Atomic structure of Si(111)-(√3 × √3 )R30°-Al studied by dynamical low-energy electron diffraction

We have carried out a quantitative low-energy electron-diffraction intensity analysis of a Si(111)-(√3 × √3 )R30°-Al structure. We found that Al atoms on a √3 × √3 array are absorbed on the threefold-symmetrical sites above the Si atoms in the second layer of the Si\{111\} surface. Atomic coordinates and bond lengths have been determined for the Al overlayer and all atoms in the first three layers of the substrate. With this model, some surface bonds are stretched by 3.4% (maximum), while others are compressed by 5.1% (maximum).