Isotope-doped carbon nanotube and method and apparatus for forming the same

Abstract

An isotope-doped carbon nanotube ( 40 ) includes a plurality of first carbon nanotube segments ( 402 ) having carbon-12 isotopes and a plurality of second carbon nanotube segments ( 404 ) having carbon-13 isotopes. The first and second carbon nanotube segments are alternately arranged along a longitudinal direction of the carbon nanotube. Three preferred methods employ different isotope sources to form isotope-doped carbon nanotubes. In a chemical vapor deposition method, different isotope source gases are alternately introduced. In an arc discharge method, a power source is alternately switched between different isotope anodes. In a laser ablation method, a laser is alternately focused on different isotope targets. In addition, an apparatus for implementing the preferred methods is provided.

1 . A method of forming isotope-doped nanotubes of a light element with different isotopes as labeling for indication of relative growth time of said nanotubes, comprising steps of: 
 providing a first source with first isotopes of said light element;    providing a second source with second isotopes of said light element;    providing a target close to said first source and said second source;    providing a circumstance in which the target is available for receiving both said first isotopes and said second isotopes; and    providing an activating device to alternatively introduce the first and second isotopes to said target; wherein    formed isotope-doped nanotubes extend along a longitudinal direction, and the first and the second isotopes are arranged with each other in a chronicle pattern so as to allow measurement of a growth rate of said formed nanotubes along said longitudinal direction.    
     
     
         2 . A method for forming isotope-doped carbon nanotubes, the method comprising the steps of: 
 (1) providing a first carbon source gas and a second carbon source gas respectively comprising first and second carbon isotopes;    (2) putting a substrate having a catalyst film deposited thereon into a reaction chamber;    (3) creating a vacuum in the reaction chamber, introducing a protecting gas at a predetermined pressure therein, and heating the reaction chamber up to a predetermined temperature;    (4) introducing the first carbon source gas into the reaction chamber, first carbon nanotube segments thereby being formed on the catalyst film;    (5) after a given time when the first carbon nanotube segments having the first isotope have reached a first desired length, halting introduction of the first carbon source gas and introducing the second carbon source gas into the reaction chamber, second carbon nanotube segments thereby being formed on the first carbon nanotube segments; and    (6) after a given time when the second carbon nanotube segments having the second isotope have reached a second desired length, cooling the reaction chamber down to room temperature, thereby leaving the isotope-doped carbon nanotubes are formed.    
     
     
         3 . The method of  claim 2 , wherein the catalyst film comprises iron, cobalt or nickel film.  
     
     
         4 . The method of  claim 2 , wherein the first and second carbon source gases comprise methane, ethylene, ethyne, or propadiene.  
     
     
         5 . The method of  claim 2 , wherein the protecting gas comprises helium, argon, nitrogen, or hydrogen.  
     
     
         6 . The method of  claim 2 , wherein the predetermined pressure is one atmosphere, and the predetermined temperature is in the approximate range from 650 to 750 degrees Centigrade.  
     
     
         7 . The method of  claim 2 , wherein steps (4) and (5) may respectively be repeated a desired number of times to form the carbon nanotubes, each having the first and second carbon nanotube segments alternately arranged therein.  
     
     
         8 . A method for forming isotope-doped carbon nanotubes, the method comprising the steps of: 
 (1) providing a first carbon source and a second carbon source respectively comprising first and second carbon isotopes and respectively connecting the first and second carbon sources to a positive terminal of an electricity supply;    (2) connecting a pure graphite rod to a negative terminal of the electricity supply;    (3) placing the first and second carbon sources adjacent the pure graphite rod to create an arc gap, putting the first and second carbon sources and the graphite rod into an arc discharge reaction chamber, creating a vacuum in the reaction chamber, and introducing a protecting gas at a predetermined pressure therein;    (4) applying a discharge current between the first carbon source and the pure graphite rod, first carbon nanotube segments thereby being formed on the graphite rod;    (5) after a given time, when the first carbon nanotube segments having the first isotope have reached a first desired length, stopping the discharge current from the first carbon source to the pure graphite rod and applying a discharge current between the second carbon source and the graphite rod, second carbon nanotube segments thereby being formed on the first carbon nanotube segments; and    (6) after a further given time, when the second carbon nanotube segments having the second isotope have reached a second desired length, switching off the electricity supply, thereby leaving the isotope-doped carbon nanotubes.    
     
     
         9 . The method of  claim 8 , wherein the first and second carbon sources are first and second carbon rods formed by pressing a catalyst powder and high purity graphite particles.  
     
     
         10 . The method of  claim 9 , wherein the catalyst powder comprises nickel powder, ytterbia powder, a composite of nickel powder and ytterbia powder, or cobalt powder.  
     
     
         11 . The method of  claim 9 , wherein the first and second carbon rods each have a diameter in the range from 8 to 12 millimeters and are formed at a pressure about in the range from 3300 to 3800 atmospheres.  
     
     
         12 . The method of  claim 9 , wherein the first and second carbon rods are bonded together with an adhesive insulator.  
     
     
         13 . The method of  claim 8 , wherein the protecting gas comprises helium, argon, nitrogen, or hydrogen.  
     
     
         14 . The method of  claim 8 , wherein the arc gap is about in the range from 1.5 to 2 millimeters.  
     
     
         15 . The method of  claim 8 , wherein the discharge current is in the approximate range from 90 to 110 amps.  
     
     
         16 . The method of  claim 8 , wherein steps (4) and (5) may respectively be repeated a desired number of times to form the carbon nanotubes each having the first and second carbon nanotube segments alternately arranged therein.