National Institute Of Materials Physics - Romania

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.

The goal of this paper was to investigate the antifungal activity of Enamel layers deposited on titanium substrate (Ti-Enamel) and Enamel layers deposited on titanium substrate previously coated with a vinyl polydimethylsiloxane layer (Ti-PDMS-Enamel). The physicochemical properties were also investigated. The Candida albicans biofilm development on the obtained layers was examined after 24 h, 48 h, and 72 h by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) after ethidium bromide staining. A significant inhibition of the fungal adherence and biofilm development was observed on Ti-Enamel layers. The antifungal results demonstrated that the use of new Ti-Enamel composite layers could represent a promising perspective for the prevention of fungal biofilms associated implant infections.

This paper presents some investigations of the effect of nanopatterning on the properties of aluminum layer deposited by sputtering. UV-Nanoimprint Lithography technique has been used for the realization of a 2D array of nanostructures (pillars) in aluminum film characterized by cylindrical shape and the following structural parameters: diameter between 400 nm and 490 nm, depth between 320 nm and 420 nm and periodicity of 1.1 mu m, which have been revealed by SEM and AFM measurements. The UV-Vis transmission, reflection and photoluminescence measurements have evidenced the effect of the nanopatterning on the optical properties of the A1 layer.

The aim of the current research work was to study the physicochemical and biological properties of synthesized zinc doped hydroxyapatite (ZnHAp) nanoparticles with Zn concentrations x(Zn) = 0 (HAp), x(Zn) = 0.07 (7ZnHAp), and x(Zn) = 0.1 (10ZnHAp) for potential use in biological applications. The morphology, size, compositions, and incorporation of zinc into hydroxyapatite were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Raman scattering, and X-Ray Photoelectron Spectroscopy (XPS). In addition, the cytotoxicity of ZnHAp nanoparticles was tested on both E. coli bacteria and human hepatocarcinoma cell line HepG2. The results showed that ZnHAp nanoparticles (HAp, 7ZnHAp, and 10ZnHAp) have slightly elongated morphologies with average diameters between 25 nm and 18 nm. On the other hand, a uniform and homogeneous distribution of the constituent elements (calcium, phosphorus, zinc, and oxygen) in the ZnHAp powder was noticed. Besides, FTIR and Raman analyses confirmed the proper hydroxyapatite structure of the synthesized ZnHAp nanoparticles with the signature of phosphate, carbonate, and hydroxyl groups. Moreover, it can be concluded that Zn doping at the tested concentrations is not inducing a specific prokaryote or eukaryote toxicity in HAp compounds.

The double-perovskite Sr2FeMoO6 has been obtained by solid state method at low temperature (1060 degrees C) and a very short time of synthesis (up to 4h). Both, X-ray diffraction and scanning electron microscopy (SEM) confirmed the formation of Sr2FeMoO6 oxide with grain sizes around 160 mm, and a small amount of SrMoO4 as an impurity. Mossbauer spectroscopy revealed a mixed site population with Fe and Mo ions generating a structure type with population inversion. This structure has a critical influence on the magnetic properties, as confirmed by the magnetization and TC values, i.e 3.56 mu(B)/f.u and 415 K, respectively. The Sr2FeMoO6 behavior was interpreted in terms of ferrimagnetic couplings generated by the various distributions of local interactions between Fe and Mo neighbors while comparing the ideal structure should show antiferromagnetic coupling between the two sublattices.

This paper presents the synthesis of cerium doped hydroxyapatite using low concentrations of cerium (x(Ce) = 0.01, 0.03 and 0.05) by an adapted sol-gel method. The structural and optical properties of the obtained powders have been studied by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and Photoluminescence (PL) measurements. The cerium ions successfully substituted the calcium ions from the hydroxyapatite structure without inflicting any structural alterations. With the increase of dopant concentration in the sample a decrease of the mean particle size was observed. Also, the vibrational peak intensities decreased while the intensity of the photoluminescence excitation bands increased in intensity when the cerium concentration increased from x(Ce) = 0.01 to x(Ce) = 0.05. Taken together, the results suggest that even low concentration of cerium influence the properties of hydroxyapatite but do not-cause any structural alterations.

Eu-doped CaF(2)nanocrystalline powders have been prepared by using co-precipitation technique. Structural and morphological modifications induced by annealing are followed by using Eu3+-ion probe. Theluminescence properties are changing gradually together with the morphology of doped CaF2 nanoparticles accompanied by anEu(3+)-> Eu2+ conversion. Cathodoluminescence measurements show uniform distribution of the europium dopant ions in the annealed samples accompanied by a strong increase of the integral photoluminescence signal. During annealing the cubic structure of CaF2 nanoparticles is altered going to the spherical morphology due to the Eu3+ ions incorporation. In the annealed samples Eu3+ ions are incorporated as Eu3+-O dimer centres with the coordination symmetry (C-2 nu); in the sintered samples there are two non-equivalent Eu3+ sites. The thermoluminescence peaks have been assigned to the recombination of the Eu3+ related traps in these sites.