Stable field emission from arrays of vertically aligned free-standing metallic nanowires

Stephane Xavier et al 2008 Nanotechnology 19 215601 (7pp) doi: 10.1088/0957-4484/19/21/215601

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Stephane Xavier^1,5, Stefan Mátéfi-Tempfli², Etienne Ferain³, Stephen Purcell⁴, Shaïma Enouz-Védrenne¹, Laurent Gangloff¹, Eric Minoux¹, Ludovic Hudanski¹, Pascal Vincent⁴, Jean-Philippe Schnell¹, Didier Pribat¹, Luc Piraux² and Pierre Legagneux^1,5
1 Nanocarb Laboratory, Thales—Ecole Polytechnique, Route Départementale 128, 91767 Palaiseau, France
² Unité de Physico-Chimie et de Physique des Matériaux, Croix du sud 1, B-1348 Louvain-la-Neuve, Belgium
³ Unité de Physique et de Chimie des Hauts Polymères, Croix du sud 1, B-1348 Louvain-la-Neuve, Belgium
⁴ Laboratoire de Physique de la Matière Condensée et Nanostructures, Université Claude Bernard de Lyon 1, CNRS UMR 5586, 43 Blvd du 11 Novembre 1918, 69622 Villeurbanne, France
⁵ Authors to whom any correspondence should be addressed
E-mail: stephane.xavier@thalesgroup.com and pierre.legagneux@thalesgroup.com

Abstract. We present a fully elaborated process to grow arrays of metallic nanowires with controlled geometry and density, based on electrochemical filling of nanopores in track-etched templates. Nanowire growth is performed at room temperature, atmospheric pressure and is compatible with low cost fabrication and large surfaces. This technique offers an excellent control of the orientation, shape and nanowires density. It is applied to fabricate field emission arrays with a good control of the emission site density. We have prepared Co, Ni, Cu and Rh nanowires with a height of 3 µm, a diameter of 80 nm and a density of ~10⁷ cm^-2. The electron field emission measurements and total energy distributions show that the as-grown nanowires exhibit a complex behaviour, first with emission activation under high field, followed by unstable emission. A model taking into account the effect of an oxide layer covering the nanowire surface is developed to explain this particular field emission behaviour. Finally, we present an in situ cleaning procedure by ion bombardment that collectively removes this oxide layer, leading to a stable and reproducible emission behaviour. After treatment, the emission current density is ~1 mA cm^-2 for a 30 V µm^-1 applied electric field.

Print publication: Issue 21 (28 May 2008)
Received 28 January 2008, in final form 13 March 2008
Published 21 April 2008

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Conclusion from PDF:
4. Conclusion
In conclusion, metallic nanowires grown in supported
nanoporous track-etched templates are a competitive solution
for the realization of field emission displays (FEDs) or
backlight units for liquid crystal displays. The growth
process is performed at room temperature and atmospheric
pressure, and is compatible with very large surfaces. With
this process, we have obtained nanowires made of different
materials (Co, Ni, Cu and Rh). The field emission and total
energy distribution measurements have shown that, because
of the presence of an oxide layer observed by TEM on asgrown
nanowire surfaces, emission activation is necessary
and the emission is unstable in that case. We propose here
an in situ treatment with ion bombardment to collectively
‘clean’ the nanowire array and eliminate this oxide layer.
After this in situ treatment, the NWs exhibit a stable and
reproducible emission. Activation is no longer required. We
have observed a good emission stability for several hours. This
process can be potentially used for field emission displays,
as the achieved current density is compatible with such an
application.