Huge differences between low- and high-angle twist grain boundaries: The case of ultrathin (001) Si films bonded to (001) Si wafers

Ultrathin (001) Si films bonded onto (001) Si wafers, inducing grain boundaries with twist angles varying from 0.5° to 12°, were studied by transmission electron microscopy. A great structural difference between low (ψ<5°) and high (ψ>6°) twist angles was observed. In low twist angle grain boundaries, “twist interfacial dislocations” are dissociated and produce rough interfaces with no oxide precipitates. It is the opposite in high-angle grain boundaries: there is no dissociation, the interfaces are smoother but contain oxide precipitates. These differences are not attributed to the thin thickness of one grain, but to the large atomic differences between high- and low-angle twist grain boundaries, which is not the case for tilt grain boundaries.