Date on Master's Thesis/Doctoral Dissertation

5-2009

Document Type

Master's Thesis

Degree Name

M.S.

Department (Legacy)

Department of Physics

Committee Chair

Sumanasekera, Gamini U.

Subject

Nanotubes

Abstract

This thesis is based on experimental work on electrochemically mediated charge transfer effects on Single-walled carbon nanotube bundles. The study of these effects are very important towards understanding the sensitivity of gases on nanostructures like single-walled carbon nanotubes. Chapter one covers the introduction and overview of carbon nanostructures including single-walled carbon nanotubes. Chapter two covers the experimental techniques involving sample preparation, experimental setup and data acquisition. Chapter three consists of Results and the Discussions explaining the mechanisms based on charge transfer mechanism. In the final chapter, implications and the importance of the study are explained. Single-walled carbon nanotubes are used as chemical gas sensors due to its high sensitivity and rapid response to various gases. Studying the electrical properties of single-walled carbon nanotubes increased the interest for further study related to sensor properties. Intrinsic properties of SWNT thin films have been studied extensively by measuring in situ thermoelectric power and 4 probe resistances. Recently, it has been shown that the conductivity and the type of SWNT material change dramatically due to exposure of SWNT sample to various gases. Even though several mechanisms have been proposed to explain this phenomenon, it has been a controversial since the presence of water vapor barrier is not taken into consideration for explaining the mechanism. Electrochemically mediated charge transfer has been studied by its effects on the surface conductivity of diamond. And It has been shown that a pronounced conductivity been observed in Hydrogen terminated diamond even though it shows an insulating properties. We proposed a mechanism for the change of intrinsic properties of semiconducting SWNTs by systematically shifting the Fermi energy level by the exposure of different pH saturated water vapors. Due to the change in chemical potential of the redox couple of various gas saturated water vapor and Fermi energy of SWNT will result in charge transfer from water layer to SWNT or vice versa. The changes in thermoelectric power and Resistance data correlate with relative position of the Fermi level with respect to the chemical potential of the aqueous layer. SWNT samples were prepared by Pulse Laser Vaporization technique and purified by standard chemical methods. Experiments were performed using ambient oxygen and ammonia which have been bubbled through acid and basic solutions of different pH values at atmospheric pressure and room temperature.

Share

COinS