National Institute Of Materials Physics - Romania

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849 articles found

551. 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.

552. 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.

553. 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.

554. Non-nitridated oxides: abnormal behaviour of n-4H-SiC/SiO2 capacitors at low temperature caused by near interface states

Authors: Pintilie, I; Moscatell, 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.679-680.346

Comparative studies of gate oxides on a N+ pre-implanted area (N-interface similar to 1x10(19)cm(-3)) and on a virgin Si face 4H-SiC material (N-interface similar to 1x10(16)cm(-3)) have been undertaken by means of Capacitance-Voltage (C-V) characteristics, performed at different temperatures and frequencies, and Thermal Dielectric Relaxation Current technique. In the non implanted samples, the stretch out of the C-V curves get larger as the temperature is lowered to 150K, while for lower temperatures the C-V characteristics become steeper and some discontinuities occur. These discontinuities are specific for the non-implanted sample and are associated with charging of the fast near interface states (NIToxfast) via a tunneling from the shallow interface states (D-it). The tunneling from the shallow D-it to NIToxfast supress the a.c. response of D-it, which is recovered only after most of the NIToxfast are charged with electrons.

555. TAILORING OF OPTICAL, COMPOSITIONAL AND ELECTRICAL PROPERTIES OF THE InxZn1-xO THIN FILMS OBTAINED BY COMBINATORIAL PULSED LASER DEPOSITION

Authors: Socol, G; Galca, AC; Luculescu, CR; Stanculescu, A; Socol, M; Stefan, N; Axente, E; Duta, L; Mihailescu, CM; Craciun, V; Craciun, D; Sava, V; Mihailescu, IN

Published: JAN-MAR 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 115, DOI:

Indium Zinc Oxide compositional libraries were fabricated by combinatorial pulsed laser deposition technique on glass substrate at room temperature. Two pairs of targets with In atomic concentrations, In/(In+Zn), of 28 at.% and 56 at.% or 42 at.% and 70 at.% were employed. A high transparency was observed for all the coatings with transmittance values better than 95%. The maximum thicknesses of the samples, inferred by spectroscopic ellipsometry, were within the 174-310 nm range for the simple PLD films, whereas in case of combinatorial PLD coatings were 341 or 467 nm. Energy dispersive X-ray spectroscopy revealed that In content in the combinatorial films was in the 27-52 at. % range. From atomic force microscopy histograms we evidenced a decrease of the RMS roughness down to 1 nm with the increase of the In content. As a result of the compositional library studies two minimum values of the electrical resistivity were identified at 2.3x10(-3) Omega.cm and 8.6 x 10(-4) Omega.cm, which correspond to 28.8-29.5 at.% and 44-49 at% range of Indium content.

556. Differentiation of mesenchymal stem cells onto highly adherent radio frequency-sputtered carbonated hydroxylapatite thin films

Authors: Sima, LE; Stan, GE; Morosanu, CO; Melinescu, A; Ianculescu, A; Melinte, R; Neamtu, J; Petrescu, SM

Published: DEC 15 2010, JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 95A, 1214, DOI: 10.1002/jbm.a.32947

In this work, an improved version of the radio frequency magnetron sputtering (RF-MS) technique was used to prepare highly adherent B-type carbonated hydroxylapatite (B-CHA) thin films. Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction studies proved that the coatings maintained the composition and revealed the polycrystalline structure of HA. Scanning electron microscopy analysis showed that the CHA films are rough and exhibit a homogeneous microstructure. Energy-dispersive Xray spectroscopy (EDX) mapping demonstrated a uniform distribution of the Ca and P cations while a Ca/P ratio of 1.8 was found. In addition, the FTIR experiments showed a remarkable reproducibility of the nanostructures. Human mesenchymal stem cells (hMSCs), in vitro differentiated osteoblasts, and explanted bone cells were grown over the surface of CHA coatings for periods between a few hours and 21 days. Osteoprogenitor cells maintained viability and characteristic morphology after adhesion on CHA coatings. Ki67-positive osteoblasts were the evidence of cell proliferation events. Cells showed positive staining for markers of osteoblast phenotype such as collagen type I, bone sialoprotein and osteonectin. Our data showed the formation of mineralized foci by differentiation of hMSCs to human primary osteoblasts after cultivation in osteogenic media on RF-sputtered films. The results demonstrate the capacity of B-type CHA coating to support MSCs adhesion and osteogenic differentiation ability. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 95A: 1203-1214,2010.

557. Microstructure and ferroic properties of epitaxial [gamma-Fe2O3-BiFeO3]-Bi3.25La0.75Ti3O12 composite bilayers

Authors: Gautreau, O; Harnagea, C; Gunawan, L; Botton, GA; Pintilie, L; Singh, MP; Pignolet, A

Published: DEC 1 2010, JOURNAL OF APPLIED PHYSICS, 108, DOI: 10.1063/1.3514591

Epitaxial [gamma-Fe2O3-BiFeO3]/Bi3.25La0.75Ti3O12 and Bi3.25La0.75Ti3O12/[gamma-Fe2O3-BiFeO3] composite bilayers were grown on SrRuO3 coated (111) SrTiO3 substrates in order to investigate the influence of the morphology of the gamma-Fe2O3-BiFeO3 self assembled nanocomposite layer on the multiferroic properties of the bilayer. Both types of bilayers exhibit high resistivity and simultaneously ferroelectricity and ferrimagnetism at room temperature. When the gamma-Fe2O3-BiFeO3 composite layer is sandwiched between the Bi3.25La0.75Ti3O12 film and the substrate, the BiFeO3 component is not only subjected to epitaxial strain induced by the surface on top of which it grows but also to elastic interactions with the Bi3.25La0.75Ti3O12 capping layer. The latter indeed reduce the amount of gamma-Fe2O3 inclusions, affects the morphology of the grains in the gamma-Fe2O3-BiFeO3 layer, and increases the shape anisotropy of the gamma-Fe2O3 inclusions. Additionally, this modification in the microstructure of the gamma-Fe2O3-BiFeO3 layer induces an imprint in the ferroelectric hysteresis loop as well as a decrease in the saturation magnetization, and its magnetic easy axis direction changes from in-plane to out-of plane. (c) 2010 American Institute of Physics. [doi:10.1063/1.3514591]

558. Barium magnesium tantalate thin films deposited by RF-magnetron sputtering from a stoichiometric target

Authors: Braic, V; Kiss, A; Ioachim, A; Toacsan, M; Nedelcu, L; Braic, M

Published: DEC 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 2385, DOI:

Barium magnesium tantalate thin films are attractive materials for high-performance dielectric ceramics for microwave devices, exhibiting a high dielectric constant, a low loss and a near-zero temperature coefficient. We report on the successful deposition of polycrystalline barium magnesium tantalate thin films by RF magnetron sputtering method. The structural and morphological characterization data are presented.

559. Biomineralization capability of adherent bio-glass films prepared by magnetron sputtering (vol 21, pg 1047, 2010)

Authors: Stan, GE; Pina, S; Tulyaganov, DU; Ferreira, JMF; Pasuk, I; Morosanu, CO

Published: OCT 2010, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 21, 2899, DOI: 10.1007/s10856-010-4040-6

560. Bioactive glass thin films deposited by magnetron sputtering technique: The role of working pressure

Authors: Stan, GE; Marcov, DA; Pasuk, I; Miculescu, F; Pina, S; Tulyaganov, DU; Ferreira, JMF

Published: SEP 15 2010, APPLIED SURFACE SCIENCE, 256, 7110, DOI: 10.1016/j.apsusc.2010.05.035

Bioglass coatings were prepared by radio frequency magnetron sputtering deposition at low temperature (150 degrees C) onto silicon substrates. The influence of argon pressure values used during deposition (0.2 Pa, 0.3 Pa and 0.4 Pa) on the short-range structure and biomineralization potential of the bioglass coatings was studied. The biomineralization capability was evaluated after 30 days of immersion in simulated body fluid. SEM-EDS, XRD and FTIR measurements were performed. The tests clearly showed strong biomineralization features for the bioglass films. The thickness of the chemically grown hydroxyapatite layers was more than twice greater for the BG films deposited at the highest working pressure, in comparison to those grown on the films obtained at lower working pressures. The paper attempts to explain this experimental fact based on structural and compositional considerations. (C) 2010 Elsevier B.V. All rights reserved.