National Institute Of Materials Physics - Romania

The electrochemical deposition of ZnxTey thin films was studied in an ionic liquid consisted in choline chloride - ethylene glycol eutectic mixture (Ethaline). ZnCl2 and TeO2 precursors were dissolved in 5-24 millimolar concentrations and the temperature was maintained constant at 60 degrees C. Cyclic voltammograms on Pt from electrolytes with both Te4+ and Zn2+ ions displayed three cathodic processes as limiting currents or peaks: Te underpotential deposition, codeposition of ZnTe compound, and deposition of Zn-rich binary telluride. The corresponding anodic waves or peaks were also identified. The shape of Nyquist electrochemical impedance plots recorded on various applied polarization showed that the electrode first covers with a Te film, and then the more cathodic polarization produces a co-reduction of Te4+ with Zn2+ as ZnTe compound. The formation of Zn metal-rich ZnxTey film at excessive negative polarization is indicated by the lowest value of maximum phase angle in Bode plots. The Zn/Te ratio (apparent stoichiometry) in the films deposited on Cu substrate is controlled by carrying out constant potential electrolyses with different ionic ratios in Ethaline bath. Film morphology, elemental analysis, and crystalline structure were evidenced by SEM microscopy, EDX analysis and X-ray diffraction, respectively.

This study investigated the mechanism of iron monosulfide (FeS) oxidation by dissolved oxygen (O-2(aq)). Synthetic FeS was reacted with O-2(aq) for 6 days and at 25 degrees C. We have characterized the initial and reacted FeS surface using Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX) analysis, Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). It was found that during the aqueous oxidation of FeS new solid phases (disulfide, polysulfide, elemental sulfur, ferric oxyhydroxides and Fe3O4) develop on the mineral surface. The results of potentiodynamic polarization experiments show that after 2 days of FeS electrode immersion in oxygen bearing solution (OBS) at initial pH 5.1 and 25 degrees C the modulus of cathodic Tafel slopes dramatically decreases, from 393 mV/dec to 86 mV/dec. This decrease is ascribed to the change of the mechanism of electron transfer from cathodic sites to O-2 (mechanism of cathodic process). The oxidation current densities (j(ox)) indicate that mineral oxidative dissolution is not inhibited by pH increase up to 6.7. Another conclusion, which emerges from the analysis of j(ox), is that the dissolved Fe3+ does not intermediate the aqueous oxidation of FeS. The results of electrochemical impedance spectroscopy (EIS) show that after 2 days of contact between electrode and OBS the properties of FeS/water interface change. From the analysis of the EIS, FTIR spectroscopy, Raman spectroscopy and SEM/EDX data we can conclude that the change of FeS/water interface properties accompanies the formation of new solid phases on the mineral surface. The new characteristics of the surface layer and FeS/water interface do not cause the inhibition of mineral oxidation. (C) 2016 Elsevier Inc. All rights reserved.

In melt-spun FePtB-based ribbons, the addition of Ag has been proven to decrease the temperature of phase transformation from the A1 fcc FePt phase to the hard magnetic tetragonal L1(0) phase. Alloys with 6 and 9 at.% Ag added to the initial FePtB have been synthesized by rapid solidification from the melt. The samples have been laser irradiated and submitted to nitriding procedure. This procedure has been proven beneficial for inducing complete transformation of A1 to L1(0) phase and a strong (001) texturing. Ag segregation combined to mechanisms of creation of vacancies and diffusion of N give rise to the formation of an intergranular disordered region and due to an improved interfacial coupling between FePt grains, enhanced coercivity and two-phase magnetic behavior is obtained.

Modern medicine is still struggling to find new and more effective methods for fighting off viruses, bacteria and fungi. Among the most dangerous and at times life-threatening fungi is Candida albicans. Our work is focused on surface and structural characterization of hydroxyapatite, silver doped hydroxyapatite and zinc doped hydroxyapatite deposited on a titanium substrate previously coated with polydimethylsiloxane (HAp-PDMS, Ag:HAp-PDMS, Zn:HAp-PDMS) by different techniques:Scanning Electron Microscopy (SEM), Glow Discharge Optical Emission Spectroscopy (GDOES) and Fourier Transform Infrared Spectroscopy (FTIR). The morphological studies revealed that the use of the PDMS polymer as an interlayer improves the quality of the coatings. The structural characterizations of the thin films revealed the basic constituents of both apatitic and PDMS structure. In addition, the GD depth profiles indicated the formation of a composite material as well as the successful embedding of the HAp, Zn:HAp and Ag:HAp into the polymer. On the other hand, in vitro evaluation of the antifungal properties of Ag:HAp-PDMS and Zn:HAp-PDMS demonstrated the fungicidal effects of Ag:HAp-PDMS and the potential antifungal effect of Zn:HAp-PDMS composite layers against C. albicans biofilm. The results acquired in this research complete previous research on the potential use of new complex materials produced by nanotechnology in biomedicine.

In this work we present the deposition of amorphous SiC thin films by radiofrequency dual magnetron sputtering. The dependence of the deposited films properties over the discharges electrical power and the effect of hydrogenous species (H-2 and/or D-2) addition to main discharge gas (Ar) were investigated. Accurate elemental analysis of the samples, including detection of hydrogen and deuterium, was performed by ion beam analysis (IBA) techniques: RBS (Rutherford Backscattering Spectrometry) and ERDA (Elastic Recoil Detection Analysis). SiCx thin films with thicknesses between 1700 and 4500 angstrom and C/Si ratio between 0.2/1 and 1.25/1 were obtained in different deposition conditions. The results prove that thin films of amorphous SiC with well controlled properties can be produced using radiofrequency dual magnetron sputtering. (C) 2015 Elsevier B.V. All rights reserved.

The Peierls transition of polycrystalline CuGeO3 samples was investigated by thermal and magnetic investigations. We find that spin disorder induced by chain breaking and grain boundaries has similar effects to doping but without suppressing the spin-Peierls transition temperature or the spin-Peierls gap.

High density (above 92%) superconducting bulks of MgB2 co-added with cubic BN (c-BN) and fullerenes (C-60) were obtained by the ex-situ spark plasma sintering (SPS). Compositions were (MgB2)((1-x))(C)(x)(c-BN)(0.01), x = 0.0125, 0.025, 0.05, 0.075. The co-added sample (MgB2)(0.975)(C)(0.025)(c-BN)(0.01) shows a marginally higher critical current density J(c) at intermediate magnetic fields and below 15 K than for optimum samples added with c-BN or C-60. For this sample, pinning is in the point pinning limit and the delta T-c mechanism is dominant. At high magnetic fields co-added samples are inferior to samples added with one additive, but are superior to pristine sample. Co-addition of c-BN and C-60 is not effective for vortex pinning when compared with individual addition. The result is discussed based on phase formation aspects, microstructural details and residual strain. It was found that in the presence of C-60, c-BN consumption with formation of MgNB9 is intensified with implications on different elements that influence pinning. (C) 2015 Elsevier B.V. All rights reserved.

Spectral and transport properties of electrons in confined phosphorene systems are investigated in a five hopping parameter tight-binding model, using analytical and numerical techniques. The main emphasis is on the properties of the topological edge states accommodated by the quasiflat band that characterizes the phosphorene energy spectrum. We show, in the particular case of phosphorene, how the breaking of the bipartite lattice structure gives rise to the electron-hole asymmetry of the energy spectrum. The properties of the topological edge states in the zigzag nanoribbons are analyzed under different aspects: degeneracy, localization, extension in the Brillouin zone, dispersion of the quasiflat band in magnetic field. The finite-size phosphorene plaquette exhibits a Hofstadter-type spectrum made up of two unequal butterflies separated by a gap, where a quasiflat band composed of zigzag edge states is located. The transport properties are investigated by simulating a four-lead Hall device (importantly, all leads are attached on the same zigzag side), and using the Landauer-Buttiker formalism. We find out that the chiral edge states due to the magnetic field yield quantum Hall plateaus, but the topological edge states in the gap do not support the quantum Hall effect and prove a dissipative behavior. By calculating the complex eigenenergies of the non-Hermitian effective Hamiltonian that describes the open system (plaquette+leads), we prove the superradiance effect in the energy range of the quasiflat band, with consequences for the density of states and electron transmission properties.

Implant-associated infections are a major cause of morbidity and mortality. This study was performed using titanium,samples coated by anodization with a titanium dioxide (TiO2) shielded nanotube layer. TiO2/Ti surface was modified by simple immersion in torularhodin solution and by using a mussel-inspired method based on polydopamine as bio adhesive for torularhodin immobilization. SEM analysis revealed tubular microstructures of torularhodin and the PDA ability to function as a catchy anchor between torularhodin and TiO2 surface. Corrosion resistance was associated with TiO2 barrier oxide layer and nano-organized oxide layer and the torularhodin surface modification does not bring significant changes in resistance of the oxide layer. Our results demonstrated that the torularhodin modified TiO2/Ti surface could effectively prevent adhesion and proliferation of Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis, and Pseudomonas aeruginosa. The new modified titanium surface showed good biocompatibility and well-behaved haemocompatibility. This biomaterial with enhanced antimicrobial activity holds great potential for future biomedical applications. (C) 2015 Elsevier B.V. All rights reserved.

Electrochemical deposition allows the preparation of ZnO nanostructures with precisely controlled morphology and properties, by finely tuning the process parameters. ZnO nanowires were deposited onto gold substrates by electrodeposition from a low concentration zinc nitrate bath Photolithography was employed for patterning interdigitated electrode systems onto silicon/silicon dioxide substrates and ZnO electrodeposition lead to wires connected to each other by bridging neighboring interdigits allowing electronic transport characterization. Optical measurements, i.e. reflection and photoluminescence spectroscopy, were performed and the results were correlated to electronic transport data. We found that we deal with a system for which one can apply a model of space charge limited currents with different traps energy distribution as a consequence of electrodeposition rate. Current versus temperature measurements show different behavior for lower and higher range of temperatures. Such nanowires, fabricated and contacted in a straightforward way, allow a wide area of applications ranging from conductometric bio- or chemo-sensors to optoelectronic devices. (C) 2015 Elsevier Ltd. All rights reserved.