Atomic structural variations of [0 0 0 1]-tilt grain boundaries during ZnO grain growth occurred by thermal treatments

ZnO thin films were deposited on n-Si substrates by using plasma-assisted molecular beam epitaxy. Plane-view zero-loss energy filtered transmission electron microscopy (TEM) images showed that the grain boundaries between large and small grains changed from the curve to the straight shape during ZnO grain growth. The [0 0 0 1]-tilt grain boundary of as-grown ZnO thin films changed from the zigzag facet planes into the symmetric tilt grain boundary through the asymmetric tilt grain boundary with periodic image flat planes. Such an atomic structural variation of grain boundary changes from curved grain boundaries to flat shape was due to decrease of total boundary energy during grain growth. The atomic structural variations of the [0 0 0 1]-tilt grain boundaries during ZnO grain growth occurred by thermal treatments are described on the basis of the TEM images.