Controlling the ion-induced sputter yield through anisotropic nano-structuring of surfaces

Abstract

The morphology and roughness of a surface is known to have a strong influence on the ion- induced sputter yields. Different quantities are used to describe the dependence of the sputter yield on the surface roughness, such as the root- mean square roughness, or the mean inclination angle of the surface. However, they typically consider isotropic surface structure with a ran- dom/Gaussian distribution (e.g. [1]). In the present work we investigated the sputter yields of tungsten (W) surfaces featuring nano- structures that show a direction-dependence. The sputter yields of different columnar and ridge-like structures were simulated using the combination of the ray-tracing simulation code SPRAY [2] and the binary collision approxima- tion (BCA) code SDTrimSP [3]. The effect of the beam incidence, relative to the surface nor- mal and to the orientation of the surface features, was studied. The simulated results were then compared to our experimentally measured sputter yields. For the experiments, W films were deposited on a sensitive quartz-crystal microbalance using a DC magnetron sputtering set-up, and the sur- face morphology was controlled by varying the deposition parameters (substrate angle, sputter- ing power, etc.). The surface morphology of the samples was characterized by atomic force mi- croscopy. We found that deposition under an oblique angle of 80°, known to result in nano- columnar W films [4], effectively reduced the mean inclination angle in comparison to depo- sition under normal incidence. Subsequently, the sputtering rates, induced by 2 keV Ar+ irradia- tion, were measured in-situ during ion bombard- ment, as a function of the ion incidence angle (see Figure 1.). The results indicate that the sputtering is reduced for the columnar structures, and the simulations indicate a possible direction-dependent modula- tion of the ion-induced sputter yields. Exp: Deposition at 0° Exp: Deposition at 80 Simulation: smooth Simulation: columnar 3 2.5 2 1.5 1 0.5 ° 0 0 20 40 60 Incidence angle (deg) Sputter yield (W atoms/ion) Figure 1: Measured and simulated sputter yield of W samples with varying surface morphologies (see text) under bombardment with a 2 keV Ar+ beam. References [1] P. S. Szabo et al. Surf. Interfaces 30 101924 (2022) [2] C. Cupak et al. Appl. Surf. Sci. 570 151204 (2021) [3] A. Mutzke et al. IPP Report (2019) [4] R. Gonzalez-Arrabal et al. Nucl. Mater. En- ergy 40 101704 (2024)