Single Molecular Bridging of Au Nanogap Using Aryl Halide Molecules

Single molecular junctions of benzene dihalide molecules (para-X-(C6H4)-X, X = Cl, Br, I) binding to Au electrodes were systematically studied by using the scanning tunneling microscopy break junction (STM-BJ) technique. The STM-BJ characterization revealed that the single molecular junction was formed only with 1,4-diiodobenzene, which was due to its ability to form particularly stable halogen bonds with Au electrodes for the iodide anchoring group. The conductance and strength of the metal-molecule bond of the single 1,4-diiodobenzene molecular junction were compared with that of 1,4-benzenediamine (para-H2N-(C6H4)-NH2). The conductance of a single 1,4-diiodobenzene molecular junction was 3.6 X 10(-4) G(0) (G(0) = 2e(2)/h), which was smaller than 1 x 10(-2) G(0) measured for 1,4-benzenediamine. The distances to break single molecular junctions were 0.05 and 0.03 nm for single 1,4-diiodobenzene and 1,4-benzenediamine molecular junctions, respectively. The longer breakdown distance of the single 1,4-diiodobenzene molecular junctions indicated that the Au-I bond was stronger than that of the Au-NH2 bond. The present work demonstrates that an iodide group can be utilized as an anchoring group for the single molecular junction.