Figure 2

(a) Schematic showing CN arrays of various pitch (1, 2, 6 and 8 µm) grown on a single substrate with the corresponding SAFEM current maps at extraction potentials of 140, 170, 200, 230, 260 V. Scans were performed with a constant emission current of 11 nA and a separation of 7 µm. The 6 μm and 8 μm pitch arrays emit more than two orders of magnitude more current (per emitter) than the 1 μm and 2 μm pitch arrays. A linear array separates each disparate CN pitch zone and this accounts for the observed emission current at the boundaries between each pitch area. (b) A typical β map for 1, 2, 6, 8 and 10 µm pitch CN arrays. (c) Theoretical and measured (□) variation in β_array/β_emitter as a function of emitter pitch-to-height ratio. The CN height was ~5 µm and the apparent field enhancement factor was assumed to be ~300. The slightly larger β_emitter used here, compared to the ~250 for individual CNs, was principally due to a measurement artifact. The inset illustrates the potential distribution highlighting the current limiting effects of nearest neighbor electro-static shielding for a CN height/radius of 5 μm/25 nm, an applied electric field of 1 V/μm and a potential line spacing of 0.5 V.