National Institute Of Materials Physics - Romania

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 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 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.

Developing new materials to be applied in extreme environments is an opportunity and a challenge for the future. High entropy alloys are new materials that seem promising approaches to work in nuclear fusion reactors. In this work, FeTaTiVW high entropy alloys were developed and characterized with Molecular Dynamic and Hybrid Molecular Dynamic Monte Carlo simulations. The simulation results show that phase separation originates a lower potential energy per atom and a high level of segregation compared to those of a uniform solid solution. Moreover, the experimental diffractogram of the milled powder shows the formation of a body-centred cubic-type structure and the presence of TiO2. In addition, the microstructure of the consolidated material evidenced three phases: W-rich, Ti-rich, and a phase with all the elements. This phase separation observed in the microstructure agrees with the Hybrid Molecular Dynamic Monte Carlo simulation. Moreover, the consolidated material's thermal conductivity and specific heat are almost constant from 25 degrees C to 1000 degrees C, and linear expansion increases with increasing temperature. On the other hand, specific heat and thermal expansion values are in between CuCrZr and W values (materials chosen for the reactor walls). The FeTaTiVW high entropy alloy evidences a ductile behaviour at 1000 degrees C. Therefore, the promising thermal properties of this system can be attributed to the multiple phases and systems with different compositions of the same elements, which is exciting for future developments.

Tungsten is the primary candidate armour material for the divertor target of the European demonstration fusion power plant. During operation at high temperature, pure tungsten is subject to fracture and recrystallization which results in a loss of strength and worsening of the thermal properties. Additionally, loss-of-coolant accidents with simultaneous air ingress can generate volatile and radioactive tungsten oxides. Advanced W-alloys were developed as alternative and upgrading armour materials of pure tungsten, such as potassium-doped tungsten laminates and self-passivating tungsten alloys. Three mock-ups were manufactured using potassium-doped tungsten laminates, W-10Cr-0.5Y and W-10Cr-0.5Y-0.5Zr as armour materials, each of them consisting of n degrees 4 blocks. The fabrication required optimization and upscaling of the ITER-like process which foresees oxygen-free high conductivity copper as interlayer joined to W-alloy armour block and CuCrZr ITER grade pipe welded to the Cu/W-alloy blocks by hot radial pressing. For quality control of the fabrication steps, non-destructive examination by ultrasonic testing was done on the monoblocks as received, after casting, after hot radial pressing and after high heat flux testing. The results demonstrated that these W-alloys can be used as armour materials of the European demonstration fusion power plant divertor target.

Antidepressant drugs play a crucial role in the treatment of mental health disorders, but their efficacy and safety can be compromised by drug degradation. Recent reports point to several drugs found in concentrations ranging from the limit of detection (LOD) to hundreds of ng/L in wastewater plants around the globe; hence, antidepressants can be considered emerging pollutants with potential consequences for human health and wellbeing. Understanding and implementing effective degradation strategies are essential not only to ensure the stability and potency of these medications but also for their safe disposal in line with current environment remediation goals. This review provides an overview of degradation pathways for amitriptyline, a typical tricyclic antidepressant drug, by exploring chemical routes such as oxidation, hydrolysis, and photodegradation. Connex issues such as stability-enhancing approaches through formulation and packaging considerations, regulatory guidelines, and quality control measures are also briefly noted. Specific case studies of amitriptyline degradation pathways forecast the future perspectives and challenges in this field, helping researchers and pharmaceutical manufacturers to provide guidelines for the most effective degradation pathways employed for minimal environmental impact.

Structurally disordered Pr3+-doped Ca-3(Ta,Ga)(5)O-12 - Pr:CTGG single crystal was grown by the Czochralski technique for the first time and its spectroscopic properties were investigated. Modified Judd-Ofelt analysis was applied to determine spectroscopic and laser emission characteristics. Based on low-temperature absorption and emission spectra, the partial energy levels of Pr3+ ions have been obtained and a multicenter structure of the optical spectra was highlighted. The electron-phonon interactions were also observed in the emission spectra corresponding to the P-3(0) -> H-3(4) transition under different excitation wavelengths. The fluorescence decays of the P-3(0) and D-1(2) levels were measured. The emission cross-sections corresponding to the P-3(0) -> H-3(4) (486.5 nm) and P-3(0) -> F-3(2) (652.7 nm) transitions were found to be sigma(em) = 19 x 10(-20) cm(2) and crem = 15 x 10(-20) cm(2), respectively. The values for other parameters that may predict the possibility of achieving efficient laser emission, especially at 486.5 nm, such as quantum efficiency (eta = 50 %), gain bandwidth (sigma(em) x Iota lambda(eff), = 32.2 x 10(-26) cm(3)), and optical gain (sigma(em) x tau(meas) = 12.86 x 10(-25) cm(2) s) were determined. The obtained results indicate that the Pr:CTGG crystal has a high potential for obtaining efficient laser emission in the blue domain.

In this work, the formation of the orthorhombic phase of ZrO2 together with the minor monoclinic phase were elucidated by X-ray diffraction and transmission electron microscopy. Moreover, oxidized W can be responsible for the formation of oxygen vacancies in the ZrO2 through oxygen scavenging. The ferroelectric properties of the W/ZrO2/W film capacitors were investigated through piezoresponse force microscopy (PFM) and polarizationvoltage measurements. A second-order phase transition from the polar orthorhombic phase to the non-polar tetragonal phase was observed. Density functional theory calculations confirm our experimental results and propose that oxygen vacancies are responsible for the Curie-Weiss temperature of 130 degrees C, significantly lower than the theoretical value for the bulk.

In this work, a ZnO nanowires/graphene nanohybrid was synthesized by a three steps approach. Copper substrates were covered with graphene by chemical vapor deposition, further ZnO nanowires were electrochemically deposited on the as grown graphene on copper and finally a transfer process was employed for moving the heterostructure onto a different substrate. A comprehensive structural analysis which included scanning electron microscopy, X-ray diffraction and Raman measurements revealed that the ZnO nanowires crystallize in wurtzite structure perpendicular to graphene, the process leading to the formation of a nanohybrid heterostructure. The band gap energy of the ZnO nanowires deposited on graphene was estimated to be 3.11 eV, as calculated from the reflectance spectrum analysis. The GGA-PBE+U within Grimme (DFT-D) approach was used to provide an accurate description of the interface structure in terms of electronic and optical properties, confirming that the decrease in the band gap energy of ZnO nanowires is caused by the interaction with the graphene surface. The findings of this study could serve as an experimental and theoretical reference for upcoming studies on ZnO NWs/Graphene nanohybrid-based optoelectronic applications.

Bulk nanocrystalline La0.67Ba0.33_xKxMnO3 (with x = 0, 0.05, 0.1, and 0.2) manganites have been prepared by the modified sol-gel method (Pechini). The single-phase rhombohedral crystal structure with the R-3c (no. 167) space group was verified by X-ray diffraction (XRD) and sustained by Rietveld refinement. As follows from the results of XRD structural analyses, the increase in K-doping triggers an increase in the distortion of the MnO6 octahedra, which eventually causes the narrowing of the eg bandwidth. Mn is in a mixed valence state of Mn4+/ Mn3+ as inferred by X-ray photoelectron spectroscopy. Magnetic measurements confirm that the Curie tem-perature decreases from 348 K for La0.67Ba0.33MnO3 to 316 K for La0.67Ba0.13K0.20MnO3. The increasing of the Mn4+ ion concentration at the B-site sublattice and A-site ionic disorder (sigma 2) breaks up the double exchange interaction between the Mn3+ and Mn4+ ions. The ferromagnetic to paramagnetic second-order magnetic phase transition at TC is also confirmed by electron paramagnetic resonance. According to magnetic field-dependent magnetization isotherms at different temperatures, La0.67Ba0.13K0.20MnO3 shows a relatively large magneto -caloric effect (1400 mJ cm_ 3 K_ 1 at 316 K under 5 T applied magnetic field), which raises the possibility of using this material for room-temperature micro-scale magnetic cooling.