Microstructure of cubic boron nitride (c-BN) films deposited on a Si substrate was investigated by transmission electron microscopy. The presence of cubic phase was clearly confirmed by taking the microdiffraction pattern and lattice image. Hexagonal boron nitride (/i-BN) with thickness 1-2 nm was often observed at the boundaries of c-BN films. The /i-BN phase at the boundary of the c-BN may be the reason of the high intrinsic compressive stress. It was suggested that the c-BN phase nucleated on the prism plane of /i-BN keeping the parallelism between the (111) c-BN and (0001) A-BN, although the slight deviation (~4°) was observed in some cases. The nucleation mechanism of c-BN was discussed analogous to that of diamond on graphite.
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