In situ electron microscope study on the formation and morphological evolution of carbon aggregates

Two phenomena were observed when a copper specimen was irradiated by normal electron beam in a transmission electron microscope. One is the growth of the rod-like carbon aggregates normally stemmed from the substrate of specimen, with their unique fir-like shape and pattern caused by the deposition of hydrocarbon molecules. These molecules come from the boiling and evaporating of the diffusion pump oil in the high vacuum system. The other is the evolution of the stacked morphologies from the fir-like to spindle-like, mushroom-like and ball-like. The experimental findings and theoretically analyses lead us to believe that the carbon aggregates go through an evolution process which is governed, to some degree, by the irradiation of electron beam and by the surface tension and the instability of the amorphous carbon. Moreover, during the growing process of the carbon aggregates, the magnitude of electric charges and their distributions on the deposited carbon dominate the side branching and the tip splitting. For the evolution process of the morphologies, the most important driving force is the surface tension of the carbon aggregates under the irradiation of electron beam in a vacuum system.