The Scanning–Tunneling Microscopy, the X-Ray Photoelectron Spectroscopy, the Inner-Shell-Electron Energy-Loss Spectroscopy Studies ofMTe2andM3SiTe6(M=Nb and Ta)

Abstract

The Ta N6,7and Te N4,5inner-shell-electron energy-loss spectroscopy (ISEELS) spectra and the X-ray photoelectron spectroscopy (XPS) spectra in layered transition-metal ditelluridesMTe2(M=Ta, Nb) for which metald-derived conduction bands overlap Te 5pvalence bands significantly, have been measured to study the effects of band structure on the final states and the valences of constituent atoms. For comparison we have obtained the ISEELS and XPS spectra ofM3SiTe6, which crystallizes in a layer structure akin to that ofMTe2. The atomically resolved scanning–tunneling microscopy (STM) images of NbTe2and Ta3SiTe6have been obatined to investigate a surface atomic structure as well as a surface electronic structure. It is found that the Ta 4fand Te 4dXPS spectra inMTe2reveal a dominant peak for each spin orbit (s.o.) component although two-thirds ofMatoms shift from undistorted octahedral sites to form double zigzag chains along thebaxis and the STM images indicate the existence of three different kinds of Te sites. The Ta N6,7and Te N4,5ISEELS spectra reveal a doublet for each (s.o.) component. It arises from two different final states, that is, Ta3+*4f135d2and Ta4+*4f135d1for the Ta N6,7spectrum and Te2−*4d95p6and Te−*4d95p5for the Te N4,5spectrum. The final-state valence fluctuation model is proposed to explain the experimental result.