Energy-band dispersion in oriented thin films of pentatriacontan-18-one by angle-resolved photoemission with synchrotron radiation

Abstract

Angle-resolved photoemission spectra were measured using synchrotron radiation for thin films of the pentatriacontan-18-one molecule [${\mathrm{CH}}_{3}$(${\mathrm{CH}}_{2}$${)}_{16}$CO(${\mathrm{CH}}_{2}$${)}_{16}$${\mathrm{CH}}_{3}$] with their long axes perpendicular to the substrate surface. At the preparation of the film, careful studies were made on the molecular decomposition due to vacuum evaporation and on molecular orientation in the evaporated thin films by mass spectroscopy, x-ray diffraction, and angle-resolved photoemission. Valence-band dispersion was observed along the long molecular axis. The results demonstrate that the chemical disorder of the C?O group in the ${\mathrm{CH}}_{2}$ chain does not affect the band structure so much, and the molecule shows valence-band dispersion similar to the dispersion in an ideal polyethylene chain. Further, we observed a band which was not observed in previous work. It determines the top of the valence band at the \ensuremath{\Gamma} point. Comparison with theoretical results indicates that it corresponds to a band of ${B}_{1}$ (${B}_{2g}$ at \ensuremath{\Gamma} point) symmetry which consists of only C 2p atomic orbitals directed along the carbon chain.