National Institute Of Materials Physics - Romania

A series of pyridinium salts with various counterions (Br-, NO3-, BF4-, PF6-, OTf- and SCN-) and different spacer chain lengths, which display a nematic phase, have been designed and prepared. They are derived from 4-hydroxypyridine and possess two mesogenic cyanobiphenyl groups attached to the pyridinium unit via a flexible long alkyl spacer (6, 9, 10). These salts exhibit solely a nematic phase with the thermal range influenced by the counterion employed and spacer length.

Ferroelectric (FE) thin film varactors can be a convenient technology for tuning miniature antennas. In this paper we present the design of a compact, agile, wire patch antenna integrating barium strontium titanate (Ba(1-x)SrxTiO3, BST) thin film interdigitated capacitors (IDC). The IDCs values were measured at different temperatures and bias voltages ranging from 0 to 120 V showing a capacitance variation of more than 40% between 11-13 GHz and up to 28% in the 2-3 GHz frequency interval. Their integration within a compact antenna design allows tuning its operating frequency on the whole WiFi band, with efficiencies higher than 70%.

Fe and Fe-Cr-Al thin films, both as sputtered on Si substrates as well as after subsequent annealing treatments in hydrogen atmosphere, have been investigated by means of X-ray reflectometry, magneto-optic Kerr effect and Mossbauer spectroscopy with respect to structural and related magnetic characteristics. The as deposited films are showing chemically disordered bcc structures, assigned to Fe-Si and Fe-Cr-Al-Si phases, respectively, with soft magnetism and magnetic texture, both influenced by the presence of Si, Cr and Al atoms. The softness of the films as well as the magnetic texture are strongly modified via hydrogenation treatments. In addition, such treatments induce the expulsion of Si, Cr and Al atoms from the as deposited phases, providing almost pure Fe films of much well crystallized bcc structure.

Bioactive composites of bovine derived hydroxyapatite and boron containing bioactive glass were doped with 5, 10 and 15 wt.% lanthanum oxide (La2O3). Results showed that at low sintering temperatures (800 degrees C) the doping oxide of La2O3 promoted transformation to crystalline phases. Formation of secondary phases, such as rhenanite, NaCaPO4, and calcium silicate, Ca2SiO4, were also found. La was found to act as modifier and influenced the viscosity. The increase of La2O3 content led to decrease of pore size. Porosity amount 48.1 %, at 15-240 mu m size range were reduced, to 34.4 %, with 5-80 mu m size range and particle sizes of 0.3-6 mu m to 0.09-2 mu m, respectively. In addition to that compression strength (MPa) and microhardness (HV) of the performed composite bioceramics were in the range of 25 - 110 MPa, and 121 - 364 HV, respectively. Our investigations suggested that the porosity type has a strong influence on the compressive strength and microhardness properties of the final bioceramic products.

Restoration of damaged bone tissue involves two traditional approaches: tissue grafting and alloplastic replacement. Recently, their limitations led to the development of tissue engineering, which uses degradable porous supports named "scaffolds". These porous structures (used both for tissue engineering and classic bone substitution applications) with customizable designs may be constructed by solid freeform fabrication (SFF) techniques. SFF uses various synthetic materials and may be adapted for creating ceramic-based scaffolds, which became popular due to increased demands for bone substitution materials. Among these materials, naturally derived ceramics are suitable candidates for bone replacement due to their resemblance with the mineral bone. Innovative optimization routes for preparing naturally derived ceramics with modulated properties implies the management of key parameters involved in heat treatment of animal hard tissues: temperature, heating environment, and cooling conditions. Both powders and bulk pieces are evaluated with complementary techniques that focus on compositional, morphological, and structural features. Finally, qualitative and quantitative biological assay in relevant cell culture of the compacted powders may assist extensive testing programs for further evaluation of different ceramic scaffolds. All these results contribute to effective assessment of ceramics tuning strategies and to subsequent modulation of their enhanced properties and long-term functionality.

The effects of the bonding mechanism and band alignment in a ferroelectric (FE) BaTiO3/ferromagnetic La0.6Sr0.4MnO3 heterostructure are studied using x-ray photoelectron spectroscopy and first-principles calculations. The band lineup at the interface is determined by a combination of band bending and polarization-induced modification of core-hole screening. A Schottky barrier height for electrons of 1.22 +/- 0.17 eV is obtained in the case of downwards FE polarization of the top layer. The symmetry of the bonding states is emphasized by integrating the local density of states +/- 0.2 eV around the Fermi level, and strong dependence on the FE polarization is found: upwards, polarization stabilizes Ti t(2g) (xy) orbitals, while downwards, polarization favors Ti t(2g) (yz) symmetry. It is predicted that the abrupt (La, Sr)vertical bar TiO2 interface is magnetoelectrically active, leading to a A-type antiferromagnetic coupling of the first TiO2 interface layer with the underlying manganite layer through a superexchange mechanism.

Superconducting bulks of MgB2 were obtained by the Spark Plasma Sintering (SPS) technique. Different heating rates of 20, 100, 235, 355, and 475 degrees C/min were used. Samples have high density, above 95%. The onset critical temperature T-c, is about 38.8 K. There is an optimum heating rate of similar to 100 degrees C/min to maximize the critical current density J(c0), the irreversibility field H-irr, the product (J(c0) x mu H-0(irr)), and to partially avoid formation of undesirable flux jumps at low temperatures. Significant microstructure differences were revealed for samples processed with low and high heating rates in respect to grain boundaries. (C) 2015 Elsevier B.V. All rights reserved.

Thermo-ionic Vacuum Arc evaporation method was selected for the synthesis of Fe/Cu/Ni/Cu multilayer structures on Si (1 0 0) substrates. The aim of the study was the preparation and characterization of structures featuring a giant magnetoresistance effect. This was accomplished by inducing the formation of nanosized ferromagnetic crystallites in multilayer nonmagnetic solutions via atomic inter-diffusion processes by the tuning of deposition parameters. Layer-by-layer and inter-diffused type structures were prepared and comparatively analyzed by scanning electron microscopy, X-ray microanalysis, atomic force microscopy, X-ray diffraction and high-resolution transmission electron microscopy coupled with selected area electron diffraction. We presented the influence of the microstructure on electric and magnetic properties of the submicron-sized multilayers. The dependence of the electric resistance and the magnetoresistance on the composition, structure, morphology and roughness of the layers was established. We obtained an electric resistance value of 1.22 Omega for the layer-by-layer type structure, and 0.46 Omega for the inter-diffusion designed structure. Using the atomic inter-diffusion we succeeded in achieving an improvement of the magnetoresistive effect, from 0.1% to 2.3%. (C) 2015 Elsevier B.V. All rights reserved.

The chemical modification of the niobium (Nb) surface after irradiation with femtosecond laser pulses was investigated by scanning electron microscopy coupled with energy dispersive spectroscopy, atomic force microscopy, grazing incidence X-ray diffraction, and micro-Raman spectroscopy. The physical-chemical analyses indicated that the laser treatment results in oxidation of the Nb surface, as well as in the formation of Nb hydrides. Remarkably, after the samples' washing in ethanol, a strong Surface-Enhanced Raman Scattering (SERS) signal originating from the toluene residual traces was evidenced. Further, it was observed that the laser irradiated Nb surface is able to provide a SERS enhancement of similar to 1.3 x 10(3) times for rhodamine 6G solutions. Thus, for the first time it was shown that Nb/Nb oxide surfaces could exhibit SERS functionality, and so one can expect applications in biological/biochemical screening or for sensing of dangerous environmental substances. (C) 2015 AIP Publishing LLC.

Ba0.95Ce0.05Ti0.9875O3 nanowires were fabricated by sol-gel method using as template a polycarbonate membrane with channels of 100 nm diameter. FE-SEM analyses showed that continuous gel wires of length up to 17 mu m and an average diameter of 81 nm, were obtained. After calcination at 700 degrees C for 1 h, these green 1D nanostructures were converted into well-crystallised wires with an average diameter of 59.7 nm, as high-resolution transmission electron microscopy and selected area electron diffraction indicated. The piezoelectric activity of the Ba0.95Ce0.05Ti0.9875O3 nanowires was investigated using piezoresponse force microscopy (PFM) correlated with atomic force microscopy. The results of PFM measurements indicated that the wires exhibit a significant fraction of ferroelectric domains larger than the grains size and a good piezoelectric response.