STUDY OF CRYSTALLOGRAPHIC TRANSFORMATION OF CARBON FOILS UNDER ION IRRADIATION

Self-supporting carbon foils of typical areal density (5-10) mu g/cm**2 are irradiated with (0. 1-1. 0) mu A/mm**2 Helium ions at (100-400) KeV. Characteristic variations of the surface and the crystallographic structure of the foils are observed. A reduction of the optical transmission is accompanied by a contraction of the irradiated region resulting in wrinkles within the non-irradiated parts. By means of electron diffraction a continuous crystallographic transformation (graphitization) in the foil is observed. The rate of graphitization depends on the current density, the energy of the projectiles and the time of irradiation. It is shown that the same kind of crystallization can be produced by heat treatment of the foils with temperatures up to 1300 K.