CURRENT-INDUCED MATERIAL TRANSPORT IN PRECIOUS-METAL COVERINGS ON CARBON STUDIED BY SCANNING-TUNNELING-MICROSCOPY AND SCANNING TUNNELING POTENTIOMETRY

We prepared ultrathin films of Pt and Au on a carbon thin film surface. The growth of the metal covering was studied by measurement of the electrical resistance during the deposition process. It was found that the platinum covering on the carbon surface is dosed at a lower mean thickness than the gold one. The microstructural investigations were done by scanning probe microscopy. We used simultaneously the techniques of scanning tunneling microscopy (STM) and scanning tunneling potentiometry (SIP) to follow the structural changes due to an applied electric potential in air and at room temperature. In our experimental arrangement, the topography is measured by AC tunneling. The local electric potential is obtained from the DC component of the tunneling current. We observed material transport phenomena which drastically affect the topography and the corresponding potential distribution. The STM/STP results concerning the Pt/C system indicate a directed material transport on the carbon surface from the anode to the cathode. A disturbed spot within the carbon him acts as a sink for the migrating atoms. The observed direction of the material transport is in accordance with former results obtained for the Au/C system.