The symposium features a series of scientific presentations by graduate students and Post-docs whose research is based at CHESS and a brief overview of CHESS.
Schedule
5:15 pm - Welcome
5:20 pm - Xin Huang (Cornell University)
5:40 pm - Gabrielle Illava (Cornell University)
6:00 pm - Pizza
6:30 pm - Connor Buhariwalla (McMaster University)
6:50 pm - David Agyeman-Budu (Cornell University)
Speakers and Talk Titles
Xin Huang - Cornell University
"Effect of Surface Structure of SrTiO3 on the Catalysis of Photo-Assisted Water Splitting"
Abstract: SrTiO3 (STO) is a promising semiconductor material for the water splitting reaction since its valence and conduction bands lie at appropriate energy positions for the simultaneous photo-induced evolution of hydrogen and oxygen even at zero applied bias. While much is known about the bulk electronic structure of STO as well as its surface structure in vacuum, much less is known about the atomic structure of the catalytically active surface, especially how changes in the surface structure and composition influence its photocatalytic properties. In this talk, I will present our results on the surface effect on the photocatalytic properties of STO, with in operando techniques, including scanning electrochemical microscopy and surface X-ray diffraction, in an effort to assess the catalytic properties and surface atomic structure. A surface reconstruction on STO was observed during the photo-induced water splitting at zero applied bias, which was different from the surface found in air or vacuum. “Training” the surface by cycling the potential to positive values both irreversibly altered the surface structure and enhanced the catalytic activity at zero external bias by 300%. Based on the interpretation of joint density functional theory from surface X-ray diffraction data, the “trained” active surface of STO has a biaxially strained anatase-like structure.
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Gabrielle Illava - Cornell University
"Protein Denaturation at High Pressure, Technology Development and Implementation in Small Angle X-ray Scattering (SAXS)"
Abstract: Pressure is a particularly useful thermodynamic perturbation of proteins since its effects arise because of differences in molar volume between biomolecular conformational states. Measurement of these differences through SAXS is ideal to obtain global shape information as the protein unfolds under pressure. Providing the high-pressure SAXS cell for study of pressure-effects on biological molecules to the CHESS user community is a worthwhile endeavor since no other synchrotron facility in the United States has this technique available. Results of the first successful experiment will be discussed in addition to future directions in high-pressure bioSAXS and protein crystallography.
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Connor Buhariwalla - McMaster University
"Magnetic Ground State Selection Through Quenched Charge Correlation"
Abstract: Frustrated magnetism, where disordered and exotic ground states can be selected at low temperatures, is a rich field in condensed matter physics as there are many variations of competing interactions and anisotropy that real materials can display. Quenched disorder, whether naturally occurring or intentionally introduced, can also be very important to ground state selection in such materials. I will discuss how synchrotron x-ray measurements of charge correlations in such materials can be used to characterize the quenched disorder, and ultimately to understand the role of the disorder in ground state selection. I will illustrate this with two recent examples.
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David Agyeman-Budu - Cornell University
"Collimating Channel Array Optics for Confocal X-ray Fluorescence Microscopy"
Abstract: Confocal X-ray Fluorescence (CXRF) microscopy is an x-ray scanning probe technique which enables the detection of x-ray fluorescence from a localized, micron-scale 3D volume of an extended, unthinned sample. It is realized by combining direct photon excitation from a condenser optic to the subsequent fluorescent radiation detection via a collection optic coupled to an energy dispersive detector. The foci overlap of both optics defines the probe volume which is translated through the sample. Our implementation of this technique is utilizing a novel collection optic - Collimating Channel Arrays (CCAs) which were developed at CHESS. These optics are lithographically fabricated from germanium substrates and they have been demonstrated to have a nearly independent energy resolution. We present the design considerations and fabrication of the CCAs, the iterative improvements made so far in addition to characterization of the depth resolution and channel acceptance of optic and etch process.