Amorphous carbon films obtained by pulsed-laser ablation of graphite have been investigated by high-resolution x-ray absorption spectroscopy (XAS). The onset of the 1s → σ* transitions lies in the gap between π* and σ* states in graphite, indicating a high content of sp3 hybridization in the films. A sharp peak similar to the core exciton in diamond is observed and assigned to a core exciton in sp3-hybridized disordered C atoms. The observed binding-energy shift of ~ 0.5 eV with respect to the diamond core exciton can be explanined in terms of a higher localization of the excited state induced by disorder. This result supports a Frenkel model to describe the core exciton in sp3-hybridized carbon.

Authors thank the Spanish Ministerio de Educación y Ciencia for financial support.

Peer reviewed