The mechanism of twin formation and strain evolution in highly mismatched sputter-grown ZnO/Al2O3 (00•1) hetero-epitaxial films was investigated. Based upon real-time synchrotron X-ray scattering measurements, the existence of a transition thickness at which the twin of 30° rotated domains started to nucleate within the ZnO films was revealed. It was shown that the twin growth above the transition thickness stopped as the strain almost fully relaxed, which indicated that the twin in the sputter-grown ZnO was a mechanical twin, not a growth twin. A schematic modelling of twin formation during the early growth stages was presented.

Mechanism of Twin Formation in Sputter-Grown ZnO/Al2O3(0001) Hetero-Epitaxial Films. Kim, I.W., Lee, K.M.: Thin Solid Films, 2008, 516[15], 4921-4