National Institute Of Materials Physics - Romania

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.

Dye-doped polymer thin films were obtained by spin-coating of 8% polyvinylpyrrolidone (PVP) solutions (in ethanol). Ni or ZnO nanowires were incorporated in Rhodamine 6G doped polymer films (10(-4) M dye concentration). Optical and morphological properties of simple dye-doped polymer films and films containing metallic or semiconducting nanostructures were investigated. Optical microscopy and scanning electron microscopy were used to image the nanowires. The presence of Ni nanowires induces a small shift (2-3 nm) to longer wavelengths on the emission band of Rh 6G doped PVP film. The ZnO nanowires' presence was confirmed by X-ray diffraction measurements. An enhancement of the emission of the dye doped polymer is induced by the semiconducting structures. (C) 2015 Elsevier B.V. All rights reserved.

The inhibitory and antimicrobial effects of silver particles have been known since ancient times. In the last few years, a major health problem has arisen due to pathogenic bacteria resistance to antimicrobial agents. The antibacterial activities of new materials including hydroxyapatite (HAp), silver-doped hydroxyapatite (Ag:HAp) and various types of antibiotics such as tetracycline (T-HAp and T-Ag:HAp) or ciprofloxacin (C-HAp and C-Ag:HAp) have not been studied so far. In this study we reported, for the first time, the preparation and characterization of various thin films based on hydroxyapatite and silver-doped hydroxyapatite combined with tetracycline or ciprofloxacin. The structural and chemical characterization of hydroxyapatite and silver-doped hydroxyapatite thin films has been evaluated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The morphological studies of the HAp, Ag: HAp, T-HAp, T-Ag: HAp, C-HAp and C-Ag: HAp thin solid films were performed using scanning electron microscopy (SEM). In order to study the chemical composition of the coatings, energy dispersive X-ray analysis (EDX) and glow discharge optical emission spectroscopy (GDOES) measurements have been used, obtaining information on the distribution of the elements throughout the film. These studies have confirmed the purity of the prepared hydroxyapatite and silver-doped hydroxyapatite thin films obtained from composite targets containing Ca10-xAgx(PO4)(6)(OH)(2) with x(Ag) = 0 (HAp) and x(Ag) = 0.2 (Ag: HAp). On the other hand, the major aim of this study was the evaluation of the antibacterial activities of ciprofloxacin and tetracycline in the presence of HAp and Ag: HAp thin layers against Staphylococcus aureus and Escherichia coli strains. The antibacterial activities of ciprofloxacin and tetracycline against Staphylococcus aureus and Escherichia coli test strains increased in the presence of HAp and Ag: HAp thin layers.

By combining the electrospinning method advantages (high surface-to-volume ratio, controlled morphology, varied composition and flexibility for the resulting structures) with the electrical activity of polyaniline, a new core-shell-type material with potential applications in the field of artificial muscles was synthesized. Thus, a poly(methylmethacrylate) solution was electrospun in optimized conditions to obtain randomly oriented polymer fiber webs. Further, a gold layer was sputtered on their surface in order to make them conductive and improve the mechanical properties. The metalized fiber webs were then covered with a PANI layer by in situ electrochemical polymerization starting from aniline and using sulphuric acid as oxidizing agent. By applying a small voltage on PANI-coated fiber webs in the presence of an electrolyte, the oxidation state of PANI changes, which is followed by the device color modification. The morphological, electrical and biological properties of the resulting multilayered material were also investigated. (C) 2015 Elsevier B.V. All rights reserved.

This article reports the synthesis and characterization of several types of organic-inorganic nanocomposites based on epoxy resin/monoglycidylether-terminated poly(dimethylsiloxane) reinforced with 2, 5, or 10 wt% polyhedral oligomeric silsesquioxanes (POSS) bearing one glycidyl (1GE-POSS) or eight glycidyl(8GE-POSS) groups. The morphological features of the studied samples were established through atomic force microscopy, contact angle measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy, and it was demonstrated that 8GE-POSS is well dispersed within the polymer matrix, while 1GE-POSS exhibits a high tendency to form aggregates. Differential scanning calorimetry (DSC) and Fourier transform infrared resonance (FTIR) measurements are used to follow the curing behavior and to study the polymerization kinetics of epoxy groups. As evidenced by DSC and FTIR results, the inclusion of 8GE-POSS within the polymer matrix leads to a lower epoxy polymerization rate of the resulted nanocomposites than those reinforced with 1GE-POSS. The dynamic mechanical analysis results revealed that the thermomechanical properties are gradually improved with increasing of 8GE-POSS content due to the higher cross-linking density.