Field emitters based on porous aluminum oxide templates

Abstract

The field-emission properties of cold cathodes produced using nano-porous anodic aluminum oxide (AAO) templates are reported. Several types of field emitters were fabricated: aligned copper nanowires grown halfway up the parallel nano-pores of the AAO; aligned multiwalled carbon nanotubes grown to the top of the pores; surfaces overgrown with random tangles of carbon nanotubes; and empty AAO templates. Significant field-emission currents (field enhancement values ∼ 1800) were obtained at threshold voltages as low as 80 V (corresponding to fields of 3–4 V/μm) on samples of nanotube tangles. Perfectly aligned carbon nanotubes were less efficient field emitters and had lower field enhancement values. These observations are explained in terms of the mean separation of active tips in the two sets of samples. Empty templates and metal nanowire arrays show lower field enhancements and higher threshold electric fields (40–70 V/μm). In these samples significant field-emission currents are produced at relatively low applied voltages of 110–300 V due to the small inter-electrode separations achieved on depositing a metal grid directly on the surface of the porous template.

Microscopy and computational modelling to elucidate the enhancement factor for field electron emitters

“…Reported values for g range from a few tens to ten thousand or more (Xu, 1995;Davydov et al, 1999). The knowledge of g enables the field F t at the surface of the emitting tip to be found from the macroscopic field, hence b from Eq.…”

Fabrication and Applications of Metal Nanowire Arrays Electrodeposited in Ordered Porous Templates

“…Ratio of anode to cathode currents is constant while the calculated enhancement factor was almost the same as the aspect ratio of the Co wires. The turn-on voltage (12 V/μm) is comparable to that of CNTs (1-10 V/μm) [Davydov et al, 1999]. Deviation from the F-N relationship (solid line) at higher fields is attributed to an undesired serial resistance (R = 4 MΩ) in the experimental set-up.…”

Growth of Carbon Nanofibers on Electroless Ni-P Alloy Catalyst

“…These excellent field emission properties of Ni-P catalyzed-CNTs may be attributed to the random orientation and small diameter of CNTs. As Davydov and co-workers 24 pointed out, perfectly aligned carbon nanotubes were less efficient field emitters and had lower field enhancement than chaotic carbon nanotubes. Groning and co-workers 25 also suggested that some random CNTs exhibited better field emission properties than aligned CNTs.…”