Etude de la pulvérisation du dioxyde d'uranium induite par des ions lourds multichargés de basse et très basse énergie cinétique (effet de la charge du projectile)

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Editorial

International audienc

Folding two dimensional crystals by swift heavy ion irradiation

International audienceIon irradiation of graphene, the showcase model of two dimensional crystals, has been successfully applied to induce various modifications in the graphene crystal. One of these modifications is the formation of origami like foldings in graphene which are created by swift heavy ion irradiation under glancing incidence angle. These foldings can be applied to locally alter the physical properties of graphene like mechanical strength or chemical reactivity. In this work we show that the formation of foldings in two dimensional crystals is not restricted to graphene but can be applied for other materials like MoS2 and hexagonal BN as well. Further we show that chemical vapour deposited graphene forms foldings after swift heavy ion irradiation while chemical vapour deposited MoS2 does not

Interaction of swift ion beams with surfaces: Sputtering of secondary ions from LiF studied by XY-TOF-SIMS

International audienceSputtering occurs as a result of deposition of kinetic or potential energy in solids irradiated with swift particles. We studied ejection of secondary ions from LiF induced by swift heavy ion impact. A new UHV system allows measuring the mass distributions and the velocity vectors of each emitted secondary ion by means of time-of-flight and imaging techniques (XY-TOF-SIMS) with controlled target surfaces. We present results performed at GANIL (Caen) with Ca beams at 7.6 and 9 MeV/u (electronic stopping regime). Under UHV conditions, particles emitted from cleaved LiF monocrystals include the omnipresent hydrogen, and the two isotopes of natural LiF (6Li+ and 7Li+). Two groups of clusters, namely Lin+ and (LiF)nLi+ appear. The cluster size (n) dependence of the cluster ion yields Y(n) can be described by an exponential function. LiF emission as ionic clusters (LiF)nLi+ with n ≥ 2 is dominant over emission as monomers LiFLi+

Interaction of swift ion beams with surfaces: Sputtering of secondary ions from LiF studied by XY-TOF-SIMS

International audienceSputtering occurs as a result of deposition of kinetic or potential energy in solids irradiated with swift particles. We studied ejection of secondary ions from LiF induced by swift heavy ion impact. A new UHV system allows measuring the mass distributions and the velocity vectors of each emitted secondary ion by means of time-of-flight and imaging techniques (XY-TOF-SIMS) with controlled target surfaces. We present results performed at GANIL (Caen) with Ca beams at 7.6 and 9 MeV/u (electronic stopping regime). Under UHV conditions, particles emitted from cleaved LiF monocrystals include the omnipresent hydrogen, and the two isotopes of natural LiF (6Li+ and 7Li+). Two groups of clusters, namely Lin+ and (LiF)nLi+ appear. The cluster size (n) dependence of the cluster ion yields Y(n) can be described by an exponential function. LiF emission as ionic clusters (LiF)nLi+ with n ≥ 2 is dominant over emission as monomers LiFLi+

Highly active single-layer MoS2 catalysts synthesized by swift heavy ion irradiation

Two-dimensional molybdenum-disulfide (MoS2) catalysts can achieve high catalytic activity for the hydrogen evolution reaction upon appropriate modification of their surface. The intrinsic inertness of the compound's basal planes can be overcome by either increasing the number of catalytically active edge sites or by enhancing the activity of the basal planes via a controlled creation of sulfur vacancies. Here, we report a novel method of activating the MoS2 surface using swift heavy ion irradiation. The creation of nanometer-scale structures by an ion beam, in combination with the partial sulfur depletion of the basal planes, leads to a large increase of the number of low-coordinated Mo atoms, which can form bonds with adsorbing species. This results in a decreased onset potential for hydrogen evolution, as well as in a significant enhancement of the electrochemical current density by over 160% as compared to an identical but non-irradiated MoS2 surface.Peer reviewe

AODO: Secondary ion emission and surface modification

International audienceIn order to study the sputtering of secondary ions from well characterized surfaces, we constructed a new UHV system named AODO. It consists of a detector chamber, a target preparation and analysis chamber, and a target transfer rod. We present the lay-out of this new instrument. The detector allows measuring the time-of-flight of emitted secondary ions and their position on a 2D imaging detector (XY-TOF imaging technique). The analysis chamber can be used to study surface modification by means of LEED (low energy electron diffraction). We show preliminary results of the evolution of the LEED patterns as a function of the projectile fluence during irradiation of HOPG (highly oriented pyrolytic graphite) with slow Xe14+ ions at ARIBE (the low energy, highly charged ion beam line of the French heavy ion accelerator GANIL)

Fabrication of nanoporous graphene/polymer composite membranes

International audienceGraphene is currently investigated as a promising membrane material in which selective pores can be created depending on the requirements of the application. However, to handle large-area nanoporous graphene a stable support material is needed. Here, we report on composite membranes consisting of large-area single layer nanoporous graphene supported by a porous polymer. The fabrication is based on ion-track nanotechnology with swift heavy ions directly creating atomic pores in the graphene lattice and damaged tracks in the polymer support. Subsequent chemical etching converts the latent ion tracks in the supporting polymer foil, here polyethylene terephthalate (PET), into open microchannels while the perfectly aligned pores in the graphene top layer remain unaffected. To avoid unintentional damage creation and delamination of the graphene layer from the substrate, the graphene is encapsulated by a protecting poly(methyl methacrylate) (PMMA) layer. By this procedure a stable composite membrane is obtained consisting of nanoporous graphene (coverage close to 100%) suspended across selfaligned track-etched microchannels in a polymer support film. Our method presents a facile way to create high quality suspended graphene of tunable pore size supported on a flexible porous polymeric support, thus enabling the development of membranes for fast and selective ultrafiltration separation processes

Sputtering of LiF and other halide crystals in the electronic energy loss regime

International audienceSputtering experiments were performed by irradiating LiF, NaCl, and RbCl crystals with various swift heavy ions like S, Ni, I, Au with energies between 60 and 210 MeV, C$_{60}$ clusters between 12 and 30 MeV or Pb ions between 730 and 6040 MeV. Sputtered species are collected on arc-shaped catchers and subsequently analyzed by elastic recoil detection analysis or Rutherford backscattering analysis. The study focuses on angular distributions and total yields for LiF and covers a broad range of experimental parameters including cleaved or rough sample surfaces, ion fluence, beam incident angles, and different ion velocities leading to electronic energy loss (S$_{e}$) values from 5 to 45 keV/nm. In most cases, the angular distribution has two components, a jet-like peak perpendicular to the surface sample superimposed on a broad isotropic cosine distribution whatever is the beam incident angle. The observation of the jet depends mainly on the surface flatness and angle of ion incidence. However, the jet does not appear clearly when irradiated with C$_{60}$ cluster. The sputtering yield is stoichiometric and characterized by huge total yields of up to a few 10$^{5}$ atoms per incident ion. The yield follows a power law as function of electronic energy loss, Y follows an exponential law with S$_{e}^{n}$ with n ~ 4. While the azimuthal symmetry for sputtering is observed at low ion velocity (~1 MeV/u), it seems to be lost at high velocity (>4 MeV/u). The data provide a comprehensive overview how the angular distribution and the total sputtering yield scale with the energy loss, beam incidence angle and ion velocity. Complementary experiments have been done with NaCl and RbCl targets confirming the observation made for LiF.[graphic not available: see fulltext][graphic not available: see fulltext