Conductance of Molecular Junctions Formed with Silver Electrodes

We compare the conductance of a series of amine-terminated oligophenyl and alkane molecular junctions formed with Ag and Au electrodes using the scanning tunneling microscope based break-junction technique. For these molecules that conduct through the highest occupied molecular orbital, junctions formed with Au electrodes are more conductive than those formed with Ag electrodes, consistent with the lower work function for Ag. The measured conductance decays exponentially with molecular backbone length with a decay constant that is essentially the same for Ag and Au electrodes. However, the formation and evolution of molecular junctions upon elongation are very different for these two metals. Specifically, junctions formed with Ag electrodes sustain significantly longer elongation when compared with Au due to a difference in the initial gap opened up when the metal point-contact is broken. Using this observation and density functional theory calculations of junction structure and conductance we explain the trends observed in the single molecule junction conductance. Our work thus opens a new path to the conductance measurements of a single molecule junction in Ag electrodes.