Nanotribological investigations of materials, coatings and lubricants for nanotechnology applications at high sliding velocities.

摘要

The advent of micro/nanostructures and the subsequent miniaturization of moving components for various nanotechnology applications, such as micro/nanoelectromechanical systems (MEMS/NEMS), have ascribed paramount importance to the tribology and mechanics on the nanoscale. Most of these micro/nanodevices and components operate at very high sliding velocities (of the order of tens of mm/s to few m/s). Atomic force microscopy (AFM) studies to investigate potential materials, coatings and lubricants for these devices have been rendered inadequate due to the inherent limitations on the highest sliding velocities achievable with commercial AFMs (250 mum/s). The development of a new AFM based technique, done as part of this research work, has allowed nanotribological investigations over a wide range of velocities (up to 10 mm/s). The impacts of this research on the design and development of nanotechnology applications are profound. Research conducted on various materials, coatings and lubricants reveals a strong velocity dependence of friction, adhesion and wear on the nanoscale. Based on the experimental evidence, theoretical formulations have been conducted for nanoscale friction behavior to design a comprehensive analytical model that explains the velocity dependence. The model takes into consideration the contributions of adhesion at the tip-sample interface, high impact velocity related deformations at the contacting asperities and atomic scale stick-slip. Dominant friction mechanisms are identified and the critical operating parameters corresponding to their transitions are defined.; Wear studies are conducted at high sliding velocities for materials, coatings and lubricants to understand the primary failure mechanisms. A novel AFM based nanowear mapping technique is developed to map wear on the nanoscale and the interdependence of normal load and sliding velocity on sample surface wear is studied. This technique helps identify and classify wear mechanisms and determine the critical parameters responsible for their transitions. The promising tribological properties exhibited by diamondlike carbon (DLC) coating and its role as a potential protective coating for nanotechnology applications are discussed. Scale dependence of micro/nano-friction and -adhesion is also studied. The primary reason for the scale dependence is the sample surface roughness and the higher contact pressures that are encountered on the nanoscale. This study emphasizes the fact that material behavior on one scale cannot be assumed to hold on another scale. The interdependence of mechanical and tribological properties for various materials has been explored and tribologically ideal materials with low adhesion and friction for nanotechnology applications have been identified.