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Epitaxy (epitaxial crystal growth)
Epitaxy is the growth of a crystal on the surface of a second crystal of a different chemical nature where the crystal growth follows a certain fixed orientation. Such growth can be caused by precipitation from a solution, electroplating, surface oxidation, gas phase deposition or vacuum evaporation .
This form of crystal growth occurs especially in substances whose lattice structure and lattice pitches are similar to the metal substrate. Since forces originating from the atoms of the substrate are strongest across the distance of several atoms, the atoms of the growing crystal which are under the influence of these forces will initially fill the gaps with the lowest potential and the crystal continues to grow from there. In tin-lead coating, it is possible to thermally decompose the metal substrate by reaction with a halogenous fluxing agent and then produce a tin-lead layer by epitaxial growth.