Angle-resolved photoemission from oriented thin films of long alkyl molecules: valence band dispersion

Abstract

Angle-resolved photoemission spectra were measured using synchrotron radiation for oriented thin films of hexatriacontane, CH3(CH2)34CH3, and pentatriacontan-18-one, CH3(CH2)16CO(CH2)16CH3, with their long axes perpendicular to the substrate surface. The valence band dispersion was observed along the long molecular axis over the whole Brillouin zone for both compounds. The results demonstrate that the chemical disorder caused by the C=O group in the CH2 chain does not affect the band structure so much and both compounds show valence band dispersion similar to the dispersion in an ideal polyethylene chain. Further, we observed a band which was not observed in our previous work. It determines the top of the valence band at the Γ point. Comparison with theoretical results indicates that it corresponds to a band of B1 (B2g at Γ) symmetry which consists of only C2p atomic orbitals directed along the carbon chain.