Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – Forming a platelet shape or a small diameter – elongate,...
Reexamination Certificate
1999-02-18
2001-04-24
Gulakowski, Randy (Department: 1746)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
Forming a platelet shape or a small diameter, elongate,...
C423S345000, C427S589000
Reexamination Certificate
active
06221154
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a method and an apparatus for the growth of beta-silicon carbide nanorods, and to the preparation of patterned field-emitters by chemical vapor deposition (CVD).
BACKGROUND OF THE INVENTION
After the discovery of carbon nanotubes by Iijima (Nature, 354, p.56, 1991), nanotubes and nanowires
anorods of various materials, including Si, SiC, Ge, etc, have been synthesized (Zhang et al., Applied Physics Letter, 72, p.1835, 1998; Dai et al., Nature, 375, p. 769, 1995).
For potential mechanical applications, silicon carbide nanorods have attracted great interest because micrometer-sized SiC whiskers are widely used to strengthen composite materials. Recent work reported that the elasticity and strength of SiC nanostructures are considerably greater than those of larger SiC structures. The physical and electrical properties of silicon carbide also make it an interesting semiconductor for high temperature, high power and high speed device applications.
Various growth techniques have been used to synthesize SiC whiskers with diameters in micrometer or sub-micrometer scale, for example, carbothermal reduction of silica (Hollar and Kim, Ceramic Engineering Science Proceeding, 12, p. 979, 1991), decomposition of organic silicon compounds (Addamiano, Journal of Crystal Growth, 58, p.617, 1982) and reduction between silicon halides and tetrachloromethane (Janeuay, Ceramic Industry, 4, p.42, 1992), etc. Dai et al. (Nature (London), 375, p.769, 1995) have reported the synthesis of SiC nanorods by a two-step method, called carbon nanotube template-mediated growth. However, this process requires the preparation of carbon nanotubes before obtaining SiC nanorods, which implies additional production steps and increased cost. Recently, beta-SiC nanorods with diameters of about 30 nm have been prepared by carbothermal reduction of sol-gel derived silica xerogels containing carbon nano-particles (Meng et al., Solid State Communications, 106, p.215, 1998). However, as the nanorods have to be grown on the surface of xerogels, this method can hardly be applied for electronic device fabrication.
Carbon nanotubes are one of the popular materials used in field-emitters (W. A. de Heer et al., Science, 270, p. 1179, 1995), but silicon carbide nanorods have never been used in this field.
For the purpose of the present specification the term “nanorod” should be understood to define a filament having a diameter of the order of 10 to 100 nm.
SUMMARY OF INVENTION
The present invention provides a method for synthesizing &bgr;-SiC nanorods, and the preparation of patterned field-emitters by a simple one-step synthesizing method.
It is an object of the invention to provide a method and an apparatus for the growth of beta-silicon carbide nanorods, and preparation of patterned field-emitters that may be performed in a CVD chamber.
According to the present invention therefore there is provided a method for the growth of beta-silicon carbide nanorods on a substrate by chemical vapor deposition, wherein solid carbon and solid silicon are used as the carbon and silicon sources, hydrogen is used as a reactant gas, and wherein a metal powder is used as a catalyst.
The source of silicon and carbon used in the method is preferably a plate or target formed from silicon powder, graphite and a metal powder as catalyst. The catalyst may be any of iron, chromium or nickel or a combination thereof.
Preferably the substrate may be a silicon wafer.
The nanorods may be grown by any form of CVD technique, but a preferred method is to use a hot filament excitation technique. The filament temperature may be maintained in the range of from about 1800° C. to 2300° C. The substrate is preferably maintained at a temperature of from about 600° C. to 1300° C.
The distance between the filament and the source may be varied to optimise growth. Preferably the distance is between 1 to 4 mm. Similarly the distance between the filament and the substrate may be varied to optimise growth. Preferably the distance between the substrate and the filament is maintained between about 1 to 7 mm.
The deposition time may also be varied to optimise growth. Typical deposition times vary from 3 to 180 minutes.
The substrate may also preferably be electrically biased, by at least 200 V. The electrical bias may be either purely DC, pulsed DC, AC, or radiofrequency.
The nanorods may preferably be deposited on the substrate to form a pattern. For example in one method of achieving a patterned deposition the substrate is a silicon wafer coated with a silicon dioxide layer and the substrate is photoengraved with a desired pattern prior to deposition of the nanorods, and wherein after deposition of the nanorods the silicon dioxide layer is removed by chemical etching.
A patterned deposition is particularly useful in allowing the present invention to be used to form a patterned field emitter array wherein the individual &bgr;-silicon carbide nanorods form the field emitters of the array.
Viewed from another broad aspect the present invention provides apparatus for the chemical vapor deposition of beta-silicon carbide nanorods, comprising a chemical vapor deposition chamber, means for holding a substrate in the chamber, means for supporting one or more filaments in the chamber, and means for supporting a pressed solid plate in the chamber, the one or more filaments being supported between the substrate and the solid plate in use, means for adjusting the spacing between the substrate and the source, and means for heating the substrate, wherein the solid plate comprises a plate or target formed from compressed silicon powder, graphite powder and a metal powder catalyst.
Preferably the apparatus also includes means for electrically biasing the substrate holding means relative to the pressed solid plate.
Viewed from another broad aspect the present invention provides a method for the preparation of a patterned field-emitter material comprising (a) forming beta-silicon carbide nanorods on a substrate by chemcial vapor deposition, and (b) removing selected areas of said nanorods by chemical etching to a leave a desired pattern.
REFERENCES:
patent: 3632405 (1972-01-01), Knippenberg et al.
patent: 4873070 (1989-10-01), Kaji et al.
patent: 4911781 (1990-03-01), Fox et al.
patent: 5525556 (1996-06-01), Dunmead et al.
patent: 5997832 (1999-12-01), Lieber et al.
patent: 6031250 (2000-02-01), Brandes et al.
patent: 6113722 (2000-09-01), Hoffman et al.
Honglie Dai, et al.; “Synthesis and characterization of carbide nanorods”;Nature;Jun. 1995; vol. 375, pp. 769-772.
Sumio Iijima; “Helical microtubules of graphitic carbon”;Nature;Nov. 7, 1991; vol. 354, pp. 56-58.
Y.F. Zhang, et al.; “Silicon nanowires prepared by laser ablation at high temperature”;Applied Physics Letters;Apr. 13, 1998; vol. 72, No. 15, pp. 1835-1837.
William E. Hollar, Jr., et al.; “Review of VLS SiC Whisker Growth Technology”;Ceram. Eng. Sci. Proc.;1991; pp. 979-991.
Arrigo Addamiano; “Preparation and Properties of 2H SiC Crystals”;Journal of Crystal Growth;1982; pp. 617-622.
Janeuay; “Art: Reinforcing Tomorrow's Technology”;Ceramic Industry;Apr. 1991; pp. 42-44.
G.W. Meng, et al.; “Synthesis of ” A &bgr;-SiC Nanorod within a SiO2 Nanorod “One Dimensional Composite Nanostructures”;Solid State Communications;1998; vol. 106, No. 4, pp. 215-219.
Walt A. de Heer, et al.; “A Carbon Nanotube Field-Emission Electron Source”;Science;Nov. 17, 1995; vol. 270, pp. 1179-1180.
Au Frederick Chi Kan
Bello Igor
Lai Carol Hau Ling
Lee Chun-Sing
Lee Shuit-Tong
City University of Hong Kong
Gulakowski Randy
Merchant & Gould P.C.
Olsen Allan
LandOfFree
Method for growing beta-silicon carbide nanorods, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for growing beta-silicon carbide nanorods, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for growing beta-silicon carbide nanorods, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2467080