Alignment mechanism of carbon nanofibers produced by plasma-enhanced chemical-vapor deposition

We report experimental evidence showing a direct correlation between the al ignment of carbon nanofibers (CNFs) prepared by plasma-enhanced chemical-va por deposition and the location of the catalyst particle during CNF growth. In particular, we find that CNFs that have a catalyst particle at the tip (i.e., growth proceeds from the tip) align along the electric-field lines, whereas CNFs with the particle at the base (i.e., growth proceeds from the base) grow in random orientations. We propose a model that explains the ali gnment process as a result of a feedback mechanism associated with a nonuni form stress (part tensile, part compressive) that is created across the int erface of the catalyst particle with the CNF due to electrostatic forces. F urthermore, we propose that the alignment seen recently in some dense CNF f ilms is due to a crowding effect and is not directly the result of electros tatic forces. (C) 2001 American Institute of Physics.