Self-orientation of short single-walled carbon nanotubes deposited on graphite

In view of practical handling of single-walled carbon nanotubes (SWNTs), here we present cutting procedures and spontaneous ordering of SWNTs deposited on highly oriented pyrolytic graphite (HOPG). Purified SWNTs were cut by ultrasonication in H2SO4/HNO3 mixture and further in de-ionized water. Thus, prepared short SWNTs were resuspended in methanol and dropped on a freshly cleaved HOPG surface. Scanning tunneling microscopy under a vacuum revealed that the short tubes of 20-100 nm in length were aligned along the basal axis of the HOPG lattice. Tunneling spectroscopy obtained from the oriented tubes indicated a semiconducting behavior, which was characterized in relation to their helical structure. The observed orientation of SWNTs was attributed to their one-dimensional electronic nature along the tube axis with the HOPG lattice. (C) 2001 American Institute of Physics.