Abstract
Carbon nanotubes have a host of properties that make them excellent candidates for electron emitters. A significant amount of research has been conducted on nanotube-based field-emitters over the past two decades, and they have been investigated for devices ranging from flat-panel displays to vacuum tubes and electron microscopes. Other electron emission mechanisms from carbon nanotubes, such as photoemission, secondary emission, and thermionic emission, have also been studied, although to a lesser degree than field-emission. This paper presents an overview of the topic, with emphasis on these less-explored mechanisms, although field-emission is also discussed. We will see that not only is electron emission from nanotubes promising for electron-source applications, but also its study could reveal unusual phenomena and open the door to new devices that are not directly related to electron beams.
Highlights
Electron emission, that is, the transfer of electrons from one medium to another, is ubiquitous in electronics
Depending on the application, it may be extremely challenging to realize the full benefits of a nanotube emitter: for instance, in an electron microscope or lithography system, one may desire to have the emission spot precisely located on the electron-optical axis
While this is an important model and widely useful, one has to keep in mind that it was originally developed for a metallic emitter with a flat surface
Summary
That is, the transfer of electrons from one medium to another, is ubiquitous in electronics. There have been significant advances in electron emission and control with temporal resolution down to the femtosecond domain and beyond [7, 11, 12] for time-resolved imaging and diffraction analysis. Electron-beam lithography is a powerful technique for highresolution patterning [14] In all these systems, the electron emitter ( known as cathode or electron source) is one of the crucial components. A large body of literature exists on field-electron emission from carbon nanotubes, spanning almost two decades of work and including several excellent reviews. I will review some of the applications of such electron sources and discuss how the unusual properties of nanotubes enable novel concepts, notably in energy conversion and solar electricity generation. I will close the paper by proposing a device that I call the optophononic transistor/switch, which has been inspired directly by what we have learnt from light-induced electron emission experiments on carbon nanotubes
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