Electric field and potential around localized scatterers in thin metal   films studied by scanning tunneling potentiometry
  Direct observation of electric potential and field variation near local scatterers like grain boundaries, triple points and voids in thin platinum films studied by scanning tunneling potentiometry is presented. The field is highest at a void, followed by a triple point and a grain boundary. The local field near a void can even be four orders of magnitude higher than the macroscopic field. This indicates that the void is the most likely place for an electromigration induced failure. The field build up near a scatterer strongly depends on the grain connectivity which is quantified by the average grain boundary reflection coefficient, estimated from the resistivity. 
Geetha Ramaswamy and A. K. Raychaudhuri