Influence of the spatial and temporal structure of the deposited-energy distribution in swift-ion-induced sputtering

International audienceThe sputter processes occurring under swift-ion bombardment in the electronic-stopping regime are investigated by molecular-dynamics simulations performed for a Lennard-Jones solid (Ar). Two aspects of the dynamics of the excited electronic subsystem are included in the simulation and their influence on the sputter yield is studied. First, we assume the energy transfer from the electronic to the atomic system not to be instantaneous, but to last for a period of time τ. For τ≳1ps, we find the sputter yield Y to become strongly nonlinear as a function of the stopping power dE/dx. Second, we test the influence of a nonhomogeneous spatial distribution of the electronic excitations. It is shown that such a spatial distribution also leads to a strongly nonlinear dependence of Y on dE/dx.

Ejection of Nanoclusters from Gold Nanoislet Layers by 38 keV Au Ions in the Elastic Stopping Mode

Total absolute yields of the ejected gold were obtained regardless of the type of the particles are--atoms, clusters, nanoclusters,--as well as absolute yields of gold nanoclusters, from nanoislet gold targets under bombardment by monoatomic gold ions at 45° to the target surface with the energy 38 keV, i.e., in the "purely" elastic stopping mode −6 keV/nm up to the fluence of 4*1012 cm2. Three targets had gold nanoislets on the substrate surface: 2-12 nm; −18 nm; −35 nm, the most probable sizes being 7.1; 9.4; 17.5 nm respectively. The part of the surface area covered with gold was known. Total transfer of gold was determined by means of the neutron-activation analysis and decreased from 450 to 20 at/ion. The number of the ejected gold nanoclusters was determined using TEM and decreased from ∼0.06 to <0.01 per one 38 keV Au ion with the increase of the most probable sizes of the nanoislets on the target from 7.1 to 17.5 nm. The yields appeared to be surprisingly high, which is of scientific and practical importance. Tentative estimations were made using molecular dynamics simulations

Desorption of gold nanoclusters from gold nanodispersed targets by 200 keV Au5 polyatomic ions in the elastic stopping mode: Experiment and molecular-dynamics simulation

Au nanoislet targets (empty set 2–60 nm) were bombarded by 200 keV polyatomic ions (40 keV/atom), which deposit their energy mainly in the nuclear stopping mode: ∑(dE/dx)n = 30 keV/nm and ∑(dE/dx)e = 2 keV/nm. The matter desorbed in the form of nanoclusters was registered by TEM. The total transfer of matter was determined by neutron-activation analysis. The total yield of the ejected gold reached high values of up to 2.6 × 104 atoms per Au5 ion. The major part (2 × 104 atoms per ion Au5) of the emission is in the form of nanoclusters. The results are compared with the data of similar experiments with 1 MeV Au5 (200 keV/atom) and other projectiles. The analysis of the experimental data and the comparison to molecular-dynamics simulation results of the desorption process show that the desorption of Au nanoislets is induced by their melting, build-up of pressure and thermal expansion

Desorption of nanoclusters from gold nanodispersed layers by 72 keV Au400_{400} ions: Experiment and molecular dynamics simulation

International audienceThe interaction of 72 keV Au400 ions (with a diameter of approximately 2 nm) with nanodispersed gold targets has been studied. These interactions are dominated by elastic collisions. The gold nanodispersed target with 2–12 nm nanoislets was bombarded with a fluence of 1.7 × 1012 ions/cm2. The desorbed nanoclusters were collected on carbon foils supported by TEM-grids. Intact 29 nm gold nanoclusters were found on the collectors. The desorption yield (normalized to the total cross-section of the projectile-cluster interaction) was estimated to be 0.62 nanocluster/projectile. Preliminary estimates were made using molecular dynamic simulations for comparison with the experimental results