Interplay between Morphology and Electronic Structure in α‑Sexithiophene Films on Au(111)

The properties of organic films are strongly influenced by their growth and structure. In this work, we link the results from three different techniques to elucidate the interplay between the morphology and the electronic structure of alpha-sexithiophene films grown on Au(111) surfaces. Photoelectron emission microscopy and thermal desorption spectroscopy reveal the growth of a two-layer thick wetting layer at room temperature. On top of the wetting layer, the molecules start to form mu m-sized crystallites, which are statistically distributed over the surface. This transition in the growth mode is reflected in the electronic structure of the system, studied by two-photon photoemission spectroscopy. While in the wetting layer, exciton formation is suppressed by the interaction with the metal substrate, Frenkel excitons with picosecond lifetimes are observed in the three-dimensional crystallites.