Synthesis and structural characterization of catalyst-free carbon micro-cones.

We report the growth of vertically oriented carbon micro-cones without using any foreign catalyst on silicon (100) substrate by microwave plasma assisted chemical vapour deposition method. The average height and bottom diameter of the carbon micro-cones are approximately 20 microm and approximately 1.4 microm, respectively. The diameters of the carbon micro-cones decrease gradually from bottom to tip, terminating in a nanotube structure. Mechanical damage of micro-cones resulted in the breaking and partial removal of the carbon micro-cones to show the structures possessed a nanotube core. Outside the micro-cone, the nanotubes showed a flattened ribbon structure. Electron microscopy and micro-Raman spectroscopy shows the nanotubes are multi walled and highly graphitic, with low structural disorder. The advanced vacuum electron emission devices could be fabricated with the carbon micro-cones grown directly on silicon substrate without using any catalyst.