The early stages of Si homoepitaxy on Si(100) were studied by using low-temperature scanning tunnelling microscopy. Adsorbed atoms and epitaxial dimers were observed. The adsorbed atoms formed previously unobserved pairs which coupled via a substrate-mediated interaction. Transient non-thermal atomic motion led to the formation of atom pairs and epitaxial dimers. It was noted that paired atoms acted as if they were constrained by a potential trough, and exhibited a lower barrier to motion than did unpaired atoms. The paired atoms were observed to coalesce into a normal epitaxially oriented Si dimer.

R.A.Wolkow: Physical Review Letters, 1995, 74[22], 4448-51