Aligned conical carbon nanotubes

Aligned conical carbon nanotubes (CCNTs) have been synthesized on catalyst-coated Si (100) substrates by a D.C. plasma-assisted hot filament chemical vapor deposition process. The same technique under slightly different deposition conditions has been used to grow aligned conventional carbon nanotubes. The conical shape is due to secondary graphitic growth on the main nanotube. This growth results in the formation of a series of inverted lampshade-type structures stacked over each other, which gives the CNT the appearance of a cone. The CCNT structures are typically 2 mu m at the base with an inner diameter of 100 nm and 2000 nm long. Patterned growth, e.g., arrays of 6 mu m x 6 mu m square, has been achieved. Field emission from CCNTs for use in flat panel displays is also reported. (C) 2000 Kluwer Academic Publishers.