Enhanced electron field emission from carbon nanotubes without activation
A method for forming cathodes for use in field emission devices using nanoparticles, such as carbon nanotubes (CNTs), is disclosed. The CNT layer comprises the electron emitting material on the surface of the cathode. Using the methods of the present invention, the density of the deposited CNTs may be modulated by forming emitter islands on the surface of the cathode. The size and distribution of the CNT emitter islands serve to optimize the field emission properties of the resulting CNT layer. In one embodiment, the CNT emitter islands are formed using a screen-printing deposition method. The present invention may be practiced without further process steps after deposition which activate or align the carbon nanotubes for field emission.
1. A method for forming a field emission cathode device comprising the step of depositing a surface layer of nanoparticles-material on a substrate such that said surface layer of nanoparticles-material forms a plurality of field emitting islands that are physically isolated from each other, wherein the nanoparticle-material is deposited using a 355-mesh screen having a mesh opening of about 25-30 microns wide.
2. The method of claim 1 , wherein said field emitting islands of nanoparticle-material:
are greater than about 10 nm wide;
have more than about 10 nm distance between each other; and
are greater than about 1 nm thick.
3. The method of claim 1 , wherein said substrate comprises a conducting electrode layer.
4. The method of claim 1 , wherein said nanoparticles-material layer is deposited by methods chosen from the group consisting of: screen-printing, brushing, spraying, dispersing, ink-jet printing, nano-imprinting, dip-pen lithography, x-ray lithography, optical lithography, and any combination thereof.
5. The method of claim 1 , wherein the nanoparticles-material contains carbon nanotubes selected from the group consisting of: single-wall carbon nanotubes, double-wall carbon nanotubes, multiwall carbon nanotubes, buckytubes, carbon fibrils, chemically-modified carbon nanotubes, derivatized carbon nanotubes, metallic carbon nanotubes, semiconducting carbon nanotubes, and any combination thereof.
6. The method of claim 1 , wherein the nanoparticle-material contains 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, and any combination thereof.
7. The method of claim 1 , wherein the nanoparticles-material is screen-printed on the substrate to thereby form the plurality of field emitting islands of the nanoparticles-material that are physically isolated from each other.