Dresden 2003 – wissenschaftliches Programm

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O: Oberflächenphysik

O 20: Halbleiteroberfl
ächen und -grenzfl
ächen

O 20.11: Vortrag

Dienstag, 25. März 2003, 17:30–17:45, FOE/ANOR

A LEEM study of the Ge(001)-(2x1)-(1x1) phase transition; domain wall proliferation and dimer break-up — •Bene Poelsema, Esther van Vroonhoven, and Harold Zandvliet — MESA+ Research Institute, University of Twente, Enschede, NL

Two conflicting models have been proposed for the (2x1)-(1x1) phase transition on Ge(001): In one the phase transition is driven by vacancy pair creation and dimer break-up. The other claims that the phase transition involves (2x1) domain wall proliferation rather than dimer break-up. Elements of both models apply around the phase transition: Our results demonstrate that domain wall proliferation sets in around 950 K, leading to loss of contrast in LEEM around 1050 K. The dimers remain clearly visible up to  1130 K. However, their concentration is a strong function of the substrate temperature above 1030 K. A quantitative description of the thermal behavior of the dimer concentration is possible only by assuming a random distribution of dimers. It requires the inclusion of a configuration entropy term in the total free energy of the system. For the first time on (001) surfaces of group IV, we have directly extracted the dimer formation energy semiconductors, being 1.6 eV. per pair.