Raman measurements from the films as grown on a-plane and c-plane sapphire using both TEB and TMB are shown in Fig. . The sp 2 -BN Raman peak at 1370 cm -1 is observed for all the grown films and appears unshifted from the corresponding peak in the reference bulk h-BN sample (top spectrum). The broad band peaking around 1580 cm -1 observed in all samples is indicative of the G band of amorphous carbon (expected between 1500 cm -1 and 1600 cm -1 ) while the D band is expected at 1350 cm -1 . The D band from carbon is partly overlapped by the BN peak, but its contribution can still be distinguished as it extends to lower frequencies than the BN peak.