FORMATION OF HIGH-ALIGNMENT CARBON-NANOTUBES AND APPLICATION

Kusunoki等人。据报道，碳纳米管(CNT)是通过在一定的真空条件下，在1700℃的条件下进行热处理，在垂直方向上密集地形成碳纳米管[Appl.太棒了。Let.，77(2000)531].在这种被称为表面分解法的过程中，硅原子被选择性地从碳化硅表面蒸发出来，而剩余的碳原子被集中在一起形成排列的碳纳米管。在这种方法中，碳纳米管在没有任何金属或气体的催化作用下生长。在另一极面上，碳化硅(0001)面上只有几层平行于表面的石墨层，无法得到碳纳米管。在我们以前的超高真空扫描隧道显微镜研究中，在高于1300℃的温度下对碳化硅(000-1)C晶面进行热处理后，出现了许多石墨微区。超高真空条件下，碳化硅(000-1)面上未形成碳纳米管的原因尚未得到解释。为了探讨碳纳米管在碳化硅(000-1)晶面上的形成机理，我们进行了横截面的透射电子显微镜观察。在超高真空中对碳化硅(0 0 0-1)C晶面进行12 0 0℃热处理后，在扫描隧道显微镜图像中，在石墨的磁区边界上出现了许多突起，可能是碳纳米管的前驱。当该表面在1700℃的低真空下进行热处理时，表面形成了碳纳米管。另一方面，在1050℃的超高真空中退火后，表面被无缺陷的石墨层覆盖。在1700℃的低真空条件下热处理后，未在表面生成碳纳米管。碳化硅(000-1)面上的石墨层形态抑制了碳纳米管的生长。

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.