The role of feedstock flux in the coordinated, diameter-selective growth of single-wall carbon nanotubes

David B. Geohegan,†, Alex A. Puretzky,† Jeremy J. Jackson,† Christopher M. Rouleau,† Gyula Eres,‡ and Karren L. More‡
†Center for Nanophase Materials Sciences and
‡Materials Science and Technology Division,
Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6488, United States

PDF of article published in ACS Nano 5(10) 8311 (2011).

Time-dependence of the optical reflectivity (left panel, blue) resulting from the acetylene gas pulse (red), indicating rapid, aligned growth of a 2.2 micron-long nanotube array (inset, showing SEM image cross-section) within 0.5 seconds.  Right:  Distributions of nanotube diameters from pulsed growth with different acetylene partial pressures.

Achievement
Pulsed chemical vapor deposition (CVD) with in situ optical diagnostics were used to measure the nucleation and growth kinetics of single-wall carbon nanotube (SWNT) arrays on sub-second time scales and to understand the important role that the flux of acetylene feedstock plays in determining the diameters of nanotubes that grow successfully.  Understanding the factors that determine the diameters and densities of the nanotubes within the arrays is important for their development as extraordinary thermal and electrical conductors for energy applications. New time-resolved kinetics measurements and modeling1 revealed how the partial pressure of acetylene controls not only the nucleation time and efficiency of nanotubes growing from catalyst nanoparticle ensembles, but also determines their diameters.  This discovery reveals a dynamic self-selectivity of catalyst ensembles in the cooperative growth of aligned nanostructure arrays. This introduces a mechanism to control the density, diameters, and lengths of the nanostructures using flux-controlled pulses and enables their rapid nucleation and more uniform growth.

Credit - Note: Synthesis science sponsored by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy.  Sample characterization by Raman spectroscopy at the Center for Nanophase Materials Sciences (CNMS) and electron microscopy at the Shared Research Equipment (SHaRE) User Facility sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.