Local transport properties of thin bismuth films studied by scanning tunneling potentiometry

Charge transport in 20-30-Å-thick Bi films is studied by scanning tunneling potentiometry at room temperature. Deposition at $T=140\mathrm{}$ K onto InP-based multilayer substrates leads to flat and continuous films that are subjected to a lateral current density of up to 8×${10}^6$ A/${\mathrm{cm}}^2$. We find that scattering at surface defects and grain boundaries gives rise to discontinuities in the local electrochemical potential. In particular, we observe dipole-shaped potential variations near small holes in the film. The influence of diffusive and ballistic transport on the formation of these dipoles is discussed.