Temperature induced transition from hexagonal to circular pits in graphite oxidation by O2

We report on an in-situ monitoring of graphite oxidation using a high temperature environmental scanning electron microscope. A morphological transition is clearly identified around 1040 K between hexagonal pits at low temperatures and circular pits at high temperatures, with apparently no change in the kinetic law. A kinetic Monte Carlo model allows rationalizing these findings in terms of the competitive oxidation of armchair and zig-zag edge sites and provides an estimate of the rate laws associated to these two events. Extended to three dimensions, the model also explains the “in-depth” transition between the stepwise hexagons and the hemispheres observed by atomic force microscopy.

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