Publications

The electronic, magnetic and optical properties of doped CdS:Mn and co-doped CdS:Mn, Cr cubic structures were studied via Density Functional Theory and subsequently compared with the properties of undoped CdS. The doped compound presents semiconducting character similar to the undoped CdS, while the co-doped compound exhibits half metallic properties with a high spin polarization at the Fermi energy. The magnetic moments as well as the trend of magnetic exchange parameters of CdS:Mn and CdS:Mn,Cr, have been analyzed, in addition to the dielectric functions, by starting from calculated density of states for spin polarized configurations. The calculated absorption coefficients lead to direct information on the spectral energy distribution in the range of optoelectronic applications. The optical band gaps of doped and co-doped compounds are higher as compared to the undoped CdS, making the first compounds more interesting for possible technological applications for high density magneto-optical recording. (C) 2018 Elsevier B.V. All rights reserved.

Three phenacyl derivatives have been investigated as potential inhibitors for the aqueous oxidation of sphalerite (ZnS) in air-equilibrated solutions of HCl (pH 2.5 and 25 degrees C) using potentyodynamic polarization, aqueous batch experiments, scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) analysis, Fourier transform infrared (FTIR) spectroscopy, Raman scattering and quantum chemical calculations. Findings show that the studied phenacyl derivatives are inhibitors of sphalerite aqueous oxidation. Quantum chemical calculations indicate that the adsorption of phenacyl derivatives on ZnS is energetically favorable and accounts for the observed inhibiting effects.

Undoped and Ni-doped TiO2 thin films, with Ni concentration in the range 3-9 at.%, were obtained by reactive magnetron co-sputtering. A combined analysis by X-ray photoelectron spectroscopy and extended X-ray absorption-edge fine structure shows that Ni2+ substitutes for Ti4+ in the TiO2 lattice and promotes, at higher Ni amounts, a structural transition of the host from anatase to rutile. Several difficulties of the extended X-ray absorption-edge fine structure analysis, in the case of Ni-doped TiO2, are also discussed. X-ray diffraction data revealed that a large amount of the films material is in amorphous state. The films are very smooth, with root mean square roughness values (below 1.5 nm) decreasing with the increase of the Ni content. The hydrophilic properties of TiO2, modified by Ni doping, are also investigated.

Nanostructured Cu mol. 5% doped perovskite material Ba0.75Sr0.25TiO3 was synthesized under hydrothermal conditions and further on deposited via RF sputtering technique onto commercial Al2O3 substrates provided with Au interdigital electrodes and Pt heater. The obtained thin films have been analyzed by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM, TEM), X-ray photoelectron spectroscopy (XPS), Differential Scanning Calorimetry-Thermogravimetry (DSC-TG) and electrical investigations. The H2S (5-90 ppm) gas-surface interaction at moderate operating temperature (T-op = 250 degrees C) associated with the interplay between the pre-adsorbed oxygen species and surface dipolar hydroxyl groups, has been highlighted by simultaneous work function and electrical resistance measurements. By correlation with the XPS spectra, the dominant role of surface hydroxylation was revealed and the subsequent gas sensing mechanism under operando conditions has been addressed. (C) 2018 Elsevier B.V. All rights reserved.

We present a study on the growth and characterization of high-quality single-layer MoS2 with a single orientation, i.e. without the presence of mirror domains. This single orientation of the MoS2 layer is established by means of x-ray photoelectron diffraction. The high quality is evidenced by combining scanning tunneling microscopy with x-ray photoelectron spectroscopy measurements. Spin-and angle-resolved photoemission experiments performed on the sample revealed complete spin-polarization of the valence band states near the K and -K points of the Brillouin zone. These findings open up the possibility to exploit the spin and valley degrees of freedom for encoding and processing information in devices that are based on epitaxially grown materials.

Lighting and display technologies are evolving at tremendous rates nowadays; new device architectures based on new, microscopic building blocks are being developed. Besides high light-emission efficiencies, qualities including low cost, low environmental impact, flexibility, or lightweightness are sought for developing new types of devices. Electrospun polymer fibers represent an interesting type of such microscopic structures that can be employed in developing new functionalities. White-light-emitting fiber mats were prepared by the electrospinning of different dye-doped polymer solutions. Two approaches were used in order to obtain white-light emissions: the overlapping of single-dye-doped electrospun fiber mats, and the electrospinning of mixtures of different ratios of single-dye-doped polymer solutions. Scanning electron microscopy (SEM) was used to investigate the morphologies of the electrospun fibers with diameters ranging between 300 nm and 1 mu m. Optical absorption and photoluminescence (PL) were evaluated for single-dye-doped submicronic fiber mats, for overlapping mats, and for fiber mats obtained from different compositions of mixtures. Depending on the ratios of the mixtures of different dyes, the luminance was balanced between blue and red emissions. Commission Internationale de L'Eclairage (CIE) measurements depict this fine-tuning of the colors' intensities, and the right composition for white-light emission of the submicronic fiber mats was found.

Hybrid ferromagnetic/piezoelectric core-shell nanoparticles and ceramics have potential for a wide range of applications due to their tunability, electronic and magnetic properties. In this study, we designed a core-shell-type nanostructure of composition CoFe2O4/BNT-BT0.08, where BNT-BT0.08 is the abbreviation of bismuth, sodium titanate (Bi0.5Na0.5TiO3, BNT) doped with 8 mol% barium titanate (BaTiO3, BT). This multiferroic composite was prepared by covering CoFe2O4 nanoparticles with a shell of BNT-BT0.08 using the sol-gel technique. Scanning and transmission electron microscopy confirmed formation of a core-shell structure. The results of microstructure, dielectric, piezoelectric and magnetic investigations demonstrated that this heterostructure shows simultaneously electrical and magnetic behavior, at room temperature. XRD pattern of core-shell composite CoFe2O4/BNT-BT0.08 powder reveals only cubic CoFe2O4 and rhombohedral Bi0.5Na0.5TiO3 phases. CoFe2O4/BNT-BT0.08 core-shell nanostructure sample shows high values of permittivity (epsilon >= 600) together with high dielectric losses (tan delta >= 1) in the low-frequency range (nu <= 10(4) Hz). PFM and polarization hysteresis indicated a ferroelectric domains structure and remnant polarization of similar to 2.6 A mu C/cm(2) for the ceramics pellets samples of CoFe2O4/BNT-BT0.08. The present study reveals the possibility of coating nanoparticles onto nanometer-sized core particles, using controlled sol-gel process, in order to prepare multifunctional core-shell composites for piezoelectric and magnetoelectronic sensors.

Herein, the spectral and transport properties in the finite phosphorene lattice are investigated using the tight-binding model in the presence of Anderson disorder potential. The focus is on the zig-zag edge states localization, provided by the numerically calculated inverse participation number. At low disorder, the zig-zag states undergo a localization process, keeping their 1D character, while further increasing the disorder leads to delocalization due to hybridization with the extended 2D states. The disorder-induced changes in the electronic conductance, from one zig-zag edge to the other, are also discussed.

The demand of calcium phosphate bioceramics for biomedical applications is constantly increasing. Efficient and cost-effective production can be achieved using naturally derived materials. In this work, calcium phosphate powders, obtained from dolomitic marble and Mytilus galloprovincialis seashells by a previously reported and improved Rathje method were used to fabricate microporous pellets through cold isostatic pressing followed by sintering at 1200 degrees C. The interaction of the developed materials with MC3T3-E1 pre-osteoblasts was explored in terms of cell adhesion, morphology, viability, proliferation, and differentiation to evaluate their potential for bone regeneration. Results showed appropriate cell adhesion and high viability without distinguishable differences in the morphological features. Likewise, the pre-osteoblast proliferation overtime on both naturally derived calcium phosphate materials showed a statistically significant increase comparable to that of commercial hydroxyapatite, used as reference material. Furthermore, evaluation of the intracellular alkaline phosphatase activity and collagen synthesis and deposition, used as markers of the osteogenic ability of these bioceramics, revealed that all samples promoted pre-osteoblast differentiation. However, a seashell-derived ceramic demonstrated a higher efficacy in inducing cell differentiation, almost equivalent to that of the commercial hydroxyapatite. Therefore, data obtained demonstrate that this naturally sourced calcium-phosphate material holds promise for applications in bone tissue regeneration.

We investigated the magnetic and thermodynamic properties of rolled tantalum in superconducting state. The magnetization shows a crossover from type I to type II superconductivity as the magnetic field increases beyond the thermodynamic critical field. In both regimes, the sample shows a substantial irreversibility of the magnetization which we attribute to the pinning of the entities that characterize the intermediate and mixed states. Magnetic relaxation data taken in the intermediate state shows an important contribution of the quantum tunnelling below 3.7 K.