Double layer-coated carbon nanotubes: Field emission and secondary-electron emission properties under presence of intense electric field
(a) Potential diagram between grounded circular wall and nanotube (or nanorod) that is biased at a negative voltage . (b) Experimental scheme of secondary-electron emission measurement.
plots in FE from pristine and coated nanotubes. (a) represents (i) pristine, (ii) MgO-coated, and (iii) -coated MWNTs, and (b) represents FN plot of them. (Inset image: SEM image of -coated MWNT.)
Band-diagram representation of the quasitunneling process associated with (a) pristine nanotubes, (b) MgO-coated nanotubes, and (c) -coated nanotubes. The work function of the nanotube is assumed to be , and the electron affinities for MgO and CsI are equal to 1.3 and , respectively. The band gaps of MgO and CsI are taken as 8 and , respectively.
(Color online) Emission stability of pristine, MgO-, and -coated SWNT emitters as function of time under vacuum, exposure, and vacuum again, in sequence. In the first stage, we measured FE of the sample at a vacuum pressure of for , added to the chamber up to , then measured FE for another . Next, we measured FE again at a vacuum pressure of after evacuating from the chamber, i.e., the same base pressure with the initial stage of the experiment.
Secondary-electron emission yield of the (a) MgO-coated and -coated SWNTs and (b) MgO-coated and -coated MWNTs. To obtain the line of (-✫-) monolayer coating and (-★-) double-layer coating in Fig. 5, a negative potential was driven on the sample and the remaining parts of the vacuum chamber were grounded.
Measured turn-on fields and calculated values obtained from Figs. 2(a) and 2(b), respectively, for pristine, MgO-coated, and -coated SWNTs/MWNTs. The maximum values obtained from Figs. 5(a) and 5(b) for both the same coated samples.
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