Investigating Defects in the Sensing Mechanism of Carbon Nanotube Field-Effect Transistors
Abstract
In nanotechnology, understanding the effect of interfaces and defects becomes critically
important in determining a material’s properties and device performance. It is well known that
one-dimensional and two-dimensional materials exhibit excellent physical, electrical, thermal,
and optical properties, making them highly desirable for a wide array of applications. However,
their low dimensionality also means they can be heavily affected by defects in the material and
the interfaces they form with other materials commonly used in semiconductor device
fabrication. Carbon nanotubes are one such material that is often used in sensing applications.
The best and most commonly used device configuration for carbon nanotube-based sensors is the
field-effect transistor. To fabricate a carbon nanotube field-effect transistor, metal contact
electrodes must be deposited on either side of a semiconducting carbon nanotube. The resulting
interface between the metal and the nanotube form a Schottky barrier, which can have an
important role in establishing transistor characteristics. Modifications to this interface by the
environment can modulate the barrier and produce a commensurate change in the overall
performance of the device. Transistor operation may also be modified by the presence of defects
in the carbon nanotube structure. The role of defects and the interplay between the Schottky
barrier at the interface and the defects present in the carbon nanotube represent critical areas of
interest when studying sensors based on carbon nanotube field-effect transistors. Therefore, the
iv
purpose of this study is to explore how defects in carbon nanotubes can affect the sensing
mechanism, and to assess its relative importance when compared with modulations of the
Schottky barrier in carbon nanotube field-effect transistor-based sensors. To explore this effect,
carbon nanotube field-effect transistors have been fabricated as gas sensors, specifically to detect
ammonia (an electron donor) and nitrogen dioxide (an electron acceptor). Gas exposure
measurements were performed on near pristine (low defect) nanotube devices and compared with
highly-defective nanotube devices. By utilizing selective passivation of critical device areas to
isolate the sensing mechanism, results show that the presence of defects has a critical role in the
sensing mechanism of carbon nanotube field-effect transistor gas sensors. Results also suggest a
resolution to the long-standing debate over the sensing mechanism of these devices. These
results represent an important step toward understanding the effect of both interfaces and defects
for carbon nanotube sensor development and adds a critical piece of understanding necessary for
the development of future nanoscale sensors.
Description
Ph.D.
Permanent Link
http://hdl.handle.net/10822/1055016Date Published
2019Subject
Type
Publisher
Georgetown University
Extent
159 leaves
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Mechanism of Gas Sensing in Carbon Nanotube Field Effect Transistors
Dube, Isha (Georgetown University, 2014)Gas sensors based on carbon nanotubes in the field effect transistor configuration have exhibited impressive sensitivities compared to the existing technologies. However, the lack of an understanding of the gas sensing ...