Electronic structure of α-sexithiophene ultrathin films grown on passivated Si(0 0 1) surfaces

We have investigated the valence electronic states of α-sexithiophene (α-6T) on three passivated Si(0 0 1) surfaces, oxidized Si(0 0 1), water-adsorbed Si(0 0 1) and ethylene-adsorbed Si(0 0 1), using ultraviolet photoelectron spectroscopy (UPS). At a thickness of α-6T layer below 0.5 nm, clear features of the π states are observed for water-adsorbed Si(0 0 1) and ethylene-adsorbed Si(0 0 1), whereas broad features are observed for oxidized Si(0 0 1). This difference is attributed to the formation of well-ordered stacking on water-adsorbed Si(0 0 1) and ethylene-adsorbed Si(0 0 1).