Structural Features of CVD Graphite

CVD graphite can have several structural forms columnar, laminar, or isotropic. The columnar form is shown in Fig. 7.2. The crystallites are deposited with the basal planes (ab directions) essentially parallel to the deposition surface. Their structure tends to be columnar (cone-like) as a result of uninterrupted grain growth toward the reactant source. 

The laminar form consists of essentially parallel layers or concentric shells if deposited on a particle or fiber as shown in Fig. 

Both columnar and laminar structures are optically active to polarized light and usually have similar physical properties. 

The isotropic form has little graphitic characteristic and essentially no optical activity. It is composed of very fine grains without observable orientation and for this reason, it is known as isotropic carbon rather than isotropic graphite. It is often obtained in fluidized-bed deposition, possibly due to continuous surface regeneration by the mechanical rubbing action of the bed. An isotropic structure, observed by transmission electron microscopy, is shown in Fig. 7.4.111] 

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