Grain boundaries in diamond films on Si(001)

Grain boundaries in [001]-oriented diamond films deposited on Si(001) by microwave-assisted chemical vapor deposition have been investigated in plan-view and cross-section samples using high-resolution electron microscopy. The poly-crystalline diamond films used in this study had large fractions of [001]-oriented grains with typical lateral dimensions of 2 μm at film thicknesses beyond 10 μm. Grains with growth orientations near (001) exhibit generally small-angle orientation deviations between their crystal lattices. Small-angle grain boundaries of symmetric and asymmetric geometry with misorientation angles below 15° are investigated in both [110]- and [001]-directions. It is found that the structures of such small-angle grain boundaries can be described by a dislocation model. These grain boundaries are on average parallel to the {110}-plane and contain in many cases micro-facets parallel to {111}-planes. Large-angle grain boundaries with tilt angles up to 40° are also observed in interconnected films of smaller thickness. In all cases structural units with large open volumes and additional second phases are not found at the grain boundaries.