Projectile size effects on cluster formation in sputtering

Abstract

We have investigated the formation of neutral clusters during self-sputtering of a silver surface under bombardment with Ag þ m projectile ions (m ¼ 1, 2, 3). Particular emphasis was put on the size distribution of the sputtered clusters and its dependence on the projectile nuclearity m under conditions of constant impact velocity. It is found that the relative abundance of larger clusters increases from mono-to diatomic but decreases again from di-to triatomic projectiles. At the same time, the total sputtering yield exhibits a strong non-linear increase in both cases. This finding breaks the unique correlation between cluster abundance pattern and sputtering yield that has been observed many times in the past. The results indicate that the nature of the cluster formation process in sputtering must change at large sputtering yields connected with polyatomic projectile impact.

The influence of crater formation for electron excitation processes in cluster induced collision cascades

“…In this paper, we focus our attention on the discussion of the calculated sputter yields which are listed in Table 1. These values can now be compared with published experimental data derived from secondary neutral mass spectroscopy (SNMS) measurements on a polycrystalline silver surface bombarded with Ag þ n projectiles [21]. For the 7-keV atom bombardment, all friction models result in a similar sputter yield which is almost equal to the experimental value.…”

“…All impact points were chosen inside an irreducible zone on the Agð1 1 1Þ surface. The impact energies of 20 keV and 7 keV for cluster and single atom bombardment, respectively, were chosen in order to facilitate direct comparison to experimental data [21] (note that these energies ensure nearly constant impact velocity in both cases). In all cases, the calculations were performed for (i) simple Lindhard friction (k = const), (ii) electronic friction scaled with the local electron density via the model of Caro and Victoria (k ¼ kðn e Þ) and (iii) Lindhard friction scaled with the local atom density (k ¼ kðn a Þ).…”

“…[21] were derived from measured SNMS spectra. More specifically, the neutral particles emitted from the surface were detected by means of time of flight mass spectrometry in combination with laser postionization.…”

“…In Ref. [21], it was assumed that the emission velocity distribution of sputtered atoms does not change between atomic and cluster impact. Measurements of the kinetic energy distribution of sputtered indium atoms performed later, on the other hand, reveal a strong alteration of the emission velocity distribution by changing from 5-keV Au to 10-keV Au 2 projectiles [26].…”

“…Thereby, its exhibits a mean value of about 3.4 km/s and a peak at about 0.75 km/s, while the particles sputtered after 7-keV Ag 1 bombardment exhibits a most probable velocity of about 2 km/ s. Using the calculated average inverse velocities of particles sputtered after 7-keV Ag 1 bombardment v À1 D E , respectively, to rescale the published experimental sputter yields Y exp[21] results in a rescaled sputter yield (Y real )…”