During in situ scanning tunneling microscopy (STM) observations of quenched Si(111) surfaces at a temperature around 400-500 ℃, the structure with the adatom arrangement which is not coincident with the normal dimer-adatom-stacking-fault (DAS) structure was often observed. The flipping between this structure and the normal DAS stacking-fault (SF) half unit frequently occurred. From the adatom arrangement and the strong preference of the adatoms to the sites adjacent to the dimers, it has been concluded that the dimers in the DAS structures are rearranged frequently during the flipping.
The successive STM images of the quenched Si(111) surface obtained at 420 ℃. The image of (b) was taken 8.8 s after (a). The structures pointed out by the arrows in (a) have the adatom arrangement different from the normal DAS structure. Three of them were changed to the normal 7×7 SF half units as indicated by the arrows in (b).