Growth twins in nanocrystalline thin films with grain sizes of 5 to 50nm were investigated by means of high-resolution transmission electron microscopy. They exhibited a {101}<101> geometry, metal-atom mirror symmetry, and a slight distortion of the O atoms. Multiple twins and step twin boundaries, with a density about 1015/m2, were frequently observed in the films. It was deduced that there were Sn interstitials at step twin boundaries, and that electronic donors were associated with the interstitials.

J.G.Zheng, X.Pan, M.Schweizer, F.Zhou, U.Weimar, W.Göpel, M.Rühle: Journal of Applied Physics, 1996, 79[10], 7688-94