Structural and mechanical properties of nanostructured tungsten oxide thin films

This study presents structural and mechanical properties of WO₃ thin films deposited on glass substrates at different temperatures by radio frequency reactive magnetron sputtering. WO₃ films deposited at temperatures up to 200°C are found as amorphous, but crystalline at 300 and 400°C. Chemical analysis reveals the overstoichiometry of the films. The diffusion of sodium ions from glass substrates occurs at higher temperatures. The adhesion critical loads of WO₃ films deposited at room temperature and at 200, 300 and 400°C are found to be 670, 990, 1080 and 830 mN respectively using microscratch tests with a 25 μm probe. Scratch hardness increases with the rise of temperature. The depth of penetration and wear track width decrease with temperature, indicating an improved penetration and wear resistance at temperatures up to 300°C. Scanning electron microscopy images reveal that the coatings fail due to wedge and recovery spallation during scratch and wear tests respectively.