▎ 摘　　要

Cold field emission sources are capable of providing highly coherent and bright electron beams. However, they suffer from some well-known practical difficulties that have prevented their widespread use: unmanageably stringent ultrahigh vacuum requirements, relatively large current instabilities, and rapid emission decays in periods as short as 1-2 h, requiring regular flashing (Joule heating). This paper presents the microfabrication and a successful emission test of a micron-sized concentric ring-graphene cathode cold field emitter, without any observable wall collapse. The cathode is designed to have a nanometer size ring-edge, while its radius can measure several microns or larger, providing stable electron emission under high vacuum conditions. The turn-on electric field of a ring-cathode source can be dramatically lowered by introducing a thin layer of nickel nanoparticles by an in-situ focused ion beam process. The dependence of field enhancement on the anode-cathode distance and the ring-cathode radius has been systematically studied.