Publications

This review paper delves into the concept of critical current density (Jc) in high-temperature superconductors (HTS) across macroscopic, mesoscopic, and microscopic perspectives. Through this exploration, a comprehensive range of connections is unveiled aiming to foster advancements in the physics, materials science, and the engineering of applied superconductors. Beginning with the macroscopic interpretation of Jc as a central material law, the review traces its development from C.P. Bean's foundational work to modern extensions. Mesoscopic challenges in understanding vortex dynamics and their coherence with thermodynamic anisotropy regimes are addressed, underscoring the importance of understanding the limitations and corrections implicit in the macroscopic measurement of J0, linked with mesoscopic phenomena such as irradiation effects, defect manipulation, and vortex interactions. The transition to supercritical current densities is also discussed, detailing the superconductor behavior beyond critical thresholds with a focus on flux-flow instability regimes relevant to fault current limiters and fusion energy magnets. Enhancing J0 through tailored material microstructures, engineered pinning centers, grain boundary manipulation, and controlled doping is explored, along with radiation techniques and their impact on large-scale energy systems. Emphasizing the critical role of J0, this review focuses on its physical optimization and engineering manipulation, highlighting its significance across diverse sectors.

Layers of HfO2 and (Hf,Zr)O2 crystalline nano-particles are synthesized via direct liquid injection atomic layer deposition, and a comprehensive set of structural, chemical, and electrical characterizations is employed to elucidate their phase composition and functional behavior. X-ray photoelectron spectroscopy revealed a compositional contrast between the films: (Hf,Zr)O2 layers contained up to 45% stoichiometric oxide, while pure HfO2 films are dominated by sub-oxides, especially under strongly reducing conditions, in which exclusively sub-oxide phases and p-type semiconducting behavior is revealed. Electrical measurements indicated room-temperature stabilization of polar phases and tetragonal-to-orthorhombic phase transition with a Curie temperature near 200 K. FTIR spectroscopy confirmed the presence of tetragonal and orthorhombic HfO2 phases, providing insight into minor features observed approximate to 30 degrees (2 theta) in X-ray diffraction patterns. Notably, devices incorporating an AlN interlayer demonstrated a significant enhancement in pyroelectric performance, suggesting this strategy to advance the pyroelectric performance of HfO2-based materials, supporting their development for lead-free sensor technologies.

In this work, we investigate the electrical properties of a ternary biocomposite material based on a vinyl resin (VR) matrix filled with two types of fillers, namely green microcrystalline cellulose (MCC) and carbon nanotubes (CNT), over a frequency range of 10-1 to 107 Hz and a temperature range from 10 to 130 degrees C. Thermal analyses were carried out using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), which revealed significant changes in the glass transition and degradation temperatures of the biocomposite, respectively. The electrical measurements were analyzed using two formalisms: (i) Electrical conductivity, which showed the presence of two distinct low-frequency behaviors associated with quasi-dc conductivity below the glass transition temperature and dc conductivity above it, along with high-frequency dispersion, which allows determining the ac conductivity mechanisms using Jonscher's power law, and (ii) Electric modulus, which revealed a low-temperature relaxation originating from water dipole polarization and two high-temperature dielectric relaxation processes. The first high-temperature relaxation, observed at low frequencies, was attributed to the Maxwell-Wagner-Sillars (MWS) effect, while the second, appearing at high frequencies, was associated with the alpha-relaxation. These relaxations were modeled using Bergman's equation. Furthermore, the temperature dependence of the relaxation time and dc conductivity were analysed using an Arrhenius representation.

Zinc oxide (ZnO) semiconducting nanoparticles were added to a nematic liquid crystal (NLC) mixture E7, and the influence of these particles on the spectroscopic and dielectric properties of the E7 mixture was studied. ZnO nanoparticles were obtained using a recently developed green method involving clove extract. The proportion of ZnO:LC in the mixture was varied between 1:99 and 95:5% to ensure accessibility of the particle surface for interactions with LC. These natural compounds not only facilitate the formation of stable nanostructures, but also promote surface functionalization, influencing the resulting morphology, crystallinity, and dispersion behavior of the nanoparticles in the host media. Because the classical fitting models were inadequate in our systems with multiple overlapping relaxation and conduction processes, derivative-based numerical methods were employed. Such approaches enabled the resolution of up to three distinct dielectric relaxation processes and allowed the extraction of characteristic frequencies and activation energies, and insight into the underlying interfacial phenomena between the ZnO nanoparticles and LC molecules was obtained. We assumed that the interaction between the two components of the composites (NLC and ZnO) was weak, which contributes to a deeper understanding of the interplay between biofunctionalized nanostructures and anisotropic soft matter environments.

The results of experimental investigation of the fundamental optical absorption edge of glassy thin films of the AsS3-GeS4 system are presented and discussed. The films were grown via thermal vacuum evaporation of powder of relevant glasses onto optical quartz substrates. The study was focused on the optical measurements to reveal the character and spectral position of the absorption edge, as well as to the effect of both glass composition and annealing on optical forbidden gaps and characteristic energies (triangle) of glasses in question. The absorption edge was found to concur with usual behavior established for disordered materials: at high photon energy hv > Eg, it is described by a parabolic function but at low energy hv < Eg by an exponential law (Urbach tail). The quadratic part of the absorption edge allowed to determine the optical forbidden gap Eg. It is shown that the glass composition and the thermal treatment influence the spectral position and slope of both parts of the absorption edge, but they especially strongly affect the slope of the exponential tail. The results are explained in terms of topological transformations due to glass composition change and structural self-organization, as well as their effect on concentration and energetic distribution of localized states inside of the forbidden gap.

Wide band gap semiconductors are essential for next-generation photovoltaics, especially indoor tandem applications, because they align well with both the solar spectrum and artificial light sources. Quaternary chalcogenides, such as Cu2ZnSnS4 (CZTS), offer tunable bandgaps, stability, and earth abundance. In this study, Ag-alloyed CZTS (ACZTS) thin films were synthesized via a controlled chemical solution process involving spin coating deposition process and sulfur annealing. Elemental composition and morphology analyses confirmed uniform grain distribution and precise control of the Ag/Cu ratio. Structural characterization via X-ray diffraction and Raman spectroscopy revealed a gradual transformation from the kesterite to the stannite phase as the Ag concentration increased. This transformation was accompanied by lattice expansion and a change in crystallite size. Optical measurements showed a clear widening of the bandgap from approximately 1.5 eV of pure CZTS to about 1.7 eV at high Ag levels, supporting its potential use as a top absorber in tandem solar cells. These findings demonstrate that alloying with Ag effectively tailors the properties of CZTS, making it a promising, non-toxic candidate for stable and efficient use in solar cells for indoor environments or high-efficiency tandem applications.

In this study, V2O5/FTO were synthesized using spin-coating deposition, followed by thermal annealing at 573 K. The formation of an orthorhombic V2O5 crystalline phase was confirmed by X-ray diffraction and Raman spectroscopy. Optical analysis in the visible light spectrum revealed an average transmittance of approximately 75 % and a band gap of 2.78 eV. Scanning electron microscopy images showed uniform nanograins distributed across the entire film surface, Energy-dispersive X-ray spectroscopy confirmed the elemental composition and homogeneous distribution of elements within the film. The electrochemical performances of the films were evaluated in different aqueous electrolytes at different concentrations, using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy measurements. Among the various tested electrolytes, neutral aqueous media, specifically 2 M KCl and 1.5 M Na2SO4 demonstrated the most favorable supercapacitive performance. V2O5/FTO exhibited its highest areal capacitance of 13.38 mF center dot cm-2 in 2 M KCl at 10 mV.s-1, while 1.5 M Na2SO4 yielded a slightly lower value of 12.45 mF center dot cm-2. Notably, at higher chargedischarge rates, the films demonstrated superior capacitive performance in Na2SO4 compared to KCl. Moreover, after 400 cycles the electrodes showed a capacitance retention of 55 % in Na2SO4, indicating their superior electrochemical durability.

Chronic inflammation and persistent infections represent major obstacles to effective wound healing, underscoring the urgent need for innovative, eco-friendly biomaterials capable of combating microbial contamination and oxidative stress. In this study, we investigated the in vitro biological activities of a gold-titanium dioxide (AuNPs/TiO2) composite, synthesized via an environmentally friendly approach, employing an ethylenediamine-hyaluronic acid derivative as both a reducing and stabilizing agent. The composite was analyzed using various techniques, including Transmission Electron Microscopy, X-ray elemental mappings, X-ray diffraction, and X-ray spectroscopy. We evaluated the biological properties of the material through antimicrobial and anti-adherence assays, alongside hemolysis, cytotoxicity, oxidative stress levels, and wound healing potential. The green-derived AuNPs/TiO2 demonstrated moderate to potent antimicrobial and anti-adhesion activity (minimum inhibitory concentrations ranging from 0.625 to 5 mg/mL) against both standard and clinical isolates. The material showed low hemolysis rates (<5 %) at bioactive concentrations. Additionally, keratinocyte viability and membrane integrity were largely preserved at the tested concentrations, with no detectable increase in pro-inflammatory nitric oxide levels. Intracellular antioxidant defenses were maintained, and lipid peroxidation was minimal. In an in vitro scratch assay, AuNPs/TiO2 promoted keratinocyte migration, suggesting a promising potential to enhance tissue repair. In summary, the biomaterial exhibits promising multifunctional properties, including effective antimicrobial and anti-adhesion activity, excellent biocompatibility with minimal hemolysis, and the ability to enhance keratinocyte migration and intracellular antioxidant defenses. These findings highlight its potential as a safe and effective biomaterial for accelerating wound healing and addressing infection-related challenges.

Tin selenide (SnSe) thin films were co-electrodeposited onto ITO/glass substrates from an aqueous solution containing tin(II) dichloride (SnCl2) and selenium dioxide (SeO2) as precursors, with ethylene diamine tetra-acetic acid (EDTA) as a complexing agent at 50 degrees C. The electrochemical behavior and co-deposition potentials of Sn, Se, and SnSe were analyzed using cyclic voltammetry. The influence of deposition potential on the structural, morphological, compositional, and optical properties of SnSe films was examined through X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, diffuse reflectance spectroscopy, and UV-Vis-NIR spectroscopy. The films consist of randomly arranged nanosheets and exhibit an absorption coefficient exceeding 104 cm- 1 in the visible range, and an optical band gap between 1.2 and 1.45 eV. The optimal sample showed the highest purity of the SnSe phase and the most desirable stoichiometric composition among all the prepared samples.

Two series of photocatalysts (TYAu, TYCeAu) were obtained. Ti was incorporated by direct synthesis with zeolite Y, while Ce and Au were immobilized by double incipient wetness impregnation method. The experimental weight percents (XRF analysis) were for titanium (0.7 %, 1.9 %, 3.5 %), Ce (1 %), and Au (0.3 %, 0.1 %). The typical crystalline structure of zeolite Y was preserved in all samples except those with 3.5 % Ti, where XRD revealed reduced pattern intensity. SEM and TEM analyses showed morphological changes at higher Ti contents. CO2-TPD confirmed a decrease in basicity with increasing Ti, consistent with the diminished zeolite contribution. XPS analysis indicated the presence of varying Au0/Au+ and Ce3+/Ce4+ ratios on the surface, depending on the Ti content. The intra- and extraframework TiO2 as amorphous or anatase phases were Raman confirmed in ceriumcontaining samples. For materials with high Ti content, the dominant effect was from the Ce and Ti species, accentuated by gold. The surface plasmon resonance effect of Au nanoparticles and decreasing in band gap energy after Ce immobilization was evidenced by UV-Vis spectroscopy. The photocatalytic properties of the synthesized materials were evaluated in CO2 reduction with water and H2 production via water splitting under visible light (525 nm). Higher Ti content enhanced CO2 conversion and reduced CH4 selectivity, favoring the production of CH3OH and CH2O. A greater amount of hydrogen was produced by the samples with the lowest Ti concentration while the reaction was favored by the presence of cerium in the rich titanium samples.