Carbon nanotube with a graphitic outer layer: process and application

Abstract

A method for manufacturing carbon nanotubes with an integrally attached outer graphitic layer is disclosed. The graphitic layer improves the ability to handle and manipulate the nanometer size nanotube device in various applications, such as a probe tip in scanning probe microscopes and optical microscopes, orbs an electron emitting device. A thermal chemical vapor deposition reactor is the preferred reaction vessel in which a transition metal catalyst with an inert gas, hydrogen gas and a carbon-containing gas mixture are heated at various temperatures in a range between 500° C. and 1000° C. with gases and temperatures being adjusted periodically during the reaction times required to grow the nanotube core and subsequently grow the desired outer graphitic layer.

1 - 21 . (canceled)  
     
     
         22 . A system for manufacturing a nanotube device having a carbon nanotube core integrally attached outer graphitic layer comprising: 
 means for preparing a transition metal catalyst on a selected substrate;    means for placing the transition metal catalyst and the substrate of step in a reaction vessel to create a reaction product;    means for purging the reaction vessel by beating said vessel to a temperature between approximately 500° C. and approximately 750° C. while introducing a gaseous mixture of hydrogen and an inert gas;    means for growing a carbon nanotube core by changing the gaseous mixture to a stream consisting of approximately 10% carbon-containing gas and approximately 90% inert gas, while increasing the temperature of the reaction vessel to a range between approximately 750° C. and approximately 900° C.;    means for growing an integrally attached graphitic outer layer on the carbon nanotube core by changing the reaction parameters to promote the distinct formation of carbon material selected from the group consisting of amorphous carbon, graphitic carbon and mixtures thereof;    means for removing the carbon nanotube with graphitic outer layer from the reaction vessel; and    means for mechanically breaking away a portion of the graphitic outer layer to leave the carbon nanotube core partially exposed.    
     
     
         23 . The system of  claim 22 , wherein the growing means includes: 
 means for introducing to the reaction vessel a gaseous mixture consisting of approximately 5% carbon-containing gas, approximately 5% hydrogen gas and approximately 90% inert gas while increasing the temperature of the reaction vessel to a range between approximately 900.degree. C. and approximately 1000.degree. C. to promote the growth of an amorphous carbon material;    means for maintaining the conditions of the preparing means for a period of time from approximately 30 minutes to approximately one hour; and, thereafter; and    means for annealing the reaction product by introducing to the reaction vessel a gaseous mixture consisting of approximately 10% carbon-containing gas and approximately 90% inert gas while maintaining the temperature of the reaction vessel at approximately 1000.degree. C. to promote the growth of a graphitic carbon coating.    
     
     
         24 . The system of  claim 22 , wherein the graphitic outer layer forms on the carbon nanotube core at temperatures between approximately 900.degree. C. and approximately 1000.degree. C.  
     
     
         25 . The system of  claim 22 , wherein the graphitic outer layer forms on the carbon nanotube core at temperatures of approximately 1000.degree. C.  
     
     
         26 . The system of  claim 22 , wherein the transition metal catalyst is selected from the group consisting of cobalt, nickel, iron, mixtures and alloys thereof.  
     
     
         27 . The system of  claim 22 , wherein the transition metal catalyst is a mixture of 50% iron and 50% nickel.  
     
     
         28 . The system of  claim 22 , wherein the selected substrate for the transition metal catalyst is silicon.  
     
     
         29 . The system of  claim 22 , wherein the inert gas is selected from a group consisting of argon, helium and nitrogen.  
     
     
         30 . The system of  claim 22 , wherein the carbon-containing gas is selected from the group consisting of methane, ethane, propane, butane, ethylene, cyclohexane, carbon monoxide and carbon dioxide.  
     
     
         31 . The system of  claim 22 , wherein the carbon-containing gas is methane.  
     
     
         32 . A system for manufacturing a nanotube device having a carbon nanotube core integrally attached outer graphitic layer comprising: 
 means for preparing a transition metal catalyst on a selected substrate;    means for placing the transition metal catalyst and the substrate of step in a reaction vessel to create a reaction product;    means for purging the reaction vessel by heating said vessel to a temperature between approximately 500° C. and approximately 750° C. while introducing a gaseous mixture of hydrogen and an inert gas;    means for growing a carbon nanotube core by changing the gaseous mixture to a stream consisting of approximately 10% carbon-containing gas and approximately 90% inert gas, while increasing the temperature of the reaction vessel to a range between approximately 750° C. and approximately 900° C.; and    means for growing an integrally attached graphitic outer layer on the carbon nanotube core by changing the reaction parameters to promote the distinct formation of carbon material selected from the group consisting of amorphous carbon, graphitic carbon and mixtures thereof, wherein a carbon nanotube device can be formed therefrom.    
     
     
         33 . A system for manufacturing a nanotube device, comprising: 
 a nanotube core grown inside of an outer layer;    a mechanically removable portion of the outer layer that is mechanically removable to reveal and expose a tip portion of the nanotube core.    
     
     
         34 . The system of  claim 33 , wherein the nanotube core is carbon.  
     
     
         35 . The system of  claim 33 , wherein the outer layer is graphitic carbon.  
     
     
         36 . The system of  claim 34 , wherein the outer layer is graphitic carbon.