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

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.