Localized FFT analysis of the epitaxially grown r-B4C on the C-face shows the twinning of the r-B4C crystal, evidenced by the mirrored FFT pattern observed in Region I and Region II with respect to each other, the FFTs are taken from the marked regions in the HRTEM micrograph as indicated in Fig. . The two stackings merge in Region III of Fig. , which is supported by the superposition of FFT reflection spots. The additional reflections observed in the FFT from Region III are forbidden but occur due to stacking faults formed during the coalescence of twinned r-B4C crystals. FFT of the entire film region in the micrograph has been labeled as Region IV, with reflection spots similar, or identical, to those seen in Region III. Dashed lines in the HRTEM micrograph are used to show the grain boundary as the film grows in the pyramidal triangular microstructure, this growth microstructure starts already at the film/substrate interface. A localized FFT analysis of the r-B4C film grown on the Si-face of 4H-SiC is presented in Fig. HRTEM images recorded from the film/substrate interfaces are shown in Fig. . No difference in interface roughness is noted between the Si-and C-faces, suggesting that surface etching and step bunching of the substrates do not affect crystal stacking between the two substrate surfaces.