High electric field fabrication of oriented nanostructures
A method of growing carbon nanostructures on a conductive substrate without the need for a vacuum or low-pressure environment provides high electrical field strengths to generate the necessary carbon ions from a feedstock gas and to promote alignment and separation of the resulting structures. In one embodiment, substantially uniform “vertical” nanostructures may be formed around the periphery of an extended wire for use in corona discharge applications or the like. Growth on a planar substrate may provide use with a variety of apparatus requiring a high specific surface conductor such as capacitors, batteries, and solar cells.
1. A method of growing oriented nanostructures comprising the steps of:
(a) providing a conductive substrate for receiving the nanostructures;
(b) introducing a carbon feedstock gas to flow at substantially atmospheric pressure in a space proximate to the conductive substrate; and
(c) imposing a substantially DC electrical field between the conductive substrate and at least one proximate electrode at substantially atmospheric pressure to break down the carbon feedstock gas and to orient carbon of the carbon feedstock gas for reconstitution as carbon nanostructures on the substrate.
2. The method of claim 1 wherein the electrical field is in excess of 100 volts per millimeter.
3. The method of claim 2 wherein structures of the electrodes have substantially different facing areas to present an asymmetric electrical field.
4. The method of claim 3 including the step of preheating the carbon feedstock gas.
5. The method of claim 1 further including the step of introducing oxygen radicals to the carbon feedstock gas.
6. The method of claim 5 wherein the oxygen radicals are OH radicals derived from water vapor.
7. The method of claim 5 further including the step of thermally annealing the substrate in a reducing environment after formation of the carbon nanostructures.
8. The method of claim 1 wherein the carbon nanostructures are carbon nanowalls.
9. The method of claim 1 wherein the proximate electrode is at least one sharpened and conductive tip facing the conductive substrate and the conductive substrate is a substantially planar surface.
10. The method of claim 9 wherein the proximate electrode is an array of sharp and conductive tips.
11. The method of claim 1 wherein the proximate electrode is a substantially planar surface and the conductive substrate is an elongated wire.
12. The method of claim 1 wherein the substrate is provided free from catalytic materials.
13. The method of claim 1 wherein the substrate is provided with electrically attached carbon nanotubes and the carbon nanostructures are carbon nanowalls growing from the carbon nanotubes.
14. The method of claim 1 wherein the substrate includes at least a first and second conductive region spatially separated from each other and adapted to permit mutual electrical isolation of the first and second conductive regions after step (c).
15. An array of carbon nanostructures comprising carbon nanotubes having first ends attached to a conductive substrate and extending outward therefrom and second ends bonded to at least one carbon nanowall by carbon sp2 bonds to be intrinsically fused thereto, the at least one carbon nanowall extending outward from the second ends and removed from the conductive substrate.