Structural analysis of conical carbon nanofibers

Conical carbon nanofibers are a relatively new type of carbon nanomaterial that has received considerable scientific and commercial interest due to its physical properties. However, its structure and growth mechanism have still not been determined conclusively. In this study the structure of these materials was investigated employing molecular models and structural analyses and compared with reported experimental observations, principally of cone apex angles. The results showed that stacked cone models could not explain the wide variety of apex angles observed for these nanofibers and related structures. Cone–helix models, originally proposed for other carbon conical structures, allow a variety of apex angle structures and were found to be applicable for nanofibers as well. An equation was developed that allows for prediction of cone–helix structures with good graphitic alignment. Such structures were also shown to be more compatible with the physical properties and growth mechanism of nanofibers than stacked cone structures. From these results a cone–helix structure, and a new cone–helical growth mechanism for the nanofibers based on heterogeneous nucleation on conical catalyst particles, are proposed.