Erosion of amorphous carbon layers in the afterglow of oxygen microwave plasma

We present a study of the interaction of amorphous hydrogenated carbon deposits (a-C:H) with neutral oxygen atoms. Samples of a-C:H were exposed to an atomic oxygen rich atmosphere at surface temperatures from 473 K to 623 K. The source of atomic oxygen was microwave plasma, created in oxygen at pressures between 50 Pa and 200 Pa by means of a surfatron. The density of neutral oxygen atoms reached up to 4 ∙ 1021/m3. The densities of neutral atoms were measured by means of a catalytic probe. The erosion process was monitored by means of an infrared pyrometer. At each sample surface temperature, the erosion rates were found to linearly increase with the atomic oxygen density. This allowed us to calculate the reaction rate coefficient at corresponding surface temperatures. The reaction rate coefficient was found to increase exponentially with the sample surface temperature.

► Formation of a-C:H will present serious safety issues in fusion devices. ► Layers of a-C:H could be efficiently removed by oxidation. ► We present a study of removal of a-C:H by atomic oxygen. ► Erosion rates as high as 36 nm/s were measured. ► Erosion rates increase linearly with atomic oxygen density.