Electric lamp and discharge devices – Discharge devices having an electrode of particular material
Reexamination Certificate
1998-05-12
2001-10-30
Patel, Ashok (Department: 2875)
Electric lamp and discharge devices
Discharge devices having an electrode of particular material
C313S310000, C313S34600R
Reexamination Certificate
active
06310431
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to the use of annealed carbon soot as an electron field emitter and particularly to its use in making a field emitter cathode.
BACKGROUND OF THE INVENTION
Field emission electron sources, often referred to as field emission materials or field emitters, can be used in a variety of electronic applications, e.g., vacuum electronic devices, flat panel computer and television displays, emission gate amplifiers, klystrons and lighting devices.
Display screens are used in a wide variety of applications such as home and commercial televisions, laptop and desktop computers and indoor and outdoor advertising and information presentations. Flat panel displays are only a few inches thick in contrast to the deep cathode ray tube monitors found on most televisions and desktop computers. Flat panel displays are a necessity for laptop computers, but also provide advantages in weight and size for many of the other applications. Currently laptop computer flat panel displays use liquid crystals which can be switched from a transparent state to an opaque state by the application of small electrical signals. It is difficult to reliably produce these displays in sizes larger than that suitable for laptop computers.
Plasma displays have been proposed as an alternative to liquid crystal displays. A plasma display uses tiny pixel cells of electrically charged gases to produce an image and requires relatively large electrical power to operate.
Flat panel displays having a cathode using a field emission electron source, i.e., a field emission material or field emitter, and a phosphor capable of emitting light upon bombardment by electrons emitted by the field emitter have been proposed. Such displays have the potential for providing the visual display advantages of the conventional cathode ray tube and the depth, weight and power consumption advantages of the other flat panel displays. U.S. Pat. Nos. 4,857,799 and 5,015,912 disclose matrix-addressed flat panel displays using micro-tip cathodes constructed of tungsten, molybdenum or silicon. WO 94-15352, WO 94-15350 and WO 94-28571 disclose flat panel displays wherein the cathodes have relatively flat emission surfaces.
Field emission has been observed in two kinds of nanotube carbon structures. L. A. Chernozatonskii et al., Chem. Phys. Letters 233, 63 (1995) and Mat. Res. Soc. Symp. Proc. Vol. 359, 99 (1995) have produced films of nanotube carbon structures on various substrates by the electron evaporation of graphite in 10
−5
-10
−6
Torr. These films consist of aligned tube-like carbon molecules standing next to one another. Two types of tube-like molecules are formed; the A-tubelites whose structure includes single-layer graphite-like tubules forming filaments-bundles 10-30 nm in diameter and the B-tubelites, including mostly multilayer graphite-like tubes 10-30 nm in diameter with conoid or dome-like caps. They report considerable field electron emission from the surface of these structures and attribute it to the high concentration of the field at the nano-dimensional tips. B. H. Fishbine et al., Mat. Res. Soc. Symp. Proc. Vol. 359, 93 (1995) discuss experiments and theory directed towards the development of a buckytube (i.e., a carbon nanotube) cold field emitter array cathode.
W. A. de Heer & D. Ugarte, Chem. Phys. Letters 207, 480 (1993) and D. Ugarte, Carbon 32, 1245 (1994) discuss the production and heat treatment of carbon soot. Fullerenes are produced by the condensation of electric-arc-produced carbon vapor in a low pressure atmosphere. The fullerenes produced are soluble and easily removed from the soot. The soot is then subjected to a heat treatment and at temperatures of above 2000° C. small closed shell particles are formed. These onion-like particles are hollow polyhedral particles with walls consisting of 2 to about 8 carbon basal plane layers.
What are needed are additional and/or improved field emitting materials suitable for use in field emitter cathodes which are, in turn, useful in display panels and other electronic devices. Other objects and advantages of the invention will become apparent to those skilled in the art upon reference to the figures and the detailed description of the invention which hereinafter follows.
SUMMARY OF THE INVENTION
The present invention provides an electron field emitter comprised of annealed carbon soot, i.e., carbon soot which has been heated to temperatures of at least about 2000° C., preferably at least about 2500° C., and most preferably at least about 2850° C., in an inert atmosphere. During heating, this temperature is preferably maintained for at least about 5 minutes.
The invention also provides for field emitter cathodes comprised of annealed carbon soot attached to the surface of a substrate.
Annealed carbon soot field emitters and field emitter cathodes made therefrom are useful in vacuum electronic devices, flat panel computer and television displays, emission gate amplifiers, klystrons and lighting devices. The display panels can be planar or curved.
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D. Urgate, High-Temperature Behaviour of “Fullerene Black”,Carbon,vol. 32, No. 7, 1245-1248, Dec. 1994.
W. S. Basca et al., Raman Spectroscopy of Closed-Shell Carbon Particles,Chemical Physics Letters,vol. 211, Nos. 4, 5, 346-352, Aug. 20, 1993.
L. A. Chernozatonskii, et al., Electron Field Emission From Nanofilament Carbon Films,Chemical Physics Letters,233, 63-68, Feb. 3, 1995.
Chernozatonskii et al., Nanotube Carbon Structure Tips—A Source of High Field Emission of Electrons,Mat. Res. Soc. Symp. Proc.,359, 99-104, Dec. 1995.
B. H. Fishbine et al., Buckytube Cold Field Emitter Array Cathode Experiments,Mat. Res. Soc. Symp. Proc.,359, 93-98, Dec. 1995.
Walt A. de Heer et al., Carbon Onions Produced By Heat Treatment of Carbon Soot and Their Relation To The 217.5 nm Interstellar Absorption Feature,Chemical Physics Letters,207, 480-486, May 28, 1993.
Kratschmer et al., Solid C60: A New Form of Carbon,Nature,vol. 347, 354-358, Sep. 27, 1990.
Davanloo et al., Laser Plasma Diamond,J. Mater. Res.,vol. 5, No. 11, 2398-2404, Nov., 1990.
Blanchet-Fincher Graciela Beatriz
Holstein William Leo
Shah Syed Ismat Ullah
Subramoney Shekhar
E. I. Du Pont de Nemours and Company
Patel Ashok
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