These results agree with suggestions from a recent surface study of BN growth on a-cut Al2O3, which described it to be more suitable for the growth of h-BN. The presence of AlN 0002 and AlN 0004 peaks on both c-cut and a-cut Al2O3 evidently dictates the epitaxial r-BN film growth on these substrates. Supported by previous studies that have shown that h-BN initially nucleates epitaxially followed by r-BN epitaxial film growth on AlN (0001) grown on c-cut sapphire. In contrast, for r-cut and m-cut Al2O3 we don't detect AlN 0002 and AlN 0004 peaks, instead we observe AlN (112 ̅ 0) and mostly AlN (101 ̅ 3) growth on these cuts respectively. Since the crystal direction of the AlN film dictates the growth direction of the r-BN film, we would expect growth of crystalline BN films on these substrates. Instead, a-BN growth is observed on r-cut and m-cut substrates.