Synergistic Interaction of CH3 and Atomic Hydrogen

We let a beam of atomic hydrogen and a beam of methyl radicals interact with the film surface simultaneously. This can be considered the simplest of all multi-species experiments first, H and CH3 are the simplest radicalic hydrocarbon species. Second, by restricting ourselves to radicals, the interaction of the beams with the film is purely chemical and expected to be limited to the very surface. Third, the effect of each species separately is already known the previous section described the temperature dependent interaction of CH3 radicals with the a-C H surface. The interaction of atomic hydrogen with carbonaceous materials has been studied extensively in the past by various groups [53,56,57]. A rate equation model describing chemical erosion by atomic hydrogen is well-established [53,58]. 

We are led to the conclusion that it is not sufficient to consider only dangling bonds (i.e., chemisorption sites) and hydrogen-terminated surface sites. An extended model is proposed which is described in detail in [28,45]. We merely summarize the main aspects here the incorporation of the impinging 

In Fig. 11.11, model results of the surface coverages 0db, 0 and 0H3 are shown as a function of the atomic hydrogen flux density. The important point here is that a substantial fraction of the surface is dynamically covered with methyl groups ( 9h3)- In the framework of our model, these need to be cross linked with each other before they can be activated for further chemisorption events. Not visible from the logarithmic scaling is the fact that at zero hydrogen flux, 6 113 is equal to one. It is this dynamical surface cov- 

Apart from revealing the important microscopic processes, this model has another benefit it allows to determine the corresponding cross-sections given 

---