Growth of carbon nanofibers studied by using transmission electron microscopy

This work is focused on studies of structure, morphology and growth of carbon nanofibers (CNFs), which are synthesized using chemical vapor deposition methods. The structure and morphology of the NFs are investigated by means of transmission electron microscopy (TEM). Formation mechanism of the helix CNFs has attracted much attention of research in recent years. In the present research the morphology and structure of both CNFs and related catalyst particles are investigated in details by means of electron imaging and electron diffraction techniques. The relations between the catalysts and the morphology of the CNFs are determined. It is found out that two types ofhelical structures exist, i. e. single-side-growth helical structure and double-side-growth helical structure, depending on catalyst materials. For the Fe3C catalyst the carbon nanohelices (CNHs) are related to the hexahedron morphology of the catalyst particles at the tip of the fiber. Difference in growth velocities on different crystallographic surface planes leads to rotation ofthe catalyst particle, and in turn to the rotation of the growth fronts of nanohelix. For the Cu catalyst, it is found that the size of the catalyst particles plays a crucial role in the formation of the helical structures. Small size of catalyst particles favors formation of the helical fibers, while large size of catalysts results in the straight fibers. The size effects are found additionally morphology-dependent of the Cu catalysts.