Microstructural evolution in lubricious ZnO films grown by pulsed laser deposition

Zinc oxide (ZnO) is well known to the electronic industry as a piezoelectri c material. Recent research from this laboratory also indicates the potenti al of ZnO as a tribological material. The current work describes the evolut ion of microstructure with deposition parameters in pulsed laser deposited ZnO thin films, specifically targeted for friction and wear applications. F ilms were characterized by high resolution scanning electron microscopy (SE M), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Fr iction and wear measurements were made using a ball-on-disk tribometer. Fil ms were grown in vacuum (V) as well as in 5 mTorr of oxygen (O-2), while th e substrates were kept at room temperature (RT). The RT/V ZnO films have (0 02) columnar texture with an average column width of 20 nm. The RT/O-2 film s also are nanoclumnar with (002) texture, but each column is a mosaic of l ow-angle boundaries. Deformation mechanisms associated with nanocrystalline grain structure were analyzed with particular reference to sliding contact . Mechanisms to provide the observed low friction of RT/O-2 films (mu = 0.1 5-0.20) have been activated by its mosaic structure. (C) 2000 Elsevier Scie nce S.A. All rights reserved.