Abstract
With a variable-temperature scanning tunneling microscope (STM), we study the structural phase transition of Pb nano-domains on Si(111). Our STM observations indicate that no coverage change occurs across the phase transition, 1×1↔ √7 × √3. On the 1×1 structure, Pb adatoms are located at the T 1 site and the coverage is exactly 1 ML, which was also confirmed by Rutherford backscattering measurements. The √7 × √3 phase is basically a distorted 1×1 structure with some Pb adatoms slightly displaced from their T 1 site to form trimer rows. Therefore, this phase transition may involve only small displacements of Pb atoms without breaking the Pb-Si bonds. Our STM observations also show that the transition temperature decreases with decreasing domain size. The boundaries of the nano-domains are also found to have effects on the transition. At temperatures around the transition temperature, temporal fluctuations in structures can be seen, suggesting it to be a continuous transition. Careful examination of the change in the surface structure near the transition temperature reveals the fast dynamics associated with the thermal fluctuations. © 2005 THE PHYSICAL SOCIETY OF THE REPUBLIC OF CHINA.