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Overview
 Carbon Nanotubes -- tiny tubes about 10,000 times thinner than a human hair -- consist of rolled up sheets of carbon hexagons. Multiwalled carbon nanotubes were discovered in 1991 by Sumio Iijima of NEC. In early 1993, Iijima and Almaden's Don Bethune discovered that transition metals can catalyze the growth of single-wall carbon nanotubes. The precisely-defined structures of the single-walled nanotubes led to an explosion of experimental and theoretical research into their properties and applications. They show great potential for use as minuscule wires or in ultrasmall electronic devices. To build those devices, scientists must be able to manipulate the Nanotubes in a controlled way. IBM researchers using an atomic force microscope (AFM), an instrument whose tip can apply accurately measured forces to atoms and molecules, have recently devised a means of changing a nanotube's position, shape and orientation, as well as cutting it.
ALSO:
Chip Evolution: IBM Scientists Develop Breakthrough Transistor Technology with Carbon Nanotubes
Yorktown Heights, N.Y., April 27, 2001 ... IBM scientists developed a breakthrough transistor technology that could preview how computer chips can be made smaller and faster than what is currently possible with silicon. [ More picture options ]
How it works
 How it works
Tobias Hertel, Robert Walkup, Richard Martel and Phaedon Avouris at IBM's Thomas J. Watson Research Center found that van der Waals forces -- attractive forces among atoms and molecules -- hold Nanotubes firmly against the surfaces they are placed on. Thus the researchers were able to change the Nanotubes' positions and orientations, and to alter their shape, by bending them. They distorted the Nanotubes in various ways using calibrated AFM forces; the strong interaction with the surface then stabilized the distorted Nanotubes. By applying particularly large forces, the researchers were able to cut the Nanotubes. For that to happen, however, the Nanotubes had to be anchored to the surface more firmly than normal, by means of chemical bonds rather than the physical van der Waals forces.
These studies led to the important conclusion that the van der Waals interaction between the Nanotubes and the surfaces on which they rest is itself strong enough to change the shape of Nanotubes. In general, they tend to adapt to the shape of the surface on which they sit by bending and becoming slightly squashed. Those changes can cause the properties of Nanotubes on surfaces to differ from those of perfect Nanotubes, which are straight and have circular cross-sections. This raises the possibility of tailoring Nanotubes' properties by intentionally changing their shapes. [ More picture options ]
 Structure of a single-walled carbon nanotube
 Electron microscope image of a multi-walled carbon nanotube across metal electrodes
 Figure 1. Schematic of a carbon nanotube field-effect transistor. The nanotube acts as the channel that bridges the source and drain electrodes. The current flow in the nanotube is controlled by the voltage applied to the gate electrode.
 Figure 2. Graph showing the amount of current flowing through a nanotube field-effect transistor as a function of the voltage applied to the gate electrode. When the gate voltage is positive the current involves negative electrons, while for negative voltage the current involves positive holes.
Future Applications
As the electronic circuits on computer chips become smaller and smaller, conventional transistors run into physical limitations caused by extreme miniaturization. Nanotubes hold the promise of creating novel devices, such as carbon-based single-electron transistors, that will allow the miniaturization to continue beyond the limits of current silicon-based device technology. IBM scientists are now examining the basic properties of carbon Nanotubes and the feasibility of using them as the basis for a new class of nanoelectronic devices.
For Researchers
Links to related topics
IBM Research Nanoscale Science Website
Scientific American Article: "Turn of the Gear"
American Scientist Article on Nanotubes
Nanotube History of Nanotubes with Lots of Links
Subscribe to BuckyNews
(weekly news updates in the world of BuckyTubes)
Purchase Nanotubes from Alfa/Aesar
IBM CyberDigest Articles
Nanotube Research at Universities
Prof. Richard Smalley Group Webpage
(Nobel prize for discovery of buckyballs)
Prof. David Tomanek's (Mich. State) Nanotube Page
Links to additional Nanotube Images:
Nanotube Manipulation
Molecular Manipulation
Nanotube Field-Effect Transistor
Nanotube Theory
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