IN-SITU SCANNING-TUNNELING-MICROSCOPY STUDIES OF CURRENT-DRIVEN MASS-TRANSPORT IN AG

We present the results of an ultrahigh vacuum (UHV) scanning-tunneling -microscopy study of large scale mass transport in current carrying me tal films. Scans were taken in situ on a current carrying 2100-angstro m-thick Ag film with current densities ranging from 5.0 X 10(4) A/cm2 up to 3.2 X 10(5) A/cm2, at which point the sample failed due to a run away thermal fusing mechanism. Axial UHV inchworms allowed us to obtai n data from the same 2-mum-square region of the sample throughout the experiment in spite of large temperature-induced drifts. Calculations of the driving forces demonstrate that the electromigration driving fo rce was dominant for this current range. Significant topographical cha nges were observed including current aligned grain growth, current ind uced faceting, and complex mass flow divergences. A model that explain s the observed divergences is presented. It is based upon diffusion in the presence of local inhomogeneities of the electric field.