National Institute Of Materials Physics - Romania

We report on specific heat and resistivity measurements under hydrostatic pressure on the quasi-one dimensional metal TlxV6S8. We studied the interplay between the low temperature superconducting (SC) ground state and a high temperature charge density wave (CDW) instability. We observed a clear dependency of the physical properties of TlxV6S8 on the Tl concentration x. The CDW anomaly is present in all investigated samples that are strongly enhanced at half Tl filling, x = 0.47. This is also the only composition for which no signature of superconductivity is observed. The specific heat results regarding the SC phase in Tl0.63V6S8 suggest that this compound is a highly anisotropic, weak coupling superconductor. Pressure suppresses both SC and CDW transitions to lower temperatures. Nevertheless, as the CDW gap is closed at a critical pressure p(c), the increase in the density of states leads to a small enhancement of T-c suggesting that SC and CDW compete for parts of the Fermi-surface.

We report the synthesis of novel nanocomposites based on Fe@C nanoparticles obtained from Fe(CO)(5) and C2H4/H-2 by laser pyrolysis technique using a three nozzles injector. The alpha Fe-FexCy@C particles (below 24 nm diameter) were first functionalized with hydrophilic groups using Na carboxymethylcellulose. Oxidic precursors (Si(OC2H5)(4) or Ti(OC2H5)(4)) dissolved in ethanol were mixed with ethanolic suspensions of hydrophilized Fe@C nanoparticles using strong ultrasonication, then with water (at different pH values) and finally the Fe-containing composites were recovered by magnetic separation. The SiO2 and TiO2-coated powders were characterized by XRD, FT-IR and TEM techniques and their magnetic hysteresis curves were recorded at different temperatures. Both composites contain submicron aggregates of Fe@C nanoparticles embedded in/surrounded by a disordered porous oxidic matrix/shell. Near superparamagnetic behavior and room temperature and 26 Am-2/kg (for Fe@C/SiO2) or 57Am(2)/kg (for Fe@C/TiO2) saturation magnetization values were recorded and a blocking temperature around 500K was extrapolated. (C) 2013 Elsevier B.V. All rights reserved.

This paper reports on producing SiC based nanostructures (SiC, W-SiC, CNS-SiC) by pulsed laser deposition (PLD) and radio-frequency plasma assisted PLD. Simple and composite targets (SiC, 3/4 SiC + 1/4 tungsten and 3/4 SiC + 1/4 graphite) were irradiated by a 266 nm pulsed laser beam having a pulse duration of 7 ns. The silicon substrates were kept either at room temperature or heated up to 600 degrees C. The depositions were performed in argon at various pressures, ranging from 0.05 mbar up to 2 mbar. The influence of deposition parameters on the structure, surface morphology and composition of different SiC based structures was studied by atomic force microscopy, scanning electron microscopy, secondary ion mass spectrometry, transmission electron microscopy and selected area electron diffraction. Fibers, tubes, nanoparticles and rolled sheets structures were obtained by varying laser fluence, substrate temperature, gas pressure and radio-frequency power. (C) 2013 Elsevier B. V. All rights reserved.

We report on thin film deposition by matrix assisted pulsed laser evaporation (MAPLE) of two polymer-drug composite thin film systems. A pulsed KrF* excimer laser source (lambda = 248 nm, tau = 25ns, nu = 10 Hz) was used to deposit composite thin films of poly(D,L-lactide) (PDLLA) containing several gentamicin concentrations. FTIR spectroscopy was used to demonstrate that MAPLE-transferred materials exhibited chemical structures similar to those of drop cast materials. Scanning electron microscopy data indicated that MAPLE may be used to fabricate thin films of good morphological quality. The activity of PDLLA-gentamicin composite thin films against Staphylococcus aureus bacteria was demonstrated using drop testing. The influence of drug concentration on microbial viability was also assessed. Our studies indicate that polymer-drug composite thin films prepared by MAPLE may be used to impart antimicrobial activity to implants, medical devices, and other contact surfaces. (C) 2013 Elsevier B.V. All rights reserved.

Self-assembled layers of 4,4'-thio-bis-benzene-thiolate spontaneously adsorbed on p-doped GaAs(1 1 1)A and GaAs(1 1 1)B electrodes were examined by EIS, XPS, and AFM investigations. XPS data provide evidence that (i) both As and Ga atoms are involved in the thiolate formation no matter which one is prevailing on the semiconducting surface and (ii) only one of the two thiol groups participates in the chemisorption bond. EIS and AFM results point to a more stable thiolate layer formed on the As-terminated surface than that formed on the Ga-terminated surface due to stronger self-assembling effects developed between the adsorbed species. (C) 2013 Elsevier Ltd. All rights reserved.

Epitaxial SrCuO2 thin films were grown on (0 0 1) SrTiO3 substrates by pulsed laser deposition using a stoichiometric target. X-ray diffraction indicated that the SrCuO2 films undergo a structural phase transition as a function of the substrate temperature. Films deposited at temperatures below 600 degrees C exhibit a tetragonal phase with the c-axis oriented along the growth direction while films deposited at temperatures above 700 degrees C exhibit an orthorhombic phase with the b-axis oriented along the growth direction. Atomic force microscopy indicated that the as-grown film surfaces are rather smooth and the roughness increases with increasing substrate temperature. Energy dispersive X-ray spectroscopy in agreement with X-ray diffraction intensity ratio data revealed that all films are non-stoichiometric and contain Sr vacancies (Sr/Cu similar to 0.8). The influence of film-substrate lattice matching and substrate temperature on the structural phase transition is discussed. (C) 2012 Elsevier B.V. All rights reserved.

Ba(X1/3Ta2/3)O-3 (X = Mg, Zn) thin films were grown on commercial Pt-coated Si substrates by radiofrequency plasma beam assisted pulsed laser deposition (RF-PLD) method. Single phase Ba(Mg1/3Ta2/3)O-3 and Ba(Zn1/3Ta2/3)O-3 ceramic targets having an ordered hexagonal structure (with P (3) over bar m1 space group) were used for deposition. Structural, morphological and surface characterizations of the Ba(X1/3Ta2/3)O-3 (BXT) films were performed using X-ray diffraction, scanning electron microscopy and atomic force microscopy. X-ray diffraction studies evidenced a cubic (disordered) perovskite structure, with unit cell typical for Pm3m space group. Scanning electron microscopy investigations showed that BXT films have a columnar microstructure, which is oriented perpendicular to the substrate. The temperature dependence of the dielectric permittivity of the films was recorded at 100 kHz. Unlike targets, the BXT films exhibit positive values of the temperature coefficient of the dielectric permittivity. BaMg1/3Ta2/3O3 and BaZn1/3Ta2/3O3 thin films with dielectric constant of about 22.5 and 25, respectively have been obtained. (C) 2012 Elsevier B.V. All rights reserved.

A simple approach to fabricate periodic arrays of conical bumps on silicon (Si) substrate is reported. In the process, a single pulse from a 200 fs laser at 387 nm wavelength was applied on a self-assembled monolayer of 700 nm and 390 nm diameter silica spheres on a n-doped Si (1 0 0) wafer. The surface was irradiated at normal incidence by immersing the silicon substrates in a glass container filled with 1, 1, 2 trichlor-trifluorethan liquid precursors. After laser irradiation, at laser fluences in the range from 1 to 40 J/cm(2), a regular array of conical Si bumps was fabricated. The density of the Si bumps can be varied by varying the particle size diameter. The influence of the medium on the near-field interactions for both sizes silica particles layer is investigated. (C) 2013 Elsevier B.V. All rights reserved.

We report results of noncellular tests, revealing the occurrence of photocatalytic interactions between titanium dioxide (TiO2, titania) nanoparticles and the MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium-bromide] cytotoxicity indicator. These interactions induce the reduction of MTT and formation of purple formazan under biologically relevant conditions. Classical MU assays have been performed to evaluate the production of formazan in DMEM-F12 and RPMI-1640 cell culture media (containing 10% fetal bovine serum-FBS) treated with Degussa-P25 TiO2 nanoparticles, in the absence of cells. The colorimetric determinations revealed the noncellular MU to formazan transformation induced by TiO2 nanoparticles, under conditions commonly used for in vitro cytotoxicity testing of nanomaterials. The formazan precipitation was found to be proportional to the TiO2 concentration, being enhanced under laboratory daylight exposure. The photocatalytic nature of the studied effect was assessed under UV irradiation at 365 nm. The biological significance of the reported reaction was established with respect to cellular reference experiments performed on V79-4, HeLa and B16 cell lines. The results show false viability increases with up to 14% (for TiO2 concentrations generally higher than 50 mu g/ml), induced by the TiO2-MTT reaction. This type of artifacts may lead to underestimated toxicity or false proliferation results. (C) 2013 Elsevier Ltd. All rights reserved.

Homojunction transparent thin-film In2O3 transistors were fabricated at room temperature. Self-assembled In2O3 source-channel-drain structures were grown by pulsed electron beam deposition using a shadow mask with a 300 mu m diameter wire as an obstacle placed at similar to 100 mu m distance from the substrate for growing the channel region behind it. The film resistivity varies from similar to 7 x 10(8) Omega cm in the channel region to similar to 10(-3) Omega cm in the source-drain regions. We explain this fact by the relative depletion of the indium incorporated in the channel region of the film due to the reduced flux of ablated species arriving on the substrate behind the obstacle, leading to a relative enrichment in oxygen compared to the source and drain regions. The gate insulator is a Y2O3 film grown by RF magnetron sputtering. The transistor operates in enhanced mode. The subthreshold swing is similar to 0.26 V/decade with an on/off current ratio of 1.5 x 10(7), and the saturation channel mobility is greater than 45 cm(2) V-1 s(-1).