Observation of Finite-Size Effects on a Structural Phase Transition of 2D Nano-Domains

Ing-Shouh Hwang ； Shih-Hsin Chang ； Chung-Kai Fang ； Lih-Juann Chen ； Tien T. Tsong

《Chinese Journal of Physics》 43卷1S期 (2005/02) Pp. 182-189

並列摘要

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 T1 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 T1 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.