Transcript Document
Diamonds and Dust There’s Plenty of Tubes at the Bottom Nanotubes: Roll Your Own • Some History • Discovery of Carbon NT’s • Electronics on Really Short Length Scales • New Tubes • Applications “There’s Plenty of Room at the Bottom” Richard Feynman (Caltech,1959) Now, the name of this talk is ``There is Plenty of Room at the Bottom''---not just ``There is Room at the Bottom.'' I now want to show that there is plenty of room. I will not now discuss how we are going to do it, but only what is possible in principle---in other words, what is possible according to the laws of physics. I am not inventing anti-gravity, which is possible someday only if the laws are not what we think. I am telling you what could be done if the laws are what we think; we are not doing it simply because we haven't yet gotten around to it. The 2001 Feynman Prizes Theoretical Nanotechnology Mark Ratner Northwestern University Molecular Electronics Experimental Nanotechnology Charles Lieber Harvard University Carbon Nanotubes Carbon nanotube contacting platinum electrodes Gate Source Drain Allotropes of elemental carbon Images of carbon NT’s In 1991 Sumio Iijima discovered that multiwalled carbon nanotubes were formed during the sythesis of higher fullerenes. By using catalysts ropes of single wall carbon nanotubes (SWNT’s) can be made. Resolving atomic structure in a NT rope Although the tubes are well ordered, the STM images rarely show the sixfold symmetry of the graphene lattice. The images reveal the backscattering of electron waves from defects on the walls. Electron Backscattering on Single Wall Carbon Nanotubes Observed by Scanning Tunneling Microscopy, Europhysics Lett. 47, 601-607 (1999). Forming stripes in the interference pattern A defect residing on a single sublattice launches a chiral wave In the electronic charge density. Small is different In an ordinary wire, the charge transport is diffusive. But when there is no scattering… In a very short one dimensional wire, the charge transport is ballistic. (Rolf Landauer, 1957) The contacts are part of the device All the scattering at contacts, hence all the voltage drop Quantized resistance RK. For NT’s small is even more different than you think ! The electron energy depends on its wavelength… …but the electrons are strongly diffracted by the graphene lattice-the E(l) relation is unconventional Rolling-up a graphene sheet The wrapping has to match the period of the graphene lattice (m,n) m=n mod(m-n,3) = ±1 mod(m-n,3) = 0, mn The map of wrappings It matters how the tube is bent and twisted Twist (but not bend) can backscatter electrons on an armchair tube. this is responsible for the T-linear observered resistivity. It matters how the tube is contacted High impedance contact leads to the “Coulomb blockade” instead of conventional transistor characteristic It matters what is inside the tube Transmission electron microscopy (TEM) shows C60 inside the tubes. A … scanning tunneling spectroscopy shows that they scatter electrons on the walls. It matters what is outside the tube Tube with highly transparent contacts can acts as a diode.. or not..depending on the postion and voltage on an STM tip. Heteropolar NT’s of Boron Nitride BN is the III-V homolog to graphene. The B and N occupy different sublattices -- this lowers the symmetry and leads to new physical effects The NT’s can have an electric dipole moment that depends on the wrapping No dipole moment for any armchair tube because of its mirror symmetry The NT’s can have an electric dipole moment that depends on the wrapping But the nearby (5,4) wrapping is polar. The NT’s can have an electric dipole moment that depends on the wrapping and P is reversed for the (5,6) structure. This can be changed by pulling and twisting… NT’s are molecular piezoelectrics, where P is sensitive to twist and stretch, so strain <=>voltage ! …or by exciting electrons with light The photogalvanic properties of armchair and helical NT’s are not found in any homogeneous bulk material Applications Epoxy Composites Nanocircuits/Devices Scanning Probe Tips Field Emission Displays + applications in optical materials, sensors and biophysics Nano is BIG in the popular literature Nano is everywhere (but the servings are only micro.) For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled. (from Richard Feynman’s commentary on the report on the Challenger disaster. )