Electric lamp and discharge devices – Discharge devices having a multipointed or serrated edge...
Reexamination Certificate
1998-11-12
2001-05-15
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Discharge devices having a multipointed or serrated edge...
C313S311000, C313S34600R, C313S495000, C445S024000, C445S050000
Reexamination Certificate
active
06232706
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to carbon nanotubes. The present invention also relates to methods for making bundles of aligned carbon nanotubes. The present invention is also related to carbon nanotube field emission devices such as used in flat panel displays.
BACKGROUND
Field emission devices have potential applications in flat panel displays. Field emitters used in flat panel displays must be stable, long lasting and should have a relatively uniform emission over the surface of the display.
Carbon nanotubes are very small tube-shaped molecules having the structure of a graphite molecule rolled into a tube. Carbon nanotubes are electrically conductive along their length, chemically stable, and can have very small diameters (much less than 100 nanometers) and large aspect ratios (length/diameter). Due to these properties and other properties, it has been suggested that carbon nanotubes can be used as field emission devices.
However, it has been unclear how to realize a field emission device exploiting carbon nanotubes. They are difficult to work with in bulk, and, on a microscopic level, often form an impossibly tangled mess resembling a hairball. To produce a useful field emission device for flat panel displays, the carbon nanotubes should be patterned into individual field emitters. A problem with present methods of making carbon nanotube field emitters is that it is not clear how to pattern the carbon nanotube to provide arrays of emitters.
U.S. Pat. No. 5,773,921 to Keesman et al. discloses a field emission device which employs sharp-edged graphite wafers. Carbon nanotubes are disposed on the sharp edge of the graphite wafers and help to increase field emission. The carbon nanotubes are disposed on the graphite wafers by sputtering a nearby graphite target. The carbon nanotubes are not aligned in any way.
U.S. Pat. No. 4,272,699 to Faubel et al. discloses an ion source which uses carbon fiber field emitters. The carbon fibers are bundled together and an electric field is applied to the bundle. The carbon fibers are held by a macroscopic mechanical device that holds the fibers parallel. Such a mechanical device cannot be used with carbon nanotubes, which are orders of magnitude smaller than the carbon fibers used by Faubel et al.
U.S. Pat. No. 5,773,834 to Yamamoto et al. describes a method of making carbon nanotubes on the surface of a carbon-containing substrate by ion bombardment. The carbon nanotubes produced can be used as field emitters. The carbon nanotubes produced according to Yamamoto are not aligned, and in particular, are not aligned perpendicular to the substrate. Also, Yamamoto does not disclose how to pattern the substrate to provide individual field emitters.
Yet another problem with present methods for making carbon nanotube field emitters is that scale-up to large wafers is difficult or not possible.
There exists a need in the art for a method of producing aligned carbon nanotubes. In particular, such aligned carbon nanotubes can be used as superior field emission devices.
OBJECTS AND ADVANTAGES
Accordingly, it is a primary object of the present invention to provide:
1) a method of making aligned bundles of carbon nanotubes; and
2) a field emission device using aligned bundles of carbon nanotubes as field emitters;
3) a field emission device that can have arrays of emitters;
4) a method of making field emitters that can be scaled to large substrates.
These and other objects and advantages will be apparent upon reading the following description and accompanying drawings.
SUMMARY
These objects and advantages are attained by a field emission device having a refractory substrate composed of silicon or quartz, a catalyst material on top of the substrate, and a bundle of aligned parallel carbon nanotubes extending from the catalyst material in a direction perpendicular to the substrate.
Preferably, the substrate has a top layer of porous silicon, with the catalyst material disposed on the porous layer. Particularly, the porous layer can be composed of an upper nanoporous layer with small pores on top of a macroscopic porous layer with larger pores. The catalyst material is preferably iron oxide.
The substrate my also have a smooth, nonporous surface, or a rough surface.
The carbon nanotube bundles may be within 10-22 nanometers in diameter and may be up to 300 microns tall. Also, the carbon nanotubes may be multi-walled.
Preferably, the catalyst material is confined to a patterned region. This results in the bundle extending from the patterned region. The bundle has the same footprint size and shape as the patterned region of the catalyst material.
The carbon nanotube bundles may have a flat top, or a bowl-shaped top.
The present invention also includes a method of making bundles of aligned carbon nanotubes on a substrate of silicon or quartz. The method includes the steps of depositing a catalyst material on a top surface of the substrate, and then exposing the substrate to a carbon containing gas.
Preferably, the substrate is a silicon substrate with a porous top surface. The top surface may be made porous by electrochemical etching.
The catalyst material is preferably iron oxide. The iron oxide may be deposited by depositing a thin film of iron, and then oxidizing the iron film. The iron film may be oxidized by exposing it to oxygen at elevated temperature. Preferably, the original iron film is bout 5 nanometers thick.
The carbon containing gas may be ethylene.
REFERENCES:
patent: 4272699 (1981-06-01), Faubel et al.
patent: 5697827 (1997-12-01), Rabinowitz
patent: 5725524 (1998-03-01), Debe
patent: 5726524 (1998-03-01), Debe
patent: 5773834 (1998-06-01), Yamamoto et al.
patent: 5773921 (1998-06-01), Keesmann et al.
patent: 5872422 (1999-02-01), Xu et al.
patent: 5973444 (1998-03-01), Xu et al.
patent: 0913508 (1988-10-01), None
patent: 9805920 (1998-02-01), None
Chapline Michael
Dai Hongjie
Fan Shou-shan
Franklin Nathan
Tombler Thomas
Haynes Mack
Lumen Intellectual Property Services Inc.
Patel Nimeshkumar D.
The Board of Trustees of the Leland Stanford Junior University
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