Carbon nanotubes (CNT) are allotropes of carbon with a cylindrical nanostructure and are categorized as single-walled nanotubes (SWCNTs) and multi-walled nanotubes (M-WNT). SWNTs can be grown on Si substrates using a chemical vapor deposition (CVD) method. MWNTs consist of multiple rolled layers (concentric tubes) of graphite. SWNT are an important variety of carbon nanotube because they exhibit electric properties that are not shared by the MWNT variants. Several methods of separating semiconducting and metallic CNTs are known. The CAS (Chinese academy of sciences) has defined CNT research as a key area for nanotechnology development in China.