Self-organized pattern formation in the oxidation of supported iron thin films. i. an experimental study

Abstract

The evolution of patterned morphology during thermal oxidation of a supported metal thin film is examined as a case of strained reaction-diffusion system; the strain originates from the large density difference between the oxide and the metal. In the moderate temperature regime, where bulk diffusion is weak, the pattern reflects the length scale of the original metal film grain structure, with local features characteristic of self-organized chemical microreactors, as well as large scale polygonal surface undulations presumably caused by stress accommodation. At higher temperature, where bulk diffusion is brisk, the process of Ostwald ripening strongly reforms the morphology formed at lower temperature, and leads to distributed spiral-type configurations. These observations and analysis are supported by a simulation study reported in the accompanying paper II by Abhijit S. Ogale.