Zheng Xiaohong, Dai Zhenxiang, Zeng Zhi
Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China.
J Phys Condens Matter. 2009 Apr 8;21(14):145502. doi: 10.1088/0953-8984/21/14/145502. Epub 2009 Mar 13.
The role of electrodes in the transport properties of molecular devices is investigated by taking C(60) as an example and using gold nanowire and a gold atomic chain as the electrodes. The calculations are done by an ab initio method combined with the non-equilibrium Green function technique. We find that devices in which a single C(60) molecule is connected with different electrodes show completely different transport behavior. In the case of nanowire/C(60)/nanowire the device shows a metallic behavior with a big equilibrium conductance (about 2.18G(0)) and the current increases rapidly and almost linearly starting from zero. The transmission function shows wide peaks and platforms around the Fermi level. While in the atomic-chain/C(60)/atomic-chain case, the device shows resonant tunneling behavior and the Fermi level lies between the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) transmission peaks. This results in a current that is one order of magnitude smaller than that in the nanowire/C(60)/nanowire system and the current increases very slowly until the bias is big enough to include the LUMO peak in the bias window. The big difference in the conductance and the current arises from the different coupling between the electrodes and the C(60) and the different number of channels in the electrodes.
以C(60)为例，采用金纳米线和金原子链作为电极，研究了电极在分子器件输运性质中的作用。计算采用从头算方法结合非平衡格林函数技术。我们发现，单个C(60)分子与不同电极相连的器件表现出完全不同的输运行为。在纳米线/C(60)/纳米线的情况下，器件表现出金属行为，具有较大的平衡电导（约2.18G(0)），电流从零开始迅速增加且几乎呈线性。传输函数在费米能级附近显示出宽峰和平台。而在原子链/C(60)/原子链的情况下，器件表现出共振隧穿行为，费米能级位于最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）传输峰之间。这导致电流比纳米线/C(60)/纳米线系统中的电流小一个数量级，并且电流增加非常缓慢，直到偏压足够大，使LUMO峰包含在偏压窗口内。电导和电流的巨大差异源于电极与C(60)之间不同的耦合以及电极中不同的通道数。
