Vacuum–ultraviolet photoelectron spectroscopy of hexatriacontane (n-C36H74) polycrystal: A model compound of polyethylene

Abstract

Photoelectron spectra of hexatriacontane (n-C36H74) films evaporated in situ under vacuum were measured at 12 photon energies between 11.4 eV and 21.2 eV. The escape depth of the photoelectrons was found to be much less than 10 nm. Although five valence band features on the photoelectron spectra are expected in this region from the findings by the XPS method, only one or two valence band features were observed; four features from the conduction band were found to dominate the spectra. The short escape depth and the smearing out of the valence band structure are attributed to scattering, which includes the scattering by phonons, and the appearance of the conduction band structure is attributed to accumulation of the secondary electrons to the high density of states parts associated with the conduction bands. The threshold energy of photoemission was found to be 9.1±0.5 eV. The finding for the evaporated films of polyethylene, despite some degree of decomposition, gave essentially the same result. The results for the conduction bands were compared with the theoretical band calculation on an isolated polyethylene chain. The lack of reliable theoretical calculations of the conduction band of solid polyethylene is pointed out.