Paramagnetic properties and hydrogen-related structural relaxation effects in magnetron-sputtered a-C:H thin films

Abstract The concentration of paramagnetic centres in various carbon-based materials can differ by orders of magnitude. The nature of the related `defects' is unclear, though distorted or clustered π-states are likely to play a role. In this work we investigate the relationships existing between the features of the room-temperature electron-spin-resonance (ESR) signal and different hydrogen concentrations and bonding configurations in a set of magnetron-sputtered a-C:H films. We show that a sharp transition in the paramagnetic properties occurs in films prepared with intermediate (∼40%) H2 content in the deposition atmosphere, a feature probably associated with two different stabilisation mechanisms of the paramagnetic centres.