Structure analysis of Ge dimer on Si (001) by medium-energy ion scattering blocking profiles from embedded Ge layers

We propose a novel technique for determining the surface structure quantitatively and accurately by modifying the substrate, and apply it to the structure analysis of Ge dimers on the Si (001) surface. One or two atomic layers of Ge were embedded below 4–12 ML of Si overlayer by molecular-beam epitaxy and with atomic scale layer precision. The ions scattered from embedded Ge layers are blocked by the reconstructed surface atoms. Since the origin of the signals are restricted, the scattering-blocking pairs are uniquely assigned. In addition, the effect of thermal vibration can be minimized by choosing a distance between scattering and blocking atoms that is suitable for analysis. Therefore, we can observe the sharp and simple blocking profile of embedded Ge signals, and can determine the atomic displacements of reconstructed surfaces. The bond length of the Ge–Ge dimer on Si (001) surface was determined by this method to be 2.4 Å.