The in-plane epitaxial relationships for BN films grown on each substrate were determined by Fig. presents a top-view SEM micrograph and Fig. is a cross-section TEM micrograph of BN grown on a-plane sapphire using TEB. The top-view micrograph shows a few triangular structures, henceforth referred to as region I in Fig. , surrounded by less ordered growth, referred to as region II. Similar surface morphologies have been observed in several other studies on crystalline BN. The cross-section micrograph suggests that the triangular area is a truncated triagonal pyramid. The BN thickness in the triangular pyramidal growth region I is about 35 nm, compared to about 8 nm in the less ordered region II. Pyramidal BN regions were found in films grown on a-plane and c-plane sapphire grown using TMB and a-plane sapphire grown using TEB.