Physics of Electron Emission and Beam Dynamics from a Single Diamond Field Emitter

Abstract

Many applications such as compact accelerators and electron microscopy demand high brightness electron beams with small beam size and ultra-low emittance. Electric-field-assisted diamond emitters manufactured from semiconductor processes has been recognized as a leading candidate for such compact sources. The micro-scale pyramid structure of the emitter has the desirable attribute of significant electric field enhancement at the sharp interfaces (apex and edges) to facilitate electron emission. We investigate the dependence of field enhancement on the geometric shape. To account for the semiconductor charge transport in the bulk material and the tunneling through the surface, a first-principle semiclassical Monte Carlo emission model is developed and applied to the diamond pyramid. Combining the results from the Monte Carlo and the geometric field enhancement calculation, we construct a simple model to qualitatively explain the measured emission characteristics. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> The electron beam formation and dynamics in a 1D diode setup are simulated with a particle-in-cell code to obtain the macroscopic observables such as the beam energy, voltage, and divergence. The physical characteristics and parametric dependence of the emitted beam are compared with experiments and understood through the analysis of particle trajectory in a model field configuration.2 We further develop an effective mass based theoretical model accounting for the conduction band quantization in a high aspect ratio semiconductor nanostructure and the corresponding Monte Carlo implementation to describe electron transport and subsequent electron emission from the nanotip of the emitter. The effects of level quantization, electron scattering due to the nanotip diameter variation, and electron-phonon scattering on the nanotip emission properties are identified and compared with the case of a bulk slab. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>