Formation of thallium islands on theSi(111)−7×7surface

Abstract

We have studied the formation of thallium (Tl) islands on the $\mathrm{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ surface by utilizing synchrotron x-ray scattering. The Si substrate is found to maintain its $7\ifmmode\times\else\texttimes\fi{}7$ periodicity until metastable Tl islands of three different morphologies grow to their maximum size at room temperature. Analysis of several Bragg reflections from these Tl islands reveals that the three different types of Tl islands having different thermal stability can be characterized by their unique basal planes---(001), (100), and (101). Upon increasing the Tl dose the most abundant islands with a basal plane of (001) grow their lateral size up to a limiting value of $38\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ while their lattice parameter approaches a bulk value of $0.2996\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. We interpret our data primarily in terms of strain-limited growth of the Stranski-Krastanov type.