The x-ray standing wave technique is an experimental method that can accurately determine the precise crystallographic positions of atoms within a crystalline unit cell. As we have seen in preceding chapters of this book, this unique ability arises from the interferometric nature of an x-ray standing wave experiment that measures both the amplitude and phase of the hkl Fourier component of the electronic charge density of a crystal. What will be demonstrated in this chapter is that, alternatively, once the crystallographic positions of the atoms are known, the x-ray standing wave technique may be used to determine the contribution of each atom of the unit cell to the total electronic structure of the material when conjoined with high resolution, high energy x-ray photoelectron spectroscopy (XPS). This unique ability is achieved by energy analyzing the resulting valence photoelectron emission spectra in a standard, angle-integrated, high energy XPS experiment while setting the phase of the x-ray standing wave interference field so that the maximum of the electric field intensity is systematically placed at each of the different crystallographic sites of the crystal. It will be shown that the electron distribution curves (EDC s) obtained in the valence XSW experiment are directly related to the individual electronic single-particle partial densities of states of the atoms within the unit cell. The valence XSW technique therefore is a direct measurement of the chemical hybridization that occurs within a solid; consequently, it may be used to study the nature of the solid-state chemical bond and to test the validity of theoretical calculations that predict solid-state electronic structure.
Citation: Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment
Pub Type: Journals
Cu, electronic structure, GaAs, Ge, many body effects, matrix element effects, partial density of states, TiO2, V2O3