We were able to systematically control crystallographic characteristics and electrical properties of nickel oxide epitaxial thin films integrated with cubic yttria-stabilized zirconia (c-YSZ)-buffered silicon(001) substrates. The NiO epilayers were grown under several oxygen partial pressures by pulsed laser deposition. The out-of-plane orientation of the NiO layers showed an interesting behavior where it changed from ⟨111⟩ at lower pressures (7 × 10–6 Torr) to ⟨100⟩ at higher pressures (5 × 10–2 Torr). This observation was attributed to the nature of surface termination and templating effect of the c-YSZ{100} platform at different pressures. With the use of θ–2θ and φ scans of X-ray diffraction, the epitaxial alignment across the NiO/c-YSZ interface was determined to be {111}NiO|||{100}c‑YSZ and ⟨110⟩NiO||⟨100⟩c‑YSZ for the heterostructure grown under a low pressure and {100}NiO||{100}c‑YSZ and ⟨100⟩NiO||⟨100⟩c‑YSZ for the heterostructure grown under a high oxygen pressure. Our high-resolution TEM studies revealed formation of atomically sharp interfaces with no evidence of interfacial reaction and confirmed the established epitaxial relationships. n-Type electrical conductivity was observed in the NiO epilayers grown under lower pressures, which was turned into p-type in the films deposited under higher oxygen partial pressures. Besides, the electrical resistivity increased with the growth pressure. These observations were correlated to the nature of point defects in the NiO crystal. The formation of oxygen vacancies and metallic nickel at lower pressures and excess oxygen and trivalent nickel at higher pressures was revealed by XPS. We established a structure–property correlation in NiO/c-YSZ{100}/Si{100} thin film epitaxial heterostructures with special emphasis on the stoichiometry and crystallographic characteristics.

We report the control of semiconductor to metal transition in VO2(010) epilayers integrated with Si{100} substrates buffered with an NiO[111]/YSZ[100] intermediate layer. VO2 epitaxial thin films were grown at different thicknesses varying from 10 to 200 nm using pulsed laser deposition technique. An epitaxial relationship of VO2(010)‖NiO(111)‖ YSZ(001)‖Si(001) and VO2[100]‖NiO[110]‖ YSZ[100]‖Si[100] was established at room temperature. The crystallographic alignment across the VO2/NiO interface changes to VO2(100)‖NiO(111) and VO2[001]‖NiO[110] at the temperature of growth giving rise to a misfit strain of about 33.5% and 3.0% along two orthogonal in-plane orientations. The transition temperature was observed to vary from about 353 to 341 K, the transition amplitude increased by about five orders of magnitude, and the hysteresis decreased to about 3 K, as the thickness of VO2 layers increased from about 10 to 200 nm. These observations were explained based on strain characteristics, overall defect content and grain boundaries, and phenomenological thermodynamic models.

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We grew TiO2-Al2O3 nanocomposite coatings on titanium substrates by electrophoretic enhanced microarc oxidation (EEMAO) technique under several voltages and established a correlation between microstructure, surface hardness, and corrosion resistance of the coatings in sulfuric acid and sodium chloride solutions. Structural analysis revealed that the coatings contained anatase, rutile, alumina, and tialite phases. Formation kinetics of tialite phase was studied. It was found that increasing the voltage gives rise to a coarser morphology, i.e., larger pore size, and incorporation of more alumina nanoparticles into the layers. It is shown that surface hardness of the titanium substrates increased by a factor of 4 following EEMAO treatment. Corrosion resistance of titanium was enhanced significantly. Resistance against pitting corrosion was improved as well. We proposed a formation mechanism for the TiO2-Al2O3 composite coatings at different voltages based on the chemical and electrochemical foundations.