Size changes of stacking-fault (SF) half units of dimer-adatom-stacking-fault structures have been investigated by high-temperature scanning tunneling microscopy (STM) observations on the quenched Si(111) surface at the temperatures of 380-500℃. A great number of the successive STM images have clearly shown that a SF half unit changes only to one size larger or smaller SF half unit and that the appearance and disappearance of a SF half unit always occur via the SF half units with the smaller size. These results can be explained by the model that the SF region expands or shrinks through the one-by-one movements of Si atoms to the SF or unfaulted sites associated with the new dimer formation or destruction during its size change process. The activation energy for the size change process has been measured to be 1.8±0.3 eV for 7×7 SF → 9×9 SF and 2.0±0.3 eV for 9×9 SF → 7×7 SF.
A series of STM images of quenched Si(111) surface acquired at 460℃. The images of (b)-(j) were taken 9, 18, 44, 70, 264, 678, 959, 1003, and 1135 s after (a), respectively. As pointed out by the arrows, a SF half unit sharing one corner hole appeared with the size of 5×5 in (b), expanded up to the size of 13×13 in (b)-(f), then shrank in (f)-(i), and disappeared in (j). The expansion and the shrinkage of the SF unit occurs step by step in its size.