Physikalisches Institut, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Straße 10, 48149, Münster, Germany.
Center for Nanotechnology, Heisenbergstraße 11, 48149, Münster, Germany.
Small. 2021 Sep;17(35):e2101637. doi: 10.1002/smll.202101637. Epub 2021 Jul 21.
Providing fundamental insights in atomic interactions, dedicated methods in atomic force microscopy allow measuring the threshold forces needed to move single adsorbed atoms or molecules. However, the chemical and structural properties of the probe-tip can drastically influence the results. Establishing atomically defined contacts in such experiments, the tips in the present study are functionalized with various chemically and structurally different terminations. Xenon atoms are moved along an atomically defined metal/metal-oxide boundary where all tips show a pulling mechanism and slight force variations, which are assigned to polarization effects within the tip-sample junction. Detaching Xe atoms from the boundary involves a significantly higher energy barrier where chemical reactive Cu-tips cause Xe pickup before any lateral manipulation. Passivating the tip by inert probe particles (Xe or CO) allows further approaching the surface Xe atom. Yet, the small vertical attraction and pronounced tip relaxations prevent reaching sufficient threshold forces inducing manipulation. In contrast, the high structural rigidity of oxygen-terminated Cu-tips allows manipulations even beyond the threshold where they evolve from initial pulling, via sliding to pushing mode. The detailed quantitative analysis of the processes in the atomically defined junctions emphasizes the mechanical and chemical interactions for highly controlled experiments with piconewton sensitivity.
提供原子相互作用的基本见解，原子力显微镜中的专用方法允许测量移动单个吸附原子或分子所需的阈值力。然而，探针尖端的化学和结构特性会极大地影响结果。在这些实验中建立原子定义的接触，本研究中的尖端用各种化学和结构上不同的末端官能化。氙原子沿着原子定义的金属/金属氧化物边界移动，所有尖端都显示出拉伸机制和轻微的力变化，这归因于尖端-样品结内的极化效应。从边界上分离 Xe 原子需要一个明显更高的能量势垒，其中化学活性 Cu 尖端在任何横向操纵之前都会导致 Xe 吸附。用惰性探针粒子（Xe 或 CO）钝化尖端可以进一步接近表面 Xe 原子。然而，微小的垂直吸引力和明显的尖端松弛阻止了达到足够的阈值力以诱导操纵。相比之下，氧端接 Cu 尖端的高结构刚性允许操纵，甚至超过了它们从初始拉伸通过滑动到推动模式的阈值。原子定义结中过程的详细定量分析强调了具有皮牛顿灵敏度的高度可控实验中的机械和化学相互作用。
