Journal
ACS NANO
Volume 14, Issue 7, Pages 8806-8815Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.0c03406
Keywords
resonant photoemission; atomically thick dielectric coating; plasmon field confinement; ultrafast lasers; multiphoton absorption; optical field tunneling
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Funding
- National Research Foundation Singapore [NRF2017-NRF-NSFC002-015]
- A*STAR [SERC A1685b0005]
- Air Force Office of Scientific Research (AFOSR) YIP Grant [FA9550-18-1-0061]
- Office of Naval Research (ONR) YIP Grant [N00014-20-1-2681]
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By proposing an atomically thick dielectric coating on a metal nanoemitter, we theoretically show that the optical field tunneling of ultrafast-laser-induced photoemission can occur at an ultralow incident field strength of 0.03 V/nm. This coating strongly confines plasmonic fields and provides secondary field enhancement beyond the geometrical plasmon field enhancement effect, which can substantially reduce the barrier and enable more efficient photoemission. We numerically demonstrate that a 1 nm thick layer of SiO2 around a Au-nanopyramid will enhance the resonant photoemission current density by 2 orders of magnitude, where the transition from multiphoton absorption to optical field tunneling is accessed at an incident laser intensity at least 10 times lower than that of the bare nanoemitter. The effects of the coating properties such as refractive index, thickness, and geometrical settings are studied, and tunable photoemission is numerically demonstrated by using different ultrafast lasers. Our approach can also directly be extended to nonmetal emitters, to-for example-2D material coatings, and to plasmon-induced hot carrier generation.
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