Multiphase growth and electronic structure of ultrathin hexaazatrinaphthylene on Au(111)

Scanning tunneling microscopy was used to study the morphological behavior of 1-2 monolayers (ML) of 5,6,11,12,17,18-hexaazatrinaphthylene (HATNA) deposited on Au(111). The first ML consisted of molecules flat on the surface, arranged in one of three different ordered phases depending on annealing parameters. The second ML assumed an upright orientation and tended to order only if the first layer was disordered. Scanning tunneling spectroscopy of 1-2 ML ordered HATNA was compared to ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy of 80 angstrom amorphous HATNA. There is good agreement between techniques in the transport band gap (similar to 3.80 eV), but the position of the Fermi level in the gap is shifted in the tunneling spectra by about 0.75 eV toward the highest occupied molecular orbital. The shift may be due to morphological effects or degradation from ultraviolet light irradiation.