Dynamics of Atomic Stick-Slip Friction

该项目的目标是在原子尺度上进一步了解摩擦滑动的动力学方面。特别是，该项目将重点研究极小的纳米级滑动接触的结构，表征接触在静态和滑动条件下的热和机械波动，以及热能在干润滑接触中对减少摩擦的影响。尽管摩擦的概念被认为是相对简单的，但对这些基本概念的审查是至关重要的。例如，虽然可以很容易地测量摩擦并对其影响进行分类，但目前还没有方法来预测两种材料接触并开始相互滑动时发生的摩擦行为。虽然到目前为止，我们现有的经验摩擦定律已经被广泛利用，但摩擦学领域的创新，或与摩擦相关的领域的创新，对于改善机械系统的环境性能、提高这些系统的耐用性以及微米/纳米机电(M/NEMS)的技术创新至关重要。考虑到生产极具能效、耐用性和低维护需求的机器的目标，需要对摩擦有更好的理解，特别强调将问题减少到物理预测值和理论。纳米技术和纳米科学通常被认为能够实现这些目标，因为复杂的摩擦问题可以简化为一个可以通过实验测量的问题，也可以在计算机模拟中完全重现。**在这个研究计划中，原子力显微镜(AFM)将被用来检查在原子平面固体润滑剂表面上滑动的纳米级小尖端之间的摩擦。AFM将用于这项研究，因为它能够测量足够小的力，以检测单个化学键断裂事件，以及沿表面横向滑动尖端原子距离。用原子力显微镜测量摩擦的一个问题是，可以达到的典型滑动速度约为100纳米/S，而典型机器的滑动速度为m/S。将在实验中采取措施纠正这一不足。此外，还将考察机械振动对减摩的影响，并分析它们对速度相关摩擦的贡献。这项基础性研究为建立摩擦预测模型奠定了基础，并将对研究机构和工业界的科学技术产生深远的影响。

The objective of this project is to gain further understanding of the dynamic aspects of frictional sliding at the atomic scale. In particular, this project will be focused on examining the structure of extremely small, nanoscale sliding contacts, characterizing the thermal and mechanical fluctuations of the contact under static and sliding conditions, and the effect thermal energy has on reducing friction in dry lubricated contacts. Examination of such fundamental concepts is crucial, despite the fact that the concept of friction is considered relatively simple. For example, although it is possible to easily measure friction and catalogue its effects, there currently exists no method of predicting the friction behaviour that will occur when two materials are brought into contact and begin to slide against each other. While our existing empirical friction laws have been widely exploited to date, innovation in the field of tribology, or the field concerned with understanding friction, is critical for improved environmental performance of mechanical systems, enhanced durability of these systems, and technological innovation of micro-/nano-electromechanical (M/NEMS). Given the goal of producing machines that are extremely energy efficient, long-lasting, and have low maintenance needs, an improved understanding of friction, with a specific emphasis of reducing the problem to physically predictive values and theories, is required. Nanotechnology and nanoscience are often thought of enabling these goals, as the complex problem of friction can be reduced in complexity to one that can be experimentally measured as well as completely re-created within a computer simulation.**In this research program, atomic force microscopy (AFM) will be used to examine friction between small, nanometre-sized tips sliding on a surface of atomically flat solid lubricants. AFM will be used in this study because it is able to measure forces sufficiently small to detect single chemical bonds breaking events, as well as laterally slide the tip along the surface by atomic distances. One issue with measuring friction with an AFM is that typical sliding speeds that can be achieved are on the order of 100 nm/s while typical machines operate at m/s sliding speeds. Measures will be taken to correct this deficiency in experiments. Furthermore, the influence of mechanical vibrations on reducing friction will be examined and their contributions to velocity dependent friction will be analyzed. This fundamental research represents the groundwork for reaching predictive models of friction, and will have far reaching impact on science and technology both in research institutions and industry.