Nanotribology of single crystal ZnO surfaces: Restructuring at high temperature annealing

Abstract

Atomic force microscopy is used to study low friction structures formed on single crystal zinc oxide because of annealing. Zinc oxide thin films deposited in this laboratory showed low friction (∼0.2) and long wear life (over one million cycles) in humid air at room temperature. Research into the mechanisms for this low friction behavior, far exceeding the life of typical solid lubricants (e.g., MoS2 and graphite) led to the present work, which focuses on the nanotribology of single crystal ZnO surfaces. Thermal annealing was used to cause surface reconstruction and defect formation. Etch pits were formed on the (101̄0) surface and roughening or reconstruction occurred on the (0001) surface. These pits and roughened areas showed low friction that could be originating from interactions of defects and restructured crystal faces due to adsorbates. Adhesion and relative contact stiffness were not significantly different between friction contrasting regions. The results of lateral force microscope analysis of the different single crystal surfaces are presented here.