Nature and evolution of ESR active centers in ta-C:H

We analyse the structure and the electron spin resonance signal in ta-C:H films. We evidence the role of topological and structural disorders, i.e., of distortions and spread in size and shape of sp2 clusters respectively, in determining the spin density in such materials. We focused on the relationship between the stress release and the lowering of the spin density due to annealing. The relevance of hydrogen content and of sp2 clustering is addressed too. In order to quantify such effects, in the limit of the approximations made, we estimate the value and the temperature evolution of the structural and topological disorder potentials. Their value turns out to be close to theoretical predictions.