The 1/3 monolayer (ML) Sn/Si(111)-(√3 X √3)R30° surface structure has been extensively studied using low-energy electron diffraction (LEED) and x-ray standing waves (XSW). The summation of several XSW measured hkl Fourier components provides a three-dimensional, model-independent direct-space image of the Sn atomic distribution. While the image demonstrates that the Sn atoms are located at Si(111) T4-adsorption sites, it alone can not determine whether or not the Sn atomic distribution is flat or asymmetric. However, conventional XSW analysis can make this distinction, concluding that one-third of the Sn atoms are located 0.26 Å higher than the remaining two-thirds. This "one up and two down" distribution result is consistent with the vertical displacements predicted by a dynamical fluctuations model of the surface. For a second sample with a slightly different surface preparation a √3 LEED pattern was again observed, but in this case the direct space XSW imaging technique clearly revealed that a significant fraction of the Sn atoms were substituting for Si atoms in the bottom of the Si surface bilayer.
|Original language||English (US)|
|Number of pages||7|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Dec 2004|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics