National Institute Of Materials Physics - Romania

Publications

838 articles found

641. DLTS measurements of radiation induced defects in epitaxial and MCz silicon detectors

Authors: Honniger, F; Fretwurst, E; Lindstrom, G; Kramberger, G; Pintilie, I; Roder, R

Published: DEC 11 2007, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 583, 108, DOI: 10.1016/j.nima.2007.08.202

n-Type epitaxial silicon layers of different thickness and resistivity, grown on highly Sb doped CZ-substrate by ITME (Warsaw), and n-type MCz silicon supplied by Okmetic (Finland) were used for the processing of planar diodes at CiS (Erfurt). For the epi-diodes a standard as well as a diffusion oxygenation process was employed. Irradiations had been performed with 26 MeV protons at the cyclotron of the Karlsruhe University and with neutrons at the TRIGA reactor of the Ljubljana University. Microscopic investigations using the DLTS method were done. The correlation of the IO(2i)-defect and the oxygen concentration was studied by a depth-profile measurement. The annealing behavior of the IO(2i)-defect at different temperatures was investigated and the activation energy extracted. (C) 2007 Elsevier B.V. All rights reserved.

642. Radiation damage studies on MCz and standard and oxygen enriched epitaxial silicon devices

Authors: Fretwurst, E; Honniger, F; Kramberger, G; Lindstrom, G; Pintilie, I; Roder, R

Published: DEC 11 2007, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 583, 63, DOI: 10.1016/j.nima.2007.08.194

N-type epitaxial layers of 72 mu m thickness and a resistivity of 150 Omega cm have been grown on highly Sb-doped Cz-substrates at ITME (Warsaw). The diode processing was performed at CiS-Erfurt. For comparison a batch of 280 mu m thick n-type MCZ wafers with a resistivity of >600 Omega cm from Okmetic (Finland) was added to the process run. Depth profiles of the oxygen and carbon concentration were measured via the SIMS-method on as grown epi-layers and after different device-process steps at CiS including an oxygen enrichment at 1100 degrees C for 24 h. For the MCz material the profiles were measured on untreated samples and after the full device process. Irradiation runs were performed with neutrons at the TRIGA reactor of Ljubljana up to a fluence value of 10(16) cm(-2). The development of the macroscopic device parameters (effective doping concentration and charge collection for a-particles) as function of fluence is presented for the standard and oxygenated epi-devices and compared with the MCz-diodes. The results are discussed in the frame of defect studies resulting from TSC-measurements. (C) 2007 Elsevier B.V. All rights reserved.

643. Electrical characteristics of nano-PbS/SiO2/Si heterostructures obtained by chemical bath method

Authors: Goldenblum, A; Stancu, V; Buda, M; Iordache, G; Botila, T; Negrila, C

Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3802, DOI:

The PbS/SiO2/Si structures show a clockwise hysteresis of capacitance-voltage (C-V) characteristics. The loop width increases with temperature and sweep time. The conductance-voltage (G-V) characteristics also present a hysteresis effect with two bumps. Both characteristics show a strong shift with frequency. We show that these effects are determined by the positive mobile ions injected in the oxide region during the chemical bath deposition of PbS and by the high concentration Of Si/SiO2 interface states. The corresponding C-V and G-V characteristics are simulated and the main peculiarities of the experimental results are well reproduced by the modeled curves.

644. Synthesis of calcium phosphate thin layers of increased biological activity by chemical growth in simulated body fluids

Authors: Neamtu, J; Stan, GE; Morosanu, C; Ducu, C; Popescu, A; Mihailescu, IN

Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3826, DOI:

We studied the chemical growth of calcium phosphate nanostructured coatings onto silicon wafers pre-covered with carbonated polycrystalline hydroxyapatite films. Silicon wafers were covered with hydroxyapatite thin layers by radio frequency magnetron sputtering and then immersed in 370 degrees C simulated body fluids for up to 20 days. Immersed structures were extracted every 2 days for studies by Fourier transform IR spectrometry. The chemically grown layers were further analyzed by X-ray diffraction and scanning electron microscopy. The growth kinetics of calcium phosphate deposits was monitored by estimating the area of phosphate, carbonate and water stretching bands of the recorded infra-red vibrational spectra. Sequential annealing in vacuum up to 950 degrees C was applied to elucidate the nature of incorporated water. Our studies revealed that the layers growing in simulated body fluid are rougher than initial hydroxyapatite interlayers, contain carbonates, include water in interlayer's voids and have therefore an increased biological activity for promoting faster implants integration with human bone tissues.

645. Thickness-driven antiferroelectric-to-ferroelectric phase transition of thin PbZrO3 layers in epitaxial PbZrO3/PbZr0.8Ti0.2O3 multilayers (vol 91, art no 122915, 2007)

Authors: Boldyreva, K; Pintilie, L; Lotnyk, A; Misirlioglu, IB; Alexe, M; Hesse, D

Published: NOV 12 2007, APPLIED PHYSICS LETTERS, 91, DOI: 10.1063/1.2811708

646. High k materials used to manufacture miniaturised dielectric antennas for military applications

Authors: Nicolaescu, I; Ioachim, A; Toacsan, I; Radu, I; Banciu, G

Published: NOV 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3597, DOI:

The microwaves are used for both civilian and military applications for communication and detection. Due to the emerging applications and the need for more bandwidth as well as for high speed there is a strong competition for ultra high frequencies devices. As it is know the size of different kind of microwave components is in a certain relation with the wavelength divided by root square of the dielectric permittivity. So the size of microwave component can be decreased by increasing the dielectric permittivity. Dielectric materials based on TiO2 are recommended for applications in electromagnetism and optics due to their nonlinear properties, to high value of the dielectric permittivity and their temperature behavior. The paper describes very shortly the technology applied to manufacture high dielectric permittivity materials based on TiO2 and microwave devices designed with this. In addition, the experimental data measured for a dielectric antenna are presented.

647. Thickness-driven antiferroelectric-to-ferroelectric phase transition of thin PbZrO3 layers in epitaxial PbZrO3/Pb(Zr0.8Ti0.2)O-3 multilayers

Authors: Boldyreva, K; Pintilie, L; Lotnyk, A; Misirlioglu, IB; Alexe, M; Hesse, D

Published: SEP 17 2007, APPLIED PHYSICS LETTERS, 91, DOI: 10.1063/1.2789401

Epitaxial antiferroelectric/ferroelectric PbZrO3/PbZr0.8Ti0.2O3 multilayers were grown on SrRuO3-electroded SrTiO3(100) substrates by pulsed laser deposition. Polarization-field and switching current-voltage curves show a mixed antiferroelectric-ferroelectric behavior of the multilayers with an individual layer thickness above 10 nm, whereas below 10 nm the multilayers show only ferroelectric behavior. Clearly the PbZrO3 layers thinner than 10 nm experienced a transition into the ferroelectric state. X-ray diffraction reciprocal space mapping showed a corresponding orthorhombic-to-rhombohedral transition of the PbZrO3 layers. The observations are discussed in terms of the influence of strain.

648. Structure of PZT thin films deposited on stainless steel and on platinum/silicon substrate

Authors: Stancu, V; Sava, F; Lisca, M; Pintilie, L; Popescu, M

Published: SEP 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2969, DOI:

Pb(Zr1-xTix)O-3 (PZT) thin films were prepared by sol-gel method on stainless steel (SS) and on platinum-coated silicon substrate (Pt/Si). The structure revealed by X-ray diffraction shows strong crystallographic orientation: (110) and (100), respectively. A small amount of pyrochlore phases (Pb-2(Zr,Ti)(2)O6-delta is formed in the films deposited on SS substrate. The crystallite size shows significant differences: d((00l))((SS)) = 27.1 nm, d((h00))((Pt)) = 88 nm. The tetragonal splitting is (Delta c/c)((SS)) = 3.55 % and (Delta c/c)((Pt)) = 3.32 %.

649. Thickness dependence of crystallization process for hydroxyapatite thin films

Authors: Mercioniu, I; Ciuca, S; Pasuk, I; Slav, A; Morosanu, C; Bercu, M

Published: AUG 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2538, DOI:

Hydroxyapatite (HAP) thin films (0.2 pm, 0.3 pm and 1.2 mu m thickness) were grown by RF magnetron sputtering in argon atmosphere onto silicon substrates at high deposition rates (0.6 mu m/h). Crystalline HAP films were obtained using a low temperature (100 degrees C) followed by post-deposition annealing at 300 degrees C, 450 degrees C, 500 degrees C and 550 degrees C in environmental air for 1 hour. An important influence of the films thickness upon the crystallization degree was noticed at intermediate annealing temperatures, as obtained from XRD measurements. For low and high temperatures similar values were obtained with a better crystallization degree for the thinner films. FTIR absorption led to the same conclusion considering the shape of stretching and bending PO4 lines. This suggests that the crystallization process has a diffusion component besides usual thermal activation process.

650. An algorithm for preparing bioactive fluorinated hydroxyapatite coatings by sol gel technique

Authors: Stan, GE; Ferreira, JMF

Published: AUG 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2542, DOI:

Fluorinated hydroxyapatite [Ca-10(PO4)(6)(OH)(x)F1-x] implantologic structures could constitute an alternative to classic hydroxyapatite [Ca-10(PO4)6(OH)21 ones in medical applications due to their bioactivity and low solubility. Bioactive apatites are usually used as coatings onto surface of biocompatible metals, leading to implants which take advantage of the coating's bioactivity and good mechanical properties of metals. In this work, powders and apatite type films were prepared on Ti6Al4V medical grade alloy using three sol-gel chemical routes by mixing different calcium and phosphorous precursors Ca(NO3)2, P2O5 and C6H15PO3, and two fluoride reagents: HPF6 and NH4F. The resulting calcium phosphates and fluorapatite/hydroxyapatite solid solution (FHA) compounds were investigated by SEM, XRD and evaluated in vitro in SBF Kokubo solution. An efficient preparation algorithm was designed for the Ca(NO3)(2+) C6H15PO3+ NH4F chemical route which produced monophasic powders with a high crystallinity degree. This chemical route led to FHA sol-gel coatings with bioactive potential.