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In situ reflection high-energy electron diffraction, atomic force
microscopy and photoluminescence spectroscopy have been combined to analyze the
kinetics of the growth mode transition in the Ge/Si(001) system. By performing
experiments in the dynamic growth regime and under growth interruption, we
clearly establish the existence of intermediate clusters. We show that these
clusters are metastable both in view of structural and optical properties. In
particular, experiments performed with growth interruption have revealed that the
two-dimensional wetting layers undergo a morphological instability well before
reaching the critical thickness.
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