Patent Publication Number: US-2007116634-A1

Title: Apparatus and method for manufacturing carbon nanotubes

Description:
TECHNICAL FIELD  
      The present invention relates to apparatuses and methods for manufacturing carbon nanotubes, and particularly to an apparatus and method for manufacturing carbon nanotubes by a chemical vapor deposition method.  
     DISCUSSION OF RELATED ART  
      Carbon nanotubes are tubules of carbon generally having a length of 5 to 100 micrometers and a diameter of 5 to 100 nanometers. Carbon nanotubes are composed of a number of co-axial cylinders of graphite sheets and have recently received a great deal of attention for use in different fields such as field emitters, gas storage and separation, chemical sensors and high strength composites. Carbon nanotubes have many promising properties such as a high strength and low weight, high energy and fuel storage capability, good electron emission capability and many advantageous thermal, chemical and surface properties.  
      Currently there are three principal methods to manufacture carbon nanotubes, namely arc discharge, laser ablation and chemical vapor deposition. Among these, the chemical vapor deposition method is perhaps most widely used.  
      A general apparatus for manufacturing carbon nanotubes with a chemical vapor deposition method includes a reaction furnace and a substrate with a catalyst layer thereon in the reaction furnace. A process for manufacturing carbon nanotubes with above-described apparatus includes the steps of:  
      (1) providing a substrate with a catalyst layer and placing it in the reaction furnace;  
      (2) heating the reaction furnace to a predetermined temperature;  
      (3) supplying a carbon source gas into the reaction furnace and growing carbon nanotubes by a chemical vapor deposition method.  
      Such a manufacturing process suffers from the disadvantage that the growth direction of carbon nanotubes is affected by the flow direction of the gas, so the alignment of carbon nanotubes is not good.  
      What is needed, therefore, is an apparatus and method for manufacturing aligned carbon nanotubes.  
     SUMMARY  
      An apparatus and method for manufacturing aligned carbon nanotubes according to a preferred embodiment is provided.  
      The apparatus includes a reaction chamber having a gas inlet at a lower portion thereof configured for introducing a carbon source gas into the reaction chamber with a gas outlet in an upper portion thereof, the reaction chamber defining a carbon source gas flow route, a substrate holder arranged between the gas inlet and gas outlet in the reaction chamber, and at least one substrate having a number of through holes defined therein configured for facilitating the flow of carbon source gas therethrough and a catalyst layer formed on a surface thereof facing the gas inlet, the at least one substrate being positioned in the carbon source gas flow route by the substrate holder.  
      The method includes the steps of:  
      (a) providing a substrate having a number of through holes defined therein and a catalyst layer formed on a first surface thereof;  
      (b) orienting and positioning the substrate in a manner such that the first surface of the substrate faces downwardly;  
      (c) supplying and directing a carbon source gas to flow vertically from the first surface to an opposite second surface of the substrate for growing carbon nanotubes thereon by a chemical vapor deposition method. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The features and advantages of the present apparatus and method for manufacturing carbon nanotubes, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments thereof taken in conjunction with the accompanying drawings.  
       FIG. 1  is a schematic, front view of an apparatus for manufacturing carbon nanotubes in accordance with a first preferred embodiment of the present invention;  
       FIG. 2  is schematic, top view of a substrate of the apparatus in accordance with the first preferred embodiment of the present invention;  
       FIG. 3  is a schematic, front view of an apparatus for manufacturing carbon nanotubes in accordance with a second preferred embodiment of the present invention;  
       FIG. 4  is schematic, top view of a substrate holder of the apparatus in accordance with the second preferred embodiment of the present invention.  
       FIG. 5  is schematic, top view of a substrate of the apparatus in accordance with the second preferred embodiment of the present invention.  
       FIG. 6  is a schematic, front view of an apparatus for manufacturing carbon nanotubes in accordance with a third preferred embodiment of the present invention; and  
       FIG. 7  is schematic, top view of a substrate of the apparatus in accordance with the second preferred embodiment of the present invention.  
      Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one preferred embodiment of the present apparatus and method for manufacturing carbon nanotubes, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Reference will now be made to the drawings to describe in detail the preferred embodiments of the present apparatus and method for manufacturing carbon nanotubes.  
      Referring to  FIG. 1 , an apparatus  100  for manufacturing carbon nanotubes according to a first preferred embodiment is shown. The apparatus  100  includes a reaction chamber  110 , a heating device  120 , and a substrate  130 .  
      The reaction chamber  110  has a gas inlet  112 , a gas outlet  114  and a substrate holder  116 . The gas inlet  112  is configured at a bottom of the reaction chamber  110  for introducing a carbon source gas into the reaction chamber  110 . The gas outlet  114  is configured at a top of the reaction chamber  110  for outputting gas. Preferably, the gas outlet  14  is directly opposite to the gas inlet  112 , thus a reaction gas input from the gas inlet  112  can flow directly from the bottom of the reaction chamber  110  to the top of the reaction chamber  110 . The substrate holder  116  is arranged between the gas inlet  112  and gas outlet  114  in the reaction chamber  110  for holding the substrate  130 . As such, the reaction gas can flow through an area for holding the substrate  130  in a direction substantially parallel to a growth direction of carbon nanotubes.  
      The heating device  120  is configured adjacent the reaction chamber  110  for heating the reaction chamber  110 . In this embodiment, the heating device  120  is disposed around the reaction chamber  110 . The heating device  120  may be high temperature furnace, high frequency furnace etc.  
      The substrate  130  is held on the substrate holder  116 .  
      Referring to  FIG. 2 , the substrate  130  defines a number of through holes  132  for facilitating the flowing of reaction gas therethrough. The through holes  132  can be distributed irregularly or regularly in the substrate  130 . A diameter of each of the through holes  132  may be in a range from 0.5 microns to 1 micron. A catalyst layer  134  is formed on a surface of the substrate for growing carbon nanotubes. The catalyst layer  134  can be composed of a catalyst material used for growth of carbon nanotubes, such as iron, cobalt, nickel etc.  
      A method for manufacturing carbon nanotubes using the apparatus  100  according to an aspect of present invention includes the steps in no particular order of:  
      (a) a substrate  130  is provided, and a number of the through holes  132  are defined therein and a catalyst layer  134  is formed on a first surface thereof;  
      (b) the substrate  130  is oriented and positioned in a manner such that the first surface of the substrate  130  faces downwardly;  
      (c) a carbon source gas is supplied and directed to flow vertically from the first surface to an opposite second surface of the substrate  130  for growing carbon nanotubes thereon by a chemical vapor deposition method.  
      In the step (a), the through holes  132  can be made using a photolithography method, and in the present embodiment they are formed using a drilling method. A diameter of each of the through holes  132  is in a range from 0.5 microns to 1 micron. The catalyst layer  134  can be formed using a method selected from the group consisting of ion plating, radio frequency magnetron sputtering, vacuum evaporation, and chemical vapor deposition.  
      In the step (b), the first surface of the substrate  130  faces downwardly so as to make the growth direction of carbon nanotubes consistent with gravitational pull.  
      In the step (c), the catalyst layer  134  is first heated to 500˜900° C. with a heating device  120  such as high temperature furnace or high frequency furnace around the reaction chamber  110 ; a mixed gas including carbon source gas such as methane, acetylene, ethylene, carbon monoxide or a mixture thereof and protective gas such as helium, argon, hydrogen, or ammonia are then supplied; the carbon source gas is cracked at the catalyst layer  134  to grow carbon nanotubes.  
      Referring to  FIGS. 3-5 , an apparatus  200  for manufacturing carbon nanotubes according to a second embodiment is shown. Similar to the apparatus  100  of the first embodiment, the apparatus  200  includes a reaction chamber  210  and a heating device  220  around the reaction chamber  210 , wherein the reaction chamber  210  defines a gas inlet  212  configured at a bottom of the reaction chamber  210  and a gas outlet  214  configured at a top of the reaction chamber  210 . The difference between apparatus  200  and apparatus  100  is that the substrate holder  216  has a post  2162  extending upwardly for supporting a number of substrates  230  thereon and a number of through holes  2164  aligned therein with respect to the through holes  232  of the substrates  230  in an area opposite to the at least one substrate for facilitating reaction gas therethrough, and a number of washers  400  surrounding the post  2162  to separate the substrates  230  from each other. Each of the substrates  230  has an engaging hole  236  spatially corresponding to the post  2162 . As such, the substrates  230  are secured to the substrate holder by extension of the post  2162  through the engaging hole  236 .  
      A method for manufacturing carbon nanotubes with the apparatus  200  of the second preferred embodiment is described in detail as follows:  
      (1) a number of substrates  230  are provided, and a engaging holes  236  and a number of through holes  232  arc formed in each of the substrates  230 , and a catalyst layer  234  formed on a first surface of each of the substrates  230 ;  
      (2) the substrates  230  are placed on the substrate holder  216 ;  
      (3) a carbon source gas is supplied into the reaction chamber  210  through the gas inlet  212  from bottom to top and growing carbon nanotubes by a chemical vapor deposition method.  
      In the step (2), the substrates  230  are secured to the substrate holder  216  by the post  2162  of the substrate holder  216  extending through the engaging hole  236  in series with a predetermined space, and the substrates  230  are spaced apart from each other. Generally the space is greater than the growth height of carbon nanotubes. In the present embodiment, the substrates  230  are spaced from each other by a number of washers  400 . The catalyst layer  234  of each of the substrates  230  faces the gas inlet  212  to make the growth direction of carbon nanotubes consistent with gravitational pull.  
      Referring to  FIG. 6  and  FIG. 7 , an apparatus  300  for manufacturing carbon nanotubes according to a third embodiment is shown. Similar to the apparatus  100  of the first embodiment, the apparatus  300  includes a reaction chamber  310  and a heating device  320  around the reaction chamber  310 , wherein the reaction chamber  310  defines a gas inlet  312  configured at a bottom of the reaction chamber  310  and a gas outlet  314  configured at a top of the reaction chamber  310 . However, the substrate holder  316  has a couple of posts  3162  extending upwardly for supporting a number of substrates  330  thereon, and a number of washers  500  surrounding each of the posts  2162  to separate the substrates  230  from each other. Each of the substrates  330  has a couple of engaging holes  336  for engaging a corresponding couple of posts  3162 . As such, the couple of posts  3162  can extend through the engaging holes  336  so as to hold the substrates  330  thereon.  
      A method for manufacturing carbon nanotubes with the apparatus  300  of the third preferred embodiment is described in detail as follows:  
      (1) a reaction chamber  310  having a gas inlet  312  and a gas outlet  314  at a bottom and a top thereof respectively is provided, a substrate holder  316  arranged therein, and the substrate holder  316  having a couple of posts  3162 ;  
      (2) a number of substrates  330  are provided, and a couple of engaging holes  336  and a number of through holes  332  are formed in each of the substrates  330 , and a catalyst layer  334  is formed on a surface of each of the substrates  330 ;  
      (3) the substrates  330  are placed on the substrate holder  316 ;  
      (4) a carbon source gas is supplied into the reaction chamber  310  through the gas inlet  312  from bottom to top and growing carbon nanotubes by a chemical vapor deposition method.  
      In the step (3), The substrates  330  are secured to the substrate holder  316  by the post  3162  of the substrate holder  316  extending through the engaging hole  336  in series with a predetermined space, and the substrates  330  are spaced apart from each other. Generally the space is greater than the growth height of carbon nanotubes. In the present embodiment, the substrates  330  are spaced from each other by a number of washers  500 . The catalyst layer  334  of each of the substrates  330  faces the gas inlet  312  to make the growth direction of carbon nanotubes consistent with gravity direction of that  
      An advantage of the above-described apparatuses are that the catalyst layer of the substrates face the gas inlet and are orientated with the flow direction of the carbon source gas so as to manufacture aligned carbon nanotubes under gravity.  
      Another advantage of the above-described apparatuses are that a number of substrates having a number of through holes therein can be spaced on the substrate holder according to a predetermined space so as to mass-produce aligned carbon nanotubes.  
      While the present invention has been described as having preferred or exemplary embodiments, the embodiments 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 embodiments using the general principles of the invention as claimed. Furthermore, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and which fall within the limits of the appended claims or equivalents thereof.