Abstract:
Provided is a method of fabricating carbon nanotubes using a focused ion beam (FIB). The method includes: preparing a substrate; scanning the substrate with the FIB; and growing the carbon nanotubes on the scanned substrate.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     Priority is claimed to Korean Patent Application No. 10-2005-0005813, filed on Jan. 21, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method of fabricating carbon nanotubes, and more particularly to, a method of fabricating carbon nanotubes using a focused ion beam (FIB).  
         [0004]     2. Description of the Related Art  
         [0005]     Carbon nanotubes have specific structural and electrical properties and are widely used in many devices, for example, backlights for field emission displays (FEDs) and liquid crystal displays (LCDs), nanoelectronic devices, actuators, and batteries, etc.  
         [0006]     Conventional methods of fabricating carbon nanotubes include physical methods, such as an arc discharge method and laser vaporization, and chemical methods, such as chemical vapor deposition (CVD).  
         [0007]      FIG. 1  is a schematic view of an arc discharge apparatus used in performing a conventional arc discharge method.  
         [0008]     Referring to  FIG. 1 , in order to perform the arc discharge method, a cathode electrode  11  and an anode electrode  13 , which are graphite bars, are installed in the apparatus and a voltage is applied between the electrodes  11  and  13 , thereby generating a discharge between the electrodes  11  and  13 . When the discharge occurs, carbon crusts separated from the graphite bar acting as the anode electrode  13  are attracted and attached to the graphite bar acting as the cathode electrode  11 , which is maintained at a low temperature.  
         [0009]      FIG. 2  is a schematic view of a laser vaporization apparatus used in performing a conventional laser vaporization method.  
         [0010]     Referring to  FIG. 2 , in order to perform the laser vaporization method, a reaction furnace  27  is maintained at about 1200° C., and then a laser beam  21  is irradiated to a graphite  23  in the reaction furnace  27  to vaporize the graphite  23 . The vaporized graphite  23  is adsorbed onto a collector  25  maintained at a low temperature.  
         [0011]      FIG. 3  is a schematic view of an apparatus used in performing a conventional plasma enhanced chemical vapor deposition (PECVD) method. In the PECVD method, a reaction gas in a vacuum tube is discharged due to an energy of a radio-frequency (RF) wave electric field or a direct current applied between two electrodes.  
         [0012]     Referring to  FIG. 3 , a substrate  31  on which carbon nanotubes are to be synthesized is disposed on a grounded bottom electrode  32  and a reaction gas is supplied between a top electrode  34  and the bottom electrode  32 . A heat resistant heater  33  is disposed below the bottom electrode  32  or filaments  35  are disposed between the top electrode  34  and the bottom electrode  32 , to decompose the reaction gas. The energy required to decompose the reaction gas and synthesize the carbon nanotubes is supplied from an RF power supply  37 .  
         [0013]     In the conventional physical or chemical methods, a processing accuracy is low and a selective patterning on a fine portion of the substrate cannot be easily performed. Thus, the carbon nanotubes cannot be easily selectively grown on the fine portion according to the desired pattern.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention provides a method of fabricating carbon nanotubes using a focused ion beam (FIB), in which the carbon nanotubes can be selectively grown at the nano-level on a fine portion of a substrate.  
         [0015]     According to an aspect of the present invention, there is provided a method of fabricating carbon nanotubes using an FIB, comprising: preparing a substrate; scanning the substrate with the FIB; and growing the carbon nanotubes on the scanned substrate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0017]      FIG. 1  is a schematic view of an arc discharge apparatus used in performing a conventional arc discharge method;  
         [0018]      FIG. 2  is a schematic view of a laser vaporization apparatus used in performing a conventional laser vaporization method;  
         [0019]      FIG. 3  is a schematic view of an apparatus used in performing a conventional plasma enhanced chemical vapor deposition (PECVD) method;  
         [0020]      FIGS. 4A through 4C  are schematic views illustrating a method of fabricating carbon nanotubes using a focused ion beam (FIB) according to an embodiment of the present invention;  
         [0021]      FIGS. 5A through 5D  are schematic views illustrating a method of fabricating carbon nanotubes using an FIB according to another embodiment of the present invention;  
         [0022]      FIG. 6  is a view of carbon nanotubes obtained using a method of fabricating carbon nanotubes using an FIB according to an embodiment of the present invention;  
         [0023]      FIG. 7  is an enlarged view of a portion A illustrated in  FIG. 6 ; and  
         [0024]      FIG. 8  is a view of a portion of a pattern formed using an FIB. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Hereinafter, a method of fabricating carbon nanotubes using a focused ion beam (FIB) according to exemplary embodiments of the present invention will be described in more detail with reference to the attached drawings. Like reference numerals in the drawings denotes like elements.  
         [0026]      FIGS. 4A through 4C  are schematic views illustrating a method of fabricating carbon nanotubes using an FIB according to an embodiment of the present invention.  
         [0027]     Referring to  FIG. 4A , a substrate  10  is prepared. The substrate  10  may be composed of at least one material selected from the group consisting of Si, SiO 2 , Al 2 O 3 , GaN, GaAs, SiC, and SiN, for example.  
         [0028]     Referring to  FIG. 4B , a surface of the substrate  10  is scanned with the FIB. Then, ions  12  contained in the FIB are implanted into the surface of the substrate  10 . The ions  12  may be gallium (Ga) ions. An FIB apparatus projecting the FIB has a very high capability of decomposing a sample and allows for a nano-level decomposition of the sample. Thus, by scanning the substrate  10  with the FIB, the substrate  10  can be scanned with nano-level accuracy. Further, a predetermined portion of the substrate  10  can be selectively scanned using the high decomposition capability of the FIB apparatus, and thus, various patterns can be easily formed on the substrate  10 .  
         [0029]     Referring to  FIG. 4C , the carbon nanotubes  13  are grown on the scanned substrate  10 . At this time, the ions  12  function as growth nuclei for the carbon nanotubes  13  and thus, the carbon nanotubes  13  are vertically grown based on the ions  12 . A hydrocarbon gas, such as CH 4 , C 2 H 2 , C 2 H 4 , and C 2 H 6  may be used to grow the carbon nanotubes  13 . The carbon nanotubes  13  may be grown using a chemical vapor deposition (CVD) method, for example, a thermal CVD method and a plasma enhanced chemical vapor deposition (PECVD) method. When the carbon nanotubes  13  are grown using the thermal CVD method, a growth uniformity of the carbon nanotubes  13  is very high and the carbon nanotubes  13  can have a smaller diameter than in the PECVD method, and as a result, the carbon nanotubes  13  can have a low turn-on voltage. When the carbon nanotubes  13  are grown using the PECVD method, the carbon nanotubes  13  can be more easily vertically grown on the substrate  10  and synthesized at a lower temperature than in the thermal CVD method. The vertical growth of the carbon nanotubes  13  depends on a direction of the electric field applied between the anode electrode and the cathode electrode in the PECVD system, and thus, the growth direction of the carbon nanotubes  13  can be controlled by the direction of the electric field. Since the growth direction of the carbon nanotubes  13  is constant, a density of growth can be easily controlled and electrons can be easily emitted due to the electric field.  
         [0030]      FIGS. 5A through 5D  are schematic views illustrating a method of fabricating carbon nanotubes using an FIB according to another embodiment of the present invention.  
         [0031]     Referring to  FIG. 5A , a substrate  20  is prepared. The substrate  20  may be composed of at least one material selected from the group consisting of Si, SiO 2 , Al 2 O 3 , GaN, GaAs, SiC, and SiN, for example.  
         [0032]     Referring to  FIG. 5B , the substrate  20  is patterned using the FIB to form a predetermined pattern  21 . In this embodiment, the patterning of the substrate  20  is performed using an FIB apparatus having a very high decomposition capability, and thus the substrate  20  can be patterned with nano-level accuracy.  
         [0033]     Referring to  FIG. 5C , a surface of the substrate  20  is scanned with the FIB. Then, ions  22 , for example, Ga ions, contained in the FIB are implanted into the surface of the substrate  20 . During this scanning process, the ions  22  may be projected onto a portion of the substrate  20  on which the pattern  21  is not formed, and then implanted onto the portion.  
         [0034]     Referring to  FIG. 5D , the carbon nanotubes  23  are grown on the scanned substrate  20 . At this time, the ions  22  function as growth nuclei for the carbon nanotubes  23  and thus, the carbon nanotubes  23  are vertically grown based on the ions  22 . As described above, when the ions  22  are disposed on the portion of the substrate  20  on which the pattern  21  is not formed, the carbon nanotubes  23  are grown on the surface of the portion of the substrate  20  on which the pattern  21  is not formed. That is, the nano-level pattern  21  is formed on the surface of the substrate  20  using the FIB apparatus having a nano-level decomposition capability and thus, the carbon nanotubes  23  may be grown on the substrate  20  according to the pattern  21 . Thus, according to the present embodiment, the carbon nanotubes  23  can be selectively grown on the fine portion of the substrate  20  and the pattern  21  can be easily formed in various forms.  
         [0035]     A hydrocarbon gas, such as CH 4 , C 2 H 2 , C 2 H 4 , and C 2 H 6  may be used to grow the carbon nanotubes  23 . The carbon nanotubes  23  may be grown using a CVD method, for example, a thermal CVD method and a PECVD method.  
         [0036]      FIG. 6  is a view of carbon nanotubes obtained using a method of fabricating carbon nanotubes using an FIB according to an embodiment of the present invention.  FIG. 7  is an enlarged view of a portion A illustrated in  FIG. 6 .  FIG. 8  is a view of a portion of a pattern formed using an FIB.  
         [0037]     Referring to  FIGS. 6 through 8 , a predetermined pattern  41  is formed on a substrate  40  using the FIB and the carbon nanotubes  43  are grown on the patterned substrate  40 . Ga ions contained in the FIB function as growth nuclei for the carbon nanotubes  43  and the carbon nanotubes  43  may be grown a portion of the substrate  40  on which the pattern  41  is not formed. Thus, according to the present embodiment, due to the use of the FIB, the pattern  41  can be selectively formed at the nano-level on the substrate  40  and easily formed in various forms.  
         [0038]     In a method of fabricating carbon nanotubes using an FIB according to the present invention, by scanning a substrate with the FIB, the carbon nanotubes may be selectively grown at the nano-level on a fine portion of the substrate and the pattern can be easily formed in various forms.  
         [0039]     Due to the above effects, the method of fabricating the carbon nanotubes using the FIB can be used in the fabrication of transistor arrays in a semiconductor process and sensors, for example, gas sensors, chemical sensors, and biosensors.  
         [0040]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.