Abstract :
We have determined the structure and positions of Ge and Sb dimer atoms on a Si 001.-2=1 surface using
medium-energy ion scattering MEIS., and demonstrated that the surface structure can be determined with a much higher
accuracy by modifying the layer structure of the substrate. When a heavy atom layer in this case Ge layer.is embedded
with atomic scale layer precision, the blocking processes of scattered ions from the embedded layer are restricted and dips in
the blocking profiles can be uniquely assigned to the scattering-blocking pairs. In addition, the effect of thermal vibration
becomes small because a suitable distance between scattering and blocking atoms can be selected. Therefore, we can observe
sharp blocking dips in the profile of embedded Ge signals, and they can be assigned to the dimer structures on the
reconstructed surface. Based on the proposed method, the bond length and the tilt angle of asymmetric Ge–Ge dimers are
determined to be 2.4"0.1 A° and 13.5"2.08. The bond length of symmetric Sb–Sb dimers is determined to be 2.84"0.1
° A. q1998 Elsevier Science B.V. All rights reserved.
