Single Molecule Dynamics at a Mechanically Controllable Break Junction in Solution at Room Temperature

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• 作者：Tatsuya Konishi ; Manabu Kiguchi ; Mai Takase ; Fumika Nagasawa ; Hideki Nabika ; Katsuyoshi Ikeda ; Kohei Uosaki ; Kosei Ueno ; Hiroaki Misawa ; Kei Murakoshi
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：January 23, 2013
• 年：2013
• 卷：135
• 期：3
• 页码：1009-1014
• 全文大小：372K
• 年卷期：v.135,no.3(January 23, 2013)
• ISSN：1520-5126

文摘

The in situ observation of geometrical and electronic structural dynamics of a single molecule junction is critically important in order to further progress in molecular electronics. Observations of single molecular junctions are difficult, however, because of sensitivity limits. Here, we report surface-enhanced Raman scattering (SERS) of a single 4,4鈥?bipyridine molecule under conditions of in situ current flow in a nanogap, by using nano-fabricated, mechanically controllable break junction (MCBJ) electrodes. When adsorbed at room temperature on metal nanoelectrodes in solution to form a single molecule junction, statistical analysis showed that nontotally symmetric b₁ and b₂ modes of 4,4鈥?bipyridine were strongly enhanced relative to observations of the same modes in solid or aqueous solutions. Significant changes in SERS intensity, energy (wavenumber), and selectivity of Raman vibrational bands that are coincident with current fluctuations provide information on distinct states of electronic and geometrical structure of the single molecule junction, even under large thermal fluctuations occurring at room temperature. We observed the dynamics of 4,4鈥?bipyridine motion between vertical and tilting configurations in the Au nanogap via b₁ and b₂ mode switching. A slight increase in the tilting angle of the molecule was also observed by noting the increase in the energies of Raman modes and the decrease in conductance of the molecular junction.