Single
Molecular Bridging of Au Nanogap Using Aryl
Halide Molecules
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Abstract
Single molecular junctions of benzene
dihalide molecules (<i>para</i>-X–(C<sub>6</sub>H<sub>4</sub>)–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 (<i>para-</i>H<sub>2</sub>N–(C<sub>6</sub>H<sub>4</sub>)–NH<sub>2</sub>). The
conductance of a single 1,4-diiodobenzene molecular junction was 3.6
× 10<sup>–4</sup> <i>G</i><sub>0</sub> (<i>G</i><sub>0</sub> = 2e<sup>2</sup>/h), which was smaller than
1 × 10<sup>–2</sup> <i>G</i><sub>0</sub> 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–NH<sub>2</sub> bond. The present work demonstrates that an iodide group can be
utilized as an anchoring group for the single molecular junction
