The initial oxidation of epsilon-Fe2N1-x: growth kinetics

The oxidation kinetics of epsilon-Fe2N1-x, subjected either to a sputter cl eaning pretreatment or a sputter cleaning and an additional annealing pretr eatment, at P-O2 = 1 x 10(-4) Pa and at temperatures ranging from 300 to 50 0 K, was investigated with ellipsometry. The initial oxidation rate of sput ter cleaned + annealed epsilon-Fe2N1-x was observed to be lower than of spu tter cleaned epsilon-Fe2N1-x, but upon prolonged oxidation sputter cleaned + annealed epsilon-Fe2N1-x attained a higher oxidation rate than sputter cl eaned epsilon-Fe2N1-x. The oxidation kinetics was interpreted using the mod el due to Fromhold and Cook wherein cation and electron currents in the gro wing oxide film are coupled. The effect of the nitrogen concentration in th e iron-nitride substrate on the oxidation kinetics could be discussed in te rms of this model and related to the morphology and phase constitution of t he oxide film. (C) 1999 Elsevier Science S.A. All rights reserved.