Many important energy systems are based on the complexity of material architecture, chemistry and interactions among constituents within. To understand and thus ultimately control the energy applications calls for in-situ/operando characterization tools. Recently, we have developed the in-situ/operando soft X-ray spectroscopic systems for the studies of catalytic and electrochemical reactions, and reveal how to overcome the challenge that soft X-rays cannot easily peek into the high-pressure catalytic or liquid electrochemical reactions. The unique design of in-situ/operando soft X-ray spectroscopy instrumentation and fabrication principle and one example are presented.
Bandgap, band edge positions as well as the overall band structure of semiconductors are of crucial importance in
photoelectrochemical and photocatalytic applications. The energy position of the band edge level can be controlled by
the electronegativity of the dopants, the pH of the solution (flatband potential variation of 60 mV per pH unit), as well as
by quantum confinement effects. Accordingly, band edges and bandgap can be tailored to achieve specific electronic,
optical or photocatalytic properties. Synchrotron radiation with photon energy at or below 1 keV is giving new insight
into such areas as condensed matter physics and extreme ultraviolet optics technology. In the soft x-ray region, the
question tends to be, what are the electrons doing as they migrated between the atoms. In this paper, I will present a
number of soft x-ray spectroscopic study of nanostructured 3d metal compounds Fe2O3 and ZnO.
How do we learn about chemisorption and physisorption of hydrides and the kinetics of hydrogen adsorption and
desorption? These are profound challenges with us for decades. Soft-x-ray spectroscopy will be will be a unique tool to
study the electronic properties of fundamental materials, nanoporous, and complex hydrides and in-situ study the
kinetics of hydrogen adsorption and desorption. To facilitate the search for most efficient hydrogen-generation and -
storage compounds, a fundamental understanding of the electronic properties is essential. Hydrogen strongly affects the
electronic and structural properties of many materials.
The electronic structure ultimately determines the properties of matter. Photon-in/photon-out soft-x-ray spectroscopy has
been the subject to a revived interest owing to the new generation synchrotron facilities and high performance beamline
and instruments. Soft-x-ray absorption spectroscopy (XAS) probes the local unoccupied electronic structure, soft-x-ray
emission spectroscopy (XES) probes the local occupied electronic structure, and resonant inelastic soft-x-ray scattering
(RIXS) probes the intrinsic low-energy excitations, such as charge transfer, proton energy transfer etc. A number of
examples, including some recent experimental findings, then illustrate the potential of XAS and XES applications in
hydrogen energy sciences.
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. 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. Soft X-ray spectroscopy has 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 introduction of selectively excited soft X-ray emission has opened a new field of study by disclosing many new possibilities of soft X-ray resonant inelastic scattering. In this paper, some recent findings regarding soft X-ray absorption and emission studies of various nanostructured systems are presented.
Electronic spectra of promising materials for rechargeable lithium batteries, LiC6 and LiMn2O4, have been studied. Theoretical calculations in combination with experiments for the π*0 and σ* x-ray absorption edges are reported for the pure graphite and the graphite intercalation compound, LiC6. The anisotropy of the absorption
spectra is due to the difference in the optical matrix elements for two different polarizations, which is a result of the anisotropic crystallographic and electronic properties of LiC6. Theory and experiment agree well for the rr and a resonances. By comparing calculations which include the effect of the core hole with similar calculations which do not, we conclude that is x-ray absorption in LiC6 is partly associated with an excitonic effect. The
electronic structure and optical absorption spectrum of LiMn204 spinel has been calculated and compared with available experimental data. The calculated absorption coefficient appeared to be in agreement with experiment, and the features of the absorption are associated with transitions between the exchange and crystal-field split t2g and eg d-bands of manganese in LiMn2O4 spinel.
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