National Institute Of Materials Physics - Romania

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472 articles found

321. ON THE PASSIVATION OF GaAs SURFACE BY SULFIDE COMPOUNDS

Authors: Ghita, RV; Negrila, CC; Cotirlan, C; Logofatu, C

Published: JUL-SEP 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 1344, DOI:

A genuine GaAs surface is covered with a layer (similar to few nm) of native oxide pinning the surface Fermi level within the band gap of semiconductor. In this work is presented a study of GaAs surface passivation by sulfur compounds inorganic and organic (alkane thiols), a method that combines both chemical and electronic passivation. At the surface of GaAs it is developed an adherent layer of sulfur compound as a result of chemical interaction of sulfur ions with GaAs surface, a compound putted into evidence by scanning electron microscopy (SEM) images, photoluminescence analysis, second harmonic generation (SHG) measurement and Raman spectroscopy. Using X-ray photoelectron spectroscopy (XPS) it is putted into evidence the presence of covalent bonds Ga-S and AsS as a result of chemical interaction with sulf ions. Electrical characteristic of AuGeNi/thiol/GaAs structure is presented in I (V) recorded in the region of small currents.

322. Surface free energy of smooth and dehydroxylated fused quartz from contact angle measurements using some particular organics as probe liquids

Authors: Zgura, I; Moldovan, R; Negrila, CC; Frunza, S; Cotorobai, VF; Frunza, L

Published: JUL-AUG 2013, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 15, 634, DOI:

The dispersion and the polar independent contributions to the surface free energy in the case of fused quartz plates were evaluated by contact angle measurements against a series of liquids like water, glycerol, ethylene glycol, dimethyl sulfoxide and a nematic mixture NP5 of azoxybenzene type compounds. The smooth fused quartz plates were thermally pretreated at 240 degrees C and 1000 degrees C to decrease the number of surface hydroxyl groups; their surface was characterized by X-ray photoelectron spectroscopy. The contact angle data were further processed applying either the approach of Owens-Wendt with geometric mean or the Wu's approach of harmonic mean of nonpolar and polar interactions. The liquids were chosen thus to fulfill Della Volpe and Siboni's criterion namely that these have the condition number of system matrix low enough. The values obtained for the components of surface free energy were discussed in comparison with the results obtained in literature for crystalline quartz or for other silica forms as bulk or films. The study has shown a decrease of the polar component of the surface tension by increase of the pretreatment temperature.

323. A new green, ascorbic acid-assisted method for versatile synthesis of Au-graphene hybrids as efficient surface-enhanced Raman scattering platforms

Authors: Iliut, M; Leordean, C; Canpean, V; Teodorescu, CM; Astilean, S

Published: 2013, JOURNAL OF MATERIALS CHEMISTRY C, 1, 4104, DOI: 10.1039/c3tc30177j

A new green method for the synthesis of reduced graphene oxide-gold nanoparticle (rGO-AuNP) hybrids in aqueous solution that exploits the ability of ascorbic acid (AA) to operate as an effective dual agent for both graphene oxide (GO) and gold ion reduction is reported. Through careful investigation of the production of rGO-AuNP hybrids stabilized with polyvinylpyrrolidone (PVP), several versatile routes were devised with the aim of controlling the size, shape and distribution of AuNPs anchored onto the graphene sheets as well as the GO reduction. Particularly, when rGO is used as a platform for Au ion nucleation, a relative sparse distribution of AuNPs of size ranging from 20 nm to 50 nm is noticed. In contrast, when gold ions are added to the solution prior to any GO reduction, the density of large AuNPs is rather low relative to the uniformly packed small sized AuNPs (3-12 nm). The progress of GO reduction is explained by considering the contribution of the catalytic activity of AuNPs, besides the reducing activity of AA. Finally, a plausible mechanism for the nucleation and distribution of AuNPs onto the graphenic surface is assumed, highlighting the significance of oxygen moieties. The green method developed here is promising for the fabrication of gold-graphene nanocomposites with tunable surface "decoration", suitable for surface-enhanced Raman spectroscopy (SERS).

324. Structural and optical properties of c-axis oriented aluminum nitride thin films prepared at low temperature by reactive radio-frequency magnetron sputtering

Authors: Galca, AC; Stan, GE; Trinca, LM; Negrila, CC; Nistor, LC

Published: DEC 1 2012, THIN SOLID FILMS, 524, 333, DOI: 10.1016/j.tsf.2012.10.015

Spectroscopic ellipsometry, X-ray diffraction and transmission electron microscopy experiments are employed to characterize aluminum nitride (AlN) thin films obtained by radio-frequency magnetron sputtering at low temperature (approximate to 50 degrees C). To understand the growth mechanism and to get in depth information of such films by using ex situ characterization techniques, the AlN thin film sample series were prepared for different sputtering times, while keeping constant all the other deposition conditions. The diffraction studies reveal a [002] oriented growth of the AlN thin films. The misorientation of this crystallographic axis to the normal to the surface reduces progressively with film growth. A nonmonotonic behavior of the AlN pseudo-refractive index versus deposition time indicates a complex depth profile of the AlN thin films optical properties. The difference in orientation dispersion of the [002] crystallite axis, the variation of defects concentration and each constituent atom density influence the refractive index evolution. Our interpretation validity was verified by producing and characterizing samples obtained at intermediate deposition time. The AlN thin films show also very good pull-out adherence values. (C) 2012 Elsevier B. V. All rights reserved.

325. Heterogeneous amination of bromobenzene over titania-supported gold catalysts

Authors: Ciobanu, M; Cojocaru, B; Teodorescu, C; Vasiliu, F; Coman, SM; Leitner, W; Parvulescu, VI

Published: DEC 2012, JOURNAL OF CATALYSIS, 296, 54, DOI: 10.1016/j.jcat.2012.09.002

Amination of bromobenzene with aniline was carried out on heterogeneous Au-TiO2 catalysts prepared using the deposition-precipitation method. The deposition of gold in loadings in the range 0.1-0.9 wt.% on titania occurred with the formation of gold particles with controlled size and oxidation state as demonstrated from TEM and XPS measurements. In addition, Raman and DR-UV-Vis investigation of these catalysts showed that the interaction of Au particles with the support stabilized the metallic state of gold. Catalytic results demonstrated that the conversion and selectivity depended on the gold-particle size and dispersion, while the mechanism of reaction was in direct relation with the reaction medium. Working in DMC, the solvent was playing the role of base. The advantage of working in DMC was avoiding the formation of KBr which is very difficult to be separated from the reaction products. HBr resulted as a by-product formed adducts with the coupling product, which was separated as crystals at room temperature by a simple filtration. However, in DMC, the reaction occurred with low selectivities. In dioxane, the presence of potassium ethoxide as base was mandatory. The reaction occurred with very high selectivities for moderate conversions. The conversion was limited by KBr released from the reaction. However, the use of the heterogeneous catalyst has the advantage of scavenger, since KBr becomes chemisorbed on the surface and could be simple removed by percolation and the catalyst can be reused. (C) 2012 Elsevier Inc. All rights reserved.

326. Epitaxial ferromagnetic samarium and samarium silicide synthesized on Si(001)

Authors: Costescu, RM; Gheorghe, NG; Husanu, MA; Lungu, GA; Macovei, D; Pintilie, I; Popescu, DG; Teodorescu, CM

Published: OCT 2012, JOURNAL OF MATERIALS SCIENCE, 47, DOI: 10.1007/s10853-012-6672-z

Samarium is deposited on Si(001) at various temperatures (room temperature to 400 A degrees C), and the surface structure, interface reactivity, electron configuration, and magnetic properties are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and magneto-optical Kerr effect (MOKE), respectively. It is found that metal Sm is present on samples prepared at room temperature with an interface layer containing mostly Sm2+ and a lower amount of Sm3+. When samples are prepared at high temperature, much less Sm-0 is found with an increasing amount of Sm2+. Freshly prepared Sm-0 and SmSi2 layers react strongly with oxygen from the residual gas, promoting formation of Sm2O3 at the expense of both metal Sm and SmSi2. Room temperature ferromagnetism is observed for all prepared layers with a decrease of the saturation magnetisation when samples are prepared at high temperature. It is found that ferromagnetism implies mostly Sm3+ and Sm metal. In addition to these findings, this work proposes a new assignment of the Sm 3d chemically shifted components. Also, a noticeable variation of the XPS Sm 3d spin-orbit splitting is found as a function of the Sm ionization state.

327. Thermal behaviour of some new complexes with decaaza bismacrocyclic ligand as potential antimicrobial species

Authors: Bucur, C; Badea, M; Larisa, C; Marinescu, D; Grecu, MN; Stanica, N; Chifiriuc, MC; Olar, R

Published: OCT 2012, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 110, 241, DOI: 10.1007/s10973-012-2199-4

Novel complexes of type M2L(CH3COO)(4)center dot nH(2)O (M:Ni, n = 4; M:Cu, n = 2 and M:Zn, n = 0; L: ligand resulted in 1,2-phenylenediamine, 3,6-diazaoctane-1,8-diamine and formaldehyde template condensation) were synthesised and characterised. The features of complexes have been assigned from microanalytical, IR, UV-Vis, H-1 NMR, EPR as well as magnetic data at room temperature. Processes as water elimination as well as oxidative degradation of both organic components (bismacrocycle and acetate) were observed. The final product of decomposition was metal (II) oxide as powder X-ray diffraction indicates.

328. Study of the corrosion products formed on carbon steel surface in hydrochloric acid solution

Authors: Samide, A; Tutunaru, B; Dobritescu, A; Negrila, C

Published: OCT 2012, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 110, 152, DOI: 10.1007/s10973-011-2186-1

Effect of an antibacterial drug, sulfacetamide, IUPAC name N-[(4-aminophenyl) sulfonyl] acetamide (APSA), on the corrosion products formed on carbon steel surface in 1.0 mol L-1 HCl solution has been investigated using mass loss, X-ray photoelectron spectroscopy (XPS), and simultaneous thermal and differential scanning calorimetry/differential thermal analysis (TG/DSC/DTA). Mass loss measurements reveal that the corrosion rate of carbon steel is retarded by APSA and that the inhibition efficiency of this inhibitor increases with increasing the concentration. XPS analysis shows that, at this stage, the main product of corrosion is a non-stoichiometric Fe3+ oxyhydroxide, consisting of a mixture of FeO(OH) in anhydrous or hydrated forms, containing Cl- inclusions and adsorbed APSA molecules. The mechanism of inhibition was discussed in light of the chemical structure of the investigated inhibitor. The corrosion products were analyzed using TG/DSC/DTA technique.

329. Matrix assisted pulsed laser evaporation of Mn-12(Propionate) thin films

Authors: Pervolaraki, M; Sima, F; Socol, G; Teodorescu, CM; Gheorghe, NG; Socol, M; Mihailescu, IN; Moushi, EE; Tasiopoulos, AJ; Athanasopoulos, GI; Viskadourakis, Z; Giapintzakis, J

Published: SEP 15 2012, APPLIED SURFACE SCIENCE, 258, 9474, DOI: 10.1016/j.apsusc.2011.10.136

Single molecule magnets are of great interest due to a multitude of potential applications for some of which thin films are required. Traditional physical vapor deposition techniques are not suitable for the deposition of these fragile materials with low decomposition temperatures. Matrix Assisted Pulsed Laser Evaporation technique has been employed for the growth of thin films of the single molecule magnet Mn-12(Propionate) on Si and glass substrates. In this paper we report on the appropriate growth conditions and also the morphology, chemical composition and magnetic behavior of the films. Continuous Mn-12(Propionate) films with properties similar to bulk materials have been obtained. (c) 2011 Elsevier B.V. All rights reserved.

330. The Meyer-Neldel rule in amorphous TiO2 films with different Fe content

Authors: Mardare, D; Yildiz, A; Apetrei, R; Rambu, P; Florea, D; Gheorghe, NG; Macovei, D; Teodorescu, CM; Luca, D

Published: SEP 2012, JOURNAL OF MATERIALS RESEARCH, 27, 2277, DOI: 10.1557/jmr.2012.193

Amorphous titania thin films with increasing Fe content have been prepared by RF magnetron sputtering. X-ray absorption spectroscopy revealed modifications of both local structures/environment of the Ti and Fe atoms, with formation of phases containing amorphous material and a magnetite-like phase. The temperature dependence of the electrical conductivity of the films was investigated for temperatures higher than half of the Debye temperature (T > 391 K). It was found that the electrical conductivity in the amorphous Fe/TiO2 films obeys the Meyer-Neldel rule. The origin of this behavior is explained on the basis of the multiphonon-assisted hopping model.