Monitoring structural changes in steel thin films in electrolyte <i>in situ</i> by X-ray standing waves

Ultra-thin stainless steel films were deposited on Ru/B4C multilayers using DC magnetron sputtering and characterised by synchrotron X-rays. The X-ray standing wave (XSW) technique revealed the metal distribution with depth. Typical for stainless steel [1], the near surface region was free of nickel. The oxidation states of Cr, Ni and Fe were determined by X-ray near edge absorption structure (XANES) under XSW condition. Nickel was found to be largely metallic whereas Fe and Cr where oxidized in the surface region, forming an about 2 nm passive layer. Exposure to 0.1M KCl at cathodic potential of -0.6 V vs Ag/AgCl resulted in expansion of the steel film due to in-diffusion of hydrogen. Using XSW/XANES, structural and chemical changes of the steel film were further traced in situ as a function of electrode potential up to +0.8 V. Results will be presented in the talk.
[1] C.-O.A. Olsson, D. Landolt, Passive films on stainless steels - chemistry, structure and growth, Electrochimica Acta 48 (2003) 1093-1104. https://doi.org/10.1016/S0013-4686(02)00841-1