Observation of single-wall carbon nanotube rings by scanning tunneling microscopy and spectroscopy

摘要

Bundled ring structures of single-wall carbon nanotubes (SWCNTs) have been observed when the SWCNTs are ultrasonically dispersed in solvents [1]. Such ring structures of SWCNTs have been employed to investigate the electron transport mechanism of SWCNTs [2]. Recently, the electrical switching behavior of carbon nanotube rings as a transistor was also demonstrated by conductivity experiments with a dual scanning tunneling microscope (D-STM) [3] and with a triple-probe atomic force microscope [4]. In the D-STM experiments by Watanabe and co-workers [3], it is observed that the current between the two tips (source and drain) depends on the position of the tips and varies dramatically with the applied gate voltages. Moreover, the current-voltage measurements display a rectification effect at large gate voltages [3,4]. Until now there has been no conclusive understanding of the phenomena although it is noted that a theoretical model has been proposed for an interpretation [5].