A special type of Si magic clusters was first identified with a variable-temperature STM. They were found to be the fundamental unit in mass transport phenomena, step fluctuations, and epitaxial growth on clean Si(111) surfaces. The concept of magic clusters may have important implication on the fundamental mechanism in epitaxial growth of many covalently bonded semiconductors. As current theories consider single atoms only, these results suggest that clusters might play an important role in epitaxial growth on semiconductor surfaces. This finding will affect future theoretical modeling of epitaxial growth on semiconductor (or covalent bonded) system. In addition, electromigration of Si magic clusters on Si(111)-(7×7) surfaces was observed. For the first time, the diffusion species in electromigration has been identified. (Physical Review Letters 83, 120 (1999); Physical Review Letters 84, 5792 (2000))
