Kelvin probe microscopy measurements of surface potential change under wear at low loads

Kelvin probe microscopy has been used to detect wear precursors at ultralow loads. Samples studied include single crystal silicon (100), single crysta l silicon (100) lubricated with fully bonded Z-DOL (a perfluoropolyether), gold, aluminum and alumina. The effect of load and number of cycles on surf ace potential change under ultralow loads has been investigated. Influence of the scan parameters and the reproducibility of the experimental results have been studied. It is found that the measured change in surface potentia l is strongly affected by the scan parameters as well as the shape of the p robe. Negative wear depth on single crystal silicon (100). and single cryst al silicon (100) lubricated with fully bonded Z-DOL during early stages of sliding has been observed. (The scratched area was raised rather than depre ssed as compared to the unworn surrounding region.) Chemical analysis of un worn and worn regions of silicon and silicon lubricated with fully bonded Z -DOL was performed to reveal possible mechanisms of changes in surface pote ntial. It is believed that the removal of a thin contaminant laver. natural oxide layer or lubricant during a few wear cycles gives rise to the initia l change in surface potential. It is further believed that structural chang es which precede generation of wear debris and/or measurable wear scars occ ur under ultralow loads in the top few nanometers of the sample, which are primarily responsible for the measured changes in surface potential. (C) 20 00 Elsevier Science S.A. All rights reserved.