Growth of thallium overlayers on a Si(100) surface

Abstract

Formation of the thallium (Tl) overlayers on the $\mathrm{Si}(100)2\ifmmode\times\else\texttimes\fi{}1$ surface has been studied using scanning tunneling microscopy (STM) and first-principles total-energy calculations. It has been found that adsorption of Tl atom involves a charge transfer leading to the development of a static dipole which is responsible for the field-assisted migration of the Tl adsorbate on the surface. When the STM tip bias voltage is positive, Tl atoms are repelled out from the region underneath the tip apex. In the case of the negative bias voltage, Tl is accumulated underneath the tip. Four principal ordered $\mathrm{Tl}∕\mathrm{Si}(100)$ reconstructions have been found, namely, three $2\ifmmode\times\else\texttimes\fi{}2\text{\ensuremath{-}}\mathrm{Tl}$ reconstructions with 0.25, 0.50, and 0.75 ML of Tl and $2\ifmmode\times\else\texttimes\fi{}1\text{\ensuremath{-}}\mathrm{Tl}$ reconstruction with 1.0 ML of Tl. The possible atomic arrangement of these reconstructions has been evaluated using first-principles total-energy calculations.