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  Systems and methods of synthesis of extended length nanostructuresRelated Patent Categories: Stock Material Or Miscellaneous Articles, Web Or Sheet Containing Structurally Defined Element Or Component, Composite Having Voids In A Component (e.g., Porous, Cellular, Etc.), Voids Specified As MicroThe Patent Description & Claims data below is from USPTO Patent Application 20080014431. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED U.S. APPLICATION(S) [0001] This application claims priority to Provisional Application Ser. No. 60/536,767, filed Jan. 15, 2004, which application is hereby incorporated herein by reference. FIELD OF THE INVENTION [0002] The present invention relates to the synthesis of nanostructures, and more particularly, to the use of chemical vapor deposition (CVD) for the synthesis of such nanostructures. RELATED ART [0003] Carbon nanotubes have been known for some time. Examples of literature disclosing carbon nanotubes include, J. Catalysis, 37, 101 (1975); Journal of Crystal Growth 32, 35 (1976); "Formation of Filamentous Carbon", Chemistry of Physics of Carbon, ed. Philip L. Walker, Jr. and Peter Thrower, Vol. 14, Marcel Dekker, Inc, New York and Basel, 1978; and U.S. Pat. No. 4,663,230, issued Dec. 6, 1984. More recent interest in carbon filamentary material was stimulated by a paper by Sumio Iijima in Nature 354, 56 (1991) describing a similar material. These early studies and the work that has developed from these studies resulted in a material with remarkable mechanical and electronic properties. However, the nanotubes that these studies produced have been short and are limited for composite material reinforcement, where longer tubes may be necessary to get good load transfer from tube to tube. [0004] Some reports of long carbon nanotubes have appeared in the literature, whereby the nanotubes are grown via chemical-vapor deposition (CVD) processes. There are typically two growth modes using CVD. In "tip growth", nanotubes may be grown from catalytic particles suspended in a reaction gas, which serves as a feedstock for carbon. In this approach, if the nanotube is bonded to a substrate, the catalyst particle moves farther from the substrate as the nanotube grows. Alternatively, a catalyst particle may be embedded in a nanotube fiber that grows in two directions from the particle. In a second mode, "base growth", the catalyst particle itself is bonded to a substrate, and the nanotube fiber that grows from this particle increases in length. Base growth is typically performed on solid, non-porous substrates. Thus, diffusion of feedstock gas to the catalytic particle can become limited as a forest of nanotube fibers grows from a collection of catalytic particles on the substrate. The growing forest of fibers can create an obstruction of gas flow to the catalyst base, and can eventually limit the length of the nanotubes. Lengths of nanotubes grown with these techniques are typically about 100 microns to 500 microns long. [0005] In addition, unlike carbon nanotubes, little is known about the growth of periodic or aperiodic (carbon) prismatic structures. Carbon structures resembling "horns", which likely have been patterned by odd-shaped regions of catalyst, have been observed in SEM images. Nevertheless, it is believed that synthesis of prismatic structures having continuous graphene walls from a designed pattern has not been possible. [0006] Accordingly, it would be desirable to synthesize extended length nanostructures whereby there is minimal contamination to the nanostructures, whereby there is substantially no limit to the length of the nanostructures, and whereby the shape of the nanostructures can be specifically patterned. SUMMARY OF THE INVENTION [0007] The present invention provides, in an embodiment, a system for synthesizing nanostructures. The system includes a housing having a first end, an opposite second end, and a passageway extending between the first and second end. The system also includes a porous substrate situated within the passageway of the housing, and having an upstream surface and a downstream surface. A plurality of catalyst particles can be provided on the downstream surface of the substrate, and from which nanostructures can be synthesized upon interaction with a reaction gas. A heating mechanism may be placed circumferentially about the substrate for generating energy sufficient to maintain an environment within which nanostructures can be synthesized. A pair of flanges may be provided, each capping one end of the housing. An inlet may be positioned across the flange capping the first end of the housing for introducing reaction gas to the porous substrate. An exhaust port may be provided across the flange capping the second end of the housing for exhausting the reaction waste product. In one embodiment, a tube may be provided within the passageway of the housing to accommodate the porous substrate. In addition, a pair of electrodes may be provided, such that the substrate is situated therebetween to generate an electric field to support the nanostructures during growth. Alternatively, one electrode may be provided to accommodate the substrate concentrically therein. In this embodiment, the substrate may act as a second electrode. A mechanism may also be provided for collecting the grown nanostructures. [0008] The present invention also provides, in one embodiment, a substrate for the synthesis of nanostructures. The substrate includes a porous body having an upstream surface and a downstream surface. The substrate further includes a plurality of catalyst particles deposited on the downstream surface of the substrate, and from which nanostructures may be synthesized. The porosity of the body provides pathways through which a reaction gas can travel across the upstream surface and out the downstream surface to initiate growth of nanostructures from the catalyst particles. The substrate, in one embodiment, may be provided with pore size ranging from about 0.5 nm to about 500 microns, and a void fraction of from about 10 percent to about 95 percent. The catalyst particles on the substrate may range from about 1 nm to about 50 nm. [0009] The present invention further provides, in one embodiment, a method for synthesizing nanostructures. The method includes, providing a porous substrate having an upstream surface and a downstream surface. Next, a plurality of catalyst particles may be deposited on to the downstream surface of the substrate. In one embodiment, the particles may be deposited directly onto the substrate by one of, precipitation of the particles solution, ball milling, sputtering, electrochemical reduction, or atomization. In another embodiment, the catalyst particles may be provided by chemical reduction of metallic salts deposited from solution and dried on to the substrate. In a further embodiment, catalyst particles may be provided by reduction of particles deposited from suspension and dried on to the substrate. In yet another embodiment, the catalyst particles may be provided by reduction of metallic salts deposited from solution and dried on to the substrate. The deposited catalyst particles, in an embodiment, may be distributed substantially evenly across the downstream surface of the substrate. Thereafter, a flow of reaction gas may be directed across the upstream surface and through the downstream surface of the substrate. The reaction gas may subsequently be permitted to decompose about the catalyst particles to generate constituent atoms. The atoms may then be allowed to diffuse onto the catalyst particles for synthesis of nanostructures therefrom. The method also provides an electric field generated from electrodes to support the nanostructures while they are growing, and a supply of evacuation gas to remove reaction waste product. [0010] In another embodiment, the present invention provides a method for synthesizing prismatic structures. The method includes, providing a surface upon which a plurality of catalyst lines can be created. Next, catalyst lines can be generated on the surface, so as to form a designed pattern from which prismatic structures can be synthesized. Thereafter, a flow of reaction gas may be directed to the catalyst lines in the designed pattern. The reaction gas may subsequently be decomposed about the catalyst lines to generate constituent atoms. Diffusion of the constituent atoms may then be permitted onto the catalyst lines for the synthesis of prismatic structures. As diffusion occurs, planar carbon nanostructures (i.e., graphene planes) start to self-assemble from the lines of catalyst, in a direction perpendicular to that of the surface on which the catalyst lines are patterned. It should be noted that junctions of catalyst lines form junctions between graphene planes, and that continuous growth of the prismatic structure can occur, so long as reagent gas is continually supplied to the catalyst lines. [0011] A method is further provided, in accordance with one embodiment of the present invention, for collecting nanostructures. The method includes, providing a cylindrical surface around which the nanostructures can be collected. As the cylindrical surface rotates, the speed at which it moves may be controlled to match the speed of the slow growing nanostructures. Next, the nanostructures growing from the substrate are caused to oscillate in parallel to an axis of the cylindrical surface with an amplitude sufficiently large to accommodate fast growing nanostructures on a sinuous path upon the cylindrical surface. Thereafter, the slow growing nanostructures may be laid down on circumferential loci of the cylindrical surface, while the fast growing nanostructures may be laid down on a sinuous locus of maximum amplitude. [0012] The present invention also provides a material comprising at least one prismatic structure formed from a plurality of joined graphene planes, and the utilization of nanostructures and prismatic structures in various commercial applications. BRIEF DESCRIPTION OF THE DRAWINGS [0013] FIG. 1 illustrates, in accordance with one embodiment of the present invention, a system for the synthesis of extended length nanostructures. [0014] FIG. 2 illustrates an area within the system shown in FIG. 1 for growing extended length nanostructures. [0015] FIG. 3 illustrates a variation in the location of the heating mechanism for use in connection with the system illustrated in FIG. 1. [0016] FIGS. 4A and B illustrate, in accordance with another embodiment of the present invention, a system for the synthesis of extended length nanostructures. [0017] FIG. 5 illustrates a flow chart depicting, in accordance with one embodiment of the present invention, a process for synthesizing extended length nanostructures. [0018] FIG. 6 illustrates a micrograph, obtained via transmission electron microscopy, of a nanotube synthesized in accordance with an embodiment of the present invention. [0019] FIG. 7 illustrates a process for creating a template for synthesizing prismatic structures, in accordance with an embodiment of the present invention. Continue reading... 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