Enhanced field electron emission properties of hierarchically structured MWCNT-based cold cathodes

Abstract

Hierarchically structured MWCNT (h-MWCNT)-based cold cathodes were successfully achieved by means of a relatively simple and highly effective approach consisting of the appropriate combination of KOH-based pyramidal texturing of Si (100) substrates and PECVD growth of vertically aligned MWCNTs. By controlling the aspect ratio (AR) of the Si pyramids, we were able to tune the field electron emission (FEE) properties of the h-MWCNT cathodes. Indeed, when the AR is increased from 0 (flat Si) to 0.6, not only the emitted current density was found to increase exponentially, but more importantly its associated threshold field (TF) was reduced from 3.52 V/μm to reach a value as low as 1.95 V/μm. The analysis of the J-E emission curves in the light of the conventional Fowler-Nordheim model revealed the existence of two distinct low-field (LF) and high-field (HF) FEE regimes. In both regimes, the hierarchical structuring was found to increase significantly the associated βLF and βHF field enhancement factors of the h-MWCNT cathodes (by a factor of 1.7 and 2.2, respectively). Pyramidal texturing of the cathodes is believed to favor vacuum space charge effects, which could be invoked to account for the significant enhancement of the FEE, particularly in the HF regime where a βHF as high as 6,980 was obtained for the highest AR value of 0.6.

Field electron emission enhancement of graphenated MWCNTs emitters following their decoration with Au nanoparticles by a pulsed laser ablation process

“…These methods typically rely on processes that create smaller-diameter emitter arrays, which enhance the electric field at the emitter tip. Geometry tailoring is shown to significantly improve the FEE properties, but such approaches generally require complex, laborious, and costly microfabrication processing [7][8][9].…”

Improved Field Emission Properties of Carbon Nanostructures by Laser Surface Engineering

“…This suggests that the observed electron emission from both cathodes follows the quantum tunnelling theory. In the high field, F-N plots show a saturation behavior that may be due to thermionic emission, series resistance, and cathode geometry [ 35 , 36 ]. The field enhancement factor β (given the known fitting value of b = , and assuming Φ = 5 eV for carbon nanotubes, ref.…”

“…In practice, to correctly calculate the electric field of the CNT cathode, it requires a meshing resolution of a few nanometers, or at least less than a nanotube diameter (~5 nm). Such resolution exceeds the number of degrees of freedom, and the available computer memory; hence, in this work we used an alternative approach to semi-quantitatively estimate field enhancement which is based on the multistage field effects [ 36 , 38 ]. The total field enhancement factor (β ∑ ) is a product of the multistage cathode geometry (β ∑ = β hollow-array × β CNT-film ); the simulation is to estimate β hollow-array .…”

Parametrically Optimized Carbon Nanotube-Coated Cold Cathode Spindt Arrays

“…Making use of Spindts increases manufacturability, whilst the CNTs ensure a high emission current per unit area. Such CNT-coated Spindt-type emitters have been realized elsewhere [ 17 , 18 ], with the system benefitting from the low voltage field emission of the CNTs coupled to the large area, highly reproducible fabrication of the micronscale Spindts. Nevertheless, the geometry of such CNT-coated Spindt arrays must be optimized in order to satisfy various system requirements.…”