Paper NS-ThM6
Ultrahigh-Vacuum Scanning Tunneling Microscopy Study Into the Adsorption of N-methyl-pyrrolidone Molecules on Carbon Nanotubes

Thursday, October 18, 2007, 9:40 am, Room 616

The most common processing technique for carbon nanotubes involves dispersing them in a liquid media. However, due to their high molecular weight, nanotubes suspend and are not soluble in all known solvents. Usually, surfactants are used to overcome this obstacle.¹ Recently people found that pristine single wall carbon nanotubes can be spontaneously dispersed and even exfoliated in an N-methyl-pyrrolidone (NMP) solvent, forming a carbon nanotube solution.² The negative free energy of mixing NMP with nanotubes leads to the strongly adsorption of a huge number of NMP molecules on the nanotubes in NMP solution and even dried-powder. In our experiments, carbon nanotubes processed by the NMP solvent are deposited on clean Si(001) substrates using a dry deposition method³ and investigated using an ultrahigh-vacuum (UHV) scanning tunneling microscope (STM). We find that NMP molecules diffuse from the nanotubes and become irreversibly chemically adsorbed on Si(001) surfaces due to the strong interaction of nitrogen with Si dangling bonds, indicating NMP molecules remain bound to nanotubes even under UHV conditions. However a few remaining molecules reversibly bound to the nanotubes are observed using STM and are seen to emerge from tube bundles. The molecules can migrate on the bundles during imaging and finally become bound to the Si(001) substrate. After all NMP molecules are removed, there is no defect left on the nanotubes.

¹ G. S. Duesberg et al, Chemical Communications, 435 (Feb, 1998)
² S. D. Bergin et al, unpublished.
³ P.M. Albrecht and J. W. Lyding, App. Phys. Lett. 83, 5029 (2003).