Understanding of preferred orientation formation in rock-salt materials: the case of MgO

Abstract

We developed a kinetic model to predict the preferred orientation for the case of rock-salt MgO crystal by assuming random walk diffusion of the adatom between (111) and (100) planes during growth. This model suggests that the tendency of the (111) preferred orientation increases under high deposition rate and low activation energy for diffusion of the adatom between (111) and (100) grains because the adatoms on the (111) surface stick to the surface more strongly compared to those on the (100) plane. The theoretical model was confirmed experimentally by growing several polycrystalline MgO films using the electron beam evaporation method. We could easily control the flux and energy of MgO adatoms by modulating the emission current of the electron gun, substrate temperature, and extra energy source such as ion beam assisted deposition. Our experimental results show good qualitative agreement with the model for the various polycrystalline MgO films deposited at several growth conditions.