Observation of Hole States at Perylene/Au(110) and Au(111) Interfaces

The geometric and electronic structures of the perylene monolayers on gold single-crystal surfaces and the effect of Br doping have been investigated. Perylene molecules adsorbed on the Au(110)(1 × 2) surface form a monolayer with the molecular long axis aligned along the [11̅0] direction and the molecular plane tilted at ±15° to the short axis, in contrast with the parallel molecular plane on the Au(111) surface. The orientation of the molecules is determined by the polarization dependence of the X-ray absorption fine structure spectroscopy near the carbon K-edge (C K NEXAFS). Angle-resolved photoemission spectroscopy shows a ″binary star″ pattern for the 2D momentum map of photoemission from the perylene highest occupied molecular orbital (HOMO) on the Au(110)(1 × 2) surface, which is consistent with the tilted molecular plane. The doped Br penetrates the perylene monolayer and causes a dramatic change in the orientation of the molecules. The perylene molecules are ionized because of the charge transfer promoted by the work function increase induced by the Br adsorbed on the gold surface. Cationic perylene shows resonance with the singly unoccupied molecular orbital (SUMO) in the C K NEXAFS spectra. This resonance can be a useful spectral fingerprint for tracing the hole created in organic semiconductors.