Post-growth modification of amorphous carbon films under ion beam bombardment: grain size dependence on the film thickness

Hydrogen-free amorphous carbon films, prepared by RF magnetron sputtering were examined by transmission electron microscopy. Films with thickness from 2 to 33 nm were deposited with positive bias onto a Si substrate at room temperature in sequential thin layers. Electron diffraction patterns from specimens bombarded with a low energy Ar ion beam, without any heating treatment, revealed a transformation to polycrystalline material. Interplanar distances deduced from the characteristic polycrystalline rings were in very good agreement with the diamond d spacings. The crystallite grain size, measured from dark field imaging using (111) diamond reflection, was up to 50 nm whereas the maximum grain size value was found to increase with the thickness of the film. (C) 1998 Published by Elsevier Science S.A.