How does it feel to roll a molecule?
Sean Washburn*
Applied and Materials Sciences, Univ. North Carolina at Chapel Hill,
Chapel Hill, NC 27599-3255 USA
This is an abstract
for a presentation given at the
Ninth
Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is
available on the web.
We have used a unique set of tools developed in collaboration between materials scientists and computer sciences to manipulate individual carbon nanotubes by hand on surfaces. The instrument comprises a commercial AFM (supplied by Thermomicroscopes), a high-speed visualization system (supplied by Silicon Graphics or Dell), and haptic response feedback tool (supplied by Sensable Devices) and ethernet connections among them and a server. After years of give and take, we have arrived at a portable hand-operated, real-time microscopy paradigm that permits hands-on control of any structures that can be sensed in the microscope. Some of the features (stereo views, real-time shaded rendering, virtual world for touch and sight) added to the generic microscopy technique.
A survey of experiments involving mechanical and electrical response of carbon nanotubes will be described. For example, we have found that, when registered to an underlying graphite substrate lattice, the nanotubes (which share the same lattice cell) will roll as if on treads or gears with the atoms performing the duty of gear teeth. This locking in the nanotube lattice to the graphite lattice leads to a dramatic change in the force of friction between the nanotube and the graphite and to an order of magnitude change in the electrical transport coefficient between the nanotube and the graphite lattice. The results from one series of friction measurements exhibit clear periodic fluctuation in friction. Of course the period of the friction fluctuation matches the nanotube circumference. Different nanotubes lock in at different angles relative to the lattice as expected since different nanotubes have different chirality (wrapping of the graphene lattice to make the nanotube).
Electrical contact between the nanotube and the graphite also varies dramatically as the tube is re-oriented on the surface as expected from straight-forward considerations of the amount of atomic overlap or momentum conservation between modes in the nanotube and those in the graphite substrate. The resistance between the nanotube and the graphite passes through periodic maxima and minima as the tube orientation changes on the surface by 60°.
Details of these and other experiments made possible by the unique tools that we have developed will be reviewed.
*Corresponding Address:
Sean Washburn
Applied and Materials Sciences, Univ. North Carolina at Chapel Hill
CB 3255, Chapel Hill, NC 27599-3255 USA
Phone: 919 962 9382
Fax: 919 962 0480
Email: [email protected]
http://www.physics.unc.edu/~sean
|