Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing 100871, China.
J Chem Phys. 2013 Nov 21;139(19):194703. doi: 10.1063/1.4830399.
The transition voltage of three different asymmetric Au∕poly(phenylene) thiol∕Au molecular junctions in which the central molecule is either benzene thiol, biphenyl thiol, or terphenyl thiol is investigated by first-principles quantum transport simulations. For all the junctions, the calculated transition voltage at positive polarity is in quantitative agreement with the experimental values and shows weak dependence on alterations of the Au-phenyl contact. When compared to the strong coupling at the Au-S contact, which dominates the alignment of various molecular orbitals with respect to the electrode Fermi level, the coupling at the Au-phenyl contact produces only a weak perturbation. Therefore, variations of the Au-phenyl contact can only have a minor influence on the transition voltage. These findings not only provide an explanation to the uniformity in the transition voltages found for π-conjugated molecules measured with different experimental methods, but also demonstrate the advantage of transition voltage spectroscopy as a tool for determining the positions of molecular levels in molecular devices.
通过第一性原理量子输运模拟研究了三种不同不对称 Au∕聚（亚苯基）硫醇∕Au 分子结的过渡电压，其中中心分子分别为苯硫醇、联苯硫醇或三联苯硫醇。对于所有结，正极性下计算的过渡电压与实验值定量一致，并表现出对 Au-苯基接触变化的弱依赖性。与主导各种分子轨道相对于电极费米能级排列的 Au-S 接触的强耦合相比，Au-苯基接触产生的耦合仅产生微弱的扰动。因此，Au-苯基接触的变化只能对过渡电压产生微小的影响。这些发现不仅为使用不同实验方法测量的π共轭分子的过渡电压的一致性提供了解释，而且还展示了过渡电压光谱作为确定分子器件中分子能级位置的工具的优势。
