Department of Chemistry, Columbia University, New York, New York 10027, United States.
Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, United States.
J Phys Chem Lett. 2021 Nov 11;12(44):10802-10807. doi: 10.1021/acs.jpclett.1c03160. Epub 2021 Nov 1.
The scanning tunneling microscope-based break-junction (STM-BJ) technique is the most common method used to study the electronic properties of single-molecule junctions. It relies on repeatedly forming and rupturing a Au contact in an environment of the target molecules. The probability of junction formation is typically very high (∼70-95%), prompting questions relating to how the nanoscale structure of the Au electrode before the metal point contact ruptures alters junction formation. Here we analyze conductance traces measured with the STM-BJ setup by combining correlation analysis and multiple machine learning tools, including gradient-boosted trees and neural networks. We show that two key features describing the Au-Au contact prior to rupture determine the extent of contact relaxation (snapback) and the probability of junction formation. Importantly, our data strongly indicate that molecular junctions are formed prior to the rupture of the Au-Au contact, explaining the high probability of junction formation observed in room-temperature solution measurements.
基于扫描隧道显微镜的断键（STM-BJ）技术是研究单分子结电子性质最常用的方法。它依赖于在目标分子的环境中反复形成和断裂 Au 接触。结形成的概率通常非常高（约 70-95%），这引发了关于在金属点接触断裂之前 Au 电极的纳米级结构如何改变结形成的问题。在这里，我们通过结合相关分析和多种机器学习工具（包括梯度提升树和神经网络）来分析使用 STM-BJ 装置测量的电导轨迹。我们表明，在断裂之前描述 Au-Au 接触的两个关键特征决定了接触松弛（回跳）的程度和结形成的概率。重要的是，我们的数据强烈表明，分子结是在 Au-Au 接触断裂之前形成的，这解释了在室温溶液测量中观察到的高结形成概率。
