It is known that a single tip in a field (not explosive) emission allows to yield current density practically equal to electron stream towards the solid-vacuum boundary [1]. According to the measurements of electrical conductance [2], individual CNT is capable to sustain the current amounting to 2 mA. This value corresponds to current densities 1e7-1e8 A/sq.cm. Experimentally observed ultimate field emission current from individual CNT amounts to ~100 µΑ [3].
Taking into account the moderate emission current (~10 µΑ) from individual tip, the great number of potential emitters from CNT must allow to get total emission current up to 100 A from 1 sq.cm area. By present time there is a series of the experimental works in which the current density level close to the theoretical value is reported. For example, in [4] the current density up to 1 A/sq.cm for 16 emitters with area 0.5x0.5 sq.mm each is shown. The density of vertically standing CNT was 1e6 1/sq.cm. Peak values of the current of 30 mA at modulation frequency of 1.5 GHz and 29 MV/m field intensity were achieved.
In this connection, the decrease in measured currents for larger emitter areas (up to 1 sq.cm) seems to be unexpected. The record figures reached for emission are presented in [5]. For real emitters with total area about 1 sq.cm these values are less than 1 mA.
In our work we explore field emission properties of a new class of the emitters formed by coating the CNT-polymer composite film onto the flat metal substrate. At present we succeeded to obtain 125 mA of emission current at 7 kV voltage potential for interelectrode gap of 0.5 mm (14 V/µm) for the field emitter diameter of 1 cm. The stable values of emission current of 10-15 mA at field intensity amplitude 7-8 V/µm have been obtained at the half-period sine voltage of 50 Hz.
This study was performed within the framework of the "New Materials and Structures" program PhSD RAS and the Program of St.-Petersburg Scientific Center RAS.
[1] G.N. Fursey, Sor. Ed. J. 11 (2000) 96
[2] W.I. Milne et al., Diam. Rel. Mat. 12 (2003) 422
[3] E. Minoux et al., Nanolett. 5 (2005) 2135
[4] K.B.K. Teo et al., Nature 437 (2005) 968
[5] W.I. Milne et al., J. Vac. Sci. Tech. 24 (2006) 345
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