Model for electron diffraction of amorphous and nanocrystalline structures – application for amorphous and fullerene-like carbon allotropes.

Zsolt Czigбny

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences P.O.Box 49. H-1525 Budapest. Hungary

Lars Hultman
Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linkцping University, S-581 83 Linkцping, Sweden

Amorphous carbon and carbon-based coatings show a broad variety of properties regarding mechanical hardness, elasticity as well as electronic and optical properties. The difference in properties is due to different chemical bonding and the consequent different atomic short range ordering.

An interesting group of carbon-based materials are the so called fullerene -like (FL) solid phases like CNx and CPx where the solid is composed of FL fragments and/or packages. Multishell fullerene structures - so called nano-onions - were observed in CNx by high resolution transmission electron microscopy (HRTEM), but CPx has amorphous appearance in HRTEM images. However, the electron diffraction showed structural differences both between the CNx and CPx FL phases and compared to other amorphous carbon allotropes.

Here, we report on the calculated electron scattering of graphite and diamond nanoclusters, fullerene molecules and fragments as a function of the number of atoms. Amorphous phases are interpreted as ultrafine random nanocrystalline or nanoclustered structures with characteristic cluster size of 10-30 atoms. The short range order of amorphous carbon allotropes and FL-CNx and CPx can be qualitatively interpreted based on the relation between the calculated scattering of carbon nanoclusters and measured selected area electron diffraction (SAED) patterns.