Dynamics of Atomic Stick-Slip Friction

该项目的目标是进一步了解原子尺度上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触点的结构，表征静态和滑动条件下触点的热波动和机械波动，以及热能对减少干润滑触点摩擦的影响。尽管人们认为摩擦的概念相对简单，但对这些基本概念的研究是至关重要的。例如，虽然可以很容易地测量摩擦并对其影响进行分类，但目前还没有方法可以预测当两种材料接触并开始相互滑动时发生的摩擦行为。虽然我们现有的经验摩擦定律迄今已被广泛利用，但摩擦学领域的创新，或与理解摩擦有关的领域，对于改善机械系统的环境性能，增强这些系统的耐久性，以及微/纳米机电（M/NEMS）的技术创新至关重要。考虑到生产非常节能、持久和低维护需求的机器的目标，需要提高对摩擦的理解，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被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新创建。**在这个研究项目中，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滑动的小的、纳米大小的尖端之间的摩擦。AFM将用于这项研究，因为它能够测量足够小的力来检测单个化学键断裂事件，以及沿原子距离沿表面横向滑动尖端。用AFM测量摩擦的一个问题是，典型的滑动速度可以达到100纳米/秒左右，而典型的机器以m/s的滑动速度运行。将采取措施纠正实验中的这一缺陷。此外，将研究机械振动对减少摩擦的影响，并分析它们对速度依赖摩擦的贡献。这一基础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.