Chemical vapor deposition of pyrolytic carbon on carbon nanotubes. Part 2. Texture and structure

In a previous study we showed both the formation of genuine vapor grown carbon fibers (VGCFs) and of new and peculiar carbon nanotube-supported morphologies using a chemical vapor deposition process. Briefly, the latter are an association of beads (or fiber segments) with a more or less rough surface and more or less extended cone-based sub-morphologies with a smooth surface. The investigation of these materials regarding their texture, nanotexture and structure by transmission electron microscopy is reported, as a first step to understanding the formation mechanisms. It is shown that VGCFs exhibit a concentric texture, however with a variable microporous character and nanotexture quality. On the other hand, beads and related morphologies have a coarsely concentric microporous texture, as opposed to the cones and related morphologies, which exhibit a perfectly concentric and dense texture similar to that of perfect multiwall carbon nanotubes. Cross-sections performed with ultra-microtomy have revealed the spatial and textural relationship between cones and beads.