Interpretation of electron diffraction patterns in the presence of oriented planar faults

The presence of high planar-fault densities in thin films, e.g. nanotwinned films, leads to peculiar diffraction effects. Frequently, the planar faults are oriented perpendicular to the growth direction. For the case of (nanosized) thin films of face-centered cubic (fcc) metals, often a {111}fcc fiber texture prevails with the fiber axis parallel to the film normal. In diffraction patterns of cross-sectional transmission electron microscopy (TEM) samples of such films, as a consequence of twinning with (111) planes parallel to the surface as twinning planes, intensity streaks appear parallel to the growth direction. These intensity streaks are, however, invisible in diffraction patterns of top-view TEM samples. The latter diffraction patterns might be interpreted, at first sight, in terms of the diffraction pattern of a somehow textured fcc polycrystal. However, the diffraction-ring radii deviate from the expected radii. The consideration of intensity cylinders in reciprocal space formed by diffuse intensity streaks generated by the planar faults leads to a perfect match of the accordingly predicted radii with the observed intensity-ring radii.