Cluster impacts in organics: microscopic models and universal sputtering curves

Abstract

This article reviews the results of molecular dynamics simulations of kilo-electron-volt projectile (Ga, Au 1À400 , Bi 1À5 , C 60 , Ar 60À2000 and organic clusters) impacts with two model hydrocarbon targets, an amorphous solid made of kilodalton molecules and a crystal of polyethylene with 'infinite' chain length. The 'universal' dependences of the sputtered mass on the projectile energy, when scaled by the projectile mass, with their characteristic transition around 1 eV/amu (or~14 km/s), are analyzed and explained by the physics of the interaction. We also comment on comparisons with recent experimental sputtering data.

Molecular dynamics simulation of polymerlike thin films irradiated by fast ions: A comparison between FENE and Lennard-Jones potentials

“…Thus, part of the excitation energy of the molecules is transferred to internal vibrational modes during the ejection process, which in a real material could lead to in-flight fragmentation. Similar changes in conformation during ejection were also seen in simulations of keV ions bombarding polymeric molecular solids [31,32].…”

“…The FENE potential has been successfully used to investigate the viscoelastic and rheological properties of polymers and their dependence on chain length [29,30]. Other coarse-grained models have been already used to study the effects of energetic ions in polymers, but only at the lowenergy regime [31,32], where nuclear collisions dominate. In our simulations using the FENE potential, craters, sputtering yields, and flow of molten material are substantially reduced, as compared to the LJ system.…”

On Universality in Sputtering Yields Due to Cluster Bombardment

“…For cluster projectiles, there is the dependence of Y on the cluster size n , which is entangled with the dependence of Y on E . The typical shape of the Y on E dependence for bombardment by clusters of size less than a few thousand particles within a broad range of incident kinetic energy (∼1–1000 keV) consists of a power onset, wide linear region and final drop. , Generally, the spread in the data points can be reduced by presenting the yield per projectile atom Y / n versus energy per projectile atom E / n on a log–log plot. , This property of the Y / n on E / n dependence was observed for atomistic (Ag, Au, Si) and molecular (octane, polystyrene, Irganox) solids sputtered by cluster projectiles (Au n , C 60 , Ar n ), all of which are used in experimental and computational studies to optimize the SIMS technique. ,, The Y / n versus E / n relation has been called “universal”, and this assignment is somewhat supported by experimental and computational results, although there are two arms: one for organic solids and another for inorganic solids observed in this dependence. , The underlying physical interpretation is not, however, clear. The interpretation of the data is further muddled by either plotting together yields from clusters of different elemental composition or for solids of different chemical composition.…”

“…3,5,6 The Y/n versus E/n relation has been called "universal", and this assignment is somewhat supported by experimental and computational results, although there are two arms: one for organic solids and another for inorganic solids observed in this dependence. 6,7 The underlying physical interpretation is not, however, clear. The interpretation of the data is further muddled by either plotting together yields from clusters of different elemental composition or for solids of different chemical composition.…”

Molecular cluster emission in sputtering of amino acids by argon gas-cluster ions

“…Specific studies have demonstrated that argon cluster bombardment of organic solids may lead to a soft emission process so that large intact molecules or even molecular clusters can be desorbed (sputtered) from the surface while the fraction of fragmenting species would be small [21][22][23][24][25][26][27]. This finding was corroborated by molecular dynamics (MD) computer simulations [28][29][30]. In addition, MD simulations have illustrated quite impressively (some of) the emission scenarios that might occur under (argon) cluster bombardment of solids [31,32].…”