Field and potential around local scatterers in thin metal films studied byscanning tunneling potentiometry

We report the direct observation of electrochemical potential and local tra nsport field variations near scatterers like grain boundaries, triple point s, and voids in thin platinum films studied by scanning tunneling potentiom etry. The field is highest at a void, followed by a triple point and a grai n boundary. The local transport field near a void can even be four orders o f magnitude higher than the macroscopic field, indicating that the void is the most likely place for an electromigration induced failure. The field bu ild up for a particular type of scatterer depends on the grain connectivity . We estimate an average grain boundary reflection coefficient for the film from the temperature dependence of its resistivity. (C) 1999 American Inst itute of Physics. [S0003-6951(99)00239-9].