Scanning electron microscopy study of carbon nanotubes heated at high temperatures in air

Multiwalled carbon nanotubes (MWNTs) were dispersed in 2-butanol and dropped onto a V-ridge, lithographically patterned Si substrate that was coated with a thin layer of gold. These MWNTs were shown by scanning electron microscopy (SEM) to conform to the V-ridge surface topology at room temperature, which is thus useful for introducing kinks (at the apex of the V-ridge and the bottom of the trenches between V ridges). The substrate-supported MWNTs were then heated in air at temperatures from 673 to 1173 K for varying exposure times and were monitored with SEM. A 122 kJ mol(-1) activation energy for complete oxidation was obtained, and preferential oxidation at kink sites was observed on some MWNTs at high temperatures. The dominant mode of oxidation was either thinning of the walls of the MWNTs or sequential oxidation of the component tubes in bundles. Some MWNTs, which at room temperature conformed to the V-ridge surface topology, detached ("sprang" away) from the substrate surface, demonstrating that the MWNTs are under tensile stress, but are held to the surface by van der Waals attractive forces, which can be overcome by exposure to higher temperatures. (C) 1999 American Institute of Physics. [S0021-8979(99)04113-4].