Fractal carbon filaments grown on insulators under irradiation in an electron microscope

A new phenomenon is reported which appears during the deposition of hydrocarbon molecules on electrically charged insulators in transmission electron microscopes. Micron-sizes aggregates of ramified amorphous carbon filaments with fractal, densely branched or compact morphologies are observed. Heavy electron irradiation produces fullerene-like clusters. Under suitable conditions the aggregates show striking similarities to the shapes of many biological systems. The growth occurs in vacuum and is not diffusion limited. A simple Laplacian growth mechanism is considered which leads to the formation of fractal or non-fractal aggregates. (author)