A. John Hart
Department of Mechanical Engineering,
University of Michigan
Abstract:
We investigate growth of vertically-aligned carbon nanotube (CNT) forests
by in situ X-ray scattering, and thereby elucidate the dynamics of catalyst
particle coarsening, forest self-organization, temperature- and reactant-driven CNT
structure evolution, and growth termination. A custom-built atmospheric-pressure
CVD reactor featuring a resistively-heated substrate platform is mounted directly
in the G1 synchrotron beamline at CHESS, enabling real-time grazing incidence and
transmission scattering studies. Simultaneous laser measurement of the forest height
captures the growth kinetics, the heated platform enables rapid temperature changes
during annealing and growth, and the reactant gas is independently pre-treated to
create active carbon species. CNT diameter and growth rate are directly proportional
to the substrate temperature, and tuning of annealing and growth conditions using
SAXS-derived diameter measurements reveals that CNT forests with mean diameters ranging
from 5-25 nm can be grown from the same starting catalyst film thickness. Growth
self-terminates abruptly, accompanied by a sudden loss of alignment at the CNT-substrate
interface; this appears to be a universal chemical and/or mechanical signature in our
experiments. Our apparatus and investigation technique offer significant potential to
further understand the limiting mechanisms self-organization and growth of one-dimensional
nanostructures, and for engineering of their application-oriented characteristics.
2009 Run
Sept. 23rd to Nov. 10th
