Low Work Function Material
The present invention is directed toward methods for incorporating low work function metals and salts of such metals into carbon nanotubes for use as field emitting materials. The present invention is also directed toward field emission devices, and associated components, comprising treated carbon nanotubes that have, incorporated into them, low work function metals and/or metal salts, and methods for making same. The treatments of the carbon nanotubes with the low work function metals and/or metal salts serve to improve their field emission properties relative to untreated carbon nanotubes when employed as a cathode material in field emission devices.
1 . A method comprising the steps of:
a) dispersing carbon nanotubes in a metal salt solution comprising a solvent; and
b) removing the solvent to yield metal salt-treated carbon nanotubes.
2 . The method of claim 1 , wherein the carbon nanotubes are ground into a powder prior to dispersing them in the metal salt solution.
3 . The method of claim 1 , wherein the metal salt is selected from the group consisting of alkali metal salts, alkaline earth metal salts, transition metal salts, p-block metal salts, rare earth metal salts, and combinations thereof.
4 . The method of claim 1 , wherein the metal salt is a cesium salt.
5 . The method of claim 1 , wherein the solvent is water.
6 . The method of claim 1 , further comprising a step of washing the metal salt-treated carbon nanotubes.
7 . The method of claim 1 , further comprising a step of drying the metal salt-treated carbon nanotubes.
8 - 11 . (canceled)
12 . A method for making a field emission cathode comprising the steps of:
a) providing a substrate; and
b) depositing metal salt-treated carbon nanotubes onto the substrate.
13 . The method of claim 12 , wherein the metal salt-treated carbon nanotubes comprise an alkali metal salt.
14 . The method of claim 12 , wherein the metal salt-treated carbon nanotubes comprise a cesium salt.
15 . The method of claim 12 , wherein the metal salt-treated carbon nanotubes comprise carbon nanotubes selected from the group consisting of single-wall carbon nanotubes, double-wall carbon nanotubes, multi-wall carbon nanotubes, carbon fibrils, buckytubes, metallic carbon nanotubes, semi-conducting carbon nanotubes, semi-metallic carbon nanotubes, chiral carbon nanotubes, chemically-modified carbon nanotubes, capped carbon nanotubes, open-ended carbon nanotubes, endohedrally-modified carbon nanotubes, and combinations thereof.
16 . The method of claim 12 , wherein the metal salt-treated carbon nanotubes are deposited by a technique selected from the group consisting of spraying, electrophoretic deposition, dipping, screen-printing, ink-jet printing, dispensing, brushing, and combinations thereof.
17 . The method of claim 12 , wherein the metal salt-treated carbon nanotubes are deposited by a technique comprising spraying solvent-dispersed metal salt-treated carbon nanotubes onto the substrate.
18 . The method of claim 17 , wherein the substrate is heated during the deposition.
19 . The method of claim 12 , further comprising a step of reduction whereby at least some of the metal salt is reduced to metal.
20 . The method of claim 12 , further comprising a step of tape activation.