Carbon nanotube morphology has been engineered via simple control of applied voltage during dc plasma chemical vapor deposition growth. Below a critical applied voltage, a nanotube configuration of vertically aligned tubes with a constant diameter is obtained. Above the critical voltage, a nanocone-type configuration is obtained. The strongly field-dependent transition in morphology is attributed primarily to the plasma etching and decrease in the size of nanotube-nucleating catalyst particles. A two-step control of applied voltage allows a creation of dual-structured nanotube morphology consisting of a broad base nanocone (∼200 nm dia.) with a small diameter nanotube (∼7 nm) vertically emanating from the apex of the nanocone, which may be useful for atomic force microscopy.
Bibliographical noteFunding Information:
The authors acknowledge the support of the work by University of California Discovery Fund under Grant No. ele02-10133/Jin, NSF NIRTs under Grant Nos. DMI-0210559 and DMI-0303790, and Lawrence Livermore National Laboratory under Grant No. MI-04-006.