Scanning tunneling potentiometry studies of Y₁Ba₂Cu₃O₇__xand gold thin films

We have used a scanning tunneling microscope to study the local electrostatic potential distribution and topography of thin films of gold at room temperature and high-T_c superconducting thin films at low temperature in the presence of a transport current. On continuous gold thin films (85 A thick), high resolution scans often show abrupt changes in the potential, which are clearly associated with topographic features. On a relatively large scale (1 µm), a more uniform potential drop is observed but locally these scans also reveal small steps in the potential. These steps may be a characteristic property of transport in these thin polycrystalline films or, alternatively, could be artifacts due to discontinuous changes in the tunneling position on the sample during scanning. On high-T_csuperconducting thin films, a thin gold overlayer permits potentiometry studies at low temperature. The first low-temperature potentiometry studies show a clear change in behavior at the normal-superconductor transition.