Enhanced mechanical properties of W1-yMoyO3 nanocomposite thin films

We report on the enhanced mechanical properties of similar to 60 nm thick W-Mo-O nanocomposite films, which are of current interest as structural and electrode materials in photo-related energy technologies. W-Mo-O films were sputter-deposited onto Si(100) by varying the growth temperature (T-s) ranging from 25 to 500 degrees C. The molybdenum (Mo) content in the films was varied in the range of y = 0.05-0.15 by employing the W-Mo target with a variable Mo content. Structural and mechanical characterization was performed to understand the combined effect of the Mo content and T-s on the structure and mechanical behavior of W-Mo-O films. The results indicate that the effect of T-s is significant on the growth and microstructure of W-Mo-O films. The effect of the Mo-content is reflected in elevating the T-s needed for film crystallization coupled with the average grain-size reduction. Structural studies revealed that the W-Mo-O films were amorphous for T-s <= 300 degrees C, at which point amorphous-to-crystalline transformation occurs. Monoclinic (m) W-Mo-O nanocomposite films exhibit a combination of m-WO3 and m-MoO3 phases with m-WO3 being predominant in the matrix. The peak intensities of the m-MoO3 phase increases with increasing Mo-content. The nanoindentation results indicate a non-monotonic mechanical response in terms of hardness (H) and reduced elastic modulus (E-r) of the deposited films with increasing T-s. The effect of microstructure evolution is remarkable on the mechanical properties. Structural transformation at T-s = 300 degrees C induces a significant change in H and E-r values. The W-Mo-O with y = 0.05 exhibit maximum H (similar to 21GPa) and E-r (similar to 216GPa), where Mo-incorporation induced enhancement in mechanical characteristics is pronounced. A strain rate dependence of the H value of W-Mo-O films has been observed. Based on the results, structure-composition-mechanical property correlation in W-Mo-O films is established. Published by AIP Publishing.