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Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Materials Science and Engineering

Advisor's Name

Wonbong Choi,

Advisor's Title

Committee Chair

Advisor's Name

Roberto R. Panepucci

Advisor's Name

Chunlei Wang

Advisor's Name

Arvind Agarwal

Date of Defense

3-12-2009

Abstract

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

passivation.

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.


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