Publications

Nanocrystalline PdO films have been characterized by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. The results demonstrate that thermal oxidation in an O-2 atmosphere causes similar to 35-nm-thick nanocrystalline Pd films on SiO2/Si(100) substrates to undergo a sequence of phase transformations resulting in PdO formation, followed by PdO decomposition into metallic Pd atT > 1120 K. In the range 670-970 K, theaandctetragonal cell parameters of the nanocrystalline PdO films increase monotonically with increasing temperature. The present and previously reported data have been used to construct a model for the unit cell in the crystal structure of palladium(II) oxide. Based on the quasi-chemical approach, we propose a model that accounts for the observed increase in the tetragonal cell parameters and thep-type conductivity of the nanocrystalline PdO films in terms of the formation of excess interstitial oxygen atoms.

Titanium diffusion in tungsten is an undesirable phenomenon that may cause the drop of mechanical and thermal fatigue properties of tungsten base material and components in future fusion reactors. To avoid such as problematic, the effectiveness of two different diffusion coatings, deposited onto W base materials by means of RF magnetron sputtering (Cr and V layers), has been studied to analyze its impact on the operative brazing aspects of the W-Eurofer joints. Coatings with two different thicknesses were deposited over tungsten base material prepared using different surface roughness (0.08 and 0.09 mu m). The results indicated that Ti diffusion into tungsten base material after the brazing process was suppressed in all cases while the consecution of full metallic continuity was reached. However, both Cr and V layers were dissolved during the brazing process due to the high solubility of both elements into beta-Ti. Mechanical properties of the joints dropped especially when Cr is used but a strength higher than 100 MPa was obtained in the case of using V layers.

Organic bulk heterojunctions (BHJ) based on zinc phthalocyanine (ZnPc), fullerene compounds (C60 fullerene and [6,6]-phenyl C71 butyric acid methyl ester (PC70BM)), and 5,6,11,12-tetraphenylnaphthacene (rubrene) were fabricated through the matrix-assisted pulsed-laser evaporation (MAPLE) technique. Thus, ZnPc:C60 and ZnPc:PC70BM binary BHJ and ZnPc:rubrene:PC70BM ternary BHJ were deposited as thin films on various substrates. The preservation of the chemical structure of the organic compounds during the MAPLE deposition was confirmed by infrared spectroscopy. The structural, optical, and morphological properties of the deposited layers were investigated by X-ray diffraction (XRD), UV-Vis spectroscopy, photoluminescence (PL), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM), respectively. Further, the electrical properties of the developed structures based on ZnPc:C60, ZnPc:PC70BM, and ZnPc:rubrene:PC70BM were evaluated. The J-V characteristics of the organic structures, recorded under illumination, show that an increase in the open-circuit voltage (V-OC) is achieved in the case of the ternary blend in comparison with that obtained for the binary blends. The results evidenced that MAPLE-deposited thin films containing binary and ternary organic bulk heterojunctions can find applications in the field of photovoltaic devices.

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.