The detailed atomic structure of tetrahedral amorphous carbon

Abstract

Preparation of hydrogen-free diamond-like carbon by deposition from a filtered carbon arc produces a material with proportions of sp 3 bonding in excess of 80%, which is referred to as tetrahedral amorphous carbon (ta-C). The atomic structure of ta-C has been investigated using electron energy loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM). Neutron diffraction studies have already 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 work, EELS is used to gain valuable information on the nature of the sp 2-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 random network model. The data are consistent with an amorphous network with significant medium-range ordering, in which some C atoms may occupy hybridization states intermediate between sp 2 and sp 3.