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This paper presents an investigation into the influence of repeating cycles of hydrothermal growth processes and rapid thermal annealing (HT+RTA) on the properties of CuO thin films. An innovative hydrothermal method ensures homogeneous single-phase films initially. However, their electrical instability and susceptibility to cracking under the influence of temperature have posed a challenge to their utilization in electronic devices. To address this limitation, the HT+RTA procedure has been developed, which effectively eliminated the issue. Comprehensive surface analysis confirmed the procedure’s ability to yield continuous films in which the content of organic compounds responsible for the formation of cracks significantly decreases. Structural analysis underscored the achieved improvements in the crystalline quality of the films. The implementation of the HT+RTA procedure significantly enhances the potential of CuO films for electronic applications. Key findings from Kelvin probe force microscopy analysis demonstrate the possibility of modulating the work function of the material. In addition, scanning capacitance microscopy measurements provided information on the changes in the local carrier concentration with each repetition. These studies indicate the increased usefulness of CuO thin films obtained from the HT+RTA procedure, which expands the possibilities of their applications in electronic devices.

Today, silicon solar cells (amorphous films and wafer-based) are a main source of green energy. These cells and their components are produced by employing various technologies. Unfortunately, during the production process, chemicals that are harmful for the environment and for human life are used. For example, hydrofluoric acid is used to texture the top electrode to improve light harvesting. In this work, and also in recent ones, we report a way to obtain 3D textures on the top electrode by using zinc oxide nanorods. The efficiency of a textured solar cell structure is compared with the one obtained for a planar zinc oxide/silicon structure. The present results show the possibility to produce efficient solar cells on a relatively thin 50 μm thick silicon substrate. Solar cells with structured top electrodes were examined by numerous measuring techniques. Scanning electron microscopy revealed a grain-like morphology of the magnesium-doped zinc oxide film. The size of the grains is closely related to the structure of the nanorods. The external quantum efficiency of the cells was measured. The obtained solar cell shows response in a wide spectral range from ultraviolet to infrared. Current–voltage and current–voltage–temperature measurements were performed to evaluate basic photovoltaic parameters. At room temperature, the cells efficiency equals to 9.1% for textured structures and 5.4% for planar structures, respectively. The work, therefore, describes an environmentally friendly technology for PV architecture with surface textures increasing the efficiency of PV cells.

The structural, optical, and electrical properties of ZnO are intimately intertwined. In the present work, the structural and transport properties of 100 nm thick polycrystalline ZnO films obtained by atomic layer deposition (ALD) at a growth temperature (Tg) of 100–300 °C were investigated. The electrical properties of the films showed a dependence on the substrate (a-Al2O3 or Si (100)) and a high sensitivity to Tg, related to the deviation of the film stoichiometry as demonstrated by the RT-Hall effect. The average crystallite size increased from 20–30 nm for as grown samples to 80–100 nm after rapid thermal annealing, which affects carrier scattering. The ZnO layers deposited on silicon showed lower strain and dislocation density than on sapphire at the same Tg. The calculated half crystallite size (D/2) was higher than the Debye length (LD) for all as grown and annealed ZnO films, except for annealed ZnO/Si films grown within the ALD window (100–200 °C), indicating different homogeneity of charge carrier distribution for annealed ZnO/Si and ZnO/a-Al2O3 layers. For as grown films the hydrogen impurity concentration detected via secondary ion mass spectrometry (SIMS) was 1021 cm−3 and was decreased by two orders of magnitude after annealing, accompanied by a decrease in Urbach energy in the ZnO/a-Al2O3 layers.

Zinc oxide (ZnO) is one of the most versatile semiconductor materials with many potential applications. Understanding the interactions between the surface chemistry of ZnO along with its physico-chemical properties are essential for the development of ZnO as a robust photocatalyst for the removal of aqueous pollutants. We report on the fabrication of nanoparticle-like porous ZnO films and the correlation between the fabrication process parameters, particle size, surface oxygen vacancies (SOV), photoluminescence and photocatalytic performance. The synthesis route is unique, as highly porous zinc layers with nanoscale grains were first grown via magnetron sputtering, a vacuum-based technique, and subsequently annealed at temperatures of 400 °C, 600 °C and 800 °C in oxygen flow to oxidise them to zinc oxide (ZnO) while maintaining their porosity. Our results show that as the annealing temperature increases, nanoparticle agglomeration increases, and thus there is a decrease in the active sites for the photocatalytic reaction. However, for selected samples the annealing leads to an increase of the photocatalytic efficiency, which we explain based on the analysis of defects in the material, based on photoluminescence (PL). PL analysis showed that in the material the transition between the conduction band and the oxygen vacancy is responsible for the green emission centered at 525 nm, but the photocatalytic activity correlated best with surface states—related emission.

In order to effectively utilize the photovoltaic properties of gallium arsenide, its surface/interface needs to be properly prepared. In the experiments described here we examined eight different paths of GaAs surface treatment (cleaning, etching, passivation) which resulted in different external quantum efficiency (EQE) values of the tested photovoltaic (PV) cells. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) examinations were conducted to obtain structural details of the devices. X-ray photoelectron spectroscopy (XPS) with depth profiling was used to examine interface structure and changes in the elemental content and chemical bonds. The photoluminescence (PL) properties and bandgap measurements of the deposited layers were also reported. The highest EQE value was obtained for the samples initially etched with a citric acid-based etchant and, in the last preparation step, either passivated with ammonium sulfide aqueous solution or treated with ammonium hydroxide solution with no final passivation. Subsequent I–V measurements, however, confirmed that from these samples, only the sulfur-passivated ones provided the highest current density. The tested devices were fabricated by using the ALD method.

In this work, the properties of ZnO films of 100 nm thickness, grown using atomic layer deposition (ALD) on a–(100) and c–(001) oriented Al2O3 substrate are reported. The films were grown in the same growth conditions and parameters at six different growth temperatures (Tg) ranging from 100 °C to 300 °C. All as-grown and annealed films were found to be polycrystalline, highly (001) oriented for the c–Al2O3 and highly (101) oriented for the a–Al2O3 substrate. The manifestation of semi-polar-(101) and polar (001)–oriented ZnO films on the same substrate provided the opportunity for a comparative study in terms of the influence of polarization on the electrical and structural properties of ZnO films. It was found that the concentration of hydrogen, carbon, and nitrogen impurities in polar (001)–oriented films was considerably higher than in semi-polar (101)–oriented ZnO films. The study showed that when transparent conductive oxide applications were considered, the ZnO layers could be deposited at a temperature of about 160 °C, because, at this growth temperature, the high electrical conductivity was accompanied by surface smoothness in the nanometer scale. On the contrary, semi-polar (101)–oriented films might offer a perspective for obtaining p-type ZnO films, because the concentration of carbon and hydrogen impurities is considerably lower than in polar films.

Energy consumption steadily increases and energy production is associated with many environmental risks, e.g., generating the largest share of greenhouse gas emissions. The primary gas pollution concern is CO2, CH4, and nitrogen oxides (NOx). Environmental catalysis plays a pivotal role in NOx mitigation (DeNOx). This study investigated, for the first time, a collection of ceramic foams as potential catalyst support for selective catalytic NOx reduction (SCR). Ceramic foams could be an attractive support option for NOx removal. However, we should functionalize the surface of raw foams for such applications. A library of ceramic SiC, Al2O3, and ZrO2 foams ornamented with nanorod ZnO and TiO2 as W and V oxide support was obtained for the first time. We characterized the surface layer coating structure using the XPS, XRF and SEM, and TEM microscopy to optimize the W to V molar ratio and examine NO2 mitigation as the SCR model, which was tested only very rarely. Comparing TiO2 and ZnO systems reveals that the SCR conversion on ZnO appeared superior vs. the conversion on TiO2, while the SiC-supported catalysts were less efficient than Al2O3 and ZrO2-supported catalysts. The energy bands in optical spectra correlate with the observed activity rank.

The future applications of hyperbolic metamaterials demand stacks of materials with alternative ultra-thin conductive/dielectric films with good homogeneity of the thickness and reduced roughness level. In this work, the technology of pulsed-DC magnetron sputtering of aluminum was optimized using the Taguchi method in order to fabricate Al films with improved roughness level. The performed structural characterization proved the smaller Al domains and better homogeneity of the surface. The optimized process was used to fabricate a multilayer structure of Al/HfOx as the metamaterial media. The fabricated structures were optically characterized in the UV/VIS range. The presented findings demonstrated the tunability effect of the effective reflectance of the examined stacks. The presented results are promising for the future application of multilayer structures in novel photonic devices based on hyperbolic metamaterials.