National Synchrotron Light Source Seminar

"Path from soft x-ray microscopy to inelastic scattering"

Presented by Konstantine Kaznatcheev, Brookhaven National Laboratory

Monday, September 12, 2011, 3:00 pm — Seminar Room, Bldg. 725

Soft x-ray microscopy at a SR source takes full advantage of soft x-ray specific interactions and provides chemical sensitivity based on a distinct x-ray absorption structure that is characteristic of each chemical species. The variation of x-ray polarization extends measurements to include dichroic signals, which permits one to derive molecular orientation or element-specific magnetic moments. Large penetration length provides “bulk sensitivity” and enables the study of buried interfaces under relevant conditions (magnetic and electrical fields; in a wet, pH controlled state; or under mechanical impact). Individual angular projections can be combined in a tomographic set and give 3D reconstruction at a spatial resolution approaching 25nm. Still, as with any other technique, x-ray transmission microscopy has limitations. I will use the research examples from the Canadian Light Source Spectromicroscopy beamline to illustrate them.
In particular, the discussion will evolve around heterogeneous catalysis, where a variety of size-dependent structural, magnetic, electronic, and catalytic properties of nano-particles demands in situ fine characterization. Fischer-Tropsch synthesis provides an effective route to green, sustainable, clean bio-fuel production, but requires a development of a chemical reaction model for further improvement of catalytical activity. It is now possible (a) to construct enclosed reaction cells, (b) to identify the valence state of different nano-particles at reactive condition, and (c) to follow oxidation state variation through a chemical reaction. We can extend snap-shot imaging to sequential time evolution as reactive condition changes and, based on quantitative compositional analysis at a scale finer than 30nm, follow the chemical balance and flow of reactive products. Finer details of adsorbate–adsorbent interaction, or catalytical particle surface composition remain more obscure. The interaction of nano-particle (guest)

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