FORMATION OF HIGH-ALIGNMENT CARBON-NANOTUBES AND APPLICATION

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Kusunoki et al. have reported that carbon nanotubes (CNTs) are densely formed in vertical alignment by annealing a SiC(000-1)C-face at 1700℃ in a certain vacuum condition [Appl. Phys. Lett., 77(2000)531]. In this process called surface decomposition method, Si atoms are selectively evaporated from the SiC surface and instead residual carbon atoms are concentrated to form aligned CNTs. In this method, the CNTs have grown without any catalytic help of metals or gases. On the other polar face, SiC(0001)Si-face, they could not obtain CNTs but did only several graphite layers parallel to the surface. In our previous scanning tunneling microscopy (STM) study in the ultra-high vacuum, many domains of graphite appear after annealing the SiC(000-1)C-face at temperatures higher than 1300℃. The fact that CNTs are not formed on the SiC(000-1)C-face in the condition of ultra-high vacuum has not been explained yet. We carried out cross-sectional transmission electron microscopy (TEM) observations in order to explore the mechanism of the formation of CNTs on the SiC(000-1)C-face. After annealing the SiC(000-1)C-face at 1200℃ in the ultra-high vacuum, there appear many protrusions, which might be precursor of CNTs, in the domain boundary of the graphite in the STM image. When this surface is annealed at 1700℃ in the low vacuum, the CNTs are formed on the surface. On the other hand, the surface annealed at 1050℃ in the ultra-high vacuum is covered by the graphite layer without defects. The CNTs are not generated on the surface after being annealed at 1700℃ in the low vacuum. The CNT growth is suppressed by the morphology of the graphite layer on the SiC(000-1)C-face.