Gang Chen Seminar:
Structures at atomic scales are traditionally determined through X-ray crystallography that amplifies scattering intensities by introducing spatial periodicity. For amorphous materials and many macromolecules, such as viruses, proteins and biofilms, it is hard to determine structures due to their incapability to crystallize or change of configuration during crystallization. In this talk, I will present the application of X-ray reflectivity and a newly developed fluctuation X-ray scattering technique to study the structures of lipid membranes and randomly oriented nanoparticles. Three different types of domain registrations occurring with three distinct heights were observed in supported lipid bilayers. The inner leaflet is constrained by the substrate and becomes roughly planar leaving the outer one corrugated. The fluctuation X-ray scattering experiment has been carried out on platinum-coated gold nanoparticles randomly oriented on a substrate. A complete algorithm for determining the electron density of an individual particle from diffraction patterns of many particles randomly oriented about a single axis is demonstrated.
The ability to follow the charge separation and the redox process in the light absorber and catalyst is crucial for the design of an efficient artificial photosynthesis system. I have studied the density of states and the valence and conduction band structures of the light absorber using X-ray absorption and resonant inelastic X-ray scattering techniques, while the oxidation state and chemical bonding environment of a catalyst have been measured by XANES and EXAFS.
