▎ 摘　　要

For focused electron beam applications, the combination of high spatial resolution with high beam current is frequently required and a ring-cathode source is one novel way of achieving this. In this study, initial experimental results from a Graphene Ring-Cathode (GRC) field emitter are reported, the first of its kind, which consists of a graphene tube grown in-situ on a sharp nickel wire tip. The diameter of the GRC emitter is around 5 mu m while the edge of the ring is approximately 2.7 nm in thickness. A high emission current of similar to 30 mu A was obtained at a relatively low applied field of similar to 1.75 Vim, corresponding to an overall current density of similar to 7 x 10(4) A/cm(2). This emission current is three orders of magnitude better than that reported on LaB6 nanowire cold field emitter nanowires and a few times better than previous studies on isolated single tip CNT emitters. Also the graphene ring emitter can be precisely aligned to the axis of the beam focusing column unlike free-standing tubular graphene, eliminating errors due to misalignment with the focusing-column. The GRC field emitter is in the category of ring sources predicted to produce a high brightness-high resolution electron beam. (C) 2016 Elsevier Ltd. All rights reserved.