INTERFACE STRUCTURE OF Si(111) 3 x 3 -Ag STUDIED BY GRAZING INCIDENCE X-RAY DIFFRACTION. Koichi Akimoto, Melania Lijadi, Takayuki Susami, and Ayahiko Ichimiya, Department of Quantum Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan

Buried interface structures of Ag/Si(111) 3x3 -Ag and Ge/Si(111) 3x3 -Ag were studied by grazing incidence X-ray diffraction using synchrotron radiation. A Si(111) 3x3 -Ag surface was obtained by depositing 1 ML (7.8 X 10¹⁴/cm²) of Ag on a Si(111)7 x 7 reconstructed surface heated up to 400 - 500deg.C in an UHV chamber operating in the 10^-10 Torr range. On that surface, Ag (8 nm) and Ge (6 nm) were deposited at room temperature. The X-ray diffraction measurements using synchrotron radiation were carried out at the BL-9C of the Photon Factory, Japan. During measurements, we covered the sample with an evacuated dome in the 10^-2 -10^-3 Torr range.

For the sample of Ag/Si(111) 3x3 -Ag, a (4/3, 1/3) X-ray diffraction peak was observed, while the (4/3, 1/3) peak was not observed for the sample of Si(111) 3x3 -Ag with native oxide layers. Therefore, we conclude the 3 structure remained at the Ag/Si(111) interface. The surface Si(111) 3x3 -Ag structure was normally explained by the honeycomb-chained-trimer (HCT) model. The HCT model should give rise to the comparably intense (2/3, 2/3) peak. However, we did not observe the (2/3, 2/3) peak for the sample of Ag/Si(111) 3x3 -Ag. This fact suggests that the 3 structure at the Ag/Si(111) interface is a different type from the surface 3 structure.

For most samples of Ge/Si(111) 3x3 -Ag, X-ray diffraction peak from the 3 structure was not observed. However, the in-plane 220 diffraction peak of the Ag(111) film was found. The correlation length derived from a peak width was about 3 nm. The Ag(111) film is thought to exist under the Ge islands.