Publications

The elusive X-Defect, a defect found in low-resistivity p-type Silicon after irradiation, observed as a low-temperature shoulder of the BiOi defect (Boron-interstitial-Oxygen-interstitial complex) in Thermally Stimulated Current (TSC) measurements, was investigated to determine its properties, matching them with those of a previously identified defect. Through a combination of TSC, Deep-Level Transient Spectroscopy (DLTS), Difference-DLTS (DDLTS), numerical simulations of field-enhanced charge carrier emissions in TSC measurements and a comparison to literature, the X-Defect was identified as the singly positively charged Silicon di-vacancy V2(+/0). This assignment is supported by an agreement in activation energy, capture cross-section, trap type and charge emission process, as well as simulations comparing the effects of phonon-assisted tunnelling (PAT) and Poole-Frenkel (PF) mechanisms on TSC spectra. DDTLS measurements revealed a quadratic dependence of the activation energy on the electric field strength, confirming PAT as the prevailing mechanism over PF in the case of the radiation-induced X-Defect. Assigning the X-Defect to an electrically neutral defect in the space charge region resolves previous contradictions regarding its lack of impact on the effective doping concentration Neff.

A new mechanism is proposed for polarization switching in metal-ferroelectric-metal (MFM) structures. The switching is triggered by charge injection at electrode or grain interfaces under an external field, opposite to the initial direction of polarization. Such injection destabilizes the compensation of the polarization, and is favored by disappearance of Schottky barriers at interfaces, leading to a resistive like behavior. At the coercive voltage the depolarization field is no longer compensated and the polarization change orientation parallel to the applied field. After switching, the Schottky barriers are restored and the current start to decrease although the voltage continues to increase. This leads to a differential negative resistance until the barriers are totally restored, polarization saturated on the new direction and the depolarization field annihilated by the injected charges. In a perfect structure the switching takes place homogeneously, while the defects presence induces domains via local nucleation and fields. The model is supported by theory, showing that at switching the MFM structure has a resistive like behavior, and by experiments, showing that the voltage dependence of the current during switching is linear and that the phase change at switching, in PFM measurements performed on high quality epitaxial films, is abrupt. The analysis was performed on MFM structures based on different ferroelectric layers (e.g. Pb(Zr,Ti)O3, BaTiO3, BiFeO3 or (HfZr)O2), different metal electrodes and different structural qualities. It appears that polarization switching triggered by charge injection at interfaces is a mechanism that can be applied to all MFM structures based on oxide ferroelectrics.

Simonkolleite nano-platelets, with the chemical formula Zn-5(OH)(8)Cl-2 center dot H2O (ZHC), both undoped and Mndoped, were synthesized by a wet-chemical synthesis method. The physicochemical properties of the materials have been investigated using several complementary experimental techniques, including powder X-ray diffraction, specific surface area and porosity measurements, Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray Fluorescence, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. On the one hand, the morpho-structural characteristics of the material are not significantly affected by the dopant used at low concentrations; however, the textural characteristics, specifically the specific surface area and porosity, vary with the Mn concentration. On the other hand, the cellular response of skin cells (human fibroblasts and mouse melanoma) exposed to undoped and Mn-doped ZHC was assessed, revealing a certain dependency on the Mn concentration. It was observed that the cells' response could be correlated with both the dopant concentration and the exposure time of the cells, independent of the morpho-textural characteristics of the materials. Even at the low Mn amounts used in this study, the cells' response depends on the Mn concentration, thus showing drastic cytotoxicity in human fibroblast cells at concentrations higher than 0.25 mu g/mL, irrespective of the exposure time (24 or 48 h), but showing low cytotoxicity at concentrations lower than 0.25 mu g/mL. In contrast, the presence of Mn does not drastically affect mouse melanoma cells, even at concentrations higher than 0.5 mu g/mL, but this depends on the exposure time. To our knowledge, this is the first study on the effects of Simonkolleite on skin cells, and it is of great interest considering the current and potential applications of this material in skin wound treatment and animal food supplements.

VO2-based thermochromic thin films are promising for energy-efficient smart window applications due to their reversible metal-insulator transition near 68 degrees C. However, practical limitations such as high transition temperature, limited visible transmittance and substrate compatibility remain challenges. In this study, VO2/TiO2 bilayer thin films were deposited by PLD on glass, fused silica, and quartz substrates to investigate the effect of buffer layer, film thickness, and strain on their structural, optical, and electrical properties. Comprehensive characterization using in situ grazing incidence X-ray diffraction, synchrotron GIXRD, and high-resolution Transmission Electron Microscopy revealed that TiO2 buffer layers, in the anatase or brookite phase, significantly influences the growth orientation and strain distribution in VO2 films. Residual strain mapping indicated up to 5 % compressive strain in VO2 and >10 % tensile strain in the TiO2, promoting partial stabilization of the intermediate M2 phase. Thickness-dependent studies showed a strong trade-off between optical transmittance and electrical switching amplitude: thinner films exhibited higher luminous transmittance (up to 30 %) and sharper IR switching, while thicker films yielded larger resistivity switching contrast. These results demonstrate that interfacial strain, film thickness, and substrate choice are critical parameters for tailoring VO2-based coatings and optimizing thermochromic performance for scalable smart window technologies.

This study explores strategies to enhance the ionic conductivity of LiTi2(PO4)(3) (LTP), a promising NASICON-type solid electrolyte for next-generation solid-state batteries. Although LTP exhibits an open-framework structure favorable for Li+ diffusion, its intrinsic low ionic conductivity limits practical application. To address this, this research investigates the impact of co-doping titanium (Ti4+) with iron (Fe3+) and yttrium (Y3+) in Li1+xFeyYx-yTi2-x(PO4)(3) (where x = 0.3 and y = 0.1, 0.15, 0.2), aiming to increase charge carrier concentration and induce structural distortion beneficial for ion transport. Samples were synthesized via solid-state reaction and characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The local environment of Fe3+ was further analyzed using electron paramagnetic resonance and Mossbauer spectroscopy. Spark Plasma Sintering (SPS) was employed to obtain dense ceramics and suppress secondary phase formation. The electrical properties were investigated by impedance spectroscopy over the 150K-400K temperature range, and the relaxation dynamics and conduction mechanisms were analyzed using the modulus formalism and a.c. methods conductivity. The Li1.3Fe0.15Y0.15Ti1.7(PO4)(3) composition exhibited the highest room-temperature conductivity of 8.21 x 10(-4) S/cm, confirming the combined effect of Fe3+/Y3+ co-doping and SPS densification in enhancing the ionic transport properties of LTP-based solid electrolytes.

Carbon nanotubes (CNTs) represent promising nanoplatforms for drug delivery due to their high surface area, tunable surface chemistry, and unique physicochemical properties. This study investigated the effect of chemical functionalization on the dispersion, drug loading, release behavior, aerosolization, and preliminary in vitro cytotoxicity of CNT-based drug delivery systems, with a view toward potential intranasal applications. Pristine CNTs and CNTs functionalized with hydroxyl (-OH) and carboxyl (-COOH) groups were loaded with methylene blue as a model therapeutic compound. The nanosystems were characterized using Raman spectroscopy, UV-Vis analysis, aerosol deposition measurements, electrical mapping by conductive atomic force microscopy (C-AFM), and MTT cytotoxicity assays. Functionalization significantly enhanced CNT dispersion stability and drug release control, with COOH-CNTs exhibiting the most sustained release profile and improved cytocompatibility, maintaining cell viability above XX% at concentrations up to YY & micro;g/mL. Aerosolization tests demonstrated stable droplet formation compatible with nasal delivery devices. Overall, this work provides a proof-of-concept physicochemical and technological assessment of functionalized CNTs as potential carriers for intranasal drug delivery, laying the groundwork for future in vivo validation.

A hybrid hydroxyapatite/chitosan/microcrystalline-cellulose (CaHAp-CS-MCC) biocomposite was synthesized via a co-precipitation-lyophilization route and comprehensively characterized for potential biomedical applications. X-ray diffraction confirmed the formation of a single-phase hexagonal hydroxyapatite (P-63/m, JCPDS 09-0432) with an average crystallite size of similar to 15 nm and slight lattice contraction induced by polymer incorporation. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy evidenced strong interfacial bonding between hydroxyapatite phosphate groups and the amino and hydroxyl functionalities of chitosan and cellulose. Microscopic analyses (SEM, AFM) revealed a denser, rougher surface with root-meansquare roughness rising from 9 to 36 nm, accompanied by modified particle distribution. Nitrogen adsorption-desorption (BET) analysis indicated a decrease of specific surface area (139 -> 12 m(2) g(- 1)) and an increase of pore diameter (7.4 -> 13.3 nm), confirming partial pore filling by the organic matrix. Hemolysis indices below 2 % and >90 % HeLa-cell viability after 72 h indicated excellent hemocompatibility and cytocompatibility. The synergistic integration of crystalline hydroxyapatite with flexible, bioactive polymers yields a stable and biocompatible composite suitable for bone regeneration, implant coatings, and other advanced biomedical applications.

Monitoring superoxide anion in chronic wounds is critical for understanding oxidative stress and guiding personalized treatment. We present a novel electrochemical biosensor enabling real-time superoxide detection in cell culture, integrating enzymatic selectivity with a biocompatible electrospun membrane for direct tissue contact. The biosensor employs screen-printed electrodes (SPE) modified with electropolymerized poly(3,4ethylenedioxythiophene) (PEDOT), which enhances enzyme immobilization and signal transduction, with superoxide dismutase (SOD) for enhanced selectivity. The analytical performance of SPE/PEDOT/SOD biosensor was evaluated by fixed potential amperometry at +0.3 V with a sensitivity of 130.3 +/- 5.6 mu A cm- 2 & sdot;mM- 1, and a 1.5 mu M detection limit. A cell-based wound model was developed to simulate chronic wound conditions, using an adhesive membrane modified with electrospun Nylon fibers that provided a biocompatible surface for cell adhesion and proliferation. Cells cultured on the membrane were irradiated with UV light to induce superoxide generation, mimicking oxidative stress in chronic wounds. Although the membrane introduced a diffusion barrier that reduced sensitivity by 40 %, it ensured close contact between cells and the electrode surface, enabling accurate in situ quantification of superoxide. Chronoamperometric detection at +0.3 V revealed sharp photocurrent peaks followed by decay, consistent with ROS generation and enzymatic clearance. The PEDOT matrix exhibited a photo-amplifying effect, nearly tripling the sensitivity under UV irradiation. The developed device is suitable for real-time oxidative stress profiling in wound models with potential for ex vivo and in vivo applications.

Topological materials are promising electrocatalysts for the hydrogen evolution reaction (HER) because of their protected electronic states and exceptional carrier mobility. Among them, the topological metal Pt3Te4 (mitrofanovite) exhibits low Tafel slopes in the nanocrystals. Realizing this potential in scalable catalyst systems requires nanoscale texturing coupled with precise control of the surface chemistry under operating conditions. Herein, we demonstrate that hydrogen peroxide (H2O2)-assisted liquid-phase exfoliation (LPE) of bulk Pt3Te4 yields nanoporous nanosheets that retain their metallic character and are chemically preconditioned to develop a bias-controlled PtO2 skin that governs the catalytic activity. Crucially, spectromicroscopy resolves termination-selective oxidation: PtO2 forms exclusively on PtTe2-like terminations, whereas Pt2Te2 terminations remain metallic. Operando ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) in an electrochemical cell revealed the bias-dependent emergence of surface oxide phases in H2O2-treated nanosheets. The joint effect of the higher accessible site density imparted by nanoporosity and the emergence of a bias-controlled PtO2/PtTe2-terminated Pt3Te4 surface junction rationalizes the improved catalytic activity: the overpotential at 10 mA cm-2 decreases by similar to 30% (from 113.1 to 78.7 mV), while the exchange current density more than triples (from 0.106 to 0.347 mA cm-2), all with an unchanged Tafel slope (similar to 53 mV dec-1) and sustained stability over 50 h in acid. By combining a single scalable top-down step with operando proof that the catalytically active oxide is switched on by bias rather than being a static passivation layer, this study establishes a precise interface-engineering principle for Pt3Te4 nanosheets and a practical path to efficient, scalable HER catalysts based on nanosheets of topological metals.

Gold nanorods (AuNRs) were synthesized and optimized with the aim of obtaining strongly hydrophilic nanomaterials, suitable as a drug delivery system (DDS) for copper-based drugs. After careful purification, AuNRs were characterized by ultraviolet-visible-near-infrared spectroscopy (UV-Vis-NIR), showing two typical localized surface plasmon resonance (LSPR) bands in the range 550-750 nm. Fourier Transform Infrared (FT-IR) and high-resolution X-ray photoelectron (HR-XPS) spectroscopies verified the surface functionalization. Transmission electron microscopy (TEM) showed AuNRs with regular shape and size, with an aspect ratio (AR) of 2.6. Dynamic Light Scattering (DLS) measurements confirmed the size and the stability in water for up to 3 months. The AuNRs were conjugated with copper(I) drugs, i.e., [Cu(PTA)4]BF4 (PTA = 1,3,5-triaza-7-phosphadamantane). The drug loading procedures and efficiency were optimized, and the best loading was eta (%) = 50 +/- 7%. The non-covalent interactions of the Cu(I) complex with the AuNRs were studied by means of UV-Vis-NIR, zeta-potential, HR-TEM, FT-IR, synchrotron radiation-induced X-ray photoelectron (SR-XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. The MTT assay performed on Vero E6 cells showed that AuNRs and AuNR-Cu(I) conjugates had no significant effect on cell viability, being biocompatible, causing a reduction in cell viability only after prolonged exposure.