Time filter

Source Type

Nistor L.C.,National Institute of Materials Physics Bucharest | Ghica C.,National Institute of Materials Physics Bucharest | Kuncser V.,National Institute of Materials Physics Bucharest | Pantelica D.,Horia Hulubei National Institute of Physics and Nuclear Engineering | And 3 more authors.
Journal of Physics D: Applied Physics | Year: 2013

Highly textured ZnO thin films were implanted with Co ions at fluences of 1 × 1016 and 1 × 1017 ions cm-2. Although their microstructure observed by analytical high-resolution electron microscopy was very different, SQUID magnetometer measurements showed qualitatively similar magnetic properties. In the low-fluence film, only small modifications, such as a slight amorphization, planar defects or very small (<1-1.5 nm) Co clusters, were hardly observable. Implantation at a higher fluence led to important changes in the film structure: heavy amorphization and metallic Co precipitates were identified by electron diffraction, energy dispersive x-ray spectroscopy (EDS), electron energy loss spectroscopy and scanning transmission electron microscopy spectrum imaging. EDS microanalysis additionally revealed the presence of ∼2 at% Co atoms that were likely dissolved in the ZnO lattice at the atomic level. No Co oxides or other secondary oxide phases were detected. For both implanted samples, the dimensions of Co precipitates were below the superparamagnetic limit at room temperature. Thermo-magnetization curves and magnetic hysteresis loops measured in the temperature range from 5 to 300 K indicated two superimposed magnetic regimes, one predominant above 50 K and the other below 50 K. We analysed the possible mechanisms and quantitative contributions to explain the observed magnetic behaviour at low and room temperature. © 2013 IOP Publishing Ltd. Source

Keita A.-S.,University of Lorraine | En Naciri A.,University of Lorraine | Delachat F.,Institute dElectronique du Solide et des Systemes | Carrada M.,Institute dElectronique du Solide et des Systemes | And 3 more authors.
Thin Solid Films | Year: 2011

Spectroscopic ellipsometry (SE) measurements were carried out in order to characterize the optical properties of silicon nanoscale inclusions (Si-ni) contained in silicon-rich silicon nitride (SRSN) films. These films were deposited using the plasma enhanced chemical vapor deposition (PECVD) technique followed by rapid thermal annealing (RTA) during 1 min. We focus our study on the influence of the deposition and annealing conditions - such as the ammonia to silane flow ratio R, the annealing atmosphere and temperature - on the optical responses of the SRSN layers and the behavior of the Si-ni dielectric functions. Our results suggest that the variation of R affects in a more significant way the structure and optical properties of the SRSN films than the change of the annealing gas or temperature. © 2010 Elsevier B.V. All rights reserved. Source

Kumar H.,Indian Institute of Technology Delhi | Ghosh S.,Indian Institute of Technology Delhi | Avasthi D.K.,Inter University Accelerator Center | Kabiraj D.,Inter University Accelerator Center | And 4 more authors.
Nanoscale Research Letters | Year: 2011

Present work reports the elongation of spherical Ni nanoparticles (NPs) parallel to each other, due to bombardment with 120 MeV Au+9 ions at a fluence of 5 × 1013 ions/cm2. The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing. The elongation of Ni NPs due to interaction with Au+9 ions as investigated by cross-sectional transmission electron microscopy (TEM) shows a strong dependence on initial Ni particle size and is explained on the basis of thermal spike model. Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles. Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction. © 2011 Kumar et al. Source

Ghosh S.,Indian Institute of Technology Delhi | Kumar H.,Indian Institute of Technology Delhi | Kumar H.,University of Sao Paulo | Singh S.P.,Indian Institute of Technology Delhi | And 8 more authors.
Springer Series in Materials Science | Year: 2014

The interaction between swift heavy ions (SHI) and a solid has been identified as one of the important physical processes to generate or modify nanostructures in thin solid films. The large part of the energy which is deposited in the electronic subsystem of a material by SHI is known as electronic energy loss and gets coupled to the lattice subsystem in a complex way resulting in a transient (picoseconds to sub-nanosecond) thermal spike within a few nanometer diameter region of the thin solid film along the ion path. The temperature of this narrow zone may raise up to 1000 K or more during this time. This transient heating process is known as lattice thermal spike and can be used as a tool to engineer materials down to the nanoscale. Here we address two important consequences of lattice thermal spike; (i) elongation of metal nanoparticles embedded in dielectric thin films and (ii) generation of a-Si/c-Si nanostructures in a silicon nitride matrix. © Springer International Publishing Switzerland 2014. Source

Zlatanski M.,Institute dElectronique du Solide et des Systemes | Uhring W.,Institute dElectronique du Solide et des Systemes | Zint V.,Institute dElectronique du Solide et des Systemes | Le Normand J.-P.,Institute dElectronique du Solide et des Systemes | Mathiot D.,Institute dElectronique du Solide et des Systemes
2010 Conference on Design and Architectures for Signal and Image Processing, DASIP2010 | Year: 2010

This paper presents the state of the art of the Integrated Streak Camera (ISC) architectures in standard CMOS technology. It focuses on some of the methods required for reconstructing the luminous events profile from the chip raw data. Two main ISC architectures are presented. The first adopts the traditional for the most silicon imagers pixel array configuration, where the photocharges-induced signal is processed directly in-pixel. The second approach is based on a single light detecting vector, comparable to the slit of a Conventional Streak Camera (CSC), coupled to an amplifier stage and an analog sampling and storage unit. For both architectures, depending on the on-chip processing of the photocharges, appropriate signal reconstruction techniques are required in order to restore the luminous signal shape. A novel single vector ISC front-end architecture with an asynchronous photodiode reset scheme is presented. Algorithms allowing the luminous event reconstruction are proposed and validated through simulations for all the ISCs considered. © 2010 IEEE. Source

Discover hidden collaborations