Ion radiation albedo effect: influence of surface roughness on ion implantation and sputtering of materials

Abstract

In fusion devices, ion retention and sputtering of materials are major concerns in the selection of compatible plasma-facing materials (PFMs), especially in the context of their microstructural conditions and surface morphologies. We demonstrate how surface roughness changes ion implantation and sputtering of materials under energetic ion irradiation. Using a new, sophisticated 3D Monte Carlo (MC) code, IM3D, and a random rough surface model, ion implantation and the sputtering yields of tungsten (W) with a surface roughness varying between 0–2 µm have been studied for irradiation by 0.1–1 keV D+, He+ and Ar+ ions. It is found that both ion backscattering and sputtering yields decrease with increasing roughness; this is hereafter called the ion radiation albedo effect. This effect is mainly dominated by the direct, line-of-sight deposition of a fraction of emitted atoms onto neighboring asperities. Backscattering and sputtering increase with more oblique irradiation angles. We propose a simple analytical formula to relate rough-surface and smooth-surface results.

Effect of the Surface Roughness of Tungsten on the Sputtering Yield under Helium Irradiation: A Molecular Dynamics Study

“…Therefore, the simulation results at 50 eV and 100 eV are shown as shown in Figure 7. Experimental studies [15,19,20] show that the net sputtering yield decreased as the COD increased. In these experimental studies [15,19,20], the decrease in net sputtering yield according to the COD increase was explained as the increase in the re-deposition rate.…”

“…Experimental studies [15,19,20] show that the net sputtering yield decreased as the COD increased. In these experimental studies [15,19,20], the decrease in net sputtering yield according to the COD increase was explained as the increase in the re-deposition rate. For convenience, COD is expressed as λ, primary sputtering yield as α, and re-deposition yield as β.…”

“…In our simulations, the re-deposition yields were relatively small; thus, it was difficult to compare the magnitude of α λ and β λ with a high reliability. In previous studies [15,19,20], the net sputtering yield according to the λ change was explained through the explanation that β λ is positive and, therefore, γ λ is also positive. However, this is an incomplete explanation, as it does not take into account α λ .…”

“…Various studies have been conducted to reduce the sputtering yield by controlling the roughness of the tungsten powder [14,15]. In previous experimental studies, the sputtering yield increases as the roughness of the surface increases [15,19,20], and it was hypothesized that the trend was caused by the re-deposition process. Re-deposition refers to a phenomenon in which sputtered tungsten atoms are re-deposited on convex tungsten hills, as shown in Figure 1.…”

Sample spinning to mitigate polarization artifact and interstitial-vacancy imbalance in ion-beam irradiation

“…When using SSS, one should also note that (a) the averaging in SSS only make sense in the broad-beam limit, where the beam spot size is much bigger than the area of interest (σ i ) σ s , where σ s is millimeters and may be the sample size). It does not work for nano-beam or nano-target (surface not flat) experiments 35,36 . (b) When one chooses the maximum depth range of the designated optimized region, the regions corresponding to the free surface and implanted ion peak zone should be avoided, as the local defect distributions could be dramatically varying in these areas.…”