National Institute Of Materials Physics - Romania

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5714 articles found

3191. DEFECT PRODUCTION IN SILICON AND GERMANIUM BY LOW TEMPERATURE IRRADIATION

Authors: Lazanu, S; Lazanu, I; Lepadatu, A; Stavarache, I

Published: 2009, CAS: 2009 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI:

In this communication, we study the production of defects by energetic ions in silicon and germanium, at very low temperatures, as dependencies of non-ionizing energy loss and number of displacements on the ion kinetic energy, and also the partition of the energy deposited between ionization, creation of defects and phonons, short time after the interaction.

3192. Analysis of the Electron Traps at the 4H-SiC/SiO2 Interface of a Gate Oxide Obtained by Wet Oxidation of a Nitrogen pre-Implanted Layer

Authors: Pintilie, I; Moscatelli, F; Nipoti, R; Poggi, A; Solmi, S; Svensson, BG

Published: 2009, SILICON CARBIDE AND RELATED MATERIALS 2008, 615-617, 536, DOI: 10.4028/www.scientific.net/MSF.615-617.533

This work is focusing oil the effect of a high concentration of nitrogen (N) introduced by ion implantation at the SiO2/4H-SiC interface in MOS capacitors. The N implanted sample (N-interface similar to 1 x 10(19) cm(-3)) is compared with a non-implanted one (N-interface similar to 1 x 10(16) cm(-3)) by means of the electron interface trap density (D-it). The Dit is determined via High-Low frequency C-V method and Thermal Dielectric Relaxation Current (TDRC) technique. It is shown that the TDRC method, mainly used so far for determination of near interface oxide charges, call be exploited to gain information about the D-it too. The determined value of D-it in the N-implanted sample is nearly one order of magnitude lower than that in the sample without N implantation. Good agreement between the TDRC results and those obtained from High-Low frequency C-V measurements is obtained. Furthermore, the TDRC method shows a high accuracy and resolution of D-it,evaluation in the region close to the majority carrier band edge and gives information about the traps located into the oxide.

3193. Surface states- and field-effects at p- and n-doped GaAs(111)A/solution interface

Authors: Scurtu, R; Ionescu, NI; Lazarescu, M; Lazarescu, V

Published: 2009, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 11, 1770, DOI: 10.1039/b817045b

We have investigated the behaviour of n- and p-doped GaAs(111) A electrodes in sulfuric acid solution by electrochemical impedance spectroscopy (EIS) and second harmonic generation (SHG) measurements. The potential dependence of the SHG response was found to be closely related to the changes in the surface state population, as revealed by analysis of the impedance data. The nature of the majority of carriers turned out to be a key factor in shaping the surface state- and field-effect on the second harmonic generation process.

3194. Magnetic Temperature Transducers Made from Copper Based Soft Ferrite

Authors: Miclea, C; Tanasoiu, C; Miclea, CF; Spanulescu, I; Cioangher, M; Miclea, CT

Published: 2009, SMART MATERIALS & MICRO/NANOSYSTEMS, 54, 69, DOI:

Soft ferrites in the CuZnTi system, having the chemical composition Cu1-x-yZnxTiyFe2O4 with 0.5 <= x <= 0.7 and 0.00 <= y <= 0.05 were investigated as a function of composition, sintering temperature and cooling speed, in order to obtain materials with different Curie temperatures, between 30 and 180 degrees C and very high change rate of permeability with temperature around their Curie points. Such materials are well suited to use as high sensitive magnetic temperature sensors and transducers for temperature control. Zn and Ti additions to copper ferrite change the Curie temperature in a controllable manner, thus being possible to produce ferrite material with a fine control of the Curie point at any desired temperature. Most important was the behavior of magnetic permeability with temperature around the Curie point, where it may change with about 60 %/degrees C by a proper choice of the cooling speed of samples from the sintering temperature to room temperature. This makes such materials extremely attractive as magnetic temperature sensors of high sensitivity. Two applications Of Such materials as temperature sensors, namely an ultrathermostat and an on-off switch type relay were designed. Their functionality and performances are presented and discussed.

3195. Efficient Laser Emission of Nd-vanadates on the 1.34-mu m (4)F(3/2)->(4)I(13/2) Transition under Pumping with Diode Lasers Directly into the Emitting Level

Authors: Pavel, N; Dascalu, T; Vasile, N; Lupei, V

Published: 2009, 2009 CONFERENCE ON LASERS AND ELECTRO-OPTICS AND QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2009), VOLS 1-5, 2604, DOI:

Efficient 1.34-mu m laser emission is realized in Nd-vanadates under pumping with diode lasers at 0.88 mu m. A Nd:YVO(4) crystal yielded 3.4-W output power for 9.3-W absorbed pump power, at a slope efficiency of 0.43. (C) 2009 Optical Society of America

3196. Possible influence of two-band superconductivity on the behaviour of the second magnetization peak in La2-xSrxCuO4 single crystals

Authors: Miu, L

Published: AUG-OCT 2009, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 1139, DOI: 10.1016/j.physc.2009.05.200

An anomalous temperature T dependence of the field H-on for the onset of the second magnetization peak (SMP) in La1.81Sr0.19CuO4 single crystals (with the external magnetic field H oriented parallel to the c axis) is discussed. While the peak field H-p and the magnetization at H-p have a continuous variation with T, H-on exhibits a sudden decrease with increasing T for T similar to 11 K-15 K. The analysis of the nature of the SMP in La2-xSrxCuO4 single crystals in terms of a simple dynamic energy balance relation suggests that the observed behaviour Could be related to the particular T dependence of the superfluid density in the case of two-band Superconductivity, affecting the T variation of the elastic energy of the vortex system at low H (C) 2009 Elsevier B. V. All rights reserved.

3197. Peak-dip crossover of the differential conductance in mesoscopic systems with quantum impurities

Authors: Aldea, A; Tolea, M; Dinu, IV

Published: 2009, 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 2, 150, DOI: 10.1088/1742-6596/150/2/022001

We investigate the differential conductance dI/dV for the interacting T-shape model, using an approach based on the Keldysh formalism and the Lacroix solution for the equation of motion. A peak-dip crossover has been noticed by changing the hybridization between the two dots. For the same model, the combined interaction and interference processes give rise to the Fano-Kondo effect with an interesting crossing point of the isoterms below the Kondo temperature A tentative explanation of these effects is given in terms of the many-body spectral properties of the system.

3198. Polymer functionalization with manganites

Authors: Sandu, V; Popa, S; Ivan, I; Plapcianu, C; Sandu, E; Hurduc, N; Nor, I

Published: 2009, SECOND INTERNATIONAL CONFERENCE ON SMART MATERIALS AND NANOTECHNOLOGY IN ENGINEERING, 7493, DOI: 10.1117/12.843221

We investigated the transport properties of a series of composites made of La2/3Sr1/3MnO3 and different copolymers. The temperature dependence of the electrical resistance of the samples is strongly dependent on the nature of the polymers. We found four types of temperature dependences of the electrical resistance: i) simple current dependence of resistivity for poly(methyl-methacrylate-co-styrene) copolymers, ii) single peaked characteristics for poly(acryl amide-co-vinyl acetate), iii) multipeaked dependence found in poly(methyl-methacrylate-co-butadiene) and star type polysiloxane-g-styrene, and iv) current independent characteristics visible in the samples made with linear polysiloxane-based composites.

3199. COMMUTON - A NEW CONCEPT IN SWITCHING MATERIALS

Authors: Popescu, M; Velea, A; Lorinczi, A; Sava, F

Published: MAR-APR 2009, JOURNAL OF OVONIC RESEARCH, 5, 34, DOI:

A switching unit can be defined as the smallest unit that preserves the property of switching in memory materials. Atomic switching unit is discussed, molecular switching units are described and supramolecular units in phase change materials are evidenced and discussed. The "commuton", as basic switching unit, could give more insight into the particular properties of the switching phenomena in various solid materials.

3200. Enhancing critical current in YBCO thick films: Substrate decoration and quasi-superlattice approach

Authors: Sarkar, A; Mikheenko, P; Dang, VS; Abell, JS; Crisan, A

Published: AUG-OCT 2009, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 1553, DOI: 10.1016/j.physc.2009.05.242

For power applications of superconducting films. the critical current density (J(c)) and the thickness of the film (d) should be as high as possible. Since J(c) decreases with both thickness and magnetic field, artificial pinning centres in addition to natural ones are required to keep J(c) high. The earliest cost-effective method used for introducing artificial pinning centres was the so-called substrate decoration, i.e., growing nanoscale islands (nano-dots) of certain materials on the substrate prior to the deposition of the superconducting thin film. Later on another version of this approach proved to be successful: building up a layered distribution of a second phase using a multilayer deposition (quasi-superlattices). Several materials have been used for the Creation of artificial pinning centres. Here we report on the artificial pinning centres induced in YBCO thick films by substrate decoration and quasi-superlattice approaches using nano-dots of Pd and non-superconducting YBCO. The cross-sectional AFM images show evidence of c-axis correlated columnar defects. These defects significantly contribute to the pinning of magnetic flux and increase critical current in the films. We observed an important shift of the position of the maximum in the thickness dependence of J(c)(B) towards higher thicknesses compared with pure YBCO films by both approaches. A high J(c)(B) in our quite thick films provides a very high total critical current per cm of the film width. Critical current as high as 800 A/cm width was achieved in a 2.4 mu m thick quasi-superlattice film with non-superconducting YBCO nano-dots. (C) 2009 Elsevier B.V. All rights reserved.