Abstract:
An apparatus for manufacturing carbon nanotubes is provided. The apparatus includes a reaction chamber having a first inlet configured for introducing a carbon-containing gas thereinto and a first outlet; a heater for elevating an interior temperature of the reaction chamber, wherein the reaction chamber is configured for accommodating a substrate and the first inlet defines a route for channeling the introduced carbon-containing gas toward the substrate, the route being substantially perpendicular to a main plane of the substrate.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to carbon nanotubes, and more particularly to an apparatus and method for manufacturing carbon nanotubes by chemical vapor deposition (CVD).  
         [0003]     2. Discussion of Related Art  
         [0004]     Generally, it has been known that carbon nanotubes can be manufactured by methods including resistance heating, plasma discharge such as arc discharge with a carbon rod as a raw material, laser ablation, and chemical vapor deposition using acetylene gas.  
         [0005]     Chemical vapor deposition is a method of generating carbon nanotubes by a chemical decomposition reaction of the carbon-containing gas, using acetylene gas, methane gas, or the like containing carbon as a raw material. The chemical vapor deposition depends on a chemical reaction occurring in the carbon-source gas as part of a thermal decomposition process, thereby enabling the manufacture of high-purity carbon nanotubes. As shown in  FIG. 3 , a typical CVD apparatus  10  includes a horizontally disposed quartz tube  30  configured to accommodate a substrate  20 , upon which nanotubes can be grown. The quartz tube  30  has an inlet  32  and a corresponding outlet  34 . The substrate  20  has a catalyst layer  22  formed on a top surface thereof. During nanotube growth, a flow of carbon-containing gas is horizontally provided to move along and inside the quartz tube  30 , thereby bringing carbon elements contained in the gas to the substrate  20 .  
         [0006]     However, carbon nanotubes formed by the above-mentioned apparatus have shortcomings. During the manufacturing process, the direction of the gas flow is substantially parallel with the surface of the catalyst layer, while the nanotubes grow upwardly perpendicular to the catalyst layer  22 . As such, although rather slow, the horizontal movement of the flow disturbs the growing process of the nanotubes and alters the vertical alignment of the carbon nanotubes.  
         [0007]     Therefore, what is needed in the art is to provide an apparatus for manufacturing vertically aligned carbon nanotubes.  
       SUMMARY  
       [0008]     In one aspect of the present invention, an apparatus for manufacturing carbon nanotubes is provided. The apparatus includes: a reaction chamber having a first inlet configured for introducing a carbon-containing gas thereinto, a first outlet, a heater for elevating an interior temperature of the reaction chamber, wherein the reaction chamber is configured for accommodating a substrate and the first inlet defines a route for channeling the introduced carbon-containing gas toward the substrate, the route being substantially perpendicular to a main plane of the substrate.  
         [0009]     In another aspect of the present invention, a method for manufacturing carbon nanotubes is provided. The method includes the steps of: placing a substrate with a catalyst layer formed thereon in to a reaction chamber; introducing a carrier gas into the reaction chamber; heating the reaction chamber to a predetermined temperature; introducing a carbon-containing gas into the reaction chamber and directing the carbon-containing gas to flow toward to the substrate along a direction that is substantially perpendicular to a main plane of the substrate.  
         [0010]     Detailed features of the present carbon nanotubes manufacturing apparatus will become more apparent from the following detailed description and claims, and the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     Many aspects of the present apparatus and method can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present apparatus and method. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views, wherein:  
         [0012]      FIG. 1A  is a schematic cross-sectional view of an apparatus for manufacturing carbon nanotubes according to a first exemplary embodiment.  
         [0013]      FIG. 1B  is a schematic cross-sectional view of a substantially cube-shaped reaction chamber of the apparatus illustrated in  FIG. 1A .  
         [0014]      FIG. 1C  is a schematic cross-sectional view of a semi-cone reaction chamber of an apparatus for manufacturing carbon nanotubes according to a second embodiment.  
         [0015]      FIG. 1D  is a schematic cross-sectional view of a hemispherical reaction chamber of an apparatus for manufacturing carbon nanotubes according to a third embodiment.  
         [0016]      FIG. 2A  is a schematic cross-sectional view of an apparatus for manufacturing carbon nanotubes according to a fourth exemplary embodiment.  
         [0017]      FIG. 2B  is a schematic cross-sectional view of a reaction chamber with a inverted-funnel shaped gas guiding member of the apparatus illustrated in  FIG. 2A .  
         [0018]      FIG. 2C  is a schematic cross-sectional view of a reaction chamber with a hemispherical gas guiding member of an apparatus for manufacturing carbon nanotubes according to a fifth embodiment.  
         [0019]      FIG. 3  is a schematic cross-sectional view of a typical apparatus for manufacturing carbon nanotubes. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]     Reference will now be made to the drawings to describe the preferred embodiments of the present apparatus for manufacturing carbon nanotubes, in detail.  
         [0021]     Referring now particularly to  FIG. 1A , where an apparatus  40  for manufacturing carbon nanotubes according to a first embodiment of the present invention is shown. The apparatus  40  mainly includes a reaction chamber  60  and a heater  70 . A substrate  50  is disposed in the reaction chamber  60 . The heater  70  is configured for heating the interior of the reaction chamber  60 .  
         [0022]     The substrate  50  has a catalyst layer  52  formed on a top surface thereof. The substrate  50  is made of a material selected from a group consisting of quartz, silicon, and magnesium oxide. The material of the catalyst layer  52  is selected from a group consisting of cobalt, nickel, iron, and any appropriate alloy of them.  
         [0023]     In the first embodiment, the reaction chamber  60  is a cubic chamber as shown in  FIG. 1B . Alternately, the reaction chamber  60  could have other shapes, i.e., substantially semi-conical in a second embodiment or hemispheric in a third embodiment, as shown in  FIG. 1C  and  FIG. 1D  respectively. Referring to  FIG. 1B , the reaction chamber  60  has a first inlet  62  and a first outlet  64 . The first inlet  62  is configured in a top of the reaction chamber  60  spatially corresponding to the substrate  50 . The first outlet  64  is configured to be adjacent to a bottom of the reaction chamber  60 . Alternately, the first outlet  64  could also be formed at the bottom of the reaction chamber  60 .  
         [0024]     Additionally, the reaction chamber  60  is received in a quartz tube  80  that has a second inlet  82  at one end portion and a second outlet  84  at another end portion. The second inlet  82  is in communication with the first inlet  62  and the second outlet  84  is in communication with the first outlet  64 . In the illustrated exemplary embodiment, the second inlet  82  is in communication with the first inlet  62  via a gas guiding pipe  86 .  
         [0025]     The heater  70  can be any type of heating device that is adapted for heating the reaction chamber  60 , for example a high temperature furnace or a high frequency induction heating furnace can be used.  
         [0026]     In another aspect of the present invention, a method for manufacturing carbon nanotubes comprises the steps in no particular order of: 
    (1) placing a substrate  50  that with has a catalyst layer  52  formed thereon in to a reaction chamber  60 ;     (2) introducing a carrier gas into the reaction chamber  60 ;     (3) heating the reaction chamber  60  to a predetermined temperature;     (4) introducing a carbon-containing gas into the reaction chamber  60  and directing the carbon-containing gas to flow toward to the substrate  50  along a direction that is substantially perpendicular to a main plane of the substrate  50 .    
 
         [0031]     In step (1), the substrate  50  with a catalyst layer  52  formed thereon is fed into the reaction chamber  60 .  
         [0032]     In step (2), a carrier gas is introduced into the reaction chamber  60 . In the illustrated exemplary embodiment, the carrier gas is supplied to the second inlet  82 , then the carrier gas is transported successively passing through the gas guiding pipe  86 , the first inlet  62 . Thereafter, the carrier gas is discharged into the reaction chamber  60 . The carrier gas is selected from the group consisting of hydrogen gas, nitrogen gas, ammonia gas, and similarly inert gases.  
         [0033]     In step (3), the reaction chamber  60  is heated to a predetermined temperature by the heater  70 . Specifically, the predetermined temperature is in the range from 500° C. to 900° C.  
         [0034]     In step (4), the carbon-containing gas is introduced through the second inlet  82  for a certain time so as to grow carbon nanotubes on the substrate  50 . The carbon-containing gas is selected from a group consisting of methane, ethane, ethylene, acetylene and similar carbon containing gases.  
         [0035]     During the above-described process of manufacturing carbon nanotubes, the moving direction of the flow of carbon-containing gas is generally perpendicular to the surface of the catalyst layer, and is thus greatly advantageous for the vertical growth of carbon nanotubes. So the apparatus provided in the exemplary embodiment can be used to manufacture carbon nanotubes with high vertically oriented alignment.  
         [0036]     An apparatus  400  according to the fourth embodiment, as shown in  FIG. 2A , is described as follows. The apparatus  400  mainly includes a reaction chamber  600  and a heater  700 . A substrate  500  is received and disposed in the reaction chamber  600 . The heater  700  is configured for heating the interior of the reaction chamber  600 .  
         [0037]     Similar to the substrate  50  shown in  FIG. 1A , the substrate  500  shown in  FIG. 2A  has a catalyst layer  520  formed on a top surface thereof. The substrate  500  is made of a material selected from a group consisting of quartz, silicon, and magnesium oxide. The material of the catalyst layer  520  is selected from a group consisting of cobalt, nickel, iron, and any appropriate alloy of them.  
         [0038]     The reaction chamber  600  is a substantially cube-shaped chamber as shown in  FIG. 2B . The reaction chamber  600  has a first inlet  620 , a first outlet  640  and a gas guiding member  660 . The first inlet  620  is configured at a top of the reaction chamber  600  and spatially corresponding to the substrate  500 . The first outlet  640  is configured adjacent to a bottom of the reaction chamber  600 . Alternately, the first outlet  640  can also be formed at the bottom of the reaction chamber  600 . The gas guiding member  660  is a shell portion that has a shape of inverted-funnel as shown in  FIG. 2B . The gas guiding member  660  comprises a narrow opening coupled to the first inlet  620  and an opposite wide opening spatially corresponding to the substrate  500 . Alternately, the gas guiding member  660  could also be a shell portion having other shapes, for example, hemispherical in a fifth embodiment as shown in  FIG. 2C .  
         [0039]     Additionally, the reaction chamber  600  is received in a quartz tube  800  that has a second inlet  820  at one end portion and a second outlet  840  at another end portion. The second inlet  820  is in communication with the first inlet  620  and the second outlet  840  is in communication with the first outlet  640 . In the illustrated exemplary embodiment, the second inlet  820  is in communication with the first inlet  620  via a gas guiding pipe  860 .  
         [0040]     The heater  700  can be any type of heating device that is adapted for heating the reaction chamber  600 , for example, a high temperature furnace or a high frequency induction heating furnace.  
         [0041]     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.