A High-Brightness, Low-Energy-Spread Au Needle Point Electron Source Nanocold-Cathode Adapted to Low-Power Photoelectric Coexcitation

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Abstract
To address the requirements of vacuum electronic and optoelectronic device applications for next-generation low-power-consumption, high-brightness, low-energy-spread, and tunable electron sources, the pursuit of high-efficiency metal nanocold-cathodes with plasmon-enhanced properties in specific waveband emerges as one of potent solutions. In this study, by screening and comparing the cathode materials and structures, we propose a high-brightness, low-energy-spread Au needle nanocold-cathode point electron source adapted to low-intensity photoelectric coexcitation. The experimental results demonstrate sensitivity to excitation light and outstanding electron emission performance of this point electron source: under the coexcitation of an electrostatic field below ∼1.25 V μm–1 and a supercontinuum-spectrum laser with average intensity of ∼24 W cm–2, the source achieved an emission current of 130 nA, improving by one order of magnitude when compared to the field emission current (∼13 nA) under pure electrostatic field excitation. As the laser excitation intensity increased, its effective work function decreased from 5.1 to 2.7 eV, resulting in a significant reduction of the excitation threshold for electron emission. Benefiting from the plasmon-enhanced light-harvesting effect, the cathode exhibits high sensitivity and selectivity to the wavelength and polarization of the incident light. In the 532–675 nm plasmon resonance band, the emission current exceeds 225 nA at an average excitation intensity of only 7.05 W cm–2, ∼17 times the pure electrostatic field emission current. Meanwhile, the plasmon relaxation preferentially populates high-energy electrons and suppresses the energy spread broadening induced by the space charge effect, thereby achieving a high reduced brightness of 6.89 × 109 A m–2 sr–1 V–1 and a low-energy spread of approximately 0.5 eV. This low-power photoelectric coexcitation scheme greatly relaxes the requirements on the excitation source, providing a route for the miniaturization and integration of vacuum optoelectronic point electron sources.
Funding Information
  • Sun Yat-sen University
  • Science and Technology Planning Project of Guangdong Province (2023B1212060025)
  • Basic and Applied Basic Research Foundation of Guangdong Province (2025A1515010637)
  • National Basic Research Program of China (973 Program) (2025YFA1213400)
  • Guangdong Science and Technology Department (2025TQ09X991)
  • National Natural Science Foundation of China (NSFC) (62471498)

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