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

Abstract

We report experimental evidence showing a direct correlation between the alignment of carbon nanofibers (CNFs) prepared by plasma-enhanced chemical-vapor 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 alignment process as a result of a feedback mechanism associated with a nonuniform stress (part tensile, part compressive) that is created across the interface of the catalyst particle with the CNF due to electrostatic forces. Furthermore, we propose that the alignment seen recently in some dense CNF films is due to a crowding effect and is not directly the result of electrostatic forces.

Flame pyrolysis synthesis of self-oriented carbon nanotubes

“…This force is considered to accelerate C precipitation by stress-induced diffusion. 12 Thus a well aligned CNTs array is produced when electric field is applied.…”

Secondary electron microscopy and transmission electron microscopy studies of carbon nanotubes in C-Ni films

“…When the catalyst remains anchored to the substrate, the synthesis mode is called "base-growth". On the other hand, the growth follows a "tip-growth" mechanism when the particle lifts off the substrate and is observed at the top of the CNTs [2][3][4]. Many authors discuss different * E-mail: miroslaw.kozlowski@itr.org.pl reasons for these growth mechanisms.…”

“…Multiwall carbon nanotubes (MWCNT) films are obtained by many methods with various catalysts, but one of the most frequently used is nickel [1][2][3][4][5][6][7][8][9]. The most popular method is catalytic chemical vapor deposition (CCVD) [7].…”

Enhanced Control of Single-Walled Carbon Nanotube Properties Using MPCVD with DC Electrical Bias

“…The magnitude of interaction is of sufficient magnitude to orient SWNTs (Peng, et al, 2003;Ural, et al, 2002;Zhang, et al, 2001) and multi-walled CNTs (Jang, et al, 2003;Merkulov, et al, 2001;Meyyappan, et al, 2003) along electric field lines in situ during CVD synthesis as well as during post-synthesis processing procedures (Kamat, et al, 2004;Yamamoto, et al, 1998). Negative polarity substrate bias was systematically varied between 0 and -250V in 50V increments (Maschmann, et al, 2006d).…”