Silver Makes Better Electrical Contacts to Thiol-Terminated Silanes than Gold

Haixing Li, Timothy A. Su, María Camarasa-Gómez, Daniel Hernangómez-Pérez, Simon E. Henn, Vladislav Pokorný, Caravaggio D. Caniglia, Michael S. Inkpen, Richard Korytár, Michael L. Steigerwald, Colin Nuckolls, Ferdinand Evers, Latha Venkataraman

We report that the single molecule junction conductance of thiol-terminated silanes with Ag electrodes are higher than the conductance of those formed with Au electrodes. These results are in contrast to the trends in the metal work function Φ(Ag) < Φ(Au). As such, one would expect a better alignment of the Au Fermi level to the molecular orbital of silane that mediates charge transport. Additionally, this conductance trend is reversed when we replace the thiols with amines, highlighting the impact of metal-S covalent and metal-NH2 dative bonds in controlling the molecular conductance. Density functional theory calculations elucidate the crucial role of the chemical linkers in determining the level alignment when molecules are attached to different metal contacts. We also demonstrate that conductance of thiol terminated silanes with Pt electrodes is lower than the ones formed with Au and Ag electrodes again in contrast to what one would expect from trends in the metal work-functions.