LAUSR

Electrically driven on-chip electron sources that do not need to be heated have been long pursued because the current thermionic electron sources show the problems of high power consumption, slow temporal response, bulky size, etc., but their realization remains challenging. Here we show that a nanogap formed by two electrodes on a silicon oxide substrate functions as an electron-emitting nanodiode after the silicon oxide in the nanogap is electrically switched to a high-resistance conducting state. A nanodiode based on graphene electrodes can be turned on by a voltage of ~7 V in ~100 ns and show an emission current of up to several microamperes, corresponding to an emission density of ~10^6 A cm^-2 and emission efficiency as high as 16.6%. We attribute the electron emission to be generated from a metal-insulator-metal tunneling diode on the substrate surface formed by the rupture of conducting filaments in silicon oxide. An array of 100 nanodiodes exhibits a global emission density of 5 A cm^-2 and stable emission with negligible current degradation over tens of hours under modest vacuum. The combined advantages of a low operating voltage, fast temporal response, high emission density and efficiency, convenient fabrication and integration, and stable emission in modest vacuum make silicon oxide electron-emitting nanodiodes a promising on-chip alternative to thermionic emission sources.