has been successfully used for the non-destructive, volumetric investigation of single, unstained cells, bacteria and other biological samples. The instrument also performs well when dealing with material science specimen, like fresh cement pastes and similar.

Speaker: Prof. Marco Stampanoni (Paul Scherrer Institut)

13 Biomedical research with X-ray grating interferometry at TOMCAT

Hard X-ray grating interferometry (GI) offers a unique combination of properties that renders this X-ray imaging technique especially suitable for the application in the field of biomedical research. First, GI delivers virtually non-destructive information on the micrometer scale and, thus, can be used either complementary or alternative to destructive methods such as histology. Secondly, GI intrinsically delivers three complementary aspects of the sample, which are related to absorption, phase and dark-field contrast. Third and most importantly, GI shows a particular high sensitivity towards density variations present in the sample. We present an excerpt of the ongoing biomedical research at the TOMCAT beamline, where we take advantage of the unique properties of GI. This research is performed in collaboration with the Clinic for Cardiovascular Surgery of the University Hospital of Zurich, Switzerland. The examples include the monitoring of scaffold degradation in tissue-engineered heart valves as well as micro-structural analysis of calcified heart valves, where we used the complementary contrasts to simultaneously segment otherwise virtually inseparable tissue.

Speaker: Dr Peter Modregger (Swiss Light Source, Paul Scherrer Institut, Switzerland)

14 Ultra-fast Radiography on the Fly

Recent advances in synchrotron-based ultra-fast radiography have led to improved spatial resolution and contrast-to-noise ratios at high frame rates. These developments facilitate the observation of ever faster biological processes in vivo. Here we present a radiographic time series of wingbeats of two insects in tethered flight: the blowfly Calliphora vicina and the hoverfly Eristalis tenax, using the TOMCAT beamline of the Swiss Light Source. The temporal frequency of the projections allowed for image acquisition at over 2000 frames per second, equivalent to between ten and twenty radiographs per wingbeat. We now aim to use these data to reconstruct 3D time series of the wing hinge and neck motor systems during flight, by combining a large number of projections covering many wing-position / projection angle combinations. We have also investigated the image quality and radiobiological sustainability of mono- and polychromatic beams with different energy spectra and intensities. The high-resolution in vivo imaging technique used here is expected to drive new discoveries in animal biomechanics.

Speakers: Mr Daniel A Schwyn (Imperial College London), Dr Rajmund Mokso (Paul Scherrer Institute), Dr Simon M Walker (University of Oxford)

15 X-ray differential phase contrast tomography on a compact industrial micro CT scanner

Today's industrial X-ray micro computed tomography (µCT) specimen systems allow high resolution 3-D examination of samples in biology or materials science. Up to now, X-ray absorption contrast imaging has been the standard contrast mechanism in these systems. Recent developments showed that phase contrast imaging can lead to significant contrast enhancements [1]. In the past few years, grating interferometry has established itself as a suitable technique for differential phase contrast (DPC) imaging on conventional X-ray tubes [2]. We have developed a new imaging setup based on a grating interferometer and a microfocus X-ray tube. With a uniquely short setup length of 32cm, the setup geometry has been designed for an immediate integration into a commercial SCANCO Medical µCT 100 scanner. As opposed to conventionally used planar shaped gratings, cylindrically bent gratings are used, resolving the problem of a limited field of view [3]. Here we present the first imaging results on the µCT scanner. References: [1] A. Momose et al., Med. Phys, 22 (375-379), 1995 [2] F. Pfeiffer et al., Nature Phys., 2 (258-261), 2006 [3] T. Thüring et al., accepted for Appl. Phys. Lett., 2011

Speaker: Mr Thomas Thuering (Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland)

16 Simulation of grating-based hard X-ray imaging by combining Monte Carlo methods and wave optics

Grating-based hard X-ray imaging is a recently established imaging technique which simultaneously provides absorption, phase and dark-field contrast. Numerical simulations can provide a deeper theoretical understanding of the image formation process which may be used for optimization of both experimental set-up and data analysis procedures. Since phase contrast relies on beam coherence and dark-field contrast is related to incoherent scattering, both particle and wave like behavior of the x-rays have to be considered. Particle-like properties are realistically simulated using Monte Carlo (MC) methods, but MC neglects coherent effects such as interference. Wave-like properties on the other hand are conveniently simulated using wave optics, in which, however, incoherent scattering cannot be modeled in a straight forward way. A simulation package has been developed which combines MC with wave optics simulations. The simulation package was validated by comparison of simulated and measured tomographic images. The comparison showed good agreement. This model can now for instance be used for experimental data corrections or realistic investigations of the origin of the dark-field signal.

Speaker: Silvia Peter (Paul Scherrer Institut)

17 Silver nanoparticles and synchrotron light-based nanotoxicology: new imaging modalities

Silver nanoparticles belong to the most studied, produced and broadly distributed nanoparticles. Despite this, a critical investigation of their potential adverse effects on model living and ecological systems is still required. Along well-established biochemical tests, a reproducible and simple methodology to image their precise distribution in cells is missing. Their imaging in cells requires usually complex preparation like embedment/sectioning for electron microscopy or may have only a limited spatial resolution like in confocal Raman Microscopy. Often, studying the chemical composition and oxidation state of elements within a cell is a daring task. Our aim is thus to further exploit synchrotron radiation for nanotoxicology and contribute to develop complementary protocols for biological object imaging. To do this, we incubate a model macrophage cell line with our in house developed silver nanoparticles system and study the internal distribution of particles using ptychography, Scanning X Ray Transmission Microscopy (STXM), tomography and X ray absorption spectroscopy at the cSAXS and microXAS beamlines at SLS. We will present our first results in this poster.

Speaker: Dr Alexandre Mantion (BAM Federal Institute for Materials Research and Testing)

18 The mean acinar volume shows an unproportional growth compared to the total lung volume

The pulmonary acinus represents the functional unit of the lung. Due to a restricted availability of high resolution imaging methods the knowledge about the development of the pulmonary acini is limited. Using synchrotron radiation based tomographic microscopy we developed a method to estimate the volume of single acini throughout postnatal lung development. More than 1000 functional units of the lung, the so-called acini were isolated from tomographic datasets of rat lungs acquired at the TOMCAT beamline by closing the transition between conducting and gas-exchanging airways bronchioles semi-automatically with three-dimensional discs acting as segmentation breakpoints. The volume of each acinus was determined by subsequent voxel counting. While the volume of the right lower lung lobe increases approximately 10x during postnatal lung development from day 4 to 60, we detected a smaller increase in the volumes of the single acini (approximately 5.5x) for the same time-span. We hypothesize that at days 10 and 60 a larger number of acini is present or that the growth of the acini is unproportional in regard to its location in the lung lobe (central or peripheral parts of the lobe).

Speaker: Dr David Haberthür (Institute of Anatomy, University of Bern)

19 Towards X-ray Differential Phase Contrast Mammography

Phase contrast and scattering-based X-ray imaging are known to provide additional and complementary information to conventional, absorption-based methods and can potentially revolutionize the radiological approach to current breast imaging. Grating-based X-ray interferometry can simultaneously generate differential phase contrast (DPC) and scattering signals of the sample, in addition to the conventional absorption signal, and therefore it is considered as a promising method for better breast cancer screening and diagnosis. Recently, our research team presented the first investigation of native, non-fixed whole breast samples including regular breast tissue and breast cancer formations. In this pioneering work we designed, constructed and operated a differential phase contrast mammography (mammoDPC) demonstrator based on a conventional X-ray source and measured whole native breast specimen directly after mastectomy, under conditions which are very close to the clinical routine. The results demonstrate that this technique can indeed provide additional and useful information to complement and improve the diagnostic process in the clinical setting.

Speaker: Dr Zhentian Wang (PSI)

20 In-vivo study of lung physiology with sub-second X-ray tomographic microscopy

The development of high-speed tomographic microscopy instrumentation is of great interest for 3D in-vivo studies. An important application is the study of lung dynamics, in particular, lung inflation/deflation issues during physiological and mechanical ventilation, which is required after a premature birth or during a general anesthetic. At TOMCAT we are currently working on an ultra-fast tomography end-station with sub-second temporal resolution in 3D. The feasibility study [1] shows that high-quality tomograms can be obtained in <1s, allowing for studies of explicit gas-exchange processes during breathing at an acinar and alveolar level. To further understand these processes we aim to establish in-vivo X-ray tomography at the micrometer scale. Using this volumetric data we may then answer open questions in lung development and physiology that can help clinicians in developing new strategies to decrease ventilator-induced lung injuries in newborns and adults. Here we show some of the key components of the project (beamline settings, detectors, endstation upgrade) and how we intend to combine them to achieve our goal. [1] R. Mokso et al., AIP Conference Proceedings, XRM 2010, 2011

Speakers: Mr Goran Lovric (Paul Scherrer Institut), Dr Rajmund Mokso (Paul Scherrer Institut)

21 Ultrastructural Bone Phenomics using High Throughput Synchrotron-based X-Ray Tomography

Osteoporosis leads to a higher risk of bone fracture through decreased bone mass and architectural changes leading to decreased bone quality. While bone mass through bone mineral density (BMD) is the most important factor in assessing fracture risk, introducing architecture through morphological parameters in cortical femur bone, one of the most problematic and debilitating fracture regions, can significantly increase the predictive power. Correlating these findings with genetic information would provide the basis to begin human studies and eventually personal medicine assessing risk and targeting therapies based on genetic information. Although structural studies of cortical microstructure have been previously conducted with x-ray tomography, sample counts have typically been small. In order to map the genetic contribution, thousands of samples are needed. For our study we are using the femur bones from 1200 mice of controlled genetic background. To enable this study we developed automated measurement (robot, alignment, ROI detection) tools in combination with automated analysis (segmentation, morphological analysis) and a system to track samples through the entire process.

Speaker: Mr Kevin Mader (Paul Scherrer Institute)

22 Microstructure of food under changing external temperature

The microstructure as well as the ingredients determine the sensorial perception of food. The mixture of various ingredients leads to complex interactions that are not completely understood. Understanding these is a necessary step towards controlling the microstructure, allowing for a wide range of applications in food industry and beyond. To complement the traditionally used imaging techniques, x-ray tomography can provide direct information about the microstructure in a non-invasive way at a high spatial resolution. A new sample environment for the TOMCAT beamline is under construction, allowing the precise control of the thermal boundary conditions in a sub 0°C regime and providing insights into the fundamental physics behind coarsening and other microstructure evolutionary effects. We present the design of the cold stage as well as first results showing the benefits of propagation based phase contrast imaging (PCI). Without PCI, a differentiation between the different phases, and thus quantitative evaluation, is not possible unless contrast agents are added. Measuring the phase contrast allows for an easy discrimination between liquid sugar solution and H2O ice crystals.

Speaker: Ms Annabelle Medebach (Paul Scherrer Institut)

23 Deformation process of wood cellular structure during swelling and shrinkage

Wood is a cellular biological material with strong coupling in mechanical and moisture behavior. Imaged with synchrotron radiation phase contrast X-ray tomographic microscopy, hysteretic reversible swelling/shrinkage due to ad/desorption of water vapor displays a non-affine component, particularly in low-density earlywood. Local cellular deformation of restrained swelling is documented. These measurements are used to validate poromechanical modeling of swelling at the cellular scale.

Speaker: Dr Michele Griffa (Laboratory for Building Science and Technology, EMPA, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland)

24 Quantitativeness and Projection Processing for X-ray Ptychographic Nanotomography

Ptychographic nanotomography is a recently developed technique for which the imaging of tomographic projections relies on simultaneous phasing of multiple diffraction patterns, exploiting the accuracy of iterative phase retrieval to recover the phase of the sample for a given orientation. After tomographic reconstruction we obtain a quantitative and high-resolution map of the sample electron density. A capability currently in use for the study of cement pastes, carbon fibers, bio-nanoporous systems and bone-disease research. Here we present robust algorithms developed for alignment and processing of projections, and a method for tomographic reconstruction from wrapped phase. Advances that have significantly increased the success rate of data processing and allowed us to establish ptychographic tomography as a standard technique at cSAXS. We will further present experimental characterization of the sensitivity and accuracy in determining electron density. For this purpose we have measured a homogeneous test sample of known composition and density and investigated the compromise between resolution and sensitivity for this technique.

Speaker: Dr Manuel Guizar-Sicairos (Paul Scherrer Institut)

25 Insight into the 3D water distribution in PEFC Gas Diffusion Layer by In-situ X-ray Tomographic Microscopy

Efficient water removal and water management is crucial for the performance of polymer electrolyte fuel cells (PEFC), in particular at high current density operation. In order to better understand the distribution and transport of liquid water in the gas diffusion layer, an in-situ X-ray tomographic microscopy (XTM) setup at the TOMCAT beamline of the Swiss Light Source (SLS) was developed [1] and used to study the liquid water distribution on the pore scale level with pixel sizes of 2-3 micrometer. Due to use of the high flux ionizing synchrotron radiation, significant radiation damage may be induced during the measurement [2]. Using new CMOS camera technologies, ultra fast XTM scans can be realized even within a few seconds such that radiation damage can be limited and measurement bias is minimized. Quantitative analysis of the phase segmented XTM data allows to derive e.g. local saturation, water cluster size, water cluster connectivity, and local water thickness analysis. [1] J. Eller, T. Rosén, F. Marone, M. Stampanoni, A. Wokaun, F.N. Büchi, J. Electrochem. Soc., 158, B963 (2011). [2] A. Schneider, C. Wieser, J. Roth, L. Helfen, J.Power Sources, 195 (2010), 6349

Speakers: Dr Felix N. Büchi (Electrochemistry Laboratory, Paul Scherrer Institut, Villigen PSI, Switzerland), Dr Jörg Roth (Electrochemistry Laboratory, Paul Scherrer Institut, Villigen PSI, Switzerland)

26 Density mapping of hardened cement pastes using X-ray ptychographic nanotomography - pilot experiment

X-ray ptychographic nanotomography -as recently developed at the cSAXS beamline- allows for non-destructive, three-dimensional mapping of the electron density. Its proven quantitativeness combined with the sub-micrometre resolution makes it a suitable tool for the assessment of densities of the individual phases in complex materials, such as hardened cement pastes. Here we present results of a pilot experiment performed on a cylindrical sample of epoxy-impregnated hardened cement paste of about 30 µm in diameter. Two-dimensional cross-sections of the three-dimensional electron density map show a microstructure that bears distinct similarity to that observed by the high-resolution scanning electron microscopy. Domains of various residues of clinker grains, calcium hydroxide, calcium silicate hydrates, epoxy-resin-impregnated porosity and unimpregnated porosity are revealed and are manifested as distinguishable peaks in the histogram of the three-dimensional electron density map. On assumptions of (a) the chemical composition, (b) the purity of the analyzed regions, the mass densities of the above mentioned individual material phases are estimated.

Speaker: Dr Pavel Trtik (EMPA)

27 Novel Imaging Approach for Quantitative Morphometry of Nano-Cellulose Scaffolds

Bacterial-derived nano-cellulose (NC) is a novel material with promising biomedical applications. We focus on its potential as a non-biodegradable scaffold for cartilage tissue-engineering (TE). NC is composed of a mesh of cellulose nano-fibrils. For TE it is important to control porosity and interconnectivity to facilitate cell migration. The aim of this study was to identify a 3D imaging protocol for quantifying pore size and interconnectivity. Samples were quenched in LN2 and freeze-dried. Phase-contrast was performed at the TOMCAT beamline with a modified Bronnikov algorithm (MBA) at 10 keV with a 4x (1.85 µm, 3.7 x 3.7 mm2) and 20x objective (0.37 µm, 0.75 x 0.75 mm2). Average pore size of macropores (Ø125 µm) and micropores (<Ø5 µm) were identified with the 4x and 20x objective, respectively. Since dry NC behaves as a pure phase object (no absorption), MBA is an ideal method. In this work, NC can be easily segmented, and pore size can be obtained by distance transformation. Therefore phase-contrast X-ray tomography with MBA is a promising 3D imaging protocol for characterization of the porosity of NC.

Speaker: Mr Luc Nimeskern (ETH Zurich)

28 In-Situ Ultrafast 3D Imaging of Magma Vesiculation at High Temperature

We present new experimental results on magma vesiculation at high temperature. During in situ high temperature (400-1100 °C), room pressure experiments, the evolving 3D structure was captured by ultrafast synchrotron-based X-ray tomographic microscopy performed at the TOMCAT beamline at SLS (PSI, Villigen), with a pixel size of 2.96 microns and 1 complete tomographic dataset acquired in 1 s. Sample heating was manually controlled with a class 4 laser heating system. Hydrous crystal- and bubble-free magmatic glasses from natural obsidians were employed for the experiments. We observed four main 3D microstructures: "low porous plinian pumice" with low amount of bubbles (40 vol%), showing a narrow range in bubble size and generally spherical shape of the bubbles; "normal plinian pumice" with high content of bubbles (80 vol%), showing a range of sizes, shapes and extent of coalescence; "pseudo-reticulite" (85 vol%), showing a polyhedral cell network; "gas slug", generated by expansion of one single bubble. The real-time three-dimensional analyses provide novel insights on the nucleation and exsolution mechanisms of volatiles that occur during ascent of magmas in volcanic conduits.

Speaker: Mr Mattia Pistone (ETH - Zurich)

29 COST IE0601: Investigations of the distribution and the decontamination of classical pesticides and synthetic pyrethroids in historical wooden objects by neutron and X-ray imaging

In the second half of the 20th century many wooden museum objects were treated with pesticides to protect them against insects. Today, some of these toxic pesticides have effloresced on the surfaces or are emitted into the indoor air of storage rooms or exhibitions. In order to prevent the conservators and visitors from health risks it is inevitable to decontaminate these objects. In the project the penetration of pesticides into the wood was investigated and two decontamination methods were evaluated: A vacuum washing and a vacuum temperature method. First,dummies were immersed in a micture of pesticide with different solvents. With neutron imaging the penetration depth of three different solvents which are carriers for the pesticides was visualized. As a result depth profiles could be created. In a second step two decontamination methods were adopted to the wooden dummies. This abstract focuses on the vacuum washing method. Neutron radiography was used to visualise how deep the water of the vacuum washing cleaner penetrates the wooden structure. Furthermore, the influence on the micro structure of the wood of both decontamination methods was investigated by µ-X-ray tomography.

Speaker: Mrs Katja Hunger (Schweizerisches Nationalmuseum Zürich, Sammlungszentrum)

30 Investigating the flow instabilities in soil by neutron imaging

Instability of the quasi-steady flow unexpected by standard theory was detected in recurrent ponded infiltration experiment conducted on small undisturbed soil sample and was visualized by neutron imaging (NI). Series of NI tomography images taken during the first infiltration run showed air trapping in many of large pores and cavities in the sample. Furthermore, many of entrapped air bubbles increased in volume during the first infiltration run. Further entrapped air redistribution has been detected during the second infiltration run. The fraction of the NI visible entrapped air was calculated based on image segmentation. It was found that increase of volumetric fraction of entrapped air bubbles by only 0.005 was accompanied by decrease of quasi-saturated hydraulic conductivity to 50% of the initial value. The experimental results support the hypothesis that the effect of the gradual decrease of the flow rates is caused by entrapped air redistribution and gradual build-up of bubbles in preferential pathways. The air comes probably from the soil matrix where residual encapsulated air is being gradually replaced by water attracted to fine pores by capillary forces.

Speaker: Mr Petr Novotny (Czech Technical University in Prague)

31 Neutron radiography to visualize and quantify water flow in soil and plants

Water transport from soil towards roots is fundamental in both soil and plant sciences, despite its importance there are only a few studies measuring its dynamics and locations along root systems. The lack of experimental data is largely due to the technical problem of measuring water fluxes in soil and roots in living plants growing in soils. This study aims at developing a non-destructive method to quantitatively monitor water flow towards and along roots. To this end we used neutron radiography to trace deuterium oxide (D2O) in soil and roots. We grew lupins in 30 x 15 x 1 cm containers, which were filled with fine sand and a thin layer of coarse sand as capillary barrier to stop D2O diffusion in soil. The results showed that after D2O injection, neutron attenuation inside the roots decreased due to D2O entering the roots. By comparing day and night measurement for the same roots, we were able to quantify the net root water uptake along different roots. We conclude that neutron radiography combined with D2O injection is a promising technique to investigate root permeability and water fluxes in soil and plants and will provide important data for validating existing models.

Speaker: Mr Mohsen Zare (George Agust University of Gottingen, Germany)

32 Surface Element and Structure Characterization of Mesopotamian Iron-stone Roll Seals and Weights: 2500BC – 650 AD.

Iron stone Mesopotamian seals are common objects in the Old Babylonian Period (2500 -1600 BC) and the much later Sassanide Period (226 BC - 651 AD). The black objects are commonly referred to in museum collections as ‘heamatite’ Recently, we have demonstrated that these iron stone Mesopotamain objects consists not only of the mineral hematite (Fe2O3), but also magnetite (Fe3O4), goethite (FeO(OH)) and iron oxide - loaded calcite (FeOx – CaCO3) as well as a black glassy material (Fe-silicate glass?). We performed micro-XRF, micro-XRD and XANES on the Phoenix and Micro-Xmas beam lines at the SLS. We investigated typical examples of iron stone Mesopotamian roll-seals from the NINO and RMO collections. XRF spectra taken on Phoenix can be semi-quantitatively analysed, yielding information on the elements O, S, F, Na, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn and Fe. In the investigated duck weight object we also found Pb. Elemental maps and XRD maps of selected part of the surface has been obtained from which we can related to particular species and solid solutions. XANES spectra give further evidence on the oxidation state of the elements.

Speakers: Dr Camelia Borca (PSI-SLS), Dr Daniel Grolimund (PSI-SLS), Dr Dirk Visser (RID, TUDelft), Dr Markus Janousch (PSI-SLS), Dr Thomas Huthwelker (PSI-SLS)

33 Morphology and composition of individual tannic and shikimic acid particles studied at oxidizing environmental conditions

Organic particles have a central role in environmental processes due to their chemical and physical properties. Chemical and optical characteristics of particles can be altered by water absorption, oxidation and photochemical processes. In this study, changes in chemical composition and morphology of submicron tannic and shikimic acid particles were measured by utilizing scanning transmission X-ray Microscopy and Near edge X-ray absorption fine structure methods. Tannic acid, as an organic molecule present in nature, was chosen as a proxy of complex material present in the environment, whereas shikimic acid is a constituent of biomass burning aerosols [1]. An environmental micro reactor was facilitated in order to study the effect of ozone and humidity on tannic acid [2,3]. Changes at the oxygen edge were used to track uptake of water to the particles as a function of humidity. Changes in the shikimic acid particles were monitored in situ at the carbon edge by tracking the double bond peak at 284.4 eV during exposure to ozone. 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)

34 Molecular architecture of the Spire-actin nucleus and its implication for actin filament assembly

The Spire protein represents a new class of actin nucleation factors which contain ca. 25 amino acid long actin-binding motifs called the WH2 repeats. We have applied small angle X-ray scattering to study the architecture of several Spire/actin complexes, including the native N-terminal part of Spire (SpireNT). Spire forms stable longitudinal-like complexes, with actin loosely positioned along the stretch of WH2 domains. Actin together with the WH2 domain constitutes a rigid unit and these units are linked by unstructured and flexible linkers. Analysis of the orientation of actin domains within the complexes reveals a high rotational mobility in single actin/WH2 modules. The Spire/actin nucleus shows an open and flexible conformation, but the longitudinal-like shape is preserved. The three most unusual properties of the Spire constructs upon their interaction with actin are (i) nucleation of actin polymerization at substoichiometric Spire WH2/actin ratios, (ii) a dose-dependent decrease of polymerization-induced fluorescence signal during steady state, and (iii) an extremely fast disintegration of actin filaments upon addition of Spire constructs that contain WH2 domains.

Speaker: Dr Teemu Ikonen (Paul Scherrer Institut)

35 Combining low (SAXS) and high (crystallography) resolution structural analysis to resolve the activation mechanism of Vascular Endothelial Growth Factor Receptors

Understanding the structure of a protein gives insights into its cellular functions, but obtaining high resolution structural information on large, flexible protein complexes or membrane proteins is very challenging. Therefore, we have combined crystallography with solution small-angle X-ray scattering (SAXS) experiments for studying Vascular Endothelial Growth Factors. VEGFs regulate blood and lymph vessel formation by activating receptors VEGFR-1, -2 and -3. We solved structures of VEGFs in complex with the ligand binding domain D23 of VEGFR-2 by crystallography [1] and generated a model of the full length extracellular domain using SAXS data [2]. Combined with thermodynamic characterization, this data allowed us to (i) visualize the details of the ligand binding with insights into receptor specificity, (ii) pin-point the domains which undergo major conformational re-orientation upon ligand binding and (iii) postulate a proofreading mechanism which ensures that spontaneous receptor activation in the absence of ligand is efficiently suppressed. [1] Brozzo et al., submitted [2] Kisko et al., FASEB J 2011

Speaker: Dr Kaisa Kisko (Paul Scherrer Institut)

36 Mineral dust and iron oxide particles studied under oxidizing and acidic conditions

Metal oxides as a common part of mineral dust have an important role in the heterogeneous reactions of dust particles in the presence of ozone or acidic gases. Furthermore, mineral dust particles serve as a primary external iron source to the open ocean and the bioavailability of iron from these particles is highly dependent on the oxidation state of the metal [1,2]. In the present study we have investigated both pure and nitric acid treated iron oxide particles by Scanning transmission X-ray microscopy and Near edge X-ray absorption fine structure (NEXAFS) techniques to observe changes in morphology and functional groups of pure Fe(III)-, Fe(II,III)- and mineral dust particles. In order to follow the chemical and morphological changes in situ, particles were measured in the environmental micro reactor after exposure to ozone and nitrogen oxides [3]. Characteristic features corresponding to different oxidation states of iron were monitored by following changes at oxygen K- and iron L-edges. [1] Duce R. A. et al. Limnol. Oceanogr. 36 (1991) [2] P. Falkowski et al. Science 281 (1998) [3] T. Huthwelker et al. Rev. Sci. Instrum. 81 (2010)

Speaker: Dr Markus Lampimäki (Paul Scherrer Institute)

Plenary session

37 Award of PSI thesis medal and presentation: The artificial kagome spin-ice system: from building blocks to emergent monopoles

Arrays of dipolar coupled ferromagnetic islands, arranged in specific geometries, provide an ideal tool to directly study the behavior of frustrated systems mimicking those found in Nature. In this presentation, single domain ferromagnetic islands arranged in the two dimensional kagome spin-ice geometry have been fabricated with electron beam lithography and the magnetic configurations have been imaged employing x-ray magnetic circular dichroism in a photoemission electron microscope. This study begins with a bottom-up approach, starting with the three basic building blocks of the artificial kagome spin-ice consisting of one, two, and three rings. Here the energy characterization is presented together with results achieved after using a demagnetization procedure. After setting the baseline with the building block structures, the magnetization reversal processes in the infinite kagome spin-ice array were studied with a magnetic charge model. It is shown that magnetization reversal proceeds through the nucleation and avalanche-type dissociation of emergent monopole- antimonopole pairs along one dimensional Dirac strings.

Speaker: Dr Elena Mengotti (Laboratory for Micro and Nanotechnology, SYN department, Paul Scherrer Institut, 5232 Villigen-PSI. Switzerland)

38 News from SLS

Speaker: Prof. Johannes Friso van der Veen (Paul Scherrer Institut)

39 News from the PSI Users Association

Speaker: Prof. Bernd Schoenfeld (ETH Zürich)

40 Control of electron flow and magnetism in atomically thin transition metal oxides

Recent advances in the synthesis of transition metal oxides (TMO) heterostructures with atomically sharp interfaces open new functionalities by tuning the interfacial properties of correlated electron materials, in the same manner as for semiconductor heterostructures. Motivated by the desire to realize the potential of TMO heterostructures in controlling collective quantum phases, we have built devices out of atomically thin layers of two different TMOs - LaNiO3 and LaAlO3 - which are metallic and insulating in bulk form, respectively. To explore the behavior of electrons in the atomically thin layers, we have used a suite of advanced experimental probes such as synchrotron-based infrared ellipsometry and low-energy muon spin rotation (at the LEM beamline of the PSI). When the layers are more than three atomic monolayers thick, the electrons were found to behave in a manner closely similar to the one in the bulk. In heterostructures where the conduction electrons are confined to two atomic monolayers separated by insulating layers, their behavior changes completely, exhibiting a sequence of two collective phase transitions upon cooling. We have provided strong evidence that these transitions correspond to the onset of charge and antiferromagnetic spin order. We have thus demonstrated that the collective electronic phases in these TMO devices can be accurately controlled by adding a single atomic monolayer.

Speaker: Dr Alexander V. Boris (Max-Planck-Institut fuer Festkoerperforschung, Stuttgart, Germany)

16:00 Coffee

41 News from SINQ and SMuS

Speaker: Dr Kurt Clausen (Paul Scherrer Institut)

42 The SwissFEL X-Ray Laser Project

The Paul Scherrer Institute is planning the construction of a X-ray free electron laser (SwissFEL), which will produce 20 fsec pulses of coherent x-rays in the wavelength range 0.1 to 7 nm, with extremely high peak brightness. These characteristics will provide opportunities for new experiments in chemistry, solid state physics, biochemistry and materials science. The presentation will focus on novel applications, the description of the fundamental aspects of the planned facility, and last but not least the milestones towards the planned operation.

Speaker: Dr Rafael Abela (Paul Scherrer Institut)

43 Using SANS to probe the nano-magnetic structure and magnetic reversal of perpendicular recording media

Perpendicular magnetic recording media have recording layers that are compositionally segregated, with grains of a magnetic CoCrPt alloy separated by a thin oxide shell, typically SiO2. The average grain diameter is typically 8 nm and film thicknesses are normally in the range 11 – 16 nm. These media have their magnetic moments oriented perpendicular to the plane of the film and have sufficient perpendicular anisotropy to maintain a written bit of information against thermally activated reversal of magnetization. Determining the local magnetic structure and reversal behaviour is key to understanding the performance of perpendicular media in recording devices, but this can be problematic at the length scales required for these systems. Small-angle neutron scattering (SANS) is a very effective approach to measure these materials at a sub-10nm length scale. However, due to the small volume of material available in these thin films the experiments can be rather challenging. The difficulty is exasperated by the multi-layered architectures of writeable recording media, which contain additional layers, some of which may also be magnetic, in order to control the properties of the data storage layer. The use of polarised neutrons (SANSPoL) can be particularly useful in separating out the component of the scattering arising from the data storage layer, which is typically less than 1% of the total scattering. The methodology used to measure these systems will be discussed, and some recent finding will be presented where SANS and SANSPoL can reveal information not easily determined by other methods. This will included the measurement of magnetic switching and information on the grain-size dependant anisotropy distributions within these materials.

Speaker: Prof. Steve Lee (University of St Andrews, UK)

44 Magnetism and superconductivity in the iron-based superconductors LiFeAs and NaFeAs

The response of the superconductivity and structure of LiFeAs and NaFeAs to chemical substitutions has been probed using high-resolution X-ray diffraction measurements, magnetometry, and muon-spin rotation. The superconductivity is very sensitive to composition, with substitution of Fe by small amounts of Co or Ni in LiFeAs resulting in monotonic lowering of the superconducting Tc and the superfluid stiffness as the electron count increases. A similar effect is found in NaFeAs and it appears that electron count is the dominant factor. I will discuss the interplay and coexistence of superconducting, magnetic and structural order parameters in the latter system, where Co doping weakens the magnetism through both a suppression of T_N and a reduction in the ordered moment in the magnetically ordered phase. Further doping results in a magnetically disordered phase in which moment size continues to decrease and falls to zero at the same point as the structural distortion is removed. Our results suggest that magnetism drives the structural transition in NaFe1-xCoxAs and that its disappearance coincides with a strengthening of the superconducting order.

Speaker: Dr Tom Lancaster (University of Oxford, UK)

18:30 Dinner

Friday 16 September

Resonant Inelastic and Elastic X-ray Scattering: part I

chairman: T. Schmitt, D.-J.Huang, U.Staub, J.van den Brink

45 Welcome

Speakers: Dr Thorsten Schmitt (Paul Scherrer Institut), Urs Staub (Paul Scherrer Institut)

46 Cluster-Based Numerical Simulations for X-ray Spectroscopies in Correlated Materials

In this talk I will present an efficient scheme for calculating various x-ray spectroscopies using a combination of cluster exact diagonalization and ab-initio codes. These multi-orbital calculations include multiplet, charge-transfer, hybridization, and core-hole interactions all on the same footing, and are able to reproduce fairly well representative spectra on several transition metal oxide materials. Focus will be placed on x-ray absorption, resonant inelastic light scattering (RIXS), and the dielectric response S(q,w) of Fe- and Cu-based materials. As an example, the differences between RIXS and S(q,w) will be highlighted, with a specific focus on low energy magnon excitations.

Speaker: Thomas P Devereaux (Stanford University)

47 Cupric Oxide: a model system to explain high-Tc superconductivity ?

Cupric oxide (CuO) has recently attracted much interest as a magnetically driven multiferroic with the highest Tc (~230K). In this material a non-collinear spiral magnetic order (215K<T<230K) breaks crystal inversion symmetry, inducing ferroelectricity. We use resonant x-ray diffraction at the Cu L edges to probe the subtle changes in the Cu electronic structure occurring at the appearance of multiferroicity and test the magnetic ground-state, proposed by neutron diffraction, to be a collinear antiferromagnet. In both phases we have found a strong dependence of the diffracted intensity on the polarization of the incident light. Such dependence is totally unexpected in a simple collinear antiferromagnetic phase. In this model the Cu magnetic moment are aligned (antiferromagnetically) along the b-axis. The observed polarization dependence could reflect and be a direct measurement of the presence of orbital currents surrounding the Cu ions. Such observations are long sought proofs for theoretical model explaining the behavior of the normal state of high-Tc superconductors. Understanding such state is the key to unravel the true origin of the superconducting phase transition in cuprates materials.

Speaker: Dr V Scagnoli (Swiss Light Source, Paul Scherrer Institut, CH 5232 Villigen PSI, Switzerland)

48 Study of the electronic structure of SrFeO3-δ using soft x-ray scattering

Using resonant x-ray scattering, we report the study of electronic structures in the ion-based oxides SrFeO3-δ. SrFeO3 (SFO) has a cubic structure with an isotropic metallic behavior. The cubic perovskite SrFeO3, in which iron is present as Fe4+, exhibits the coexistence of metallic conductivity and screw-type antiferromagnetic ordering. However, the metallic state found in SrFeO3 becomes unstable with respect to a charge disproportionation on Fe ions due to the oxygen deficiency. In order to understand this oxidation effect, crystals with different oxygen contents were grown by floating zone furnace. For this study, a crystal was cut and pre-aligned to set the normal direction to be [0 0 1] direction. At low temperature, two satellite reflections were located to have the vectors of Q1=(0 0 0.5) and Q2=(0 0 0.33). The Q1 shows a transition temperature at about 65 K in accord with the antiferromagnetic transition, but Q2 exists even at room temperature. Both reflections display a resonance at the L3-edge of Fe. In addition, Q1 also shows a sharp resonance at the K-edge of oxygen, suggesting the hybridization band structure between the Fe and oxygen. References: [1] S. Srinath, et. al., Phys. Rev. B 72, 54425, 2005 [2] R. Vidya, et. al., Phys. Rev. B 74, 54422, 2006

Speaker: Dr C H Du (Department of Physics, Tamkang University, Tamsui 251, Taiwan)

10:30 Coffee

49 Ultrafast lattice and electronic dynamics in magnetite and the formation of a novel transient phase

More than 70 years after its discovery, the Verwey transition in magnetite (Fe3O4) and the character of the low-temperature phase of this material remains an active and controversial topic. Upon cooling below 123 K, magnetite undergoes a first order transition from cubic to low symmetry accompanied by an increase of the electric resistivity by two orders of magnitude. Different models have been proposed to explain this effect involving charge, orbital and lattice degrees of freedom. In order to understand the coupling between electronic and structural degrees of freedom in the Verwey transition better, we studied their dynamics with time-resolved resonant soft x-ray diffraction. We find that charge and orbital order as well as the low-temperature structural distortion all melt under the influence of an infrared pump pulse within our temporal resolution of about 250 fs. Our finding indicates a strong coupling between structural and electronic degrees of freedom in magnetite. For intermediate pump fluences a novel transient state is formed, which is characterized by a drastic energy shift of the oxygen-K resonance threshold indicating a strongly reduced band gap.

Speaker: C Schueßler-Langeheine (Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie, Germany)

50 Ultrafast non-thermal dynamics of spin and charge order in striped nickelate via femtosecond resonant soft x-ray scattering

In the striped nickelate La2-xSrxNiO4, spin order coexists with charge order, whose periodicity is half of spin order. So far, most of the studies on the stripe phase were performed in the thermal equilibrium state by varying temperatures; the dynamics of stripe phase in the time domain when the system is driven-out-of-equilibrium has not yet been studied. Using the x-ray free electron laser (XFEL) at the Linac Coherent Light Source (LCLS), we performed time resolved optical-pump and resonant soft x-ray diffraction probe experiments to study the dynamics of the spin and charge order. The dynamics are found to be distinct from the equilibrium properties. Through the analysis of the recovery time scale, the spin-charge order coupling and the vector nature of the spin order can be elucidated.

Speaker: Dr W S Lee (Stanford Institute for Materials and Energy Science, SLAC National Accelerator Lab, USA)

51 Femtosecond Time-Resolved Resonant Soft X–ray Diffraction Studies of Strongly Correlated Materials

Resonant Soft X-Ray Diffraction at the LCLS free electron laser is used to probe stimulated dynamics in two canonical strongly correlated materials. In the first example, I’ll discuss the reconstruction of the 3D scattering volume of the (.25 .25 .5) antiferromagnetic reflection in the layered compound La0.5Sr1.5MnO4 measured at the Mn L-edge. Upon stimulation at near infrared wavelengths, the full scattering volume helps us visualize a transient incommensurability in the scattering wave vector, which recovers on a timescale of under 3ps. In the second example, we study the stripe ordered cuprate La1.875Ba.125CuO4. We measure the structural, LTT-allowed, (0 0 1) reflection and the stripe ordered (.25 0 .5) reflection at the O K-edge and observe their dynamic decoupling when subjected to IR excitation resonant with an optical phonon.

Speaker: Dr R Tobey (Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton NY 11793, USA)

Advancing Quantative Chemical Imaging

chairman: D. Grolimund

52 Welcome: From qualitative towards quantitative chemical imaging

With the increasing recognition that macroscopic material properties and chemical reactivity are frequently triggered by nano- and microscopic structures and processes, the demand for „chemical microscopes“ grew rapidly. Recently, X-ray microprobe techniques advanced into leading methods concerning microscopic chemical imaging. Most advantageous are the achievable spatial resolution, the chemical selectivity as well as the fast data acquisition speed. However, in contrast to the conventional (large beam) XRF analysis, full quantification of micro beam XRF measurements is still hampered, mainly due to (microscopic) matrix phenomena. In this introductory overview, the inherent challenges of quantitative chemical imaging by micro-XRF will be delineated. Additionally, in view of the recent progress in the field, a short outlook will demonstrate on how various x-ray analytical techniques will benefit from advanced XRF spectra analysis strategies.

Speaker: Dr D Grolimund (Paul Scherrer Institut, 5232 Villigen-PSI)

53 Quantitative X-Ray Fluorescence Analysis: Fundamentals

The objective of this talk is to provide an introduction to X-ray fluorescence analysis (XRF) presenting the concepts to be retained for proper quantitative analysis. This should serve two purposes; to make sure the difficulties associated to quantitative XRF imaging are kept in mind and to simplify following the subsequent talks on XRF analysis.

Speaker: Dr V Armando Sole (European Synchrotron Radiation Facility, Grenoble, France)

54 The PyMca X-ray Fluorescence Toolkit

PyMca is a set of open source software tools for XRF analysis that is becoming a standard for users of most synchrotrons and for many X-ray tube based laboratories. This talk will present the algorithms used, the built-in features and the current developments. Following the “open policy” of the toolkit, not only the strengths, but also the limitations of PyMca in the context of the workshop will be underlined.

Speaker: Dr V Armando Sole (European Synchrotron Radiation Facility, Grenoble, France)

11:00 Coffee

55 Quantitative microscopic studies with high spatial resolution: the virtue of cross-calibration

Trace elements quantification is normally a difficult task in micro X-ray fluorescence analysis (microXRF), also inevitable in high flux synchrotron-based microXRF (SR-microXRF). However the high spatial resolution and high throughput of SR-microXRF are the advantages among chemical analysis techniques. In this work, we combined it with laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), which provided quantitative output on trace elements, but in less spatial resolution. Both techniques show 2D chemical images in agreement. Therefore, we used quantitative information from LA-ICPMS to calibrate the SR-microXRF analysis, resulting in a quantitative 2D image with high spatial resolution. [1] Wang, H. A. O.; Grolimund, D.; Van Loon, L. R.; Barmettler, K.; Borca, C. N.; Aeschlimann, B.; Günther, D. Anal. Chem. 2011, accepted.

Speaker: Dr H A O Wang (ETH Zürich, Switzerland)

56 New Possibilities in X-ray Microanalysis with an Electron Beam

The introduction of silicon drift detectors (SDD) made new applications in electron microscopy possible. Larger detector areas lead to higher collection angles and thus to a higher detection efficiency. Faster electronics improved the overall detection rate. Count rates of 100'000 cts/sec and more have become possible. Improved low energy sensitivity and the increased number of counts (for a given time) allow a better light element and trace element analysis. Dramatically reduced acquisition times for elemental mapping (minutes instead of hours) have made it possible to perform 3D elemental analysis in FIB/SEM tomography. In some transmission electron microscopes detector elements are integrated into the pole piece and allow high speed and artefact free analysis of even single atom columns. Tilt-series tomography based on X-ray intensity maps allow the reconstruction of complex chemical microstructures in 3D.

Speaker: Dr Marco Cantoni (School of Basic Sciences, EPF Lausanne, 1015 Lausanne, Switzerland)

57 The AXIL software suite for quantitative XRF analysis

Speaker: to be confirmed NN

Heterogeneous Catalysis

chairmen: M.Nachtegaal, O.Safonova, J.van Bokhoven

58 Insights in selective oligomerisation and polymerisation catalysis using stopped flow XAS techniques

The activation of [MoX3(L)] (with X = Cl, Br; L = tridentate ligands with S3 and SNS donor sets) by AlMe3, analogous to the industrially important [CrCl3(L)] catalysts for selective oligomerisation of alkenes, has been investigated by X-ray absorption (XAS) and UV-visible spectroscopies. Time-resolved stopped flow XAS, as developed by our group for homogeneous catalysis over the last few years, in combination with a newly developed freeze-quench approach, have provided new insights in the activation mechanisms. The complete alkylation of the Mo centres and a slower, stepwise sequence for [MoBr3(L)], has been established, without the evidence for directly bonded or bridged Mo-Mo dimers. Decomposition of the complexes in time resulted in precipitation of particulate Mo, as observed during catalytic tests. Links to the industrially relevant Cr systems will be made, and preliminary results shown. The novel freeze-quench approach, which can trap reaction solutions within 1 second of mixing, opens up a large field of homogeneous catalysis and liquid chemistry to be studied, being able to quench at sub second time scales, while characterisation techniques with long data acquisition can be performed.

Speaker: Dr Moniek Tromp

59 Understanding gold catalysts under working conditions

The number of publications reporting the application of gold to catalytic processes has increased dramatically since the discovery in the 1980’s that supported nanoparticles of gold can be very active catalysts for industrially important reactions [1,2]. Despite the tremendous progress in the field in terms of catalyzed reactions, understanding of the catalytic behaviour of heterogeneous gold under working conditions is very limited, which often yields to attribution of its catalytic properties to erroneous sites. With the help of XAS/XES performed under working conditions we were able to understand what happens during the induction period observed with Au/C used in the carbonilation of methanol, what the active oxidation state of gold is in the hydrogenation of nitrobenzene, and help redesign catalysts for the selective hydrogenation of olefins. [1] M. Haruta, T. Kobayachi, H. Sano, N. Yamada, Chem. Lett. 2, 405 (1987). [2] M. Haruta, Nature 437, 1098 (2005).

Speaker: Dr Jacinto Sa (ETH Zurich and Paul Scherrer Institut, Villigen, Switzerland)

60 The electronic structure of catalysts by X-ray emission based methods: Fundamental investigations and applications

The catalytic activity of catalysts is commonly guided by the interplay of geometric and electronic effects at the active center. It are the highest occupied (HOMO) and lowest unoccupied (LUMO) states that interact with the substrate in dependence of the coordination geometry. Knowledge about these three “structure factors” is therefore a key to understand catalytic mechanisms and the working principle of catalysts. X-ray emission methods using synchrotron radiation allow the determination of all three parameters in one experiment under almost any reaction conditions, like high pressures and temperatures, low catalyst concentration etc.: HERFD-XANES (High-energy resolution fluorescence detected X-ray absorption near edge structure) makes the LUMO states accessible by 1s→nd transitions, while with valence-to-core XES (X-ray emission spectroscopy) and the underlying nd→1s emission, information about the HOMOs is yielded. The two-dimensional combination of both, called valence-to-core RIXS (Resonant inelastic X-ray scattering) scans the individual nd→1s emissions in dependence of the 1s→nd excitations, by which analogue information to optical absorption spectroscopy is provided, but in an element selective manner. With the present contribution, these methods will be introduced on a common level, followed by demonstrating their potential with measurements on iron carbonyls, which serve as model compounds for catalytically active substances or intermediates in many catalytic reactions (e.g. CO-oxidation, catalytic water splitting, biomass conversion etc.). Ferrites MFeO3 as an example for heterogeneous catalysts, used in methane combustion will be discussed with special emphasis on oxidation states and site selective structural investigations of metal centers. The talk will be concluded by presentation of recent results about HERFD-XANES measurements on different cobalt compounds used for CO-oxidation and other selected examples.

Speaker: Dr Matthias Bauer (Karlsruhe Institute for Technology, Karlsruhe, Germany)

10:45 Coffee

61 In situ XAS characterization of Pd/ZnO and Pd/Ga2O3 methanol steam reforming catalysts: correlating structure and reactivity

Methanol steam reforming (MSR) is a promising reaction for H2 production for use in PEM fuel cells. In contrast to Pd on inert support oxides, which catalyzes methanol decomposition to CO and H2, Pd supported on ZnO and Ga2O3 has shown excellent activity and selectivity to the steam reforming reaction yielding H2 and CO2 [1]. Based on ex-situ characterization after reaction or reduction, this substantial difference in reactivity has been attributed to the formation of Pd-Zn and Pd-Ga alloys. In this contribution we investigated the dynamic formation and decomposition of the selective alloy phases in different reaction atmospheres and correlated the properties with the catalytic performance. Time resolved in situ x-ray absorption spectroscopy at the Pd K edge was performed at the SuperXAS beamline with simultaneous analysis of formed products by mass spectrometry. Complementary information was obtained by utilizing a range of situ spectroscopic methods of different bulk/surface sensitivity, such as FTIR spectroscopy, in situ XRD and in situ XPS. We have monitored the dynamic formation of the active Pd-Zn and Pd-Ga alloy phases under relevant reaction conditions. PdZn alloying occurred already in methanol/water via spillover and reduction of the ZnO by H2 generated in the reaction [2], while oxidative conditions resulted in the decomposition of the alloyed surface and partial decoration of the Pd nanoparticles by patches of ZnO [2]. Upon alloying, the reactivity changed from methanol decomposition (CO/H2) to MSR (CO2/H2), confirming that PdZn alloy is in fact the selective phase for MSR. Similar spectral changes occurred on Pd/Ga2O3. A full EXAFS analysis identified the formation of a Pd2Ga intermetallic compound, which was confirmed by XRD. The extent and conditions of alloy formation under reduction/reaction atmospheres, the catalytic performance and the stability with respect to surface and bulk structure of PdZn and Pd2Ga nanoparticles will be discussed and compared. [1] N. Iwasa, N. Takezawa, Top. Catal., 22, 215 (2003). [2] K. Föttinger, J.A. van Bokhoven, M. Nachtegaal, G. Rupprechter, J. Phys. Chem. Lett. 2, 428 (2011).

Speaker: Dr Karin Foettinger (Technical University Vienna, Austria)

62 Probing the active site during methane conversion over Cu-MOR with XAS

In the last decade, Groothaert et al. showed that methane can be converted to a methanol-like species at mild conditions using Cu-exchanged zeolites [1]. However, the product strongly sorbed to the surface and the process was not catalytic. To successfully activate methane by partially oxidation to a methanol derivative one must understand the reaction mechanism. This necessitates knowing the structure of the Cu sites that participate in the reaction by determining them during the different reaction conditions. This poses a challenge, since there might be different Cu sites present and not all might participate in the reaction. High energy resolved fluorescence detected X-ray absorption spectroscopy (HERFD XAS) and time resolved XAS (QuickXAS) were explored to monitor the structure of the Cu atoms under different gas feeds. In situ XAS showed the changes from Cu2+ after oxygen activation to a mixture of Cu2+ and Cu+ states of the copper particles in Cu-MOR upon methane conversion, similar to the reduction of Cu after methanol interaction. [1] Groothaert, M.H., Smeets, P.J., Sels, B.F., Jacobs, P.A., Schoonheydt, R., Selective oxidation of methane by the bis(u-oxo)dicopper core stabilized on ZSM-5 and mordenite zeolites, Journal of the American Chemical Society, 127 (2005), 1394-1395.

Speaker: Evalyn Mae Alayon (ETH Zürich, Switzerland)

63 Concentration modulation excitation QuickXAS study of LaFe0.95Pd0.05O3 under cyclic red-ox conditions for methane oxidation

LaFe0.95Pd0.05O3 is currently used as a component of automotive three-way catalysis for the emission control of stoichiometric gasoline engines. It is known that LaFe0.95Pd0.05O3 is able to segregate metallic palladium to its surface when reduced and to re-incorporate it to form a solid solution when re-oxidized, which is described as the self-regenerative function [1]. Catalytic activity measurements during methane combustion performed on LaFe0.95Pd0.05O3 (where Pd is incorporated into the LaFeO3 lattice) and 2 wt% Pd/LaFeO3 show that highest CH4-conversion rates are obtained for the impregnated material, where most of the Pd exists in the form of well dispersed nano-particles [2]. Cyclic operation between red-ox conditions of CH4-O2 and CH4 at 500°C was simulated using concentration modulation excitation QuickXAS. This operation revealed a practical strategy to improve the activity of LaFe0.95Pd0.05O3. At each switch, CH4-O2→CH4 and CH4→CH4-O2, activity was enhanced for a short time. Identical measurements on Pd/Al2O3 demonstrated that an increase of CO2 production was observed only at the CH4→CH4-O2 switch. The time-resolved QuickXAS spectra of Pd/Al2O3 show that Pd reversibly changes between partially oxidized and reduced states. The phase-resolved spectra obtained by phase sensitive detection (PSD) display a simple reduction-partial oxidation process that may be accompanied by the formation of a PdxC species, interpreted as the source of the enhanced CO2 production. The phase-resolved spectra of LaFe0.95Pd0.05O3 vary between oxidized and reduced Pd and intensity variations are more pronounced compared to Pd/Al2O3. The shape of the phase-resolved spectra is interpreted as the fingerprint of the continuous segregation and re-incorporation of Pd into LaFeO3. This reversible process is responsible for the activity improvement at every red-ox switch [3]. [1] Y. Nishihita, J. Mizuki, T. Akao, H. Tanaka, M. Uenishi, M. Kimura, T. Okamoto, N. Hamada, Nature 2002, 418, 164. [2] A. Eyssler, P. Mandaliev, A. Winkler, P. Hug, O. Safonova, R. Figi, A. Weidenkaff, D. Ferri, J. Phys Chem. C 2010, 114, 4584. [3] A. Eyssler, E. Kleymenov, A. Kupferschmid, M. Nachtegaal, M. Santhosh Kumar, P. Hug, A. Weidenkaff, D. Ferri, J. Phys. Chem. C 2011, 115, 1231.

Speaker: Dr Davide Ferri (EMPA Duebendorf, Switzerland)

Multiple Order Parameter Systems: part I

chairman: C. Niedermayer, M. Kenzelmann, H.Luetkens, C. Rüegg

64 Magnetic field effects on spin and charge ordering in La2-xSrxCuO4 superconductors and possible implications for Fermi surface reconstruction

In this contribution, the spin and charge “stripe” ordering tendencies observed by neutron and x-ray diffraction in La-based cuprate superconductors [1,2] will be discussed with emphasis on magnetic field effects on these correlations [3,4]. In particular, we will relate our new diffraction results [4] with evidence for hole-pockets arising from ARPES experiments conducted at the SIS beamline at SLS [5] and – more generally – will discuss possible implications for the interpretation of high-field quantum oscillation experiments and evidence for Fermi surface reconstruction in cuprates. [1] J. M. Tranquada et al, Nature 375, 561 (1995); M. v. Zimmermann, Europhys. Lett. 41, 629 (1998) [2] M. Fujita et al, Phys. Rev B 70, 104517 (2004) [3] B. Lake et al, Nature 415, 299 (2002); J. Chang et al, Phys. Rev. B 78, 104525 (2008) [4] N. B. Christensen et al, to be published [5] J. Chang et al, New J. Physics 10, 103016 (2008); E. Razzoli et al, New J. Physics 12, 125003 (2010)

Speaker: Dr N B Christensen (Materials Research Division, Risø-DTU, National Laboratory for Sustainable Energy, Technical University of Denmark, Denmark)

65 μSR investigation of the interplay between magnetim and superconductivity: from cuprates to oxypnictides

Here we present an extensive μSR study of the microscopic behaviour of the two prototypes of the cuprate and pnictide families, namely YBa2Cu3O6+x and REFeAsO1-xFx (RE=La, Sm, Ce ). We compare the effect of carrier doping, magnetic dilution, disorder and pressure on the electronic properties of both compounds mainly at the magnetic (M) to superconducting (SC) crossover. The studies on cuprates show a 3D phase diagrams, as a function of carrier doping and disorder, indicating the presence of a quantum critical point around which a thermally activated antiferromagnetic phase competes with SC. Here disorder suppresses both the competing order parameters and the quantum critical point, unveiling an underlying frozen magnetic state which may coexist with SC. This frozen state, which is related to the Mott- insulator character, is obviously absent in oxypnictide. In the REFeAsO family it is found that SC and static magnetism strongly compete and hardly coexist simultaneously, apart for RE=Sm and Ce within a small doping range where both order parameters are depressed. In case of coexistence both cuprates and pnictides display a short range magnetic order, related to magnetic clusters nanoscopically mixed with SC regions. A combination of recent μSR and NQR experiments on SmFe1-xRuxAsO0.85F0.15 show that superconductivity and magnetism are tightly related to two distinct well defined local electronic environments of the FeAs layers, which can be finely tuned by isoelectronic and diamagnetic Ru substitution. Indirect evidence is given that superconductivity is assisted by Fe magnetic fluctuations, which are at least partially frozen when static order appears and are absent above the Fe/Ru spin dilution threshold.

Speaker: Dr Samuele Sanna (Dipartimento di Fisica "A.Volta" e Unita CNISM di Pavia, 27100 Pavia, Italy)

66 Superconducting and magnetic properties of the FeSe1-x system

We report on a detailed study of the electronic phase diagram of FeSe1−x under pressure by means of muon-spin rotation and AC magnetization. Whereas at low pressures the system is solely superconducting at low-temperatures, one observes the occurrence of a static magnetic order at a pressure of ≃ 0.8GPa. For this pressure, bulk superconductivity coexists and competes on short length scales with the magnetic order below Tc. For pressures above 1GPa a remarkable enhancement of both the magnetic and the superconducting transition temperatures is observed. These unconventional properties establish FeSe1−x as one of the most intriguing superconducting systems investigated to date.

Speaker: Mr M Bendele (Physik-Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich and Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI)

67 The Meissner effect in a strongly underdoped cuprate well above its critical temperature

The Meissner effect and the associated perfect bulk diamagnetism are, besides zero resistance and gap opening, characteristic features of the superconducting state. In the pseudogap phase of cuprates unusual diamagnetic signals as well as anomalous proximity effects have been detected but a Meissner effect has never been observed. Here, we have probed by low energy muSR the local diamagnetic response in the normal state of an underdoped (UD) La_1.94Sr_0.06CuO_4 layer (up to 46 nm thick, critical temperature Tc'< 5 K) brought in close contact with two nearly optimally doped (OP) La_1.84Sr_0.16CuO_4 layers Tc = 32 K. We show that the entire barrier layer of thickness much larger than typical c-axis coherence lengths of cuprates exhibits Meissner effect for temperatures well above Tc' but below Tc. We determine the temperature dependence of the effective penetration depth and superfluid density in the different layers. The results indicate that superfluidity with long-range phase coherence is induced in the underdoped layer by the proximity of optimally doped layers; however, this order is very sensitive to thermal excitation. E. Morenzoni et al., Nat. Commun. 2, 272, 2011.

Speaker: Prof. Elvezio Morenzoni (Paul Scherrer Institut)

11:00 Coffee

68 Coupling of magnetic and ferroelectric hysteresis by a multi-component magnetic structure in Mn2GeO4

The family of magnetically-induced multiferroic materials that exhibit coupled magnetic and electric order offer great promise for future applications. A detailed understanding of the coupling mechanism between magnetism and ferroelectricity facilitates the development of new materials that may allow controllable multiferroic properties to emerge at room temperature. Here, we will focus on our study of the insulator Mn2GeO4. Bulk measurement and neutron diffraction experiments on single crystal samples have revealed that, in zero applied magnetic field, three different magnetic structure phases exist as a function of decreasing temperature. The lowest temperature magnetic phase is found to be multiferroic. Here, both a macroscopic ferroelectric polarization and finite magnetization emerge. Both of these orders are spontaneous and point along the crystal c-axis. To understand these macroscopic properties, neutron diffraction has been employed as a microscopic probe of the multiferroic phase. We find that the magnetic structure is composed of coupled commensurate and incommensurate components. A symmetry analysis reveals that the finite magnetization can be associated with the commensurate component, while the incommensurate component is responsible for the emergence of ferroelectricity. The coupling between the two components of the magnetic structure is inferred by the neutron diffraction results, and demonstrated by hysteretic behaviour in both magnetization and the electric polarization. Our results suggest that multi-component magnetic structures such as that found in Mn2GeO4 may provide a new route towards functional materials that exhibit both ferromagnetic and ferroelectric orders.

Speaker: Mr J S White (Laboratory for Neutron Scattering, Paul Scherrer Institut, CH-5232 Villigen, Switzerland)

69 Neutron polarimetry investigation of CuO

This presentation will give a summary of the polarized neutron experiments that have been performed at the Paul Scherrer Institut using the MuPAD spherical neutron polarimetry (SNP) set-up on TASP, [1]. It will include a discussion of the approach taken to analysis and interpretation of polarimetry data recently gathered on the high temperature multi- ferroic CuO, [2]. SNP experiments polarize the neutron beam before the scattering event in the orthog- onal directions, x, y and z, and then measure the vector components (x, y, z) of the final polarization, Pf, to give the fullest amount of information about a magnetic structure. SNP experiments allow the extraction all of the interference terms between the magnetic and nuclear scattering and also between the different components of the magnetic inter- action vector, M⊥ = (0,My,Mz), where x is along Q and y, z define the Bragg plane, [2]. The SNP set-up uses a zero-field chamber to surround the sample in order that the scattered beam cannot precess about a guide field. MuPAD, used on TASP at PSI is the only SNP zero-field environment that does not need to be cryogenically cooled, [1, 2]. Recently, there has been particular interest in the measurement of the intensity created in a polarised neutron beam from the interference of the real and imaginary components that can be present in M⊥. The intensity change only occurs when the magnetic structure is cycloidal or helical and these magnetic orders are a central theme in the study of type two multiferroic (MF) materials. Furthermore the increase in intensity is only observed when there is a single cycloidal domain, and the channel in which it is observed gives information about the handedness of the domain that is present. This talk will present the very recent polarimetry measurements that have been made on CuO, which track the change of this intensity, and hence the cycloidal domain popu- lation as a function of electric field. The results indicate the strong coupling between the magnetic structure and the application of an electric field in this high TC multiferroic. [1] M Janoschek, S Klimko, R Gaehler, B Roessli and P Boeni, Spherical neutron po- larimetry with MuPAD, Physica B, 397, 125, (2007) [2] T Kimura, Y Seiko, H Nakamura, T Siegrist and A P Ramirez, Cupric oxide as an induced-multiferroic with high-TC, Nat Mater, 7, 291, (2008) [3] F Tasset, PJ Brown, E Lelievre-Berna, T Roberts, S Pujol, J Allibon and E Bourgeat- Lami, Spherical neutron polarimetry with Cryopad-II, Physica B, 267, 69, (1999)

Speaker: Dr A Poole (Laboratory for Neutron Scattering, Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland)

Soft Condensed Matter

chairman: J. Kohlbrecher

70 Structural and Viscoelastic Properties of Semifluorinated Alkane Monolayers at the Air/Water Interface

The structural and viscoelastic properties of monolayers at the air/water interface are of substantial interest from a scientific point of view, as well as of paramount importance for technological applications from soap films to surface coatings. We currently investigate the class of semifluorinated alkanes at the air/water interface in order to develop a detailed structure-properties relation ship for this very particular class of materials. Such semifluorinated alkanes are linear alkanes, which carry in one half of the molecular chain fluorine atoms instead of hydrogen. Due to the incompatibility of the fluorocarbon and hydrocarbon fragments, such molecules are considered amphiphobic and tend to locally phase separate into intriguing 3D and 2D structures. This intrinsic structuring capability is anticipated as novel building motif in supramolecular architectures. For this purpose it is of fundamental importance to understand the structural and dynamic behaviour of these molecules, which we try to assess in monolayers at the air/water interface of a Langmuir trough in combination with an interfacial stress rheometer (ISR). While the structural organization was investigated on the water by neutron reflectivity and after transfer to solid substrates by atomic force microscopy, the rheological behaviour was studied for the floating Langmuir film by the ISR. C.O. Klein et al, "Viscoelasticity of Semifluorinated Alkanes at the Air/Water Interface", Soft Matter 2011, DOI:10.1039/C1SM05357D L. de Viguerie et al, "Effect of the Molecular Structure on the Hierarchical Self-Assembly of Semifluorinated Alkanes at the Air/Water Interface", Langmuir 2011, DOI: dx.doi.org/10.1021/la201377f

Speaker: Dr Ulrich Jonas (Institute of Electronic Structure and Laser, FORTH, Iraclion, Crete)

71 Structural changes and phase behavior of densely packed microgel particles

Colloidal suspensions of microgel particles are systems of great interest for applications and fundamental studies due to their reversible responsiveness to changes of their environment, such as temperature or hydrostatic pressure. Although it has been shown that microgel particles behave like hard spheres under many circumstances [1], they can reach states that are far beyond hard spheres due to their softness, especially at high concentrations [2]. We focus on highly concentrated poly(N-isopropylacrylamide) (pNIPAM) microgels and their volume transition as a function of temperature and hydrostatic pressure [3] and their form factors in highly overpacked states with effective volume fractions above random close packing. SANS and confocal microscopy measurements show that the particles shrink to some extent and interpenetrate in very densely packed suspensions. The SANS studies were carried out using contrast matching methods allowing the direct measurement of the form factor at very high concentrations [4]. The confocal microscopy study was done with particles dyed with two fluorescent dyes to allow the observation of particle overlap via color discrimination. Furthermore, small-

Speaker: Dr Urs Gasser (Laboratory for Neutron Scattering, Paul Scherrer Institut)

72 Formation of multistranded β-lactoglobulin amyloid fibrils and their stimuli responsive magnetic behaviour in the lyotropic liquid crystals

We investigated snapshots of the fibrillation and aggregation kinetics of multi-stranded β-lactoglobulin amyloid protein fibrils at pH 2 and 90 °C by combining scattering (SANS, DLS, DDLS) as well as atomic force microscopy (AFM) 1. Scattering techniques clearly demonstrate the structural conversion and time evolution of β-lactoglobulin monomers (2 wt %) into semi-flexible protein fibrils upon heating at 90°C. AFM allowed resolving the critical steps for the formation of single protofilaments, their alignment driven by liquid crystalline interactions and the twisting of the final fibrils due to the intra-molecular electrostatic interactions, leading to the development of multistranded twisted ribbon fibrils 2. In further, β-lactoglobulin fibrils were titrated with a sulfated polysaccharide (k-carrageenan) to determine the morphology and mechanism of complex formation. SANS and microscopy indicated the complex formation of spherical aggregates attached along their contour length of the multistranded twisted protein fibrils, arranged in a necklace configuration 3. In addition, we investigated the encapsulation of the β-lactoglobulin fibrils, fibrils coated with magnetic nanoparticles into the three different types of lyotropic liquid crystalline (LLC) meso phases. Mesophases composed of glycerol monolinoleate, linoleic acid and water yielding respectively lamellar, inverse bicontinuous cubic and inverse columnar hexagonal symmetries 4. The impact of fibrils confinement within the LLC on their secondary structure, spatial organization and their response to an external magnetic field stimulus5 was studied by combining small angle X-ray and neutron scattering (SAXS, SANS), ATR-FTIR and AFM techniques. [1] Bolisetty, S. et al, Soft Matter 2011, 7, 493. [2] Adamcik, J. et al, Nature Nanotechnology 2010, 5, 423. [3] Jones, O. G. et al, Biomacromolecules 2011, 12, 3056. [4] Amar-Yuli, I. et al, Soft Matter 2011, 7, 3348. [5] Vallooran, J. J. et al, Advanced Materials. 2011 accepted

Speaker: Dr Sreenat Bolisetty (Institute for Food Science and Nutrition, ETH Zürich, Switzerland)

73 Structural changes of proteins revealed by time-resolved SAXS

Dronpa may be regarded as the prototype of photochromic proteins. These fluorescent proteins can be reversibly switched between a fluorescent bright and a non-fluorescent dark state by light excitation of the chromophore. Although the X-ray structure of Dronpa in both states has been determined in great detail little is known about the actual switching process itself. We performed time-resolved SAXS experiments in solution to gain a detailed picture of the structural dynamics in this photo-switchable protein. For that purpose, our optical laser system has been attached to the cSAXS beamline and the optically induced changes have been probed by X-rays. Constructing three dimensional models from the data uncovered conformational alternations of the beta-can topology. In this talk, I will report on these experiments and demonstrate the capabilities of time-resolved photo-SAXS techniques in soft condensed matter science.

Speaker: Mr Marcel Petri (Max Planck Institute for Biophysical Chemistry)

Poster session II and lunch

74 Sample Environment News

The sample environment team at PSI provides expertise and support for systems to manipulate the sample or its environment during experiments at large scale facilities. A variety of cryostats, furnaces and cryo-magnets enable experiments under extreme conditions. Over the past years we have extended the experimental possibilities substantially. We will present a selection of new setups which have been successfully used for neutron scattering experiments. This includes examples such as a new horizontal magnet of 6.8 T, electric fields at low and ultra low temperatures using voltages up to 6 kV and high currents at the mK temperature range.

Speaker: Dr Marek Bartkowiak (Paul Scherrer Institut)

75 Resonant inelastic x-ray scattering spectra of one-dimensional Mott insulators

Excitation spectra of resonant inelastic x-ray scattering (RIXS) processes in one-dimensional Mott insulators are presented and discussed. The RIXS cross section of Hubbard and extended Hubbard models on finite half-filled chains is evaluated using exact diagonalization. The fundamental features of the obtained spectra reveal the different magnetic excitations occuring in indirect and direct RIXS processes, corresponding to copper K- and L-edge resonances in experiments on quasi-1D cuprates. The spectral features for each process are studied in a broad range of parameter sets and it is shown that by comparison to experiment, physical properties, such as the effect of the intermediate state core hole, can be quantitatively estimated.

Speaker: Dr S Kourtis (Institute for Theoretical Solid State Physics, IFW Dresden, 01171 Dresden, Germany)

76 Resonant Inelastic X-ray Scattering and Electron Energy-Loss Spectroscopy on La1-xSr1+xMnO4

We present a combined resonant inelastic x-ray scattering (RIXS) and electron energy-loss spectroscopy (EELS) study of the single layered manganite La1-xSr1+xMnO4 (LSMO). The RIXS planes were measured at the Mn K-edge at the ID 26 at the ESRF revealing the presence of intermediate and final states with different symmetries. A strong excitation is observed around 2eV for all doping levels by RIXS. In contrast to this, the excitations measured by EELS in this energy region are strongly doping dependent, revealing the occurrence of doping induced excitations around 1.65 eV. The different behavior observed by RIXS and EELS, shows that both methods probe different excitations occurring in the same energy range. The origin of the spectral weight seen in RIXS and EELS is discussed in terms of intersite dd excitations and doping induced electronic polarons, respectively. Pursuing the comparison between RIXS and EELS further, we calculate the RIXS planes using the ultrashort core-hole lifetime approximation (UCL) and the EELS data. A rough qualitative agreement is found, but many of the characteristic features of the spectral weight distribution within the RIXS planes can not be captured. This is most likely caused by the presence of several intermediate states, which are close in energy. In this case the UCL cannot be used. The presented data shows that RIXS and EELS are powerful complementary methods for the study of correlated electron dynamics.

Speaker: Dr R Kraus (IFW Dresden, PF 270116, D-01171 Dresden, Germany)

77 Fingerprints of orbital physics in RIXS

Resonant Inelastic X-ray Scattering (RIXS) has become nowadays one of the main experimental techniques to investigate elementary excitations in strongly correlated materials, and above all, cuprates. We describe a simple way to analytically calculate the scattering intensities in the case of copper L edge in the single ion picture. We use this result to obtain the scattering intensities of spin waves in systems with different orbital ground states. It occurs that even in this case, RIXS intensities behave differently depending on the type of orbital order.

Speaker: Dr P Marra (IFW Dresden, Dresden, 01069, Germany)

78 In situ Soft X-ray Emission Spectroscopy of Iron Phthalocyanine-based Oxygen Reduction Catalysts for Polymer Electrolyte Fuel Cells

Carbon-based catalysts such as pyrolyzed Fe phthalocyane (FePc) show high oxygen reduction reaction (ORR) activities and are expected to be cathode catalyst alternative to Pt for polymer electrolyte fuel cells. To clarify the origin of the ORR activity, we have studied the electronic structure of the catalysts under vacuum condition. However, in situ observation of the electronic structure during exposure to ambient oxygen is required since the actual catalytic process occurs at such condition. X-ray emission spectroscopy (XES) is useful to investigate the electronic states of materials under ambient pressure. We have fabricated a sample cell for in situ XES and investigated the O2 adsorption effect to the FePc-based catalysts using ultra-high resolution soft XES station (HORNET) at BL07LSU of SPring-8. Thin catalyst layer (~1μm) is coated on Si3N4 membrane which separates vacuum condition from the atmospheric environment. Comparing in situ Fe 2p XES spectra under 1 atm Ar and O2 pressure, a drastic change of valence structure caused by O2 adsorption was observed. It is revealed that the adsorption site of the pyrolyzed catalysts is different from that of the precursor FePc.

Speaker: Mr H Niwa (University of Tokyo)

79 Magnetic exchange coupling in 3d-4f molecular nanomagnets investigated by X-ray magnetic circular dichroism

Single-molecule magnets are exchange-coupled spin clusters showing slow relaxation of magnetization. In recent years, efforts have been intensified to increase the magnetization reversal barrier and thus enhance relaxation times by combining rare earth ions with transition-metal ions. Rare-earth ions exhibit very large magnetic anisotropies due to their strong spin-orbit coupling and their mostly unquenched orbital momentum. In this contribution we use X-ray magnetic circular dichroism to observe element-specific magnetization curves. In conjunction with SQUID magnetization and susceptibility measurements, we are able to obtain information about the magnetic coupling between 3d and 4f ions.

Speaker: Dr Jan Gui-Hyon Dreiser (Paul Scherrer Institut)

80 X-ray absorption spectroscopy at the Mn K-edge in mutliferroic rare earth manganate thin films

Orthorhombic rare earth manganates are materials showing a strongly coupled ferroelectric and magnetic order parameter at low temperatures. To better understand the influence of the MnO6 octahedron distortion on the magnetic ordering, the electronic structure of Mn in TbMnO3 and LuMnO3 thin films grown by pulsed laser deposition was investigated using XAS at the Mn K edge. XANES spectral changes are observed for the o-TbMnO3 films grown on different substrates, indicating the influence of film strain on the Mn-O bonding. The linear polarized XANES spectrum of an o-LuMnO3 film shows a strong polarization dependency of the white line position indicating the strong anisotropy of the x-ray absorption in the MnO6 octahedron. The influence of the rare earth element is also observed by comparing the o-LuMnO3 and o-TbMnO3 spectra where the white line of o-LuMnO3 shifts toward higher energy.

Speaker: Ms Yi Hu (General Energy Research, Paul Scherrer Institute)

81 Epitaxial multiferroic composite heterostructures probed with x-rays and neutrons

In this work, we have used element-specific soft X-ray photoemission electron microscopy (X-PEEM) and polarized neutron reflectivity (PNR) to determine the influence of piezoelectric-ferroelectric BaTiO3 (BTO) on the magnetic properties of magnetostrictive ferromagnetic spinel CoFe2O4 and NiFe2O4 thin films. By using a combination of circular and linear dichroism spectro-microscopy as well as neutron reflectivity, we have spatially mapped magneto-electric interactions in a model system of a ferroelectric substrate with an epitaxial ferromagnetic film as cap layer. By performing temperature, angular, and polarization dependent studies, we have found that this strain-induced effect strongly influences the magnetic anisotropy of individual 250 nm wide magnetic domains of the spinel films. The observation of magneto-electric interactions in individual domains has provided valuable insight into strain-driven domain nucleation and reorientation, important for implementation of artificial multiferroic materials in devices utilizing electric-field control of the magnetization.

Speaker: Dr Rajesh Vilas Chopdekar (Paul Scherrer Institut)

82 Magnetical Characterization of o-LuMnO3 and TbMnO3 thin films

Magnetoelectrics, materials with ferromagnetism and -electricity in the same phase gained a lot of interest with the discovery of materials with improved properties. A strong coupling, caused by the magnetic-ordering induced polarization, has been found in orthorhombic rare-earth manganates. These materials are of large interest for basic research as well as for applications like high-sensitivity sensors and novel storage materials. TbMnO3 and LuMnO3 were grown as thin films on (110) YAlO3 by pulsed laser deposition. XRD has shown phase pure growth and good crystalline quality. The epitaxial growth introduces strain as a parameter, thus allows to investigate the multiferroic properties as a function of the structural parameters and temperature. For a 90nm LuMnO3 thin film a magnetic Bragg peak, characteristic for an E-type AFM structure, was observed by neutron diffraction, an important improvement for neutron scattering characterization of thin films. Polarized neutron reflectometry points to the existence of a strain-induced ferromagnetism at the substrate/film interface. This is also evidenced by depth-dependent spin-dynamics measured by low energy muon spin spectrometry.

Speaker: Mr Matthias Bator (Paul Scherrer Institut)

83 Magnetic anisotropy in the geometrically frustrated system CuFeO2

The compound CuFeO2 has a delafossite structure where triangular layers of magnetic Fe3+ are separated by non-magnetic Cu1+ and O2- layers. CuFeO2 orders in a collinear four sublattice (4SL) structure below TN2=11K, with the magnetic moments along c. Associated with TN2 is a first order structural transition from hexagonal to orthorhombic. For temperature between TN1=14K and TN2 the system is in an incommensurate magnetic phase. One puzzling question about this system concerns its strong magnetic anisotropy observed. Fe3+ (d5), which is the only magnetic ion in the system, has a spin only ground state, so no anisotropy is expected. That motivated us to use x-ray magnetic circular dichroism (XMCD) probing separately the orbital and spin moments of the Fe3+ ions. In this work we present our XMCD data on Fe L-edges as a function of temperature revealing how the spin and orbital moments vary across the phase transition in CuFeO2. These results are discussed in the context to the observed magnetic anisotropy.

Speaker: Dr Cinthia Piamonteze (Paul Scherrer Institut)

84 SCES investigation via X-ray magnetic resonant techniques

After pioneering experiments on the interaction between X-rays and spins, the advent of third generation synchrotron machines has definitely shown the versatility of Magnetic Resonant Elastic and Inelastic X-Ray Scattering in the investigation of magnetic materials. In particular, the techniques benefits of chemical selectivity, high Q resolution and sensitivity to the angular part of magnetic moment to access fundamental microscopic information, resulting in powerful tools, complementary to neutron diffraction. Nowadays, the investigation of complex and elusive magnetic structures, even in externally applied electric and magnetic fields is possible. Results obtained on forefront scientific cases as frustrated magnetic systems [1], collinear and cycloidal multiferroics [2] are presented. In particular, magnetic structures solution, phase diagrams definition and magnetic interaction patterns determination have been successfully achieved, directly contributing to the understanding of key mechanisms active in the aforementioned classes of compounds. [1] Phys. Rev. B 77 (2008) 140403R, Phys. Rev. B 78 (2008) 100406R [2] Phys. Rev. B 78 (2008) 104407, Phys. Rev. B 83 (2011) 054438

Speaker: Dr Claudio Mazzoli (Politecnico di Milano)

85 Effect of Strontium doping on the Oxygen Diffusion in La2-xSrxCuO4±δ samples Investigated by Oxygen Isotope Back Exchange

In order to investigate the effect of strontium on the oxygen diffusion in as grown single crystals of La2-xSrxCuO4±δ (x =0, 0.05, 0.1, 0.15) we first did Oxygen Isotope Back Exchange (OIBE) experiments between 40 0C to 1000 0C We proved that free oxygen mobility can be realized for x = 0, 0.05 already below 500 0C but is depressed for x = 0.1 and 0.15. This gives evidence that low temperature oxygen mobility can be suppressed by replacing La with Sr. In order to correlate structure and oxygen diffusion as a function of temperature we did neutron diffraction measurement on grain free 0.15 single crystal on TriCS@PSI. We are planning neutron single diffraction measurements on grain free 0.05 single crystal on RESI@FRM II , both to be combined with X-ray single crystal data. SIMS (yields the diffusion constant and anisotropy on a macroscopic scale by observing the 18O diffusion on oriented single crystals) will support this on a macroscopic scale

Speaker: Mr Ravi Sura (University de Rennes1 and PSI)

86 ARPES study of spin-density wave order in FeTe single crystals & FeTeOx Films

We have performed an ARPES investigation of FeTe single crystals/films, as well as thin fims of the the novel superconductor FeTeOx [Y.F. Nie et al., Phys. Rev. B 82, 020508(R) (2010)]. Our results from the single crystals reflect the previously reported Fermi surface pocket around the X-point [(pi, 0)], possibly connected to a spin-density wave (SDW) order [Y. Xia, PRL 103, 037002 (2009)]. Unlike this previous report, our results also reveal the presence of an energy gap, which would be expected from the SDW order. The temperature dependence shows that the gap closes in the rough vicinity of the magnetic transition temperature, supporting it's interpretation as reflecting the SDW state. Finally, we were also able to acquire ARPES data from cleaved FeTe and FeTeOx thin films, where the FeTe films display similar features as the bulk samples. Funding Source: DOE-BES through contract DE-FG02-00ER45801 and the Swiss National Science Foundation (Project 6, NCCR MaNEP).

Speaker: Dr Martin Mansson (Laboratory for Solid State Physics, ETH Zurich)

87 Microscopic magnetic nature of the quasi-one-dimensional antiferromagnet BaCo2V2O8

BaCo2V2O8, belongs to a wide group of quasi-1D antiferromagnets (AF). The Q1D compounds display a variety of fascinating ground states governed by the strong spin-spin coupling along the 1D direction and a much weaker coupling along other directions. BaCo2V2O8 display a long-range AF order below TN=5 K and possibly short-range order all the way up to 30 K. Further, a novel type of field induced magnetic order has been found for T<1.8 K and Hc>3.9 T. It was determined to be an incommensurate spin structure caused by quantum fluctuations, fitting well to theoretical predictions for a so-called Tomonaga-Luttinger liquid (TLL). To the best of our knowledge, we present here the first investigation of the microscopic magnetic nature of single crystalline BaCo2V2O8 samples. Our data reveal several clear muon frequencies below TN indicating the onset of a long-range order. Above 5 K, the muSR spectra are well fitted to a simple power-exponential relaxing function. The temperature dependence of the relaxation-rate as well as the power display a clear anomaly around T=40 K, indicating the onset of short-range 1D correllations. Finally we also present initial field dependent data.

Speaker: Dr Martin Mansson (Laboratory for Solid State Physics, ETH Zurich)

88 Spin-density Wave Order in the 2D Heavy Fermion System CePt2In7

The title compound is a recently discovered heavy fermion material where the spacing between Ce-In planes is drastically increased. Consequently, CePt2In7 inherit a truly 2D electronic structure. It was recently discovered that CePt2In7 is not only AF (TN=5.3 K) at ambient pressure but also becomes SC under pressure with a maximum transition temperature Tc=2.1 K at P=3.12 GPa. At lower pressures an intriguing coexistence of the AF order and SC phase is found, and that with increasing pressure Tc is increasing while TN decreases. The growth of the SC on the expense of the AF order suggests a crossover behavior of the Ce-4f electrons from localized to itinerant, similar to what is considered for the well known CeRhIn5 compound. In the presented work the low-temperature microscopic magnetic properties of the quasi-2D heavy fermion compound, CePt2In7 are investigated by using muSR. Clear evidence for the formation of a SDW order is presented. The magnetic order parameter fit well to a modified BSC gap-energy function in a strong-coupling scenario, possibly predicting the evolution of unconventional pairing in the pressure induced superconducting phase of this compound.

Speaker: Dr Martin Mansson (Laboratory for Solid State Physics, ETH Zurich)

89 Ion-texturing & Dynamics in Layered Compounds: From Electric Automobiles to Frustrated Magnetism

The drastic change from an insulating antiferromagnet to a superconducting state in cuprates, is probably the best example of how a slight change in carrier-density governs the magnetic/electronic properties of a material. Further, also ion-order within the intermediate charge-reservoir layers is of importance e.g. charge-order in the battery-type material NaxCoO2. In this compound, a novel low- temperature magnetic phase was presented, connected to the thermal history above 200K i.e. also ion-dynamics is crucial. From the context of rechargeable batteries for electrical automobiles, we present a novel experimental method [Sugiyama-PRL/103/147601/(2009)] to investigate microscopic ion-dynamics in lithium-transition-metal-oxides (Li-TMO's). By using muon-spin relaxation we obtained unique results from many different Li-TMO's. Here we summarize these results and the importance for development of novel thin-film batteries is discussed. Finally, we will present our latest results, regarding Na-dynamics in magnetically frustrated NaxCoO2 so as to understand the possibility of tuning it's magnetic/electronic properties. Funding: Toyota Central Research & Development Labs. Inc.

Speaker: Dr Martin Mansson (Laboratory for Solid State Physics, ETH Zurich)

90 Magnetic order and transitions in the spin-web compound Cu3TeO6

The spin-web compound tricopper-tellurate Cu3TeO6, belongs to an intriguing group of materials where the magnetism is governed by 3d9 copper Cu(2+) ions. Cu3TeO6 has been sparsely experimentally studied and in fact only one published investigation can be found regarding its magnetic properties. However, recently an inelastic neutron scattering (INS) study of the magnon dispersion in Cu3TeO6 was performed at the FOCUS time-of-fight neutron spectrometer of PSI [Zaharko, unpublished]. Among other interesting findings in the spectrum, a large amount of diffuse scattering appears at T>TN. The origin of this diffuse scattering is far from understood and at present it is not even clear if it is purely magnetically induced or not. It could possibly originate from short-range magnetic order above the transition. Here, we have used the unique power of muSR to investigate the possible existence of short-range magnetic order above TN for Cu3TeO6. Our results show a clear long-range magnetic order below TN as indicated by clear oscillations in the ZF spectra. At TN=61.7 K a very sharp transition is observed and both wTF and ZF data clearly show that no magnetic order is present above TN

Speaker: Dr Martin Mansson (Laboratory for Solid State Physics, ETH Zurich)

91 Magnetic order and frustrated dynamics in Li(Ni[0.8]Co[0.1]Mn[0.1])O2: a study by muSR and SQUID magnetometry

Recently, the mixed metal oxides of the form Li(Ni[1/3]Co[1/3]Mn[1/3])O2, have become the centre of attention as promising candidates for novel battery material. These materials have also revealed very interesting magnetic properties. The title compound, was from magnetometry measurements [1] found to be a percolating spin system interacting via AFM and FM superexchange interactions of different strength. On cooling, evidence of spin glass behaviour in 2D is found followed by a completely frustrated system in 3D at the lowest temperature. From aging experiments, a coexistence of ordered and frustrated states are found. The aging behaviour prevails up to the paramagnetic region which suggests that parts of the compound remain frustrated for all temperatures below Tc. Our wTF muSR results clearly show how the magnetically ordered fraction is gradually building up in steps over an extended temperature range. From ZF muSR we further see that no clear long-range magnetic order is present at lowest temperature as indicated by the absence of clear clear oscillatios in the time spectrum. [1] J.M. Wikberg et al., sJ. Appl. Phys. 180, 083909 (2010).

Speaker: Dr Martin Mansson (Laboratory for Solid State Physics, ETH Zurich)

92 Magnetic order induced energy-gap in Sr2IrO4

For many years the interest for transition metal oxides (TMO) has been dominated by the layered copper (3d) oxides e.g. high-temperature superconductors. With developments in sample growing technique, scientists have started to move down the periodic table. Our work focuses on the related 5d TMO, Sr2IrO4, which is expected to display a spin-1/2 Kramers doublet ground state. However, while Sr2RuO4 shows the expected metallic behaviour, Sr2IrO4 display an energy-gap at the Fermi level. Of many suggestions for the origin of this gap, only two possible suggestions remains: (1) A spin-density wave (SDW) order, or (2) A relativistic spin-orbital (SO) coupling, as recently proposed by ARPES measurements and LDA calculations. Here, we have used the power of muSR to investigate the possible presence of static magnetic order in this compound. From ZF measurements we find a long-range magnet order below Tc=240 K. Consequently, the energy-gap could most likely be deduced to the presence of magnetic ordering e.g. SDW. This also fits fits well into a recent suggestion that Sr2IrO4 could display high-temperature superconductivity upon electron doping.

Speaker: Dr Martin Mansson (Laboratory for Solid State Physics, ETH Zurich)

93 Magnetic ground state of alpha-NaFeO2

Many alkali transition-metal dioxides (AMO$_2$ with M =V, Cr, Fe, Co, and Ni) belong to the rhombohedral systems (space group R3m) crystallizing with the layered alpha-NaFeO2 structure. These compounds have been heavily investigated since the 1970s, originally due to their complex magnetic nature caused by the layered structure. Recently, the presence of both incommensurate (IC) AF order at 4 < T < 11 K and short-range order until at least 50 K was proposed for alpha-NaFeO2 with TN=4 K by neutron measurements [1]. In order to study the magnetic ground state of alpha-NaFeO2, in which Fe[3+] ions form a two-dimensional triangular lattice, we have measured muSR spectra in the T range between 1.8 and 50 K using a powder sample. ZF-measurements reveal the presence of quasi-static magnetic order below 9.5 K, although the oscillation amplitude is very weak in the $T$-range between 4 and 7 K. Furthermore, the ZF measurements indicate the absence of any short-range order above 20 K. [1] T. McQueen et al., Phys. Rev. B 76, 024420 (2007).

Speaker: Dr Martin Mansson (Laboratory for Solid State Physics, ETH Zurich)

94 Soft X-ray ARPES Investigation of High-temperature Superconductors

When performing ARPES using low photon energies the experiments suffer from a number of limitations, e.g. a limited probing depth. In connection, there have been questions raised regarding the electronic structure amongst the layered cuprates being 2D or 3D in nature. To discern a possible kz-dependence using low photon-energies is a very tricky task. To interpret the data correctly one needs to account for the fact that the final state is not free electron like. Further, at low photon energies the probe depth is of the order 4 A, which implies a large uncertainty, dkz=1/4 A−1. In most of the high-temperature superconductors, the lattice parameter c is large and the Brillouin zone (BZ) is hence ”compressed” in kz. Consequently, dkz is more than half the BZ. When using soft x-rays, the probe depth is ~15 A, i.e. dkz=1/15 A−1. This improvement in kz-resolution makes it much easier to distinguish a kz-dependence of the Fermi surface (FS) topology. Among other things, SX-ARPES data probing the electronic structure of the high-Tc cuprate La1.48Nd0.4Sr0.12CuO4 will be presented. The FS topology at is remarkably different, indicating kz-dispersion from strong interlayer coupling.

Speaker: Dr Martin Mansson (Laboratory for Solid State Physics, ETH Zurich)

95 Soft X-ray Angle-resolved Photoemission Spectroscopy Study on Iron-based Superconductor Ba1-xKxFe2As2

Iron-based superconductors have attracted much attention because of the unexpected high transition temperatures. The mechanism of superconducting state in iron pnictides is considered to be different from high-Tccuprates. In contrast to two-dimensionality of Co-O plane in cuprates, hole-doped Ba1-xKxFe2As2(BKFA) has been reported to show the superconducting gap depending on kz momentum.Investigation of bulk three-dimensional electronic structure will provide therefore further understanding of physical properties of BKFA. Soft X-ray angle-resolved photoemission spectroscopy (SX-ARPES) is one of the most promising methods to measure bulk band structure of materials due to the increase of probing depth and high kz-momentum resolution. In this study, we have investigated the shape and kz-dependence of the Fermi surfaces(FSs) in BKFA. The experimental FSs show alternatingin-plane shapes and modulation along kz direction corresponding to periodicity of the Brillouin zones. These effects show clear polarization dependence reflecting orbital character of the bands forming the FS. These results provide with experimental information on the dimensionality and orbital character of FSs.

Speaker: Dr Masaki Kobayashi (Paul Sherrer Institut)

96 Electronic correlations in LaRu2P2 superconductor studied by Angle Resolved Photoemission Spectroscopy

The details of the electronic structure are important for understanding how superconductivity emerges in iron-based superconductors. The presence of long parts of Fermi surface (FS) connected by a fixed wave vector Q, the so-called FS nesting, has been proposed to be the driving force for the formation of the Spin Density Wave (SDW), and it may also produce the pairing interaction for superconductivity in pnictides. To examine this idea we made a comprehensive study of the electronic structure of LaRu2P2. This compound has the same crystal structure as the mostly studied 122-type pnictides, but its superconducting transition temperature is 4 K that is much lower than the optimally doped 122 pnictides (e.g. Ba1-xKxFe2As2). In this contribution we shall first report the electronic structure of LaRu2P2 measured in ARPES experiments, as well as the detailed comparison to the band structure calculation. Then we shall outline the similarity and quantitative difference in the electronic states of LaRu2P2 and Ba1-xKxFe2As2, and discuss the relevance of correlation effects and of Fermi surface nesting.

Speaker: Mr Elia Razzoli (Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland)

97 Signatures of Electron-Phonon Coupling in Oxygen K-Edge RIXS on quasi-1D edge-shared cuprates.

Continued advancements in RIXS instrumentation have significantly increased the resolution of these experiments. As a result, features within 60-100 meV of the elastic line are becoming resolvable and recent experiments at the oxygen-K edge of the quasi-1D edge-shared cuprate Ca_{2+x}Y_{2-x}Cu_5O_{10} have uncovered detailed peak structure near the elastic line. In this poster we interpret these features as being due to coupling to a particular oxygen phonon mode and present large-scale exact diagonalization calculation for multi-band Hubbard clusters with the inclusion of lattice degrees of freedom. This model reproduces both the peak structure near the elastic line as well as its observed doping dependence. Furthermore, the coupling strength inferred from this study indicates a sizable strength of el-ph coupling with implications for other cuprate systems.

Speaker: Dr Steven Johnston (IFW Dresden)

98 Optimising Magnetic Switching

The main goals of this study are a systematic study and subsequent optimisation of microwave assisted magnetisation switching in magnetic structures. Stroboscopic time-resolved imaging of resonant magnetic eigenmodes and the detection of switching events are carried out with energy and polarisation dependent Scanning Transmission X-ray Microscopy at the PolLux beamline of the Swiss Light Source (SLS). These provide quantitative information about the magnetic state and its time evolution. The investigation is concentrated on magnetic thin-film patterns with physical dimensions in the micron and deep sub-micron range. Samples have been fabricated at the Laboratory for Micro- and Nano-technology (LMN) at Paul Scherrer Institut. In a first step we are determining the eigenfrequencies as a function of the sample size and shape as well as the microwave power (CW) needed to induce switching. Following on from these initial results, we will investigate controlled and optimised switching using adequately shaped RF-pulses.

Speaker: Ms Stephanie Stevenson (Paul Scherrer Institut)

99 Controlling spins in adsorbed molecules by a chemical switch

Using X-ray magnetic circular dichroism (XMCD), we present conclusive evidence that the spin of an organometallic molecule coupled to a ferromagnetic substrate can be switched between magnetic off and on states by a chemical stimulus. This is achieved by nitric oxide (NO) functioning as an axial ligand of cobalt(II) tetraphenyl-porphyrin (CoTPP) ferromagnetically coupled to nickel thin-film (Ni(001)). On NO addition, the coordination sphere of Co is modified and a NO–CoTPP nitrosyl complex is formed, which corresponds to an off state of the Co spin. Thermal dissociation of the NO from the nitrosyl complex restores the on state of the Co spin. The NO-induced reversible off–on switching of surface-adsorbed molecular spins observed here is attributed to a spin trans effect.

Speaker: Mr Jan Nowakowski (Laboratory for Micro and Nanotechnology, Paul Scherrer Institut)

100 Polarizing protons using photoexcited triplet states and its application to build a neutron spin filter

Polarized protons have a strong spin dependent interaction with neutrons and offer an interesting alternative to a polarized 3He spin filter. A concept for a polarized proton spin filter based on a rather new scheme of dynamic nuclear polarization (DNP) employing photoexcited triplet states, has been realized. It requires neither high fields nor very low temperatures to achieve high proton polarizations. The novel DNP scheme and its technical implementation are described and the results of a test of principle experiment with such a filter on the cold white neutron beam of BOA at SINQ are presented.

Speaker: Mr Martin Haag (Paul Scherrer Institute, CH-5252 Villigen, Switzerland)

101 Kinetics of particle formation during laser ablation synthesis in solution

Laser ablation synthesis in solution is a versatile technique to produce nanoparticles of a large variety of materials. Understanding the involved mechanisms implies the study of the kinetics on the nanoscale with high time resolution. A time gating technique has been applied to resolve the particle formation process with small angle scattering with a resolution of tens of microseconds. The structural kinetics will be discussed together with the prospects.

Speaker: Dr Anton Plech (Institut für Synchrotronstrahlung, KIT)

102 Operando fluorescence x-ray absorption spectroscopy studies of proton-exchange membrane fuel cell

A test setup for membrane-electrode-assemblies (MEAs) of proton exchange membrane fuel cells which allows in-situ fluorescence X-ray absorption spectroscopy studies of one electrode with safe exclusion of contributions from the counter electrode is described. Interference by the counter electrode is excluded by geometry in which the incoming beam has a small angle of incidence with the electrode layer. The cell was constructed by introducing minor modifications to an electrochemical state-of-the-art MEA test setup, which ensures realistic electrochemical test conditions. In measurements on Pt/C and PtCo/C cathodes combined with Pt/C anodes (H2/O2 feed), good data quality was demonstrated both for the majority element Pt as well as for Co despite on its low surface density in the order of 0.02 mg/cm2. Severe leaching phenomena of the PtCo alloy particles of the cathode were observed during use of the MEA, which set on already during potentiostatic experiments with the setup. The leaching was detected by extensive loss of long-range order around Co and significant changes also in Pt LIII EXAFS, but remained without significant influence on the cell performance.

Speaker: Dr Ilya Sinev (Ruhr-University Bochum, Bochum, Germany)

103 Thermal Demagnetization on Artificial Spin Ice

Artificial spin ice systems, consisting of two-dimensional arrangements of single-domain nanomagnets, allow the study of frustration and emergent magnetic monopoles [1, 2]. Synchrotron x-ray photoemission electron microscopy allows direct imaging of the magnetic state of each nanomagnet, having moments pointing in one of two orientations parallel to their long axis. Our recent studies of the basic building blocks of an artificial Kagome spin ice, consisting of permalloy or cobalt islands, indicated that as the number of rings is increased there is a decrease in the ability to achieve the low-energy states following demagnetization [1]. More recently, we have demonstrated the existence of emergent magnetic monopoles and their associated Dirac strings in a quasi-infinite nanomagnet array [2]. We now wish to study systems where we can observe thermally driven moment fluctuations and with these systems try to achieve long range order in large area arrays. First results indicate that we are indeed able to observe moments flipping on a timescale of a few minutes. [1] E. Mengotti, et al., Phys. Rev. B 78, 144402 (2008) [2] E. Mengotti, at al., Nature Physics 7, 68 (2011)

Speaker: Mr Alan Farhan (PSI)

104 Rotational Motion in LiBH4/LiI Solid Solutions

Lithium borohydride (LiBH4) is an ionic crystal, consisting of (Li)+ cations and (BH4)- anions. It undergoes an order/disorder transition at 380 K. The dynamic disorder of the HT phase originates from rotational jumps of the (BH4)- anions. The transition is accompanied by an increase of Li ionic conductivity by more than 3 orders of magnitude. The HT phase of LiBH4 can be stabilized by addition of lithium halides, resulting in the enhanced conductivity at room temperature. We investigated the localized rotational diffusion of the (BH4)- anions in LiBH4/LiI solid solutions by means of quasielastic and inelastic neutron scattering. The (BH4)- motions are thermally activated and characterized by activation energies in the order of 40 meV. Typical dwell times between jumps are in the picosecond range at temperatures of about 200 K. The motion is dominated by 90° reorientations around the 4-fold symmetry axis of the tetrahedraly shaped (BH4)- ions. The presence of iodide markedly reduces activation energies and increases the rotational frequencies by more than a factor of 100. The addition of iodide lowers the transition temperature, stabilizing the disordered HT phase well below RT.

Speaker: Dr Arndt Remhof (Empa)

105 Interaction of water with Ceramic Proton Conductors

Proton conductors are promising solid electrolyte materials for ceramic fuel cells operating at intermediate temperature. Protons are introduced in the form of water to those oxygen defected sites. We found by electrochemical impedance spectroscopy at high pressure that compressing the lattice decreases proton conductivity, which indicates that the protons need "space" to move freely in the lattice. We are probing the proton diffusion in the atomic scale by quasielastic neutron scattering under high pressure. Also, our recent results in neutron scattering from SINQ reveal that the onset temperature of lateral proton diffusion coincides with its thermal lattice expansion, which exhibits a contraction for protonated BaZr0.9Y0.1O2.95 at T = 648 K, suggesting a correlation of toughening of the lattice and proton conductivity.

Speaker: Qianli Chen (Empa)

106 Density profile of water confined in nanoslit

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. Numerous surface force experiments have been performed on such systems. However, force studies do not provide information on the molecular structure of the confined water. Recently we have adapted a surface force apparatus for specular X-ray reflectivity (XRR) determination of the electron density profile of the confined fluid across the gap. The confinement device features two freshly cleaved, cylindrically curved, mica membranes in crossed geometry, which are brought close together in order to create an atomically flat contact area. We determined by use of XRR the distance between the surfaces and the electron density profile of the naturally present water across the hydrophilic gap at nominal zero humidity. The mica surfaces were found to be apart by 1.35 nm. Water electron density profiles providing the best fit to the measured XRR-data show distinct peaks, indicating molecular layering of the water molecules. The results are in agreement with the predictions of recent Monte Carlo simulations. The average volume electron density of the confined water is 0.34 Å-3, a value similar to that of bulk water.

Speaker: Dr S Chodankar (Paul Scherrer Institut)

107 µ-XRF and µ-XANES study of Np sorption on Opalinus Clay

Until now the problem of high-level nuclear waste storage has not been solved. Argillaceous rocks such as Opalinus Clay (OPA) are considered by several European countries as a potential host rock formation for nuclear waste repositories. With respect to the long term storage of spent nuclear fuel, 237Np will be one of the main contributors to the radiotoxicity of this waste material. To predict the migration behaviour of neptunium in the case of a release from the storage place, the interactions with the surrounding clay formation have to be investigated in detail. The radionuclide retardation will be defined by different mechanisms such as sorption and diffusion. Natural heterogeneous OPA from Mont Terri, Switzerland, was used in our study at the SLS MicroXAS beamline to investigate the speciation of Np(V) on OPA thin sections as well as in an intact OPA bore core from a diffusion experiment. Spatial distributions of Np, Fe and Ca were determined by µ XRF mapping. The examination of intensive Np spots by Np LIII-edge XANES spectroscopy showed that Np(V) is partly reduced to Np(IV), probably by Fe(II) minerals. This reduction process significantly reduces the mobility of Np in OPA.

Speaker: Mr Daniel Fröhlich (Universität Mainz)

108 Interaction of Pu with Opalinus Clay studied by µ-XRF, µ-XRD, and µ-XANES

Plutonium will be a major contributor to the radiotoxicity of high-level nuclear waste after a storage time of more than 1,000 years due to the long half-lives of Pu-239, Pu-240, and Pu-242. Argillaceous rocks are under consideration as potential host rock formation for the construction of high-level nuclear waste repositories by several European countries, i.e., Belgium, France, Germany, and Switzerland. The interaction of Pu-242 with Opalinus Clay (OPA) from Mont Terri, Switzerland, was studied on a microscopic scale at the SLS MicroXAS beamline. The elemental distributions of Pu, Ca, Fe, and Mn on two OPA thin sections that were contacted with Pu(VI) solutions for 72 h and in an intact OPA bore core in which Pu was diffused over a period of one month were measured by µ-XRF. All samples contained Pu “hot spots” that were investigated by Pu LIII-edge µ-XANES and µ-XRD. As an important result, we found that the highly soluble Pu(VI) was retained by OPA in the reduced and less mobile tetravalent oxidation state of Pu.

Speakers: Mr Daniel Fröhlich (Johannes Gutenberg University Mainz), Dr Daniel Grolimund (PSI), Mr Jakob Drebert (Johannes Gutenberg University Mainz), Dr Samer Amayri (Johannes Gutenberg University Mainz), Prof. Tobias Reich (Johannes Gutenberg University Mainz), Mr Ugras Kaplan (Johannes Gutenberg Universität Mainz)

109 Structural modification in irradiated UO2 fuel investigated using micro-XRD and micro-XAFS spectroscopy

Uranium dioxide nuclear fuel, UO2, with fissile 235U is normally used in commercial power plants. Fission of 235U generates light and heavy fission fragments and disturbs both cation-cation and cation-anion network in the fuel matrix. Uranium dioxide can also exist as a hyper-stoichiometric UO2+x following oxidation. Nonstoichiometry in UO2 fuel may result a decreased thermal conductivity, increased thermal expansion and/or a greater volatility and fission FP release rate. In this work micro-focused X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) spectroscopy are used to examine the lattice structure of UO2 and next the neighbor atomic environment of uranium in a UO2 pellet irradiated to a medium burn-up condition. Micro-structures evolved at two different radial positions, the center-region and the rim-area, of the irradiated fuel pellet are examined. Results are compared with the corresponding results of an unirradiated (pristine) UO2 pellet. Structural changes in the irradiated UO2 grains, lattice parameters, local distortion and lattice dilation in the irradiated material are also measured from XRD data. All these results will be presented and discussed.

Speaker: Mr Cyprian Mieszczynski (Paul Scherrer Institute)

110 Fate of silver nanoparticles in sewers and wastewater treatment plants

Silver nanoparticles (Ag-NP) are used in an increasing range of consumer products. They are mainly released into the environment via their discharge into sewers and after passing through wastewater treatment plants (WWTP). To determine the risks for aquatic environments arising from the use of Ag-NP, data on their fate in sewers and WWTPs are required. We recently studied the transformation and retention of Ag-NP stabilized with fatty acid ester in a pilot-scale WWTP by combining a mass balance analysis with the characterization of Ag-NP transformation processes using electron microscopy (EM) and X-ray absorption spectroscopy (XAS) at the Ag K-edge (SuperXAS beamline; SLS) (1). In continuing work, we will investigate the transformation of Ag-NP with different sizes and surface coatings in batch experiments, in a sewer pipe, and in a pilot-scale WWTP using EM and XAS for the detailed characterization of Ag-NP transformation processes. Our results will contribute to the reliable assessment of the risks associated with the increasing use of Ag-NP. (1) Kaegi et al. (2011) Behavior of metallic silver nanoparticles in a pilot wastewater treatment plant. Environ. Sci. Technol. 45, 3902.

Speaker: Dr Andreas Voegelin (Eawag)

111 Extreme UV Interference Lithography of Carbon Nanosheets and Graphene

Two-dimensional (2D) carbon nanomaterials, e.g., graphene, graphene oxide, carbon nanosheets and ultrathin polymeric films have recently received an enormous attention due to their potential for use in electronics, chemical or biological sensors and filters, nanocomposite materials, etc. Most of these applications require lithographic patterning of these 2D carbon materials with the nanoscale resolution. In this respect, Extreme UV Interference Lithography (EUV-IL) opens broad prospects providing the large-scale nanopattering and very high resolution with an ultimate limit in the sub-10 nm range. We employ EUV-IL at the SLS XIL-II beamline to generate nanopatterns (dots, lines and grids) in 1 nm thin supramolecular sheets consisting of aromatic molecular precursors and graphene. We characterize these nanopatterns with a Helium Ion Microscope (HIM) which is sensitive to both topographic and chemical features. Nanopatterns of various geometries in the supported and suspended sheets are demonstrated.

Speaker: Mr Andreas Winter (Univesity of Bielefeld)

112 In situ neutron diffraction during tensile loading of oxide dispersion strengthened steels: effect of the material microstructure

Ferritic oxide dispersion strengthened (ODS) steels are considered as candidate materials for fuel claddings in Generation IV nuclear energy systems. Amongst their prerequisite properties, ODS steels have to retain their dimensional stability over the operating conditions targeted for this next generation of nuclear reactors. Mechanical testing is thus necessary to ascertain that these materials comply with the requirements of the nuclear safety specifications. The aims of the present work are thus to determine (i) the tensile properties of two ODS steels with distinct microstructure and (ii) the effect of the anisotropy of the grain microstructure on their microscopic mechanical properties. In situ neutron diffraction during tensile loading has been carried out at POLDI. During deformation, the evolution of the lattice strain has been derived through the profile analysis of several Bragg diffraction peaks. Post-deformation fractography and microstructural studies have been performed using SEM and TEM. A deeper insight into the interplay microstructure / mechanical properties has been obtained. This is crucial for the design optimization of such nuclear-energy related materials.

Speaker: Annick Froideval (High Temperature Materials, LNM / NES, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland)

113 Radiation induced structural changes in Fe-Cr alloys studied by EXAFS

We investigate irradiation damage mechanisms and changes in microstructure upon ion-beam implantation of the model Fe1-x Crx alloys, with x up to 20%. Fe+-beam implantation simulates the effect of neutron irradiation with respect to formation and evolution of atomic displacement cascades. The ion-irradiated samples are not activated and can be easily handled as non-radioactive specimens. We used EXAFS technique to investigate the changes in atomic structure leading to formation of displacement cascades which affect the fundamental mechanical properties of these materials. Additionally, TEM imaging of the post-irradiated specimens is used to determine the density and sizes of dislocation loops.

Speaker: Dr A Idhil (Paul Scherrer Institut, 5232-Villigen-PSI, Switzerland)

114 Investigating the magnetization curves of individual nanoparticles at finite temperatures

Increasing the storage density in future magnetic memory devices to the ultimate limit will require to address information at the level of individual nanoparticles. However, at small sizes thermal excitations can lead to undesired fluctuations of the magnetization and will affect their response to magnetic fields. In this contribution we use photoemission electron microscopy (PEEM) together with x-ray magnetic circular dichroism (XMCD) to detect the magnetization of individual Fe nanoparticles at room temperature. By varying the particle size we observe the transition from the superparamagnetic state to stable ferromagnetism at a particle size of about 12 nm. Applying a magnetic field allows us to record magnetization curves of the particles in both states and in the transition regime. The data are compared to the predictions of simple macro spin models. The role of non-collinear spin structures on the mechanism of the thermally induced magnetization reversal is also discussed.

Speaker: Ms Ana Maria Balan (Swiss Light Source, Paul Scherrer Institut)

115 Local atomic arrangements in Ni-Pt

The microstructure of the bulk and surface of Ni-Pt alloys has attracted much interest over the years. For Ni-Pt surfaces, the segregation reversal is the most striking feature, with Ni enrichment for the top layer of a (110) surface and Pt enrichment for the top layer of (110) and (111) surfaces. Strong ordering for nearest neighbors and the different strength of Pt segregation into different layers were found as being the reason. For bulk Ni-Pt, ab initio electron structure calculation and x-ray diffuse scattering both revealed the presence of a new phase, NiPt3 with L12 superstructure, below about 400°C. To investigate the region between surface and bulk, diffuse x-ray scattering under grazing incidence was done. Here, the (100) and (110) surfaces of Ni-23 at.% Pt were measured for states above the bulk order-disorder transition temperature. The atomic arrangements always show local L12 features. As the microstructure is no longer homogeneous close to the surface due to surface segregation and relaxation, additional information from literature / from crystal truncation rods (fundamental and superstructure) is required to model the atomic arrangements.

Speakers: Prof. Bernd Schönfeld (ETH Zürich), Dr Markus Engelke (ETH Zürich)

116 Trace elements in PM10, PM2.5 and PM1.0 aerosols

Suzanne Visser (PSI), M. Furger (PSI), U. Flechsig (SLS,PSI), K. Appel (DESY), A. S. H. Prevot (PSI) and U. Baltensperger (PSI) Ambient aerosol samples were taken in several megacities (e.g. Paris, Los Angeles) with a Rotating Drum Impactor (RDI). The RDI sampled aerosol particles with a volumetric flow of 16.6 l min-1 (1 m3 h-1) and particle size segregation in the ranges of 10-2.5 μm, 2.5-1.0 μm and 1.0 to approximately 0.1 μm (Richard et al. 2010). Sampling time was 2 hours. Subsequently, the elemental composition was analyzed using synchrotron radiation induced X-ray fluorescence spectrometry (SR-XRF) at the X05DA beamline (elements with Z = 13-30; Al-Zn) at the Swiss Light Source and at the beamline L (elements with Z = 24-82; Cr-Pb) at HASYLAB at DESY. Raw counts per element were calibrated using external reference standards on thin foils measured with the same beamline setup (Bukowiecki et al. 2005 and Richard et al. 2010). The elemental composition of aerosols is used to identify the spatial and temporal variability of emission sources in megacities. Bukowiecki et al. Environ. Sci. Technol. 39, 5754-5762 (2005). Richard et al. Atmos. Meas. Tech. 3, 1473-1485 (2010).

Speaker: Ms Suzanne Visser (MSc)

Resonant Inelastic and Elastic X-ray Scattering: part II

chairman: T. Schmitt, D.-J.Huang, U.Staub, J.van den Brink

117 Advanced Cu L3 edge RIXS studies of layered cuprate thin films

High resolution soft x-ray RIXS has been quickly evolving and among its initial applications the study of layered cuprates has emerged as probably the most successful. This is due to the favorable combination of an exceptionally strong resonant enhancement at the Cu L3 edge with a particularly simple theoretical description of the RIXS process for the 3d9 configuration. Thus the energies of dd excitations were recently determined for several insulating parent compounds [1]. And the measurement of spin-wave dispersion with RIXS was first demonstrated [2,3]. Soon after Cu L RIXS has been used on high Tc superconductors (LSCO, YBCO, NdBCO) revealing the exceptional persistence of mid-range magnetic correlation also in the superconducting state [3,4]. We present here recent results obtained on epitaxial films, with spectra measured both at the SLS ADRESS and at the ESRF ID08 beam lines. In doped and undoped NdBa2Cu3O7-δ we have studied the unexpected behavior of the elastic peak. Our results suggest the presence of dynamical stripe formation at critical doping levels. In undoped CaCuO2 we have studied the dependence of the crystal field and superexchange interaction as function of the epitaxial strain and of the interface density. [1] M Moretti Sala et al, N. J. Phys 13 043026 (2011) [2] L.J.P. Ament et al, Phys. Rev. Lett. 103, 117003 (2009) [3] L. Braicovich et al, Phys. Rev. Lett. 104, 077002 (2010) [4] M. Le Tacon et al, Nat. Phys. 2041 (2011)

Speaker: Dr Giacomo Ghiringhelli (CNR/SPIN and Dipartimento di Fisica, Politecnico di Milano, Italy)

118 Measuring spin excitations in insulating and superconducting cuprates by soft x-ray RIXS

Resonant inelastic x-ray scattering (RIXS) offers a unique view on local and collective excitations in strongly correlated materials, complementary to established techniques like neutrons, optics, or photoemission. The commissioning at the Swiss Light Source of the high-resolution (E/ΔE~10'000) SAXES soft x-ray spectrometer opened the way to measurements of the full spin wave spectrum in the cuprates, and the accurate evaluation of crucial model parameters. I will discuss RIXS data for the paradigmatic AFM parent compound SrCuO2Cl2 and, for Bi-2212, the evolution of the magnetic excitations into the superconducting part of the phase diagram.

Speaker: Prof. Marco Grioni (EPF Lausanne, Switzerland)

119 Correlated ab initio methods for the description of RIXS excitations in solids

Fully ab initio wavefunction-based methods from modern quantum chemistry are employed for the study of the electronic structure of correlated transition-metal com- pounds. We focus on the computation of N-particle excitations like those probed by optical absorption or RIXS (resonant inelastic x-ray scattering) measurements. The strong correlations are treated within the CASSCF (complete-active-space self- consistent-field) approximation while remaining correlation effects are handled by either multireference configuration-interaction techniques or second-order perturba- tion theory [1]. Since such correlation calculations can be carried out only for a finite region of the extended crystal, the remaining part of the solid is described at the Hartree-Fock level [2]. Results for the d-orbital electronic structure and su- perexchange interactions in a number of layered Cu and Ir oxide compounds are compared with recent RIXS data. [1] T. Helgaker, P. Jørgensen, and J. Olsen, Molecular Electronic-Structure Theory (Wiley, Chichester, 2000) [2] L. Hozoi, L. Siurakshina, P. Fulde, and J. van den Brink, Nature Sci. Rep., in press (available at arXiv:1012.3603)

Speaker: Dr L Hozoi (Institute for Theoretical Solid State Physics, IFW Dresden, 01171 Dresden, Germany)

15:40 Coffee

120 Inelastic X-ray Scattering Studies of Cuprate Spin Dynamics: The case of a single La2CuO4 layer

The dynamics of S = ½ quantum spins on a 2D square lattice lie at the heart of the mystery of the cuprates. In bulk cuprates such as La2CuO4, the presence of a weak inter-layer coupling (and other interactions) stabilizes 3D Neel order up to high temperatures. In a truly 2D system however, thermal fluctuations melt long range order at any finite temperature. Here, we utilize Cu L-edge RIXS to measure the spin response of isolated one-unit-cell thick layers of La2CuO4. We show that coherent magnons persist even in a single layer of La2CuO4 despite the loss of magnetic order, with no evidence for resonating valence bond (RVB)-like spin correlations. We also observe a high-energy magnetic continuum in the transverse and longitudinal magnetic response. This high-energy continuum is not well described any existing theories. In contrast, K-edge RIXS is sensitive to two spin-flip processes and we utilize this to measure the two-magnon response, providing further constraints on the spin Hamiltonian. Work reported here was supported in part by the US DOE under DEAC02-98CH10886 and by the Center for Emergent Superconductivity funded by the US DOE, Office of Basic Energy Sciences.

Speaker: J P Hill (Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton NY 11793, USA)

121 Magnetic excitation spectra of a novel spin-orbit coupled Mott insulator Sr2IrO4

Strong relativistic spin-orbit coupling (SOC) in 5d transition metal oxides provides a new route to realizing novel magnetic systems. Depending on the lattice geometry, expected magnetic systems range from conventional Heisenberg magnets to the more exotic Kitaev model and a topological Mott insulator. In the particular case of square lattice geometry relevant for Sr2IrO4, the superexchange interactions among the spin-orbit entangled electrons form a Heisenberg antiferromaget, rendering the low energy physics much akin to that in the high temperature superconducting curpates. In this talk, I will present the magnetic excitation spectra of Sr2IrO4, a magnon branch of which shows striking similarities to that in the cuprates. Further, novel high-energy, spin-orbit entangled modes are found in Sr2IrO4, which arise from interplay between spin-orbit coupling and electron correlations.

Speaker: Dr B J Kim (Material Science Division, Argonne National Lab, USA)

122 Multiplet code for X-ray spectroscopy - a new approach for low symmetry

The analysis and interpretation of state-of-the-art synchrotron x-ray measurements often have to rely on the theoretical understanding of the splittings of the atomic energy levels relevant to the case, and the simulation of spectra. Besides electron-electron interaction and spin-orbit coupling, the crystal field may contribute to the multiplets in a non-trivial fashion, particularly when the crystal symmetry is low. The existing multiplet codes based on describing the crystal field by its symmetry are therefore not suited to cases where the symmetry is destroyed. We therefore propose a computational approach to calculating the multiplets and XAS/RIXS spectra that does not require a knowledge of the crystal field symmetry, but where the crystal structure is entered as point charges. The Coulomb interactions and the crystal field as point charges are explicitly calculated, while the spin-orbit interaction is obtained from the solution of the atomistic Dirac equation in the density functional theory formalism. Therefore no parameterisation is required in order to calculate the multiplets. Scaling factors aiming at adjusting the screening effects on the radial functions are however available and can be used to fit the spectra. Various XAS and RIXS examples will be discussed, in particular in view of the polarisation dependence and symmetry of the crystal field.

Speaker: Dr A Uldry (Condensed Matter Theory, Paul Scherrer Institut, Villigen, Switzerland)

123 Imprinting magnetic information in manganites with X-rays

Manganite compounds have attracted a lot of the scientific interest by virtue of the unusual electronic and magnetic properties among them 'colossal magnetoresistance', and large magnetoresistive response. Here we report the writing, the in-situ observation and erasing of magnetic bits to Pr0.5Ca0.5MnO3 by illuminating with X-rays. Opposite to what is known so far, the antiferromagnetic magnetic signal increased, the magnetic order improved and the magnitude of the imprinted information could be controlled. We attribute this effect to the canting of manganese magnetic moments by the X-rays, accompanied by changes in the structure established by increase of the conductance. This photodoping effect manifests strong interaction of X-rays with magnetic structures and contributes to further understanding of photoconductivity. Furthermore, the ability to imprint information with a new technique may also lead to further insight in the interaction of X-rays with matter and a new development of memory devices.

Speaker: Dr M Garganourakis (Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland)

18:30 Workshop Dinner

Imaging

chairman: A.Kaestner, M. Stampanoni

124 Neutron Radiography Investigations to Study Material Behaviour in Loss of Coolant Nuclear Accidents

Neutron radiography is used to study safety related material processes occurring in design basis loss of coolant accidents (LOCA) and severe accidents (accidents beyond LOCA). The investigations comprises in-situ and ex-situ experiments to study the hydrogen uptake of zirconium alloys used as fuel rod cladding material and the redistribution of absorber materials in damaged control rods. The in-situ investigations have shown that the hydrogen uptake occurs rapidly during the first seconds. Later, the hydrogen concentration in the materials decreases slowly. Also hydrogen diffusion in zirconium alloys were studied in-situ. As example for the ex-situ investigations the hydrogen distribution in specimens prepared from LOCA simulation test were shown. Hydrogen bands close to the burst cracks were found. They are oriented non-symmetrically to the cladding tube axis. During severe accidents control rods are damaged by the eutectic interaction between cladding tube (SS) and guide tube (zirconium alloy). The contact between both tubes results in local melting the molten absorber material (AgInCd) flows out of this molten spot and is redistributed.

Speaker: Mr Mirco Grosse (Karlsruhe Institute of Technology)

125 Visualization and quantification of liquid water transport in softwood by means of neutron radiography

Liquid water uptake in three softwood species, in the radial, tangential and longitudinal directions, is investigated using neutron radiography at the wood growth ring scale. The high sensitivity of neutron to hydrogen atoms enables an accurate determination of the moisture content evolution in the wood. The spatial and temporal evolution of water content distribution during liquid water transport shows that latewood cells play a significant role in water uptake compared to earlywood cells and that ray tracheids contribute to liquid transport, particularly in radial and tangential directions. All water transport is accompanied by vapor sorption in the cell walls which can also be imaged with neutron radiography. In addition, we perform decane uptake experiments, as this non-polar liquid is not adsorbed in the cell walls, to study liquid transport in the absence of wood swelling.

Speaker: Dr Marjan Sedighi Gilani (Wood Laboratory, EMPA, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland and Chair of Building Physics, Institute for Technology in Architecture, ETHZ, Zürich, Switzerland)

126 In-Situ Investigations of Materials Using Ultra-Fast X-Ray Tomographic Microscopy and Laser Heating

Non-destructive synchrotron X-ray tomographic microscopy is ideal for studying the dynamics of materials systems in real time. To exploit the state‐of‐the‐art capabilities at the TOMCAT beamline of the SLS, a moderate to high temperature furnace has been developed. Powered by two diode lasers, it provides controlled, localized heating in a temperature range of 400 to 1600°C. When coupled with the ultra-fast technique, where a full data set of hundreds of projections over 180° can be captured in less than 1s, a user can explore many materials systems and their dynamics in‐situ under various thermal modalities. In one mode, the lasers achieve nearly isothermal conditions at a given location with a prescribed time-dependent temperature. This is typically used to study isothermal phase transformations such as nucleation and growth of bubble foams in silicate melts under conditions that mimic volcanic eruptions. In another mode, similar to Bridgman solidification of metals, the power of the laser is fixed and the specimen moves at a constant speed in a user-defined thermal gradient. Examples will be presented indicating the interest and versatility of this novel technique.

Speaker: Dr Julie L Fife (Paul Scherrer Institut)

127 Imaging and mechanics of liquid foam flows

Liquid foams are surprising materials, even though common in our everyday life. Their structure is mainly made of gas bubbles surrounded by a continuous liquid phase and stabilized by surfactants. Owing to this multiphasic composition, they behave like solids when submitted to small stress, and flow like liquids beyond a critical yield stress. These intermediate properties directly lead to numerous applications from food processing to ore/oil extraction. Coupling mechanical measurements with direct observations of the structure is necessary to understand their behavior and design foams with prerequisite properties. Different experimental approaches and results will be presented. They overcome the fact that foams are very diffusive at optical wavelengths. First, the use of 2D systems, which consist of bubbles monolayers, allows to get important insights about bubbles deformation and dynamics and to develop original tools to link their structure and mechanical properties. Second, the use of high speed X-ray tomography, which recent development has shown to be a promising non intrusive method, allows to track individually thousand of bubbles inside real 3D foam.

Speaker: Dr Christophe Raufaste (University of Nice, LPMC)

15:40 Coffee

128 Soft and complex matter investigations using neutron imaging: An overview

Diffusion of solvents in and through soft and complex matter matrices is not only of fundamental interest but is also important for applications as wide-ranging as drug delivery and food packaging. Due to the relatively recent advent of digital detector systems and stable, high resolution scintillators, neutron radiography can now be used to follow in real time and in-situ solvent influx into such samples. In this presentation I will illustrate the potential of this technique to yield high quality quantitative data for a range of systems. These include biologically-relevant lipids, polymers and nanoporous materials. After presenting an overview of our results, I will discuss in detail some specific examples which illustrate several experimental and data analysis details particular to this type of sample.

Speaker: Dr Helen Hermes (Heinrich-Heine-University Düsseldorf)

129 TOMCAT grating interferometry for biomedical imaging: Revealing the details of Alzheimer's Disease

New developments in biomedical imaging are often the source of exciting new insights into biological systems. Such a recent technology – implemented at the TOMCAT beamline – takes advantage of the coherent nature of synchrotron light to measure minute differences in the refractive index, at an unprecedented combination of sensitivity and spatial resolution. We will give a detailed account on the principle and instrumentation of the two-grating setup, which allows for measurement of refraction angles on the order of microradians. To demonstrate the new capabilities of this setup we present a visualization of the most prominent pathological feature of Alzheimer's Disease (AD), the amyloid pathology, in the brain of an AD mouse model [1]. Amyloid plaques consist of spherical proteinaceous aggregates with a diameter of a few tens of microns that accumulate througout the brain of AD patients. With the grating interferometer, we are now able to visualize and quantitatively evaluate the plaques over large regions of interest, which will give new insight into the progression of the disease. [1] Pinzer et al., submitted to PNAS

Speakers: Dr Bernd Pinzer (Swiss Light Source, Paul Scherrer Institut (PSI), 5232, Villigen-PSI), Dr Matthias Cacquevel (École Polytechnique Fédérale de Lausanne (EPFL), Brain Mind Institute, 1015, Lausanne)

130 Material Transport in 19th century Paint Grounds. Part I: Porosity Characterization by X-ray Tomography

Paintings are complex systems that remain chemically active long their completion by the artist. Increasing evidence shows that moisture plays a role as a reagent and in material transport. Our study focuses on Cuno Amiet, a Swiss painter from the late 19th - 20th century who used absorbent, porous preparation layers (i.e. ground layers) increasing their sensitivity to moisture. Several of his paintings showed evidence of the formation and mobility of degradation products. To better understand the interaction of the ground/paint layers with moisture, characterisation of the morphology of the ground layer is a fundamental first step. Here, we show XTM results obtained on a paint ground sample of Cuno Amiet’s Portrait of Max Leu (1898) and on ground reconstructions. These samples exhibit microscale pores connected by a sub-micron network. On Amiet’s sample, small micropores abundant at the surface and larger voids close to the canvas could be distinguished, giving valuable insight on the preparation technique. Current work is underway to compare these results with other Amiet’s paintings and with model grounds reconstructed according to historical recipes used by the painter.

Speaker: Dr Claire Gervais (SIK-ISEA)

131 Nanoscopic bone imaging for computational fluid dynamics in osteoporosis research

Bone undergoes continuous turnover or remodeling, where the well-coordinated action of all the bone cells keeps bone tissue healthy. Bone diseases, aging, and disuse detrimentally affect remodeling, causing severe bone loss and consequent fragility, as observed in osteoporotic patients. Osteocytes, the most abundant bone cells, orchestrate bone remodeling and act as bone mechanosensors. However, the actual mechanotransductive pathway is still under debate. One likely pathway is the fluid flow within the lacuno-canalicular network (LCN), where osteocytes reside. Yet, due to the remote location within the mineralized bone matrix and small dimensions (∼ 100 nm), the LCN could not be assessed in 3D1 so far. Due to a recent advent of new imaging techniques at nanoscopic resolutions, such as ptychographic CT2 and serial FIB/SEM3, we could now assess the LCN quantitatively in 3D. This allows computational simulations based on realistic LCN models to investigate load-induced fluid flow at a sub-cellular level, triggering bone mechanobiology. Bibliography: 1. Schneider P. et al. Bone 2010;47:848-58. 2. Dierolf M. et al. Nature 2010;467:436-9. 3. Schneider P. et al. Bone 2011;49:304-1.

Speaker: Ms Ilaria Chiapparini (Institute for Biomechanics, ETH Zurich, Zurich)

Multiple Order Parameter Systems: part II

chairman: C. Niedermayer, M. Kenzelmann, H.Luetkens, C. Rüegg

132 Origins and Electronic Structure of the 2D Electron Gas at the LaAlO3/SrTiO3 Interface

A unique system at the SIS beamline combines two powerful condensed matter experimental tools: a pulsed laser deposition (PLD) growth chamber and high-resolution angle-resolved photoemission spectroscopy (ARPES), connected by in situ UHV transfer. The PLD-ARPES system allows us to study the momentum-resolved electronic structure of novel materials that have not previously been accessible to standalone ARPES. Recently we have investigated the metallic 2D electron gas (2DEG) formed at the interface of the bulk band insulators LaAlO3 (LAO) and SrTiO3 (STO). Our work has achieved the first correct, full determination of the Fermi surface of the 2DEG at the surface of electron-doped STO. Moreover, after depositing LAO over STO, we have directly observed the interfacial 2DEG. The side-by-side comparison of bare STO and LAO/STO gives important clues about the origins and physics of the electronic states at the interface.

Speaker: Dr Nicholas C. Plumb (Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland)

133 In-situ ARPES study of La2/3Sr1/3MnO3 / SrTiO3 thin films: Fermi Surface Topology

Hole-doped manganese perovskites La1-xSrxMnO3 (LSMO) have stimulated a renewed scientific and technological interest because of their complex electronic and magnetic properties. Angle-resolved photoemission (ARPES), which directly probes the k-dependent electronic structure, could not be used to study LSMO single crystals because of their isotropic cubic symmetry (no preferential cleaving plane). The only alternative approach is to grow high-quality thin films and measure them in-situ ARPES. Our pioneering work [1] provided essential information about the low-energy electronic structure of LSMO, such as broad dispersive peaks and the clear observation of k-dependent spectral weight at the Fermi level. Here we report the complete topology of the Fermi Surface (FS) for LSMO thin films grown on SrTiO3 substrates and discuss our data in relation to the existing theoretical calculations and ARPES results of the similar layered manganites. The FS consists of an electron pocket centered at G point, formed by the (out-of-plane) 3z2-r2 electronic states, and hole cuboids centered at M points, mainly of (in-plane) x2-y2 character. [1] M. Shi et al., Phys. Rev. B 70 (2004) 140407

Speaker: Dr Mihaela FALUB (Paul Scherrer Institut, Swiss Light Source)

134 Soft-X-Ray ARPES View of Three-Dimensional Electronic Structure

ARPES experiments in the soft-X-ray energy range bring advantages of free-electron final states, simplified matrix elements and increasing photoelectron escape depth. The latter, along with enhancement of the bulk sensitivity, improves intrinsic resolution in surface-perpendicular momentum. This enables investigations of electronic structure under reliable control of the three-dimensional (3D) momentum k. Soft-X-ray ARPES experiments at SLS are performed at the ADRESS beamline operating in a photon energy range from 300 to 1600 eV. High photon flux topping up 10^13 photons/s/0.01%BW at 1 keV has allowed us to break through the notorious problem of small valence band crossection in the soft-X-ray range. Our pilot experiments included determination of 3D Fermi surface (FS) of VSe2, with its warping giving rise to 3D charge density waves (CDWs), exciton mediated CDWs in TiSe2, alternating shapes of the FS in 3D pnictides, hybridization effects in heavy-fermion systems, and FS of buried layers in LaNiO3/LaAlO3 hererostructures. Our results demonstrate an immense potential of soft-X-ray ARPES to deliver a clear view of electronic structure with resolution in 3D k-space.

Speaker: Dr Vladimir Strocov (Swiss Light Source, Paul Scherrer Insitute)

15:45 Coffee

135 Investigation of Ferromagnetic Semiconductors through Depth Resolved Spin Resonance Techniques

Technologically, a semiconductor which is also a ferromagnet has exciting potential for spintronic applications, where logic and memory operations could in principle be integrated on a single device. Artificial heterostructures based on such ferromagnets show immense promise, in particular for the injection of polarised spins into a semiconducting substrate. From a fundamental perspective, understanding ferromagnetism in a novel material which is also a semiconductor is an important challenge. Although no consensus on the mechanism has yet been reached, it is now established that the interaction between the magnetic atoms in prototypical systems like the III-V semiconducting materials Ga1−xMnxAs/GaAs or EuO1-x/doped Si is induced by charge carriers in the semiconductor host. 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. The unusual interplay between magnetism and transport properties opens up the interesting and potentially technologically useful possibility of modulating magnetic behaviour by controlling the charge carrier properties, through doping, applied electric fields or photoexcitation. These heterostructures may be produced in thin film form using non-equilibrium techniques such as molecular beam epitaxy. Investigations using local probes which are sensitive to magnetic structure on a nanometre lengthscale 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 mu-SR and beta-detected Nuclear Magnetic Resonance (beta-NMR), complementary spin resonance techniques.

Speaker: Dr S R Dunsiger (Physik Department, Technische Universität München, Garching, Germany)

136 Ultrafast magnetization dynamics in GdFeCo

Nanostructures of GdFeCo have been fabricated using lithography and lift-off techniques. Their magnetic properties were revealed using the Photoemission Electron Microscope (PEEM) available at the SIM beamline. Employing fs-optical excitation, we have been able to manipulate the magnetization of the nanostructures on very short time scales. By performing these experiments we have found experimental evidence for a novel mechanism of magnetization reversal in a ferrimagnet, which is triggered by a heat pulse only. In general, magnetization reversal is driven by a quantity that can be represented by a vector such as an external magnetic field or an applied current while in our experiment the reversal happens only by heating the system on the time scale of the exchange interaction of the two sublattices. We have further investigated the structures by performing Time Resolved X-ray Magnetic Circular Dichroïsm (TR-XMCD) and observed that the magnetization reversal occurs on a time scale faster than our resolution limit of 50 ps. We will report and discuss our latest results, obtained in both static and time resolved modes and the mechanism of the magnetization reversal will be described.

Speaker: Dr Souliman El Moussaoui (Paul Scherrer Institut)

137 Inelastic neutron scattering of the frustrated quantum spin ladder BiCu2PO6

Quantum spin ladders provide an exciting opportunity to study aspects of quantum critical phenomena and low-dimensional physics, serving as a bridge between 1 and 2 dimensional quantum systems [1]. BiCu2PO6 (BCPO) is a new spin 1 two-leg ladder system, with an energy scale of 2 exchange interactions in the range between the values found in cuprate ladders (~100meV) and the metal-organic ladders (~1meV). Quantum fluctuations prevent long-range order in the system, resulting in a disordered groundstate with gapped triplet excitations. Next-nearest-neighbour ex- change along the ladder direction introduces frustration in the system, which enhances quantum fluctuations and is thought to have a significant e↵ect on magnon dispersion[2]. Inelastic Neutron Scattering (INS) experiments were conducted on BCPO, resulting in the ob- servation of magnon excitation branches incommensurate with the crystal lattice with a spin gap of Delta ~ 1.8meV. Results from INS studies on the thermal Triple Axis Spectrometer (TAS) IN22 (ILL, Grenoble) suggest magnetic excitations extending up to 40meV, with dominant dispersion along the b and c axes; respectively the ladder leg and rung directions. High resolution studies on the cold neutron TAS instruments TASP (SINQ, PSI) and IN14 (ILL, Grenoble) near the gap minimum reveal multiple exciations with a strongly Q-dependent structure factor, which exhibit Zeeman splitting under applied field. The collected results and preliminary analysis of the excitations across a range of reciprocal lattice vectors and applied field values will be presented and discussed. [1] E. Dagotto and T. M. Rice, Science 271, 618 (1996). [2] O. Mentre et al. Phys. Rev. B 80, 180413(R) (2009).

Speaker: Mr P Merchant (University College London UCL, UK)

XFEL Experiments in Condensed Matter

chairman: B.Patterson

138 Instruments for condensed matter studies at European XFEL and FLASH

Updated radiation parameters and beamline layouts for the European XFEL facility under construction in Hamburg, Germany, will be presented. Furthermore, initial thoughts are introduced about the layout of the scientific instruments, with emphasis on applications in condensed-matter. The current status of condensed-matter research at FLASH and the LCLS will be reviewed and an outlook to major areas of application is given. One repeatedly discussed issue is the sample excitation by the intense x-ray FEL pulses, in particular for the high repetition rates available at the European XFEL. Simulation results for various configurations will be discussed.

Speaker: Thomas Tschentscher (European XFEL Hamburg)

139 Working Principles of High-Gain Free-Electron Lasers

Free-electron Lasers are radiation sources, based on the interaction of an relativistic electron beam with its radiation field within an undulator. The process of a collective instability causes the coherent emission at a freely tunable wavelength. As radiation devices FELs surpasses 3rd generation sources in terms of peak brilliance and opens up new classes of experiments such as e.g. lenseless imaging of molecules and atom clusters. This presentation gives a brief introduction into the physics of FELs and the performance as a radiation source.

Speaker: Dr Sven Reiche (Paul Scherrer Institut, SwissFEL group, 5232-Villigen-PSI, Switzerland)

140 A time-resolved, resonant soft x-ray scattering spectroscopy experiment at the LCLS: Time scale hierarchy in stripe-phase nickelates

In a hole-doped Mott insulator, spatially-ordered, nano-scale spin and charge patterns can emerge and form “stripes”. In this phase, holes form one-dimensional charge stripes, which serve as anti-phase domain walls between anti-ferromagnetically ordered spin stripes. While the stripe phase has been extensively studied in thermal equilibrium, its dynamics remain largely unexplored. Using the LCLS X-ray FEL, we perform time-resolved optical pump and resonant soft x-ray scattering spectroscopy probe on the stripe phase of doped nickelates. We find that the dynamics of the spin and charge stripe order are distinct from the thermal evolution. Moreover, an analysis of the initial and long recovery times reveals rich hierarchical time scales for charge and spin stripes, shedding new light on the surprising non-equilibrium physics of stripe-ordered systems. *Full author list: Y. D. Chuang, W. S. Lee, R. G. Moore, L. Patthey, M. Trigo, D. H. Lu, P. S. Kirchmann, M. Yi, O. Krupin, M. Langner, N. Huse, J. S. Robinson, Y. Chen, Y .Zhu, S. Y. Zhou, D. A. Reis, R. A. Kaindl, R. W. Schoenlein, D. Doering, P. Denes, W. F. Schlotter, J. J. Turner, S. L. Johnson, M. Först, T. Sasagawa, A. Sorini, B

Speaker: Dr Luc Patthey (Paul Scherrer Institut)

141 Cross-correlation based 2D structure determination from multi-particle X-ray diffraction images

In 1977, Kam proposed the cross-correlation method for 3D structure determination from X-ray diffraction images of multiple, identical, randomly oriented particles. The main obstacle to the practical application at the nanoscale, namely the requirement of short but intense incoming X-ray pulses, may be overcome with Free Electron Laser sources. We present the results of pilot experiments performed at a synchrotron X-ray source. The simplifications with respect to the original idea consist in the reduction of the dimensionality of the experiment from 3D to 2D, and in the "freezing" of the rotational motion of the particles to, allow sufficiently long acquisition time. We demonstrate the potential of the cross-correlation method by reconstructing the 2D structure of gold nanoparticles with size of the order of 360 nm and less.

Speaker: Dr Bill Pedrini (Paul Scherrer Institut)

15:50 Coffee

142 Quantum optics and nonlinear physics with x-rays

Nonlinear effects in the light-matter interaction arise when the optical properties of the medium are modified due to the presence of photons. The key quantity that determines these effects is the photon degeneracy, i.e., the number of photons per mode of the radiation field. At very high photon numbers, the light modulates the microscopic charge distribution, leading to phenomena like high-harmonic generation, frequency mixing, up- and down-conversion and more. With the advent of x-ray lasers it becomes appealing to explore these effects at wavelengths comparable to interatomic spacings, a situation that has not been encountered before. Quantum optical and nonlinear effects, however, do not require a high photon degeneracy, but can be observed at the single-photon level if the mode structure of the vacuum is modified, e.g., in a cavity. I will show that effects like electromagnetically induced transparency can be observed by employing Mössbauer isotopes as two-level systems embedded in planar x-ray waveguides. Perspectives for experiments at existing and future light sources will be discussed.

Speaker: Dr Ralf Roehlsberger (DESY Hamburg)

143 Langevin dynamics and probing the atomic scale

Thermal fluctuations at the atomic scale play a fundamental role in the dynamics of microscopic processes such as magnetism, transport and micro-structural evolution. Langevin dynamics can sometimes provide a description of such phenomenon and its mathematical realization constitutes one example of a stochastic differential equation. In this talk, the Langevin approach is introduced and discussed in the context of the short time and length scales accessible to current and future generation light sources.

Speaker: Dr Peter Derlet (Paul Scherrer Institut)

144 Open discussion - SwissFEL user wishes

Speaker: Bruce Patterson (Paul Scherrer Institut)

145 SACLA Progress Report

A progress report will be given on the commissioning phase of the Japanese X-ray laser project SACLA, located at the SPRING-8 campus.

Speaker: Prof. T Ishikawa (Riken Harima Institute, Sayo, Hyogo 679-5148, Japan)

no session

Saturday 17 September

Resonant Inelastic and Elastic X-ray Scattering: part III

chairman: T. Schmitt, D.-J.Huang, U.Staub, J.van den Brink

146 Probing the Local Magnetic Order of Quasi-1D Cuprates with RIXS

We have performed Resonant Inelastic X-ray Scattering (RIXS) at the Cu L- and O K-resonance at the ADRESS beamline of the Swiss Light Source on the quasi-one-dimensional cuprates Li2CuO2 and CuGeO3, prototype edge-sharing chain compounds showing different magnetic ground states at low temperature. The RIXS spectra display a complicated interplay of low-energy excitations from charge, orbital and lattice degrees of freedom. In particular, we discuss charge transfer related spectral components in the scenario of exotic Zhang-Rice (ZR) singlet and triplet excitations which can be reached in the final state with O K-edge RIXS. Temperature dependent measurements evidence specific temperature behavior for the related peaks, strongly depending on the nature of the magnetic ground state. Our interpretation is further supported by state-of-the-art cluster-based RIXS calculations. Comparing the excitation energy of both ZR features allows to directly determine the binding energy of the Zhang-Rice singlet in Li2CuO2 from the spectra. Finally, this study suggests RIXS as an excellent probe for investigating local magnetic order.

Speaker: Dr C Monney (Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland,)

147 Elementary spin and orbital excitations in low-dimensional Cuprates

Quantum effects become important, when the space symmetry is lowered. In the extreme case of one dimension the fundamental degrees of freedom of the electron can break up into separate quasi-particles carrying the spin, charge or orbital degrees of freedom. Here we report on studies of elementary excitations in quasi 1D cuprates, the spin-ladder/spin-chain compound Sr14Cu24O41 and the spin-chain Sr2CuO3, using Resonant Inelastic X-ray Scattering at the SAXES spectrometer at the ADRESS BL of the SLS at PSI, Switzerland. When the incident photon energy is tuned to the Cu 2p-3d resonance, elementary spin and orbital excitations can be observed in the low-energy and medium-energy range of 0-800 meV and 1.5-2.5 eV, respectively. Improvement of theoretical understanding of the X-ray scattering process allows for a quantitative analysis of the data. In the medium-energy range we observe for the first time the deconfinement of spinons and orbitons.

Speaker: Dr J Schlappa (Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany)

148 Spin-Orbital Separation Observed with RIXS in Sr2CuO3

Due to the recent advancements in experiment and theory, the resonant inelastic x-ray scattering (RIXS) performed at the L edge of transition metal ions is emerging as a powerful probe to study salient features of the strongly correlated electron systems. For example a recently performed RIXS experiment at the copper L3 edge in quasi one-dimensional Sr2CuO3 reveals orbital excitations with a surprisingly large dispersion. This first undoubted observation of a dispersing orbital excitation in a transition metal oxide is already interesting in itself. A detailed theoretical study, however, shows that this dispersion evidences a fractionalization of spin and orbital excitations in Sr2CuO3 and is due to spin-orbital separation of the RIXS excitation: in the one-dimensional CuO3 chains the orbital degree of freedom decouples from the spin one and becomes mobile with an unexpectedly large dispersion. This fractionalization of the excitation bears similarities to the spin-charge separation that has previously been observed with ARPES.

Speaker: Dr K Wohlfeld (Leibniz Institute for Solid State and Materials Research IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany)

149 Orbital and magnetic excitations in the weakly coupled spin chain system CaCu2O3

Recently, resonant inelastic X-ray scattering (RIXS) on the 1D spin chain system Sr2CuO3 has revealed an unprecedented dispersion of d-d excitations [1]. This result has been under-stood as an effect of strong interaction between spin and orbital degrees-of-freedom taking place within a single chain. In this talk we report on Cu L3 RIXS in quasi 1D CaCu2O3 con-sisting of two coupled spin chains. Due to its buckled geometry, the inter-chain interaction of this system is one order of magnitude smaller than the in-chain interaction. Therefore, Ca-Cu2O3 is an ideal model system to study the effect of a weak inter-chain interaction on both, the low (spin excitation) and the high (d-d excitations) energy scale. Although the dispersion of the spinon continuum can largely be accounted for by neglecting the presence of the inter-chain interaction, surprisingly no dispersion has been found for the d-d excitations. This rais-es the question if the dispersion of orbital excitations is effectively being quenched as soon as two chains are connected to each other. The important role played by inter-chain interactions for the magnetic and orbital excitations in this class of compounds will be discussed in this context. [1] J. Schlappa, K. Wohlfeld, J. van den Brink, T. Schmitt et al., private communication.

Speaker: Dr V Bisogni (IFW Dresden, Dresden, 01069, Germany)

10:40 Coffee

150 In-Situ RIXS Study of Charge Transfer in Artificial Photocatalysts

There are emerging technologies of using nanostructured semiconductors and charge transfer processes for solar conversion to chemical fuels for energy use and storage. The ability to control the particle size, morphology and composition of nanoparticles is of crucial importance nowadays considering the extensive high-tech applications of 3d metal compounds in the applications of photosynthesis. XAS, XES, and RIXS are probes of the local, molecular electronic structure particularly relevant to catalysis: oxidation state, coordination environment, π-backbonding/σ-donation, d-p hybridization, and metal-ligand charge transfer. The presentation shows that the electronic structure of the reaction intermediates of the catalysts is obtained from L-edge XAS, XES and RIXS of the transition metals. The charge transfer in Co3O4 nanoclusters grown in silica nanopores that act as efficient and robust catalysts for water oxidation has been revealed, so as to an all-inorganic, oxo-bridged heterobinuclear TiIVOMnII group covalently anchored on a silica nanopore surface as charge-transfer chromophores for driving multielectron catalysts in artificial photosynthetic systems.

Speaker: Dr Jinghua Guo (Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA)

151 Resonant Inelastic Soft X-ray Scattering with Vibrational Resolution

Most fundamental questions regarding the function of complex molecular systems are related to different molecular building blocks and their local electronic and dynamic properties. Resonant Inelastic X-ray Scattering (RIXS) has for a long time allowed access to site-specific electronic structure information on the atomic length scale. As a photon-in/photon-out technique, it is also ideally suited for the investigation of liquids. However, the lack of adequate sources has up to now limited the access to direct information about local coordination and dynamics and only a fraction of the inherent advantages have been exploited. We present RIXS spectra of liquids (acetone, water) and gases (O2, CO2) excited at the oxygen K-edge with a resolution o of E/dE~10000. For the first time, we are able to resolve single vibrational modes, opening a wealth of new possibilities such as mapping local potential energy surfaces of the electronic ground state which no other technique can access. Highly energy resolved spectra obtained at the ADRESS beamline at the SLS are presented along with ab-initio multimode scattering calculations that resemble the data in very high detail.

Speaker: Ms A. Pietzsch (MAX-lab, Lund University, Lund, Sweden)

152 X-ray femtochemistry: Mapping the valence electronic structure of dissociating molecules with femtosecond RIXS at the free electron laser LCLS

We present our recent results on how we follow both the occupied and unoccupied valence orbitals of dissociating Fe(CO)5 molecules in solution with femtosecond RIXS at the free electron laser LCLS (Stanford, USA). A pump-laser wavelength of 267 nm is used for resonant metal-to-ligand charge transfer excitation. The evolution of the valence electronic structure is probed with RIXS at the Fe L-edge as Fe(CO)5 dissociates into Fe(CO)4 and CO in ethanol solution. We use a recently built set up with a liquid jet in vacuum and a soft x-ray RIXS spectrometer. Our results reveal the coupling of orbital population, chare transfer and structural dynamics during dissociation and solvation of the photoproducts up to 3 picoseconds after initiating the reaction. They give unique insight into the coordinatively unsaturated carbonyl intermediate Fe(CO)4 and give complete access to the dissociation dynamics of a fundamentally important chemical bond with sigma-donation and pi-back donation between the metal center and the carbonyl groups. We believe that femtosecond RIXS gives unique access to the coupling of transient electronic structure and nuclear dynamics during chemical reactions. This contribution will conclude with recent and complementary results with steady-state RIXS on liquids and solutions obtained with the same experimental set up at BESSY II.

Speaker: Dr Ph Wernet (Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany)

153 RIXS in free molecules: Polarization and dynamical aspects

We present main results obtained using RIXS on free molecules, sensitive to sub-femtosecond nuclear dynamics after inner-shell photoexcitation. The core-excited lifetime is used as a characteristic time to probe nuclear rearrangements. Kα emission spectra at the Cl K edge illustrated the molecular x-ray emission features and their strong correlation with the ab initio potential energy curves calculated [1]. Excellent agreement between experimental and theoretical data is obtained when interference effects due to the coherent excitation of different electronic states are taken into account [2]. Moreover, sensitivity of the method to chemical environment has been used to probe the molecular field effects on the ionization energies and electronic distribution which affects the molecular spectra [3,4]. [1] M. Simon et al, Phys. Rev. A 73, 020706(R) (2006). [2] M. Kavčič et al, Phys. Rev. Lett. 105, 113004 (2010). [3] R. Guillemin et al, Phys. Rev. Lett. 101, 133003 (2008). [4] S. Carniato et al, Phys. Rev. A 80, 032513 (2009).

Speaker: Dr L Journel (Laboratoire de Chimie Physique – Matière et Rayonnement, Université Pierre et Marie Curie et CNRS, UMR7614, 11, rue Pierre et Marie Curie, 75231 Paris Cedex 05)

RIXS - Poster session and lunch

Resonant Inelastic and Elastic X-ray Scattering: part IV

chairman: T. Schmitt, D.-J.Huang, U.Staub, J.van den Brink

154 Intense paramagnon excitations in a large family of high-temperature superconductors

Motivated by the search for the mechanism of high-temperature superconductivity, an intense research effort has been focused on the evolution of the spin excitation spectrum upon doping from the antiferromagnetic (AF) to the superconducting states of the cuprates. Because of technical limitations, however, the experimental investigation of doped cuprates has been largely focused on low energy excitations (<100 meV) in a small range of momentum space. Here we use RIXS to show that a large family of superconductors, encompassing the model compound YBa2Cu3O7, exhibits damped spin excitations - paramagnons - with dispersions and spectral weights similar to those of magnons in undoped AF cuprates over much of the Brillouin zone. This is in excellent agreement with the spin excitations obtained by exact diagonalization of the t-J Hamiltonian on finite-sized clusters. A numerical solution of the Eliashberg equations based on our experimental findings for YBa2Cu3O7 reproduces its TC within a factor of two. The discovery of a well-defined, surprisingly simple spin excitation branch over a wide range of doping levels thus strongly supports magnetic Cooper pairing models for the cuprates.

Speaker: Dr M Le Tacon (Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany)

155 Theory of Inelastic X-Ray Resonance Scattering in Iron Arsenides

It has been recognized that both spin and orbital degrees of freedom are the key to understanding the physics of iron arsenides. Theoretical calculations within the random-phase approximation for a five-orbital Hubbard model have nicely explained spin excitations observed by inelastic neutron scattering experiments for antiferromagnetic (AF) phase [1]. In order to clarify the interplay of spin and orbital degrees of freedom in the energy and momentum spaces, we propose resonant inelastic x-ray scattering (RIXS) tuned for Fe L3 edge [2]. In the AF phase, we find that the magnon excitations predominantly composed of single orbital component appear with a weak intensity as compared with orbital excitations lying just above the magnon excitations. The dominant orbital excitations are found to be accompanied by the spin-flip process, producing composite excitations of the coupled orbital-spin degrees of freedom. We also predict the polarization and momentum dependence of the Fe L3-edge RIXS prior to forthcoming experiments. [1] E. Kaneshita and T. Tohyama,, Phys. Rev. B 82, 094441 (2010). [2] E. Kaneshita, K. Tsutsui, , and T. Tohyama, to be published I Phys. Rev. B.

Speaker: Dr T Tohyama (Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan)

156 Dispersive High-Energy Spin Excitations In Iron Pnictide Superconductors Investigated With Resonant Inelastic X-Ray Scattering

The discovery of iron-based high temperature superconductivity has triggered tremendous research efforts in searching for novel high-Tc superconductors and in understanding the related fundamental physics. Unlike the cuprates whose parent compounds are long-range ordered antiferromagnetic Mott insulators, the iron-based parent compounds are ‘spin-density wave’ metals with delocalized electronic structure and more itinerant magnetism. Recent ARPES studies provides cumulative evidence that superconductivity in iron-based materials may be connected with interband pair scattering between the quasi-nested electron-hole Fermi surfaces. On the other hand, the observation of spin fluctuations by Inelastic Neutron Scattering (INS) in these materials, similar to those seen in cuprates, suggests that cuprate and iron-based high-Tc superconductors may share a common pairing mechanism. Recent developments of the high-resolution resonant inelastic X-ray scattering (RIXS) technique [1] have enabled investigations of magnetic excitations in cuprates [2,3], which show excellent agreement with results from INS. In this presentation we demonstrate that RIXS can be used to measure collective magnetic excitations in iron-based superconductors despite their much stronger itinerancy compared to cuprates. The persistence of high-energy spin excitations even in optimally doped pnictide superconductors in a wide range of temperatures strongly suggests a spin-mediated Cooper pairing mechanism as proposed in cuprate superconductors. [1] G. Ghiringhelli et al., Rev. Sci. Instrum. 77, 113108 (2006); V. N. Strocov et al., J. Synch. Radiat. 17, 631 (2010) [2] J. Schlappa et al., Phys. Rev. Lett. 103, 047401 (2009) [3] L. Braicovich et al., Phys. Rev. Lett. 104, 077002 (2010)

Speaker: Dr K J Zhou (Swiss Light Source, Paul Scherrer Institut, CH 5232 Villigen PSI, Switzerland)

15:10 Coffee

157 Present status of Soft X-ray RIXS in SPring-8; electronic structure of liquids and protein

Soft X-ray RIXS is a powerful tool for studies of electronic structure of various materials, such as semiconductors, ionic materials, simple metals, and strongly correlated materials. Furthermore, Soft X-ray RIXS is also powerful for the liquids and wet samples. Electronic structures of these materials are very challenging. We will discuss about the electronic states of transition metal ions of proteins in water, which play important roles in protein-function [1]. The electronic structure of acetic acid is also discused [2,3] . Recently, the University of Tokyo constructed a new beamline that has a 25-m long undulator. We will introduce the new RIXS spectrometer whose resolution is about 10,000[4]. References [1] Harada et al., Journal of the Physical society of Japan. 78(2009) 44802. [2] Horikawa et al., Phys.Chem.Chem.Phys., 11(2009)8786 and 12(2010)9165 [3] Tokushima et al., Phys.Chem.Chem.Phys., 11(2009)1679 [4] Harada et al., unpublished.

Speaker: Dr S Shin (Institute for Solid State Physics, the University of Tokyo laboratory, Chiba 277-8581, Japan and RIKEN Spring-8, Hyogo 679-5148, Japan)

158 Status of AERHA, a new soft X-ray emission spectrometer at Synchrotron SOLEIL

A new X-ray spectrometer for soft X-rays has recently come into operation at the French national synchrotron facility. The design targets of AERHA (Adjustable Energy Resolution – High Acceptance) aimed at optimized trade-off between energy resolution and instrument transmission. The instrument covers energies between 50 and 1000 eV with a resolving power in excess of 6000 while maintaining an effective angular acceptance higher than 100 micro-steradians. The first part of my talk will be focused on considerations of optical design and implementation, also showing the first recorded spectra. Our scientific interests and the opportunities offered by the new instrument will be discussed and placed in perspective relative to experiments performed at other light sources.

Speaker: Dr S G Chiuzbaian (UPMC (Univ. Paris 6), Laboratoire de Chimie Physique - Matière et Rayonnement (UMR 7614), F-75005 Paris, France and Synchrotron SOLEIL, F-91192 Gif Sur Yvette, France)

159 A High-Resolution RIXS Spectrometer Using an Energy-Compensation Principle

Resonant inelastic resonant soft x-ray scattering (RIXS) is an effective spectro-scopic method for unraveling electronic structures of solids, because of recent technological advances in synchrotron radiation sources and beamlines. NSRRC has designed and constructed an experimental setup of RIXS in the soft x-ray re-gime. Ray-tracing results show that the efficiency of a RIXS setup with an active grating monochromator (AGM) and an active grating spectrometer (AGS) is higher than that of a conventional design by nearly two orders of magnitude, while a high spectral resolution is maintained. Our commissioning results show that the total energy resolution of RIXS system is ~ 140 meV at the energy of 930 eV. Here we will present the design concept and commissioning results of RIXS on transition-metal oxides such as NiO, La2CuO4 and 1D spin systems with the new AGM-AGS RIXS setup.

Speaker: Dr D J Huang (National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan)