National Institute Of Materials Physics - Romania

The electrospinning technique was employed for the preparation of SnO2 fibers starting from a precursor solution consisting of a tin salt, polyvinylpyrrolidone as carrier polymer and N,N-dimethylformamide as dispersion medium. In order to achieve single-phase crystalline structures, the as-spun fibers were calcined at 500, 700 or 900 degrees C, with two different heating rates of 1 or 10 degrees C/min. The thermally treated samples were characterized in terms of structure, morphology and bandgap by employing X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and UV-Vis spectroscopy. A fine tuning of the bandgap width was attained through the selection of different values for the electrospinning and calcination parameters.

The aim of this study was to investigate the antifungal activity of samarium doped hydroxyapatite (Ca10-xSmx(PO4)(6)(OH)(2), x(Sm) = 0.02 and x(Sm) = 0.05) layers deposited on titanium substrate by a thermal evaporation technique. The morphology of the samarium doped hydroxyapatite layers deposited on a Ti (Ti-Sm:HAp_2 and Ti-Sm: HAp_5) substrate were investigated using scanning electron microscopy (SEM). The antifungal activity of the Sm:HAp layers was assessed using Candida albicans ATCC 10231 fungal strain. The biofilm development of the C. albicans on the Sm: HAp layers was investigated by confocal laser scanning microscopy (CLSM). The results have evidenced a significant inhibition of the fungal cells adherence and biofilm development on the Sm: HAp layers.

Commercial MgB2 powder was loaded into a Fe-tube, by plastic deformation a tape of similar to 0.5 mm in thickness and 6.9 mm in width was obtained. Short pieces were processed by Spark Plasma Sintering (SPS) at 950, 1050 and 1150 degrees C for 3 min. The optimum sintering temperature is 1050 degrees C. From magnetic/electrical measurements, the onset critical temperature and the irreversibility field at 5 K were 38.7 / 38.9 K and 6.2 / 13.5 T, respectively. The pinning-force-related parameters indicate that the dominant flux pinning mechanism is of point pinning type. Contribution of grain boundary pinning is stronger at lower temperatures.

The aim of this study consisted to develop novel synthetic magnetite nanoparticles (nFe(3)O(4)) with preferential reactivity to trace elements (TE) for possible environmental applications as adsorbents. The synthetic magnetite materials obtained through the co-precipitation of both Fe3+ and Fe2+ ions (Fe2+ / Fe3+ = 0.5) were characterized by a set of complementary techniques: X-ray diffraction, transmission and scanning electron microscopy, Fourier transform infrared and Raman spectroscopy, and BET adsorption method. The resulting nFe(3)O(4) displayed a wide specific surface area (100 m(2) g(-1)) with particles reaching a size of about 10 nm, smaller than those of the well-crystallized commercial ones (cFe(3)O(4)) estimated at 80 nm while showing a BET surface area of 6.8 m(2) The adsorption properties of the synthetic nFe(3)O(4) magnetite nanoparticles were characterized and compared to the commercial analogous with the adsorption of both As and Cu. The equilibrium adsorption isotherms were properly fitted with Langmuir and Freundlich equation models and suggested that the developed iron oxides nanoparticles display a certain potential for removal and/or immobilization of TE from contaminated waters and/or soils, with an increase of 69.5% of the adsorbed amount compared to that of the commercial ones. (C) 2016 Elsevier B.V. All rights reserved.

Single ZnO nanowires prepared by wet and dry methods are used as channels in high performance back-gated field effect transistors working in low power operation mode, with on-off ratios up to 10(5) and mobilities up to 167 cm(2) V-1 s(-1). The nanowires' properties, generated by the growth techniques, influence the parameters of the transistors, therefore a throughout comparison is made.

We develop a manifest non-Hermitian approach of spectral and transport properties of two-dimensional mesoscopic systems in a strong magnetic field. The finite system to which several terminals are attached constitutes an open system that can be described by an effective Hamiltonian. The lifetime of the quantum states expressed by the energy imaginary part depends specifically on the lead-system coupling and makes the difference among three regimes: resonant, integer quantum Hall effect, and superradiant. The discussion is carried on in terms of edge state lifetime in different gaps, channel formation, role of hybridization, and transmission coefficients quantization. A toy model helps in understanding non-Hermitian aspects in open systems.

We investigate band bending effects occurring at the interface between atomically clean Ge(001) and molecular beam epitaxy (MBE) deposited copper and platinum. Low energy electron diffraction(LEED) confirmed the crystallinity of the surface, evidenced the formation of (2 x 1) and (1 x 2) reconstructions, and revealed that it is strongly affected with metal deposition. X-ray photoelectron spectroscopy (XPS) data let us assume a Stranski-Krastanov growth mechanism and confirmed that the observed band bending is associated to an ohmic contact in both cases. For the platinum contact, the high values of the apparent inelastic mean free path (IMFP) derived from the evolution of the XPS intensities indicate a prevalence of mixture of Pt with Ge nearby the interface. Pt deposited on Ge(001) does not behave like a Schottky contact, as one may have expected due to the higher work function of platinum. The observed effect is similar to the ease where interfacial Pt had a lower work function by 2.25/1.96 eV than that of metallic Pt. We propose a model to explain this fact by the effective mass variation or to the conduction band broadening due to the strong intermixing of platinum with germanium under the surface. (C) 2016 Elsevier B.V. All rights reserved.

Multiple and complex functionalities are a demand nowadays for almost all materials, including common day-to-day materials such as paper, textiles, wood, etc. In the present report, the surface temperature control of different types of materials, including paper and textiles, was demonstrated by Joule heating of metallic-web transparent electrodes both by direct current and by RF induced eddy currents. Polymeric submicronic fiber webs were prepared by electrospinning, and metal sputtering was subsequently performed to transform them into flexible transparent electrodes. These electrodes were thermally attached to different substrates, including paper, textiles and glass. Using thermochromic inks, we demonstrated a high degree of control of the substrates' surface temperature by means of the Joule effect. Metallic fiber webs appear to be excellently suited for use as transparent electrodes for controlling the surface temperature of common materials, their highly flexible nature being a major advantage when dealing with rough, bendable substrates. This kind of result could not be achieved on bendable substrates with rough surfaces such as paper or textiles while employing classical transparent electrodes i.e. metal oxides. Moreover, contactless heating with induced currents is a premiere for transparent electrodes and opens up a score of new application fields.

Passivated zinc oxide nanowires (NW) were used to improve the charge injection in organic lightemitting diode (OLED) structures. Conducting polymers, deposited on the well-dispersed ZnO NW, were used to modify the electrical conductivity across the OLED structure because the charge transport is influenced by the interface interactions. Passivation with polymers improves the transport characteristics of the device due to the interaction between ZnONWand PEDOT:PSS polymer. The hole current density increases with the ZnO NW concentration, which made the current injection more balanced and therefore enhanced the electroluminescence efficiency. A templateless electrochemical deposition method was used to grow zinc oxide nanowires on an ITO/glass substrate because parameters such as the densities and dimensions of the nanowires can be controlled to produce thin and well dispersed structures.