National Institute Of Materials Physics - Romania

Publications

5714 articles found

1561. Dense, Regular GaAs Nanowire Arrays by Catalyst-Free Vapor Phase Epitaxy for Light Harvesting

Authors: Jin, JH; Stoica, T; Trellenkamp, S; Chen, Y; Anttu, N; Migunov, V; Kawabata, RMS; Buenconsejo, PJS; Lam, YM; Haas, F; Hardtdegen, H; Grutzmacher, D; Kardynal, BE

Published: AUG 31 2016, ACS APPLIED MATERIALS & INTERFACES, 8, 22492, DOI: 10.1021/acsami.6b05581

Density dependent growth and optical properties of periodic arrays of GaAs nanowires (NWs) by fast selective area growth MOVPE are investigated. As the period of the arrays is decreased from 500 nm down to 100 nm, a volume growth enhancement by a factor of up to four compared with the growth of a planar layer is observed. This increase is explained as resulting from increased collection of precursors on the side walls of the nanowires due to the gas flow redistribution in the space between the NWs. Normal spectral reflectance of the arrays is strongly reduced compared with a flat substrate surface in all fabricated arrays. Electromagnetic modeling reveals that this reduction is caused by antireflective action of the nanowire arrays and nanowire-diameter dependent light absorption. Irrespective of the periodicity and diameter, Raman scattering and grazing angle X-ray diffraction show signal from zinc blende and wurtzite phases, the latter-originating from stacking faults, as observed by high resolution transmission electron microscopy. Raman spectra contain intense surface phonons peaks, whose intensity depends strongly on the nanowire diameters as a result of potential structural changes and as well as variations of optical field distribution in the nanowires.

1562. Novel facile method for obtaining CdSe/polyaniline/C-60 composite materials

Authors: Rusen, E; Diacon, A; Mocanu, A; Nistor, LC

Published: AUG 30 2016, SCIENTIFIC REPORTS, 6, DOI: 10.1038/srep32237

This study presents a novel method for the oxidative polymerization of aniline (ANI) by employing fullerene C-60/cadmium selenide (CdSe) quantum dots, as promoting agent of the polymerization system. The polymerization initiation mechanism is based on the difference between the HOMO-LUMO energy levels of the components which permits the formation of a continuous donor-acceptor exchange. Both the polymerization reaction evolution and the molecular weights of the obtained polymers have been characterized. The novelty of the paper consists in the synthesis of a novel nanocomposite material through a novel polymerization technique. The resulting material containing PANI, CdSe quantum dots and C-60 has been characterized by UV-Vis, NIR, fluorescence, TEM and GPC analyses.

1563. Electrochromic properties of polyaniline-coated fiber webs for tissue engineering applications

Authors: Beregoi, M; Busuioc, C; Evanghelidis, A; Matei, E; Iordache, F; Radu, M; Dinischiotu, A; Enculescu, I

Published: AUG 30 2016, INTERNATIONAL JOURNAL OF PHARMACEUTICS, 510, 473, DOI: 10.1016/j.ijpharm.2015.11.055

By combining the electrospinning method advantages (high surface-to-volume ratio, controlled morphology, varied composition and flexibility for the resulting structures) with the electrical activity of polyaniline, a new core-shell-type material with potential applications in the field of artificial muscles was synthesized. Thus, a poly(methylmethacrylate) solution was electrospun in optimized conditions to obtain randomly oriented polymer fiber webs. Further, a gold layer was sputtered on their surface in order to make them conductive and improve the mechanical properties. The metalized fiber webs were then covered with a PANI layer by in situ electrochemical polymerization starting from aniline and using sulphuric acid as oxidizing agent. By applying a small voltage on PANI-coated fiber webs in the presence of an electrolyte, the oxidation state of PANI changes, which is followed by the device color modification. The morphological, electrical and biological properties of the resulting multilayered material were also investigated. (C) 2015 Elsevier B.V. All rights reserved.

1564. Transparent field-effect transistors based on AlN-gate dielectric and IGZO-channel semiconductor

Authors: Besleaga, C; Stan, GE; Pintilie, I; Barquinha, P; Fortunato, E; Martins, R

Published: AUG 30 2016, APPLIED SURFACE SCIENCE, 379, 276, DOI: 10.1016/j.apsusc.2016.04.083

The degradation of thin-film transistors (TFTs) caused by the self-heating effect constitutes a problem to be solved for the next generation of displays. Aluminum nitride (AlN) is a viable alternative for gate dielectric of TFTs due to its good thermal conductivity, matching coefficient of thermal expansion to indium-gallium-zinc-oxide, and excellent stability at high temperatures. Here, AlN thin films of different thicknesses were fabricated by a low temperature reactive radio-frequency magnetron sputtering process, using a low cost, metallic Al target. Their electrical properties have been thoroughly assessed. Furthermore, the 200 nm and 500 nm thick AlN layers have been integrated as gate-dielectric in transparent TFTs with indium-gallium-zinc-oxide as channel semiconductor. Our study emphasizes the potential of AlN thin films for transparent electronics, whilst the functionality of the fabricated field-effect transistors is explored and discussed. (C) 2016 Elsevier B.V. All rights reserved.

1565. Combined ab initio and XPS Investigations of the Electronic Interactions of L-Cysteine Adsorbed on GaAs(100)

Authors: Juarez, MF; Toader, AM; Negrila, C; Santos, E; Lazarescu, V

Published: AUG 16 2016, CHEMISTRYSELECT, 1, 3634, DOI: 10.1002/slct.201600589

The adsorption of L-cysteine from ethanol solutions on GaAs(1 0 0) surfaces has been studied by XPS and density-functional theory (DFT). XPS data reveal that the formation of the adsorbate involves preferentially the As-sites for p-GaAs(1 0 0) and the Ga-sites for n-GaAs(1 0 0). The adsorbed species show different orientations of the functional groups to the surface for the different substrates. DFT calculations performed for both Ga-dimers and As-dimers terminated surfaces show that the adsorption is energetically favourable on both substrates. However, the adsorption energy is more negative on top of Ga-atoms. Here an important contribution for the stabilization of the adsorbate is the interaction of the functional groups with the surface. The parallel orientation found for the Ga-bound species by DFT calculations is in good agreement with the shift in the binding energy of the NH2/NH3+ species observed by XPS analysis.

1566. New-developed TiO2-based photocatalytic nano particles exhibit biocompatibility on MRC-5 lung fibroblasts after short-term exposure

Authors: Dinischiotu, A; Nica, CI; Stan, MS; Dumitrescu, I; Diamandescu, L

Published: AUG 10 2016, JOURNAL OF BIOTECHNOLOGY, 231, S67, DOI: 10.1016/j.jbiotec.2016.05.246

1567. Rise in power of Yb:YCOB for green light generation by self-frequency doubling

Authors: Khaled, F; Loiseau, P; Aka, G; Gheorghe, L

Published: AUG 1 2016, OPTICS LETTERS, 41, 3610, DOI: 10.1364/OL.41.003607

Spectroscopic properties and self-frequency-doubling laser performance are presented for Yb:YCa4O(BO3)(3) (Yb:YCOB) crystals oriented for type I second-harmonic generation in the ZX plane. In a plane-concave cavity 10 cm long, up to 330 mW of green light (544.5 nm) is obtained for 14.7 W of laser diode incident pump power. Broad emission bands and weak anisotropy in the 1060-1100 nm range between the two eigenstates of polarization may explain the instability of the self-frequency-doubled output power. (C) 2016 Optical Society of America

1568. Ferritin surplus in mouse spleen 14 months after intravenous injection of iron oxide nanoparticles at clinical dose

Authors: Tamion, A; Hillenkamp, M; Hillion, A; Maraloiu, VA; Vlaicu, ID; Stefan, M; Ghica, D; Rositi, H; Chauveau, F; Blanchin, MG; Wiart, M; Dupuis, V

Published: AUG 2016, NANO RESEARCH, 9, 2410, DOI: 10.1007/s12274-016-1126-6

In this study, we followed the biodegradation of ultra-small superparamagnetic iron oxide nanoparticles injected intravenously at clinical doses in mice. An advanced fitting procedure for magnetic susceptibility curves and low-temperature hysteresis loops was used to fully characterize the magnetic size distribution as well as the magnetic anisotropy energy of the injected P904 nanoparticles (Guerbet Laboratory). Additional magnetometry measurements and transmission electronic microscopy observations were systematically performed to examine dehydrated samples from the spleen and liver of healthy C57B16 mice after nanoparticle injection, with sacrifice of the mice for up to 14 months. At 3 months after injection, the magnetic properties of the spleen and liver were dramatically different. While the liver showed no magnetic signals other than those also present in the reference species, the spleen showed an increased magnetic signal attributed to ferritin. This surplus of ferritin remained constant up to 14 months after injection.

1569. Effect of polyhedral oligomeric silsesquioxane nanoreinforcement on the properties of epoxy resin/monoglycidylether-terminated poly(dimethylsiloxane) nanocomposites

Authors: Florea, NM; Lungu. A; Balanuca, B; Badica, P; Craciun, L; Damian, CM; Enculescu, M; Ionescu, C; Tihan, G; Iovu, H

Published: AUG 2016, HIGH PERFORMANCE POLYMERS, 28, 734, DOI: 10.1177/0954008315595447

This article reports the synthesis and characterization of several types of organic-inorganic nanocomposites based on epoxy resin/monoglycidylether-terminated poly(dimethylsiloxane) reinforced with 2, 5, or 10 wt% polyhedral oligomeric silsesquioxanes (POSS) bearing one glycidyl (1GE-POSS) or eight glycidyl(8GE-POSS) groups. The morphological features of the studied samples were established through atomic force microscopy, contact angle measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy, and it was demonstrated that 8GE-POSS is well dispersed within the polymer matrix, while 1GE-POSS exhibits a high tendency to form aggregates. Differential scanning calorimetry (DSC) and Fourier transform infrared resonance (FTIR) measurements are used to follow the curing behavior and to study the polymerization kinetics of epoxy groups. As evidenced by DSC and FTIR results, the inclusion of 8GE-POSS within the polymer matrix leads to a lower epoxy polymerization rate of the resulted nanocomposites than those reinforced with 1GE-POSS. The dynamic mechanical analysis results revealed that the thermomechanical properties are gradually improved with increasing of 8GE-POSS content due to the higher cross-linking density.

1570. Low level NO2 detection under humid background and associated sensing mechanism for mesoporous SnO2

Authors: Stanoiu, A; Somacescu, S; Calderon-Moreno, JM; Teodorescu, VS; Florea, OG; Sackmann, A; Simion, CE

Published: AUG 2016, SENSORS AND ACTUATORS B-CHEMICAL, 231, 174, DOI: 10.1016/j.snb.2016.02.137

Mesoporous SnO2 prepared by a hydrothermal synthesis route assisted by the ionic surfactant Cetyltrimethylammonium bromide, has rutile-type tetragonal symmetry, small homogeneous nanocrystallite size of similar to 4 nm and good thermal stability. Porosity analysis revealed high surface area similar to 127 m(2)/g and a narrow pore size distribution, with an average pore diameter similar to 4 nm. The mesoporous structure is likewise advantageous towards enhancing the surface reactivity and subsequent gas sensing performances. The role played by the surface hydroxylation on the NO2 sensing mechanism was discussed with respect to the associated photoelectron spectral components. Under humid air, associated with the in-field conditions, the highest sensitivity was attained at 150 degrees C, were the sensor signal towards NO2 is 4 times higher than the one recorded in dry air. This feature has been experimentally demonstrated by simultaneous electrical resistance and work function changes measurements conducted in the range of 400-5000 ppb NO2. (C) 2016 Elsevier B.V. All rights reserved.