It was recalled that tetrahedral amorphous C was a dense form of amorphous C, with a structure that consisted of a highly tetrahedral bonding network. Some 20% of the atoms in the tetragonal form were sp2 hybridized, and the presence of these sites played an important role in determining the properties of the material. Here, 50keV C+ and 200keV Xe+ ion implantation was used to damage the structure in a controlled manner. The structure of the samples following ion bombardment was monitored by exploiting a dose-dependence of the electrical conductivity, as well as by using Raman spectroscopy, electron diffraction, and electron energy loss spectroscopy. It was shown that the damage was mainly in the form of an increased concentration of sp2-bonded sites. With increasing dose, the structure changed from an essentially tetrahedral network, which contained sp2 sites as defects, to an essentially sp2-bonded structure in which there was a high degree of in-plane disorder; combined with a regular stacking of the planes.

D.G.McCulloch, E.G.Gerstner, D.R.McKenzie, S.Prawer, R.Kalish: Physical Review B, 1995, 52[2], 850-7