Electron transport in stepped Bi 2 Se 3 thin films.

We analyse the electron transport in a 16 quintuple layer thick stepped Bi2 Se3 film grown on Si(1 1 1) by means of scanning tunnelling potentiometry (STP) and multi-point probe measurements. Scanning tunnelling microscopy images reveal that the local structure of the Bi2 Se3 film is dominated by terrace steps and domain boundaries. From a microscopic study on the nm scale by STP, we find a mostly linear gradient of the voltage on the Bi2 Se3 terraces which is interrupted by voltage drops at the position of the domain boundaries. The voltage drops indicate that the domain boundaries are scatterers for the electron transport. Macroscopic resistance measurements (2PP and in-line 4PP measurement) on the µm scale support the microscopic results. An additional rotational square 4PP measurement shows an electrical anisotropy of the sheet conductance parallel and perpendicular to the Bi2 Se3 steps of about 10%. This is a result of the anisotropic step distribution at the stepped Bi2 Se3 surface while domain boundaries are distributed isotropically. The determined value of the conductivity of the Bi2 Se3 steps of about 1000 S cm-1 verifies the value of an earlier STP study.