Comparison of surface modification and erosion of high-Z metals due to carbon ion implantation

Abstract

In this work we investigated the erosion and carbon deposition behavior of different high-Z materials, namely W, Ta, Pt and Au during irradiation by 2.4 keV C 12 ions in the temperature range from 300 to 1073 K. During the bombardment the sample's weight was monitored and information about erosion and deposition was deduced from the dependence of the weight change on the ion fluence. We found a strong temperature dependence of the weight change. Two processes were found to contribute to the temperature dependence, namely diffusion and radiation enhanced sublimation (RES) of the deposited carbon. For modeling of the weight-change measurements these two processes were investigated in separate experiments. Diffusion profiles of C in W were measured and evaluated using a concentration dependent diffusion coefficient D(C). The carbon erosion due to RES at elevated temperatures was investigated in C self-sputtering experiments. The information gained during these two experiments was then used in computer simulations of the temperature dependent weight change of W and Ta samples during C bombardment. In order to model the simultaneous diffusion and erosion, the Monte Carlo code TRIDYN was coupled to the newly developed diffusion code DIFFUSEDC, which solves the general form of Fick's second law with a concentration dependent diffusion coefficient using a finite difference approach. By using this model we were able to reproduce the experimental results from the weight change measurements. The model allows extrapolation to temperatures and ion fluxes not accessible in ion beam experiments.