X-RAY ABSORPTION IN LAYERED CRYSTALS.

摘要

Extended x-ray absorption fine struture (EXAFS) spectra have been obtained for a group of layered transitional-metal dichalcogenide crystals, including the nonstoichiometric compounds Ti(,1+x)Se(,2) and the alloys Zr(,x)Ti(,1-x)Se(,2). Fourier transform analysis of the EXAFS spectra has been performed in order to test the theoretical phase and amplitude functions of Teo and Lee. Application of this analytic procedure to spectra of Zr(,x)Ti(,1-x)Se(,2), for x = .07, .11, and .21, indicates that the Zr substitutes for Ti and that the Zr-Se interatomic distance is 2.63 (ANGSTROM), as compared to the Ti-Se distance (2.53 (ANGSTROM)) in TiSe(,2), and the Zr-Se distance (2.68 (ANGSTROM)) in ZrSe(,2).;High resolution x-ray absorption spectra of several layered crystals are presented. The Ti K threshold spectrum of TiSe(,2) contains structure similar to that of theoretically-calculated density-of-states curves. The x-ray absorption spectrum of hexagonal BN at the Boron K threshold is displayed as a function of angle in the p-polarization geometry. The lineshape is interpreted in terms of an effective mass theory of excitonic absorption.