Atomic site determination of a high-purity SiC grain boundary

The grain-boundary atomic structure of a high-purity alpha-SiC bicrystal was investigated by atomic-resolution high-voltage transmission electron microscopy (ARHVTEM). The angular relation of the boundary corresponded to a 70.5degrees rotation around the [11 (2) over bar0] axis. The boundary plane was parallel to the (0001) plane of one of the crystals and the. (1 (1) over bar 02) plane of the other. The structural unit of this boundary consisted of five-seven-six-six-six-six-membered rings. The atomic site and atomic species of both the slicon and the carbon in the grain boundary were successfully distinguished in the ARHVTEM image. All the atomic pairs, except for only one pair in the unit period of the boundary, consisted of unlike atoms. The pair of like atoms consisted of silicon atoms and was located in between the five- and seven-membered rings. The atomic species of the threefold-coordinated atom was directly shown from the contrast of the ARHVTEM image to be carbon.