Lubricity of zinc oxide thin films: Study of deposition parameters and Si as an additive

Zinc oxide preferentially crystallizes into a wurzite structure and has a u nique set of properties. There have been numerous studies on doped zinc oxi de thin films as an optical coating or as a semiconductor material. However , very little work has been reported on its tribological properties. Recent reports from this laboratory revealed that ZnO has good potential for cont rolling friction and wear. ZnO has an open structure and favorable coordina tion number, which permits zinc to freely move to different positions in th e crystal lattice and to accommodate external atoms as substitutes. The nat ure of the substitution and the concentration of Zn interstitials may be us ed to control tribological performance. In this work, thin films of zinc ox ide were deposited by pulsed laser ablation while silicon was added simulta neously by magnetron sputtering. The effects of deposition geometry and oxy gen partial pressure on stoichiometry and microstructure were evaluated. It was found that the angle of deposition and oxygen partial pressure control coating texture. Depositions normal to the sample surface, along with 10 m torr of oxygen, produced strong (002) texture. These conditions were select ed for Si-doping studies. The tribological characteristics of Si-doped coat ings were evaluated at both room and high temperature. Addition of Si aroun d 7-8% gave a coefficient of friction of about 0.2 at 300 degreesC, decreas ing to 0.13 around 500 degreesC.