%0 Journal Article
%T Carbon Nanotube Electron Sources: From Electron Beams to Energy Conversion and Optophononics
%A Alireza Nojeh
%J ISRN Nanomaterials
%D 2014
%R 10.1155/2014/879827
%X 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. 1. Introduction Electron emission, that is, the transfer of electrons from one medium to another, is ubiquitous in electronics. Electron emission from a material into vacuum (Figure 1) forms the basis of vacuum tubes and amplifiers [1], which predate solid-state devices [2] and still continue to be in widespread use in high-power, high-speed electronics¡ªthe mobility of electrons is, after all, very high in vacuum, where they do not face scattering by a lattice. But the applications of electron emission go far beyond signal amplification. From traditional cathode-ray tubes to modern field-emission flat-panel technologies, electron sources can enable bright and fast displays [1]. Electron microscopy has become a popular platform for material and device imaging [3¨C7], inspection, and failure analysis [8, 9], pushing imaging resolution to the sub-£¿ngstrom scale [10]. 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. Analytical characterization techniques such as Auger spectroscopy, electron-energy-loss spectroscopy, and energy-dispersive X-ray spectroscopy are now being routinely used and often incorporated into commercial electron microscopes [13]. Electron-beam lithography is a powerful technique for high-resolution patterning [14]. In all these systems, the electron emitter (also known as cathode or electron source) is one of the crucial components. Medical imaging is another area where electron sources are in extensive use, notably in X-ray generation [1] and electron-beam tomography. Electron-beam welding,
%U http://www.hindawi.com/journals/isrn.nanomaterials/2014/879827/