National Institute Of Materials Physics - Romania

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5781 articles found

2791. VOLTAGE PERCOLATION THRESHOLDS EVIDENCED IN THE ELECTRICAL BEHAVIOUR OF DIFFERENT NANOSTRUCTURES

Authors: Stavarache, I

Published: JUL-SEP 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 1083, DOI:

Percolation phenomena are investigated and discussed in three kinds of nanostructures: first two are nanocrystalline silicon-based systems, Si nanodots embedded in amorphous SiO2 matrix and porous silicon formed by an oxidized nanowire network, and the third consisting of a multi-walled carbon nanotube network embedded in amorphous SiN. The current-voltage characteristics measured on first two systems present voltage percolation thresholds with the same shape - a saturation plateau region of the current, followed by an abrupt increase. The current-voltage and conductance-voltage curves measured on multi-walled carbon nanotube network embedded in amorphous SiN present non-periodic and temperature independent oscillations. These oscillations are interpreted as voltage percolation thresholds.

2792. Shape Memory NiTi Alloys Obtained by Powder Metallurgy Route

Authors: Lucaci, M; Valeanu, M; Orban, RL; Tsakiris, V; Cirstea, DC; Leonat, L

Published: 2011, RESEARCHES IN POWDER METALLURGY, 672, +, DOI: 10.4028/www.scientific.net/MSF.672.99

The effect of Fe, respective Cu, additions as substitute for Ni in NiTi shape memory alloys (SMAs) on the delaying of its phase transition and narrowing hysteresis are well known, NiTi-Fe and NiTi-Cu SMAs having applications especially to the actuators that require such properties. These SMAs are currently produced by conventional melting methods, which are energo-intensive and impose very severe processing conditions to avoid contamination. The results of researches presented in this paper prove the possibility of these SMAs obtaining by powder metallurgy via reactive sintering - more advantageous from both technical and economic point of view. A beneficial effect on both sintering and homogeneity of the obtained SMAs proved to have a controlled mechanical alloying applied to powder mixture before compacting and sintering.

2793. The Influence of Magnetron Sputtering Conditions on the Physical Properties of (001) Oriented Nanostructured ZnO Thin Films

Authors: Simon, S; Besleaga, C; Stan, GE; Ion, L; Arghir, I; Antohe, S

Published: 2011, PHYSICS CONFERENCE (TIM-10), 1387, DOI: 10.1063/1.3647074

Smooth, transparent and highly oriented nanostructured ZnO films were synthesized by RF-magnetron sputtering onto Si(100) substrates. A mild-pressed zinc oxide powder target was used for all depositions. The sputtering parameters were varied in order to obtain structures with good adherence and crystallinity. The depositions were carried out in inert argon atmosphere at four sputtering pressures (0.2 Pa, 0.25 Pa, 0.3 Pa and 0.45 Pa). ZnO films were deposited at 150 degrees C. The films were characterized from structural (XRD) and morphological (AFM) point of view. The influence of each sputtering parameter on the morphological and structural properties is discussed.

2794. CuS NANOPARTICLES OBTAINED IN PRESENCE OF ONE SURFACTANT

Authors: Simonescu, CM; Capatina, C; Teodorescu, VS; Florea, G

Published: 2011, METALURGIA INTERNATIONAL, 16, 146, DOI:

In this study, copper sulfide CuS (covellite) was obtained, starting from the Cu(CH3COO)(2)center dot H2O and thiourea ((NH2CSNH2) system, and working in presence or absence of sodium-bis(2-ohylhexyl) sulfosuccinate (Na-AOT). Samples obtained from Cu(CH3COO)(2)center dot H2O:NH2CSNH2:Na-AOT system were deposited as thin films on the glass substrates. CuS samples obtained were characterized by X ray diffraction, IR spectroscopy, TEM transmission electron microscopy and SAED - selected area electron diffraction. The influence of surfactant on the shape and size of CuS (covellite) nanocrystals was established.

2795. Microwave antennas based on Ba1-xPbxNd2Ti5O14

Authors: Ene-Dobre, M; Banciu, MG; Nedelcu, L; Stoica, G; Busuioc, C; Alexandru, HV

Published: SEP-OCT 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 1304, DOI:

The Ba1-xPbxNd2Ti5O14 ceramic material (BNT) is very attractive for applications at frequencies around few GHz [1]. The temperature coefficient of the resonant frequency T-f decreases from + 70 ppm/degrees C to - 15 ppm/degrees C with the Pb content x increase up to 0.5. The samples with high Pb content exhibit a dielectric constant up to 86.6, but the product Q x f is several times lower than for such microwave ceramics as zirconium tin titanate [1-2]. When a product Q x f higher than 6000 is required in order to use the BNT materials at high frequencies, then the Pb content can result from the tradeoff between small temperature coefficient T-f and high quality factor Q. The features of the BNT dielectric resonators lead to the development of miniaturized dielectric resonator antenna (DRA) with improved characteristics. The DRAs of BNT ceramics presented in this paper exhibit an increased bandwidth due to an optimal height over diameter ratio. For an increased gain and shaping of the overall radiation pattern, an array of dielectric resonator antennas is proposed.

2796. The influence of excess nitrogen, on the electrical properties of the 4H-SiC/SiO2 interface

Authors: Pintilie, I; Moscatelli, F; Nipoti, R; Poggi, A; Solmi, S; Lovlie, LS; Svensson, BG

Published: 2011, SILICON CARBIDE AND RELATED MATERIALS 2010, 679-680, +, DOI: 10.4028/www.scientific.net/MSF.679-680.326

The effect of nitrogen (N) introduced by ion implantation at the SiO2/4H-SiC interface on the capacitance of the MOS capacitors is investigated. The Thermal Dielectric Relaxation Current (TDRC) technique and Capacitance-Voltage (C-V) measurements performed at different temperatures and probe frequencies on an N implanted sample and on a virgin sample were employed for this purpose. There are three types of defects located at or near the interface, D-it, NIToxfast and NIToxslow that can be distinguished. Only D-it and NIToxfast respond to the a.c. small, high frequency signal at temperatures above 150K. The separation of D-it from the NIToxfast states have enabled us to study the influence of the excess of interfacial Nitrogen on each of the mentioned defects. It has been found that the N-implantation process fully suppresses the formation of NIToxfast and partially NIToxslow and D-it. Theoretical C-V characteristics were computed, based on the defect distributions determined by TDRC, and compared with the experimental ones showing a close agreement.

2797. Illumination-dependent HF Etching of AlAs Sacrificial Layers for the Formation of "Rolled Up" Nanotubes from Strained InGaAs/GaAs Films

Authors: Costescu, RM

Published: 2011, PHYSICS CONFERENCE (TIM-10), 1387, DOI: 10.1063/1.3647071

Rolled-up nanostructures formed from lattice mismatched III-V heterojunction films by taking advantage of a strain-induced self-rolling mechanism represent a useful type of building blocks for nanotechnology, with possible applications in high-speed microelectronic and optoelectronic devices. This work investigated the effect of illumination on the hydrofluoric acid etching of AlAs sacrificial layers with systematically varied thicknesses in order to release and roll up MBE grown InGaAs/GaAs bilayers. Based on this "etch suppression effect" (ESE), we propose an illumination-assisted technique that offers an advantage over other methods of rolling up nano-objects on a substrate from inherently strained films because it allows control over the positioning of rolled-up micro- and nanotubes independently from lithographic methods. For thicknesses of AlAs below 10 nm, we found two etching regimes for the area under illumination: one at low illumination intensities, in which the etching and releasing proceeds as expected and one at higher intensities in which the etching and any releasing are completely suppressed. The "etch suppression" area is well defined by the illumination spot, which can be used to realize well-controlled heterogeneously etched regions on the same sample.

2798. Bovine Serum Albumin 3D Structure Determination by THz Spectroscopy and Molecular Modeling

Authors: Mernea, M; Leca, A; Dascalu, T; Mihailescu, D

Published: 2011, TERAHERTZ AND MID INFRARED RADIATION: GENERATION, DETECTION AND APPLICATIONS, +, DOI: 10.1007/978-94-007-0769-6_14

The low frequency collective movements of proteins associated with biologically relevant conformational transitions are situated in the terahertz (THz) spectral region. THz spectroscopy experiments have revealed that each molecular species has a unique absorption pattern in THz domain. We used time-domain THz spectroscopy (TDS) to study the conformation and flexibility of bovine serum albumin (BSA), a protein whose 3D structure is unknown. We performed THz spectroscopy experiments on lyophilized BSA. Theoretical spectra were obtained by normal modes analysis performed on BSA structures generated by homology modeling and molecular dynamics simulations. The agreement between experimental and theoretical data allowed us to validate the model of BSA and also to gain insight into BSA vibrations in THz domain.

2799. BNT ADVANCED CERAMICS FOR SLOT COUPLED DIELECTRIC RESONATOR ANTENNAS

Authors: Nicolaescu, I; Banciu, MG; Nedelcu, L; Avadanei, O; Radu, I

Published: 2011, 2011 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2011), 34TH EDITION, VOLS 1 AND 2, 196, DOI:

Barium neodymium titanate (BNT) material was prepared and characterized. The very high dielectric constant, high Qxf product and controllable temperature coefficient recommend the BNT material for microwave applications. Slot coupled antennas with BNT resonators are investigated. The resonator shape effect on the antenna bandwidth is discussed.

2800. From synthetic to natural nanoparticles: monitoring the biodegradation of SPIO (P904) into ferritin by electron microscopy

Authors: Lopez-Castro, JD; Maraloiu, AV; Delgado, JJ; Calvino, JJ; Blanchin, MG; Galvez, N; Dominguez-Vera, JM

Published: 2011, NANOSCALE, 3, 4599, DOI: 10.1039/c1nr10980d

A strong focus on Superparamagnetic Iron Oxide Nanoparticles (SPIOs) has been appreciated recently especially for their use in Magnetic Resonance Imaging (MRI). However, some questions are being raised over these particles due to their long-term toxicity related to the production of toxic free iron during their biodegradation. Here we show by Electron Microscopy how SPIOs (P904) (Guerbet, Paris) are degraded after they are taken up by macrophages, so that iron from the SPIO core is progressively incorporated into the iron-storing protein ferritin (a nontoxic form of iron).