National Institute Of Materials Physics - Romania

The present research explores for the first time the intricate relationship between sulfurization temperature at unusual high temperatures (up to 700 degrees C) and the structural/optoelectronic properties of Cu-2(Zn,Cd)SnS4 (CZCTS) thin films, synthesized via a two-step sequential process involving the precursor film deposition using aprotic molecular ink followed by thermal treatment in sulfur atmosphere. X-ray diffraction patterns confirms the tetragonal structure. Scanning Electron Micrographs revealed significant grain growth, with grain sizes increasing from similar to 0.3 mu m at 620 degrees C to similar to 1.5 mu m at 680 degrees C, effectively reducing grain boundary recombination. Energy dispersive X-ray spectroscopy demonstrated a Cu-poor and Zn-rich composition, with a consistent Cd incorporation of similar to 3.7 at%. Raman spectroscopy showcases the homogeneity and purity of the CZCTS crystalline structure. Precise control of the sulfurization temperature plays a crucial role in determining the photovoltaic characteristics of CZCTS-based solar cells. By increasing the grain size and preventing the thermal decomposition of the CZTS phase, the photovoltaic performance peaked at a sulfurization temperature of 680 degrees C, achieving a power conversion efficiency (PCE) of 10.4%, with an open-circuit voltage of 0.701 V, a short-circuit current density of 24.3 mA/cm(2) and a fill factor of 60.8%. External quantum efficiency reached a maximum of 83.3% at 580 nm. The bandgap of the CZCTS absorber was determined to be 1.48 eV, optimal for photovoltaic applications. However, further increasing the sulfurization temperature to 700 degrees C resulted in a lower PCE of 8.5%, attributed to interface degradation and secondary phase formation. Temperature-dependent current-voltage measurements revealed a reduction in recombination losses, with an activation energy of 1.24 eV at the CZCTS/CdS interface, indicating effective defect passivation by Cd incorporation. The optimized films, sulfurized at 680 degrees C, displayed an absorber thickness of similar to 1.2 mu m after sulfurization, providing efficient light absorption and charge transport. The findings not only emphasize the critical role of sulfurization temperature in engineering CZCTS film and subsequently their functionality but also provide valuable insights for fine tuning their performance in the field of photovoltaic applications.

A multiphase high-entropy diboride (Ti0.25Ta0.25Hf0.25Zr0.25)B2 is obtained by spark plasma sintering from a mixture of single-metal diborides. The as-prepared material at the microscale can be defined as a composite where grains of a Ta-rich/Ti-poor complex diboride phase are the reinforcement and grains of Ta-poor/Ti-rich complex diboride are the matrix. However, at the nanoscale, the grains are heterogeneous, composed of regions with a multitude of complex diboride compositions. The interface between nanoregions is compositionally graded and has an irregular shape. The four-metal diboride shows a deformation-resistant mechanism under bending load. A strengthening process is active, increasing the room temperature bending strength (326 MPa) by approximate to 50% at 1800 degrees C (488 MPa). A ductile behavior with a deformation strain of approximate to 7.5% is observed at 2000 degrees C while bending strength (407 MPa) is approximate to 25% above the value at room temperature. At 2000 degrees C, observation of dislocations propagating from one compositional nanoregion to another and with a different density suggests dislocation contribution, first of all, to plasticity. The peculiar heterogeneity of this material at nano- and microscales is considered the reason for the remarkable mechanical response to bending load at different temperatures.

This study presents annealing time variation as an alternative approach for tuning structural and ionic defects in SnO2 nanoparticles (NPs) synthesized by a modified Pechini method, to modulate charge transfer and the formation of reactive oxygen species (ROS), enabling a correlation of these with photocatalytic activity. Structural refinements of the X-ray diffraction (XRD) data, combined with Raman and infrared (IR) spectroscopy, revealed that the samples adopted a tetragonal P42/mnm symmetry, with a distinct short-range structural order (associated with intraoctahedral [SnO6] distortions), which strongly depends on the annealing time. Field emission scanning electron microscopy (FE-SEM), scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (STEM/EDX), high-resolution transmission electron microscopy (HRTEM), and Brunauer-Emmett-Teller (BET) analyses showed the formation of homogeneous NPs smaller than 50 nm in the SnO2 samples, with a surface area between 12.072 and 14.102 m2 g-1. The presence of unusual reduced Sn3+ species associated with oxygen vacancies (VO) was evidenced by electron paramagnetic resonance (EPR) spectroscopy, and Sn2+ was characterized by Sn MNN Auger electron emission. The amount of these defects also depends on the annealing time. The synergistic effect and the photocatalytic mechanism were then elucidated. The degree of intraoctahedral [SnO6] distortions and the amounts of Sn3+:VO defects play a fundamental role in the charge transfer mechanism to modulate ROS generation during photoexcitation, as indicated by the photohydroxylation of terephthalic acid (TA) and in situ spin-trapping EPR measurements. Specifically, we show the formation of two main ROS, center dot OOH and center dot OH, which leads to a different photocatalytic pathway in SnO2 NPs. In conclusion, our study enlightens and uncovers the importance of choosing appropriate conditions for materials processing to fine-tune structural and electronic properties to design other functional materials.

The present study investigates the influence of strontium (Sr) content on the intrinsic properties of barium strontium titanate (Ba1-xSrxTiO3, BST) which was successfully prepared by the conventional solid-state reaction with different concentrations of strontium (x = 0, 0.3, 0.5, 0.6, 0.7, 1). The resulting samples were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and diffuse reflectance spectroscopy, the dielectric properties being also investigated. Structural and vibrational analyses reveal a structural phase transition from tetragonal to cubic at x = 0.4, with a linear decline of the tetragonality ratio as well as a shrinkage in the unit cell volume that occur with increasing Sr content. The morphological study shows that the grain size decreases as the Sr content increases in the tetragonal phase. Yet, upon the phase transition from tetragonal to cubic, the grain size initially increases, followed by a subsequent decrease with further Sr addition. It has been found that the band gap shows a decrease as Sr content increases. The temperature dependence of the dielectric parameters reveals that the Curie temperature as well as the dielectric constant and the loss tangent are strongly affected by the addition of Sr. The activation energy derived from the dielectric response, was found to be in the range 0.685-1.065eV, suggesting the dominance of doubly ionized oxygen vacancy for conduction and relaxation mechanism. Ab initio calculations were done employing the Linear Combination of Atomic Orbitals (LCAO) method. The bandgap energy (Eg) and the structural parameters were calculated using various types of exchange-correlation functionals (PWGGA, PBE, B3LYP and PBE0). A good agreement with the experimental results is achieved using the PBE0 functional. This study contributes to a better understanding of the structure-property relationship in BaSrTiO3 and provides valuable insights for optimizing its performance in various technological applications.

The study of spectral gamma-ray logs plays a critical role in understanding the lithofacies and depositional environments of subsurface geologic formations. This research focuses on the Lam Member within the Habban oilfield, located in the Sab'atayn Basin, Yemen. By integrating spectral gamma-ray data with core analysis and other geological datasets, this study aims to provide insights into the stratigraphic distribution, mineral composition, and depositional processes of the Lam Member. Key parameters, such as thorium, uranium, and potassium concentrations, recorded from two wells were analyzed to infer sedimentary characteristics and environmental conditions. The results reveal significant lithologic heterogeneity and suggest a complex interplay of fluvial and marine depositional systems, enhancing the understanding of the basin petroleum potential. The Lam Member comprises interbedded carbonate (dolomite) and claystone with intercalated sandstone. Spectral gamma-ray results indicate that clay minerals primarily consist of mixed-layer clays, chlorite, kaolinite, and minor illite. Based on the Th/U ratio (less than 2), the depositional environment is identified as marine.

Amyloid beta (A(3) peptide aggregates are well-established biomarkers for Alzheimer's disease, though the complete etiology of this disorder remains elusive. Developing biointerfaces to elucidate the physiological roles of these peptides is essential. This study investigates the aggregation, fibrillation, and interaction of A(3 peptides with conductive, biocompatible nanostructured materials designed for applications involving neuronal cells. Various conductive, rigid, and flexible surfaces, both functionalized and non-functionalized with A(340 fibrils, were fabricated. These included glass substrates and poly(methyl methacrylate) electrospun fiber networks coated with gold via magnetron sputtering. The substrates were also functionalized through physical adsorption with poly-L-lysine and collagen, known to support cell proliferation, as well as with the inverse-A(340 peptide and an Amyloid Protein Non-A(3 Component, and the results were compared. The scaffolds were characterized using scanning electron microscopy, X-ray diffraction, atomic force microscopy, contact angle and electrical measurements, while their biological interactions were assessed using MTS assays, fluorescence imaging, and scanning electron microscopy. Fibroblast L929 and neuroblastoma SH-SY5Y cell lines were used as models, with results indicating an elevated cell viability, comparable to the control. The developed nanostructured surfaces are highly promising for integration into advanced neuromorphic engineering devices, as they have proven capable of maintaining their structural integrity when exposed to proteases.

Background/Objectives: In this paper, we report the development of the first chrome-doped hydroxyapatite in a poly (vinyl alcohol) (PVA) matrix enriched with amoxicillin for biomedical applications. The development of chromium-doped hydroxyapatite coatings in a PVA matrix enriched with amoxicillin aims to provide new biomaterials with improved physico-chemical and biological properties, making them promising candidates for biomedical applications. Methods: Through ultrasound studies, we obtained valuable information on the stability of the samples. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, metallographic microscopy (MM), and atomic force microscopy (AFM) were employed for the characterization of the samples. The biocompatibility of the CrHApAPV and CrHApAPV-Ax coatings was assessed using the MG63 human osteoblast-like cell line. To evaluate the cytotoxic potential of these coatings, the cell viability was quantified using the MTT assay after 24 h of incubation. The antibacterial activity of the coatings was evaluated with the aid of the reference strain Pseudomonas aeruginosa ATCC 27853 (P. aeruginosa). Results: The XRD patterns of CrHApAPV and CrHApAPV-Ax samples were examined to evaluate the effects of PVA and amoxicillin on the lattice parameters, unit cell volume, and average crystallite sizes. The results of the in vitro antibacterial assay demonstrated that both the CrHApAPV and CrHApAPV-Ax coatings exhibited very good antibacterial properties for all the tested time intervals. Conclusions: Our results underline the stability of the analyzed samples. Moreover, our physico-chemical and biological studies highlight that CrHApAPV and CrHApAPV-Ax coatings could be considered promising materials for biomedical uses.

This study presents an ultrasound-assisted synthesis of (3-cyclodextrin/hydroxyapatite composites to be used as green and safe auxiliaries in the tanning process. A combination of spectroscopic and non-spectroscopic techniques such as DLS (dynamic light scattering), ZP (zeta potential), XRD (X-ray diffraction), SEM (scanning electron microscopy) and ATR-FTIR (attenuated total reflectance-Fourier transform infrared spectroscopy) were used to thoroughly characterize the eight composites obtained by varying the ultrasound process parameters. While not cytotoxic, all composites had strong antibacterial action against Brevibacterium lines, Staphylococcus aureus, Escherichia coli, and Staphylococcus epidermis. All composites underwent lab-scale tanning tests, but only those exhibiting the most suitable set of tanning abilities underwent pilot-scale testing. The composites' interaction with the collagen matrix was assessed by micro-DSC (micro-differential scanning calorimetry), TG/DTG/ DTA (thermal analysis), 1H unilateral NMR (proton nuclear magnetic resonance), ATR-FTIR, in-situ temperature synchrotron-based XRD and standard tests (UNI EN ISO 3380: 2015, UNI EN ISO 2589: 2016, UNI EN ISO 105B02:2014). Thermal stability, dye penetration, thickness, colour fastness, surface appearance and microbiological protection were all improved for the leather treated with a small amount of composite added to the wet finish float. These findings demonstrate the benefits of (3-cyclodextrin/hydroxyapatite composites as safe and sustainable tanning additives.

We present a comprehensive investigation into the synthesis, phase evolution and valence state of vanadium (V) in V1_xFexO2 (x = 0 %, 0.5 %, 0.75 %, 1.0 %) compounds. Polycrystalline samples have been synthesized with solid-state reaction method, followed by thermal annealing. X-Ray Powder Diffraction (XRPD) analyzed by Le Bail method revealed the transformation from monoclinic (M1) phase (space group: P21/c) to triclinic (T) one with increasing Fe concentration. Additionally, a monoclinic (M2) phase (space group: C2/m) emerged at 1.0 % Fe doping. Temperature-dependent XRPD and diffuse reflectance measurements elucidated the phase transitions during heating cycles, showing the impact of Fe doping on the system's behavior. The construction of a complete phase diagram for the V1_xFexO2 system (x <= 1.0 %) was achieved, addressing ambiguities in the low-Fe concentration region. X-ray Photoelectron Spectroscopy (XPS) further confirmed the influence of Fe doping on the vanadium valence states, indicating an increase of V5+ sites and therefore a lattice distortion and stabilization of the triclinic phase. The metal-insulator transition temperature (TMIT) appears to be almost constant. Post-annealing led to the reinstatement of the M1 phase in all samples, and a modified phase diagram was constructed. The accompanied decrease of V5+ ions contributed to the destabilization of the T and M2 phases, favoring the thermodynamically stable M1 phase. The findings provide valuable insights into the complex phase behavior of V1_xFexO2 compounds, showcasing a significant interplay between charge redistribution, the vanadium valence state, and the oxygen defects of the system.

In this study, we developed a ternary nanocomposite using graphene oxide (GO), multiwalled carbon nanotubes (MWCNTs), and tungsten trioxide (WO3), nanostructures, synthesized via a straightforward chemical process with ultrasound assistance. The initial composition was GO/MWCNT, later combined with WO3 to form the GO/ MWCNT: WO3 (25/25:50) structure. Characterization was performed using X-ray diffraction, which revealed the multiphase nature of the WO3 nanostructures. Scanning Electron Microscopy showed the one-dimensional CNTs interwoven with graphene oxide sheets decorated with densely populated WO3 nanopetals. Fourier transform infrared and Raman spectroscopy confirmed the chemical composition of the system. The photocatalytic degradation of Rhodamine-B in water under visible light irradiation was significantly enhanced using the GO/