Fe catalytic growth, microstructure, and low-threshold field emission properties of open ended tubular graphite cones

Large-area tubular graphite cones (TGCs) with an open end were successfully synthesized on Si substrates by microwave plasma assisted chemical vapor deposition using a thin Fe film as catalyst. As-grown TGCs are uniformly distributed on the Si surface with a density of 5.8x10(5)/cm(2) and an average growth rate of 0.6 mu m/min. Some of them are very sharp with an apex angle as small as 2 degrees-3 degrees. Combined observations by transmission electron microscopy and cross-sectional scanning electron microscopy clarified that the TGCs possess a hollow nanotube core, a metal-free open tip and that the Fe catalyst is located in the root, strongly supporting the base-growth mechanism of TGCs. Scanning confocal micro-Raman spectroscopy along an individual TGC shows that the integrated intensity ratio of D to G band of individual TGC at tips (0.12) is an order of magnitude less than that at roots (1.2), confirming that the tip is highly crystalline whereas the root is of poor quality. Their field emission performance exhibits a turn-on field as low as 1.8 V/mu m and highly stable emission characteristics. The present study opens the way to site selective growth of TGCs and demonstrates its use as a potentially excellent emitter. (C) 2008 American Institute of Physics.