Conduction-band effects in the appearance-potential spectra of transition-metal dichalcogenides

Abstract

The $L_{3,2}$ appearance potential spectra (APS) of titanium or vanadium in Ti${\mathrm{S}}_2$, Ti${\mathrm{Se}}_2$, and V${\mathrm{Se}}_2$ show a doubly peaked $L_3$ threshold quite different from the single peak observed for the pure transition metals or for the same levels in the compounds using x-ray photoelectron spectroscopy. We show that this is a consequence of the crystal-field splitting of the $d$-like conduction band in these materials and that the APS threshold shape may be interpreted in terms of the derivative of the self-convolution of the conduction-band density of states. Determination of the latter by deconvolution of the threshold function gives excellent agreement with data from x-ray and synchrotron absorption studies.