National Institute Of Materials Physics - Romania

Magneto-optical measurements enable the identification of Fe2+ and Fe3+ in the R and S blocks of BaFe12O19 Mhexaferrite powder obtained by sol -gel processing, followed by thermal annealing at 900 C for 3 hours. The ferromagnetic phase is evidenced by the spin-majority configuration (Fe3+) due to their unpaired electrons between d -d orbitals, while the Fe2+ in the low spin possesses diamagnetic behavior strongly dependent on the surrounded crystal field. Additionally, the irradiation with gamma rays changes the ratio between Fe2+/Fe3+, mainly on the surface of BaFe12O19 nanocrystals. These changes were confirmed by X-ray Photoelectron Spectroscopy measurements, in which the concentration of Fe2+ increased from 69% to 82%, while the one of Fe3+ decreased from 31% to 18%. he thermoluminescent measurements reveal the same changes of Fe3+ in Fe2+ by electron capturing during irradiation, which is released as a red emission after recombination processes. The changes are explained by the increasing of some Fe-O bonds along the c-axis, mainly due to breaking a part of these bonds. The X-ray analysis confirms the changing of the parameters for the BaFe12O19 hexagonal structure.

Considering the increasing need for sustainable and economical energy storage solutions, the integration of layered materials such as MoS2 into these systems represents an important step toward enhancing energy sustainability and efficiency. Exploring environmentally responsible fabrication techniques, this study assesses wrinkled MoS2 thin films synthesized from distinct Mo and MoS2 targets, followed by sulfurization conducted in a graphite box. We utilized magnetron sputtering to deposit precursor Mo and MoS2 films on Si substrates, achieving thicknesses below 20 nm. This novel approach decreases sulfur by up to tenfold during sulfurization due to the confined space technique, contributing also to avoiding the formation of toxic gases such as SO2 or the necessity of using H2S, aligning with sustainable materials development. Thinner MoS2 layers were obtained post-sulfurization from the MoS2 precursors, as shown by X-ray reflectometry. Raman spectroscopy and grazing X-ray diffraction analyses confirmed the amorphous nature of the as-deposited films. Post-sulfurization, both types of films exhibited crystalline hexagonal MoS2 phases, with the sulfurized Mo showing a polycrystalline nature with a (100) orientation and sulfurized MoS2 displaying a (00L) preferred orientation. The X-ray photoelectron spectroscopy results supported a Mo:S ratio of 1:2 on the surface of the films obtained using the MoS2 precursor films, confirming the stoichiometry obtained by means of energy dispersive X-ray spectroscopy. Scanning electron microscopy and atomic force microscopy images revealed micrometer-sized clusters potentially formed during rapid cooling post-sulfurization, with an increased average roughness. These results open the way for the further exploration of wrinkled MoS2 thin films in advanced energy storage technologies.

Kesterite-based copper zinc tin sulfide (CZTS) and copper zinc tin selenide (CZTSe) thin films have attracted considerable attention as promising materials for sustainable and cost-effective thin-film solar cells. However, the successful integration of these materials into photovoltaic devices is hindered by the coexistence of secondary phases, which can significantly affect device performance and stability. This review article provides a comprehensive overview of recent progress and challenges in controlling secondary phases in kesterite CZTS and CZTSe thin films. Drawing from relevant studies, we discuss state-of-the-art strategies and techniques employed to mitigate the formation of secondary phases. These include a range of deposition methods, such as electrodeposition, sol-gel, spray pyrolysis, evaporation, pulsed laser deposition, and sputtering, each presenting distinct benefits in enhancing phase purity. This study highlights the importance of employing various characterization techniques, such as X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, for the precise identification of secondary phases in CZTS and CZTSe thin films. Furthermore, the review discusses innovative strategies and techniques aimed at mitigating the occurrence of secondary phases, including process optimization, compositional tuning, and post-deposition treatments. These approaches offer promising avenues for enhancing the purity and performance of kesterite-based thin-film solar cells. Challenges and open questions in this field are addressed, and potential future research directions are proposed. By comprehensively analyzing recent advancements, this review contributes to a deeper understanding of secondary phase-related issues in kesterite CZT(S/Se) thin films, paving the way for enhanced performance and commercial viability of thin-film solar cell technologies.

This paper tackles the influence of the functionalization of polystyrene and graphene oxide (GO) composites on the flammability characteristics. A microscale combustion calorimeter (MCC) was used to experimentally determine the heat release capacity (HRC), the specific heat release rate (HRR) and the total heat released (THR). Neural models were designed that correlate the THR with a number of parameters related to the composition and type of flame retardant used, the heating rate, the amount of residue, the HRC, the peak heat release rate (PHRR), the temperature at the peak pyrolysis rate (TPHRR) and the time elapsed until the occurrence of the peak heat release rate (Time). The best results in the training, validation and testing stages were achieved with the neural model with 9 neurons in the input layer, 40 neurons in the hidden layer and one neuron in the output layer. This model was incorporated into an optimization procedure, based on a genetic algorithm, to establish the values of the input parameters used in the training of the neural networks, in order to generate a minimum THR value, which is the output parameter. Since the synthesis of polystyrene particles with different GO concentrations is costly, this research helps to reduce the number of experimental tests and allows to determine the best GO concentration by means of neural models and genetic algorithms.

In the quest for advanced materials suitable for next-generation electronic and optoelectronic applications, tungsten disulfide (WS2) ultrathin films have emerged as promising candidates due to their unique properties. However, obtaining WS2 directly on the desired substrate, eliminating the need for transfer, which produces additional defects, poses many challenges. This paper aims to explore the synthesis of WS2 ultrathin films via physical vapor deposition (PVD) followed by sulfurization in a confined space, addressing the challenge of film formation for practical applications. Precursor layers of tungsten and WS2 were deposited by RF magnetron sputtering. Subsequent sulfurization treatments were conducted in a small, closed, graphite box to produce WS2 films. The physical and chemical properties of these precursor and sulfurized layers were thoroughly characterized using techniques such as X-ray reflectometry (XRR), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The findings reveal notable distinctions in film thickness, structural orientation, and chemical composition, attributable to the different precursor used. Particularly, the sulfurized layers from the tungsten precursor exhibited a preferred orientation of WS2 crystallites with their (00L) planes parallel to the substrate surface, along with a deviation from parallelism in a small angular range. This study highlights the necessity of precise control over deposition and sulfurization parameters to tailor the properties of WS2 films for specific technological applications.

This paper tackles the influence of the functionalization of polystyrene and graphene oxide (GO) composites on the flammability characteristics. A microscale combustion calorimeter (MCC) was used to experimentally determine the heat release capacity (HRC), the specific heat release rate (HRR) and the total heat released (THR). Neural models were designed that correlate the THR with a number of parameters related to the composition and type of flame retardant used, the heating rate, the amount of residue, the HRC, the peak heat release rate (PHRR), the temperature at the peak pyrolysis rate (TPHRR) and the time elapsed until the occurrence of the peak heat release rate (Time). The best results in the training, validation and testing stages were achieved with the neural model with 9 neurons in the input layer, 40 neurons in the hidden layer and one neuron in the output layer. This model was incorporated into an optimization procedure, based on a genetic algorithm, to establish the values of the input parameters used in the training of the neural networks, in order to generate a minimum THR value, which is the output parameter. Since the synthesis of polystyrene particles with different GO concentrations is costly, this research helps to reduce the number of experimental tests and allows to determine the best GO concentration by means of neural models and genetic algorithms.

This study investigates the morphological changes induced by femtosecond (fs) laser pulses in arsenic trisulfide (As2S3) thin films and gold-arsenic trisulfide (Au\As2S3) heterostructures, grown by pulsed laser deposition (PLD). By means of a direct laser writing experimental setup, the films were systematically irradiated at various laser power and irradiation times to observe their effects on surface modifications. AFM was employed for morphological and topological characterization. Our results reveal a clear transition threshold between photoexpansion and photoevaporation phenomena under different femtosecond laser power regimes, occurring between 1 and 1.5 mW, irrespective of exposure time. Notably, the presence of a gold layer in the heterostructure minimally influenced this threshold. A maximum photoexpansion of 5.2% was obtained in As2S3 films, while the Au\As2S3 heterostructure exhibited a peak photoexpansion of 0.8%. The study also includes a comparative analysis of continuous-wave (cw) laser irradiation, confirming the efficiency of fs laser pulses in inducing photoexpansion effects.

Undoped and Sm3+doped 45P2O5-45Na2O-2Al2O3-8BaO glasses were synthesized by the melt-quenching technique. The glass structure and luminescence properties were investigated by using Raman spectroscopy, scanning electron microscopy (SEM), spectroscopic ellipsometry, Judd-Ofelt theory and photoluminescence. Electron microscopy showed the homogeneity of samples. Raman spectroscopy revealed that the overall struc-ture of the glass was unaffected by the doping of Sm3+ and ellipsometry was used to measure the optical constants. Judd-Ofelt (JO) analysis was performed on the absorption bands of Sm3+ (4f5) and the three phenomenological parameters (omega 2, omega 4, and omega 6) were computed and then used to determine radiative properties such as the radiative transition probability (Ar), the fluorescent branching ratio (beta r), the stimulated emission cross-section (sigma e) and the radiative lifetime (tau rad). Photoluminescence (PL) spectrum showed the typical four transitions of Sm3+ at wavelengths of 564, 600, 645 and 703 nm corresponding to 4G5/2 -> 6H5/2, 6H7/2, 6H9/2 and 6H11/2, respectively. The spectroscopic quality factors omega 4/omega 6, the predicted lifetime (tau rad) calculated using the JO method and the experimentally lifetime (tau exp) for the 4G5/2level were calculated and discussed. The glass color purity is as high as 98%, which makes it a potential candidate for laser emission.

Recent progress concerning the development of counter electrode material (CE) from the dye-sensitized solar cells (DSSCs) and the electrode material (EM) within supercapacitors is reviewed. From composites based on carbon nanotubes (CNTs) and conducting polymers (CPs) to their biggest competitor, namely composites based on graphene or graphene derivate (GD) and CPs, there are many methods of synthesis that influence the morphology and the functionalization inside the composite, making them valuable candidates for EM both inside DSSCs and in supercapacitors devices. From the combination of CPs with carbon-based materials, such as CNT and graphene or GD, the perfect network is created, and so the charge transfer takes place faster and more easily. Inside composites, between the functional groups of the components, different functionalizations are formed, namely covalent or non-covalent, which further provide the so-called synergic effect. Inside CPs/CNTs, CNTs could play the role of template but could also be wrapped in a CP film due to pi-pi coupling enhancing the composite conductivity. Active in regenerating the redox couple I-/I3-, the weakly bound electrons play a key role inside CPs/GD composites.

. The study on efflorescence in salts collected from Curtea de Arges cathedral's exterior wall during restorations aimed to characterize compounds and lithic material using SEM-EDX, XRD, Raman, FTIR. Radiocarbon measurements using AMS method and FTIR results demonstrate decarbonation/recarbonation at the compound-lithic interface but further research is required.