Qualitative analysis of the asymmetric I-V curve in STM molecular junctions
Received date: 2018-03-08
Online published: 2020-04-29
分子器件的量子输运特性实验(上大部分)是通过扫描隧道显微镜(scanningtunneling microscopy, STM)来完成测量的,其测量结果经常会出现非对称的电流-电压(asymmetric I-V, AIV)曲线、负微分电导(negative differential conductance,NDC)等区别于宏观器件的一些输运特性. 基于有限元方法和参数建模,给出了一个有局域态存在情况下的输运体系的哈密顿量.同时结合非平衡格林函数方法, 对输运体系的电子密度展开自洽场的计算,并在自洽收敛之后分析器件的隧穿电流. 用模型参数描绘了分子结的配置,包括分子结的电极耦合强度、分子能级、局域态的能级等因素的作用,定性分析了器件中局域态及其几何结构的非对称性对纳米器件输运性质的影响.结果显示, 采用 STM 的分子结实验中出现 AIV 和 NDC,其本质原因是体系本征的局域态的偏置.
钱利江, 李惟驹, 张义邴, 陈竞哲 . STM 分子结中电流非对称性的定性分析[J]. 上海大学学报(自然科学版), 2020 , 26(2) : 197 -206 . DOI: 10.12066/j.issn.1007-2861.2028
Quantum transport properties of molecular devices are mostly measured by scanning tunneling microscopy (STM). The results show abnormal features such as asymmetric I-V (AIV) curve or negative differential conductance (NDC), which are not to be observed in the case of common macroscopic devices. Based on finite element method and parameter models, the Hamiltonian of a sample system with a local state is presented. The non-equilibrium Green's function method is used to calculate the electron density and the tunneling current of the device after self-consistent convergence. After investigating the effects of different parameters, including the electrode coupling strength, molecular energy level, local energy level, the influences of the local states and geometrical asymmetry on the transport properties of molecular devices have been analyzed. It is concluded that the intrinsic region of AIV and NDC in STM related molecular devices experiments is the offset of the local states in the tip.
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