National Institute Of Materials Physics - Romania

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.

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.

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.

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.

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.