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

The L3,2 appearance potential spectra (APS) of titanium or vanadium in TiS₂, TiSe₂, and VSe₂ show a doubly peaked L₃ 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.