Gallium oxide (Ga2O3) thin films were produced by sputter deposition by varying the substrate temperature (T s) in a wide range (T s = 25–800 °C). The structural characteristics and optical properties of Ga2O3 films were evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), Rutherford backscattering spectrometry (RBS), and spectrophotometric measurements. The effect of growth temperature is significant on the chemistry, crystal structure, and morphology of Ga2O3 films. XRD and SEM analyses indicate that the Ga2O3 films grown at lower temperatures were amorphous, while those grown at T s ≥ 500 °C were nanocrystalline. RBS measurements indicate the well-maintained stoichiometry of Ga2O3 films at T s = 300–800 °C. The spectral transmission of the films increased with increasing temperature. The band gap of the films varied from 4.96 to 5.17 eV for a variation in T s in the range 25–800 °C. A relationship between microstructure and optical property is discussed.

Lightweighting of automobiles by use of novel low-cost, high strength-to-weight ratio structural materials can reduce the consumption of fossil fuels and in turn CO2 emission. Working towards this goal we achieved high strength in a low cost β-titanium alloy, Ti–1Al–8V–5Fe (Ti185), by hierarchical nanostructure consisting of homogenous distribution of micron-scale and nanoscale α-phase precipitates within the β-phase matrix. The sequence of phase transformation leading to this hierarchical nanostructure is explored using electron microscopy and atom probe tomography. Our results suggest that the high number density of nanoscale α-phase precipitates in the β-phase matrix is due to ω assisted nucleation of α resulting in high tensile strength, greater than any current commercial titanium alloy. Thus hierarchical nanostructured Ti185 serves as an excellent candidate for replacing costlier titanium alloys and other structural alloys for cost-effective lightweighting applications.

Tungsten (W) incorporated gallium oxide (Ga 2 O 3 ) (GWO) thin films were deposited by radio-frequency magnetron cosputtering of W-metal and Ga 2 O 3 -ceramic targets. Films were produced by varying sputtering power applied to the W-target in order to achieve variable W-content (0−12 at. %) into Ga 2 O 3 while substrate temperature was kept constant at 500 °C. Chemical composition, chemical valence states, microstructure, and crystal structure of as-deposited and annealed GWO films were evaluated as a function of W-content. The structural and chemical analyses indicate that the samples deposited without any W-incorporation are stoichiometric, nanocrystalline Ga 2 O 3 films, which crystallize in β-phase monoclinic structure. While GWO films also crystallize in monoclinic β-Ga 2 O 3 phase, W-incorporation induces surface amorphization as revealed by structural studies. The chemical valence state of Ga ions probed by X-ray photoelectron spectroscopic (XPS) analyses is characterized by the highest oxidation state, i.e., Ga 3+ . No changes in Ga chemical state are noted for variable W-incorporation in the range of 0−12 at. %. Rutherford backscattering spectrometry (RBS) analyses indicate the uniform distribution of W-content in the GWO films. However, XPS analyses indicate the formation of mixed valence states for W ions, which may be responsible for surface amorphization in GWO films. GWO films were stable up to 900 °C, at which point thermally induced secondary phase (W-oxide) formation was observed. A transition to mesoporous structure coupled with W interdiffusion occurs due to thermal annealing as derived from the chemical analyses at the GWO films' surface as well as depth profiling toward the GWO−Si interface. Surface imaging analyses indicate thermally induced morphological changes are dependent on W-concentration in the GWO films. Thermally induced diffusion of W in the film is responsible for the observed formation of pores of variable size; the maximum pore radius noted was ∼27 nm for GWO films with highest W-content. The electronic charge redistribution appears to be dominated by the hydroxyl groups and W-chemistry as evident in XPS analyses. RBS data indicate that the extent of diffusion and intermixing layer depth are dependent on W-content in the GWO films. Thermally induced W-diffusion and depth penetration into the Si substrate with Si−W−Ga 2 O 3 intermixing at the interface is evident only in GWO samples with highest (12 at. %) Wincorporation. A model has been formulated to account for the mechanism of W-incorporation, thermal stability, and interdiffusion via pore formation in GWO films.