Understanding the resistive switching (RS) mechanisms in memristive devices is crucial for developing non-volatile memory technologies. Here, we investigate the memristor effect in hydrothermally grown Au-nanoseeded CuO films. Based on I-V measurements, conductive-AFM, S/TEM, and EDS analyses, we examine the changes within the switching layer associated with RS. Our results reveal a filamentary mechanism of RS. Notably, EDS mapping shows directional Au redistribution between the bottom nanoseeds and the top electrode, while Cu and O remain uniformly distributed. These findings support an electrochemical metallization (ECM)-like filamentary mechanism driven by Au species migration. The use of Au-nanoseeds, required by the solution-based growth method, critically affects filament formation and RS behavior. Our results emphasize the importance of microstructure and electrode-oxide interfaces in determining the switching mechanism in oxide-based memristors.

With the spread of nanotechnology use in industry, exposure to nanomaterials is currently exponentially increasing. With reports indicating nanoparticles’ ability to pass through key biological barriers—gastrointestinal, lung, skin, blood-brain and the placenta barriers—the question of their safety, particularly the risks associated with embryonic development, arises. The aim of this article is to verify the impact of ZnO nanoparticles, which are commonly used and considered to be safe for adult organisms on the developing embryo. In the current study, the influence of the dose and shape of ZnO nanoparticles (oval vs. long) was evaluated in the chicken embryo model. The oxidative stress (superoxide dismutase (SOD)) activity, malondialdehyde (MDA) and carbonylated protein ((CP) levels), and gene expression changes (full genomic microarray study) were tested. We found that at both doses (10 µg/mL and 100 µg/mL, 100 µL into the air chamber) neither elongated nor oval ZnO nanoparticles changed in ovo mortality. Long ZnO nanoparticles had a lesser and more delayed impact on evaluated parameters, regardless of their higher in vitro toxicity. However, both nanoparticle forms induced changes in the oxidoreductive potential and affected expression of a significant number (1487 for oval and 548 for long ZnO nanoparticles) of identified genes during early embryo development.

The current study was inspired by the observation of separated regions grouping donors and acceptors in ZnO:N, which was reported using photoemission spectroscopy, surface photovoltage, and cathodoluminescence imaging [Phys. Rev. Appl. 2022, 18, 044021; Phys. Status Solidi A 2023, 220, 2200466]. The correspondence of these regions with individual crystallites suggests that strain may have a significant influence on the formation of shallow acceptor levels in ZnO. In the present paper, using density functional theory, we investigate the electronic and diffusion properties of Zn vacancy in the presence of the NOH2 group in ZnO:N from the point of view of the efficient formation of VZnNOH x acceptor complexes. We show that strain noticeably affects the migration properties of zinc vacancy. In particular, compressive strain facilitates the migration of Zn vacancy, and if it is high enough, the migration barrier drops to zero. It is also shown that the VZnNOH x complexes are easily formed in the presence of C i H2 groups. Photoluminescence spectra measured for ZnO:N films showing different strain conditions and cathodoluminescence images support the above conclusions.

Agreement is found between the experimentally and theoretically determined branch point level for ZnO located (2.7 +/- 0.1) eV above the valence band maximum. This result is obtained on the basis of a combined study where its experimental position is extracted from temperature-dependent capacitance versus voltage measurements on AZO/n-Zn(1-x)MgxO:Al/SiOx/p-Si heterostructures with Mg content equal to approximate to 0.07 and approximate to 0.23 combined with transmission electron microscopy and ellipsometry measurements to assess the SiOx interlayer contribution. This analysis confirms the values previously published in Schifano et al. J. Appl. Phys. 136, 245304 (2024). In contrast, density-functional theory calculations are used for obtaining the theoretical estimates. A similar comparison, in the MgO case, reveals a difference of approximate to 0.6 eV between the theoretically predicted and experimentally obtained values placed (4.3 +/- 0.1) and (3.7 +/- 0.4) eV above the valence band maximum, respectively. In this case, the assumption of a linear variation of the ZnMgO branch-point level between the two binary compounds, ZnO and MgO, used for the extraction of the experimental value, is among the probable causes of the residual difference found. Overall, the presented results indicate that the whole set of p(O) related valence bands should be included for a precise determination of the branch point energies if ab-initio methods are used.

This study investigated the influence of chemical reagent selection on the properties of ZnO nanoparticles synthesized using the microwave-assisted hydrothermal method to control the intensities of near-band-edge (NBE) and defect-related deep-level (DLE) emissions. Two zinc precursors—zinc nitrate and zinc chloride—along with three different precipitating agents (NaOH, KOH, and NH4OH) were used. ZnO nanoparticles from the ZnCl2 precursor exhibited two orders of magnitude higher NBE/DLE intensity ratio compared to those obtained from zinc nitrate characterized by a higher contribution from defect-related emissions. Chlorine ions in ZnO nanoparticles play a key role in passivating defects by forming V0-Cl2 complexes, quenching luminescence associated with oxygen vacancies (V0). Thermal treatment in a nitrogen atmosphere enhanced defect-related luminescence, possibly due to chlorine atom diffusion. This study highlights a successful synthesis of ZnO nanoparticles with low defect-related luminescence (DLE) achieved via the microwave-assisted hydrothermal method, a result rarely reported in the literature. The results emphasize the importance of reagent selection in controlling the morphology and optical properties, especially the defect density of ZnO nanoparticles. Optimizing these properties is crucial for biomedical applications such as bioimaging, antibacterial treatments, and photocatalysis.

The research explored the spontaneous formation of the BAp precursor on surfaces of HfO2 films obtained by Atomic Layer Deposition (ALD). It has been found that a careful selection of ALD growth conditions, followed by rapid thermal annealing (RTP) is crucial to achieve bioactivity of the films. Simulated Body Fluid experiment was used as a reliable test of the film's functionality as bone implant coating. SEM, XRD and XPS investigations proved that amorphous calcium orthophosphate structures were formed on the HfO2 films. These structures are of importance for biomineralization of bones. Physical and chemical characterization of the films was an integral part of the research. Such approach allowed us to achieve biomaterial functionality while maintaining the films' quality. The finding has significance for future progress in personalized traumatological medicine.

We have developed a new generation of markers based on wide band gap metal oxides (mainly ZnO, ZrO2) activated with rare earth ions (Eu, Er, Tb) for use as fluorescent markers. These markers are used for early detection of tumors. It has been shown that these markers after intra-gastric (alimentary uptake) introduction penetrate the area of tumors. In the case of lung tumors, the method was 100% selectable. In the following works, oxide matrices with scintillation properties have been selected to stimulate by X-ray radiation of emission of rare earth ions. Such markers can be used not only for the detection of tumor-related changes, but also for therapy by local stimulation of porphyrin compounds used in photodynamic (PDT) cancer therapy. The stimulated porphyrin compounds generate highly reactive singlet oxygen, destroying tumor cells. The modified markers can also be used as a safer contrast in magnetic resonance imaging (MRI). The possibility of targeted drug transport through markers to the area of lesions has also been demonstrated. Markers can cross the blood-brain barrier, which opens up new perspectives for detection and treatment, including the treatment of neurodegenerative diseases. In summary, we developed a new generation of fluorescence markers and contrasts used in MRI. The key of invention (patented) is eco-friendly production of biodegradable conjugates of oxide nanoparticles with drugs. The final product is optimized for uptake after oral application and direct transfer to tumors (including brain tumors). The developed markers passed tests for their biocompatibility. Large efficiency and selectivity was proven in tests performed on animals. Two methods were developed by us to use markers for therapy – as transport agents of selected drugs and for PDT therapy.

In this work, the impact of Al doping and Mg alloying on the conduction band misalignment ( Delta EC) between ZnO and (100) Si with a SiOx interlayer was studied by combining capacitance vs voltage, Hall and x-ray diffraction measurements, energy-dispersive x-ray spectroscopy, secondary mass spectrometry, and high-resolution scanning transmission electron microscopy. To decouple the effect of the high carrier density in the ZnO-based layers due to the Al introduction, the measured Delta EC was corrected for the conduction band lowering effect taking into account the conduction band non-parabolicity of ZnO. Then, from the Mg content dependence, using the interface-induced gap states approach, branch point energies referred to the valence band maximum equal to (2.7 +/- 0.2) and (3.6 +/- 0.4) eV were extracted for ZnO and MgO, respectively. These branch point energies were obtained under the assumption of a linear variation between the respective values of the corresponding two binary compound semiconductors, ZnO and MgO, and taking into account the presence of the SiOx interlayer. Furthermore, in the case of the undoped Zn0.96Mg0.04O layers, a similar to 0.27 eV reduced Delta EC was found, with the difference with respect to Zn0.94Mg0.06O:Al attributed to the presence of a downward band bending toward the interface with SiOx . Full 1 x 1 cm test solar cells based on Zn0.8Mg0.2O:Al layers exhibited short circuit currents, open circuit voltages, fill factors, and efficiencies that varied in the (28 +/- 1)mA/cm2, (430 +/- 20) mV, (61 +/- 2)%, and (7.2 +/- 0.3)% ranges with the residual Delta EC similar to 0.6 eV being among the main causes of the reduced device performances. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0International (CC BY-NC) license

Microwave hydrothermal technique has been applied to crystallize ZrO2 nanoparticles with the sizes below 10 nm and activated with Eu. Trivalent europium ions acted also as the stabilization agent of the high temperature ZrO2 polymorphs at the room temperature. To achieve this, high concentrations - up to 20% of Eu3+ - were introduced to the zirconia host lattice. Reference samples of ZrO2 containing yttrium were synthesized to obtain pure cubic, tetragonal and monoclinic phases at constant europium concentration. Eu3+ ions have not been reduced to divalent form, however, we have observed reduction of Zr4+ ions by means of luminescence spectroscopy and electron paramagnetic resonance (EPR). The variation of Zr3+ concentration in the samples with increasing Eu3+ content seems to support the concept of trivalent ion pairs as charge compensation centers in ZrO2. Excitation of Eu3+ ions was conducted via low and high symmetry sites. Trivalent zirconium ions have been found to play a role in the excitation of Eu3+ ions at low symmetry sites.

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.

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.

This work demonstrated the optimization of HiPIMS reactive magnetron sputtering of hafnium oxynitride (HfOxNy) thin films. During the optimization procedure, employing Taguchi orthogonal tables, the parameters of examined dielectric films were explored, utilizing optical methods (spectroscopic ellipsometry and refractometry), electrical characterization (C-V, I-V measurements of MOS structures), and structural investigation (AFM, XRD, XPS). The thermal stability of fabricated HfOxNy layers, up to 800 °C, was also investigated. The presented results demonstrated the correctness of the optimization methodology. The results also demonstrated the significant stability of hafnia-based layers at up to 800 °C. No electrical parameters or surface morphology deteriorations were demonstrated. The structural analysis revealed comparable electrical properties and significantly greater immunity to high-temperature treatment in HfOxNy layers formed using HiPIMS, as compared to those formed using the standard pulsed magnetron sputtering technique. The results presented in this study confirmed that the investigated hafnium oxynitride films, fabricated through the HiPIMS process, could potentially be used as a thermally-stable gate dielectric in self-aligned MOS structures and devices.

In this work, the results of ellipsometric studies of thin films of broadband oxides (ZnO, TiO2, ZrO2) and broadband oxides doped with Al2O3 (Al2O3–ZnO, Al2O3–TiO2, Al2O3–ZrO2) are presented. All layers have been produced using the atomic layer deposition method. Ellipsometric studies were performed in the wavelength range of 193–1690 nm. Sellmeier and Cauchy models were used to describe the optical properties of the tested layers. Dispersion dependencies of refractive indices were determined for thin layers of broadband oxides on silicon substrates, and then for layers of Al2O3 admixture. The EDX investigations enabled estimation of the composition of the alloys. The Bruggeman effective medium approximation (EMA) model was used to determine the theoretical dependencies of the dispersion refractive indices of the studied alloys. The refractive index values determined using the Bruggeman EMA model are in good agreement with the values determined from the ellipsometric measurements. The doping of thin layers of ZnO, ZrO2 and TiO2 with Al2O3 enables the creation of anti-reflective layers and filters with a specific refractive index.

The development of CdMgO ternary alloy with a single cubic phase is challenging but meaningful work for technological advancement. In this work, we have grown a series of Cd1-xMgxO ternary random alloys with various Mg concentrations (x = 0, 30, 32, 45, and 55%) on quartz substrate by plasma -assisted molecular beam epitaxy technique. The structural investigations of alloys were performed using the X-ray diffraction technique. The decreases in average crystallite size and lattice parameters were observed with an increase in Mg content in the alloys. X-ray diffraction analysis confirms that a single cubic phase is obtained for alloy compositions. The elemental and morphological studies were carried out using energy-dispersive X-ray spectroscopy and atomic force microscope technique, respectively. The optical investigation was carried out using UV-Vis spectroscopy. The optical bandgaps were estimated using the Tauc relation. The results varied from 2.34 to 3.47 eV by varying the Mg content from zero to 55% in the alloys. The Urbach energy increases from 112 to 350 meV, which suggests a more disordered localized state with an increase in Mg incorporation in the alloys.

ZnO nanoparticles (NPs) doped with iron were synthesized by the microwave-hydrothermal method using various reagents. The properties of these NPs were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL), cathodoluminescence (CL) measurements. In the article, we discuss the surprising results of optical studies of ZnO:Fe NPs. The phenomenon of luminescence quenching by the magnetic ion, characteristic for bulk materials, was not observed. We examined three potential reasons for this observation.

Atomic layer deposition of HfO2 from TDMAH and water or ammonia water at different temperatures below 400 °C is studied. Growth per cycle (GPC) has been recorded in the range of 1.2–1.6 Å. At low temperatures (≤100 °C), the films grew faster and are structurally more disordered, amorphous and/or polycrystalline with crystal sizes up to 29 nm, compared to the films grown at higher temperatures. At high temperatures of 240 °C, the films are better crystallized with crystal sizes of 38–40 nm but grew slower. GPC, dielectric constant, and crystalline structure are improved by depositing at temperatures above 300 °C. The dielectric constant value and the roughness of the films have been determined for monoclinic HfO2, a mixture of orthorhombic and monoclinic, as well as for amorphous HfO2. Moreover, the present study shows that the increase in the dielectric constant of the films can be achieved by using ammonia water as an oxygen precursor in the ALD growth. The detailed investigations of the relationship between HfO2 properties and growth parameters presented here have not been reported so far, and the possibilities of fine-tuning and controlling the structure and performance of these layers are still being sought.

A worldwide effort is under way to understand the activation of acceptor states in ZnO with the motivation to achieve persistent p‐type conductivity. In this study, cathodoluminescent (CL) imaging, electron microscopy (SEM), secondary‐ions mass spectrometry (SIMS), and X‐ray diffraction (XRD) are used to compare ZnO:N films subjected to a rapid thermal annealing process (RTP) in N2 and O2 atmosphere at 400–900 °C. The study, performed for ZnO:N films with nitrogen concentration of 2 × 1018 at cm−3 grown under O‐rich conditions is directed to establish the optimal atmosphere and temperature at which acceptor‐related CL is enhanced and correlated with structural properties. XRD shows that crystallite size increases from ≈100 to ≈250 nm with increasing annealing temperature up to 800 °C. The low‐temperature (LT) CL maps reveal that the acceptor‐ and donor‐related CL mostly derives from different crystallites. Both annealing medium and temperature influence acceptor‐related CL intensity, which is higher under oxygen annealing. It is observed that the intensity of acceptor‐related CL increases with annealing temperature up to 800 °C and then decreases. Noticeable donor‐related emission appears only after RTP at 700 °C and becomes prominent for RTP at 900 °C

Ti-based films are extensively studied as a prospective material for several applications - for UV-protection, antibacterial coating and effective photocatalytic activity. This is because Ti-based TiO2 shows relatively high reactivity and chemical stability under ultraviolet light (λ < 387 nm), whose energy exceeds the band gap (in the range 3–4 eV) of the anatase crystalline phase. However, the efforts are focused on development of photocatalytic materials exhibiting high reactivity under visible light (λ > 400 nm). Such materials should utilize the main part of the solar spectrum, and if efficient, they should work even under poor illumination, for example upon interior lighting. In this work, we concentrated on optimization of Ti-based films. Films with different chemical compositions were deposited using the atomic layer deposition (ALD) method. These films were prepared using chemical reactions between listed precursors: H2O, TiCl4, Ti(N(CH3)2)4 and Al2(CH3)6. The selection of precursors and, consequently, the modification of the ALD Ti-based process allowed the deposition of thin films with quite different structural, optical and electrical properties.

Unlike other II-VI semiconductors, CdO-based transparent oxide has great potential application for the fabrication of many optoelectronic devices. In this work, we study the growth of CdxMg1-xO alloys on m- and on c-plane sapphire substrates in Cd-rich to Mg-rich conditions using the plasma-assisted molecular beam epitaxy method. A structural and morphological study of CdMgO random alloys was carried out using X-ray diffraction and Atomic Force Microscope (AFM) techniques whereas composition analysis was done by Energy-dispersive X-ray (EDX) spectroscopy method. The optical properties of thin films were investigated by UV–Vis spectroscopy at room temperature. X-ray analysis confirmed the presence of cubic rock salt structure with <111> CdMgO crystallographic orientation on c-plane sapphire and <110> CdMgO preferential orientation on m-plane sapphire. The surface roughness was measured by the AFM. From the absorption curve, the optical bandgaps were determined using Tauc relation and it was found that the bandgap of films is influenced by the incorporation of Mg2+ ions into the CdO lattice. Bowing parameter was calculated for both samples on m- and c-sapphires.

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.