THE DETAILED ATOMIC-STRUCTURE OF TETRAHEDRAL AMORPHOUS-CARBON

Preparation of hydrogen-free diamond-like carbon by deposition from a filtered carbon arc produces a material with proportions of sp3 bondin g in excess of 80%, which is referred to as tetrahedral amorphous carb on (ta-C). The atomic structure of ta-C has been investigated using el ectron energy loss spectroscopy (EELS) and high-resolution transmissio n electron microscopy (HRTEM). Neutron diffraction studies have alread y shown that the average structure of ta-C, described through C-C bond lengths and angles, has much in common with a-Si and a-Ge. In this wo rk, EELS is used to gain valuable information on the nature of the sp2 -bonded component of ta-C, and the presence of non-random features in HRTEM images of ta-C raises questions concerning the validity of a ran dom network model. The data are consistent with an amorphous network w ith significant medium-range ordering, in which some C atoms may occup y hybridization states intermediate between sp2 and sp3.