National Institute Of Materials Physics - Romania

Cu2ZnSnS4 (CZTS) is an economically and environmentally friendly alternative to other toxic and expensive materials used for photovoltaics, however, the variation in the composition during synthesis is often followed by the occurrence of the secondary binary and ternary crystalline phases. These phases produce changes in the optical absorption edge important in cell efficiency. We explore here the secondary phases that emerge in a combinatorial Cu2S-ZnS-SnS2 thin films library. Thin films with a composition gradient were prepared by simultaneous magnetron sputtering from three binary chalcogenide targets (Cu2S, SnS2 and ZnS). Then, the samples were crystallized by sulfurization annealing at 450 degrees C under argon flow. Their composition was measured by energy dispersive X-ray spectroscopy (EDX), whereas the structural and optical properties were investigated by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy and optical transmission measurements. As already known, we found that annealing in a sulfur environment is beneficial, increasing the crystallinity of the samples. Raman spectroscopy revealed the presence of CZTS in all the samples from the library. Secondary crystalline phases such as SnS2, ZnS and Cu-S are also formed in the samples depending on their proximity to the binary chalcogenide targets. The formation of ZnS or Cu-S strongly correlates with the Zn/Sn and Cu/Zn ratio of the total sample composition. The presence of these phases produces a variation in the bandgap between 1.41 eV and 1.68 eV. This study reveals that as we go further away from CZTS in the composition space, in the quasi-ternary Cu2S-ZnS-SnS2 diagram, secondary crystalline phases arise and increase in number, whereas the bandgap takes values outside the optimum range for photovoltaic applications.

The nature of dark matter is still an open problem. The simplest assumption is that gravity is the only force certainly coupled to dark matter and thus the micro black holes could be a viable candidate. We investigated the possibility of direct detection of charged micro black holes with masses around and upward the Planck scale (10(-5) g), ensuring a classical gravitational treatment of these objects in the next generation huge LAr detectors. We show that the signals (ionization and scintillation) produced in LAr enable the discrimination between micro black holes and other particles. It is expected that the trajectories of these micro black holes will appear as crossing the whole active medium, in any direction, producing uniform ionization and scintillation on the whole path.

In this work, new evidence for the photodegradation reactions of acetaminophen (AC) is reported by photoluminescence (PL), Raman scattering and FTIR spectroscopy. Under excitation wavelength of 320 nm, AC shows a PL band in the spectral range of 340-550 nm, whose intensity decreases by exposure to UV light. The chemical interaction of AC with the NaOH solutions, having the concentration ranging between 0.001 and 0.3 M, induces a gradual enhancement of the photoluminescence excitation (PLE) and PL spectra, when the exposure time of samples at the UV light increases until 140 min, as a result of the formation of p-aminophenol and sodium acetate. This behavior is not influenced by the excipients or other active compounds in pharmaceutical products as demonstrated by PLE and PL studies. Experimental arguments for the obtaining of p-aminophenol and sodium acetate, when AC has interacted with NaOH, are shown by Raman scattering and FTIR spectroscopy.

xHfO(2)-(1-x)alpha-Fe2O3 (x = 0.1, 0.3, 0.5 and 0.7) nanoparticles system was obtained using mechanochemical activation by high energy ball milling for time periods ranging from 0 to 12 h. X-ray diffraction patterns revealed the presence of two phases, a hafnium-doped hematite and an iron-doped hafnia, which competed with each other to form a solid solution. The trend observed in the lattice parameters using Rietveld refinement was consistent with differences in ionic radii between Hf and Fe. Crystallite sizes for both hematite and hafnia were analyzed as function of milling time using the Scherrer method and found to decrease down to similar to 15 nm for all molar concentrations used. Mossbauer spectroscopy revealed the presence of 1-5 sextets corresponding to different numbers of Hf nearest neighbors of Fe in the hematite structure. The different hyperfine magnetic fields could be resolved in the model of local atomic environment. Substitutions of Fe in hafnia gave rise to a nonmagnetic phase represented by a quadrupole split doublet, whose abundance was found to increase with ball milling time. Hysteresis loops recorded at 5 K showed that the Hf-doped system does not saturate in an applied magnetic field of 5 T. The Morin transition was observed during zero-field-cooling-field cooling (ZFC-FC) in an external magnetic field of 200 Oe. Differential scanning calorimetry with thermal gravimetric analysis (DSC-TGA) evidenced an exothermic peak for the starting oxides and an endothermic peak for the solid solution.

In this work, the ferroelectric and fatigue characteristics of Au/0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3(BCZT)/Si metal-ferroelectric-semiconductor (MFS) structures are investigated. Moreover, the effect of introducing a thin dielectric HfO2-Al2O3 (HAO) layer with different thicknesses between the BCZT layer and the Si substrate on the ferroelectric characteristics in the metal-ferroelectric-insulator-semiconductor (MFIS) configuration is evaluated. It is evidenced that the insertion of the HAO layer with a thickness of 8 nm improves the memory window of the capacitance-voltage (C-V) curves by 106% compared to the value obtained in the MFS structure and reduces the leakage currents. Furthermore, the Au/BCZT/HAO (8 nm)/Si structure shows a remarkable remnant polarization (P-r) of 7.8 mu C/cm(2), with a coercive voltage of 1.9 V. The obtained value for P-r corresponds to a six times enhancement when compared to the value obtained in the Au/BCZT/Si structure. In addition, the fatigue studies reveal that the P-r obtained in the Au/BCZT/HAO/Si structure slightly decreases (3%) with continuous cycling, up to 10(9) cycles. The present work evidences that Au/BCZT/HAO/Si structures are promising for nonvolatile memory applications.

The development of robust, safe, cost-effective and efficient photocatalytic systems for water splitting should take into account the presence of a proper and powerful photon absorber and an efficient, low-cost and earth-abundant electrocatalyst to perform the reaction at high conversions. In this study, Ni-Zn/TiO(2)ternary composites with high photocatalytic activity for water splitting under UV irradiation were successfully prepared via a simple and low-cost deposition-precipitation route. Thus, different Ni : Zn molar ratios (1 : 0, 1 : 1, 3 : 1, 6 : 1, 9 : 1, and 0 : 1) were deposited on TiO(2)in order to reach a total metal loading of 50 wt. %. The obtained composites were characterized using several techniques, such as: X-ray diffraction, UV-Vis spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The most active synthesized composite, namely Ni-Zn/TiO2(9 : 1), exhibits H(2)generation rate above 17 mmols g(-1) h(-1), which is nearly one thousand times higher than that obtained with TiO(2)Evonik P25. Our study demonstrates that TiO(2)becomes a degenerated semiconductor in the presence of Ni and ZnO, with remarkable photocatalytic properties. Thus, the obtained results can open new opportunities in the preparation of very active materials for hydrogen production based on the optimization of three-component structures.

Y-modified LDHs with atomic Mg2+/(Al3+ + Y3+) of 3 and Al3+/Y3+ ratios of 0.5, 1 and 1.5 were prepared following two preparation methods, i.e. the co-precipitation and mechano-chemical one. The substitution of Al by Y in the brucite-type layer was less effective for the samples prepared by co-precipitation compared to those prepared via mechano-chemical route. In spite the fact yttrium has a larger ionic radius (0.9 angstrom) the structural characterizations of these solids confirmed that the layered structure incorporates part of it in the octahedral positions. Further, the reconstruction of the layered structure after an exposure to water for 1 h was more effective for the solid prepared by co-precipitation. The yttrium modified LDHs showed better catalytic activities for cyclohexene oxidation to the corresponding epoxide than the un-modified LDH sample. Then, mixed oxides derived from yttrium-LDH showed very high conversions and selectivities for the synthesis of chalcone.

Hydroxyapatite (HAp) and samarium doped hydroxyapatite, Ca10-xSmx(PO4)(6)(OH)(2),x(Sm)= 0.05, (5SmHAp), coatings were prepared by sol-gel process using the dip coating method. The stability of 5SmHAp suspension was evaluated by ultrasound measurements. Fourier transform infrared spectroscopy (FTIR) was used to examine the optical characteristics of HAp and 5SmHAp nanoparticles in suspension and coatings. The FTIR analysis revealed the presence of the functional groups specific to the structure of hydroxyapatite in the 5SmHAp suspensions and coatings. The morphology of 5SmHAp nanoparticles in suspension was evaluated by transmission electron microscopy (TEM). Moreover, scanning electron microscope (SEM) was used to evaluate the morphology of nanoparticle in suspension and the morphology of the surface on the coating. The SEM and TEM studies on 5SmHAp nanoparticles in suspension showed that our samples consist of nanometric particles with elongated morphology. The SEM micrographs of HAp and 5SmHAp coatings pointed out that the coatings are continuous and homogeneous. The surface morphology of the 5SmHAp coatings was also assessed by Atomic Force Microscopy (AFM) studies. The AFM results emphasized that the coatings presented the morphology of a uniformly deposited layer with no cracks and fissures. The crystal structure of 5SmHAp coating was characterized by X-ray diffraction (XRD). The surface composition of 5SmHAp coating was analyzed by X-ray photoelectron spectroscopy (XPS). The XRD and XPS analysis shown that the Sm(3+)ions have been incorporated into the 5SmHAp synthesized material. The antifungal properties of the 5SmHAp suspensions and coatings were studied usingCandida albicansATCC 10231 (C. albicans) fungal strains. The quantitative results of the antifungal assay showed that colony forming unity development was inhibited from the early phase of adherence in the case of both suspensions and coatings. Furthermore, the adhesion, cell proliferation and biofilm formation of theC. albicanswere also investigated by AFM, SEM and Confocal Laser Scanning Microscopy (CLSM) techniques. The results highlighted that theC. albicansadhesion and cell development was inhibited by the 5SmHAp coatings. Moreover, the data also revealed that the 5SmHAp coatings were effective in stopping the biofilm formation on their surface. The toxicity of the 5SmHap was also investigated in vitro using HeLa cell line.

This study develops, for the first time, composite coatings based on silver and zinc doped hydroxyapatite in chitosan matrix (AgZnHApCs). The AgZnHApCs composite coatings were prepared by dip coating method. The hydroxyapatite (HAp), biocompatible material for regenerating and strengthening damaged bones were doped with silver and zinc ions and coated with chitosan in order to produce a uniform and homogenous coating with biocompatibility and antimicrobial properties. The stability of AgZnHApCs suspensions was evaluated by ultrasound measurements. The value of stability parameters of AgZnHApCs suspension is in good agreement with the value of bidistilled water used as reference fluid. Homogeneously dispersed solutions of AgZnHApCs were synthesized to endeavor to optimize the physico-chemical and biological characteristics of the coatings obtained at room temperature. The AgZnHApCs composite suspension and coatings were analyzed using various investigation techniques, such as X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenylte-2H-tetrazolium bromide) assay and antimicrobial studies. The optical spectroscopy, atomic force microscopy (AFM), metallographic examination and X-ray photoelectron spectroscopy (XPS) on AgZnHApCs composite coatings were also conducted. Cell culture and MTT assays demonstrate that AgZnHApCs composite suspension and coatings have no negative effect on the cell viability and proliferation. The cell morphology was not affected in presence of AgZnHApCs composite suspension and coatings. The antimicrobial assays conducted againstStaphylococcus aureusATCC 25923,Escherichia coliATCC 25922, andCandida albicansATCC 90029 microbial strains revealed that both the AgZnHApCs composite suspension and coatings exhibited great antimicrobial properties.