Publications

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.

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.

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.

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.

Some alloys exhibit not only shape memory but also thermal memory, retaining information about the highest temperature reached during heating. This phenomenon occurs when the alloy starts in the martensite phase and is then heated up to an "arrest temperature" that lies strictly within the martensite-austenite transformation range, without the transformation being completed. The "reading" of this memory is performed by cooling the alloy back into martensite and then reheating it to full austenite in a calorimeter, where the phase transition heat flow displays a dip near the arrest temperature. This unique behavior naturally qualifies such materials as temperature sensors, more precisely as maximum thermometers, which by definition indicate the maximum temperature reached during a given time interval. In this paper, we extend existing thermal memory studies to various polycrystalline shape memory alloys with Heusler structure, prepared by rapid solidification and based on NiFeGa (with Co, Al, Gd, Nd additions) and NiMnGa compositions. We analyze the possibility of shifting the transformation temperatures - and implicitly the thermal memory sensitivity range - through composition variations and thermal treatments. The thermal memory effect was consistently observed, and in fact quite readily, across all samples at various temperatures within the sensitivity interval. In contrast to classical maximum thermometers, these materials are capable of also memorizing multiple temperatures, as long as they are recorded in a strictly decreasing order. The use of sample groups and calibration aspects are discussed. Finally, we emphasize that shape memory alloys with these compositions and preparation methods show potential for recording temperatures across a wide range - from 0 degrees C to above 100 degrees C. A statistical geometry model, based on the redistribution of the martensite plates sizes, qualitatively reproduces the observed thermal memory features.

Diamond traceability has been a major challenge for the gemological industry in recent decades. In this context, this paper presents new studies using UV-VIS-NIR spectroscopy to identify the traceability and geographical origin of diamonds. The aim of the work is to identify characteristic centers of fancy-color diamonds collected from Cullinan Mine, Democratic Republic of Congo (DRC), and the geographical regions with unknown origin. Depending on the origin of the diamonds, the UV-VIS-NIR spectra can be differentiated as follows: (i) the diamonds collected from Cullinan Mine show absorption bands assigned to N10, NV0, NV-, N3V0, N4V2, and N4V centers, which are accompanied by a vibronic structure localized between 415 and 394 nm (2.987-3.147 eV) and (ii) the diamonds from DRC show absorption bands attributed to N10, NV-, N3V0, N1+, and NVH centers. Using Raman spectroscopy, nitrogen concentration values of diamonds collected from the Cullinan mines and DRC between 41 and 185 ppm and 204-336 ppm, respectively, were reported. We prove that the simultaneous applicability of UV-VIS-NIR spectroscopy and Raman scattering as comparative tools for assessing diamond provenance can be a valuable strategy for an initial attribution of diamonds with unknown geographical origin, knowing the optical features of diamonds collected from Cullinan Mine and DRC.

The rational integration of different-dimensional nanostructures offers a powerful platform for engineering synergistic functionalities in photocatalysis. Herein, we report the controllable synthesis of novel 2D/1D graphene/silver-silver sulphide (Ag-Ag2S) hybrid nanocomposites, wherein 1D Ag-Ag2S nanowires (NWs) are uniformly anchored onto conductive graphene sheets, affording a hierarchical hybrid structure with tailored optoelectronic properties. Structural characterization via X-ray Diffraction (XRD) confirmed the coexistence of crystalline Ag, Ag2S, and Ag2O phases, evidencing both hybridization and partial oxidation during growth. Complementary Scanning Electron Microscopy (SEM) imaging revealed a homogeneous distribution of NWs across the graphene scaffold, ensuring maximized interfacial contact. Optical investigations demonstrated distinct band gap features (2.5 eV for Ag2S, 3.8 eV for Ag NWs, and 4.6 eV for Ag2O). In comparison, the composite exhibited dual transitions at 3.28 eV and 4.72 eV, attributed to interfacial charge transfer between Ag2S and graphene, alongside enhanced plasmonic carrier dynamics. FTIR analyses further corroborated the hybrid composition, highlighting O-H and C 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 C stretching vibrations of graphene, CO bands from surface PVP ligands, and Ag-S/Ag-O vibrational modes consistent with XRD assignments. Harnessing these tailored structural and electronic attributes, the graphene/Ag-Ag2S heterostructures exhibited markedly superior photocatalytic activity toward methylene blue (MB) degradation, achieving a maximum efficiency of 89.55% under acidic conditions (pH 3) after 300 min of irradiation. Kinetic analysis revealed the highest rate constant (0.386 min-1) for the graphene/Ag-Ag2S nanocatalyst in acidic medium, surpassing both pristine Ag NWs and Ag-Ag2S. This work highlights the potential of spatially engineered graphene-based heterostructures to modulate band structures, enhance charge carrier transport, and thereby improve selective photocatalytic dye removal.

Background: Hepatocellular carcinoma is associated with high mortality and increasing incidence. Sorafenib, a cornerstone of therapy for advanced hepatocellular carcinoma, presents certain disadvantages, including low bioavailability and poor water solubility. This work describes a new strategy for sorafenib-targeted delivery aimed at improving treatment efficiency and reducing side effects. Methods: Magnetic nanoparticles coated with azelaic acid were modified with aptamer molecules that specifically recognize human liver cancer cell line HepG2, ensuring specificity for the tumor tissue. The nanoparticles were further loaded with sorafenib. The obtained drug delivery system was extensively characterized using UV-Vis spectrophotometry, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. Results: The drug delivery system demonstrated a higher release of sorafenib at acidic pH compared to pH 7.4. The cell internalization of the bare and aptamer-modified magnetic nanoparticles was assessed in HepG2 and human normal foreskin fibroblasts BJ cell lines, demonstrating that the aptamer significantly enhances internalization in tumor cells, while having no impact on healthy cells. Conclusions: The sorafenib-modified nanoparticles exhibited excellent cytocompatibility with BJ cells across all tested concentrations, while showing cytotoxicity towards HepG2 cells at higher concentrations, confirming the selectivity of the system.

Despite the promise of high-k dielectrics, inherent limitations persist in transistor scaling and enhancing energy efficiency, including a fundamental threshold of 60 mV/dec for increasing drain current by an order of magnitude. Proposed solutions involve negative capacitance at the gate oxide to overcome this barrier using ferroelectric structures. Efforts to understand and regulate the switching dynamics and intricate electrostatic configurations of ferroelectric structures towards achieving negative capacitance regimes have intensified. While standalone ferroelectric capacitors cannot stabilize negative capacitance without external fields, multilayered thin films offer a promising solution. Typically, ferroelectric layers are paired with dielectrics/insulator, demonstrating steady-state negative capacitance, often at nanoscale or specific temperature domains. This study aims to stabilize negative capacitance in ferroelectric structures by inducing internal electric fields, aligning the system near coercivity, particularly in bilayer structures formed by two ferroelectric layers with slight differences in polarization values, such as p-n heterojunctions using Pb (Zr,Ti)O3 PZT) with different doping as Fe, Nb, Bi. Most of these structures exhibit evident amplification of capacitance compared to the equivalent series-connected capacitance, across a large temperature domain. The complex capacitance-frequency characteristic of these structures indicates a complex equivalent circuit. Analysis of these complex circuits compared with simple component layers concludes that at least one of the FE layers in these bilayer structures is in a negative capacitance (NC) state.

Cerium dioxide (CeO2) thin films with pyramidal nanostructures exhibiting a fractal aspect are suitable for various applications that require a large surface area. An accurate model of these films is valuable not only for optimizing the properties for specific applications but also for predicting and understanding the growth mechanism. In this paper, we present the foundation of a simulation for the growth of CeO2-x nanostructured thin films. We propose a 3-dimensional model of the surface nanostructures and link the morphology with crystallographic orientations and growth modes. To validate our model, we fabricated CeO2_ x thin films with different thicknesses using pulsed laser deposition (PLD) and characterized their morphological and structural properties. The evolution of our films shows the representative features of the Stranski-Krastanov model. The morphology changes from compact and smooth to dendritic with pyramidal nanostructures. The texture of our film also changes with thickness, and the preferential orientations are (111) and (220). Additionally, we characterize the CeO2_ x thin films from the chemical and optical points of view. The stoichiometry of CeO2 is not fully achieved, our thin films present the Ce3+ oxidation state at the surface. The formation of C-type Ce2O3 with fluorite structure can be associated with a small refractive index and small band gap.