Papers by christian dufour
Procedia Materials Science, 2014
The interaction between nuclear and electronic energy losses induced by an individual ion are des... more The interaction between nuclear and electronic energy losses induced by an individual ion are described and illustrated by four different experiments. Each experiment shows the different behaviors of the combined interactions. Defects created by nuclear energy loss are annealed by electronic energy loss in Fe by ions in the GeV energy regime, showing a competitive interaction (1+1<1). The sputtering of Ti is enhanced by electronic excitation induced by ~100 MeV ions supporting a synergetic interaction (1+1>2). Damage cross section in crystalline and amorphous SiO 2 is enhanced by ions in the MeV regime, evidencing a cooperative interaction (1+1>1 and <2). Moreover Molecular Dynamic calculations show that defects created by nuclear and electronic collisions appear to be additive (1+1 =2) in this same range of beam energy.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1998
Electronic energy loss (S e) induced modi®cation of collisional defects in Fe and Ni was theoreti... more Electronic energy loss (S e) induced modi®cation of collisional defects in Fe and Ni was theoretically studied under the framework of thermal spike model. The initial spatial density of defects created by nuclear collisions was calculated by use of binary collision theory with charge screen. Taking into account the characteristics of defect annealing substages, temperature dependent atomistic jumps and migrations, the modi®cation of collisional defects in Fe and Ni caused by S e was simulated in a cylindrical geometry. For iron, the theoretical damages were deduced from calculations and compared with experiments. It was found that the number z of quasi-free electrons in iron participating S e induced thermal spike process is about 1.5 per atom and, by use of z 1.5, the deduced defect recombination cross section values in iron are in agreement with experiments. Furthermore, three regions characterized by the concentrations of interstitials and vacancies are proposed. Similar variation tendency of damage eciency in nickel was observed from numerical calculations. Thus, the S e induced defect modi®cation in pure metals may be due to a transient thermal process.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1998
This work reports on the theoretical studies of defect production and annealing induced by electr... more This work reports on the theoretical studies of defect production and annealing induced by electronic energy loss S e in pure metal. The selected metal was a-iron in which irradiation eects produced by swift heavy ions have been well studied experimentally by Dunlop et al. [Nucl. Instr. and Meth. B 90 (1994) 330]. According to thermal spike model in metals and taking into account the principles of ion±solid interactions and thermal atomic jumps and migrations in solid, we have done numerical calculations of spatial distributions of vacancies and interstitials created by nuclear collisions, concentration-dependent thermal migration and recombination of existed defects and thermal defect generation for given swift heavy ion irradiations. The calculated results suggested that threshold S e values for defect annealing and production were about 15 and 38 keV/nm which are in agreement with experiments. The comparison of damage eciencies deduced from our numerical calculations with experimental ones have shown that S e induced defect production and annealing in pure metal can be a result of thermal transient process.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2012
Experimental investigations of ion tracks and sputtering phenomena with energetic heavy projectil... more Experimental investigations of ion tracks and sputtering phenomena with energetic heavy projectiles in the electronic energy loss regime are reexamined in metallic and insulating materials. An overview of track data such as the velocity dependence of the track size and the critical electronic energy loss for track formation is presented. Different physical characterizations of the material transformation are listed in order to deduce a track size which is independent of the observations. It will point out the differences of damage creation by electronic energy loss compared to nuclear energy loss. In the second part, we present a theoretical description of track formation based on the inelastic thermal spike model. This thermodynamic approach combines the initial size of the energy deposition with the subsequent diffusion process in the electronic and lattice subsystems of the target. The track size, resulting from the quench of a molten phase, is determined by the energy density deposited on the atoms around the ion path governed by the electron-phonon strength. Finally, we discuss the general validity of this model in metallic materials and its suitability to describe track formation in amorphizable and non-amorphizable insulators.
Acta Physica Polonica A, 2006
A description of the inelastic thermal spike model is presented in order to correlate the energy ... more A description of the inelastic thermal spike model is presented in order to correlate the energy deposited by swift heavy ions to the nanometric matter transformation induced in inorganic metallic and insulating materials. Knowing that insulator is more sensitive than metallic material and that amorphous material is in general more sensitive than a crystalline one, it appears evident that the electron-phonon coupling constant g plays a key role. It will be shown that in metallic material we are able to describe different phenomena with the same value of g: for example, track formation with defect annealing or sputtering of atoms. In insulators the emphasis is made on results obtained for amorphizable materials like SiO 2 quartz and for non-amorphizable ionic crystals like CaF2. Assuming that tracks result from a transient thermal process, a quantitative development of the model is proposed using the electron-atom mean free path λ (inversely proportional to the square root of g) as a free parameter. With this parameter it is possible to quantitatively describe track radii in a wide range of ion velocitieswhatever the bonding character of the crystal is-assuming specific criteria: tracks may result from a rapid quenching of a cylinder of matter in which the energy deposited on the lattice has overcome either the energy necessary to reach a quasi-molten phase in the case of amorphizable materials or the vaporization energy in the case of non-amorphizable materials. The evolution of the λ parameter of the considered insulator decreases versus the band gap energy. In this model, velocity effect, and a link between track formation and sputtering of atoms is established for amorphizable insulators while open questions appear for ionic crystals.
Ion Beam Processing of Materials and Deposition Processes of Protective Coatings, 1996
ABSTRACT
Scientific Reports, 2016
Ion beam shaping is a novel technique with which one can shape nano-structures that are embedded ... more Ion beam shaping is a novel technique with which one can shape nano-structures that are embedded in a matrix, while simultaneously imposing their orientation in space. In this work, we demonstrate that the ion-shaping technique can be implemented successfully to engineer the morphology of hollow metallic spherical particles embedded within a silica matrix. The outer diameter of these particles ranges between 20 and 60 nm and their shell thickness between 3 and 14 nm. Samples have been irradiated with 74 MeV Kr ions at room temperature and for increasing fluences up to 3.8 × 1014 cm−2. In parallel, the experimental results have been theoretically simulated by using a three-dimensional code based on the thermal-spike model. These calculations show that the particles undergo a partial melting during the ion impact, and that the amount of molten phase is maximal when the impact is off-center, hitting only one hemisphere of the hollow nano-particle. We suggest a deformation scenario whic...
Physical Review B, 1992
Following a description used to explain a phase transformation observed after pulsed femtosecond ... more Following a description used to explain a phase transformation observed after pulsed femtosecond laser irradiation, a transient thermal process is used to describe latent-track formation after high electronic excitation induced by energetic (GeV} heavy ions. The transient thermal calculation is restricted to the amorphous materials aGe , a-Si, and a-Fe»B», for which nearly all latent-track radii and/or macroscopic thermodynamic properties are known. The heat-flow equation is solved numerically in cylindrical geometry. The time-dependent heat-generation term is assumed to be due to the electron-atom interaction. The characteristic length A, of the energy transport by secondary electrons is taken as the only free parameter and the maximum diameter of the cylinder of liquid matter is considered as the diameter of the observed latent track. Using the single value X=14 nm, we have been able to calculate these diameters in a-Si and aGe in reasonable agreement with experimental track diameters, taking into account the large differences between the macroscopic thermodynamic parameters of both materials. This k value is less than that for the crystalline state. In the case of a-Fe»B», the diameters calculated with use of X= 19 nm are in agreement with the ones determined recently by electrical-resistivity change.
Materials Science Forum, 1997
ABSTRACT
Philosophical Magazine A, 2000
Tin oxide nanometric powders have been irradiated with several swift heavy ions (Ar, Cd, Ta, Pb a... more Tin oxide nanometric powders have been irradiated with several swift heavy ions (Ar, Cd, Ta, Pb and U) and observed by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). Except for Ar ions, cylindrical tracks are visible at low¯uences. The mean track radius is all the more important since the electronic stopping power S e is high. Furthermore, the highS e irradiating ions (Pb, Ta and U) create cylindrical holes while, in the case of Cdion irradiations, the track cores remain crystallized with a di erence of contrast from the surrounding crystal. In this case, simulations of HREM images allow us to assert that an amount of matter is lost in Cd track cores. Assuming that the observed latent tracks result from a thermal process, the thermal spike model gives a good description of the observed e ects in the highS e regime. Cylindrical holes correspond to a local area where the maximum temperature reached along the ion path exceeds the boiling point. Concerning Cd-ion tracks, the temperature reached is not high enough to lead to vaporization. A sputtering e ect on surface may explain the fact that some matter remains crystallized in the track cores. Moreover, a grain size e ect during irradiation has been evidenced by TEM observations and con® rmed by thermal spike calculations.
The growing number of fields in which are studied the localized plasmon surface resonance such as... more The growing number of fields in which are studied the localized plasmon surface resonance such as light management for energy, enhanced field spectroscopy, or for integrated optical telecommunications bellow the diffraction limit is driving the development of modeling methods of these systems. In this paper, the electromagnetic properties of ion-deformed gold, sphere, prolate, nanorods and nanowires embedded within a dielectric matrix are simulated in a spectral range from visible to infra-red by means of Auxiliary Differential Equations (ADE) coupled to a Finite Difference Time Domain (FDTD) method. The electromagnetic field distribution is investigated in gold nanostructures in order to evidence the local field enhancement effect characteristic of the Localized Surface Plasmon Resonance (LPSR).
Experimental investigations of ion tracks produced with energetic heavy projectiles in the electr... more Experimental investigations of ion tracks produced with energetic heavy projectiles in the electronic energy loss regime are reviewed. Focusing on amorphisable insulators as target material, we present an overview of track phenomena such as the dependence of the track size on energy loss and beam velocity, the critical energy loss for track formation, and damage morphology along the ion tracks. Different characterization techniques for track dimensions are compared including direct, e.g. microscopic observations, as well as quantification of beam-induced damage. In the second part, we present a theoretical description of track formation based on an inelastic thermal spike model. This thermodynamic approach combines the initial size of the energy deposition with the subsequent diffusion process in the electronic subsystem of the target. The track size, resulting from the quench of a molten phase, is determined by the energy density deposited on the atoms around the ion path. Finally,...
Physica E: Low-dimensional Systems and Nanostructures, 2003
ABSTRACT Si/SiO2 multilayers were prepared by reactive magnetron sputtering of a pure silica targ... more ABSTRACT Si/SiO2 multilayers were prepared by reactive magnetron sputtering of a pure silica target and irradiated at 300K at GANIL with Kr and Pb ions whose energies were 9MeV(Se=0.72keVnm−1) and 4.6MeV per nucleon (Se=2.25keVnm−1), respectively. After a postannealing treatment, the films exhibit luminescence in the visible spectral range at room temperature. A blueshift of the photoluminescence with the increasing Se is noticed and is ascribed to a decrease in the Si grain size and/or to a decrease in the interface width.
Physics and Simulation of Optoelectronic Devices XXIII, 2015
A comparative study of the gain achievement is performed in a waveguide optical amplifier whose a... more A comparative study of the gain achievement is performed in a waveguide optical amplifier whose active layer is constituted by a silica matrix containing silicon nanograins acting as sensitizer of either neodymium ions (Nd 3+) or erbium ions (Er 3+). Due to the large difference between population levels characteristic times (ms) and finite-difference time step (10 −17 s), the conventional auxiliary differential equation and finite-difference time-domain (ADE-FDTD) method is not appropriate to treat such systems. Consequently, a new two loops algorithm based on ADE-FDTD method is presented in order to model this waveguide optical amplifier. We investigate the steady states regime of both rare earth ions and silicon nanograins levels populations as well as the electromagnetic field for different pumping powers ranging from 1 to 10 4 mW.mm-2. Furthermore, the three dimensional distribution of achievable gain per unit length has been estimated in this pumping range. The Nd 3+ doped waveguide shows a higher gross gain per unit length at 1064 nm (up to 30 dB.cm-1) than the one with Er 3+ doped active layer at 1532 nm (up to 2 dB.cm-1). Considering the experimental background losses found on those waveguides we demonstrate that a significant positive net gain can only be achieved with the Nd 3+ doped waveguide. The developed algorithm is stable and applicable to optical gain materials with emitters having a wide range of characteristic lifetimes.
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Papers by christian dufour