We report the structural chemistry and optical properties of tin (Sn)mixed gallium oxide (Ga 2 O 3 ) compounds, where the interfacial phase modulationinduced structural distortion in turn induces variations in the band gap and nonlinear optical activity. The Sn incorporation into Ga 2 O 3 causes significant reduction in the band gap and induces nonlinear optical activity upon chemical composition tuning. Detailed investigation performed on the structural chemistry, phase stabilization, surface morphology, and optical and electrochemical properties of Sn-mixed Ga 2 O 3 compounds (Ga 2−2x Sn x O 3 , 0.00 ≤ x ≤ 0.3, Ga-Sn-O) indicates that the Sn-incorporation-induced effects are significant. To produce Ga-Sn-O materials of high structural and chemical quality, we adopted a simple solid-state chemical reaction route involving first calcining and then sintering the material at higher temperatures. Structural chemistry analyses of sintered Ga-Sn-O compounds by X-ray diffraction (XRD) showed solid solution formation at lower Sn concentrations (x ≤ 0.10). The XRD analyses indicate the SnO 2 secondary phase formation at higher (x > 0.10) Sn concentrations. Surface morphology analysis using scanning electron microscopy (SEM) also showed a positive relationship between phase separation and Sn concentration. Optical absorption spectra showed a substantial redshift in the band gap (E g ), which would allow Ga-Sn-O compounds to have wide spectral selectivity. At higher Sn concentrations (x = 0.25−0.30), corroborating with structural/chemical analyses, an additional lower-energy sub-band transition that explicitly corresponds to SnO 2 appears in the optical absorption data. Importantly, the evidence of nonlinear optical activity in Ga-Sn-O, which is otherwise not traditionally known for such an activity, as well as dipolar-and quadrupolar-shaped dependence of activity with the polarization angle of the excitation source was detected. At higher concentrations (x ≥ 0.15), Sn was found to be insoluble, which can be attributed to Ga 2 O 3 and SnO 2 possessing different formation enthalpies and cation (Ga 3+ and Sn 4+ ) chemistries. The fundamental scientific understanding of the interdependence of synthetic conditions, structure, chemistry, and optical and electrochemical properties could be useful to optimize Ga-Sn-O inorganic compounds for optical, optoelectronic, and photocatalytic device applications.

Realization and optimization of the tunable/enhanced optical properties are critical to further advancing the fields of optoelectronics, photonics, and nanoelectronics. In this context, here, we demonstrate green-emission characteristics with a ∼30-fold enhancement in selectively engineered nanocrystalline Ga 2 O 3 with control over the size, phase, and interface nanostructure. Pulsed-laserdeposited β-phase Ga 2 O 3 films with an average crystallite size of ∼9 nm along with a highly dense, close-compact nanocolumnar structure with the lowest possible defect density facilitate the 30-fold enhancement in the photoluminescence (PL) intensity in the green region. Enhanced PL emission in the optimized, engineered nanoarchitecture sheds light on the design of Ga 2 O 3 materials for promising future optoelectronic/ photocatalytic applications.

The authors report on the microstructure, crystallography, and mechanical properties of size controlled nanocrystalline (nc) molybdenum (Mo) films deposited by sputtering. The nc‐Mo films of ≈100 nm thick with a variable microstructure are deposited under variable argon (Ar) sputtering pressure (PAr), which is varied in the range of 3–25 mTorr. X‐ray diffraction analyses indicate that the nc‐Mo films exhibit (110) preferential growth. However, the crystal‐quality degradation occurs for Mo films deposited at higher PAr due to difference in the adatom mobility. The average crystallite size (d) of the nc‐Mo films is in the range of 5–20 nm; size decreases with increasing PAr. The effect of sputtering pressure is significant on the microstructure, which in turn influences the mechanical characteristics of Mo films. The hardness (H) and modulus of elasticity (Er) of nc‐Mo films deposited at lower PAr are higher but decreases continuously with increasing PAr. Under optimum sputtering conditions, the best mechanical characteristics obtained for Mo films are: H = 25 GPa, Er = 360 GPa, H/Er = 0.07, and H3/ = 0.13 GPa. A size‐microstructure‐mechanical property correlation in nc‐Mo films is derived based on the results presented and discussed.

This work unfolds the fundamental mechanisms and demonstrates the tunable optical properties derived via chemical composition tailoring in tungsten (W)-doped gallium oxide (Ga 2 O 3 ) compounds. On the basis of the detailed investigation, the solubility limits of tungsten (W 6+ ) ion and associated effects on the crystal structure, morphology, and optical properties of W-doped Ga 2 O 3 (Ga 2−2x W x O 3 , 0.00 ≤ x ≤ 0.25, GWO) compounds are reported. GWO materials were synthesized via a conventional solid-state reaction route, where a two-step calcination is adopted to produce materials with a high structural and chemical quality. X-ray diffraction analyses of sintered GWO compounds reveal the formation of a solid solution of GWO compounds at lower concentrations W (x ≤ 0.10), while unreacted WO 3 secondary phase formation occurs at higher concentrations (x>0.10). Insolubility of W at higher concentrations (x ≥ 0.15) is attributed to the difference in formation enthalpies of respective oxides, i.e., Ga 2 O 3 and WO 3 . GWO compounds exhibit an interesting trend in morphology evolution as a function of W content. While intrinsic Ga 2 O 3 exhibits rod-shaped morphology, W-doped Ga 2 O 3 compounds exhibit nearly spherical-shaped grain morphology. Increasing W content (x ≥ 0.10) induces morphology transformation from spherical to faceted grains with different facets (square and hexagonal). Relatively larger grain sizes in GWO compounds might be attributed to vacancy assisted enhanced mass transport due to W incorporation and/or WO 3 induced liquid phase sintering. Our findings demonstrate a substantial red shift in band gap (E g ), which is evident from the optical absorption spectra, enabling the wide spectral selectivity of GWO compounds. W 5d orbitals induced sp−d exchange interaction between valence band and conduction band electrons accounts for the substantial red shift in E g of GWO compounds. Also, with increasing W, E g decreases linearly, obeying Vegard law up to x = 0.15 and, at this point, an abrupt E g drop prevails. The nonlinearity (bowing ef fect) behavior in E g beyond x = 0.15 is due to insolubility of W at higher concentrations. The fundamental scientific understanding of the interdependence of synthetic conditions, structure, chemistry, and band gap could be useful to optimize GWO materials for optical, optoelectronic, and photocatalytic device applications.