National Institute Of Materials Physics - Romania

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830 articles found

451. Anti-Stokes Raman Scattering and Luminescence in Carbon Nanotube Nanostructures

Authors: Lefrant, S; Buisson, JP; Mevellec, JY; Massuyeau, F; Wery, J; Baibarac, M; Baltog, I

Published: 2012, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 554, 118, DOI: 10.1080/15421406.2012.633816

In this paper, we present recent results obtained on single-walled carbon nanotubes (SWNTs) and carbon nanotube/conjugated polymer composites by using resonant Raman scattering and Surface Enhanced Raman Scattering (SERS). Besides the characterization of these materials, we report on peculiar properties observed in the anti-Stokes Raman branch of the Raman spectra. They consist in an abnormal anti-Stokes Raman emission which is explained by a mechanism reminiscent of a Coherent anti-Stokes Raman Scattering (CARS) emission. It results from a wave mixing process between the incident laser light and Stokes Raman light, generated by the SERS mechanism. In a parallel way, we have investigated in details the resonance effects which also induce anomalies in the anti-Stokes/Stokes intensity ratios, as a function of several parameters including the observation temperature, the environmental conditions, the dilution in solvents, etc. Studies extended to composites based on carbon nanotubes and conjugated polymers reveal also interesting properties. In the case of poly(bithiophene) (PBTh), one observes a strong amplification of the 1450 cm(-1) Raman line in the anti-Stokes branch, generated by the plasmon excitation of metallic tubes. This phenomenon occurs in several other conjugated polymers such as PEDOT and PPV for modes located around 1500 cm(-1). The role of metallic SWNTs is discussed. Finally, an anti-Stokes luminescence excited in the low energy tail of the absorption band of PPV and PPV/SWNTs composites has even been observed for the first time, explained through a phonon-energy up-conversion mechanism.

452. ELECTRODEPOSITION AND ANODIZING OF ZnMn ALLOY SUBMICRON WIRES

Authors: Sima, M; Sima, M

Published: JUL-SEP 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 882, DOI:

The study of the electrodeposition and anodic oxidation processes of ZnMn alloy submicron wires is reported; ZnMn wire arrays were electrodeposited using a pulse current technique and an aqueous solution containing 0.2 mol dm(-3) Zn(II)-EDTA + 0.2 mol dm(-3) MnSO4 + 0.6 mol dm(-3) sodium citrate. The obtained alloy was anodized at a current constant density, in a methoxyethanol solution containing sodium hydroxide and in an aqueous potassium zincate solution. Photoluminescence spectra and SEM images showed the presence of the oxide layer on the surface of the anodized ZnMn wires.

453. ZnO Thin Films Deposited on Textile Material Substrates for Biomedical Applications ZnO Thin Films Deposited on Textiles

Authors: Duta, L; Popescu, AC; Dorcioman, G; Mihailescu, IN; Stan, GE; Zgura, I; Enculescu, I; Dumitrescu, I

Published: 2012, TECHNOLOGICAL INNOVATIONS IN SENSING AND DETECTION OF CHEMICAL, BIOLOGICAL, RADIOLOGICAL, NUCLEAR THREATS AND ECOLOGICAL TERRORISM, 210, DOI: 10.1007/978-94-007-2488-4_20

We report on the coating with ZnO adherent thin films of cotton woven fabrics by Pulsed laser deposition technique in order to obtain innovative textile materials, presenting protective effects against UV radiations and antifungal action.

454. IMPACT OF SOLUTE MOLECULAR PROPERTIES ON THE ORGANIZATION OF NEARBY WATER: A CELLULAR AUTOMATA MODEL

Authors: Mihai, C; Velea, A; Roman, N; Tugulea, L; Moldovan, NI

Published: APR-JUN 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 475, DOI:

The goal of this study was the creation of a model to understand how solute properties influence the structure of nearby water. To this end, we used a two-dimensional cellular automaton model of aqueous solutions. The probabilities of translocation of water and solute molecules to occupy nearby sites, and their momentary distributions (including that of vacancies), are considered indicative of solute molecular mechanics and hydrophatic character, and are reflected in water molecules packing, i.e. 'organization'. We found that in the presence of hydrophilic solutes the fraction of water molecules with fewer neighbors was dominant, and inverse-proportionally dependent on their relative concentration. Hydrophobic molecules induced water organization, but this effect was countered by their own flexibility. These results show the emergence of cooperative effects in the manner the molecular milieu affects local organization of water, and suggests a mechanism through which molecular mechanics and crowding add a defining contribution to the way the solute impacts on nearby water.

455. COMBINATORIAL PULSED LASER DEPOSITION OF AG-CONTAINING CALCIUM PHOSPHATE COATINGS

Authors: Socol, G; Socol, M; Sima, L; Petrescu, S; Enculescu, M; Sima, F; Miroiu, M; Popescu-Pelin, G; Stefan, N; Cristescu, R; Mihailescu, CN; Stanculescu, A; Sutan, C; Mihailescu, IN

Published: APR-JUN 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 576, DOI:

Embedding silver (Ag) into CaPs one could expect the enhancement of the antimicrobial performances of coatings for load bearing implants. The aim of this research was to evaluate whether the cellular morphology is influenced by the variation of Ag content, as well as by the solubility and morphological features of Ag-containing CaP coatings obtained by combinatorial pulsed laser deposition technique. In this view, we developed compositional libraries of either Ag and hydroxyapatite (HA) or Ag and beta-tricalcium phosphate (beta-TCP). The Ag content along the length of the combinatorial CaP coatings increased up to a maximum of similar to 1 at.%. SEM and AFM images evidenced the abundant presence of particulates typical for CaP coatings deposited by PLD. AFM histograms showed that the samples were rough with RMS values within 61-209 nm range. Ag content values up to 0.6 at. % into HA coatings were found nontoxic for mesenchymal stem cell (MSC) growth.

456. NONLINEAR OPTICAL PROCESSES MANIFESTING AS ANDERSON LOCALIZATION OF LIGHT IN MESOSCOPIC MATERIALS

Authors: Baltog, I; Baibarac, M; Mihut, L; Smaranda, I; Lefrant, S

Published: APR-JUN 2012, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 13, 117, DOI:

Abnormal anti-Stokes Raman emission (AASRE) is defined by an anti-Stokes/Stokes intensity ratio much greater than expected on the basis of the equilibrium population of excited vibration states provided by the Boltzmann law. AASRE can be observed both in materials with intrinsic nonlinear optical properties as LiNbO3 or materials in which the nonlinear optical properties are induced by resonant optical excitation, as carbon nanotubes. Using a surface enhanced Raman scattering (SERS) device, consisting from single wall carbon nanotubes deposited on a rough Au or Ag support and LiNbO3 in form of powder, we demonstrate that under continuous single beam excitation they present AASRE whose properties are similar to a single beam pumped Coherent Anti-Stokes Raman Scattering. AASRE is usually accompanied by a coherent backscattering, it can be considered as Anderson localization of light that results from a wave-mixing mechanism of the incident laser light with a Stokes shifted Raman light produced by a spontaneous Raman light scattering process. The transport of the light inside of sample, giving rise to AASRE and coherent backscattering, is done by an elastic light scattering mechanism.

457. Dielectric relaxation of pure TGS crystals

Authors: Mindru, C; Ganea, CP; Alexandru, HV

Published: JAN-FEB 2012, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 14, 162, DOI:

Pure triglycine sulphate crystals (TGS) show peculiar dielectric behavior in the ferroelectric phase, after crossing down the Curie point. Dielectric dispersion was investigated on the frequency range 1 Hz divided by 10 MHz. Temperature was changed at a sliding rate of 0.6 degrees C/minute, crossing up and down, several times, the Curie point between 65 degrees C and -120 degrees C. The second component of permittivity, drawn versus the frequency, shows two types of relaxation in the ferroelectric phase, with the characteristic time of tau(L) similar to 10(-3) sec and tau(H) similar to 10(-7) seconds. The first is recognized to be related with ferroelectric domain wall relaxation (domain cropping), although not clearly understood yet. The second one is ascribed to the "critical slowing down" effect, similar to the relaxation in the paraelectric phase, above T-C. A third, middle relaxation time, seems to be a sort of interaction of the two previously mentioned relaxation mechanisms. Papers from the literature, analyzing molecular dynamics and structural changes, could not correlate the flipping time similar to 10(-11) sec of the NH3 group of the glycine GI in the structure (the main responsible of the ferroelectric transition), with the mentioned relaxation times. Several aspects of the dielectric parameters evolution, related to the two relaxation processes on the large temperature range shall be analyzed and discussed.

458. NEW APPROACH OF THE AC ELECTRODE POLARIZATION DURING THE MEASUREMENTS OF IMPEDANCE SPECTRA

Authors: Ganea, CP

Published: 2012, ROMANIAN JOURNAL OF PHYSICS, 57, 675, DOI:

A mathematical approach for describing the influence of the ions dissolved in a liquid crystal on the impedance measurements is presented. New independent variables allow re-formulating the basic coupled differential equations of continuity and Poisson equation as well. The obtained forms are simpler than those used up to now. Illustrative examples are analyzed.

459. ON TITANIUM OXIDE SPRAY DEPOSITED THIN FILMS FOR SOLAR CELLS APPLICATIONS

Authors: Vaiciulis, I; Girtan, M; Stanculescu, A; Leontie, L; Habelhames, F; Antohe, S

Published: OCT-DEC 2012, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 13, 342, DOI:

Titanium oxide is one of the most promising candidate for relatively low cost, simple manufacture and high-performance new generation solar cells and the recent achievements in dye-sensitized solar cells (DSSCs) efficiencies and life time confirm the fact that these new generation solar cells becomes one of the future solutions in energy conversion. In DSSCs the presence of a dense titanium oxide layer is necessary in order to avoid short circuits between electrodes. Then, the interest to have a second porous TiO2 layer is determined by the fact that compared to a flat surface, a dye-sensitized porous surface area increase the absorption and hence conduct to the increase of solar cells efficiencies. Generally these two layers are prepared by successive depositions using two different methods. In this paper we present a simple technique to prepare both layers during the same spraying process. Films morphology and structure of titanium oxide deposited on glass and ITO substrate was investigated by AFM, SEM and XRD respectively.

460. Effect of maleic anhydride-aniline derivative buffer layer on the properties of flexible substrate heterostructures: Indium tin oxide/nucleic acid base/metal

Authors: Stanculescu, A; Socol, M; Socol, G; Mihailescu, IN; Girtan, M; Preda, N; Albu, AM; Stanculescu, F

Published: DEC 1 2011, THIN SOLID FILMS, 520, 1258, DOI: 10.1016/j.tsf.2011.04.204

This paper presents some investigations on the properties of guanine (G) and cytosine (C) based heterostructures deposited on flexible substrates. The effects of two types of maleic anhydride-aniline derivatives (maleic anhydride-cyano aniline or maleic anhydride-2,4 dinitroaniline) buffer layer, deposited between indium tin oxide and (G) or (C) layer, on the optical and electrical properties of the heterostructures have been identified. The heterostructures containing a film of maleic anhydride-2,4 dinitroaniline have shown a good transparency and low photoluminescence invisible range. This buffer layer has determined an increase in the conductance only in the heterostructures based on (G) and (C) deposited on biaxially-oriented polyethylene terephthalate substrate. (C) 2011 Elsevier B. V. All rights reserved.