Shortening multiwalled carbon nanotube on atomic force microscope tip: Experiments and two possible mechanisms

Abstract

We demonstrate a technique to cut a multiwalled carbon nanotube (MWNT) attached on an atomic force microscope tip by flowing direct current through the nanotube as a method to precisely control nanotube tip length. The cutting process consists of two steps: (1) making a mechanical contact between a sharp metal wire and a target cutting position on a MWNT attached to a silicon mother tip, and (2) applying voltage between the MWNT and the metal wire until the current flow cuts the tube. To cut the MWNT without discharging, a firm mechanical and electrical contact was made between the tube and the wire. Nanotubes were reproducibly cut at the contact point, and we achieved a 30 nm cutting resolution and a 100 nm shortest tube protrusion. We simultaneously monitored the current flow through the nanotube during the cutting process and evaluated the current size of each MWNT tip at the moment of cutting. We found that the cutting process happened in two current ranges: higher than 100 μA and smaller than 1 μA. The mechanism of cutting at high current cutting process is attributed to unimolecular decomposition reaction, and we propose that at small current the cutting process may be done by chemical etching, which is activated by the current. © 2007 American Institute of Physics.