Sputtering effects during plasma immersion ion implantation of metals

Changes in the surface topography during ion bombardment are a ubiquitous effect, which is nevertheless sparsely understood, especially for polycrystalline metals. Beside nucleation and grain growth processes, sputtering of individual atoms is the dominant factor. Here, the development of the surface topography is investigated for austenitic stainless steel and CoCr alloy using oxygen, nitrogen or argon ion bombardment. For a better quantification with 3D optical profilometry, a time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used for the experiments. Beside an orientation dependent sputter yield, inversely correlated with the positive secondary ion yield for the present fcc metals, an increase in the nanoroughness with increasing fluence was observed, with the effect much more pronounced for CoCr than for stainless steel. No significant influence of the ion species was observed. In addition, an increased roughness is observed during PIII nitriding, depending on the incident ion flux. Here, the combined roughness from nitriding and SIMS depth profiling leads to a broadening of the nitrogen profile edge, which has to be corrected for.