Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

15B2/2003S2-001

Structural study of the Si(111)-6×1(3×1)-Ag Surface
by x-ray crystal truncation rod scattering
Kazushi Sumitani1, Kosuke Masuzawa1, Takashi Hoshino1, Ryuji Yoshida1, Sinichiro Nakatani1,Toshio Takahashi1, Hiroo Tajiri2, Koichi Akimoto3, Hiroshi Sugiyama4, Xiao-Wei Zhang4 andHiroshi Kawata4
1
ISSP, The Univ. of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581, Japan2JASRI, Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan3Dept. Quantum Eng., Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
4KEK-PF, Tsukuba, Ibaraki 305-0801, JapanIntroduction
The Si(111)-6×1-Ag surface is the superstructure
induced by submonolayer of silver atoms. This surface
has many interesting features. The surface, which takes
the 6×1 periodicity at room temperature, changes to the
3×1 periodicity above 500K[1]. Moreover, it was foundby low energy electron diffraction (LEED) observationthat the surface takes the c(12×2) structure below
100K[2].
Another aspect is the one-dimensional structure ofsurface atoms. It was found by LEED and photoelectron
spectroscopy that the 3×1 surfaces produced by Ag or
alkali-metals are quite similar in their structures. Thus itis reasonable to apply the structure models, which wereproposed for the 3×1 structure induced by alkali-metalson Si(111) surface, to the 6×1 structure. According tomost of the structure models, the surface Ag atoms makeone-dimensional rows. This fact expects us that thesurface has one-dimensional properties.
For understanding the properties of the surface, theprecise information about the arrangement of the surface
atoms is necessary. In this study, the surface structure wasanalyzed using crystal truncation rod (CTR) scattering. In
particular, the intensities along 00 rod enables us tounderstand the electron density perpendicular to thesurface. Thus we characterized the vertical position of
surface atoms and discussed about the surface structure.
Experiment and Discussion
The experiment was performed at BL15B2 in which a
six-circle diffractometer with a vacuum chamber isinstalled. The sample was prepared in the chamber, andthe in-situ diffraction measurements were performed
along 00 rod to obtain the information about the electron
density perpendicular to the surface. The wavelength wastuned at 0.86Åand 1.2Å.
The observed intensities along 00 rod are shown in Fig.
1. The reciprocal lattice points of l=3 and 9 are identicalto the 111 and 333 Bragg points in Mirror indices.
Around these Bragg points, the intensities show strong
asymmetry. This fact is explained by the interference
between the scattering from the surface atoms and the one
from the substrate.

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Users' Report

Fig.1 Intensity along 00 rod from the Si(111)-6×1-Ag
surface. Red open circles and blue open triangles
indicate the intensities with the wavelength of 0.86A
and 1.2A, respectively. Solid line is the calculated
intensity on assumption of HCC model.

Fig.2 Structure determined by least-squares fittinganalyses.
Least-squares fitting analyses were applied for thedetermination of the atomic arrangement perpendicular tothe surface. As a result, the best-fitted model shown inFig. 2 was obtained. The heights of the Ag and Si atoms
were determined at 3.04 ± 0.01Å and 2.31 ± 0.01Å,
respectively. The structure agrees well with thehoneycomb-chain-channel (HCC) model proposed for the
3×1 structure induced by alkali-metals[3].
It is interesting to compare the 6×1 structure withSi(111)-√3×√3-Ag surface. The heights of both Ag andreconstructed Si atoms are quite similar in two surfaces.
The positions of surface atoms do not change during thedesorption of Ag atoms.
References[1] Y. Gotoh and S. Ino, Jpn. J. Appl. Phys. 17 (1978)
2097.
[2] K. Sakamoto et al., Phys. Rev. B 65, 045305 (2001).
[3] S. C. Erwin et al., Phys. Rev. Lett. 75, 1973 (1995).
* ttaka@issp.u-tokyo.ac.jp