Plasma-based ion implantation of oxygen in stainless steel: influence of ion energy and dose

Abstract

Implantation of oxygen in stainless steel (15% Cr) via plasma-based ion implantation in a distributed ECR plasma reactor has been studied as functions of ion energy and dose. Due to the formation at the surface of dielectric films with optical index and thickness depending on the implantation time and pulse voltage (up to 44 kV), various colorations can be obtained. The experimental results demonstrate the feasibility of uniform processing, the possibility of reaching perfect control of the coloring through the dose and energy of implanted ions, and that the resulting coloration varies monotonically when increasing the dose and penetration depth of implanted oxygen. Characterization of the films by scanning electron microscopy and X-ray microanalysis shows that oxygen implantation results in strong surface oxidation, but without any significant degradation of the surface aspect. The thickness and composition profiles of the oxide layers determined using X-ray photoelectron spectroscopy combined with ellipsometry indicate that the thickness, of course, increases with ion energy and dose, but that the composition of the oxide layer resulting from the implantation process is not uniform. A uniform iron oxide layer (with a stoichiometry closed to Fe 2O 3), free from chromium, is formed in the near-surface region, while chromium segregates at the interface between the oxide layer and the bulk stainless steel to form chromium oxide Cr 2O 3.