MOLECULAR-DYNAMICS AND EXPERIMENTAL STUDIES OF PREFERRED ORIENTATION INDUCED BY COMPRESSIVE STRESS

It is well established that ion irradiation of glassy carbon with ener getic ions leads to the formation of a dense amorphous surface layer. In this work we show using cross-sectional TEM that oriented graphite- like regions are formed within the implanted layer of glassy carbon im planted with 50 keV C ions at high doses. The preferred orientation is such that the sp(2) bonded graphite-like sheets lie normal to the imp lanted surface. Stress measurements of the implanted material show the presence of a biaxial compressive stress. Molecular dynamics simulati ons of a two-dimensional analogue of graphite show a similar preferred orientation effect. Thermodynamic calculations predict that a non-hyd rostatic stress can result in preferred orientation in anisotropic mat erials such as graphite. The preferred orientation can be explained in terms of the combined effects of the mobility introduced by the impla nted ions and the anisotropic stress held.