Metal Oxidation Kinetics and the Transition from Thin to Thick Films

TL;DR

This paper presents a unified theory of metal oxidation kinetics that seamlessly describes the transition from thin to thick films, integrating Cabrera-Mott and Wagner models based on ionic transport mechanisms.

Contribution

It introduces a comprehensive model that unifies existing theories and accurately describes the transition from thin to thick film oxidation regimes.

Findings

The transition from ionic drift to diffusion transport follows a logarithmic law.

The validity ranges of Cabrera-Mott and Wagner theories are defined by Debye-Huckel length.

The model aligns with experimental observations of oxidation kinetics.

Abstract

We report an investigation of growth kinetics and transition from thin to thick films during metal oxidation. In the thin film limit (< 20 nm), Cabrera and Mott's theory is usually adopted by explicitly considering ionic drift through the oxide in response to electric fields, where the growth kinetics follow an inverse logarithmic law. It is generally accepted that Wagner's theory, involving self-diffusion, is valid only in the limit of thick film regime and leads to parabolic growth kinetics. Theory presented here unifies the two models and provides a complete description of oxidation including the transition from thin to thick film. The range of validity of Cabrera and Mott's theory and Wagner's theory can be well defined in terms of the Debye-Huckel screening length. The transition from drift-dominated ionic transport for thin film to diffusion-dominated transport for thick film is found to strictly follow the direct logarithmic law that is frequently observed in many experiments.