X-ray photoemission spectroscopy (XPS) has been applied to a highly disordered amorphous Se deposited onto a cooled (150-K) substrate. XPS spectral changes have been observed in the $4p$ bonding and $4s$ states upon thermal annealing of the film. The thermally induced growth of the upper $4p$ bonding band is in good agreement with the previously reported UPS (ultraviolet photoemission spectroscopy) measurements [Takahashi et al., Phys. Rev. B 21, 3399 (1980)]. The $4s$ band of the highly disordered film shows a round and narrow feature and transforms into a rectangular shape upon the thermal annealing. The observed change of the $4s$ band is explained by a thermally induced increase of the cluster size in the cluster-junction model proposed in the previous UPS study.

• Received 1 July 1982

DOI:https://doi.org/10.1103/PhysRevB.26.7039