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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, this chapter proposes an exhaustive approach towards optimizing CNF field emission (FE) properties. It outlines how a platform of scientific enquiry geared towards a meaningful comparison between different CNF-based emitters can be developed. 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 in the CNFs and in 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, maximum emission current, current density, emittance, and brightness.

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.

Carbon nanotube (CNT) technology is improving around the world to the point where new types of devices can be made. Spinning millimeter-length CNT into yarn and drawing ribbon and twisting into yarn have been demonstrated, and the yarn is being used as electric and thermal conductors. It is also becoming feasible to use carbon nanotube hybrid conductive tapes and yarn to make tiny electromechanical components such as wires, coils, transformers, and electric motors. These components further enable the manufacturing of precision medical devices, such as biomedical wires, sensors, actuators, manipulators, and millirobots for minimally invasive in vivo diagnosis and treatment. Precision biomedical microdevices promise to improve disease diagnosis and treatment, improve health-care delivery, and spur novel medical system development. Treatments for heart disease, cancer, neural repair, drug delivery, probing, reconstruction, and healing might be advanced using miniature precision devices. The concept of CNT-based precision medical devices is a new area of research, and the state of the art in their development and potential applications are discussed in this chapter.