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The study of contact, adhesion and friction at the atomic scale by atomic force microscopy.

机译：通过原子力显微镜研究原子尺度上的接触，粘附和摩擦。

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摘要

The physical behavior of materials in contact with one another is generally not understood at the atomic level. In an attempt to quantitatively elucidate the fundamental mechanisms involved in contact, friction, and adhesion, atomic force microscopy (AFM) studies in ultrahigh vacuum (UHV) were performed with various single crystal samples. With low applied loads, the sharp tip on the end of the AFM cantilever forms a nanometer-sized single asperity contact with a sample. Adhesion, loading, and friction forces acting between the tip and each sample were measured for these ideal contacts.;To perform the experiments, a novel UHV AFM was designed, built and characterized. The instrument is the first variable temperature UHV AFM, and allows flexibility for sample exchange, AFM measurement positioning, and surface science investigations of the sample.;In order to calibrate AFM measurements accurately, a novel technique was developed for the calibration of lateral forces and was applied whenever possible. The relative lateral to normal force sensitivity is determined by measuring these forces on surfaces which are tilted with respect to the scanning plane. The predicted geometrical coupling of forces is compared with the output signals to determine the relative sensitivity of the instrument.;The occurrence of atomic-scale stick-slip friction forces was investigated with a number of samples. Consideration of instrumental effects reveals that the apparent topography displayed in these measurements is in fact due to two-dimensional frictional forces.;Friction between the mica(0001) surface and various tips was measured as a function of applied load in UHV. At low applied loads, friction is observed to deviate from the macroscopic law of Amonton. Instead of being proportional to the applied load, friction is proportional to the area of contact predicted by the theory of elastic contact mechanics. The variation of friction with applied load was observed to depend upon the tip shape in accordance with the theory of contact mechanics. This result demonstrates that quantitative knowledge of the tip shape is crucial for extracting meaningful and reproducible results from AFM measurements.;A new instrumental technique was developed which allowed the measurement of the lateral contact stiffness. This measurement provides further insight into the properties of the tip-sample contact, as it is proportional to the contact radius and the elastic shear modulus. A comparison between measurements in ambient and vacuum on mica samples with silicon nitride tips produces dramatically contrasting friction and contact area behavior, due to the presence of a water meniscus in ambient conditions.;A series of alkali halides were studied to compare their frictional properties. KF(001), KCl(001) and KBr(001) samples were cleaved and probed in UHV with a silicon nitride tip. The surfaces exhibit atomically flat terraces with predominantly monatomic steps. With these materials, tip-sample contact creates higher friction domains on the terraces. The structure, topography and degree of friction force contrast of these domains is material dependent. We propose that the observed domains result from surface structural changes created by low load tip-sample contact on these relatively soft materials and that this behavior is an example of the initial stages of wear at the atomic scale. (Abstract shortened by UMI.)
机译：彼此接触的材料的物理行为通常在原子水平上是无法理解的。为了定量阐明接触，摩擦和附着的基本机理，对各种单晶样品进行了超高真空（UHV）中的原子力显微镜（AFM）研究。在较低的施加载荷下，AFM悬臂末端的尖锐尖端会与样品形成纳米级的单次粗糙接触。对于这些理想的接触点，测量了针尖与每个样品之​​间作用的粘附力，载荷和摩擦力。为了进行实验，设计，构建并表征了一种新型的UHV AFM。该仪器是首款可变温度UHV AFM，可灵活地进行样品交换，AFM测量定位和样品表面科学研究。为了准确校准AFM测量，开发了一种用于校准横向力和力的新技术。在可能的情况下被应用。通过测量相对于扫描平面倾斜的表面上的这些力，可以确定相对于法向力的横向力。将预测的力的几何耦合与输出信号进行比较，以确定仪器的相对灵敏度。通过大量样本研究了原子级粘滑摩擦力的发生。考虑到仪器效果，这些测量中显示的表面形貌实际上是由于二维摩擦力引起的。云母（0001）表面与各种尖端之间的摩擦是作为特高压中所施加载荷的函数进行测量的。在较低的施加载荷下，观察到摩擦力偏离了Amonton的宏观规律。摩擦与弹性接触力学理论预测的接触面积成正比，而不是与施加的载荷成正比。根据接触力学理论，观察到摩擦力随施加载荷的变化取决于尖端形状。该结果表明，尖端形状的定量知识对于从AFM测量中提取有意义的和可重复的结果至关重要。开发了一种新的仪器技术，可以测量横向接触刚度。由于它与接触半径和弹性剪切模量成正比，因此该测量可进一步了解尖端样品接触的特性。由于在环境条件下会出现水弯液面，因此对具有氮化硅针尖的云母样品在环境和真空下进行的测量结果产生了截然不同的摩擦和接触面积行为。研究了一系列卤化碱以比较它们的摩擦性能。将KF（001），KCl（001）和KBr（001）样品裂解并在具有氮化硅尖端的UHV中进行探测。这些表面呈现出原子平坦的阶地，主要具有单原子阶梯。使用这些材料，尖端样品接触会在平台上产生更高的摩擦区域。这些区域的结构，形貌和摩擦力对比程度取决于材料。我们认为，观察到的区域是由低载荷尖端样品在这些相对较软的材料上接触所产生的表面结构变化引起的，并且这种行为是原子尺度上磨损初始阶段的一个例子。 （摘要由UMI缩短。）

著录项

  • 作者

    Carpick, Robert William.;

  • 作者单位

    University of California, Berkeley.;

  • 授予单位 University of California, Berkeley.;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 1997
  • 页码 179 p.
  • 总页数 179
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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