Individual SWNT based thermoelectric power chemical sensors

Abstract

ABSTRACT Electrical properties of individual Single-Walled Carbon Nanotube/rope in the configurations of 2-probe resistance, field effect transistor (FET), and thermopower have been measured. It is shown that oxygen adsorption in SWNTs is indeed a physisorption process. The p-type behavior of SWNTs in the ambient is believed to be due to the Fermi level pinning at impurity states of O 2- near the top of the valence band of the tube. Chemisorption processes involving ammonia and nitrous oxide have been explored by studying FET properties. The thermoelectric power of individual ropes of SWNTs is measured and related to the FET properties. Keywords: SWNT, Thermoelectric Power, Oxyg en sensor, Change of resistance 1. INTRODUCTION Chemical Sensors have made a great impact on everyday life. Over the past decade the de velopment of simple, robust, solid state sensors whose operation is based on the transduction of the binding of an analyte at the active surface of the sensor to a measurable signal has been in demand. Most often the measurable signal is the change in electrical properties such as resistance, capacitance or optical properties of the active element. There has been a very strong demand for producing highly sensitive, selective and cost effective sensors. Due to which the research has emphasized on developing new materials for sensing flammable and volatile chemicals, biological agents etc. Single walled carbon nanotubes (SWNTs) are 1d quantum wires which have unique physical and chemical properties for potential applications. Chemical sensors based on these SWNT s have numerous advantages over conventional solid state chemical sensors. These include extreme sensitivity, good selectivity and faster response time. The most important advantage includes using them at room temperature as compar ed to the solid state sensors which only respond at high temperature. The interaction between the nanotube and the molecular gas species can significantly make an impact on the electrical and thermal properties of the SWNTs. There have been studies done on changes in the electrical transport and thermal properties on the bundles of nanotubes [1 - 4] as well as individual nanotube [5 - 7] due to the interaction to the gas molecules. In this paper we discuss the various adsorption/desorption kinetics study of oxygen and other organic vapors using the study of individual SWNT as a 2-probe resistance configuration, Field Effect Transistor (FET) configuration for individual SWNTs and thermoelectric power (TEP) measurement of individual bundles of SWNTs.