Scanning Tunneling Microscopy Reveals Surface Diffusion of Single Double-Decker Phthalocyanine Molecules at the Solution/Solid Interface
Scanning Tunneling Microscopy Reveals Surface Diffusion of Single Double-Decker Phthalocyanine Molecules at the Solution/Solid Interface
复制标题
DOI：
10.1021/acs.jpcc.1c08103
复制
发表时间：
2022-03-03
影响因子：
3.7
通讯作者：
Hipps, K. W.
中科院分区：
文献类型：
--
作者：
Rana, Shammi;Johnson, Kristen N.;Hipps, K. W.
采用扫描隧道显微镜（STM）对溶液/固体界面和氩气/固体界面的单分子扩散进行了观察和定量。本工作通过分析连续STM图像中的分子轨迹，研究温度、溶剂和STM尖端对分离分子表面扩散的影响。Y[C6S-Pc](2)在苯辛烷中的表面扩散是热激活的，在5℃时几乎没有观察到运动，而在30℃以上，分子运动和/或吸附/脱附非常迅速，以至于很难跟踪单个分子。分子的表面扩散也依赖于溶剂；偶极矩较大的溶剂（可能与Au（111）的相互作用较大）降低了扩散系数，而没有溶剂（即氩气/固体界面）则增加了扩散系数。在室温下，通过改变样品偏置电压来量化STM尖端的影响，扩散系数在0.6 × 10（-17）和16 × 10(-17) cm(2)/s之间变化。这是第一次对溶液/固体界面上的单分子（相对于空位）扩散进行定量研究。这项研究的一个重要意义是，即使在很强的吸附物-衬底相互作用的情况下，STM尖端也可以显著地调动表面分子，从而增强自组装膜的形成。此外，由于尖端诱发的位移不是单向的，因此不能通过分析一个设定点和扫描速率的位移来诊断尖端诱发的运动。在任何基于stm的溶液-固体界面自组装动力学研究中都必须特别注意。
Scanning tunneling microscopy (STM) was used to observe and quantify single-molecule diffusion at the solution/solid interface and at the argon/solid interface. This work investigates the influence of the temperature, solvent, and STM tip on isolated molecular surface diffusion through analysis of the molecular trajectories in sequential STM images. The surface diffusion of Y[C6S-Pc](2) in phenyloctane was found to be thermally activated with almost no motion observed at 5 degrees C, whereas, above 30 degrees C molecular motion and/or adsorption/desorption are so rapid that it becomes difficult to track single molecules. The surface diffusion of molecules also depended on solvents; solvents with greater dipole moments (and presumably greater interaction with Au(111)) reduced diffusivity, while the absence of a solvent (i.e., argon/solid interface) increased diffusivity. At room temperature, the influence of the STM tip was quantified by varying the sample bias voltage, with the diffusion coefficient varying between 0.6 x 10(-17) and 16 x 10(-17) cm(2)/s. This is the first quantitative study of single-molecule (as opposed to vacancy) diffusion at the solution/solid interface. An important implication of this study is that even in the case of very strong adsorbate-substrate interactions, the STM tip can significantly mobilize surface molecules and thereby enhance the formation of self-assembled films. Moreover, because the tip-induced displacements are not unidirectional, one cannot diagnose tip-induced motion by analyzing the displacements at one set-point and scan rate. Particular care must be taken in any STM-based studies of self-assembly kinetics at the solution-solid interface.