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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.

Nanocrystalline and amorphous Ga2O3 films (%200 nm) with variable structural quality are produced by sputter-deposition by varying the substrate temperature (T s ¼ 25-700 C). The effect of T s is significant on the microstructure and mechanical behavior of Ga 2 O 3 films. The variation in mechanical behavior studied by nano-indentation and nano-scratch testing reveal distinct trends, which are directly related to the structure and morphology of Ga 2 O 3 films. All the Ga 2 O 3 films deposited at T s < 500 C are amorphous; the amorphous-to-crystalline transformation occurs at T s ¼ 500 C. Ga 2 O 3 films deposited at T s ! 500 C are nanocrystalline, β-phase. The corresponding mechanical characteristics, namely the hardness (H) and elastic modulus (E r ), show a strong correlation with structural characteristics. The H and E r increases from 17 to 27 GPa and 250 to 290 GPa, respectively, with increasing T s from 25 to 700 C. The plasticity index, which is the ratio of H/E r , is almost constant for the Ga 2 O 3 films. The strain-rate sensitivity measurements performed to determine the applicability in practical applications indicate the best performance of size controlled, nanocrystalline Ga 2 O 3 films, which can be mechanically regarded as nano-composite structures. The mechanical characteristics, scratch behavior, and strain rate sensitivity indicate the role of microstructure on the mechanical performance of Ga 2 O 3 films.Gallium oxide exhibits polymorphism. The α, β, γ, δ, and e phases of Ga 2 O 3 are widely known. [16,18,[25][26][27] Among these polymorphs, monoclinic β-Ga 2 O 3 is thermally stable with a band gap of %5 eV and high breakdown field 8 MV cm À1 . [28] β-Ga 2 O 3 exhibits n-type conductivity, which is related to donor centers involving oxygen vacancies and/or impurities. The high thermal stability of β-Ga 2 O 3 (melting point %1900 C) is quite useful in the design and development of high-temperature chemical sensors, which can be readily used in automotive industry and power plants. [2] Furthermore, the high-temperature stability coupled with deep ultraviolet transparency makes Ga 2 O 3 based materials as the potential candidates for chemical sensors in extreme environments and transparent electrodes in UV optoelectronics, photonics, and thin-film transistors. [29][30][31] However, in all these applications, fundamental understanding of the structure, thermodynamic conditions, and mechanical characteristics is the key to achieving enhanced device performance.

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