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Abstract: TiO2, which is high in refractive index and dielectric constant, plays an important role in the fields of optics and electronics. In this work, TiO2 films were prepared on glass substrates by the technique of ion beam assisted electron beam evaporation. The films were deposited at 50, 150 and 300°C, respectively. Then the as-deposited TiO2 films were annealed at 450°C for 1h in vacuum atmosphere. Structures and optical properties of TiO2 films were characterized by XRD, SEM, ellipsometry and spectrophotometer. As a result, the structure and the refractive index of films were improved by both the annealing and the increasing of the deposition temperature. The UV–vis transmittance spectra also confirmed that the deposition temperature has a significant effect on the transparency of the thin films. The highest transparency over the visible wavelength region of spectra was obtained at the deposition temperature of 300°C. The allowed direct band gap at the deposition temperature ranging from 50 to 300°C was estimated to be in the range from 3.81 to 3.92eV. [Copyright &y& Elsevier]

Composite photocatalyst with heterostructure is often recognized as an effective strategy to achieve efficient charge separation and increase carrier concentration. In this study, the (1 1 0) and (1 0 1) surfaces of TiO 2 and SnO 2 were chosen to construct the abrupt and graded TiO 2 /SnO 2 hetero-structures. The interface properties and band offsets of four heterostructures are calculated and analyzed in detail. It was found that the graded heterostructures are more stable and easier to preparation than the abrupt heterostructures, the charge depletion and accumulation occur at both ends of the transition layer. The interfacial electric field caused by this effect allows the photo-generated electron-hole pairs to be easily separated and transferred in the opposite direction at the interface, which is important for improving the photocatalytic activity. In addition, the intrinsic mechanism of the four hetero-structures is discussed according to the analysis of the band offset, which belongs to the type II heterostructures. For TiO 2 /SnO 2 -(1 1 0) heterostructure, the photo-generated electrons transfer from the conduction band of TiO 2 to the conduction band of SnO 2 , while the photo-generated holes transfer from the SnO 2 to the valence band of TiO 2 . This phenomenon leads to the accumulation of the photo-generated electrons in the conduction band of TiO 2 , accumulation of the photo-generated holes in the valence band of SnO 2 . In short, the graded heterostructure has more favorable effects to enhance the photocatalytic activity than that of the abrupt heterostructure. The internal electric field at the TiO 2 /SnO 2 interface acts as a selector for photo-generated carriers, which may lead to higher photocatalytic quantum efficiency and carrier concentration under the same external conditions. These intrinsic photocatalytic mechanisms and the interpretation of the interfacial microscopic properties of heterostructure can be used as a basis for the design of the sensing devices and composite photocatalysts with heterostructures. [ABSTRACT FROM AUTHOR]

[Display omitted] • The MoNbTaWTi-based refractory high entropy alloy coatings by laser cladding. • TiN/(Nb, Ti) 5 Si 3 particles were in-situ synthesized by adding nano-Si 3 N 4. • The high-entropy alloy coating structure primarily consisted of BCC, TiN, and (Nb, Ti) 5 Si 3 phase. • The Si 3 N 4 -2.0 coating exhibits the best wear resistance with an average hardness of 628.07 HV 0.1. MoNbTaW Refractory High Entropy Alloy (RHEA) coating has caught the extensive interest of researchers due to its simple body-centered cubic structure and excellent room temperature plasticity. However, it is difficult to prepare refractory high-entropy alloy coatings by laser melting due to its high melting point. In this study, MoNbTaWTi (Si 3 N 4) x: (weight ratio; x = 0.5, 1.0, 1.5 and 2.0) RHEA composite coatings were fabricated by laser cladding on the Ti-6Al-4V alloy. The experimental results show that laser cladding may produce TiN/(Nb, Ti) 5 Si 3 ceramic particles and BCC phases in- situ in the coating when nano-Si 3 N 4 is added. Moreover, the in-situ reaction between element Ti and element N in the molten pool can be release a large amount of heat, which can efficiently facilitate the synthesis of RHEA coating. The in-situ generated TiN/(Nb, Ti) 5 Si 3 ceramic particles significantly increase the hardness and wear resistance of the composite coatings. The influence of the content of Si 3 N 4 on the ceramic morphology, microstructure, microhardness, and tribology of RHEA coatings was comprehensively evaluated. [ABSTRACT FROM AUTHOR]