X-ray photoemission studies of W 4f core levels of electrochromic HxWO3 films

Abstract

Using x‐ray photoelectron spectroscopy (XPS), W 4f core level spectra of electrochromic H_xWO₃ films have been investigated as a function of the injected charge. W 4f peaks become broader with increasing injected charge. The line shape analysis of W 4f XPS spectra of amorphous H_xWO₃ films reveals that each spin‐orbit split component consists of two peaks. It is also found that, as the injected charge increases, the intensity of the low binding energy (BE) peaks, the asymmetry factor of core lines, and the intrinsic lifetime width increase systematically. Composite structures of W 4f peaks have been attributed to the existence of the different final states, screened by different numbers of W 5d electrons. The low BE peaks are considered to correspond to the locally screened final states, with one more W 5d electrons than in the ground state, which arise from midgap state conduction electrons near E_F. There is also a possibility that a mixture of fine scale phases contributes to composite structures and broader linewidths in H_xWO₃.