Nanotribological properties of ALD-processed bilayer TiO2/ZnO films

TiO2/ZnO films grown by atomic layer deposition (ALD) demonstrated nanotribological behaviors using scratch testing. TEM profiles obtained an amorphous structure TiO2 and nanocrystalline structure ZnO, whereas the sample has significant interface between the TiO2/ZnO films. The experimental results show the relative XRD peak intensities are mainly contributed by a wurtzite oxide ZnO structure and no signal from the amorphous TiO2. With respect to tribology, increased friction causes plastic deformation between the TiO2 and ZnO films, in addition to delamination and particle loosening. The plastic deformation caused by adhesion and/or cohesion failure is reflected in the nanoscratch traces. The pile-up events at a loading penetration of 30 nm were measured at 21.8 mu N for RT, 22.4 mu N for 300 degrees C, and 36 mu N for 400 degrees C. In comparison to the other conditions, the TiO2/ZnO films annealed at 400 degrees C exhibited higher scratch resistance and friction with large debris, indicating the wear volume is reduced with increased annealing temperature and loading. (C) 2014 Elsevier Ltd. All rights reserved.