Study on the one-dimensional structure of metals on semiconductor surfaces and buried interfaces

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The surface structure of Si(111)-6xl-Ag was investigated using surface X-ray diffraction techniques at the Photon Factory. By analyzing the CTR scattering intensities along 00 rod, the positions of the Ag and reconstructed Si atoms perpendicular to the surface were determined. The results agreed well with the HCC model proposed for a 3xl structure induced by alkali-metals on a Si(111) substrate. The heights of the surface Ag and Si atoms thus determined show that those surface atoms make little perpendicular displacement when the surface structure changes from Si(111)-√<3>x√<3>-Ag to Si(111)-6xl-Ag by the desorption of the Ag atoms. From the GIXD measurement, the in-plane arrangement of the surface Ag atoms was determined. The results indicate that the Ag atoms move large distances laterally at the phase transition between the 6xl and 3xl structures.Next we studied the structure of Si(111)-5x2-Au using surface X-ray diffraction. The surface structure was analyzed from the measurements of diffraction spots observed by GIXD. The least-squrares fit was done for the three models; Marks and Plass model proposed by transmission electron diffraction (1995) and theoretical models based on the first principles calculations by Erwin (2003) and Riikonen (2005). The results indicate that the most probable model is Erwin's model, but the structural parameters should be modified considerably. Similarly, we studied the Si(111)-5x2-Au structure when the surface is buried with a amorphous silicon layer of about 5 nm thickness. We could clearly observe some diffraction spots from the buried interface. The CTR scattering intensity distributions observed were consistent with those calculated for Erwin's model.