Nano-Thermal and Electrical Transport
Electrical resistance is the archetypal physical quantity and Ohm's law the best-known physics equation. But in fact both of these properties become fuzzy and unreliable as the scale of the electrical device approaches the nanoscale.
For a metal or a semiconductor when the size of the resistor becomes comparable with the distance a conduction electron travels before it scatters off an atom then the simple concept of resistance breaks down. This is the ballistic conduction regime where resistance of a conductor no longer increases with length. It occurs at different length scales for different materials but is typically in the nanoscale.
Less obviously a similar process happens for the transport of heat. Electrons and phonons contribute to heat transfer in solids and both of these exhibit ballistic conduction at the nanoscale.
The practical implications of nanoscale transport include the fact that extremely high electrical and thermal conductance can be achieved and these properties could be crucial in the future extension of Moore's law to ever smaller chips. Already power dissipation in CMOS chips is a seriously limiting factor to future improvements. Ion transport through biological membranes is another area in which macroscopic electrical transport concepts are expected to require modification.
At NPL we have studied the electrical and thermal transport in artificial materials such as carbon nanotubes and ion channels in artificial bi-layer membranes. In addition we are investigating the extraordinary mechanical properties of carbon nanotubes (in which we were the first group to observe ballistic phonon transport) as a route to observing quantum behaviour in a nanoscale mechanical resonator.