Pulsed laser deposition of nanostructured dichromium trioxide thin films

The aim of this work is to investigate the relationship between the nanostructure and the physical properties of Cr2O3 thin films grown on Silicon (100) by KrF excimer laser ablation of a chromia target in oxygen ambient, at temperatures ranging from 20 to 950 degrees C. Compared to other more conventional techniques, pulsed laser deposition induces the growth of dense, non-porous films with uniform grain size and having the stoichiometry of the ablated target. Indeed, for all films, X-ray diffraction, infra-red spectroscopy and Rutherford back-scattering analyses confirm that Cr2O3 is the only phase present in the grown layers. However, a significant improvement in the crystalline quality and a reduction of the stress are observed with increasing deposition temperatures. These effects are accompanied by an increase in the grain size of the films from 50 to 200 nm as measured by atomic force microscopy. The optical band gap was evaluated by spectroscopic ellipsometry and a value of 3.25 eV was determined for films grown at 525 degrees C and above. Nanoindentation measurements indicate that films with hardness and elastic modulus values as high as 20 and 220 GPa, respectively, can be synthesized at 600 degrees C or below, but further increase in deposition temperature leads to a deterioration of the mechanical properties. It was found that the hardness value of the films is linearly correlated to the inverse square root of the grain size thereby suggesting a Hall-Petch like behavior. Slight divergence from this behavior is detected at low deposition temperature, due to the presence of residual stresses in the layers. (c) 2006 Elsevier B.V. All rights reserved.