Rough-surface effect on sputtering of Cr bombarded by low-energy He plasma

The formation of microscopic cone-like structures on a Cr surface is observed under He plasma exposure at a low incident ion energy of ∼106 eV in the PISCES-A linear plasma device. 2D emission profiles of the Cr I line intensity, measured with a hyperspectral imaging camera, are compared with those modeled using the GITR Monte Carlo impurity transport code coupled with the SDTrimSP binary collision code. With the growth of cones, the experimental 2D emission profile becomes axially elongated and the emission intensity significantly drops, and these observations are successfully reproduced in the simulation. The simulation reveals that the deposition of sputtered Cr atoms onto the neighboring cones results in a more over-cosine-like angular distribution, i.e., a narrower distribution with more particles ejected in the surface normal direction, of sputtered Cr atoms with a significant reduction of the sputtering yield.