Pseudomorphic-to-close-packed transition. I. General formulation

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Abstract
Monolayers (ML’s) of Ni and Co grow at equilibrium on {110} W and Mo substrates, with which they bond strongly and have large negative misfits, pseudomorphically until completion of the pseudomorphic monolayer. When excess atoms are deposited atop the pseudomorphic monolayer, it transforms to a misfitting, more or less close-packed (cp) monolayer with misfit dislocations at the monolayer-substrate interface. In nonequilibrium growth, the pseudomorphic-to-close-packed transition occurs in monolayer islands before completion of the pseudomorphic ML. The main objectives of the paper are (i) to show that the pseudomorphic ML is more stable than the close-packed monolayer and (ii) to develop an understanding of the pseudomorphic-to-close-packed transition. In paper I we introduce force models and derive expressions for (a) equilibrium zero-order energies of complete and incomplete misfit dislocations having displacement vectors equal to a lattice and half a lattice vector, respectively, and (b) equilibrium first-order energy for incomplete misfit dislocations (assumed to yield the lowest energy configuration), these two being the candidates for minimum energy of the close-packed monolayer. The numerical computation of parameters (using embedded-atom methods) and derived energies (including anharmonic pseudomorphic strain energy), needed to answer the relevant questions, are left for paper II.