The features of aluminum localization and the mechanism of donor center formation in ZnO:Al layers synthesized by high-frequency magnetron sputtering are studied. It is shown that aluminum predominantly localizes at grain boundaries of zinc oxide in its own oxide phase. The mechanism of aluminum oxidation at grain boundaries significantly depends on the oxygen content in the working chamber: during sputtering in an atmosphere of pure argon under conditions of oxygen deficiency, aluminum oxidation occurs as a result of interaction with oxygen from the surface layer of zinc oxide crystallites, forming surface donor centers at grain boundaries. With an increase in the partial pressure of oxygen, aluminum is predominantly oxidized by oxygen from the gas atmosphere, forming its own barrier phase at grain boundaries.

Since the stability of functional properties of a transparent conducting three-layer structure ZnO:Ga/Ag/ZnO:Ga is important for practical application, we studied its long-term durability and thermal stability in air environment. It has been demonstrated that after prolonged interaction with the air environment at room temperature (for ~ 1000 days) and further heat treatment in air at temperatures of up to 450oC (for up to 10 h), the three-layer structure retains its integrity and is characterized by a low sheet resistance Rs=2.8 Ω/sq at average transmittance in the visible range Tav=82.1%. Keywords: transparent electrode, multilayer structure, ZnO, Ag, Ga, sheet resistance, transparence, stability, heat treatment.

This work presents the structural and morphological characterization and the results of studies of the luminescence and photocatalytic properties of ZnO tetrapods synthesized by high-temperature pyrolysis. It was demonstrated that the morphology and structural parameters of ZnO tetrapods are defined by the location in the synthesis zone. All samples are characterized by pseudo-three-dimensional morphology of tetrapods. The correlation was found between the luminescence properties and photocatalytic activity of tetrapods. The highest photodegradation rates of methylene blue under UV radiation were demonstrated by ZnO tetrapods grown in the zones closest to and farthest from the air-inlet window (the rate constants were 54 × 10–3 and 50 × 10–3 min–1, respectively).

The paper investigates the influence of the deposition temperature on the morphology and structural-phase composition of the ZnO-based substrate material with a thickness of over 50 μm during the magnetron sputtering of hot ceramic targets. The study revealed the influence of the deposition temperature on the growth rate, morphology, and structural parameters of the ZnO single crystal precipitate. It was shown that the ZnO deposition rates during the spluttering of hot ceramic targets were ultra-high (up to 1.5 μm/min). The authors propose a method for the formation of both smooth and microporous ZnO-based substrate materials without using template technologies. The results obtained in the work can be widely used in optoelectronics and nitride technologies

The influence of temperature of amorphous SiO2/Si substrates on the formation of ultra-smooth highly oriented ZnO(0001) films by direct current magnetron sputtering has been studied. It has been shown that ZnO films obtained at a substrate temperature of 500°С have a lamellar shape of crystallites regardless of the growth rate in the range 1–7 nm/s. This feature of the crystallite morphology is associated with the minimum root-mean-square surface roughness of 0.9 nm for traditional high-speed deposition methods. The ultra-smooth surface of the films and the lamellar shape of the ZnO crystallites are mainly due to the two-dimensional mechanism of film formation under conditions of charging the growing surface in the magnetron discharge plasma.

The specific features of aluminum localization and the mechanism of formation of donor centers in ZnO:Al layers synthesized by rf magnetron sputtering have been investigated. It is shown that aluminum is mainly localized on intergranular boundaries of zinc oxide in the intrinsic oxide phase. The mechanism of Al oxidation on grain boundaries depends strongly on the oxygen content in the working chamber: during sputtering in a pure argon atmosphere with oxygen deficit, aluminum oxidation occurs as a result of the interaction of the surface layer of zinc oxide crystallites with oxygen, which leads to the formation of surface donor centers on grain boundaries. With an increase in partial oxygen pressure aluminum is mainly oxidized by the oxygen from the gas atmosphere, forming an intrinsic barrier phase on grain boundaries.

The effect of enhancement the hydrophobic properties of the ensemble of micro- and nanostructures ZnO as a result of coating with gold was discovered. For the first time, it has been shown that coating the ensemble with a micro- and nanoparticle ZnO layer of gold leads to a sharp increase in the wetting edge angle from 145 to 168o (water drop volume 5 mm3) and a decrease in the hydrophobicity/hydrophilicity transition time under ultraviolet irradiation. Keywords: ZnO, gold, superhydrophobic. Keywords: ZnO, gold, superhydrophobic

This paper presents the initial results of the synthesis of β-Ga2O3 luminescent ceramics via plasma gas-thermal spraying synthesis, where low-temperature plasma of an argon and nitrogen mixture was employed. A direct current electric arc generator of high-enthalpy plasma jet with a self-aligning arc length and an expanding channel of an output electrode served as a plasma source. The feedstock material consisted of a polydisperse powder of monocrystalline β-Ga2O3 with particle sizes ranging from 5 to 50 μm. The study presents the results of both theoretical and experimental studies on the heating rate and average temperature of gallium oxide particles in a plasma jet. The results of computational modelling of the synthesis process of β-Ga2O3 via plasma gas-thermal spraying are shown. The obtained ceramic samples were characterized using scanning electron microscopy and X-ray diffraction analysis. Our results indicate that the synthesis process yielded ceramics with a layered texture. The stoichiometric composition of ceramics exhibited a shift towards gallium-rich content. X-ray diffraction data demonstrated a reduction in the lattice parameters and unit cell volume of β-Ga2O3 ceramic structure. Radioluminescence spectra of β-Ga2O3 ceramics revealed an intensive emission band with a maximum at ~360 nm and non-exponential decay. The synthesized β-Ga2O3 ceramics possess potential applications in scintillation detectors.

The results of studying the structural features of samples of zinc-oxide films obtained by magnetron deposition on chips of lanthanum-magnesium hexaaluminate and the surface of sapphire substrates with a gold buffer layer are presented. Analysis of the structure and morphology of the films is carried out using a set of methods, including high-resolution X-ray diffractometry, the method of constructing pole figures, and transmission electron microscopy. It is shown that when using cleavages of lanthanum-magnesium hexaaluminate, an epitaxial ZnO film is formed without signs of growth rotating domains. The use of a gold buffer layer during growth on sapphire substrates improves the crystalline quality of ZnO films, but does not completely suppress domain growth.

— The results of a comprehensive study of the relationship between the luminescence and photocatalytic properties of ZnO tetrapods synthesized by carbothermal synthesis with their structural and phase composition are presented. According to X-ray diffraction and high-resolution electron microscopy data, ZnO tetrapods of crystal quality are formed during carbothermal synthesis. According to X-ray photoelectron spectroscopy, a high density of local states is observed near the Fermi level, which indicates the presence of intrinsic defects in ZnO and defect levels related to them in the band gap. The increased sensitivity of ZnO tetrapods in the visible region of the spectrum in the processes of the photocatalytic degradation of methyl orange is related to the presence of intrinsic defects. According to X-ray luminescence and cathodoluminescence data, ZnO tetrapods have low scintillation characteristics when exposed to a flux of fast electrons with energies above 60 keV and X-ray radiation: exposure leads to the destruction of ZnO tetrapods and multiple intensification of the green luminescence band.

The paper investigates the characteristics of the formation and morphology of microstructured zirconium oxynitride (ZrON) films, taking into account structural polymorphism during the impact of atmospheric-pressure microwave nitrogen plasma with the influx of active oxygen from the surrounding atmosphere. Optical, hydrophobic, Raman-active properties of ZrON films have been studied. X-ray diffractometry (XRD), scanning electron microscopy (SEM), ellipsometry method, and Raman spectroscopy, and moisture-resistance properties are used as analytical research methods. It is shown that during the short-term impact of microwave plasma, a morphologically heterogeneous ZrON film can be formed with a set of microhills with a uniform phase composition along the surface. The phase composition of the ZrON surface corresponds to the monoclinic structure of ZrO2. In the volume of the film, a predominantly tetragonal structure of ZrO2 is observed, as well as inclusions of the monoclinic structure of ZrO2. A mechanism for the formation of a ZrON film, taking into account polymorphism and phase transitions, is proposed. The optical properties of ZrON films are determined by both the dielectric phase of ZrO2 and the inclusions of the high-conductivity phase of ZrN. A combination of such factors as the developed microrelief and monoclinic surface structure, as well as nitride phase inclusions, enhance the hydrophobic properties of the ZrON film surface. It is shown that the surface hydrophobicity and resonant effects on ZrN inclusions allow for the enhancement of the Raman spectrum intensity due to the high concentration of analyte molecules in the scanning area.

A comparative study of the growth process of transparent conductive films based on Ga-doped ZnO is carried out during the magnetron sputtering of a traditional ZnO:Ga ceramic target and ZnO:Ga–Zn composite targets with a Zn metal phase content of 10 to 30 wt %. The influence of the composition of composite targets and substrate temperature on the functional characteristics and microstructure of transparent conductive films is studied. It is demonstrated that an increase in the zinc content in the composition of the composite target when the substrate is heated to 200°C and above helps to improve the structural perfection of ZnO:Ga films and reduce their resistivity due to an increase in the concentration of charge carriers against the background of a high value of Hall mobility. All ZnO:Ga films obtained by sputtering composite targets at a substrate temperature of 200°C and above demonstrate high optical transmittance in the visible region.

The results of studying the specific features of the growth of zinc oxide films formed on sapphire substrates by magnetron sputtering in an inhomogeneous electric field are presented. The films have been analyzed by high-resolution X-ray diffractometry, pole figure technique, and electron microscopy. A sequence of changes in the lateral structure with an increase in the film thickness, which depends also on the local potential, is revealed. Thus, regions with a higher surface potential correspond to the ZnOá10 0ñ(0001)||Al2O3á11 0ñ(0001) epitaxial ratio with the least lattice mismatch.

Porous films of metals and metal oxides have gained growing attention as potential materials for use in applications that require large, specific surface areas, such as sensors, supercapacitors, and batteries. In this study, a “black-metal”-like porous Zn–ZnO composite layer was grown by room temperature co-sputtering of Zn metal and ZnO:Ga (3 at/%) ceramic targets. Following deposition, a porous ZnO layer was obtained by a subsequent thermal annealing process at 400 °C in air. The morphology and structural properties of the obtained porous layered objects were analyzed. The porosity and chemical characteristics of the nanostructured ZnO layer obtained with the method herein described make it suitable to be used as a sensitivity-enhancing active layered element in quartz crystal microbalance (QCM)-based ultraviolet (UV) sensors. The prepared resonant ZnO/QCM sensors under UV radiation exhibited maximum shift up to 35 Hz for several “on-off” UV cycles, excellent response, and recovery times of 11 and 12 s, respectively.

Method of electric arc synthesis of composite microparticles metal-semiconductor-dielectric based on titanium, titanium nitride and rutile with productivity up to 10 g/min is proposed. Using diffraction and microscopic methods, the morphology and structural-phase composition of the synthesized microparticles were studied. Using the example of methylene blue degradation, the photocatalytic activity of synthesized microparticles in the visible radiation range was demonstrated and its possible mechanism was proposed. Keywords: titanium, rutile, titanium nitride, microparticles, photocatalysis, visible light.

This paper reports on the high photocatalytic activity of ZnO tetrapods (ZnO-Ts) using visible/solar light and hydrodynamic water flow. It was shown that surface oxygen defects are a key factor in the photocatalytic activity of the ZnO-Ts. The ability to control the surface wettability of the ZnO-Ts and the associated concentration of surface defects was demonstrated. It was demonstrated that the photocatalytic activity during the MB decomposition process under direct and simulated sunlight is essentially identical. This presents excellent prospects for utilizing the material in solar photocatalysis.

Method of electric arc synthesis of composite microparticles metal-semiconductor-dielectric based on titanium, titanium nitride and rutile with productivity up to 10 g/min is proposed. Using diffraction and microscopic methods, the morphology and structural-phase composition of the synthesized microparticles were studied. Using the example of methylene blue degradation, the photocatalytic activity of synthesized microparticles in the visible radiation range was demonstrated and its possible mechanism was proposed.

The presented work studies the processes of synthesis of ZnO microstructures using atmospheric-pressure microwave nitrogen plasma and investigates their photocatalytic activity in the processes of degradation of 2,4-dinitrophenol and the antibiotic ciprofloxacin when irradiated with sunlight. The work proposes an effective method for formation of photosensitive ZnO powders. Due to the features of plasma treatment in the open atmosphere of zinc metal microparticles, ZnO structures are formed with sizes from hundreds of nanometers to several micrometers with various micromorphologies. The lattice parameters of ZnO structures are characteristic of a hexagonal unit with a = 3.258 Å and c = 5.21 Å, volume 47.95 Å3. The size of the crystallites is 48 nm. The plasma treatment was performed by means of a 2.45-GHz plasmatron at a power input of 1 kW in nitrogen flow at a rate of 1–10 L/min. Zn microparticles were injected into the microwave plasma at a mass rate of 20 g/min. High photoactivity was demonstrated (rate constants 0.036 min−1 and 0.051 min−1) of synthesized ZnO structures during photo-degradation of 2,4-dinitrophenol and ciprofloxacin, respectively, when exposed to solar radiation. Photo-active structures of ZnO synthesized using microwave plasma can find application in processes of mineralization of toxic organic compounds. Structures of ZnO synthesized using microwave plasma can find application in processes of mineralization of toxic organic compounds, and also in scintillation detectors, phosphors.

The paper presents the results of a comprehensive study of the structural-phase composition, morphology, optical, luminescent, and scintillation characteristics of thick ZnO films fabricated by magnetron sputtering. By using a hot ceramic target, extremely rapid growth (~50 µm/h) of ZnO microfilms more than 100 µm thick was performed, which is an advantage for the industrial production of scintillation detectors. The effects of post-growth treatment of the fabricated films in low-temperature plasma were studied and a significant improvement in their crystalline and optical quality was shown. As a result, the films exhibit intense near-band-edge luminescence in the near-UV region with a decay time of <1 ns. Plasma treatment also allowed to significantly weaken the visible defect luminescence excited in the near-surface regions of the films. A study of the luminescence mechanisms in the synthesized films revealed that their near-band-edge emission at room temperature is formed by phonon replicas of free exciton recombination emission. Particularly, the first phonon replica plays the main role in the case of optical excitation, while upon X-ray excitation, the second phonon replica dominates. It was also shown that the green band peaking at ~510 nm (2.43 eV) is due to surface emission centers, while longer wavelength (>550 nm) green-yellow emission originates mainly from bulk parts of the films.