AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP11
Evidence of Surface Pre-melting of Bi Ultrathin Film on Si(111)

Tuesday, November 4, 2003, 5:30 pm, Room Hall A-C

Session: Poster Session
Presenter: S. Yaginuma, Tohoku University, Japan
Authors: S. Yaginuma, Tohoku University, Japan
T. Nagao, Tohoku University and PRESTO, JST, Japan
J.T. Sadowski, Tohoku University, Japan
Y. Fujikawa, Tohoku University, Japan
T. Sakurai, Tohoku University, Japan
Correspondent: Click to Email
Semimetal bismuth has attracted much attention because of its various unique transport properties. Recently, we have successfully fabricated high-quality Bi (001) films on the Si (111)-7x7 substrate. The Bi (001)/Si (111) system self-organized into an atomically flat single crystal Bi (001) film, experiencing the unique orientation flipping from interconnected close-packed Bi {012} films to the two-dimensional (2D) Bi (001) films, which then grew into a nearly perfect uniform film by layer by layer growth. Temperature-dependent spot-profile-analysis low-energy electron diffraction (SPA-LEED) study revealed that suitable annealing of the as-deposited Bi (001) films resulted in an increase of the peak intensity and a change in the spot profile, marked improvement in the crystallinity and surface roughness. The resulting surface was ideally flat over the ~100 nm range. With this ideal 2D system, we further performed the systematic SPA-LEED experiment as a function of annealing temperature and estimated the surface Debye temperature to be approximately 90 K. In addition to the expected Debye-Waller decrease, a steeper decrease in the spot intensity was observed above 350 K in a reversible manner without hysteresis. Since the separate in-situ STM observations have clarified the decrease in step density, this anomalous thermal behavior of the diffraction peak intensity is attributed to the surface pre-melting instead of the surface roughening. By fitting the data with the logarithmic growth law, the correlation length of this phase transition was determined within the length of one bilayer. Negligible thickness dependence reflects the layered structure of Bi with mobile bilayer stacking. A possible mechanism of the surface pre-melting of the Bi (001) films will be discussed.