Atomic structure of tetrahedral amorphous carbon

One form of diamond-like carbon - prepared free of hydrogen by deposition from a filtered C arc - possesses proportions of sp3 bonding in excess of 80%, and is therefore called tetrahedral amorphous carbon (ta-C). Neutron diffraction, high resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS) have been used to study the atomic structure of the material. Neutron diffraction has shown that the average structure of ta-C is in many ways similar to that of a-Si and a-Ge. HRTEM, used to probe medium-range ordering on a scale of 0.5-1.0 nm, indicates the presence of non-random features, and this raises questions concerning the validity of a random network model. Along with valuable information from EELS on the sp2-bonded component, the structural data are consistent with an amorphous network in which some C atoms occupy hybridisation states intermediate between sp3 and sp2.