RELATED APPLICATIONS 
       [0001]    This application is a continuation application of patent application Ser. No. 11/586,976 filed on Oct. 26, 2006 from which it claims the benefit of priority under 35 U.S.C. 120. Both, this application and the patent application Ser. No. 11/586,976 claim the benefit of priority under 35 USC 119 from Chinese Patent Application 200510120716.6, filed on Dec. 16, 2005. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The disclosure relates generally to nanotubes, and more particularly to a carbon nanotube yarn and method for making the same. 
         [0004]    2. Discussion of Related Art 
         [0005]    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 can be composed of a number of co-axial cylinders of graphite sheets and have recently attracted a great deal of attention for use in different fields such as field emitters, gas storage and separation, chemical sensors and high strength composites. However, carbon nanotubes are almost never used in microscopic applications at present as it is very difficult to manipulate the carbon nanotubes as a microscopic level. So, assembling carbon nanotubes into macroscopic structures is of great importance to their applications at the macroscopic level. 
         [0006]    That a long macroscopic carbon nanotube yarn can be drawn out from a super-aligned carbon nanotube array has been disclosed in U.S. Pat. No. 7,045,108. The carbon nanotube yarn includes a plurality of carbon nanotube bundles that are joined end to end by van der Waals attractive force, and each of the carbon nanotube bundles includes a plurality of carbon nanotubes substantially parallel to each other. Referring to  FIG. 7 , a simple model of a continued carbon nanotube yarn  14  being drawn out from a super-aligned carbon nanotube array  10  is shown. A number of carbon nanotube bundles  12  are joined end to end by van der Waals attractive force to form the continued carbon nanotube yarn  14 . However, in general, the carbon nanotube yarn  14  is several centimeters in length and several microns in thickness. A ratio of surface area to volume of the carbon nanotube yarn  14  is very great, and the surface of it is very clean, so it is very sticky and as such macroscopic level application of the carbon nanotube yarn  14  is restricted to a great extent. 
         [0007]    That a long macroscopic carbon nanotube yarn can be drawn out from a super-aligned carbon nanotube array has been disclosed in U.S. Pat. No. 7,045,108. The carbon nanotube yarn includes a plurality of carbon nanotube bundles that are joined end to end by van der Waals attractive force, and each of the carbon nanotube bundles includes a plurality of carbon nanotubes substantially parallel to each other. Referring to  FIG. 7 , a simple model of a continued carbon nanotube yarn  14  being drawn out from a super-aligned carbon nanotube array  10  is shown. A number of carbon nanotube bundles  12  are joined end to end by van der Waals attractive force to form the continued carbon nanotube yarn  14 . However, in general, the carbon nanotube yarn  14  is several centimeters in length and several microns in thickness. A ratio of surface area to volume of the carbon nanotube yarn  14  is very great, and the surface of it is very clean, so it is very sticky and as such macroscopic level application of the carbon nanotube yarn  14  is restricted to a great extent. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Many aspects of the embodiments can be better understood with references 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 embodiments. 
           [0009]      FIG. 1  is a schematic view of a device for making a carbon nanotube yarn in accordance with a preferred embodiment of the present invention. 
           [0010]      FIG. 2  is a scan electronic microscopy (SEM) photograph of a carbon nanotube yarn string. 
           [0011]      FIG. 3  is an enlarged sectional view of a tube with a through hole of the device of  FIG. 1 . 
           [0012]      FIG. 4  is an enlarged sectional view of a tube connecting and coupling to a rod. 
           [0013]      FIG. 5  is an enlarged sectional view of a tube connecting and coupling to two rods. 
           [0014]      FIG. 6  is a SEM photograph of a carbon nanotube yarn of a preferred embodiment of the present invention. 
           [0015]      FIG. 7  is schematic view of a conventional carbon nanotube yarn being drawn out from a carbon nanotube array. 
       
    
    
       [0016]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one preferred embodiment of the disclosure, in one form, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner. 
       DETAILED DESCRIPTION 
       [0017]    Reference will now be made to the drawings to describe embodiments of the present apparatus and method for making an array of carbon nanotubes, in detail. 
         [0018]    Referring to  FIG. 1 , a method for making carbon nanotube yarn includes the steps of: 
         [0019]    (1) providing a carbon nanotube array  20 ; 
         [0020]    (2) drawing out a number of carbon nanotube yarn strings  22  from the carbon nanotube array  20 ; 
         [0021]    (3) treating the number of carbon nanotube yarn strings  22  using an organic solvent  50  in a manner such that the number of carbon nanotube yarn strings  22  are formed into a single strand of carbon nanotube yarn  30 . 
         [0022]    In the step (1), the carbon nanotube array  20  is generally a super-aligned carbon nanotube array. The carbon nanotube array  20  can be manufactured using a chemical vapor deposition method. The method is disclosed in U.S. Pat. No. 7,045,108, which is incorporated herein by reference. For illustrative purposes, the method for manufacturing the carbon nanotube array  20  is described below, and includes the steps of: 
         [0023]    (a) providing a substantially flat and smooth substrate, the substrate can be a p-type or n-type silicon wafer; 
         [0024]    (b) depositing a catalyst on the substrate, the catalyst being selected from the group consisting of iron, cobalt, nickel or alloys of the same; 
         [0025]    (c) annealing the substrate with the catalyst in protective gas at 300˜400° C. for about 10 hours; 
         [0026]    (d) heating the annealed substrate with the catalyst to 500˜700° C., supplying a mixture of carbon containing gas and protective gas, controlling a difference between the local temperature of the catalyst and the environmental temperature to be at least 50° C., controlling a partial pressure of the carbon containing gas to be less than 0.2, and growing a number of carbon nanotubes on the substrate after 5˜30 minutes such that the carbon nanotube array  20  is formed on the substrate. The carbon containing gas can be a hydrocarbon such as acetylene, ethane etc. The protective gas can be an inert gas or nitrogen gas. 
         [0027]    The superficial density of the carbon nanotube array  20  manufactured by above-described process with carbon nanotube bundles being compactly bundled up together is higher. The van der Waals attractive force between adjacent carbon nanotube bundles is strong, and diameters of the carbon nanotubes are correspondingly substantial. 
         [0028]    In the step (2), the carbon nanotube yarn strings  22  may be drawn out from the carbon nanotube array  20  with a tool with a sharp tip, such as a tweezers. Specifically, an initial carbon nanotube bundle with a number of carbon nanotubes of the carbon nanotube array  20  can be drawn out with tweezers. As a carbon nanotube bundle is drawn out, other carbon nanotube bundles are also drawn out due to the van der Waals attractive force between ends of adjacent bundles and a successive carbon nanotube yarn string  22  is formed. The carbon nanotube yarn string  22  may have a length of several centimeters and a thickness of several microns. Referring to  FIG. 2 , a SEM photograph of the carbon nanotube yarn string  22  of the present embodiment is shown. In the present embodiment, a number of carbon nanotube yarn string  22  are drawn out from the carbon nanotube array  20 . 
         [0029]    In the step (3), referring to  FIGS. 1 and 3 , a device for continuously soaking the carbon nanotube yarn strings  22  is shown. The device includes a container  40  for containing the organic solvent  50  therein, a tube  42  and a vessel  60  configured for collecting the organic solvent. The tube  42  is coupled to a bottom of the container  40  and is in communication with the container  40 . The tube has a through hole  44  defined therein for allowing the carbon nanotube yarn strings  22  to pass therethrough. The container  40  is configured for supplying the organic solvent  50  to the tube  42 . A method for soaking the carbon nanotube yarn strings  22  in the organic solvent  50  thereby shrinking the carbon nanotube yarn strings  22  into a single strand of carbon nanotube yarn  30  using above-described device is described below, which includes the steps in no particular order of: 
         [0030]    (a) placing the container  40  above the carbon nanotube yarn strings  22 , the container  40  containing the organic solvent  50  for treating the carbon nanotube yarn strings  22 ; 
         [0031]    (b) supplying the organic solvent  50  to the tube  42 , wherein the organic solvent  50  may be a volatilizable organic solvent such as ethanol, methanol, acetone, dichloroethane or chloroform; 
         [0032]    (c) placing the vessel  60  below the through hole  44  of the tube  42  for collecting leaking organic solvent; 
         [0033]    (d) passing the carbon nanotube yarn strings  22  through the through hole  44  of the tube  42  continuously to soak the carbon nanotube yarn strings  22  in the organic solvent  50 , thereby shrinking the carbon nanotube yarn strings  22  into the carbon nanotube yarn  30  with a diameter of 20˜30 microns under the action of surface tension of the organic solvent  50 .  FIG. 6  shows a SEM photograph of the carbon nanotube yarn  30  of the present embodiment. 
         [0034]    Alternatively, the tube  42  can have no through hole  44  defined therein, and it can be connected and coupled to a rod.  FIG. 4  shows that the tube  42  is connected and coupled to a rod  92 . The organic solvent  50  can flow along surface of the rod  92  and the carbon nanotube yarn strings  22  can be attached over or below the rod  92 , thereby the carbon nanotube yarn strings  22  shrink into the carbon nanotube yarn  30  due to the surface tension of the organic solvent  50 . 
         [0035]    Of course, the tube  42  can also be connected and coupled to more than one rod, and the more than one rod align together in a parallel form. Referring to  FIG. 5 , that the tube  42  being connected and coupled to two rods  94  is shown. The organic solvent  50  can flow along surface of the rods  94  and the carbon nanotube yarn strings  22  can be attached over or below the rods  94 , thereby the carbon nanotube yarn strings  22  shrink into the carbon nanotube yarn  30  due to the surface tension of the organic solvent  50 . 
         [0036]    The carbon nanotube yarn  30  includes a number of carbon nanotube yarn strings packed closely together, and each of the carbon nanotube yarn strings includes a number of carbon nanotube bundles which are joined end to end by van der Waals attractive force, and each of the carbon nanotube bundles includes a number of carbon nanotubes substantially parallel to each other. The ratio of surface area to volume of the carbon nanotube yarn  30  is low and the carbon nanotube yarn  30  therefore has non-stick properties. 
         [0037]    The carbon nanotube yarn  30  can be coiled onto a bobbin  80  with a electromotor  70  or by hand. 
         [0038]    Alternatively, the carbon nanotube yarn strings  22  can be soaked by directly soaking the entire carbon nanotube yarn strings  22  in an organic solvent  50 , a shrunk carbon nanotube yarn  30  can be obtained after the soaked carbon nanotube yarn strings  22  are pulled out from the solvent under the action of surface tension of the organic solvent  50 . Of course, just one carbon nanotube yarn string drawn out from the carbon nanotube array  20  can be shrunk into a carbon nanotube yarn  30  with above-described steps. 
         [0039]    As mentioned above, there is a through hole  44  defined through the tube  42 . Referring to  FIG. 3 , the through hole  44  can be divided into two parts formed in the lateral wall of the tube  42 , namely, an inlet  44   a  and an outlet  44   b . When the tube  42  is positioned in the position shown in  FIG. 3 , the inlet  44   a  is formed in a left side of the tube  42  and the outlet  44   b  is formed in a right side of the tube  42 . The inlet  44   a  is capable of accepting one or more carbon nanotube yarn strings  22  and the outlet  44   b  is capable of accepting the carbon nanotube yarn  30 . The inlet  44   a  is larger than the outlet  44   b  for converging the carbon nanotube yarn  30  and facilitating the carbon nanotube yarn  30  to go through the tube  42 . Further, a converging structure  46  can be located on an outer surface of the tube  42  and has a converging passageway  46   a  therethrough. The converging passageway  46   a  is in direct communication with the outlet  44   b.    
         [0040]    It is to be understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. It is understood that any element of any one embodiment is considered to be disclosed to be incorporated with any other embodiment. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention. 
         [0041]    It is also to be understood that above description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.
An apparatus for making a carbon nanotube yarn includes a tube and a collecting means. The tube has an opening capable of introducing organic solvent into the tube. The tube further has an inlet and an outlet defined through lateral walls thereof. The inlet is capable of accepting one or more carbon nanotube yarn strings and the outlet is capable of accepting the carbon nanotube yarn. The collecting means is positioned around the tube for collecting the carbon nanotube yarn as it comes out of the outlet.