报告人：Dr. Jinghua Guo
（Advanced Light Source, Lawrence Berkeley National Laboratory）
报告题目：Soft X-Ray Spectroscopic Study of Nanostructured Materials
The ability to control the particle size and morphology of nanoparticles is of crucial importance nowadays both from a fundamental and industrial point of view considering the tremendous amount of high-tech applications of nanostructured 3d metal compounds in the applications of solar photovoltaic and photoelectrochemical cells, chemical, gas and biosensors, supercapacitors etc. Controlling the crystallographic structure and the arrangement of atoms along the surface of nanostructured material will determine most of its physical properties.
In general, electronic structure ultimately determines the properties of matter. In the soft x-ray region, the question tends to be, what are the electrons doing as they migrated between the atoms? Soft x-ray absorption spectroscopy (XAS) and emission spectroscopy (XES) have some basic features that are important to consider. X-ray is originating from an electronic transition between a localized core state and a valence state. As a core state is involved, elemental selectivity is obtained because the core levels of different elements are well separated in energy, meaning that the involvement of the inner level makes this probe localized to one specific atomic site around which the electronic structure is reflected as a partial density-of-states contribution. The participation of valence electrons gives the method chemical state sensitivity and further, the dipole nature of the transitions gives particular symmetry information.
The new generation synchrotron radiation sources producing intensive tunable monochromatized soft x-ray beams have opened up new possibilities for soft x-ray spectroscopy. The possibility to select the energy of the excitation has created an extra degree of freedom. The high-resolution selectively excitation has opened a new field of study by disclosing many new possibilities of soft-x-ray resonant inelastic scattering (RIXS). In this presentation, some instrumentation development and recent findings regarding XAS, XES, and RIXS studies of various nanostructured systems are presented. The results reveal the electronic structure of the 3d metal compounds in pure form and their variations upon doping. Also, in-situ characterization of metal nanocrystal suspensions demonstrated the way for real-time studies of nanomaterial growth and chemical reactions.