Ultrathin monolayer of rubrene on Au(111) induced by charge transfer

摘要

An ultrathin self-assembly monolayer of rubrene on Au(111) has been fabricated and studied by scanning tunneling microscopy. The apparent thickness of such monolayer is 0.08 nm and close to the radius of a carbon atom. Moreover, the rubrene molecules within the second layer prefer adsorbing on to the positions corresponding to the herringbone structure underneath the Au(111)- while the Au surface is fully covered by a monolayer of rubrene. With the assistant with theoretical simulations, we reveal that small apparent height of such monolayer is due to the coupling between the molecular orbitals and the gold surface. About 0.237 electron per rubrene molecule is transferred to the surface, and as a consequence, an interfacial dipole is formed on the rubrene/Au interface. The formation of such interfacial dipole induced by charge transfer from molecules to surfaces is believed to be applied in organic molecules adsorbed on metal surfaces.