This study focuses on the effect of the substrate temperature (T_S) on the quality of VO₂ thin films prepared by DC magnetron sputtering. T_S was varied from 350 to 600 °C and the effects on the surface morphology, microstructure, optical and electrical properties of the films were investigated. The results show that T_S below 500 °C favors the growth of V₂O₅ phase, whereas higher T_S (≥500 °C) facilitates the formation of the VO₂ phase. Optical characterization of the as-prepared VO₂ films displayed a reduced optical transmittance ($\tilde{T}$) across the near-infrared region (NIR), reduced phase transition temperature (T_t), and broadened hysteresis width (ΔH) through the phase transition region. In addition, a decline of the luminous modulation $(\mathsf{\Delta }{\tilde{T}}_{\mathrm{lum}})$ and solar modulation ($\mathsf{\Delta }{\tilde{T}}_{\mathrm{sol}}$) efficiencies of the as-prepared films have been determined. Furthermore, compared with the high-quality films reported previously, the electrical conductivity (σ) as a function of temperature (T) reveals reduced conductivity contrast (Δσ) between the insulating and metallic phases of the VO₂ films, which was of the order of 2. These outcomes indicated the presence of defects and unrelaxed lattice strain in the films. Further, the comparison of present results with those in the literature from similar works show that the preparation of high-quality films at T_S lower than 650 °C presents significant challenges.

In this work, VO₂ thin films were deposited on Si wafers (onto (100) surface) by DC magnetron sputtering under different cathode bias voltages. The effects of substrate biasing on the structural and optical properties were investigated. The results show that the metal–insulator transition (MIT) temperature of VO₂ thin films can be increased up to 14 K by applying a cathode bias voltage, compared to deposition conditions without any bias. The decrease in the transition efficiency and increase in the transition temperature are attributed to the enlarged grain size, increased defects, and the residual stress in the VO₂ thin films induced by biasing. The optical transmittance measurements for different thickness films indicate an attenuation coefficient of 3.1 × 10⁷ m⁻¹ at 2000 nm or an extinction coefficient of 4.9 in the metal phase. The optical transmittance vs wavelength characteristics point to an indirect bandgap of 0.6 ± 0.05 eV and significant scattering in the bulk and/or at the interface.

Concrete has been widely used in pavements and buildings, and it is necessary to increase its hardness in order to resist deformation, penetration, and abrasion for these applications. This study explores the effects of addition of CuO and/or TiO₂ nanoparticles on the hardness of cement mortar. Scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, and Rockwell hardness testing were used to study the microstructure, chemical and phase composition, and hardness. The results showed that the addition of nanoparticles can effectively improve the hardness of cement mortar by improving the microstructure and hydration process. This is because they offer additional nucleation sites for hydrates to deposit on, producing a more compact microstructure with finer grains. As the concentration of nanoparticles added increases, the enhancement is more obvious and stable. However, after the concentration reaches its maximum level, the hardness starts to decrease due to the formation of defects, mainly voids, caused by excess nanoparticles. CuO and TiO₂ nanoparticles show similar effects on the microstructure and hardness, but the addition of both CuO and TiO₂ nanoparticles with similar amounts shows denser microstructure and higher hardness as they densify the composites.

The authors would like to correct a typographical error in their paper