Synthesis of Carbon Nanotubes by Selectively Heating Catalyst

Abstract

A catalytic chemical vapor deposition method and apparatus for synthesizing carbon nanotubes and/or carbon nanofibers (CNTs) on a substrate involves selectively heating a catalyst for CNT synthesis on or near the surface of the substrate. Selective heating of the catalyst is achieved using inductive heating from a radio frequency source. Selective heating of the catalyst prevents heating of the substrate and enables the synthesis of CNTs on temperature sensitive substrates.

1 . A method for forming carbon nanotubes on a substrate comprising the step of:
 providing a catalyst distributed on the surface of the substrate and   simultaneously delivering a supply of hydrocarbons to the catalyst and selectively heating the catalyst using a radio frequency source using a catalytic chemical vapor deposition process, to form carbon nanotubes on the substrate.   
     
     
         2 . The method of  claim 1 , wherein the radio frequency source is tuned to a frequency that heats catalyst specifically. 
     
     
         3 . The method of  claim 2 , wherein the radio frequency source is tuned to a frequency that is dependent on the size of catalyst particles. 
     
     
         4 . The method of  claim 1  wherein the catalyst is in the form of nanoparticles distributed on a substrate. 
     
     
         5 . The method of  claim 1  wherein the catalyst is selected from the group consisting of Ni, Fe, Co, Cu, Al, V, Y, Mo, Pt, Pd and their binary and ternary alloys. 
     
     
         6 . The method of  claim 1  further comprising the step of actively cooling the substrate during carbon nanotube formation. 
     
     
         7 . The method of  claim 1  wherein the catalytic chemical vapor deposition process is a plasma enhanced catalytic chemical vapor deposition process. 
     
     
         8 . The method of  claim 1  wherein the radio frequency electromagnetic field is generated by an radio frequency source other than that used to that used to sustain discharge in the plasma-enhanced chemical vapor deposition process. 
     
     
         9 . The method of  claim 6  wherein the radio frequency used is between 1 GHz and 100 GHz. 
     
     
         10 . The method of  claim 1  wherein the carbon nanotubes are aligned. 
     
     
         11 . The method of  claim 1  wherein the substrate is a temperature-sensitive substrate. 
     
     
         12 . The method of  claim 1  wherein a supply of oxygen gas is supplied to the catalyst simultaneously with the supply of hydrocarbon gas. 
     
     
         13 . An apparatus for catalytic chemical vapor deposition synthesis of carbon nanotubes on a substrate comprising:
 a) a catalyst distributed on the surface of the substrate,   b) a means of delivering a supply of hydrocarbons to the catalyst,   c) a radio frequency source for creating plasma discharge, and   d) a radio frequency source positioned to selectively heat the catalyst by induction.   
     
     
         14 . The apparatus of  claim 13  wherein the radio frequency source for creating plasma discharge produces radio waves having a frequency of 13.56 MHz and the radio frequency source positioned to selectively heat the catalyst by induction produces radio waves having a frequency of between 1 and 100 GHz. 
     
     
         15 . The apparatus of  claim 13  wherein the radio frequency source positioned to selectively heat the catalyst by induction is a tunable radio frequency source. 
     
     
         16 . The apparatus of  claim 13  further comprising mass flow controllers to regulate the flow of hydrocarbons delivered to the catalyst. 
     
     
         17 . The apparatus of  claim 13  further comprising a means for delivering oxygen to the catalyst.