RESUMEN
We report the results of synthesis of zinc selenide (ZnSe) nanocrystals into SiO2/Si track templates formed by irradiation with 200 MeV Xe ions up to a fluence of 107 ions/cm2. Zinc selenide nanocrystals were obtained by chemical deposition from the alkaline aqueous solution. Scanning electron microscopy, X-ray diffractometry, Raman and photoluminescence spectroscopy, and electrical measurements were used for characterization of synthesized ZnSe/SiO2nanoporous/Si nanocomposites. XRD data for as-deposited precipitates revealed the formation of ZnSe nanocrystals with cubic crystal structure, spatial syngony F-43m (216). According to non-empirical calculations using GGA-PBE and HSE06 functionals, ZnSe crystal is a direct-zone crystal with a minimum bandgap width of 2.36 eV and anisotropic electronic distribution. It was found that a thermal treatment of synthesized nanocomposites at 800 °C results in an increase in ZnSe nanocrystallites size as well as an increase in emission intensity of created precipitates in a broad UV-VIS spectra range. However, vacuum conditions of annealing still do not completely prevent the oxidation of zinc selenide, and a formation of hexagonal ZnO phase is registered in the annealed samples. The current-voltage characteristics of the synthesized nanocomposites proved to have n-type conductivity, as well as increased conductivity after annealing.
RESUMEN
Electrochemical deposition into a prepared SiO2/Si-p ion track template was used to make orthorhombic SnO2 vertical nanowires (NWs) for this study. As a result, a SnO2-NWs/SiO2/Si nanoheterostructure with an orthorhombic crystal structure of SnO2 nanowires was obtained. Photoluminescence excited by light with a wavelength of 240 nm has a low intensity, arising mainly due to defects such as oxygen vacancies and interstitial tin or tin with damaged bonds. The current-voltage characteristic measurement showed that the SnO2-NWs/SiO2/Si nanoheterostructure made this way has many p-n junctions.
RESUMEN
The synthesis of ß-Ga2O3 ceramic was achieved using high-energy electron beams for the first time. The irradiation of gallium oxide powder in a copper crucible using a 1.4 MeV electron beam resulted in a monolithic ceramic structure, eliminating powder particles and imperfections. The synthesized ß-Ga2O3 ceramic exhibited a close-to-ideal composition of O/Ga in a 3:2 ratio. X-ray diffraction analysis confirmed a monoclinic structure (space group C2/m) that matched the reference diagram before and after annealing. Photoluminescence spectra revealed multiple luminescence peaks at blue (~2.7 eV) and UV (3.3, 3.4, 3.8 eV) wavelengths for the synthesized ceramic and commercial crystals. Raman spectroscopy confirmed the bonding modes in the synthesized ceramic. The electron beam-assisted method offers a rapid and cost-effective approach for ß-Ga2O3 ceramic production without requiring additional equipment or complex manipulations. This method holds promise for fabricating refractory ceramics with high melting points, both doped and undoped.
RESUMEN
Indium tin oxide thin films were deposited by magnetron sputtering on ceramic aluminum nitride substrates and were annealed at temperatures of 500 °C and 600 °C. The structural, optical, electrically conductive and gas-sensitive properties of indium tin oxide thin films were studied. The possibility of developing sensors with low nominal resistance and relatively high sensitivity to gases was shown. The resistance of indium tin oxide thin films annealed at 500 °C in pure dry air did not exceed 350 Ohms and dropped by about 2 times when increasing the annealing temperature to 100 °C. Indium tin oxide thin films annealed at 500 °C were characterized by high sensitivity to gases. The maximum responses to 2000 ppm hydrogen, 1000 ppm ammonia and 100 ppm nitrogen dioxide for these films were 2.21 arbitrary units, 2.39 arbitrary units and 2.14 arbitrary units at operating temperatures of 400 °C, 350 °C and 350 °C, respectively. These films were characterized by short response and recovery times. The drift of indium tin oxide thin-film gas-sensitive characteristics during cyclic exposure to reducing gases did not exceed 1%. A qualitative model of the sensory effect is proposed.
RESUMEN
First-principles density functional theory (DFT) is employed to study the electronic structure of oxygen and gallium vacancies in monoclinic bulk ß-Ga2O3 crystals. Hybrid exchange-correlation functional B3LYP within the density functional theory and supercell approach were successfully used to simulate isolated point defects in ß-Ga2O3. Based on the results of our calculations, we predict that an oxygen vacancy in ß-Ga2O3 is a deep donor defect which cannot be an effective source of electrons and, thus, is not responsible for n-type conductivity in ß-Ga2O3. On the other hand, all types of charge states of gallium vacancies are sufficiently deep acceptors with transition levels more than 1.5 eV above the valence band of the crystal. Due to high formation energy of above 10 eV, they cannot be considered as a source of p-type conductivity in ß-Ga2O3.