Stranski-Krastanov morphology

Fig. 32. The Ge2p core level peaks excited by A1 Ka radiation. The solid line represents the Ge2/> reference spectrum, the dotted line represents the spectrum from the Ge/Si(001) sample, assuming the nanostructure shown in the respective insets. The Stranski-Krastanov morphology can be ruled out for this system [127]. Reprinted with permission from M. Schleberger et al., J. Vac. Sci. Techn. A15, 3032 (1997), 1997, The American Vacuum Society.

The experimental results have been obtained almost entirely from LEED, UPS and LEELS measurements for coverages ranging from a fraction of a monolayer to 20 monolayers, but an important point has been the use of molecular beam techniques for metal deposition to minimze contamination effects. (The metal was effused from clean Knudsen sources.) If we consider first the LEED observations, the initial state is a thermally produced 111 7 x 7 structure. The 7x7 periodicity is retained up to 1 monolayer of metal deposit, but as an extrinsic 7x7 pattern induced by the metal rather than a simple decrease in intensity of the Si 7 x 7 reflections. This was quoted as evidence of an essentially two-dimensional morphology for the metal deposit, since the formation of three-dimensional nuclei with clean silicon between them would have only reduced the intensity of the intrinsic 7x7 pattern. Beyond one monlayer, growth could follow a Stranski-Krastanov mode, however. 

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