National Institute Of Materials Physics - Romania

Publications

849 articles found

471. BNT-BT0.08 wires derived from sol-gel precursor and their piezoelectric behavior

Authors: Cernea, M; Pintilie, L; Trupina, L; Vasile, BS; Chirila, C; Pasuk, I

Published: MAY 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1668-4

Lead-free piezoelectric (Bi0.5Na0.5)(0.92)Ba0.08TiO3, (abbreviated as BNT-BT0.08) wires were prepared using its corresponding precursor sol and, a polycarbonate template membrane. The polycarbonate membrane used has a thickness of 30 mu m and pore diameter of 300 nm. Uniform surface morphology of the wires with average diameter of 145 nm and a length of about 20 mu m was obtained when the concentration of the sol was 0.3 M. The ferroelectric and piezoelectric properties of an individual BNT-BT0.08 wire were investigated using the PFM technique. The hysteresis loops between the PFM phase and DC bias and, the characteristic butterfly loops of the PFM amplitude versus DC bias, indicated a ferroelectric and piezoelectric behavior of as-obtained BNT-BT0.08 wires.

472. Structural properties of silver doped hydroxyapatite and their biocompatibility

Authors: Ciobanu, CS; Iconaru, SL; Pasuk, I; Vasile, BS; Lupu, AR; Hermenean, A; Dinischiotu, A; Predoi, D

Published: APR 1 2013, MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS, 33, 1402, DOI: 10.1016/j.msec.2012.12.042

The aim of this study was to obtain a novel hydroxyapatite-based material with high biocompatibility. The structural properties of the samples were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The X-ray diffraction studies revealed the characteristic peaks of hydroxyapatite in each sample. Other phases or impurities were not observed. The scanning electron microscopy observations suggest that the doping components have no influence on the surface morphology of the samples, which reveals a homogeneous aspect of the synthesized particles for all samples. The presence of calcium (Ca), phosphor (P), oxygen (O) and silver (Ag) in the Ag:HAp is confirmed by energy dispersive X-ray (EDAX) and X-ray Photoelectron Spectroscopy analyses. Nanocrystalline silver doped HAp stimulated viability and potentiated the activation of murine macrophages. (C) 2012 Elsevier B.V. All rights reserved.

473. Miniature x-ray tubes: current state and future prospects

Authors: Filip, V; Filip, LD; Okuyama, F

Published: MAR 2013, JOURNAL OF INSTRUMENTATION, 8, DOI: 10.1088/1748-0221/8/03/T03005

Over the last decade, field emission miniature x-ray tubes emerged as cutting-edge applications of nanotechnology, possessing massive potential for use in various important fields, including that of precision medical therapy. The article essentially presents a review of such new devices reported in the literature. Additional discussions on the necessity of stabilizing the electron beam that generates x-rays are also included, and a simple technique for minimizing the current fluctuations is described. It is also pointed out that further miniaturization of field emission x-ray sources may need new concepts in designing the tube in shapes acting as "self focusing" structures for the electron beams.

474. Novel doped hydroxyapatite thin films obtained by pulsed laser deposition

Authors: Duta, L; Oktar, FN; Stan, GE; Popescu-Pelin, G; Serban, N; Luculescu, C; Mihailescu, IN

Published: JAN 15 2013, APPLIED SURFACE SCIENCE, 265, 49, DOI: 10.1016/j.apsusc.2012.10.077

We report on the synthesis of novel ovine and bovine derived hydroxyapatite thin films on titanium substrates by pulsed laser deposition for a new generation of implants. The calcination treatment applied to produce the hydroxyapatite powders from ovine/bovine bones was intended to induce crystallization and to prohibit the transmission of diseases. The deposited films were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy. Pull-off adherence and profilometry measurements were also carried out. X-ray diffraction ascertained the polycrystalline hydroxyapatite nature of the powders and films. Fourier transform infrared spectroscopy evidenced the vibrational bands characteristic to a hydroxyapatite material slightly carbonated. The micrographs of the films showed a uniform distribution of spheroidal particulates with a mean diameter of similar to 2 mu m. Pull-off measurements demonstrated excellent bonding strength values between the hydroxyapatite films and the titanium substrates. Because of their physical-chemical properties and low cost fabrication from renewable resources, we think that these new coating materials could be considered as a prospective competitor to synthetic hydroxyapatite used for implantology applications. (C) 2012 Elsevier B.V. All rights reserved.

475. Casimir effect demonstrated by Raman spectroscopy on trilayer graphene intercalated into stiff layered structures of surfactant

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

Published: JAN 2013, CARBON, 51, 142, DOI: 10.1016/j.carbon.2012.08.021

Polarized Raman scattering studies on stiff layered structure of surfactant intercalated with trilayer graphene were performed at different intensities and excitation wavelengths. The D and 2D Raman bands reach the highest and lowest intensity when the polarization of laser excitation light is oriented along and perpendicular on the edges. The 2D band discloses two lorentzian components, separated by similar to 40 cm(-1), which result from the action of interplanar forces, of Casimir nature. The value of similar to 40 cm(-1) is close to the energy value associated with E-2g interplanar layer shear mode evidenced so far only by neutron spectrometry. A new result regards the opposite variation of the intensities of D and 2D bands with the increase of the wavelength of the excitation light. This originates in the different origin of the D and 2D bands; the former is dependent on disorder including also the graphene edges while the latter, results from in a double resonant mechanism combined with a Casimir effect. One demonstrates that the magnitude of Casimir force, which activates interlayer vibration modes, depends on the carrier density on the graphene sheets which can be varied both by the intensity and the wavelength of the excitation laser light. (C) 2012 Elsevier Ltd. All rights reserved.

476. Study of High-dose X-ray Radiation Damage of Silicon Sensors

Authors: Schwandt, J; Fretwurst, E; Klanner, R; Pintilie, I; Zhang, JG

Published: 2013, DAMAGE TO VUV, EUV, AND X-RAY OPTICS IV; AND EUV AND X-RAY OPTICS: SYNERGY BETWEEN LABORATORY AND SPACE III, 8777, DOI: 10.1117/12.2019514

The high intensity and high repetition rate of the XFEL, the European X-ray Free-Electron Laser presently under construction in Hamburg, results in X-ray doses of up to 1 GGy in silicon sensors for 3 years of operation. Within the AGIPD Collaboration the Hamburg group has systematically studied X-ray-radiation damage using test structures and segmented sensors fabricated on high-ohmic n-type silicon. MOS Capacitors and Gate-Controlled Diodes from 4 vendors with different crystal orientations and different technological parameters, as well as strip sensors have been irradiated in the dose range between 10 kGy and 1 GGy. Current-Voltage, Capacitance/Conductance-Voltage and Thermal Dielectric Relaxation Current measurements were used to extract oxide-charge densities, interface-trap densities and surface-current densities as function of dose and annealing conditions. The results have been implemented into TCAD simulations, and the radiation performance of strip sensors and guard-ring structures simulated and compared to experimental results. Finally, with the help of detailed TCAD simulations, the layout and technological parameters of the AGIPD pixel sensor have been optimized. It is found that the optimization for sensors exposed to high X-ray doses is significantly different than for non-irradiated sensors, and that the specifications of the AGIPD sensor can be met. In 2012 sensors have been ordered, the first batch has been delivered recently, and first results on a comparison between simulations and measurements will be presented.

477. ELECTROCHEMICAL DEPOSITED HYDROXYAPATITE ON PRE-TREATED CP-TI SURFACES

Authors: Chivu, AE; Ciuca, S; Bojin, D; Stan, GE; Gebert, A; Eckert, J

Published: 2013, METALURGIA INTERNATIONAL, 18, 38, DOI:

Commercially pure titanium (CP-Ti) offers a good corrosion resistance and tissue tolerance. The interfacial phenomena between biomaterial and biological fluids depend especially on surface chemistry, energy, roughness and topography of the implant Different methods are used to modify CP-Ti surface in order to improve its bonding properties to bone tissue. Besides the mechanical approaches, chemical etching and chemical oxidation, there are also other procedures improving the biocornpatibility. One of the most important involves the deposition of a bioceramic thin layer on the metallic surface. A bioceramics frequently used is hydroxyapatite (HA), the mineral component of the bone. In this paper. the main objective was to study the effects of different surface pretreatments on adherence of hydroxyapatite layer obtained by electrochemical method. The CP-Ti substrate was used in different treated states of the surface. The applicability of the electrochemical technique is relieved by the fact that it is a very rapid method, requires relatively low temperatures, being also very versatile. The obtained coatings were studied by scanning electron microscopy (SEM) associated with EDX (Energy dispersive X-ray spectroscopy, X-ray diffraction method (XRD). The adherence of the layers was evaluated by the "pull-out" test. The quality of the coating (morphology and adhesion properties) is decisively influenced by the electrochemical parameters and also by the surface state.

478. THE INFLUENCE OF HOST BONE SUBSTRATE IN TITANIUM MESH CRANIOPLASTY

Authors: Chiriac, A; Stan, GE; Iliescu, B; Poeata, I

Published: APR-JUN 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 735, DOI:

Reconstructive surgery of bone defects in the calvarium makes use of a multitude of biological and artificial materials. Due to the increased number of such medical casuistry in the recent years, a special attention was dedicated to the biocompatibility and osteointegrative properties of various types of biomaterials. Titanium emerged to be a promising cranioplasty material due to its excellent mechanical properties and biocompatibility. However, the way the host calvarial bone reacts to the titanium implant has not been fully understood. Here, we evaluate the influence of cranial bone substrate on the osteoconduction and osseointegration of titanium mesh implants. The pattern of bone tissue reaction in the areas of contact with metallic implant is analyzed by means of bone density measurements on the computer tomography images. Twenty-eight patients underwent cranioplasty with titanium mesh implants for bone cranial defects due to different aetiology. With the aid of visual analogue scales, the patients' status (osteointegration degree, comfort and cosmetics) was evaluated after 3 - 14 months since surgery (implantation).

479. Wireless AlN sensor for condition based monitoring of industrial equipment

Authors: Ionescu, G; Ionescu, O; Popovici, S; Costea, S; Dumitru, V; Brezeanu, M; Stan, GE; Pasuk, I

Published: 2013, 2013 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1-2, 58, DOI:

This paper reports on the experimental realization and characterization of a wireless sensing system for machine-tool condition based monitoring. The system comprises a vibration sensor, an ARDUINO Leonardo development board and an RM 42 Blue tooth module. The sensing principle is based on a vibration sensor which includes a piezoelectric AlN layer deposited by sputtering on a flexible stainless steel foil. The functional testing of the sensor using a test stand for asynchronous engines equipped with frequency convertors is demonstrated.

480. Evidence of tunneling in n-4H-SiC/SiO2 capacitors at low temperatures

Authors: Filip, LD; Pintilie, I; Svensson, BG

Published: 2013, SILICON CARBIDE AND RELATED MATERIALS 2012, 740-742, +, DOI: 10.4028/www.scientific.net/MSF.740-742.557

In this work, anomalous discontinuities observed in Capacitance-Voltage (C-V) characteristics on non-nitridated n-4H-SiC/SiO2 capacitors at low temperature are addressed. The appearance of abrupt capacitance minima, always at the same gate voltages (4V and 8V) and independent on probe frequency, led us to consider a resonant electron tunneling process from neutral donor states present at the SiC/SiO2 interface into two well defined energy levels in the oxide layer. Results of numerical simulations based on this model describe quantitatively the experimentally observed discontinuities at 4V and 8V and provide strong evidence for the presence resonant tunneling.