Microstructure and Mechanical Properties of Sputter-Deposited Nanocrystalline W1-yMoYO3 Thin Films
Currently, there is a wide-spread interest in the design and development of indium (In) free transparent conductive oxides (TCOs) for utilization in photovoltaics and optoelectronics. Tungsten oxide (WO3)-based materials are being explored for their utilization in solar cells, photo-electrochemical cells (PECs), electrochromic (EC) "smart windows," information displays, variable reflectance mirrors, and photo-detector materials. Designing ternary compounds or composite/hybrid structures coupled with tailoring the nano-architectures of WO3-based materials has been considered to be attractive develop potential candidates with enhanced performance. In this context, in this thesis work, an attempt is made to prepare W-Mo-O nanocomposite films, which can be considered 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=25–500 °C); Mo content 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 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. 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. 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. Based on the results, structure-composition-mechanical property correlation in W-Mo-O films is established.
Lopez, Gabriel Alberto, "Microstructure and Mechanical Properties of Sputter-Deposited Nanocrystalline W1-yMoYO3 Thin Films" (2017). ETD Collection for University of Texas, El Paso. AAI10689357.