Fabrication of highly oriented carbon-nanotube films and its application to an emitter with high efficiency

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In order to investigate the initial stage of carbon-nanotube(CNT) formation at the surface decomposition of SiC, we heated the SiC single-crystal substrates (6H-type, C-face polished) in vacuum using an infrared mirror furnace and a turbo-molecular pump, and we analyzed the structure change at the surfaces by means of spectro-ellipsometric measurements.Up to 1100℃, the change in spectra could be interpreted as the decrease of thickness of SiO_2 layer (-4 nm) on the SiC substrate. At 1150℃ and above, however, spectra were distinctly different from those of the samples heated up to 1100℃, and could be interpreted with a three-phase model, in which the surface layer consists of graphite including X% of voids, where the surface layer thickness t=10-50 nm and X=50-70%. This indicates that the surface decomposition of SiC is initiated at this temperature and that the spectro-ellipsometric measurements can detect small changes of optical properties of surface due to the initiation of decomposition.When the substrates were heated for a longer time (80-640 min) at 1300℃, the spectra were essentially different again, and they could be interpreted with a four-phase model, in which the surface layer consists of two graphite layers including different percentages of voids, where the thickness of surface layers t_1=20-50 nm, t_2=20-60 nm and the percentages of voids X=-90%, Y=-50%. This implied that formation of CNT would start at this temperature. This formation was also detected by FE-SEMI observation.Furthermore, we tried to fabricate CNT films by means of H-CVD method using camphor, and found out that carbon nanotubes can be grown using ferrocene as a catalyst.