Imaging Strain Fields

Strain fields at the low-angle twist grain boundary between SrTiO3 and Nb:SrTiO3 imaged by scanning transmission electron microscopy (STEM).
(a) High-angle annular dark field (HAADF) is strongly affected by the orientation of the crystal. The right side of the bicrystal is oriented ‘‘on axis’’, hence in channeling condition and appears much brighter. The strain field at the grain boundary causes minor contrast variations in HAADF. (b) In low-angle annular dark field (LAADF) imaging the strain field at the grain boundary can be detected through its distortion of adjacent atomic sites and subsequent dechanneling of the electron beam from the cation columns. (c) LAADF image of uniformly spaced dislocations at the grain boundary.