National Institute Of Materials Physics - Romania

The bulk polymerization reaction of N-vinylcarbazole (VK) at 70 degrees C in the presence of single-walled carbon nanotubes (SWNTs) leads to a new composite, whose optical properties were studied by photoluminescence (PL), surface enhanced Raman scattering (SERS) and Fourier transform infrared (FTIR) spectroscopies. A dramatic reduction of the poly(N-vinylcarbazole) (PVK) PL efficiency and a change in the vibrational structure of the PL spectrum of this polymer were observed by adding SWNTs to the synthesis mixture. Steric hindrance effects were evidenced both in SERS spectra of the VK when it interacts mechanico-chemically with SWNTs and in FTIR spectra of the un-doped PVK/SWNTs' composites. Cyclic voltammetry was used to demonstrate the doping process of PVK in PVK/SWNTs' composite. (c) 2007 Elsevier Ltd. All rights reserved.

Comparative experiments regarding electrodeposition of zinc oxide either as films on Pt and Au substrates or as microwires grown in microporous polycarbonate membranes were carried out using nitrate aqueous solutions as electrolyte. Linear sweep voltammetry and electrochemical impedance spectroscopy together with SEM and XRD techniques were used for investigation. The equivalent electrical circuits for fitting experimental results were similar to those for characterisation of metal/polymer coating systems.

Barium strontium titanate (BST) bulk ceramic with composition Ba0.5Sr0.5TiO3 was produced by solid-state reaction and was used as target for PLD thin film deposition. A Nd-YAG laser, working at 5-10 Hz and different wavelengths has been used. Thin films of stoichiometric BST were deposited on alumina substrate with the thickness between 400 and 500 nm. An aditional annealing was carried out at 800 degrees C for 6 h. XRD and SEM were used for sample characterization. Capacity measurements were performed versus temperature at 100 kHz in a large temperature range. A diffuse ferroelectric-paraelectric phase transition with T-C = -72 degrees C for the BST thin film was determined. A 5% tunability was measured in the transition region. (c) 2007 Elsevier B.V. All rights reserved.

Amorphous SnSe, films were prepared by pulsed laser deposition (PLD) from solid polycrystalline targets. The atomic scale structure has been revealed by X-ray diffraction. Hardness and electrical properties were measured. Strong gas sensing properties have been evidenced for the first time in heat treated films. (c) 2007 Elsevier B.V. All rights reserved.

Photoluminescence (PL) spectra recorded at room temperature (RT) in polycrystalline BaFCI:Eu2+ X-ray storage phosphor have shown the europium associated luminescences, a broad luminescence band at 385nm (3.22eV) with a 3.3 +/- 0.1 mu s PL lifetime accompanied by a luminescence line at about 368nm (3.37eV). The energy difference Delta EB-L =226cm(-1) between the two excited levels from which the europium associated band and line luminescences took place was computed. An additional broad luminescence band at about 425nm (2.92eV) with 0.7 +/- 0.1 mu s PL lifetime has been attributed to the europium luminescence perturbed by an impurity. Time resolved spectroscopy measurements have shown that no other impurity luminescences (like oxygen-vacancy centres) can be observed at RT except the europium associated ones.

In order to be used for medical applications, a material must exhibit many specific characteristics, of which the most fundamental is related to biocompatibility. Lately, the iron oxide nanoparticles are preferred for biomedical applications because they present a superparamagnetic behaviour at room temperature. The preparation method and conditions of iron oxide nanoparticles represents some of the most important challenges that will determine the particle size and shape, the size distribution, the surface chemistry of the particles and consequently their magnetic properties. The samples were characterized by X-ray diffractions (XRD), transmission electron microscopy (TEM) and infrared spectroscopy.

This paper presents a study of the thermal regime associated with the experimental configuration used for the growth of doped organic crystals from the melt in Bridgman-Stockbarger configurations. For different systems, host: metadinitrobenzene (m-DNB), benzil/guest: m-DNB, naphthalene, iodine, I have investigated the effect of the changes in the experimental conditions (dopant type and concentration, c=0.5-3 wt %, thermal gradient at the growth interface, Delta T=6-33 degrees C, moving speed of the solid-liquid interface, V=0.7-2.7 mm/h) on the crystals growth process. I have made comparisons between the particularities of the incorporation mechanism of the big acceptor (atom:iodine c=0.5; 1; 2 wt %; molecule: m-DNB and naphthalene c=1.5; 3 wt %) and clopant segregation mechanism, and the transmission properties of different monocomponent crystalline organic matrix (m-DNB and benzil). I have also investigated the influence of the simultaneous presence of two dopants (m-DNB or naphthalene/iodine) in organic benzil matrix and their effect on the optical properties. have evaluated the growth interface stability in our Bridgman-Stockbarger experimental configuration and analysed the conditions for the generation of the morphological instabilities in benzil-dopant system.

The iron oxide-based nanomaterials have a great importance because of their impact on a wide number of industries. They have many properties and applications in domains as: environmental protection, biomedical, catalysis, information displays and electronics. In order to avoid the tendency of nanoparticles to aggregate, they are often included in sol-gel derived silica matrices, thus being also ensured a homogeneous dispersion of the ultra-fine metal oxide particles in the host matrix. The reasons of the attempt are both an economic and a non-pollutant one, tacking into account the fact that it is well known that aqueous silica sol is cheaper and less toxic than TEOS. The Fe3O4 was introduced in the reaction mixture as aqueous suspension. A final iron content related to SiO2 of 3% wt. was chosen for the prepared nanocomposite. Thermal analysis, IR spectroscopy, XRD and TEM methods have been used for the structural characterisation,. Some experiments of water depollution (from As) have been proceeded using the prepared Fe3O4-SiO2 nanocomposite.

Metallic nanowires with magnetic properties were prepared by electrochemical deposition in nanoporous ion track membranes. Thus, we prepared Co-Cu alloy and Co/Cu multilayered nanowires. The technique allows the preparation of uniform arrays of parallel nanowires with desired properties. The process of electrochemical deposition of metals in nanoporous membranes was studied by means of cyclic voltammetry and impedance spectroscopy. The influences of deposition conditions such as bath composition, temperature and deposition potential on the morphological, structural and compositional properties of the nanowires were systematically studied.

Sandwich type (MIS) heterostructures based on layers of organic semiconductors as meta-dinitrobenzene (m-DNB) and perylene or perylene derivative 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) have been prepared using alternative methods (rapid thermal directional solidification or two-steps, vacuum evaporation and deposition process) on different substrates (single crystal silicon wafer and textolite covered with copper film). Subsequently indium, gallium, aluminium of high purity (5N) and silver have been used for the preparations of the metallic contacts. This paper presents some investigations of the contact between different organic semiconductors and several metals: meta-dinitrobenzene/Cu, perylene/In, peryiene/Al, perylene/Ga, perylene/Ag, PTCDA/AI, PTCDA/Ga, and PTCDA/Ag. The comparative study of the electrical conduction properties of these organic semi conductor/metal contacts has emphasised significant differences depending on the metal type, metal/organic semiconductor interface properties and quality of the contact, which is determined by the preparation method (pressing, melting, vacuum evaporation, painting) and selected contact cinfiguration. The experimental data obtained using the 2 points contact geometry have evidenced linear or power IN dependences of the investigated metallic contacts emphasising the importance of the space-charge phenomenon and defects on the charge carriers' transport in these structures.