STRUCTURAL DETERMINATION OF SI(100)2X2-AL BY TENSOR LEED

The structure of a Si(100)2 X 2-Al surface at 0.5 monolayers is determined by tensor low-energy electron diffraction. The parallel dimer model is more favorable than the orthogonal dimer model. The R factor for the optimized parallel dimer structure is 0.15. The bond length of the Al dimer is almost equal to the value expected from the Pauling covalent radii. All bond lengths in five surface layers including Si-Al and Si dimer bonds are within the range of 5% from the bulk value. The distortion extends at least through the first five layers into the bulk.