ABSTRACT
The theory and simulation of vacuum nanoelectronics (VNE) often uses standard models, in particular the canonical equations of field emission, thermal emission, and photoemission, but these equations are increasingly challenged by processes and configurations characteristic of VNE, in particular, size, shape, and temperature. Simple models are used to explore the physics behind the approximations in the Canonical equations. Next, the effects of processes such as heating, as attends current flow through nanowires and nanofibers, is considered. Time factors associated with emission, in particular, tunneling time and the Hartman effect, 570and transit time across an anode-cathode (AK) gap, are examined. Lastly, the emission barrier is affected by a non-planar image charge, field variation near highly curved surfaces, depletion barriers of semiconductors, and other mechanisms. The modifications lead to a general quadratic barrier model examined in terms of the Gamow tunneling factor and a shape factor method.
Vacuum nanoelectronics has evolved considerably from the early days when the promise of field emission from tungsten wires for microwave devices [2, 9, 14, 20] was envisioned to be harnessed by microfabricated field emitters created by thin-film deposition and micromachining [27, 90–93, 98]. But harnessed it was through the development of emitters capable of rapid emission modulation and operation in inductive output amplifiers, traveling wave tubes, and high power microwave devices [35, 70, 72, 75, 88, 89, 96, 101, 102] using a variety of sources such as Spindt-type field emitter arrays, semiconductor field emitters, carbon fibers, and others. Progress in integrating photoemission processes [34, 76, 95] addresses the call for very short bunches of electrons for particle accelerators, rf guns, and free electron lasers [32, 68, 69]. The engineering behind these applications is profound, but fortunately, a basic understanding of the physics governing how electrons are coaxed into vacuum is understandable using simple models and the effects of that physics on the beams produced. Particular attention is directed to tunneling behavior, thermal-field effects on current density, photoemission effects, space charge, transit time, and beam properties.
