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Doctor of Philosophy
Materials Science and Engineering
Roberto R. Panepucci
Date of Defense
Unique electrical and mechanical properties of single-walled carbon nanotubes
(SWNTs) have made them one of the most promising candidates for next-generation
nanoelectronics. Efficient utilization of the exceptional properties of SWNTs requires
controlling their growth direction (e.g., vertical, horizontal) and morphologies (e.g.,
straight, junction, coiled).
In this dissertation, the catalytic effect on the branching of SWNTs, Y-shaped
SWNTs (Y-SWNTs), was investigated. The formation of Y-shaped branches was found
to be dependent on the composition of the catalysts. Easier carbide formers have a strong
tendency to attach to the sidewall of SWNTs and thus enhance the degree of branching.
Y-SWNTs based field-effect transistors (FETs) were fabricated and modulated by the
metallic branch of the Y-SWNTs, exhibiting ambipolar characteristics at room
temperature. A subthreshold swing of 700 mV/decade and an on/off ratio of 105 with a
low off-state current of 10-13 A were obtained. The transport phenomena associated with
Y- and cross-junction configurations reveals that the conduction mechanism in the SWNT junctions is governed by thermionic emission at T > 100 K and by tunneling at T
< 100 K.
Furthermore, horizontally aligned SWNTs were synthesized by the controlled
modification of external fields and forces. High performance carbon nanotube FETs and
logic circuit were demonstrated utilizing the aligned SWNTs. It is found that the
hysteresis in CNTFETs can be eliminated by removing absorbed water molecules on the
CNT/SiO2 interface by vacuum annealing, hydrophobic surface treatment, and surface
SWNT “serpentines” were synthesized by utilization of the interaction between drag
force from gas flow and Van der Waals force with substrates. The curvature of bent
SWNTs could be tailored by adjusting the gas flow rate, and changing the gas flow
direction with respect to the step-edges on a single-crystal quartz substrate. Resistivity of
bent SWNTs was observed to increase with curvature, which can be attributed to local
deformations and possible chirality shift at curved part.
Our results show the successful synthesis of SWNTs having controllable
morphologies and directionality. The capability of tailoring the electrical properties of
SWNTs makes it possible to build an all-nanotube device by integrating SWNTs, having
different functionalities, into complex circuits.
Huang, Jun, "Controlled Growth of Carbon Nanotubes for High Performance Nanoelectronics" (2009). FIU Electronic Theses and Dissertations. Paper 282.