structural phase transition on Si(111)-√3x√3-Ag surface studied by x-ray diffraction

T. Takahashi,^a H. Tajiri,^a K. Sumitani,^a S. Nakatani,^a A. Nojima,^a

K. Akimoto,^b H. Sugiyama,^c X. Zhang,^a and H. Kawata ^c

^aInstitute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8581, Japan; ^bDepartment of Quantum Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan; ^cPhoton Factory, High Energy Accelerator Research Organization, Tsukuba 305-0801, Japan (ttaka@issp.u-tokyo.ac.jp).

A Si(111)-√3x√3-Ag (for short √3-Ag) surface structure at room temperature is generally accepted as a honeycomb chained triangle (HCT) structure with a number of experimental and theoretical results[1]. However, recently, Aizawa et al.[2] reported that the most stable structure of the surface is not the HCT structure but an in-equivalent triangle (IET) structure by means of first principles calculations and scanning tunneling microscopy at low temperatures. Structural reinvestigations on the √3-Ag surface by x-ray diffraction have revealed that the √3-Ag surface transforms from the HCT structure of high temperature phase into the IET structure of low temperature one at 150K[3]. In addition, an abrupt change in x-ray scattering intensities in the vicinity of the transition temperature has implied the displacive phase transition[3]. However, properties of the phase transition on the surface are still unclear in detail.

In this work, we further studied the √3-Ag surface structure, especially around the transition temperature of 150K by x-ray diffraction. We discuss critical exponents and an order parameter in this system based on anharmonic thermal vibration analyses.

References

1 Takahashi, T., Nakatani, S. (1993) Surf. Sci. 282, 17, and references there in.

2 Aizawa, H., Tsukada, M., Sato, N., Hasegawa, S. (1999) Surf. Sci. Lett. 429, L509.

3 Tajiri, H., Sumitani, K., Nakatani, S., Nojima, A., Takahashi, T., Akimoto, K., Sugiyama, H., Zhang, X., Kawata, H. (2002) submitted to Phys. Rev. B.