Computer modeling of angular emission from Ag(100) and Mo(100) surfaces due to Arn cluster bombardment

Abstract

Defects and morphological changes in nanothin Cu films on polycrystalline Mo analyzed by thermal helium desorption spectrometry Molecular dynamics computer simulations are employed to investigate the effect of projectile size and surface morphology on the angular emission stimulated by impact of Ar gas cluster projectiles. Argon clusters of sizes n ¼ 10-1000 and kinetic energies of 10 and 20 keV Ar n aimed at normal incidence are used to sputter Ag(100) and Mo(100) samples. The total sputtering yield is larger for Ag(100) than for Mo(100). The ratio of sputtering yields is inversely proportional to the ratio of sublimation energies of these solids for projectiles between Ar 20 and Ar 250 . In both systems, the angular distributions are sensitive to both the projectile size and the surface roughness. The maximum of angular spectra shifts from direction normal to the surface toward off-normal direction with the increase in the projectile size. An opposite trend is observed with the increase in the surface roughness. Formation of a cloud composed of projectile atoms and the enhanced lateral material relocation caused by projectile lateral expansion upon impact are the main factors responsible for promoting off-normal ejection. On the other hand, material ejection from randomly inclined surface areas and the influence of nearby topography are found to be responsible for enhancing ejection along the surface normal for rough surfaces.

Spatial distribution of particles sputtered from single crystals by gas cluster ions

“…The simulation results showed that many atoms are sputtered as dimers, trimers and larger clusters that can rotate around the center of mass, which is in a good agreement with the results by other authors [5]. The number of such sputtered clusters for the Cu target is much higher than that for the Mo one.…”

“…Note that the similar distributions were observed for bombardment of Ag(100) surface by Ar clusters [5]. The centers of spots visible in Fig.…”

“…5 and affects the surrounding medium. This process leads to a faster increase in the crater diameter as compared to a change of its depth [5]. As it was pointed in [5], this process leads to strong side jet of Ar atoms.…”

“…The polar distributions of the sputtered material in the azimuthal direction corresponding to the maximum of the spots as well as the distribution between the spots are further away from the surface normal in case of larger Ar cluster for both Cu and Mo targets. This means that this kind of anisotropy cannot be considered as the Wehner spots, as mentioned in [5]. This conclusion is based on the fact that numerous experiments have shown that the angular positions of Wehner spots are determined only by the crystal structure of the irradiated surface.…”

“…However, the simulations are more often performed with single crystal lattices. In a recent paper [5] the anisotropy over the azimuthal angle of the spatial distributions of Ag and Mo atoms sputtered from single-crystal targets with 10 keV Ar clusters has been found. This is surprising because the crystalline structure in the impact area is destroyed during the cluster impact on the target surface.…”