SEM image of a part of the double-gate FEA with 4 × 104 molybdenum emitter tips. The insets show a close up of a single emitter with extraction and collimation gate aperture openings (left bottom) and the tip-apex (right top).
Schematic illustration of the experimental setup. The double-gate FEA in the field emission microscope generates a collimated electron beam under the potential voltages Vem , Vext , and Vcol . The currents Iem , Iext , and Icol were simultaneously monitored to evaluate the current Inet reaching the screen. Using a retractable Faraday cup (not shown), Inet can be measured directly.
Images of field emission beams generated by the double-gate FEA with 4 × 104 emitters at different collimation strength denoted by the ratio kcol ( ). (a)-(c) were observed before the Ne gas conditioning with Vem of −72 V, whereas (d)-(f) were observed after the Ne gas conditioning with Vem of −69 V. The maximum current reaching the screen at zero kcol was ∼ 5 μA for both cases. All the beams are displayed with the same intensity scale, highlighting the large beam brightness enhancement at kcol of 0.99 and 1.00.
Variation of Rs with the increase of kcol before and after the neon conditioning. The rms radius R 0 equal to 0.57 mm of the FEA was subtracted from Rs for the experiment. The solid lines show the calculated Rs versus kcol obtained by the full 3D simulation of a single-emitter at values of Vem equal to −72 V and −69 V. The beam images at kcol equal to 0 and 1.00 at Vem of −69 V obtained after the neon gas conditioning are also displayed.
Current-voltage characteristics of the 40 000 tip FEA measured during the beam collimation experiment of Figure 3 , (a) before the neon gas conditioning with Vem of −72 V, (b) after the neon gas conditioning with Vem of −69 V. The simulated current-voltage characteristics (c) at Vem of −72 V and (d) at Vem of −69 V were obtained together with the calculation of the relations displayed in Figure 4 .
(a) Evolution of the emission current-voltage characteristics during the conditioning. (b) Fowler-Nordheim plot of the I-Vs shown in (a). (c) The evolution of the Fowler-Nordheim fitting parameters AFN and BFN in UHV and during the neon gas conditioning.
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