ATOMIC-STRUCTURE OF TETRAHEDRAL AMORPHOUS-CARBON

One form of diamond-like carbon - prepared free of hydrogen by deposit ion from a filtered C are - possesses proportions of sp(3) bonding in excess of 80%, and is therefore called tetrahedral amorphous carbon (t a-C). Neutron diffraction, high resolution transmission electron micro scopy (HRTEM) and electron energy-loss spectroscopy (EELS) have been u sed 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 o n 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 networ k model. Along with valuable information from EELS on the sp(2)-bonded component, the structural data are consistent with an amorphous netwo rk in which some C atoms occupy hybridisation states intermediate betw een sp(3) and sp(2).