Single-wall carbon nanotubes (SWCNTs) can be either semiconducting or metallic, depending on their tube diameters and chiral angles. Semiconducting SWCNTs (s-SWCNTs) are promising candidate as the channel material of high-performance field effect transistors, while metallic SWCNTs (m-SWCNTs) can be used for the fabrication of transparent conductive films and interconnectors. As-prepared SWCNT samples are usually a mixture of s- and m-SWCNTs. Therefore, it is highly important to prepare s-SWCNTs and m-SWCNTs selectively. We studied the growth mechanism and oxidation process of CNTs by using an in situ TEM method, and the structure-dependent stability of SWCNTs was revealed[1].