STRAIN-INDUCED CHANGE IN THE ELASTICALLY SOFT DIRECTION OF EPITAXIALLY GROWN FACE-CENTERED-CUBIC METALS

The theory of epitaxial strain energy is extended beyond the harmonic approximation to account for large film/substrate lattice mismatch. We find that for fee noble metals (i) directions [001] and [111] soften under tensile biaxial strain (unlike zincblende semiconductors) while (ii) [110] and [201] soften under compressive biaxial strain. Conseque ntly, (iii) upon sufficient compression [201] becomes the softest dire ction (lowest elastic energy), but (iv) [110] is the hardest direction for large tensile strain. (v) The dramatic softening of [001] in fee noble metals upon biaxial tensile strain is caused by small fcc/bcc en ergy differences for these materials. These results can be used in sel ecting the substrate orientation for effective epitaxial growth of pur e elements and A(p)B(q) superlattices, as well as to explain the shape s of coherent precipitates in phase separating alloys. (C) 1998 Americ an Institute of Physics.