Journal of Electron Spectroscopy and Related Phenomena 154 (2007) 69–78 Morphology and composition of nanoscale surface oxides on Fe–20Cr–18Ni{111} austenitic stainless steel M. Lampim¨ aki, K. Lahtonen, P. Jussila, M. Hirsim¨ aki, M. Valden ∗ Surface Science Laboratory, Tampere University of Technology, P.O. Box 692, FIN-33101, Tampere, Finland Received 18 October 2006; received in revised form 3 December 2006; accepted 3 December 2006 Available online 8 December 2006 Abstract Surface oxidation ranging from initial stages to the onset of passive oxide layer formation have been investigated on Fe–20Cr–18Ni{111} single crystal surface by X-ray photoelectron spectroscopy (XPS). Surface segregation of the alloying elements and the morphology of the surface oxide nanostructure were characterized quantitatively by inelastic electron background analysis. Our results demonstrate that by increasing the oxidation temperature the relative concentrations of Fe 2+ and Fe 3+ cations increase due to their enhanced mobility. Higher temperature also improves the mobility of chromium, thus enhancing its segregation to the oxygen-rich surface and thereby reinforcing the passive layer on the alloy. This is in agreement with the results showing the sudden decrease in oxide film thickness at the oxidation temperatures exceeding 600K. Additionally, a pronounced segregation of metallic nickel is found in the interface between the surface oxide layer and the bulk alloy. © 2006 Elsevier B.V. All rights reserved. Keywords: Single crystal; Austenitic; Stainless steel; Segregation; Alloys; Oxidation; X-ray photoelectron spectroscopy; Morphology 1. Introduction Stainless steels are utilized in several modern applications due to their excellent corrosion resistance, physical and mechan- ical properties. Austenitic stainless steels are widely used, for example, in high temperature applications as a result of their enhanced elevated temperature strength [1]. Recently, the ver- satility of stainless steel materials have been demonstrated by the development of novel nano-particle modified steels suitable for future high temperature applications, such as future nuclear fusion power plants [2,3]. In order to further develop such novel materials, it is imper- ative to understand better the physicochemical properties of low dimensional structures and surfaces in general. Insights into the interdependence between surface phenomena, such as adsorption, surface compound formation, segregation and self-organization, and environmental parameters (gas phase composition, material composition, pressure and temperature), are required for systematic development of novel materials on the nanometer scale. ∗ Corresponding author. Tel.: +358 3 3115 2555; fax: +358 3 3115 2674. E-mail address: mika.valden@tut.fi (M. Valden). Stainless steel is a versatile but also challenging surface for such investigations. It consists of iron, nickel and chromium as well as a number of trace impurities or alloying elements (typically sulphur, aluminum, carbon, molybdenum, titanium, manganese and nitrogen) and it exhibits several structural phases depending on the chemical composition and temperature of the material. In addition to such well-known bulk properties, the chemical composition and the surface morphology are also sensitive to the temperature and composition of the gas phase interacting with the steel surface. In fact, the excellent corrosion resistance of stainless steel stems from segregation phenom- ena of chromium induced by the sample temperature and the presence of oxygen on the surface. The general consensus in materials science is that stainless steel oxidation is self-limited at high temperatures and under atmospheric conditions by a passive film consisting of a thin Cr 2 O 3 -rich layer that acts as a diffusion barrier against the Fe and Cr cations thus inhibiting further oxidation towards bulk. However, in order to better understand and control the formation of oxide on stainless steels, it is important to investigate the surface compound formation processes at the onset of oxidation when the oxide layer is only a few nanometers thick and may lack the long-range order necessary for high-resolution transmission electron microscopy (TEM) studies. 0368-2048/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2006.12.002