Depth of origin of sputtered atoms: Exploring the dependence on relevant target properties to identify the correlation with low-energy ranges

Abstract

The correlation of the depth of origin (DoO) of sputtered atoms with relevant properties of the bombarded target has not yet been clarified in a satisfactory manner. We have carried out SDTrimSP (Monte Carlo) simulations to study the dependence of depth differential sputtering yields on the following parameters: the position of the primary knock-on atom, the surface binding energy, E s , the target density, N, and the target atomic number, Z 2 . All calculations were performed with normally incident projectiles, either Xe or targetatom-like, with energies between 40 eV and 10 keV. The mean DoO,  x , was found to depend on E s, with a power p between 0.10 (0.1 keV) and 0.26 (10 keV Xe). In prior work, lack of knowledge of this weak E s -dependence did not allow the relation between  x and N to be uncovered properly. To proceed further, differential yields were calculated for targets ranging from carbon to uranium with deliberately varied N, but keeping E s fixed (4.72 eV). The product N x  turned out to depend very little on N. Hence, it is appropriate to specify the origin of sputtered atoms in terms of the equivalent areal density rather than in units depth. For medium-mass or heavy target atoms, i.e., for Z 2 > 20, N x  was largely independent of Z 2 . For Z 2 < 20, N x  increased with decreasing Z 2 . Projected ranges x p calculated for targetatom-like projectiles at energies ≤ 40 eV exhibited almost the same Z 2 -dependence as  x . This finding suggests that  x is determined by the range of the recoils mobilized in the collision cascade. The results of this study are compared with previously published data, with sometimes distinctly different definitions of  x . The idea is recapitulated that the most appropriate way of quantifying the DoO is to quote the fraction of atoms ejected from the top (or outermost) layer of atoms. The fractions determined by SDTrimSP range from about 98% to 75%, for impact energies between 40eV and 10 keV and Z 2 > 20.

Transition Elements in Supernova Presolar Grains: Condensation versus Implantation

“…It is a general practice to use heat of sublimation as SBE, however, the results do not match the experimental data obtained (at energies quite lower than the one discussed in this paper) specially for strong electronegative elements like O, C, etc. since strong ionic bonds can form between atoms in the top layer and those in the bulk (Wittmaack & Mutzke 2012;Mutzke & Eckstein 2008). We use the model developed by Kudriavtsev et al (2005), which takes into account weighted contributions from ionic and covalent bonds to calculate SBE.…”

Analytical and numerical depth resolution functions in sputter profiling

“…In addition, these authors presented an analytical solution of the convolution integral as a delta layer response function or depth resolution function (DRF). Since then, the complete empirical DRF for SIMS, consisting of two exponentials and one Gaussian, was elaborated further and was successfully applied to numerous SIMS depth profiles of thin layers, notably atomic monolayers [39][40][41][42][43][44][45]. In 2003, the delta layer response function for SIMS after Dowsett et al was accepted as an ISO standard by the technical committee TC 201 on Surface Chemical Analysis [4].…”

“…By comparison of profiles of B delta layers in Si grown at different temperatures, Dowsett and Chu [39] come to the conclusion that  u = 0 is inherent in SIMS. In a recent paper on the depth of origin of the secondary particles in SIMS, Wittmaack and Mutzke [40] find that in most cases, 98% to 75% of them are from the first monolayer (Note that this applies for atomic ion bombardment and may be different for large cluster ions [47,48]). Thus, there is clear evidence that  u can be looked upon as an outer parameter, describing an artifact by deviations of instrumental or sample related conditions from the idealized assumptions, useful to interpret experimental results.…”

Highly accurate nuclear and electronic stopping cross sections derived using Monte Carlo simulations to reproduce measured range data

“…SDTrimSP can handle both 'static' targets (S), renewed after every impact, or 'dynamically' altered targets (D) with a composition changing due to retained projectiles or bombardment induced mixing. Various aspects of sputtering (SP) may also be studied [35]. Here only the static code is of interest, but improvements in numerical procedures implemented in course of time were taken advantage of [35].…”

“…Various aspects of sputtering (SP) may also be studied [35]. Here only the static code is of interest, but improvements in numerical procedures implemented in course of time were taken advantage of [35].…”