Substituent effect on the conductance of single-molecule junctions formed with silver electrodes

Abstract

We investigated the substituent effect on the conductance of the molecular junctions formed with Ag electrodes by using a scanning tunneling microscope break-junction (STM-BJ) technique. For 1,4-diaminobenzene (BDA) molecules, we measured an increased conductance with a methyl group as an electron-donating substituent and a decreased conductance with a chlorine group as an electron-withdrawing substituent. These results can be explained by using the gap between the Ag Fermi level and the molecule occupied state which varies with the substituents. Furthermore, we found that the molecular elongation lengths were ~0.3 nm for all BDA derivatives with the different substituents in the Ag electrodes, proving the same length of these molecules. Our works provide a significance of the chemical substituents on electron transport in Ag electrodes for single molecule devices in the future.