Measuring sliding friction at the single atom scale

最近，我们使用侧向力显微镜（LFM）来研究吸附在金属表面上的有机小分子。由于LFM是在低温下进行的，因此尖端顶点可以被设计成以单个明确定义的原子结束。我们发现，当我们拿起一个一氧化碳（CO）分子时，我们对在表面原子对上横向滑动时耗散的能量很敏感。这是第一次在单原子水平上实现普朗特-汤姆林森滑动摩擦模型的原子控制，也是一个非常灵敏的测量：能量耗散的垂直依赖性比扫描隧道显微镜中的隧道电流敏感十倍以上。这项资助申请中的拟议工作围绕着我们独特的能力，即直接观察具有原子特征的单原子粗糙体的能量耗散。我建议进行摩擦的基础研究，并探索使用这种能量耗散作为一种测量技术。为了在普朗特-汤姆林森模型的框架下测量摩擦，我们将在不同的速度下进行测量，并使用不同的探针粒子刚度。我们还将在低温下使用相同的传感器同时测量垂直力和横向力。我们将继续与我们的理论合作者一起建立从原子起点模拟宏观摩擦的方法。

Recently, we used lateral force microscopy (LFM) to investigate small organic molecules adsorbed on a metal surface. Because LFM was performed at low temperature, the tip apex could be engineered to end in a single well-defined atom. We discovered that when we picked up a single carbon monoxide (CO) molecule, we were sensitive to the energy dissipated as we slid laterally over pairs of surface atoms. This was the first atomically-controlled realization of the Prandtl-Tomlinson model of sliding friction at the single atom level, and an amazingly sensitive measurement: The vertical dependence of the energy dissipation is over ten times more sensitive than that of the tunneling current in scanning tunneling microscopy. The proposed work in this grant application centres around our unique ability to directly observe energy dissipation with an atomically-characterized single-atom asperity. I propose performing fundamental studies of friction and exploring the use of this energy dissipation as a measurement technique. To measure friction in the framework of the Prandtl-Tomlinson model, we are going to perform measurements at various velocities, and with different stiffnesses of the probe particle. We are also going to incorporate simultaneous measurements of vertical forces as well as lateral forces with the same sensor operating at low temperature. We will continue to work with our theoretical collaborators to establish methods to simulate macroscopic friction from an atomic starting point.