No abstract

Multiwalled carbon nanotubes ͑MWNT's͒ on Si͑5 5 12͒ surfaces are demonstrated to be cut only by a negatively biased conducting tip of an atomic force microscope ͑AFM͒. By scanning with the AFM tip across a 30-nm-diam MWNT in contact mode, we could cut the MWNT only at a negative tip voltage below a threshold. As the tip-moving speed increased, the magnitude of the threshold voltage was increased. A graphite surface was etched in comparison by the same method. It was also etched only at a negative tip voltage below a threshold. As the magnitude of the bias voltage increased, the etch depth of the graphite surface increased exponentially to reach 7.9 nm, a thickness of 23 atomic layers of graphite, at a bias voltage of Ϫ10 V. The etching current from the graphite surface to the negatively biased tip was found to follow the Fowler-Nordheim equation and attributed to field-emission electrons from the negatively biased tip. The etch depth of the graphite surface was also found to follow the bias voltage dependence of the Fowler-Nordheim equation. The graphite etching is thus found to be controlled by the field-emission current so that we may propose a cutting mechanism based on the field-emission current density of the Fowler-Nordheim equation: both the MWNT cutting and graphite etching encounter the same reaction where the activation energy is supplied by electrons that are field emitted from the negatively biased AFM tip.Carbon nanotubes have attracted intensive attention due to their remarkable electronic and mechanical properties since their discovery in 1991. 1 Nanotubes could be bent, straightened, moved, rolled, and slid by the tip of an atomic force microscope ͑AFM͒. 2,3 Single-walled carbon nanotubes ͑SWNT's͒ could be worked by an AFM tip to make circuits of nanotubes, 4 to show single-electron charging, 5 and to fabricate a room-temperature single-electron transistor. 6 Also SWNT's were reported to be cut by the biased tip of a scanning tunneling microscope ͑STM͒ on a gold surface in ultrahigh vacuum. 7 The two small areas of the multiwalled carbon nanotube ͑MWNT͒ connected to electrodes were etched in oxygen plasma to form an island of MWNT's and the Coulomb blockade effect was observed at 4.5 K. 8 Carbon nanotubes were also incorporated between two layers of e-beam resist to be used as a shadow mask, blocking metal deposition at one point along a thin wire. 9 If a MWNT of a given diameter can be cut in precise length by an AFM tip at a specific position of quantum dots or nanowires, it can function as a conducting component of nanodevices such as a single-electron transistor and a resonant tunneling diode.In this experimental work, we want to report our quantitative results in which MWNT's on Si͑5 5 12͒ surfaces were cut by only a negatively biased conducting tip of an AFM in contrast to a previous report 7 where a positively biased tip was also cutting the nanotubes in ultrahigh vacuum. Recently Park et al. 10 reported that nanotubes of 3 nm diameter could be cut by applying only a negative voltage, large...

No abstract

No abstract

No abstract