Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States.
Nano Lett. 2013 Jul 10;13(7):3358-64. doi: 10.1021/nl401654s. Epub 2013 Jun 5.
We compare the conductance of a series of amine-terminated oligophenyl and alkane molecular junctions formed with Ag and Au electrodes using the scanning tunneling microscope based break-junction technique. For these molecules that conduct through the highest occupied molecular orbital, junctions formed with Au electrodes are more conductive than those formed with Ag electrodes, consistent with the lower work function for Ag. The measured conductance decays exponentially with molecular backbone length with a decay constant that is essentially the same for Ag and Au electrodes. However, the formation and evolution of molecular junctions upon elongation are very different for these two metals. Specifically, junctions formed with Ag electrodes sustain significantly longer elongation when compared with Au due to a difference in the initial gap opened up when the metal point-contact is broken. Using this observation and density functional theory calculations of junction structure and conductance we explain the trends observed in the single molecule junction conductance. Our work thus opens a new path to the conductance measurements of a single molecule junction in Ag electrodes.
我们使用基于扫描隧道显微镜的断键技术比较了一系列由 Ag 和 Au 电极形成的胺端寡聚苯和烷烃分子键的电导。对于通过最高占据分子轨道传导的这些分子，与 Ag 电极形成的键比与 Au 电极形成的键更具导电性，这与 Ag 的功函数较低一致。测量的电导随分子主链长度呈指数衰减，对于 Ag 和 Au 电极，衰减常数基本相同。然而，这两种金属的分子键的形成和演变非常不同。具体而言，与 Au 相比，Ag 电极形成的键在伸长时可以承受更长的伸长，这是由于金属点接触断开时初始间隙的差异。利用这一观察结果和对键结构和电导的密度泛函理论计算，我们解释了在单分子键电导中观察到的趋势。因此，我们的工作为在 Ag 电极中单分子键的电导测量开辟了一条新途径。
