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(a) Zoomed in electrostatic field obtained by finite element simulation showing the edge effect of a CNT pillar with a height and diameter; (b) SEM image of a height and diameter CNT pillar structure; and (c) SEM image of a CPA with an average height and diameter of , demonstrating the mechanical instability of a smaller diameter CNT pillars.
(a) SEM image of a tCPA. [(b) and (c)] Simulated e-field vs radial distance for both arrays of CNT structures, namely the solid pillar and the toroid structures, using COMSOL MULTIPHYSICS. Cut line for electric field vs radius plot was taken to be at the maximum electric field for each of the two structures. Both structures are in height and have the same diameter.
Experimental curves of the tCPA and solid CPA grown directly on (a) FeCrAl alloy substrates and on (b) patterned Fe catalyst films on Si substrates; and (c) stability test of tCPA and solid CPA grown on patterned Fe catalyst films on Si substrates, showing a lower electric field to generate the same 0.5 mA emission current for the tCPA.
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