  Controlled electromigration of gold nanowires of different cross-sectional
areas to form nanogap junctions is studied using a feedback method. A linear
correlation between the cross sectional area of the gold nanowires and the
power dissipated in the junction during electromigration is observed,
indicating that the feedback mechanism operates primarily by controlling the
temperature of the junction during electromigration. We also show that the role
of the external feedback circuit is to prevent thermal runaway; minimization of
series resistance allows controlled electromigration to a significant range of
junction resistances with a simple voltage ramp.
