To understand the material removal mechanisms on a nanoscale and at ultralow loads, a modified atomic force microscope (AFM) with a three-sided pyramidal diamond tip (similar to 160 nm radius) was used for microwear/machining of a single crystal silicon (100) at ambient temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the material removal mechanisms change with applied normal load. Fine wear debris formed at a normal load of 20 mu N. At low normal loads, the material is removed by abrasive wear associated with plastic deformation. No bend contours and dislocations were found in the wear marks at a normal load of 20 mu N. At heavy normal loads (40-80 mu N), most of the wear debris are ribbon-like or curly chip-like. TEM images of wear marks made at 40 mu N showed bend contours in and around the wear marks, suggesting that presence of residual stresses. At a normal load of 80 mu N, both bend contours and dislocation arrays were observed in the wear marks. No microcracks were found in the wear marks generated at heavy loads. TEM electron diffraction patterns of the wear marks show that no phase transformation occurred in the microwear process. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) indicated that the wear debris was oxidized. These results suggest that, at heavy loads, the material is primarily removed by abrasive wear associated with plastic deformation, as commonly observed in metal cutting with a small contribution from elastic fracture. (C) 1998 Published by Elsevier Science S.A. All rights reserved.
