National Institute Of Materials Physics - Romania

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860 articles found

601. INFLUENCE OF ANNEALING TREATMENT OF NANO-HYDROXYAPATITE BIOCERAMICS ON THE VIBRATIONAL PROPERTIES

Authors: Ciobanu, CS; Andronescu, E; Stoicu, A; Florea, O; Le Coustumer, P; Galaup, S; Djouadi, A; Mevellec, JY; Musa, I; Massuyeau, F; Prodan, AM; Lafdi, K; Trusca, R; Pasuk, I; Predoi, D

Published: APR-JUN 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 624, DOI:

Nano-hydroxyapatite bio-ceramics were synthesized by sol-gel method. The gel was dried at 80 degrees C for 96 h. The dried gels were individually heated at a rate of 5 degrees C/min up to 600 degrees C, 800 degrees C, and 1000 degrees C. X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used for to characterize the composition, morphology and particle size of samples. At 800 degrees C a small amount of CaO (about 0.3 wt%) was detected in which increased after annealing at 1000 degrees C (about 1.1 wt%). The crystallites are elongated along the c crystallographic axis, but the size anisotropy decreases with increasing temperature above 800 degrees C. The size along the elongation axis increased from 43 nm at 80 degrees C to about 143 nm at 1000 degrees C, as determined by XRD, and from 120 to 280 nm, as measured by TEM. The functional groups were analyzed using Fourier transform infrared (FTIR) and Raman spectroscopies confirming the presence of various and PO43 and OH- bands in the samples. After calcination at 1000 degrees C the bands are more intense which indicates an increase in the cristallynity. The photoluminescence (PL) of HAp treated at various temperatures (80, 600, 800, 1000 degrees C) was also studied. hFOB 1.19 osteoblats cells were used to determine cell proliferation, viability and citotoxicity after interaction with the prepared bioceramics. To evaluate cell proliferation rate quantitative by the hFOB 1.19 cells on HAp samples were cultured to 4 days. Cellular morphology was investigated using FESEM to obtain qualitative information of osteoblast cells on HAp samples. The number of hFOB 1.19 cells on control HAp_80, HAp_600, HAp_800 and HAp_1000 was 400 +/- 30, 360 +/- 25, 350 +/- 21, 320 +/- 16 and 300 +/- 10 after 4 days. Our results proved that the HAp sintered at 1000 degrees C promoted osteoblast cell attachment and adhesion.

602. A COMPLEX INVESTIGATIONS OF THE IRON AND GOLD INCLUSIONS IN MINERALS SPECIES AT NANOSIZE SCALE

Authors: Constantinescu, S; Udubasa, SS; Popescu-Pogrion, N; Mercioniu, I; Udubasa, G

Published: 2011, ROMANIAN JOURNAL OF PHYSICS, 56, 718, DOI:

The combined investigation techniques, electron probe microanalysis (EPMA), Mossbauer spectroscopy (NGR), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD),) evidenced the third level of the inclusions at nanosize scale for specific minerals of different Romanian metamorphic deposits. So, NGR technique reveals the contribution of the (Mn, Fe) oxides - small particles at standard (RT) and at very low temperature (LHeT) in the Fe-52 gamma - ray signal of manganoan-fayalites (Razoare deposit). The EM analysis techniques confirmed the presence of the nanometric Fe and Mn oxides inclusions in manganoan fayalites, as well as of pyroxferroite (Razoare deposit). On the other hand, an extensive investigation of the gold ores in the South Carpathians (Costesti, Valea lui Stan and Jidostita) has been performed by using a fruitful combination among the above mentioned complementary mineralogical and structural methods. The investigation of the representative sulfide samples by the structural techniques relieved new minerals in the gold ores, the presence of submicroscopic inclusions of uytenbogaardtite, cobaltite and loellingite as well as the "coral like" aggregates of nanometric gold.

603. PREPARATION AND ELECTRICAL CHARACTERIZATION OF SiGe NANOSTRUCTURES

Authors: Stavarache, I; Lepadatu, AM; Pasuk, I; Teodorescu, VS; Ciurea, ML

Published: 2011, 2011 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2011), 34TH EDITION, VOLS 1 AND 2, 52, DOI:

This paper presents the preparation and investigation of structure and electrical properties of nanostructures consisting of Si1-xGex nanocrystals. Nanostructures were prepared by RF magnetron sputtering, followed by thermal annealing. X-ray diffraction, TEM, high resolution TEM and SAED measurements were performed. Current-voltage and current-temperature characteristics were taken. Nanostructures have different electrical behavior. Current-voltage curves are linear, while current-temperature curves are dependent on the annealing temperature. In films annealed at 650 degrees C, electrical transport is controlled by quantum confinement effect and localized states (current-temperature characteristics), while in films annealed at 900 degrees C it is controlled by tunneling of thermally activated carriers between neighboring nanocrystals.

604. TRAPPING ASPECTS IN SILICON-BASED NANOSTRUCTURES

Authors: Ciurea, ML

Published: OCT-DEC 2011, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 12, 323, DOI:

Trapping aspects in two typical silicon-based nanostructures are investigated. Both 1D nanocrystalline porous silicon structures and 2D (nc-Si/CaF2)50 multilayered structures are considered. The curves of relaxation current versus temperature were obtained using the thermally stimulated currents method without external bias. Two types of maxima (rather broad maxima and spikes) were experimentally evidenced. The spikes are due to the stress-induced traps and their parameters are temperature dependent. To describe the trapping-detrapping-retrapping processes, a general model was proposed. The temperature dependence of stress-induced trap concentrations was described by a power law and the corresponding temperature dependence of cross-sections by a Gaussian law. The model was successfully applied on available experimental data.

605. INVESTIGATION OF MAGNETITE FORMATION IN THE PRESENCE OF HYDRAZINE DIHYDROCHLORIDE

Authors: Gingasu, D; Mindru, I; Patron, LA; Calderon-Moreno, JM; Diamandescu, L; Tuna, F; Popescu, T

Published: JUL-SEP 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 1072, DOI:

Fe(3)O(4) nanoparticles were synthesized by a wet chemical method using Fe(III)/Fe(II) - hydrazine dihydrochloride systems. The structure, morphology, and magnetic properties of magnetite were examined by X-ray powder diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), Mossbauer spectroscopy and superconducting quantum interference device (SQUID). Almost all the particles exhibit superparamagnetic like properties at room temperature. This behavior can be correlated with the size of the particles which ranged between 20-70 nm.

606. VOLTAGE PERCOLATION THRESHOLDS EVIDENCED IN THE ELECTRICAL BEHAVIOUR OF DIFFERENT NANOSTRUCTURES

Authors: Stavarache, I

Published: JUL-SEP 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 1083, DOI:

Percolation phenomena are investigated and discussed in three kinds of nanostructures: first two are nanocrystalline silicon-based systems, Si nanodots embedded in amorphous SiO2 matrix and porous silicon formed by an oxidized nanowire network, and the third consisting of a multi-walled carbon nanotube network embedded in amorphous SiN. The current-voltage characteristics measured on first two systems present voltage percolation thresholds with the same shape - a saturation plateau region of the current, followed by an abrupt increase. The current-voltage and conductance-voltage curves measured on multi-walled carbon nanotube network embedded in amorphous SiN present non-periodic and temperature independent oscillations. These oscillations are interpreted as voltage percolation thresholds.

607. STUDIES OF LONG TIME AND TRANSIENT EFFECTS INDUCED BY RADIATION IN CRYSTALLINE MATERIALS

Authors: Lazanu, S; Lazanu, I; Iordache, G; Stavarache, I; Lepadatu, A; Slav, A

Published: 2011, 2011 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2011), 34TH EDITION, VOLS 1 AND 2, 264, DOI:

The long time degradation produced by particles and ions in crystalline materials used for devices to work in space, or for detectors in HEP and astroparticles, is characterised by the non-ionising energy loss, which is calculated in the frame of an analytical model. The transient phenomena as short time degradation are characterised by the time and space dependencies of the lattice and electron temperatures near the projectile trajectory. These processes are considered in the frame of a thermal spike model, which takes into account both ionization and nuclear energy loss processes.

608. STUDY OF Ge NANOPARTICLES EMBEDDED IN AN AMORPHOUS SiO2 MATRIX WITH PHOTOCONDUCTIVE PROPERTIES

Authors: Lepadatu, AM; Stavarache, I; Stoica, TF; Ciurea, ML

Published: JAN-MAR 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 73, DOI:

Electrical and photoconductive properties of films consisting of amorphous Ge nanoparticles uniformly distributed in amorphous SiO2 were studied. These films were prepared by sol-gel method and treated by rapid thermal annealing technique. Measurements of current-voltage and conductance-temperature characteristics, spectral and bias dependences of the photocurrent on samples with coplanar geometry of electrodes, were performed. The current-voltage characteristics have a weak rectifying behaviour. The variable range hopping transport mechanism, described by the Mott law, in amorphous materials, in the absence of dominant Coulomb interactions, was evidenced in the temperature dependence of the dark current. The samples exhibit very good photoconductive properties, explained by taking into account the Ge clusters and defects, produced by the rapid thermal annealing.

609. PREPARATION INDUCED ELECTRICAL BEHAVIOUR OF GeSiO NANOSTRUCTURES

Authors: Stavarache, I; Lepadatu, AM; Ciurea, ML

Published: 2011, 2011 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2011), 34TH EDITION, VOLS 1 AND 2, 34, DOI:

GeSiO nanostructures obtained by using two different preparation methods, sol-gel and magnetron-sputtering were studied. They are formed from Ge nanoparticles dispersed in amorphous matrix, with different morphology depending on the preparation method. Electrical investigations (current-voltage and current-temperature measurements) were performed and experimental results were modelled. It was shown that preparation conditions induce the electrical behaviour of GeSiO films, so that the electrical transport in sputtered films is governed by a hopping mechanism, while in sol-gel ones it is dominated by the junction formed at the interface with Si substrate. Also, the temperature dependence of current shows different hopping mechanisms.

610. Electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride

Authors: Stavarache, I; Lepadatu, AM; Teodorescu, VS; Ciurea, ML; Iancu, V; Dragoman, M; Konstantinidis, G; Buiculescu, R

Published: 2011, NANOSCALE RESEARCH LETTERS, 6, DOI: 10.1186/1556-276X-6-88

The electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride is studied by measuring the voltage and temperature dependences of the current. The microstructure of the network is investigated by cross-sectional transmission electron microscopy. The multi-walled carbon nanotube network has an uniform spatial extension in the silicon nitride matrix. The current-voltage and resistance-temperature characteristics are both linear, proving the metallic behavior of the network. The I-V curves present oscillations that are further analyzed by computing the conductance-voltage characteristics. The conductance presents minima and maxima that appear at the same voltage for both bias polarities, at both 20 and 298 K, and that are not periodic. These oscillations are interpreted as due to percolation processes. The voltage percolation thresholds are identified with the conductance minima.