In the present contribution, we investigate how the electronic structure of a Au(111) surface covered by a self-assembled monolayer (SAM) of conjugated molecules depends on the packing density of the SAM. To that aim, biphenylthiol-based molecules bearing electron-rich and electron-poor substituents are studied by means of slab-type band-structure calculations. We find that the screening effects arising from the presence of neighboring molecules decisively influence the impact of the substituent as well as the adsorption-induced charge rearrangements at the metal-molecule interface. This has profound consequences not only for the alignment of the molecular levels with the Fermi energy and the SAM-induced work-function modification but also contributes to the clarification of the nature of the thiol-gold bond. The presented findings have important implications for single-molecule transport, SAM-based chemical sensing, and electrode modification in organic electronics.

• Received 30 July 2007

DOI:https://doi.org/10.1103/PhysRevB.77.045113