No "direct force" in electromigration

Abstract

In electromigration, a uniform field is applied and a dipole moves from one crystallographic site to another. The dipole has the same strength at the two sites. Because electrostatic fields are conservative, the translation occurs without change of electrostatic energy. Accordingly, the "direct force" is identically zero. Objections to this conclusion are considered. It is emphasized that in any experiment in which an electron wind is present it is important to measure $Z^{*}$ in the lattice frame of reference.