Diamonds and Dust

• Some History• Discovery of Carbon NT’s• Electronics on Really Short

Length Scales• New Tubes• Applications

There’s Plenty of Tubes at the Bottom

Nanotubes: Roll Your Own

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.

“There’s Plenty of Room at the Bottom”Richard Feynman (Caltech,1959)

The 2001 Feynman Prizes

Theoretical NanotechnologyMark Ratner Northwestern UniversityMolecular Electronics

Experimental NanotechnologyCharles LieberHarvard UniversityCarbon Nanotubes

Carbon nanotube contacting platinum electrodes

Source DrainGate

Allotropes of elemental carbon

Images of carbon NT’s

In 1991 Sumio Iijima discoveredthat 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 wellordered, the STM images rarelyshow the sixfold symmetry ofthe graphene lattice. The imagesreveal the backscattering ofelectron waves from defects on the walls.

Electron Backscattering onSingle Wall Carbon NanotubesObserved by Scanning Tunneling Microscopy, Europhysics Lett.47, 601-607 (1999).

Forming stripes in the interference pattern

A defect residing on a singlesublattice launches a chiral waveIn 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 arepart of the device

All the scattering atcontacts, hence all thevoltage drop

Quantized resistanceRK.

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() relation is unconventional

The wrapping has to match the periodof the graphene lattice (m,n)

Rolling-up a graphene sheet

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) canbackscatter electronson an armchair tube.

this is responsible forthe 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

A

Transmission electronmicroscopy (TEM) showsC60 inside the tubes.

… scanning tunneling spectroscopy shows that they scatter electrons on the walls.

It matters what is outside the tube

Tube with highly transparentcontacts can acts as a diode.. ornot..depending on the postionand voltage on an STM tip.

Heteropolar NT’s of Boron Nitride

BN is the III-V homologto 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 helicalNT’s are not found in any homogeneous bulk material

Applications

Epoxy Composites

Field Emission Displays

Scanning Probe Tips

Nanocircuits/Devices

+ 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. )