Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 49: Surface chemical reactions I
O 49.5: Vortrag
Mittwoch, 24. März 2010, 11:30–11:45, H42
Atomistic modelling of the oxidation of Co, Cr and CoCr alloy surfaces — •Janina Zimmermann1,2 and Lucio Colombi Ciacchi2,3 — 1Fraunhofer IWM, Freiburg, Deutschland — 2Fachbereich Produktionstechnik, Universität Bremen, Deutschland — 3Fraunhofer IFAM, Bremen, Deutschland
In this work, first-principles molecular dynamics based on density-functional theory is employed to investigate the early oxidation stages of the Co(0001), Cr(110) and CoCr(0001) surfaces. Oxide nucleation on cobalt follows a metastable path, with the place-exchange of metal and oxygen atoms leading to the growth of an open, pseudo-amorphous oxide structure with evident Co3O4-like features. Instead, the oxidation of Cr(110) occurs along an energy path close to thermodynamic equilibrium and limited by Cr-ion diffusion already in the earliest oxidation stages. The initial formation of highly oxidized chromate-like structures seems to be precursory for the subsequent growth of Cr2O3 thin films. The oxidation of CoCr alloys occurs via selective oxidation of chromium, which leads to vacancy formation and enables the diffusion of oxygen atoms into inner atomic layers. The outward diffusion of chromium is strongly facilitated by the matrix of amorphous cobalt oxide. These results suggest that superficial oxidation may proceed along two distinct possible pathways: a thermodynamically stable path along the potential energy minimum surface and a metastable, kinetically driven path that results from the high heat release during the dissociation of O2.