ABSTRACT

The formation process of the 7x7 reconstruction on Si(111) has been studied at the atomic level by observing unreconstructed regions remained after rapid quenching to 380°C, using scanning tunneling microscopy (STM). This article is divided into two parts: (1) Formation of isolated single stacking-faulted (F) halves; (2) Domain growth. In the first part, we have continuously recorded STM images of a single isolated F-half of the dimer-adatom-stacking-fault (DAS) structure from its birth to death. It is observed with a scanning speed of 1.7 s per frame that the F-half changes frequently its size around 9x9 and that even-sized F-halves such as 6x6, 8x8, 10x10 and 12x12 appear as intermediates during the size-changes between odd-sized F-halves, like 9x9 → 8x8 →7x7. We have also observed that irregular-type structures of the odd-sized F-halves (denoted as F’). It is found that single odd-sized F-halves appearing in the size changes are always the irregular-type structures. We have proposed the sequential size change (SSC) model for the formation and decay of isolated single F-halves in the unreconstructed region (denoted as “1x1”) as follows: “1x1” ↔ 2x2-F ↔ 3x3-F’↔ 4x4-F  ↔ 5x5-F’ ↔6X6-F ↔7x7-F’ ↔ 8x8-F ↔ 9x9-F’ ↔ 10x10-F ↔ 11x11-F’ ↔ 12x12-F ↔13x13-F’. In the second part, it has been observed that a single 9x9-F’ grows to a small 9x9 DAS domain. The creation of new isolated F-halves was very seldom at 370~380 °C. Continuous measurements showed that new F-halves are created sharing corners with existing F-halves. It is demonstrated that the formation of the F-halves in the domain growth follows the SSC model. The smallest DAS domain consists of three F-halves of the same size, arranged as a triangle. We have summarized the characteristic steps of the formation towards the smallest domain under the SSC model.