National Institute Of Materials Physics - Romania

Herein, alpha-MoO3 micro- and nanoparticles were synthesized by a modified Pechini method, and the impact of the crystal structure and crystal growth orientation on the formation of ionic defects and, consequently, on the catalytic performance of the materials in the ethylic transesterification reaction for biodiesel production was investigated. Structural refinements from X-ray diffraction data and Raman spectra revealed the formation of alpha-MoO3 in a Pbnm orthorhombic phase, with nanoplate-like morphology at 500 degrees C (thickness between 100 and 260 nm) or ribbon-like morphology at 700 degrees C (thickness between 400 and 900 nm). An anisotropic crystal orientation along the [010] direction was observed with an increase of the calcination temperature. We emphasize the dependence of the orientation change with the elimination of ionic-type defects (oxygen vacancies and reduced Mo5+ centers) by the temperature using complementary techniques such as X-ray photoelectron and electron paramagnetic resonance spectroscopies. The catalytic activity of the samples depends on the orientation process and the presence of defects that act as acid-active sites on the catalyst surface and therefore play an important role in biodiesel production. This effect was confirmed by surface stability and reactivity simulated by density functional theory calculations, suggesting that the Mo and O surface terminals greatly impacted the interface catalytic reaction. The highest catalytic performance toward the biodiesel conversion (89% of conversion at 150 degrees C for 2 h) was achieved for the polycrystalline catalyst calcined at 500 degrees C, which was correlated with random crystal orientation and the presence of reduced Mo5+ and oxygen vacancy centers on the different facets exposed on the surface. The biodiesel production was confirmed by H-1 and C-13 NMR spectroscopy and gas chromatography analysis.

In this study, we synthesized thin films of semiconductor Cu 2 CoSnS 4 (CCTS). We investigated the mechanism of CCTS electrodeposition precursor onto fluorine -doped tin oxide (FTO) surface. This investigation utilized various mixed additives (Trisodium citrate, Glycine, and Boric acid) through voltammetric and chronoamperometric techniques. The polarization cathodic indicated that the additives narrowing the potential range for electrodeposition of the four elements. The reduction of S 2 O 3 2- was mainly induced by the effect of metal ions. The current transient was analyzed using the Astley and Scharifker-Hills models. Trisodium citrate electrolyte showed an instantaneous model followed by 3D diffusion -limited growth. Both trisodium citrate mixed with glycine and trisodium citrate mixed with boric acid shifted towards the progressive nucleation model. Trisodium citrate with tartaric acid showed a strong agreement with progressive nucleation. In -situ electrochemical impedance spectroscopy (EIS) evaluated a low charge transfer resistance for CCTS precursor electrodeposition in trisodium citrate electrolyte. The X-ray diffraction and Raman analysis study revealed the stannite structure of the obtained Cu 2 CoSnS 4 thin film. The morphological properties and thickness of the films were investigated using a scanning electron microscope (SEM). The compositions were determined using energy dispersive spectroscopy which indicated different atomic ratios of Cu-Co-Sn-S. The maximum absorption was observed within the 1.5 eV range for the film deposited in the Trisodium citrate bath, as determined by spectroscopic ellipsometry.

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.

In this work, the effects of 60Co y -ray irradiation on high resistivity p -type diodes have been investigated. The diodes were exposed to dose values of 0.1, 0.2, 1, and 2 MGy. Both macroscopic (I-V, C-V) and microscopic investigations, by means of Thermally Stimulated Current (TSC) and Deep Level Transient Spectroscopy (DLTS) techniques, were conducted to characterize the radiation -induced changes. The investigated diodes were manufactured on high resistivity p -type Float Zone (FZ) silicon and were further classified into two types based on the isolation technique between the pad and guard ring: p -stop and p -spray. After irradiation, the macroscopic results of current-voltage and capacitance-voltage measurements were obtained and compared with existing literature data. Additionally, the microscopic measurements focused on the development of the concentration of different radiation -induced defects, including the Boron interstitial -Oxygen interstitial (BiOi) complex, the Carbon interstitial -Oxygen interstitial (CiOi) defect, the H40K, and the so-called I*P. To investigate the thermal stability of induced defects in the bulk, isochronal annealing studies were performed in the temperature range of 100 degrees C to 300 degrees C. These annealing processes were carried out on diodes irradiated with doses of 1 and 2 MGy. Furthermore, in order to investigate the unexpected results observed in the C-V measurements after irradiation with high dose values, the surface conductance between the pad and guard ring was measured as a function of both dose and annealing temperature.

In order to find solutions to current worldwide environmental problems, it is crucial to develop sustainable nanomaterials, ideally with multifunctional properties. Considering this, novel TiO2-SnO2@NMs (noble metals: Au and Ag) composites, for use as sustainable nanomaterials, were successfully prepared via a two-step synthesis process consisting of laser pyrolysis followed by the chemical impregnation of the collected materials with noble metals. The addition of SnO2 favors the transformation of TiO2 from a mixture with a majority Anatase phase to one with a Rutile phase majority. With consideration for their level of environmental toxicity, the features of the synthesized nanomaterials were structurally, morphologically, and optically described and assessed for environmental protection applications as gas sensors and photocatalysts. In the case of the Surface Acoustic Wave sensor, based on a pure TiO2 nanopowder, a notable difference in the frequency shift was detected in comparison to the other examined sensors. All sensors responded to the CH4 concentrations tested (0.02-0.1%). On the other hand, when methyl orange was photodegraded under visible light, the results obtained using NMs for decoration revealed that the photocatalytic activity of TiO2-SnO2@NMs was significantly improved compared to the TiO2-SnO2 binary composite, which already has an enhanced photocatalytic activity, compared to pure TiO2. Overall, this work produces nanoparticles that exhibit better sensory and photocatalytic features, as well as higher levels of biocompatibility with skin cells, for use as eco-friendly nanomaterials for a sustainable future.

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.

The corrosion protection property of three Brij-type surfactants, namely, Brij 35, Brij 56 and Brij 58P, was considered on OLC 45 carbon steel in a 0.5 M H2SO4 medium. The efficacy for these organic compounds was examined using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods, scanning electron microscopy (SEM) procedures, and Fourier transform infrared (FT-IR) spectroscopy. We hypothesized that these surfactants hinder the corrosion for OLC 45 samples through a protecting mechanism owing to the adsorption of organic molecules that form an inhibitive film or through the formation of complex oxides. These surfactants exhibited an appreciable protective effect against OLC 45 corrosion, operating as mixed inhibitors, as could be demonstrated by their influence on the electrochemical characteristics of the metallic substrates. The adsorption of surfactants over the substrates zone conformed to the representation of the Langmuir isotherm. The effect of temperature on the electrochemical comportment of the OLC 45 specimens in H2SO4 without and with Brij at 800 ppm was examined in the temperature interval of 293 to 333 K. The negative estimate of thermodynamic attributed as Gibbs free energy of adsorption presented the spontaneity of the adsorption activity. The investigation with FT-IR and SEM established the adsorption of Brij and the constitution of the corrosive components on the OLC 45 surface. Electrochemical determinations of these surfactants indicated its anticorrosion inhibition performance and the highest inhibition of 96% was reached when the Brij 35 concentration was at 800 or 1000 ppm, while for Brij 56 and Brij 58P, the highest inhibition was obtained when their concentrations were 500, 800, or 1000 ppm.

Selective growth of 2D MoS2 layers on patterned substrates is highly desired for easy fabrication of devices. Selectively grown 2D MoS2 on Mo patterned substrates for the formation of intimate metallic contact was obtained by a Mo-CVD method in which MoO2 from an oxidized Mo pattern and S powder are the growth precursors. Mo films were deposited by magnetron sputtering on SiO2(300 nm)/c-Si substrates and patterned by photolithography techniques for obtaining Mo strips and finger contact structures, with the gap between the strips and finger varied from 5 to 20 mu m. The filling of the gap by selectively grown atomically thin MoS2 plates of 1-2 monolayers (MLs) was demonstrated by scanning electron microscopy and atomic force microscopy imaging. Field effect devices for the characterization of the photosensitivity of selectively grown MoS2 have been fabricated from finger contact structures. The dark current is drastically reduced from 10(-9) to 10(-13)-10(-14) A by varying the gate voltage from +7 to -7 V, showing the n-type semiconductor behavior of the selectively grown 2D MoS2. High photosensitivity of 10(5) (%) was obtained for 4.5 x 10(-4) mW/cm(2) at 650 nm wavelength illumination. The spectral responsivity reaches values of 15-25 A/W at 600 nm wavelength and shows an energy onset of 1.72-1.77 eV corresponding to about 2 ML MoS2. The carrier-trapping effect responsible for the slow part of the device response can be caused by structural defects and also by adsorbed molecules like in gas sensors.

Bioactive glasses (BGs) are known for their selective ability to (i) form a mechanically strong interfacial bond with hard (bone) or soft tissues (gingivae or cartilages) (i.e., silica-, silica-phosphate-, phosphate-, boratephosphate-, or silica-phosphate-borate-based BGs); or (ii) serve as reservoirs for fast-release of therapeutic (osteogenic, angiogenic, anticarcinogenic, or antimicrobial) ions (i.e., phosphate-based BGs and mesoporous BGs). The strength of the bone bond yielded by the osteoproductive-capable BGs is generally equivalent to, or higher than the bone strength. The resorbability of phosphate-based BG is dependent on the content of network formers and cross-linkers. All BGs elicit excellent biochemical compatibility. However, their fracture toughness is typically less than and the elastic modulus is greater than those of bone, indicating that most BGs have suboptimal biomechanical compatibility when used in load-bearing applications. One promising approach to overcome this problem is the development of BGs in coating form, applied to the surface of load-bearing endosseous implants. This work critically assesses BG thin-layers fabricated by the radio-frequency magnetron sputtering method, an industry-ready large-scale physical vapour deposition technology. It is demonstrated that, despite the relative lack of attention paid to this technology, it enables the development of unique BG coatings with efficacious therapeutic capabilities. Here, we present an overview of the most relevant developments achieved thus far, along with the remarkable advantages, drawbacks to overcome, and future perspectives with the intention of highlighting the vast possibilities of this specific field of research.

The effect of the annealing temperature on 1% nitrogen-doped WO3 materials was studied, which were then used as electrode materials for high-performance supercapacitor (SC) devices. The supercapacitive performance of the proposed materials was strongly influenced by the doping element and the annealing temperature by directly changing the defect structure of the host material. The 1% N-doped WO3 materials annealed at different temperatures were thoroughly characterized through various characterization techniques, including electron paramagnetic resonance and photoluminescence spectroscopy, giving insight into the effect of N-doping on the defect structure and optical properties of WO3. When the WO3:N materials were used as electrode material in symmetric SCs, the doping element and the annealing temperature improved the electrochemical performance. No booster materials (such as carbon black) were used in the symmetric SC designs, showing increased specific capacitance (102 F/g) and energy density (14.6 W h/kg) values.