SURFACE ATOMIC GEOMETRY OF SI(001)-(2X1) - A LOW-ENERGY ELECTRON-DIFFRACTION STRUCTURE-ANALYSIS

The reconstruction of the Si(001)-2x1 surface consists of asymmetric a nd buckled Si dimers. The vertical separation between the up and the d own atom within the dimer is about 0.72+/-0.05 Angstrom and the dimer band length of 2.24+/-0.08 Angstrom has been found to be slightly smal ler than the Si-Si distance in the bulk. The tilt of the dimer is 19+/ -2 degrees. The formation of Si dimers induces pronounced distortions in the substrate that were detectable down to the fifth Si layer. The structure determination is based on two independent low-energy electro n diffraction data sets taken in two different laboratories. The struc tural results agree well within the error limits, though noticeable di fferences occur between the experimental data sets. These differences in the experimental data can possibly be attributed to different prepa ration procedures.