Abstract
In the previous chapter, building on recent efforts to characterize carbon nanotube fibers (CNFs) as efficient electron emission sources suitable for compact, high power, high frequency vacuum electronic devices, an exhaustive approach towards optimizing CNF field electron emission (FE) properties was proposed. It consists of a platform of scientific enquiry geared towards a meaningful comparison between different CNF-based emitters. The platform envisages an iterative procedure involving (a) the growth, processing, and functionalization of CNFs, (b) full investigation of the CNF material properties before and after FE diagnosis, and (c) multi-scale modeling of FE properties, including self-heating, shielding effects and beam characteristics for both CNFs and the emitting carbon nanotubes (CNTs) at the fiber apexes. The modeling would be applicable to a wide variety of CNFs and wire-like sources, and would provide essential feedback to the growth, processing, and functionalization of CNFs, in order to optimize their FE properties, especially long-term stability, low noise and maximum emission current, current density, emittance and brightness. In this chapter, we first report simulations of the influence of self-heating effects on the field emission (FE) properties of CNFs and their dependence on the product of the electrical and thermal conductivities of the fibers. We study the sensitivity of the FE of CNFs as the dimensions and numbers of CNTs at the apex of the fiber are varied. The influence of the field enhancement factors of both the shank of the fiber and the CNTs at its apex on the FE properties of CNFs is also analyzed. We conclude the chapter with a study of the influence of the electrostatic shielding on the FE characteristics of two CNFs as a function of the distance between the axes of the two fibers.