Scanning probe microscopy of carbon nanotubes

Multi-wall carbon nanotubes (MWNTs) deposited on various substrates were analysed by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). A dispersion of carbon nanotubes in ethanol was drawn through a 200 nm pore ceramic filter to produce a thin film of nanotubes. This film was brushed along one direction with a Teflon rod involving a change of optical properties. Scanning probe images document that brushing alters the orientation of carbon nanotubes from random to aligned within the plane. To characterize individual nanotubes, a droplet of nanotubes and nanoparticles suspension (solvent ethanol or chloroform) was applied to highly oriented pyrolytic graphite (HOPG) as well as to a polycrystalline gold film, and allowed to evaporate. This yielded a random distribution of nanotubes on the substrate. Individual nanotubes as well as aggregates of nanotubes could be Identified and characterized by STM and AFM on both HOPG and polycrystalline gold substrates. AFM measurements suggest that carbon nanotubes adhere more tightly to the gold substrate due to the higher surface roughness. The weak binding allows us to move carbon nanotubes on a graphite surface at much lower force loads than on polycrystalline gold films. STM imaging of nanotubes on polycrystalline gold films yielded atomic resolution. (C) 1998 Elsevier Science Ltd. All rights reserved.