Wang Xinzhe, Zahl Percy, Wang Hailiang, Altman Eric I, Schwarz Udo D
Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States.
Center for Functional Nanomaterials, Brookhaven National Lab, Upton, New York 11973, United States.
ACS Nano. 2024 Feb 6;18(5):4495-4506. doi: 10.1021/acsnano.3c11219. Epub 2024 Jan 24.
Recent advances in scanning probe microscopy methodology have enabled the measurement of tip-sample interactions with picometer accuracy in all three spatial dimensions, thereby providing a detailed site-specific and distance-dependent picture of the related properties. This paper explores the degree of detail and accuracy that can be achieved in locally quantifying probe-molecule interaction forces and energies for adsorbed molecules. Toward this end, cobalt phthalocyanine (CoPc), a promising CO reduction catalyst, was studied on Ag(111) as a model system using low-temperature, ultrahigh vacuum noncontact atomic force microscopy. Data were recorded as a function of distance from the surface, from which detailed three-dimensional maps of the molecule's interaction with the tip for normal and lateral forces as well as the tip-molecule interaction potential were constructed. The data were collected with a CO molecule at the tip apex, which enabled a detailed visualization of the atomic structure. Determination of the tip-substrate interaction as a function of distance allowed isolation of the molecule-tip interactions; when analyzing these in terms of a Lennard-Jones-type potential, the atomically resolved equilibrium interaction energies between the CO tethered to the tip and the CoPc molecule could be recovered. Interaction energies peaked at less than 160 meV, indicating a physisorption interaction. As expected, the interaction was weakest at the aromatic hydrogens around the periphery of the molecule and strongest surrounding the metal center. The interaction, however, did not peak directly above the Co atom but rather in pockets surrounding it.
扫描探针显微镜方法学的最新进展已能够在所有三个空间维度上以皮米精度测量针尖与样品之间的相互作用，从而提供相关特性的详细的位点特异性和距离依赖性图像。本文探讨了在局部量化吸附分子的探针 - 分子相互作用力和能量时能够达到的细节程度和精度。为此，使用低温、超高真空非接触原子力显微镜，以Ag(111)上的钴酞菁（CoPc，一种有前景的CO还原催化剂）作为模型体系进行了研究。记录的数据是表面距离的函数，据此构建了分子与针尖在法向力和侧向力作用下相互作用的详细三维图以及针尖 - 分子相互作用势。数据是在针尖顶端有一个CO分子的情况下收集的，这使得能够详细可视化原子结构。确定针尖 - 基底相互作用随距离的变化情况，可以分离出分子 - 针尖相互作用；当根据 Lennard - Jones 型势对这些相互作用进行分析时，可以得到连接在针尖上的CO与CoPc分子之间原子分辨的平衡相互作用能。相互作用能峰值小于160 meV，表明是物理吸附相互作用。正如预期的那样，分子外围的芳香氢处相互作用最弱，而金属中心周围相互作用最强。然而，相互作用的峰值并非直接在Co原子上方，而是在其周围的区域。
