On-surface and sub-surface oxygen on ideal and reconstructed Cu(100) T. Kangas a, * , K. Laasonen a , A. Puisto b , H. Pitka ¨nen b , M. Alatalo b a Department of Chemistry, University of Oulu, P.O. Box 3000, FIN-90014, Finland b Department of Electrical Engineering, Lappeenranta University of Technology, P.O. Box 20, FIN-53851, Finland Received 7 September 2004; accepted for publication 9 February 2005 Available online 18 April 2005 Abstract In order to understand the first steps of the Cu(100) oxidation we performed first principles calculations for on-sur- face and sub-surface oxygen on this surface. According to our calculations, the adsorption energies for all on-surface site oxygen atoms increase, whereas the energies of the sub-surface atoms decrease with the increasing oxygen coverage. At coverage 1 ML and higher on the reconstructed surface, structures including both on- and sub-surface atoms are energetically more favourable than structures consisting only of on-surface adsorbates. On the ideal (100) surface this change can be perceived at coverage 0.75 ML. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Density functional calculations; Oxidation; Copper; Oxygen; Single crystal surfaces 1. Introduction Surface oxidation plays a very important role in many phenomena such as corrosion and catalysis. Corrosion is usually a harmful process and a lot of effort has been done in developing materials more resistant to corrosion. A good example of this is stainless steel. On the microscopic level the corro- sion is still not well understood [1]. Participation of oxygen is crucial in many catalytic processes, especially on oxidation reactions [2]. Recently it has been observed that metal surfaces can be oxi- dized during the catalysis, and thus the active cat- alyst is in fact the metal oxide not the clean metal [3]. In this work we concentrated on the early stages of the oxidation of copper. Oxygen on Cu(100) has been the subject of sev- eral theoretical and experimental studies [4–12]. However, the sub-surface oxygen in Cu(100) is not as carefully examined. Several authors have 0039-6028/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2005.02.061 * Corresponding author. Tel.: +358 8 3551687; fax: +358 8 3551603. E-mail address: teija.kangas@oulu.fi (T. Kangas). Surface Science 584 (2005) 62–69 www.elsevier.com/locate/susc