Electronic Structure of Hexacene and Interface Properties on Au(110)

Although hexacene was first synthesized in 1939, the thin film properties, which are interesting for future applications and fundamental research, have never been investigated. Therefore, we synthesized hexacene by reduction of 6,15-hexacenequinone, evaporated hexacene, and grew films of variable thicknesses on Au(110). This allowed us to study the electronic properties and molecular orientations in the bulk as well as at the molecule–metal interface by X-ray absorption spectroscopy (XAS) and photoelectron spectroscopy. Valence band spectra of a multilayer hexacene film are compared to those of electronic states obtained from density functional theory calculations. C 1s core-level spectra show typical satellite structures of the extended aromatic π-system, similar to pentacene. XAS shows that anisotropy rises with decreasing film thickness and indicates that hexacene is almost flat lying on the Au(110) substrate. The different peak shapes of XAS spectra as a function of the film thickness, as well as changes in valence band spectra and C 1s satellite structures, indicate a strong electronic coupling of the molecular states with the states of the Au(110) substrate at the interface.