National Institute Of Materials Physics - Romania

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5714 articles found

1581. Laser-induced forward transfer of carbon nanowalls for soft electrodes fabrication

Authors: Constantinescu, C; Vizireanu, S; Ion, V; Aldica, G; Stoica, SD; Lazea-Stoyanova, A; Alloncle, AP; Delaporte, P; Dinescu, G

Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 55, DOI: 10.1016/j.apsusc.2015.09.089

Carbon nanowalls (CNW) are two-dimensional interconnected graphitic nanostructures that have a few mu m in length and height, reaching typical thicknesses of a few tens of nm. We present results on such layers synthesized in a low pressure argon plasma jet, injected with acetylene and hydrogen, on transparent substrates (quartz) heated at 600 degrees C, without catalyst. Thermogravimetric analysis reveals that the CNW are stable up to 420 degrees C in air, and Raman spectroscopy investigations highlight their graphene-like structure. Finally, using a pulsed Nd:YAG laser device (355 nm, 50 ps), we show that 2D-arrays of CNW (pixels and lines) can be printed by laser-induced forward transfer (LIFT), preserving their architecture and structure. Electrical measurements on 1 mu m thick CNW demonstrate typical values in the range of 357.5-358.4 Omega for the samples grown on Au/Cr electrodes, and in the range of 450.1-474.7 Omega for the LIFT printed lines (under positive, negative, and neutral polarization; 1 kHz-5 MHz frequency range; 500 mV and 1 V, respectively). Their morphology is highlighted by means of optical and electronic microscopy. Such structures have potential applications as soft conductive lines, in sensor development and/or embedding purposes. (C) 2015 Elsevier B.V. All rights reserved.

1582. Investigations of Ar ion irradiation effects on nanocrystalline SiC thin films

Authors: Craciun, V; Craciun, D; Socol, G; Behdad, S; Boesl, B; Himcinschi, C; Makino, H; Socol, M; Simeone, D

Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 345, DOI: 10.1016/j.apsusc.2015.12.130

The effects of 800 keV Ar ion irradiation on thin nanocrystalline SiC films grown on (100) Si substrates using the pulsed laser deposition (PLD) technique were investigated. On such PLD grown films, which were very dense, flat and smooth, X-ray reflectivity, glancing incidence X-ray diffraction and nanoindentation investigations were easily performed to evaluate changes induced by irradiation on the density, surface roughness, crystalline structure, and mechanical properties. Results indicated that the SiC films retained their crystalline nature, the cubic phase partially transforming into the hexagonal phase, which had a slightly higher lattice parameter then the as-deposited films. Simulations of X-ray reflectivity curves indicated a 3% decrease of the films density after irradiation. Nanoindentation results showed a significant decrease of the hardness and Young's modulus values with respect to those measured on as-deposited films. Raman and X-ray photoelectron spectroscopy investigations found an increase of the C-C bonds and a corresponding decrease of the Si-C bonds in the irradiated area, which could explain the degradation of mechanical properties. (C) 2015 Elsevier B.V. All rights reserved.

1583. MAPLE preparation and characterization of mixed arylenevinylene based oligomers:C-60 layers

Authors: Stanculescu, A; Socol, G; Vacareanu, L; Socol, M; Rasoga, O; Breazu, C; Girtan, M; Stanculescu, F

Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 289, DOI: 10.1016/j.apsusc.2015.11.250

This paper presents some studies about the preparation by matrix-assisted pulsed laser evaporation (MAPLE) of mixed layers based on two arylenevinylene oligomers, 1,4-bis [4-(N,N'-diphenylamino)phenylvinyl] benzene (L78) and 3,3'-bis(N-hexylcarbazole)vinylbenzene (L13) as donor and buckminsterfullerene (C-60) as acceptor, blended in three different weight ratios: 1:1, 1:2 and 1:3. The optical, morphological, structural and electrical properties of these mixed layers have been investigated emphasizing the effect of the layer composition and of the significant degree of disorder. I-V characteristics have revealed typically solar cell behaviour for the heterostructures prepared with mixed layers containing L78 (L13) and fullerene blended in a weight ratio of 1:2. The solar cell structure glass/ITO/L13:C-60/Al has shown the best parameters. (C) 2015 Elsevier B.V. All rights reserved.

1584. High atomic diffusivity during pulsed laser irradiation of TiON quasi-amorphous films

Authors: Teodorescu, VS; Maraloiu, AV; Negrea, RF; Ghica, D; Scarisoreanu, ND; Dinescu, M; Gartner, M; Blanchin, MG

Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 251, DOI: 10.1016/j.apsusc.2015.11.188

Quasi-amorphous titanium oxynitride (TiON) films were obtained by annealing sol-gel anatase TiO2 films in NH3 atmosphere at 600 degrees C. These films were irradiated with 50 laser pulses using the fourth harmonic (266 nm) radiation of the Nd-YAG laser, with an average fluence of 20 mJ/cm(2). HRTEM observations of the pulsed laser irradiated films evidenced the rutile TiO2 nanocrystallites formation. The rutile structure was not present either in the TiON films before the laser irradiation, or in the initial sol-gel anatase TiO2 films. During the laser irradiation, the film structure remains in the solid state phase, as it results from the temperature estimation and microscopic observations. For the rutile nanocrystals formation, the atomic diffusion length of the oxygen and titanium atoms should be in the nanometric range during the laser pulse action, which implies a diffusivity close to the values observed in the liquid phase. We consider that the rutile phase formation is a proof of the fast atomic diffusion in the solid amorphous matrix, during the laser irradiation. (C) 2015 Published by Elsevier B.V.

1585. Flexible heterostructures based on metal phthalocyanines thin films obtained by MAPLE

Authors: Socol, M; Preda, N; Rasoga, O; Breazu, C; Stavarache, I; Stanculescu, F; Socol, G; Gherendi, F; Grumezescu, V; Popescu-Pelin, G; Girtan, M; Stefan, N

Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 410, DOI: 10.1016/j.apsusc.2015.10.166

Heterostructures based on zinc phthalocyanine (ZnPc), magnesium phthalocyanine (MgPc) and 5,10,15,20-tetra(4-pyrydil)21H,23H-porphine (TPyP) were deposited on ITO flexible substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. Organic heterostructures containing (TPyP/ZnPc(MgPc)) stacked or (ZnPc(MgPc):TPyP) mixed layers were characterized by X-ray diffraction-XRD, photoluminescence-PL, UV-vis and FTIR spectroscopy. No chemical decomposition of the initial materials was observed. The investigated structures present a large spectral absorption in the visible range making them suitable for organic photovoltaics applications (OPV). Scanning electron microscopy-SEM and atomic force microscopy-AFM revealed morphologies typical for the films prepared by MAPLE. The current-voltage characteristics of the investigated structures, measured in dark and under light, present an improvement in the current value (similar to 3 order of magnitude larger) for the structure based on the mixed layer (Al/MgPc:TPyP/ITO) in comparison with the stacked layer (Al/MgPc//TPyP/ITO). A photogeneration process was evidenced in the case of structures Al/ZnPc:TPyP/ITO with mixed layers. (C) 2015 Elsevier B.V. All rights reserved.

1586. Multi-stage pulsed laser deposition of aluminum nitride at different temperatures

Authors: Duta, L; Stan, GE; Stroescu, H; Gartner, M; Anastasescu, M; Fogarassy, Z; Mihailescu, N; Szekeres, A; Bakalova, S; Mihailescu, IN

Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 150, DOI: 10.1016/j.apsusc.2015.10.093

We report on multi-stage pulsed laser deposition of aluminum nitride (AlN) on Si (100) wafers, at different temperatures. The first stage of deposition was carried out at 800 degrees C, the optimum temperature for AlN crystallization. In the second stage, the deposition was conducted at lower temperatures (room temperature, 350 degrees C or 450 degrees C), in ambient Nitrogen, at 0.1 Pa. The synthesized structures were analyzed by grazing incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM), atomic force microscopy and spectroscopic ellipsometry (SE). GIXRD measurements indicated that the two-stage deposited AlN samples exhibited a randomly oriented wurtzite structure with nanosized crystallites. The peaks were shifted to larger angles, indicative for smaller inter-planar distances. Remarkably, TEM images demonstrated that the high-temperature AlN "seed" layers (800 degrees C) promoted the growth of poly-crystalline AlN structures at lower deposition temperatures. When increasing the deposition temperature, the surface roughness of the samples exhibited values in the range of 0.4-2.3 nm. SE analyses showed structures which yield band gap values within the range of 4.0-5.7 eV. A correlation between the results of single and multi-stage AlN depositions was observed. (C) 2015 Elsevier B.V. All rights reserved.

1587. Role of the dithiolate backbone on the passivation of p-GaAs(111)B surface

Authors: Preda, L; Anastasescu, M; Dobrescu, G; Negrila, C; Lazarescu, V

Published: JUN 15 2016, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 771, 63, DOI: 10.1016/j.jelechem.2016.03.046

Effects of the self-assembled layers of biphenyl 4,4'-dithiol (BPDT) and 1,8-octanedithiol (ODT) on the chemical and electronic properties of p-doped GaAs (111)-As terminated substrate, (p-GaAs(111)B), were investigated in order to evidence whether the hydrocarbon moiety plays a role in tailoring the semiconductor surface properties. The electrochemical properties of the BPDT and ODT coated p-GaAs(111)B substrates were studied by Electrochemical Impedance Spectroscopy (EIS). The structural and chemical changes caused by the dithiolate layers formed on p-GaAs(111)B substrates were monitored by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) investigations, respectively. The XPS data showed that BPDT and ODT bind to pGaAs(111)B via the thiol group. The ODT layer provides better protection against the further oxidation in air of p-GaAs(111)B substrate compared to the BPDT layer. The EIS investigations are in good agreement with XPS results, pointing to better insulating properties of the ODT layer compared to the BPDT layer in the electron transfer at the electrode/solution interface. The results evidenced that backbone plays an important role in tailoring the properties of p-GaAs(111)B substrate. (C) 2016 Elsevier B.V. All rights reserved.

1588. Assessment of structural, optical and conduction properties of ZnO thin films in the presence of acceptor impurities (vol 28, 224008, 2016)

Authors: Plugaru, R; Plugaru, N

Published: JUN 8 2016, JOURNAL OF PHYSICS-CONDENSED MATTER, 28, DOI: 10.1088/0953-8984/28/18/189601

1589. Assessment of structural, optical and conduction properties of ZnO thin films in the presence of acceptor impurities

Authors: Plugaru, R; Plugaru, N

Published: JUN 8 2016, JOURNAL OF PHYSICS-CONDENSED MATTER, 28, DOI: 10.1088/0953-8984/28/22/224008

The structural, optical and electrical conduction properties of (Li/Cu,N):ZnO codoped thin films synthesized by the sol-gel method were investigated by field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), transmission and absorption, photoluminescence (PL) and I-V measurements in order to bring evidence of the formation of acceptor centers by dual-acceptor codoping processes. The (Li 3%, N 5%): ZnO films consist of crystallites with average size of 15 nm, show 95% transmission in the visible region, and an optical band gap of 3.22 eV. The PL spectra show emission maxima at 3.21 and 2.96 eV which are related to the emission of acceptor centers and the presence of defects, respectively. Li occupies interstitial sites and may form Lii-N(O) defect complexes that act as acceptor centers. The (Cu 3%, N 5%): ZnO films consist of crystallites with average size of 12 nm, and exhibit 90% transmission in the visible region. The PL spectra reveal band edge emission at 3.23 eV and defect related emission at 2.74 eV. In the (Cu, N) codoped films, copper substitutes zinc and adopts mainly the Cu1+ state. A possible defect complex involving Cu and N determines the transition from n-to p-type conductivity. These findings are in agreement with results of electronic structure calculations at the GGA-PBE level.

1590. Exciton-phonon interaction in CdS of different morphological forms manifested as stimulated Raman scattering

Authors: Baibarac, M; Nila, A; Baltog, I

Published: JUN 1 2016, OPTICAL MATERIALS EXPRESS, 6, 1895, DOI: 10.1364/OME.6.001881

Raman studies performed on different morphologies of CdS samples indicate an exciton-phonon interaction (EPI) that manifests at low temperatures by different enhancements in intensity of the Raman spectra in the Stokes and anti-Stokes branches. This effect, interpreted as stimulated Raman effect, is conditioned on the appearance and strength by the degree of overlap of the excitation laser light with the excitonic photoluminescence band. EPI is greatest in samples characterized by high light diffusing power, which means a long path of light into the sample and a great overlapping of the two optical fields, i.e., the pump laser and excitonic light. (C) 2016 Optical Society of America