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

Multiwalled carbon nanotubes (MWNTs) were dispersed in 2-butanol and droppe d onto a V-ridge, lithographically patterned Si substrate that was coated w ith a thin layer of gold. These MWNTs were shown by scanning electron micro scopy (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 MWNT s were then heated in air at temperatures from 673 to 1173 K for varying ex posure times and were monitored with SEM. A 122 kJ mol(-1) activation energ y for complete oxidation was obtained, and preferential oxidation at kink s ites was observed on some MWNTs at high temperatures. The dominant mode of oxidation was either thinning of the walls of the MWNTs or sequential oxida tion of the component tubes in bundles. Some MWNTs, which at room temperatu re conformed to the V-ridge surface topology, detached ("sprang" away) from the substrate surface, demonstrating that the MWNTs are under tensile stre ss, but are held to the surface by van der Waals attractive forces, which c an be overcome by exposure to higher temperatures. (C) 1999 American Instit ute of Physics. [S0021-8979(99)04113-4].