NEXAFS study of the growth of 4-cyano-4′-iodobiphenyl molecular crystal on GeS(0 0 1)

The electronic and atomic structures of a 4-cyano-4′-iodobiphenyl (CIB) thin film on a GeS(0 0 1) substrate were studied by atomic force microscopy (AFM) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. CIB molecules exhibit high crystallinity owing to halogen bonding and are grown as a microcrystal at a nominal thickness of 80 Å. NEXAFS measurements suggest that, at a thickness of 0.4 Å, the molecular plane tilts away from the surface plane at an angle of 12°, and the molecular axis tilts away from the GeS [0 1 0] direction by 35°. At a thickness of 80 Å, the molecular plane tilts away from the surface plane by 51°, and the molecular axis tilts away from the GeS [0 1 0] direction by 43° on average. NEXAFS spectra show a drastic reduction in the πCC* and πCN* resonances in the thicker film. This is interpreted as electron transfer, which is induced by halogen bonding, from the halogen atom.