Tribological behavior of alumina doped zinc oxide films grown by pulsed laser deposition

Abstract

Zinc oxide, a well-known piezoelectric material, has become the subject of tribological investigations. This research describes the synthesis and tribological evaluation of alumina doped zinc oxide [ZnO(Al2O3]) films grown in vacuum by a pulsed laser deposition (PLD) technique using hot pressed ZnO–5 wt % Al2O3 targets. For comparison, pure ZnO films were grown under identical PLD conditions. The films were characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Friction measurements were made using a ball-on-disk tribometer. Nanotribological studies were conducted on wear scars of ZnO and ZnO(Al2O3) films by atomic and lateral force microscopy. Both ZnO and ZnO(Al2O3) films were crystalline, with a strong (002) texture. The friction coefficient of the ZnO(Al2O3) film (μ=0.15) was considerably less than that of the pure ZnO film (μ=0.34). Wear scars on doped ZnO films were relatively smooth and, unlike in the case of pure ZnO films, no cracks were observed. Lateral force microscopy images of wear scars on ZnO(Al2O3) films showed dark contrast regions indicating the presence of a slippery phase. No such phase contrast was observed in the case of pure PLD ZnO film grown in vacuum.