Plume diagnostics and room-temperature deposition of carbon nanotubes and nano-onions at 248 nm

We report on the deposition of carbon nanotubes and nano-onions at room temperature using excimer laser radiation at 248 nm to ablate mixed graphite-nickel/cobalt targets in the presence of O₂ gas. The carbon nanotubes are frequently seen to connect individual onions and have a wall thickness on the order of 20-25 nm, with an overall external tube diameter of 100-200 nm. These tubes have notably large channel diameters and are significantly larger than typically reported single and multi-walled carbon nanotubes. The observed onion structures are both single and clustered and are 100-200 nm in diameter. Ablation of the same targets in comparable pressures of Ar does not result in these nanostructures but instead produces amorphous carbon. Ablating a pure graphite target under the same laser conditions, with or without metal, also does not yield the tubes and onions. In-situ time-resolved emission spectroscopy has been used to follow the emission from molecular carbon such as C₂, as well as metals such as Ni or Co in the different ambients.