National Institute Of Materials Physics - Romania
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471. Significant enhancement of the critical current density for cubic BN addition into ex situ spark plasma sintered MgB2
Authors:
Badica, P; Aldica, G; Burdusel, M; Popa, S; Negrea, RF; Enculescu, M; Pasuk, I; Miu, L
Published: SEP 2014, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 27, DOI: 10.1088/0953-2048/27/9/095013
High density (above 93%) superconducting bulks of MgB2 with addition of hexagonal BN (h-BN) and cubic BN (c-BN) with compositions ((MgB2) + (BN)(x), x = 0.01, 0.03, 0.05) were obtained by ex situ spark plasma sintering. All the investigated samples have the critical temperature T-c = 38.8 K. The variation of the critical current density J(c) with the external magnetic field H for h-BN added sample is almost overlapping the J(c)(H) dependence for the pristine MgB2 sample. On the other hand, J(c) for the samples added with c-BN is larger at high magnetic fields, while the decrease of J(c) at low H is very small. At T = 20 K, a J(c) of 10(2) A cm(-2) is determined for the sample with x(c-BN) = 0.005 at H = 58 kOe, and for the sample with x(c-BN) = 0.01 at 54 kOe. Magnetic relaxation measurements indicate a significant flux pinning enhancement in MgB2 samples added with c-BN. It is proposed that the disorder at the interface caused by the convenient lattice matching relationship between the lateral plane of the MgB2 crystal prism and the face of the c-BN crystal cube is responsible for the observed vortex pinning increase.
474. BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped in Anodise Alumina membrane pores array
Authors:
Secu, CE; Matei, E; Secu, M; Damian, V
Published: SEP 2014, RADIATION MEASUREMENTS, 68, 41, DOI: 10.1016/j.radmeas.2014.07.001
Sol-gel template method has been used to prepare BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped within the nanopores array (of about 200 nm size) of a comercial anodized alumina (AA) membrane. Structural and morphological measurements using electron microscopy (SEM) and X-ray diffraction (XRD) have shown the presence of the BaFBr:Eu2+ nanophosphor in the silica xerogel entrapped within the nanopores array; photoluminescence and X-ray excited luminescence measurements have shown Eu2+ luminescence at 395 nm accompanied by a broad band due to AA membrane. The method assures a relatively uniform spreading of the BaFBr nanophosphor into the AA membrane pores array without the nanoparticles agglomeration. Preliminary imaging tests have shown a spatial resolution in the micrometer range and even in the submicrometer range can be expected. As BaFBr:Eu2+ is a very efficient Xray phosphor the material might be used as X-ray micro-imaging detector. (C) 2014 Elsevier Ltd. All rights reserved.
477. Addition of Ho2O3 of different types to MgB2 in the ex-situ Spark Plasma Sintering: Simultaneous control of the critical current density at low and high magnetic fields
Authors:
Aldica, G; Popa, S; Enculescu, M; Batalu, D; Miu, L; Ferbinteanu, M; Badica, P
Published: AUG 14 2014, MATERIALS CHEMISTRY AND PHYSICS, 146, 323, DOI: 10.1016/j.matchemphys.2014.03.030
Two different types of Ho2O3 powders (showing a much different morphology) were added to MgB2 in the ex-situ Spark Plasma Sintering (SPS). In the 5-25 K range, the first Ho2O3 powder type does not significantly suppress the critical current density J(c) at low magnetic fields and the second one enhances it at high fields, while their mixture simultaneously controls J(c) at both small and high magnetic fields so that the decrease is small at low fields and there is a notable enhancement at high fields when compared to pristine sample. The control of J(c)(H) is discussed versus specific characteristics of the raw powders, the resulting microstructure of the added SPS-ed samples and pinning details from magnetic relaxation measurements. (C) 2014 Elsevier B.V. All rights reserved.
478. Field Effect Transistor with Electrodeposited ZnO Nanowire Channel
Authors:
Florica, C; Matei, E; Costas, A; Molares, MET; Enculescu, I
Published: AUG 10 2014, ELECTROCHIMICA ACTA, 137, 297, DOI: 10.1016/j.electacta.2014.05.124
ZnO nanowires were prepared by electrochemical deposition in polycarbonate ion track templates. After the deposition process the polymer templates were dissolved in dichloromethane and the nanowires were harvested by ultrasonication in isopropyl. A droplet of nanowire suspension was placed on a Si/SiO2 substrate patterned with interdigitated electrodes. By means of electron beam lithography single nanowires were selected and provided with electrical contacts. We found that in order to obtain reliable electrical contacts and typical field effect characteristics the electrode deposition process needs to be adapted to the 3 D shape of the wires and that annealing and passivation treatments are necessary. (C) 2014 Elsevier Ltd. All rights reserved.
479. Superhydrophobic ZnO networks with high water adhesion
Authors:
Florica, C; Preda, N; Enculescu, M; Zgura, I; Socol, M; Enculescu, I
Published: AUG 8 2014, NANOSCALE RESEARCH LETTERS, 9, DOI: 10.1186/1556-276X-9-385
ZnO structures were deposited using a simple chemical bath deposition technique onto interdigitated electrodes fabricated by a conventional photolithography method on SiO2/Si substrates. The X-ray diffraction studies show that the ZnO samples have a hexagonal wurtzite crystalline structure. The scanning electron microscopy observations prove that the substrates are uniformly covered by ZnO networks formed by monodisperse rods. The ZnO rod average diameter and length were tuned by controlling reactants' concentration and reaction time. Optical spectroscopy measurements demonstrate that all the samples display bandgap values and emission bands typical for ZnO. The electrical measurements reveal percolating networks which are highly sensitive when the samples are exposed to ammonia vapors, a variation in their resistance with the exposure time being evidenced. Other important characteristics are that the ZnO rod networks exhibit superhydrophobicity, with water contact angles exceeding 150 degrees and a high water droplet adhesion. Reproducible, easily scalable, and low-cost chemical bath deposition and photolithography techniques could provide a facile approach to fabricate such ZnO networks and devices based on them for a wide range of applications where multifunctionality, i.e., sensing and superhydrophobicity, properties are required.
480. Effects of substrate and ambient gas on epitaxial growth indium oxide thin films
Authors:
Nistor, M; Seiler, W; Hebert, C; Matei, E; Perriere, J
Published: JUL 15 2014, APPLIED SURFACE SCIENCE, 307, 460, DOI: 10.1016/j.apsusc.2014.04.056
Indium oxide thin films were grown by pulsed electron beam deposition method at 500 Con c-cut sapphire and (0 0 1) oriented LaAlO3 single crystal substrates in oxygen or argon gas. The effects of ambient gas and substrate symmetry on the growth of indium oxide thin films were studied. Stoichiometric In2O3 films are formed in oxygen, while oxygen deficient In2O2.5 films are grown in argon, with In metallic nanoclusters embedded in a In2O3 matrix (nanocomposite films). In both cases, epitaxial In2O3 films having the bixbyite phase were grown with various orientation relationships, depending upon the substrate symmetry and gas ambient (oxygen or argon). Domain matching epitaxy was used to describe the precise in-plane epitaxial film-substrate relationships. The differences in film texture were correlated to the differences in growth conditions, while the differences in the film properties were correlated to the film oxygen composition. (c) 2014 Elsevier B.V. All rights reserved.
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