Enhanced mechanical properties of W1−yMoyO3 nanocomposite thin films

Abstract

We report on the enhanced mechanical properties of ∼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 (Ts) ranging from 25 to 500 °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 Ts on the structure and mechanical behavior of W-Mo-O films. The results indicate that the effect of Ts is significant on the growth and microstructure of W-Mo-O films. The effect of the Mo-content is reflected in elevating the Ts needed for film crystallization coupled with the average grain-size reduction. Structural studies revealed that the W-Mo-O films were amorphous for Ts ≤ 300 °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 (Er) of the deposited films with increasing Ts. The effect of microstructure evolution is remarkable on the mechanical properties. Structural transformation at Ts = 300 °C induces a significant change in H and Er values. The W-Mo-O with y = 0.05 exhibit maximum H (∼21 GPa) and Er (∼216 GPa), 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.