980

1. BF upper left and two dark field images, the latter taken with the different 111 reflections shown in the accompanying SADP. The stronger “matrix” reflection lights up most of the bottom layer and some of the top but there are a few twin-related variants that are correspondingly dark. The twin reflections light up the rest of the material pretty much. Note the twin relation between the lower twin variant and the upper matrix variant (arrowed). 980

2. Different region from slide 1 but a similar approach and results. Note also that some of the regions in the bottom grain (arrows) don’t appear to extend to the top – not sure what this means. 992

3. BF and DF using the 111 reflection that is common to both matrix and twin (those planes parallel to the 0001 of the sapphire). The slight contrast in the DF (lower) image is probably due to the slight rotations (1-5°) that we discussed earlier.

4. BF (left) and DF (right) to show that the twin boundaries in the bottom later are not always continuous into the upper layer.

5. BF (left) and DF similar to previous slide to show that the twin boundaries in the bottom later are not always continuous into the upper layer.

6. HRTEM across barrier

7. Schematic of orientation of the different twinned variants in upper and lower layers [111]//[0001]