Laser ablation for the synthesis of carbon nanotubes
Single walled carbon nanotubes are produced in a novel apparatus by the laser-induced ablation of moving carbon target. The laser used is of high average power and ultra-fast pulsing. According to various preferred embodiments, the laser produces an output above about 50 watts/cm 2 at a repetition rate above about 15 MHz and exhibits a pulse duration below about 10 picoseconds. The carbon, carbon/catalyst target and the laser beam are moved relative to one another and a focused flow of “side pumped”, preheated inert gas is introduced near the point of ablation to minimize or eliminate interference by the ablated plume by removal of the plume and introduction of new target area for incidence with the laser beam. When the target is moved relative to the laser beam, rotational or translational movement may be imparted thereto, but rotation of the target is preferred.
1. An apparatus for the high rate production of single-walled carbon nanotubes comprising:
A) an operating chamber providing an inert environment;
B) a mechanism for maintaining said operating chamber at elevated temperature;
C) within said operating chamber a carbon or carbon/catalyst target;
D) a laser producing a high average power, ultra-fast laser beam that impacts said target in said operating chamber to produce a plume of single-walled carbon nanotubes;
E) a mechanism for imparting relative movement between said target and said laser beam;
F) a mechanism for providing a high momentum, side pumped flow of heated inert gas that deflects said plume from the area where said laser beam impacts said target; and
G) a collector for said single-walled carbon nanotubes.
2. The apparatus of claim 1 wherein said laser is a free electron laser.
3. The apparatus of claim 1 wherein said laser produces a laser beam having an average power above about 50 watts per square centimeter and a pulse duration below about 10 picoseconds.
4. The apparatus of claim 3 wherein said laser is a free electron laser.
5. The apparatus of claim 1 wherein said operating chamber is heated to a temperature about 750° C.
6. The apparatus of claim 5 wherein said operating chamber is heated to a temperature above 1000° C.
7. The apparatus of claim 1 wherein said target is cylindrical and mounted on a shaft, and said mechanism for imparting relative movement drives said shaft.
8. The apparatus of claim 1 wherein said mechanism for providing a high momentum, side pumpcd flow of heated inert gas comprises a gas supply line tortuously wound inside of said operating chamber to permit heating of said inert gas in said operating chamber.
9. The apparatus of claim 7 wherein said gas supply line is loosely helically wound about said shaft within said operating chamber.
10. The apparatus of claim 1 wherein said target comprises graphite and a metal catalyst.
11. The apparatus of claim 1 wherein said operating chamber comprises a quartz tube and further including a quartz tube side arm that provides access to said operating chamber for said laser beam.
12. The apparatus of claim 11 further including a generally annular heating element that provides the elevated temperature within said operating chamber.
13. The apparatus of claim 3 wherein said laser delivers a pulse below 5 picoseconds in duration.
14. The apparatus of claim 13 wherein said laser delivers a pulse below 1 picosecond in duration.