A LEED investigation of clean and oxygen covered Rh(100)

Abstract

The clean and oxygen covered Rh(100) surface is investigated by LEED intensity measurements and calculations. For the clean surface an almost unrelaxed surface with a slight first layer expansion (0.5 ± 2%) results. Oxygen is made to adsorb at low temperatures whereby two superstructures develop. A (2 × 2) structure at coverage θ = 1 4 is followed by a (2 × 2) p 2gg structure at θ = 1 2 . The symmetry of the latter pattern and the inspection of the intensities of the corresponding fractional order spots indicate towards a weak adsorbate induced surface reconstruction. The (2 × 2) structure, however, develops on the unreconstructed surface. For this phase a quasidynamical intensity analysis followed by a full dynamical refinement identifies oxygen as adsorbed in hollow sites. The adsorbate-substrate layer distance is 0.95 ± 0.04 Å corresponding to an oxygen radius of 0.78 ± 0.02 Å. The expansion of the first substrate layer distance found for the clean surface is reversed to a contraction of the same value. Experimental and calculated spectra agree well as described by a Pendry R-factor of 0.27.