FORMATION OF HIGH-ALIGNMENT CARBON-NANOTUBES AND APPLICATION

Kusunoki等人已经报道，通过在一定真空条件下在1700℃下退火SiC（000-1）C面，以垂直排列密集地形成碳纳米管（CNT）[Appl.Phys.Lett.，77（2000）531]。在这个被称为表面分解法的过程中，Si原子选择性地从SiC表面蒸发，而残留的碳原子则集中形成定向的CNT。在这种方法中，碳纳米管的生长没有任何金属或气体的催化帮助。在另一个极性面，SiC（0001）Si面，他们不能获得碳纳米管，但只做了几个平行于表面的石墨层。在我们以前的超高真空扫描隧道显微镜（STM）研究中，SiC（000-1）C面在1300℃以上退火后出现了许多石墨畴。在超高真空条件下SiC（000-1）C面上未形成CNT的事实尚未得到解释。我们进行了横截面透射电子显微镜（TEM）观察，以探讨在SiC（000-1）C面上的CNT的形成机制。SiC（000-1）C面在超高真空中1200℃退火后，STM图像中石墨畴界出现了许多突起，可能是碳纳米管的前驱体。在1700℃的低真空下退火后，在表面形成了碳纳米管。另一方面，在超高真空中1050℃退火的表面被无缺陷的石墨层覆盖。在1700℃低真空退火后，表面没有生成碳纳米管。碳纳米管的生长受到SiC（000-1）C面上石墨层形态的抑制。

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.