Boosting Resonant Optical Field Emission by Atomic-Thick Dielectric Coating

Abstract

Resonant optical field emission refers to photoelectron emission from nanostructures due to strong optical electric field enhanced by plasmonic resonances. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> It is usually limited by its low emission current and low quantum efficiency. We propose to boost strong-field photoemission by coating the nanopyramid field emitter with an atomic-thick dielectric coating layer. This layer greatly increases the optical field enhancement near the emitter tip, in the meanwhile, creates a reduced double tunneling profile with increased electron emission probability. We performed numerical optical simulations, and use a quantum photoemission model to predict the performance of coated field emitter. We find that with 1 nm thick layer (refractive index of 1.5) coated at the gold nanotip, the electron emission current density can be enhanced by at least two orders of magnitude over a wide range of laser intensity, thanks to the increased local optical field enhancement factor from 35 to 200 (or intensity enhancement factor of 40000). The emission current can further increase with coating of even higher refractive index. The coated field emitter may be selectively excited with different plasmonic resonant modes by choosing the wavelength of laser source, such that the electron emission patterns and the emission current are tunable. This theoretical study paves the way of developing a new category of high performance field emitters operating at tunable optical frequencies.