Angle-resolved ultraviolet photoelectron spectroscopy of thin films of bis(1,2,5-thiadiazolo)-p-quinobis (1,3-dithiole) on the MoS2 surface

In this paper we report on the angle-resolved ultraviolet photoelectron spectroscopy on ultrathin films of bis(1,2,5-thiadiazolo)-p-quinobis (1,3-dithiole) (BTQBT) deposited on a MoS2 surface with synchrotron radiation, and describe the quantitative analysis of the angular distribution of photoelectron from the highest occupied state. The observed angular distributions were better explained by those calculated with the single-scattering approximation combined with molecular orbital calculation considering intramolecularly scattered waves than the previously used independent-atomic-center approximation combined with molecular orbital calculation. Further, the low-energy-electron diffraction measurements were performed on the film. From the low-energy-electron diffraction, the two-dimensional lattice of the ultrathin films on the MoS2 was found to be MoS2(0001)-(root 13 x root 13, R = +/- 13.9 degrees)-BTQBT, and from the analysis of the photoelectron angular distributions, it was found that at the lattice points the molecules lie flat with azimuthal orientations of 19 degrees and 47 degrees with respect to each surface crystal axis of MoS2. On the basis of these results, the full structure of the thin film, the two-dimensional lattice, and full molecular orientations at the lattice points, is proposed. (C) 1997 American Institute of Physics.