National Institute Of Materials Physics - Romania

Publications

830 articles found

441. Raman scattering and anti-Stokes luminescence in poly-paraphenylene vinylene/carbon nanotubes composites

Authors: Baibarac, M; Massuyeau, F; Wery, J; Baltog, I; Lefrant, S

Published: APR 15 2012, JOURNAL OF APPLIED PHYSICS, 111, DOI: 10.1063/1.4705403

In this paper, we present Raman scattering and luminescence of poly-paraphenylene vinylene/single-walled carbon nanotubes composites, focused on data recorded in the anti-Stokes branch. We demonstrate that, when the excitation energy is in the long wavelength tail of the fundamental absorption edge, an anti-Stokes signal is generated, whose origin is a photon absorption accompanied by a phonon process from lower to upper vibronic states. The efficiency of this anti-Stokes photo-luminescence is increased when composites films are deposited onto an Au rough surface acting as a surface enhanced Raman scattering substrate. This mechanism is explained by a coherent anti-Stokes Raman scattering-like process, as observed in other nano-structured materials. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4705403]

442. Sol-gel template synthesis of luminescent glass-ceramic rods

Authors: Secu, M; Secu, CE; Sima, M

Published: APR 2012, JOURNAL OF NANOPARTICLE RESEARCH, 14, DOI: 10.1007/s11051-012-0772-1

We report an original way to prepare luminescent glass-ceramic microrods containing Eu3+ doped BaF2 nanocrystals by sol-gel chemistry within the pores of a polycarbonate template membrane. Structural characterization by scanning electron microscopy and X-ray diffraction has shown the formation of glass-ceramic microrods with 0.8-m diameter of and 10 mu m length in which BaF2 nanocrystals of about 30 nm size are embedded. Photoluminescence measurements have indicated the incorporation of Eu3+ ions inside the BaF2 nanocrystals in a broad range of sites with low coordination symmetry. The comparison made with the bulk glass-ceramic indicated an influence of the dimensional constraints imposed by the membrane pores during xerogel formation and subsequent glass ceramization.

443. Post-synthesis Carbon Nanowalls Transformation under Hydrogen, Oxygen, Nitrogen, Tetrafluoroethane and Sulfur Hexafluoride Plasma Treatments

Authors: Vizireanu, S; Ionita, MD; Dinescu, G; Enculescu, I; Baibarac, M; Baltog, I

Published: APR 2012, PLASMA PROCESSES AND POLYMERS, 9, 370, DOI: 10.1002/ppap.201100153

Carbon nanowalls (CNWs) functionalization allows the tailoring of some of their properties after they have been synthesized. Herewith we report on post-synthesis CNWs functionalization by plasma treatments. Radiofrequency plasmas generated in hydrogen, oxygen, nitrogen, tetrafluoroethane, and sulfur hexafluoride admixed to argon, were used. The changes of morphology, structure, chemical composition were determined by SEM, FTIR, Raman Spectroscopy, specifically for each gas mixture. The results point out to the surface erosion, the functional groups attachment, or to thin film coverage of CNWs material. Such processes strongly influence the material properties, as exemplified by the wettability: superhydrophilic or superhydrophobic surfaces are obtained starting from the same base CNWs material.

444. Oxidation activity of horseradish peroxidase hosted in molecular sieves: spectroscopic investigations show hindering of the enzyme activity

Authors: Frunza, L; Gheorghe, N; Ganea, CP; Eckelt, R; Kosslick, H

Published: FEB 2012, REACTION KINETICS MECHANISMS AND CATALYSIS, 105, 205, DOI: 10.1007/s11144-011-0408-y

Horseradish peroxidase immobilization inside molecular sieves with pores hexagonally structured as such or functionalized with copper ions is presented in comparison with the bidimensional immobilization onto aerosil A380 particles. Immobilization was performed under mild conditions that do not lead to enzyme denaturation. Guest-host interactions were pursued spectrophotometrically and by thermal analysis measurements. FTIR spectroscopy showed no major secondary structural change for the entrapped enzyme despite some influence of the support functionalization that can be supposed. The activity of the immobilized enzyme was tested in the oxidation of Alizarin Red S (ARS) with hydrogen peroxide. It was found that the dye oxidation is catalyzed by the enzyme in homogeneous reaction but the rate becomes much slower in heterogeneous catalytic processes with prepared catalysts. It seems that horseradish peroxidase immobilization in simple porous silica or alumino-silica post synthesis blocks the enzyme activity. In addition, copper ions make a stable complex with ARS hindering its oxidation as well.

445. Electrochemical Investigation of the Deposition/Dissolution of Selenium in Choline Chloride with Urea or Ethylene Glycol Ionic Liquids

Authors: Cojocaru, A; Sima, M

Published: FEB 2012, REVISTA DE CHIMIE, 63, 223, DOI:

The electrochemical behaviour of Se(IV) ion on Pt electrode in ionic liquids containing choline chloride - urea and choline chloride - ethylene glycol eutectics (1:2 mole ratio) was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in open air conditions. Cyclic voltammograms showed a cathodic peak of selenium massive deposition preceeded by one or more waves corresponding to UPD processes. It is followed by another cathodic peak of Se(II) anion formation. It was found a diffusion control of reduction process and, therefore, the value of the diffusion coefficient of Se(IV) ion in ChCl-urea ionic liquid at 60 degrees C was calculated. EIS spectra as Nyquist and Bode plots confirm the potential range for bulk selenium deposition and formation of thin selenium films.

446. Photoluminescence and Raman evidence for mechanico-chemical interaction of polyaniline-emeraldine base with ZnS in cubic and hexagonal phase

Authors: Scocioreanu, M; Baibarac, M; Baltog, I; Pasuk, I; Velula, T

Published: FEB 2012, JOURNAL OF SOLID STATE CHEMISTRY, 186, 223, DOI: 10.1016/j.jssc.2011.12.012

The mechanico-chemical interaction of a polyaniline-emeraldine base (PANI-EB) with ZnS in the cubic and wurtzite phases is studied by Raman spectroscopy and photoluminescence (PL). The results demonstrate that such an interaction leads to the formation of a PANI-salt and metallic Zn. Regardless of the structural form of the ZnS, the formation PANI-salt is indicated by a band in the Raman spectrum that shifts from 1162 to 1176 cm(-1) and the appearance of a new band at 1330 cm(-1) that indicates the protonated structure of a PANI-salt. The presence of the second product is determined by comparative PL studies performed on ZnS that has interacted mechanico-chemically with PANI-EB and metallic Zn powder. The variations of the PL spectra and their associated excitation spectra are explained as resulting from the charge collection processes that occur in the composite materials produced by the mechanico-chemical interaction between ZnS and PANI-EB or metallic Zn. (C) 2011 Elsevier Inc. All rights reserved.

447. Effect of the morphology on the optical and electrical properties of polycarbonate film doped with aniline derivatives monomers

Authors: Stanculescu, F; Stanculescu, A; Girtan, M; Socol, M; Rasoga, O

Published: JAN 2012, SYNTHETIC METALS, 161, 2597, DOI: 10.1016/j.synthmet.2011.09.012

In this paper we present some comparative studies between the optical and electrical properties of the films prepared by vacuum evaporation from amidic monomeric compounds obtained from maleic anhydride and aniline derivative with different functional groups [CN; NO2], and the composite films prepared by spin-coating from a polycarbonate of bisphenol A matrix embedding clusters of these amidic monomers. We have emphasised the effect of the polymeric matrix on the properties of the synthesised monomers with the purpose to change the physical properties of the films (optical transmission, luminescence, electrical conduction, optical non-linear phenomena). The correlation between the morphology of the films and the optical and electrical properties has also been investigated. (C) 2011 Elsevier B.V. All rights reserved.

448. Optical and electrical properties of arylenevinylene compounds thin films prepared by vacuum evaporation

Authors: Rasoga, O; Vacareanu, L; Grigoras, M; Enculescu, M; Socol, M; Stanculescu, F; Ionita, I; Stanculescu, A

Published: JAN 2012, SYNTHETIC METALS, 161, 2617, DOI: 10.1016/j.synthmet.2011.10.001

This paper discusses the properties of two arylenevinylene oligomers thin films deposited by vacuum evaporation on different substrates. The morphology of the thin films was investigated by scanning electron microscopy and atomic force microscopy, and the optical properties by UV-Vis and fluorescence spectroscopy. The optical nonlinear phenomenon of two-photon absorption induced fluorescence has been evidenced in the thin films of these compounds. We have also investigated the electrical properties of semiconductor/insulator/semiconductor (ITO/oligomer/Si) heterostructures in correlation with the contact energetic barriers, morphological and structural properties of the layers. (C) 2011 Elsevier B.V. All rights reserved.

449. Pentylcyanobiphenyl as Test Molecule for the Acid Sites of Powdered Titanium(IV) Oxides: Sensitivity of Core Levels to the Local Structure

Authors: Ungureanu, F; Manea, AS; Frunza, L; Frunza, S; Ganea, CP; Cotorobai, F; Diamandescu, L; Schonhals, A

Published: 2012, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 562, 217, DOI: 10.1080/15421406.2012.697416

Pentylcyanobiphenyl was used successfully as a testmolecule to show the acid sites upon some commercial nanoscaled titanium dioxide materials. The surface interactions were investigated in detail using methods sensitive to the surface or to the bulk material, e. g., X-ray photoelectron spectroscopy (XPS), infrared spectroscopy, and thermal analysis. Different oxidation states of surface Ti ions were revealed. Several species were found: the majority were bonded through the nitrogen lone pair of the cyano group, but bonding to the surface OH groups by benzene pi electrons might also appear. The N 1s lines of adsorbed 5CB were able to distinguish between Lewis acid and relatively weak Bronsted acid sites.

450. Modeling the slaving of structural fluctuations in bio-molecules to those of nearby water

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

Published: JUL-SEP 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 915, DOI:

The functions of bio-molecules depend on their structural fluctuations, which are thought to be 'slaved' (i.e. coupled) to those of nearby bulk water. Slaving was suggested to explain the universal pattern of propagation of mechanical excitations through concentrated water-containing solutions of polymers, such as the cytoplasm. To obtain a simplified model of this phenomenon, we propose to use a cellular automaton of water-based solutions. During iterations, the model computes the compactness of both the solvent and the solute (equivalent of their density), as the average number of neighbors of each class of particles. As a surrogate of slaving, we studied the temporal co-variation of these variables, using the Pearson correlation coefficient (S-av). We found that S-av depends in a biochemically-meaningful manner on the concentration of solute, on its hydrophatic character and on molecular flexibility. The simulations also show that S-av is robust to mild hypothermia. In conclusion, our cellular automaton is capable to generate a slaving-like behavior of solutes in water, as an emergent phenomenon occurring in dissolved molecular systems.