• Experimental evidence of the existence of carbon nanotubes came in 1991 when Iijima1 imaged multiwalled carbon nanotubes (MWNTs) using a transmission electron microscope.
• Two years after the observation of MWNTs, Iijima and coworkers and Bethune2 and coworkers simultaneously and independently

observed single walled carbon
nanotubes (SWNTs).

Transmission electron micrographs (TEMs) of the first observed multiwalled carbon nanotubes (MWNTs) reported by Iijima1 in 1991