ASSESSMENT OF CORRELATED THERMAL DIFFUSE SCATTERING AS A DIRECT STRUCTURAL METHOD ON THE MULTIELEMENT SURFACE SYSTEM OF${\rm Si}(111)(\sqrt3\times\sqrt3)\mbox{-}{\rm In}$

Correlated thermal diffuse scattering (CTDS), a direct structural technique using a simple oscillatory intensity variation in the medium energy electron diffraction, has been applied to the biatomic surface system of${\rm Si}(111)(\sqrt3\times\sqrt3)\mbox{-}{\rm In}$. A problem with the application of CTDS to multicomposition systems arises from the element-specific atomic scattering factors. The difference in atomic scattering factors disturbs the diffraction phase originating from the path length difference and causes the shift from the true atomic position in Patterson analysis. In order to recover the true atomic position, a numerical calibration method has been introduced. With the aid of the calibration, structural parameters for the topmost three layers of the${\rm Si}(111)(\sqrt3\times\sqrt3)\mbox{-}{\rm In}$surface have been determined with 0.1 Å accuracy. This shows that CTDS is applicable to multicomposition surface systems.