Use of a nanoscale Kelvin probe for detecting wear precursors

Abstract

A version of a Kelvin probe that has been developed for an atomic force microscope (AFM), here referred to as a nano-Kelvin probe, is used to create maps of surface potential for study of samples that have been abraded by an AFM tip. The focus is on the wear at very low loads that involve the absence of wear debris and/or wear scars. Wear scars at higher loads, where significant damage to surface has occurred, have also been studied for reference purposes. Samples studied include single crystal aluminum, alumina, gold, and silicon. It is shown that even in cases where there is little or no damage to the surface, as observed by topography scans of an AFM, there is often a large change in the potential at the surface of the sample. The change in surface potential is believed to be the result of chemical and structural changes in the first few nanometers of the sample. We have shown that, even in the case of “zero wear” (that is, no visible deformation of the surface), there can be a significant change in the surface potential inside the wear scar. This allows for the study of the onset of wear in the ultralow wear regime that is not possible with other techniques. The study of wear precursors is particularly important for the hard disk drive industry, the microelectromechanical systems industry, and other industries where the presence of any microscopic wear or debris can represent total failure.