LOW-ENERGY ELECTRON-DIFFRACTION AND X-RAY PHOTOELECTRON DIFFRACTION STUDY OF THE CS/SI(001) SURFACE - DEPENDENCE ON CS COVERAGE

Cs adsorption on a wide-terrace single-domain Si(001) surface has been studied by low-energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD) as a function of Cs coverage (theta) and substrate temperature (T(s)). For T(s)'s of approximately 110 and approximately 320 K, several surface periodicities are found which have not been reported before for this system. Azimuthal Cs 3d XPD patterns have been measured for most of the ordered surfaces. An XPD structure analysis is made for a streak x 3 surface at theta = 1/6 ML, in which a dilute arrangement of Cs atoms is deduced. An XPD structure analysis is made for the surfaces at theta = 1/3 ML taking into account a reversible transition between 2 x 6 and 2 x 3 for T(s)'s of approximately 110 and approximately 320 K, respectively. A Cs dimer model is deduced in which a modulation of atomic positions into a 2 x 6 surface is averaged in the 2 x 3 surface but is fixed in a regular way in the 2 x 6 surface.