Kinetics
The composite evolves by making two kinds of changes: elastic deformation in the substrate, and mass relocation in the epilayer. Elastic deformation does not dissipate energy, but mass transport does. Define the driving force  as the reduction of the free energy of the composite when an atom relocates by unit distance. Specify a kinetic law by relating the atomic flux linearly to the driving force;
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(8) |
where M is the mobility of atoms in the epilayer. Again isotropy is assumed in the surface; otherwise M should be replaced by a second rank tensor.
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