Quantitative analysis of weak current rectification in molecular tunnel junctions subject to mechanical deformation reveals two different rectification mechanisms for oligophenylene thiols versus alkane thiols
Quantitative analysis of weak current rectification in molecular tunnel junctions subject to mechanical deformation reveals two different rectification mechanisms for oligophenylene thiols versus alkane thiols
复制标题
对受机械变形影响的分子隧道结中弱电流整流的定量分析揭示了低聚苯硫醇与烷硫醇的两种不同的整流机制
DOI：
10.1039/d1nr04410a
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发表时间：
2021
期刊：
影响因子：
6.7
通讯作者：
Frisbie, C. Daniel
中科院分区：
文献类型：
--
作者：
Xie, Zuoti;Bâldea, Ioan;Nguyen, Quyen Van;Frisbie, C. Daniel
基于烷硫醇（CnT）和低聚苯硫醇（OPTn）自组装单层（SAM）和Au电极的金属-分子-金属结预期表现出类似的电不对称性，因为两个结都具有一个化学吸附的Au-S接触和一个物理吸附的货车范德华接触。通过在电流-电压（I-V）特性中明显的电流整流比RR来量化不对称性。在这里，我们表明，RR < 1 for CnT and RR >1 OPTn结，与预期相反，并进一步，RR的行为非常不同的CnT和OPTn结机械延伸下使用的导电探针原子力显微镜（CP-AFM）测试床。本文中提出的分析，利用先前验证的单能级模型和从头计算量子化学计算的结果，使我们能够解释CnT和OPTn在不同的电流整流机制方面令人困惑的实验结果。具体而言，在基于CNT的结的斯塔克效应创建的HOMO电平移位整流所需的，而OPTn结的电平移位产生的HOMO波函数与结静电势分布的位置相关的耦合。在这些机制的基础上，我们的量子化学计算允许定量描述的机械变形对测量的电流整流的影响。此外，我们的分析，匹配的实验，有利于直接估计的影响分子内静电屏蔽的结电位分布。总的来说，我们的检查电流整流基准分子隧道结照亮关键的物理机制，在发挥单步隧穿通过分子，并展示了定量的协议，可以在这些系统中的实验和理论之间获得。
Metal-molecule-metal junctions based on alkane thiol (CnT) and oligophenylene thiol (OPTn) self-assembled monolayers (SAMs) and Au electrodes are expected to exhibit similar electrical asymmetry, as both junctions have one chemisorbed Au–S contact and one physisorbed, van der Waals contact. Asymmetry is quantified by the current rectification ratio RR apparent in the current–voltage (I–V) characteristics. Here we show that RR < 1 for CnT and RR > 1 for OPTn junctions, in contrast to expectation, and further, that RR behaves very differently for CnT and OPTn junctions under mechanical extension using the conducting probe atomic force microscopy (CP-AFM) testbed. The analysis presented in this paper, which leverages results from the previously validated single level model and ab initio quantum chemical calculations, allows us to explain the puzzling experimental findings for CnT and OPTn in terms of different current rectification mechanisms. Specifically, in CnT-based junctions the Stark effect creates the HOMO level shifting necessary for rectification, while for OPTn junctions the level shift arises from position-dependent coupling of the HOMO wavefunction with the junction electrostatic potential profile. On the basis of these mechanisms, our quantum chemical calculations allow quantitative description of the impact of mechanical deformation on the measured current rectification. Additionally, our analysis, matched to experiment, facilitates direct estimation of the impact of intramolecular electrostatic screening on the junction potential profile. Overall, our examination of current rectification in benchmark molecular tunnel junctions illuminates key physical mechanisms at play in single step tunneling through molecules, and demonstrates the quantitative agreement that can be obtained between experiment and theory in these systems.