LITHIUM-INDUCED RECONSTRUCTIONS OF THE SI(001) SURFACE

Abstract

We report the new LEED observation that lithium atom adsorption on a Si(001) surface at room temperature or below produces a series of ordered phases, (2 x 2):Li --> (2 x 1):Li --> c(3 root 2 x root 2)R45 degrees:Li --> streaky c(3 root 2 x root 2)R45 degrees:Li --> (4 x 1):Li --> (1 x 1):Li, depending on adsorbate coverage. This observation partially contradicts previous studies which reported only two phases in the series. We discuss possible origins of the controversy. We then propose a structural model that may account for the sequential appearance of the phases most naturally by invoking a spin-flip mechanism of an impurity stabilized magnetic system. The results suggest that the first phase be a reconstruction of the silicon substrate induced by Li adsorption where asymmetric dimers arrange themselves ferromagnetically and antiferromagnetically along the [110] and [110] directions, respectively.