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.

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.

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.

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.

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.

Hafnium oxide (HfO2) thin films were deposited on n-type gallium arsenide (GaAs) substrates by Oxide-Molecular Beam Epitaxy (Oxide-MBE) method using Hafnium (Hf) metallic flow in an oxidizing atmosphere of 10-6 mbar molecular oxygen. The Hf metallic flow was provided by an e-beam evaporator and a deposition rate 10 nm/h was established. Semiconductor surface preparation was done prior to deposition, beginning with chemical wet etching and aggressively adjusted by in treatments until a desired stoichiometry was reached. Heterojunctions with HfO2 thin layers of 1 nm, 3 nm, 10 nm and 20 nm were fabricated. X-Ray Photoelectron Spectroscopy (XPS) and ARXPS(Angle Resolved XPS) in-situ analyses provided a clear picture of the structure of the interfaces, the chemical bonds and composition. The interfaces are chemically stable and abrupt. A small amount of Ga2O3 provides a passivating effect of the semiconductor surface. The electrical properties of the heterostructures were determined using the Kraut method and Reflection Electron Energy Loss Spectroscopy (REELS) technique. Band offsets Delta EC=1.75 eV and Delta EV=2.62 eV confirm a high application potential. Additionally, data on the morphology and continuity of the layers were obtained by Atomic Force Microscopy (AFM) technique while the amorphous growth was monitored by XRD(X-ray Diffraction), GIXRD (Grazing Incidence XRD) and XRR(X-ray Reflectivity) measurements. The dielectric layers showed values of the constant k in the range of 19-22, established by electrical measurements on MOS capacitors.

Cu2ZnSnS4 (CZTS) is an emerging material with significant potential as an absorber layer for solar cells. Precise control over the film preparation process is crucial for attaining optimal transport, electrical, and optical properties. This study investigates the effect of sulfurization duration on the properties of CZTS films deposited onto soda lime glass substrates via spray pyrolysis, followed by annealing at 550 degrees C in a sulfur-rich environment under argon flow. X-ray diffraction and Raman spectroscopy confirmed the formation of monophasic CZTS, with the highest phase purity observed for films sulfurized for 5 min. Scanning electron microscopy demonstrated notable morphological and microstructural enhancements due to the sulfurization process, while energydispersive spectroscopy confirmed near-ideal stoichiometric composition (Cu:Zn:Sn:S approximate to 2:1:1:4). Optical spectroscopy determined the band gap of the films to be between 1.40 and 1.50 eV. The electrical transport properties were investigated up to 130 degrees C, revealing p-type conductivity, with Seebeck coefficients ranging from 30 to 70 mu V K-2 and low electrical resistivity, displaying semiconductor-like behavior. The maximum power factor achieved was 0.36 mu W mK-2 at 130 degrees C for the sample sulfurized for 5 min. These findings suggest that a 5-min sulfurization time is optimal for producing single-phase CZTS films characterized by uniform morphology, accurate stoichiometric composition, and an ideal direct band gap. Given its favorable thermoelectric properties, CZTS shows significant promise as a material for thermoelectric applications, particularly in waste heat recovery systems. The results indicate that CZTS films could be further optimized for use in thermoelectric devices, and future studies could focus on enhancing their thermoelectric performance by adjusting sulfurization conditions and exploring material modifications.

Synthetic bone graft substitutes, including calcium phosphates (CaP), bioactive glasses (BG), and their composites with biopolymer matrices are attracting interest for bone tissue repair and regeneration. A key challenge is accurately replicating the biological structure and functionality of natural bone and optimizing the porous structure to match trabecular bone. This has been addressed by doping CaPs with therapeutic ions and using scaffolding methods like polymeric sponge replication and different additive manufacturing techniques. Biomimetic approaches employing naturally occurring porous biominerals with pore sizes comparable to those of trabecular bone, offer promising alternatives. This work reviews the hydrothermal transformation of cuttlefish bone (CB) into CaP scaffolds, while preserving its original porous structure, producing hydroxyapatite (HA, Ca10(PO4)6(OH)2), tricalcium phosphate (TCP, Ca3(PO4)2), and biphasic CaPs, both undoped and therapeutic ion-doped, constructs. Coating such biomimetic scaffolds with sol-gel-derived BG and biopolymers produces multifunctional bone graft substitutes with enhanced mechanical and biological properties. Moreover, polymeric coatings can act as drug reservoirs, enabling controlled release of therapeutic agents. The review highlights that integrating biomimetic strategies with advanced coating solutions holds great promise for creating multifunctional scaffolds that mimic nature and improve therapeutic outcomes in bone tissue engineering.

This study investigates the optimization of multiwalled carbon nanotube (MWCNT) concentration in polysiloxane-based nanocomposites to enhance the performance of triboelectric nanogenerators (TENGs). Flexible nanocomposite films were fabricated using the doctor blading method, and their triboelectric output was systematically evaluated as a function of MWCNT loading. The results reveal that incorporating MWCNTs significantly improves the electrical performance of the TENG, with the open-circuit voltage (V oc) and short-circuit current (I sc) increasing to 51 V and 5.7 mu A, respectively, at an optimal concentration of 0.05 wt %, compared to 32 V and 3.3 mu A for pristine polysiloxane films. However, further increasing the CNT content to 0.1 wt % led to a notable decline in output, attributed to nanoparticle agglomeration, which hinders effective charge transfer and promotes charge leakage. These findings underscore the crucial role of nanofiller dispersion and concentration control in the development of high-performance TENGs. This work provides valuable insights into the development of flexible, nanocomposite-based energy harvesting systems with enhanced output efficiency for wearable and portable electronic applications.