| A chemical vapor deposition process was developed which resulted in the growth of a unique carbon structure that resembles small trees. The trees are grown on a resistively heated graphite electrode where the temperature will reach 1500°C in a matter of seconds. The nucleation of the carbon microtrees is typically assisted by an iron based catalyst.; The structure of the carbon microtrees and the physical dimensions of the trees has been determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. Deposited onto a carbon nanotube core is a structure that resembles vapor grown carbon fibers. The diameter of the tree increases with increasing distance from the substrate which is a result of the deposition conditions. The atomic structure of the stalk portion of the tree is turbostratic and is classified as rough laminar graphite. At the top of the tree is a cap. There are three different types of cap on the tree that is a function of the length of the tree and ultimately the deposition temperature at that distance. The cap can range from rough laminar pyrocarbon to smooth laminar pyrocarbon to isotropic pyrocarbon. The diameter of the cap is typically much larger than the stalk.; The nucleation and growth mechanisms of the carbon microtrees was also investigated. The carbon nanotube core is nucleated and grown using an iron based catalyst particle. The mechanisms of pyrocarbon deposition are strongly affected by temperature. The deposition mechanisms can vary between being driven by gas phase kinetics, where the deposition is driven primarily by physisorption of large graphite molecules, and being driven by surface kinetics, where the deposition mechanism is through chemisorption of ethylene. The different deposition mechanisms result in the differences in microstructure between rough laminar and smooth laminar pyrocarbon. Finite element modelling of the deposition process was performed. It was found that the dominant factor in the deposition of pyrocarbon onto the carbon nanotube core, resulting in the carbon microtree structure, thermal gradient developed from the heating scheme of the substrate. |
