Carbon nanotube cold cathode
A carbon nanotube layer for a field emission cathode where individual carbon nanotubes or small groups of carbon nanotubes that stick out from the surface more than the rest of the layer are avoided. Electron fields will concentrate on these sharp points, creating an enhanced image on the phosphor, resulting in a more luminous spot than the surroundings. Activation processes further free such carbon nanotubes or groups of carbon nanotubes sticking out from the surface, exasperating the problem.
1 . A carbon nanotube (CNT) cathode comprising CNTs with a variation of lengths less than 20% for 90% of a total quantity of the CNTs.
2 . The cathode of claim 1 , wherein a flatness variation of a CNT coating using the CNTs is less than 20% before or after an activation step.
3 . The cathode of claim 1 , wherein the carbon nanotubes are selected from the group of single-wall carbon nanotubes, double-wall carbon nanotubes, multi-wall carbon nanotubes, buckytubes, carbon fibrils, chemically-modified carbon nanotubes, derivatized carbon nanotubes, metallic carbon nanotubes, semiconducting carbon nanotubes, metallized carbon nanotubes, and combinations thereof.
4 . The cathode of claim 1 , wherein the carbon nanotubes are mixed with particles selected from the group consisting of spherical particles, dish-shaped particles, lamellar particles, rod-like particles, metal particles, semiconductor particles, polymeric particles, ceramic particles, dielectric particles, clay particles, fibers, nanparticles, and combinations thereof.
5 . The cathode of claim 1 , wherein the average length of CNTs is less than 5 microns.
6 . The cathode of claim 5 , wherein a layer of cathode material comprising the CNTs has a thickness which ranges from about 10 nm to about 20 micron.
7 . A field emission display device comprising: a) an anode assembly; and b) a cathode assembly, wherein the cathode assembly comprises:
a substrate;
an electrically conducting layer deposited on the substrate;
a field emission cathode material deposited as a layer over the electrically conducting layer; and
a CNT layer utilizing the CNTs with a variation of lengths less than 20% for 90% of the total quantity of CNTs.
8 . The display of claim 7 , wherein the CNT layer is deposited by spray, screen-printing spin-coating, dispersing, ink-jet printing, electrophoresis deposition, brushing, dipping, dry coating, or other methods.