Maxwell and Sharvin conductance in gold point contacts investigated using TEM-STM

We have investigated the conductance of gold point contacts using a scannin g tunneling microscope (STM) inside a transmission electron microscope (TEM ). Measuring the conductance of these point contacts as a function of radiu s, we could directly compare it with theories both in the ballistic regime (Sharvin) as well as in the diffusive regime (Maxwell). The width of the co ntacts were between a single atom and 20 nm. Using an interpolation formula (Wexler) between the two limits, we obtain a mean free path of 4 nm, which is about ten times shorter than the room-temperature bulk value. The low v alue indicates an enhanced scattering, which is not due to high temperature in the point contact, instead a large number of scattering centers is crea ted during the point contact formation process.