Single-Molecule Junction Conductance of Terephthalic Acid Contacting Ag and Cu Electrodes Measured by an Electrochemical Method

The single-molecule junction conductance of terephthalic acid binding to Cu and Ag electrodes was measured by an electrochemical jump-to-contact scanning tunneling microscopy break junction (ECSTM-BJ) approach. The Cu and Ag electrodes were formed in-situ, via electrodeposition from a solution. The conductance histograms of the single-molecule junctions formed via the binding of terephthalic acid to the Cu and Ag electrodes showed a well-defined shape, in the absence of any data selection. The single-molecule junction conductance values for the terephthalic acid binding to the Cu electrode were 11.5 nS (high conductance) and 4 nS (low conductance), while the high and low conductance values for the Ag electrode were 10.3 and 3.8 nS, respectively. The high conductance values were typically approximately three times larger than the low conductance values, for both the Cu and the Ag electrodes. The conductance (G) value for the terephthalic acid followed the order of G(Cu)>G(Ag), which indicated the different electronic coupling efficiencies between the molecule and electrodes. In contrast with the single set conductance value measured for alkanedicarboxylic acid using the same approach, two set conductance values were found for the terephthalic acid junctions with the Cu and Ag electrodes. These results illustrated the important role of the backbone of the chain in conductance measurements. The present work demonstrated the influence of the electrode and the molecular structure on the single-molecule junction conductance.