Center for Bioelectronics and Biosensors, Biodesign Institute, and Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287, USA.
J Am Chem Soc. 2011 Nov 30;133(47):19189-97. doi: 10.1021/ja2076857. Epub 2011 Nov 3.
We report on the measurement and statistical study of thousands of current-voltage characteristics and transition voltage spectra (TVS) of single-molecule junctions with different contact geometries that are rapidly acquired using a new break junction method at room temperature. This capability allows one to obtain current-voltage, conductance voltage, and transition voltage histograms, thus adding a new dimension to the previous conductance histogram analysis at a fixed low-bias voltage for single molecules. This method confirms the low-bias conductance values of alkanedithiols and biphenyldithiol reported in literature. However, at high biases the current shows large nonlinearity and asymmetry, and TVS allows for the determination of a critically important parameter, the tunneling barrier height or energy level alignment between the molecule and the electrodes of single-molecule junctions. The energy level alignment is found to depend on the molecule and also on the contact geometry, revealing the role of contact geometry in both the contact resistance and energy level alignment of a molecular junction. Detailed statistical analysis further reveals that, despite the dependence of the energy level alignment on contact geometry, the variation in single-molecule conductance is primarily due to contact resistance rather than variations in the energy level alignment.
我们报告了使用新的室温断裂结方法测量和统计研究具有不同接触几何形状的数千个单分子结的电流-电压特性和转变电压谱（TVS）。这种能力允许获得电流-电压、电导电压和转变电压直方图，从而为以前在固定低偏压下对单分子的电导直方图分析增加了一个新的维度。该方法证实了文献中报道的烷二硫醇和联苯二硫醇的低偏压电导值。然而，在高偏压下，电流表现出很大的非线性和不对称性，TVS 允许确定一个非常重要的参数，即单分子结的分子和电极之间的隧道势垒高度或能级对准。发现能级对准取决于分子，也取决于接触几何形状，揭示了接触几何形状在分子结的接触电阻和能级对准中的作用。详细的统计分析进一步表明，尽管能级对准取决于接触几何形状，但单分子电导的变化主要是由于接触电阻，而不是能级对准的变化。
