Comparative x-ray-photoemission study of monoclinic, trigonal, and amorphous selenium

X-ray-photoemission spectra of monoclinic, trigonal, and amorphous selenium have been first measured with the same photoelectron spectrometer in order to directly compare the valence electronic states of the three allotropes of selenium. It has been found that the 4p lone pair and the 4s band of monoclinic selenium (consisting of Se8 ring molecules) are apparently narrower than those of trigonal and amorphous forms, reflecting the molecular character of the monoclinic crystal. This observation suggests that the Se8 ring molecule is not a main constituent of amorphous selenium.