Atomic structure of [0001]-tilt grain boundaries in ZnO:  A high-resolution TEM study of fiber-textured thin films

The atomic structure of [0001]-tilt grain boundaries in ZnO was investigated using high-resolution transmission electron microscopy (HRTEM) and atomistic calculations. HRTEM observation was conducted for [0001] fiber-textured ZnO thin films grown on quartz-glass substrates by the pulsed-laser deposition. The [0001]-tilt boundaries observed in the films can be classified into three types: low-angle boundaries composed of irregular dislocation arrays, boundaries with {101̅ 0} facet structures, and near-low Σ boundaries represented by symmetric periodicity units. The atomic structure of the boundaries is discussed with a focus on a Σ=7 boundary in conjunction with atomistic calculations and HRTEM image simulations. The Σ=7 boundary consists of multiple structural units that are very similar to the core structures of edge dislocations. Straight or zigzag arrangements of the dislocationlike structural units constitute other high-angle boundaries with symmetric and {101̅ 0} facet structures as well. It is suggested that [0001]-tilt boundaries in ZnO are generally described as an array of the dislocationlike units.