TABLE OF CONTENTS Electron beams play a central role in many applications and basic research tools. For example, electron emission is used in cathode ray tubes, x-ray tubes, scanning electron microscopes, and transmission electron microscopes. In many of these applications, it is desirable to obtain a high density of narrow electron beams, with each beam tightly distributed in energy. So-called electron guns, which operate on thermionic emission of electrons from hot cathodes, are extensively utilized for this purpose. However, achieving electron beams with narrow energy distributions is difficult because of thermal broadening of the emitted electrons. Thus, field emission from cold cathodes is of much interest, but requires large electric fields that cause migration of atoms at the tip surface, making it difficult to achieve stable operation over long periods of time. Carbon nanotubes may offer a solution to these issues. Indeed, carbon nanotubes have many advantages for cold field emission: the inertness and stability of nanotube tips to long periods of operation compared to metal and diamond tips; low threshold voltage for cold field emission; low temperature of operation; fast response times; low power; and small size. As will be discussed later in this chapter, prototype devices using the superior field emission properties of nanotubes have already been demonstrated. These devices include x-ray tubes [1], scanning x-ray sources [2], flat panel displays [3], and lamps [4].
Before going into the details of field emission, we begin by introducing the early experimental work that established the promise of carbon nanotubes for...
