High-resolution electron energy-loss spectroscopy of undoped and nitrogen-doped tetrahedral amorphous carbon films

Undoped and nitrogen-doped amorphous carbon (ta-C) films deposited using a filtered cathodic vacuum arc were investigated by high-resolution electron energy-loss spectroscopy in transmission. The carbon and nitrogen K-edge spectra show fine structure at the C 1s to π* excitations which gives information about the hybridization and coordination of the carbon and nitrogen atoms. The loss data were collected up to 50 eV and a Kramers-Kronig analysis was used to derive their complex dielectric functions. The ε2 spectra show two features due to excitations of π and σ valence states. The π feature is very small in ta-C deposited at 100 eV, consistent with its high sp3 content. The development of the π and σ peaks with varying sp2 content and their oscillator strengths allow us to resolve the degree of π-σ mixing which arises from disorder in more sp3-bonded carbons