Speaker
Description
With a rise in the number of lab-based APXPS systems, these instruments afford an opportunity to continue the development of multimodal capabilities for more comprehensive information of reactions at surfaces. I will discuss the methods of obtaining multimodal data from infrared reflection absorption spectroscopy (IRRAS) and environmental transmission electron microscopy (ETEM) under the same reaction environments as the lab-based APXPS system at the Center for Functional Nanomaterials at Brookhaven National Laboratory. In situ polarization-dependent IRRAS measurements have been used to confirm the reaction of CO with a Cu2(111) surface to form CO2. The uncommon IRRAS measurements of a single crystal transition metal oxide surface allow for insights into the geometry of the adsorbates. The combination of APXPS and IRRAS determine that a C 1s binding energy commonly assigned to carbonates is actually CO2. This study has implications for catalysis and also metal oxide XPS studies, where in this case the adsorbed CO and CO2 have binding energies higher than other systems. While IRRAS provides more insight into chemical environments on surfaces, ETEM can offer complementary structural information. A 50 micrometer heater on a Nano-Chip used in ETEM was adapted to a gas cell for APXPS measurements. Proof-of-concept measurements show that the heater functions identical to ETEM experiments. The gas lines in the cell enable locally high pressures above the heater, estimated to be 1 mbar with the potential for higher pressures. The rapid temperature increase of the microheater (≤1 s) also enables time resolved measurements. The reduction of an oxidized Pd film was followed with 500 ms resolution of the Pd 3d5/2 core level. This timescale matches the timescale of ETEM measurements (≥10 ms) of identical processes. Using this Nano-Chip in APXPS offers chemical information complementary to structural changes seen in ETEM. The rapid heating enables new opportunities in time-resolved APXPS. Overall, both the ETEM heater and IRRAS offer ways of combining additional information to yield a deeper understanding of surface reactions beyond the metal oxide chemistry demonstrated here.
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