Hafnium oxide (HfO₂) thin films have been made by atomic vapor deposition (AVD) onto Si substrates under different growth temperature and oxygen flow. The effect of different growth conditions on the structure and optical characteristics of deposited HfO₂ film has been studied using X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GIXRD) and variable angle spectroscopic ellipsometry (VASE). The XPS measurements and analyses revealed the insufficient chemical reaction at the lower oxygen flow rate and the film quality improved at higher oxygen flow rate. Via GIXRD, it was found that the HfO₂ films on Si were amorphous in nature, as deposited at lower deposition temperature, while being polycrystalline at higher deposition temperature. The structural phase changes from interface to surface were demonstrated. The values of optical constants and bandgaps and their variations with the growth conditions were determined accurately from VASE and XPS. All analyses indicate that appropriate substrate temperature and oxygen flow are essential to achieve high quality of the AVD-grown HfO₂ films.

The output power of the triboelectric nanogenerator (TENG) strongly depends on the performance of triboelectric materials, especially microstructures and functional groups of them. In this work, aiming at the excellent triboelectric ability, alternate-layered MXene composite films-based TENG with abundant fluorine groups(-F) through layer-by-layer stacking are designed and fabricated. Benefitting from the uniform intrinsic microstructure and increased dielectric constant, when the amount of the Nb₂CT_x nanosheets increases to 15 wt%, the TENG based on Nb₂CT_x/Ti₃C₂T_x composite nanosheets films achieves the maximum output. The short-circuit current density of 8.06 μA/cm² and voltage of 34.63 V are 8.4 times and 3.5 times over that of pure Ti₃C₂T_x films, and 3.3 times and 4.3 times over that of commercial poly(tetrafluoroethylene) (PTFE) films, respectively. Furthermore, the fabricated TENG could be attached to human body to harvest energy from human motions, such as typing, texting, and hand clapping. The results demonstrate that the alternate-layered MXene composite nanosheet films through layer-by-layer stacking possess remarkably triboelectric performance, which broaden the choice of negative triboelectric materials and supply a new choice for high output TENG.

The ocean, with its highly variable and complex meteorological conditions, harbors enormous renewable resources. Triboelectric nanogenerators (TENGs), which possess unique advantages, show exciting prospects in water wave energy collection. How to design and optimize TENGs to cover all characteristic water wave energies and achieve efficient energy utilization is emergent. In this paper, we carefully designed and fabricated a columnar multi-layer sliding TENG (CMLS-TENG) that can harvest water wave energy independent of wave height and direction. Drive rods with a hollow acrylic spherical shell were introduced to deliver wave energy, ensuring that the CMLS-TENG can work in all directions from 0° to 360°. Based on the sliding structure, switching the optimized CMLS-TENG is independent of wave heights. The optimized CMLS-TENG can achieve a total power density of 730 mW/m³ at a wave height of only 4.8 cm regardless of wave direction, which can illuminate multiple light-emitting diodes (LEDs) to provide lighting and provide power to a watch and a hygrometer for temperature and humidity monitoring. This work provides new choices and hopes for the effective collection of full-range water wave energy.

Optical properties and defect characterization of Ta-doped β-Ga ₂ O ₃ single crystals grown by the optical floating zone method.

Bulk aluminum nitride (AlN) crystals with different polarities were grown by physical vapor transport (PVT). The structural, surface, and optical properties of m-plane and c-plane AlN crystals were comparatively studied by using high-resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Temperature-dependent Raman measurements showed that the Raman shift and the full width at half maximum (FWHM) of the E₂ (high) phonon mode of the m-plane AlN crystal were larger than those of the c-plane AlN crystal, which would be correlated with the residual stress and defects in the AlN samples, respectively. Moreover, the phonon lifetime of the Raman-active modes largely decayed and its line width gradually broadened with the increase in temperature. The phonon lifetime of the Raman TO-phonon mode was changed less than that of the LO-phonon mode with temperature in the two crystals. It should be noted that the influence of inhomogeneous impurity phonon scattering on the phonon lifetime and the contribution to the Raman shift came from thermal expansion at a higher temperature. In addition, the trend of stress with increasing 1000/temperature was similar for the two AlN samples. As the temperature increased from 80 K to ~870 K, there was a temperature at which the biaxial stress of the samples transformed from compressive to tensile stress, while their certain temperature was different.