High-angle twist in GaSe

Abstract
Crystals of GaSe grown by transport reaction with iodine were found to contain high-angle twist boundaries perpendicular to their c axis. A simple model is proposed which affords the twist boundary energy in layer structures such as GaSe and MoS2 to be calculated numerically. The relative minima in the angular dependence of the calculated boundary energies coincide with the experimentally observed series of discrete twist angles in GaSe. The proposed model confirms the validity of Bollmann's geometrical criterion for the stability of high-angle grain boundaries in the special case of layer structures. It is suggested that the model may also lead to a better understanding of the formation and the orientation of the nuclei in epitaxial crystal growth.

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