NASA Langley originally developed a Free Electron Laser (FEL) ablation technique to synthesize single-walled carbon nanotubes. FEL provides a vast improvement over other techniques employed to make carbon nanotubes. The nanotubes produced by FEL are very pure, straight, homogenous, and defect-free. Most notable is that these nanotubes can be produced in much larger quantities than by other laser-based techniques.
Now, the scientists have further provided incremental improvement in this technology by creating a recipe and procedure for the inexpensive and simple production of fine-grained targets required for the synthesis of carbon nanotubes using FEL. Previously used targets employed metal powders that did not have a particularly small grain size or small size dispersibility. The targets used here are made of powder forge metals that are both small and dispersible. The targets facilitate a significant cost reduction in the supply of high-quality single-walled carbon nanotubes.
The fine-grained targets are a matrix of a prismatic edge natural flake graphite that produces strong structural pi bonds when pressed at room temperature. The targets have an approximate grain size of 2 microns. The graphite provides a carbon source that is combined with a metal catalyst made of powder forge nickel and powder forge cobalt.
Previously used targets involved pressing and binding targets with Dylon carbon cement. These particles had an approximate 200-micron particle size, which led to large regions of uncatalyzed target. The new metal powders are small (~0.5 micron), highly dispersible, and two orders of magnitude less expensive. The powders are mixed in appropriate quantities and subjected to low-energy ball-milling to ensure mingling. Targets undergo additional preparatory steps including high-pressure processing. The targets are then subjected to a series of ultrafast infrared laser light pulses at a high repetition rate to vaporize the layers of the spinning targets and create a plume of nanotubes.