Schematic representation of the thermal CVD process for the growth of CPAs directly on polished and photolithography patterned catalytic alloy substrates. A chromium and molybdenum layer patterned with photolithography selectively inhibits CNT growth on the -coated areas.
SEM images of MWCNT arrays produced by various photolithographic patterns and CVD growth times: (a) growth of a circular patterned film array on polished NiCr, diameter and edge-to-edge separation; (b) growth of square patterned film array on polished NiCr, diameter and edge-to-edge separation; (c) growth of circular patterned CPA on polished Kanthal, diameter and edge-to-edge separation; and (d) growth on square patterned CPA on polished Kanthal, diameter and edge-to-edge separation.
(a) FE plots for various types of MWCNT cathodes, including continuous films of varying density, patterned film arrays, and a CPA. (b) SEM images of patterned film arrays with three different MWCNT densities obtained from CVD growth on polished NiCr substrates.
Computed electrostatic field of a pillar as a function of radial position and pillar height. The electric field is magnified greatly at the pillar edge in a nonlinear fashion with increasing pillar height, while the electric field in the center of the pillar rises at a smaller rate with increasing pillar height. A schematic of the simulated structure is shown in the inset; a circular pillar of variable height , radius set at , and an edge radius of curvature, , set at was used.
A plot of vs pillar height shows that increases nearly exponentially with increasing pillar height. Changes in height between 0 and have a particularly large effect on , and approaches an asymptotic value beyond a pillar height of .
SEM images of patterned MWCNTs before and after high current FE: [(a) and (b)] patterned film array before FE; [(c) and (d)] CPA before FE; [(e) and (f)] patterned film array after FE; and [(g) and (h)] CPA after FE. Damage to the patterned film arrays can be clearly seen as evidenced by missing MWCNTs, whereas no alterations in the CPA structures were observed after high current emission.
Summary of FE results from patterned NiCr and Kanthal CPAs.
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