Institute of Electronic Engineering;
China Academy of Engineering Physics;
Mianyang 621999;
China;
School of Mechanics;
Civil Engineering and Architecture;
Northwestern Polytechnical University;
Xi'an 710072;
China;
Department of Civil and Environmental Engineering;
Northwestern University;
Evanston;
IL 60208;
USA;
Intermetallic compounds; Polarity effect; Electromigration; Diffusion; Size effect;