Scanning Tunneling Microscopy and Spectroscopy of Short Multiwall Carbon Nanotubes
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SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY OF SHORT MULTIWALL CARBON NANOTUBES A. Hassanien1, *, A. Mrzel2, M. Tokumoto1, X. Zhao3, Y. Ando3, and D. Tománek4 1 Nanotechnology research institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568, Japan. 2 Jozef Stefan Institute, 39 Jamova, Ljubljana 1000, Slovenia. 3 Department of Physics, MeijoUniversity, Shiogamaguchi, Tempaku-ku, Nagoya, Japan. 4 Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1116, USA.
ABSTRACT We report on the structural analysis of multiwall carbon nanotubes (MWNTs), produced by DC arc discharge in hydrogen gas, using a scanning tunneling microscope operated at ambient conditions. On a microscopic scale the images show tubes condensed in ropes as well as individual tubes which are separated from each other. Individual nanotubes exhibit various diameters (2.5-6 nm) and chiralities (0-30° ). For MWNTs rope, the outer portion is composed of highly oriented nanotubes with nearly uniform diameter (4-5 nm) and chirality. Strong correlation is found between the structural parameters and the electronic properties in which the MWNTs span the metallic-semiconductor regime. True atomic-resolution topographic STM images of the outer shell show hexagonal arrangements of carbon atoms that are unequally visible by STM tip. This suggests that the stacking nature of MWNTs, may effect the electronic band structure of the tube shells. Unlike other MWNTs produced by arc discharge in helium gas, the length of the tubes are rather short (80-500 nm), which make it feasible to use them as a components for molecular electronic devices.
INTRODUCTION Among the fascinating properties of Multiwalled Carbon Nanotubes (MWCNTs) are their electronic properties which make them reliable for applications as molecular electronic devices (field emitters1, field effect transistors2, …etc). Combined with chemical stability MWCNTs show robust structures, which can survive severe strain and high currents. Moreover, since the single shell electronic properties are very much dependent on its structural parameters3-7 (tube diameter and chiralities), MWCNTs should offer a possibility of switching between semiconducing and metallic states within the same tube. This switching between high and low conduction could be of significant technological importance (for example, constructing nanointegrated devices). Furthermore, as carbon nanotubes conduct electric current without heating, this would make them reliable for use as connectors in nano-electronic circuits. A vital step in developing technology based on carbon nanotubes is to customize their structural parameters (including their lengths). Liu et. al 8 developed a method to reduce the length of SWCNTs, however structural defects cannot be ruled out as a result of vigorous sonication in CH2Cl2. Here we present our STM investigations of pristine MWCNTs produced by arc discharge in H2 gas. Topographic STM images show MWCNTs mai
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