Chapter 10. Field Emission and Electromagnetic Wave Absorption

Abstract

Field emission materials and electromagnetic wave absorbing materials are two kinds of functional materials used in our daily lives and for national defence. Field emission is electron discharge induced by an electrostatic field. The electron is discharged from the surface of the material when subjected to a strong electric field. A field emission cathode is a cold cathode that is not electrically heated by a filament. The cold cathode has been widely used in the fields of electron guns, displays, traveling wave tubes and other vacuum electronics. Low-dimensional nanostructures have attracted considerable attention for field-emission devices due to their high aspect ratio and low curvature at the tip. A great deal of intensive research interest is driven by the enormous applications of nanostructures as field emission materials. An electromagnetic wave absorbing material (EAM) is a kind of functional material that can absorb electromagnetic waves effectively and convert electromagnetic energy into heat, or make electromagnetic wave disappear by interference. EAMs are currently gaining attention in the field of civil and military applications. Generally, demands for developing more economical EAMs with ‘low density, wide band, thin thickness, and high absorptivity’ are ever increasing. Therefore, low-dimensional nanostructures are extensively reported to be used as EAMs due to the advantages of light weight and excellent electric properties. The wurtzite structure of ZnO is a kind of unique wide bandgap semiconductor material with special electric properties, which makes ZnO one of the most attractive research topics for different functional applications. As an oxide, ZnO exhibits a high melting point and it is quite stable under harsh environments. In addition, ZnO has high breakdown strength, abundant shapes, large length–diameter ratio and sharp tip. These advantages enable ZnO nanostructures to become the most important field emission materials and EAMs. In this chapter, we give a comprehensive review of and explore the prospects of the application of ZnO nanostructures in the fields of field emission and electromagnetic wave absorption.