Electronic band states of long-range ordered aromatic thione molecules assembled on Cu(100)

Two-dimensional long-range ordered organic molecule layers can be achieved by depositing thiols on single crystalline surfaces. The aromatic thione 2-mercaptobenzoxazole (MBO) molecule (C7H5NOS) presents a S-containing head which reacts with the Cu surface, and an aromatic ring originating lateral van der Waals interactions and molecular self-organization. A long-range-ordered p(2x2) structure of MBO on Cu(100) is obtained, by MBO sublimation in highly controlled ultrahigh-vacuum conditions. The MBO molecular orbitals and interface electronic levels have been identified, also comparing the room-temperature experiment with the low-temperature (100 K) physisorption data, by angular-resolved high-resolution UV photoelectron spectroscopy. The role of S as a chemical hook for the molecule to the Cu surface is evidenced, and comparison with similar compounds suggests that the adsorption mechanism and the related electronic structure are rather general results for pi-conjugated molecules with a S-containing head. We give striking evidence of energy-band formation of MBO-Cu interaction states, bringing to light molecule-Cu extended hybrid bands, with a bandwidth of 120 meV along one main azimuthal symmetry direction of the surface Brillouin zone.