National Institute Of Materials Physics - Romania

Publications

847 articles found

601. Skin Layer Defects in Si by Optimized Treatment in Hydrogen RF Plasma

Authors: Ghica, C; Nistor, LC; Vizireanu, S; Dinescu, G; Moldovan, A; Dinescu, M

Published: DEC 20 2010, PLASMA PROCESSES AND POLYMERS, 7, 991, DOI: 10.1002/ppap.201000066

The first step of the smartcut (TM) process consists in inducing structural defects below the free surface of a silicon wafer, usually by implantation of light elements, such as hydrogen or helium. An alternative way to induce subsurface defects is by plasma treatment. In this work, we present a morphological and structural study on silicon wafers submitted to hydrogen plasma treatment, using two plasma-processing geometries. The parameters of the plasma treatment have been varied in order to limit the surface roughness and to confine the induced defects in a narrow region (50 nm) below the wafer surface. The morphological and structural investigations have been performed by AFM and TEM.

602. Study of magnetic nanovectors by Wet-STEM, a new ESEM mode in transmission

Authors: Maraloiu, VA; Hamoudeh, M; Fessi, H; Blanchin, MG

Published: DEC 15 2010, JOURNAL OF COLLOID AND INTERFACE SCIENCE, 352, 392, DOI: 10.1016/j.jcis.2010.08.066

Many nanovectors used for therapy (drug targeting radiation therapy) or diagnostic such as Magnetic Resonance Imaging (MRI) have a composite structure consisting of an organic core or organic coverage encapsulating magnetic nanoparticles and they are commonly dispersed in liquid suspensions for intravenous injection Here is presented the application of a new Environmental Scanning Electron Microscopy (ESEM) mode in transmission so called Wet-STEM for transmission imaging of droplets of such suspensions This is illustrated by Wet-STEM images from PLLA/Re nanospheres (about 100-300 nm in diameter) loaded with magnetite nanoparticles (about 10 nm in diameter) and from iron oxide core (about 5 nm in size) MRI contrast agents both examples in aqueous suspensions It is shown that the Wet STEM mode allows both the collective behavior of such nanovectors in suspension to be characterized and the inner composite structure of individual vectors to be revealed Such experimental results are discussed by comparison with Monte Carlo computer simulations of the distribution of the electrons scattered through the samples in rather large solid angles (between 20 degrees and 47 degrees) corresponding to the detection conditions (C) 2010 Elsevier Inc All rights reserved

603. CO sensing mechanism with WO3 based gas sensors

Authors: Hubner, M; Simion, CE; Haensch, A; Barsan, N; Weimar, U

Published: NOV 26 2010, SENSORS AND ACTUATORS B-CHEMICAL, 151, 106, DOI: 10.1016/j.snb.2010.09.040

The interaction between CO and WO3 based gas sensors was investigated in operando conditions by using resistance, catalytic conversion and DRIFTS measurements. The experimental results are showing that the sensing involves the reduction of the metal oxide, which is the opposite of the case of SnO2, the other extremely relevant material for semiconducting oxides based gas sensors. (C) 2010 Elsevier B.V. All rights reserved.

604. Investigations of the neodymium doped quartz glasses obtained by the hybrid sot-gel method

Authors: Niciu, H; Vasiliu, C; Manea, A; Radu, D; Secu, M; Onose, C; Ghervase, L; Niciu, D; Feraru, ID; Grigorescu, CEA

Published: OCT 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1623, DOI:

Undoped and neodymium doped quartz glasses were obtained by the hybrid sol-gel method. The vitrification was performed in He atmosphere. The Nd(3+) characteristic absorption bands in the UV and VIS were put into evidence. Investigations in the NIR range revealed a small amount (86 ppm) of OH(-) in the vitreous matrix. FTIR and Raman spectra exhibit the SiO(2) glass characteristic vibrations and also the characteristic vibrations of Si-OH and Si-Cl bonds. The photoluminescence peaks at 640, 920 and 1080 nm belonging to the Nd(3+) doped quartz glass were evidenced.

605. Multifrequency ESR Characterization of Paramagnetic Point Defects in Semiconducting Cubic BN Crystals

Authors: Nistor, SV; Stefan, M; Ghica, D; Goovaerts, E

Published: OCT 2010, APPLIED MAGNETIC RESONANCE, 39, 101, DOI: 10.1007/s00723-010-0136-x

Low-frequency (X-band) electron spin resonance (ESR) investigations on commercially available large-grained cubic boron nitride (cBN) superabrasive powders of various coloration, combined with high-frequency (W-band) ESR measurements on oriented submillimeter-size single crystallites selected from the same powder samples, resulted in a clear identification of several types of paramagnetic point defects. The resulting spin Hamiltonian parameters describing the ESR spectra observed in the 3-293 K temperature range and the photosensitivity of the paramagnetic defects observed in amber-colored cBN samples are reported. It is shown that the nature of the paramagnetic centers depends on the color of the investigated samples and that, in many cases, uncontrolled impurities seem to be involved in their structure.

606. Localization of Mn2+ Ions in Mesoporous ZnS

Authors: Nistor, SV; Stefan, M; Nistor, LC; Mateescu, CD; Birjega, R

Published: SEP 2010, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 10, 6205, DOI: 10.1166/jnn.2010.2599

Nanocrystalline cubic ZnS doped with 0.2% mol manganese, exhibiting a stable mesoporous structure, was synthesized at room temperature by a non toxic surfactant-assisted liquid liquid reaction. The X-ray diffraction measurements demonstrate the formation of a sponge-like mesoporous material built from cubic ZnS nanocrystals of 1.8 nm average sizes, with a tight distribution of pores of 1.8 nm mean diameter. The transmission electron microscopy images confirm the formation of the mesoporous structure with walls of 3.1 nm mean thickness built from cubic ZnS nanocrystallites of 2.1 nm average size. The resulting tight distribution of crystallites and pores yields a well resolved Electron Paramagnetic Resonance spectrum, with the narrowest reported component lines attributed to three types of isolated Mn2+ centers, called Mn2+ (I), Mn2+ (II) and Mn2+ (III). From the analysis of the spin Hamiltonian parameters it is shown that in the Mn2+ (I) centers the paramagnetic ion is situated at substitutional Zn sites in the ZnS nanocrystals, being also subjected to a small axial distortion. The relative concentration changes under thermal treatment experiments strongly suggest that in both Mn2+ (II) and Mn2+ (III) centers the Mn2+ ion is localized on the surface of the ZnS nanocrystallites, being bond to an oxygen ion in the first case and to an additional water molecule in the second case.

607. Blue CoAl2O4 spinel via complexation method

Authors: Mindru, I; Marinescu, G; Gingasu, D; Patron, L; Ghica, C; Giurginca, M

Published: AUG 1 2010, MATERIALS CHEMISTRY AND PHYSICS, 122, 497, DOI: 10.1016/j.matchemphys.2010.03.032

Cobalt-aluminate spinel, CoAl2O4, has been synthesized by two synthesis variants of the complexation method: tartarate and gluconate routes. The complex precursors have been characterized by IR, UV-vis spectroscopy and thermal analysis. The cobalt-aluminate spinet has been investigated by XRD, IR, UV-vis and luminescence spectroscopy and TEM. The results indicated that in both cases the single-phase nanocrystalline CoAl2O4 spinet was formed. The average crystallite size from TEM images was in the range 50-60 nm. The emission spectra of CoAl2O4 in the visible region confirmed the presence of tetrahedral coordinated Co2+ ion. (C) 2010 Elsevier B.V. All rights reserved.

608. Growth and structural characterization of Y0.6Lu0.4Ca4O(BO3)(3) new nonlinear crystal

Authors: Gheorghe, L; Achim, A; Voicu, F; Ghica, C

Published: AUG 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1683, DOI:

The nonlinear optical (NLO) crystal Y0.6Lu0.4Ca4O(BO3)(3) (starting composition) of good quality has been grown from the melt by the Czochralski pulling method. X-ray diffraction experiments show that the structure of grown crystal belongs to the monoclinic system with space group Cm and its unit cell parameters have been measured to be a = 0.80711(2)nm, b = 1.60132(1)nm, c = 0.35230(8)nm and beta = 101.166(1)degrees. The crystal possesses a wide transmission range from UV to IR, which is advantageous for applications as new NLO material for frequency doubling of solid state lasers operating in the near infrared range.

609. COLUMN STUDY OF CADMIUM ADSORPTION ONTO POLYACRYLONITRILE/HYDROXYAPATITE COMPOSITE BEAD

Authors: Wang, X; Min, BG; Lyoo, WS; Chihaia, V; Gartner, M; Stoica, TF; Bae, JY; Suh, SH

Published: AUG 2010, REVUE ROUMAINE DE CHIMIE, 55, 447, DOI:

Macroporous polyacrylonitrile/hydroxyapatite (PAN/HAp) composite bead was studied for cadmium removal in a fixed-bed column. The morphology of PAN/HAp composite bead was measured. The adsorption performance of PAN/HAp composite bead in the column was examined by varying bed height and HAp amount in PAN bead. The maximum adsorption capacity and the exhaustion time were determined from the breakthrough curves. Experimental data was described using the Adams-Bohart model. Bed height did not exert large influence on the maximum adsorption capacity and the exhaustion time. The kinetic rate constant and the adsorption capacity of the bed were found to be affected by the total HAp amount.

610. ADSORPTION COMPLEXES OF COLLAGENOUS POLYPEPTIDE-IONIC SURFACTANT IN AQUEOUS MEDIUM 2. THE INFLUENCE OF ADSORPTION COMPLEXES OF POLYPEPTIDE-IONIC SURFACTANT ON THERMAL STABILITY OF COLLAGEN TYPE I

Authors: Micutz, M; Staicu, T; Sulea, D; Leca, M; Ghica, C

Published: AUG 2010, REVUE ROUMAINE DE CHIMIE, 55, 510, DOI:

In the first part of this study it has shown that the interaction between collagenous polypeptides (collagen type I with native structure of triple helix and collagen hydrolyzates with no significant secondary structure) and ionic surfactants (sodium dodecyl sulfate and hexadecyl trimethylammonium bromide) involves the formation of micelle-like clusters of ionic surfactant adsorbed onto polypeptide backbone (polypeptide-surfactant complexes) at surfactant concentrations much lower than its cmc. The present investigation is focused on the influence of polypeptide-ionic surfactant complexation on thermal denaturation of the collagen type I extracted from calfskin and young horse tendons. On the basis of capillary viscometry, a good correlation between denaturation temperatures and activation energies of viscous flow for the dilute aqueous collagen-ionic surfactant solutions at pH 2.5 and 8.0 has been found. Beginning from that, it has established that the presence of ionic surfactant reduces thermal stability of the two collagens, with a more pronounced effect in the case of sodium dodecyl sulfate. Accordingly, it has been proposed a thermal denaturation mechanism of the collagen triple helix in the presence of ionic surfactants.