Diffraction of He and Ne and selective adsorption of He on Rh(110)

Diffraction studies on clean Rh(110) have been performed with room-temperature and low-temperature He and Ne beams. The corrugation amplitude perpendicular to the close-packed rows as observed with He is z(01)=0.15 A. Regarding analogous data for Ni, Cu, Pd, and Ag, this value fits well into the now clearly discernible trend that z(01) increases strongly with increasing lattice constant. The corrugation amplitude along the close-packed rows, z(10), on the other hand, does not show such systematic behavior. Compared to the other metals, the value for Rh, z(10)=0.065 A, is exceptionally large. z(01) measured with Ne is about twice as large as observed with He in accord with previous observations on other metals. Selective adsorption structures of He on Rh (110) were traced with low-temperature beams of different wavelengths and allowed the determination of four bound-state levels. The measured energies were fitted with different analytical potential forms and yield a potential-well depth of 8.2 meV. © 1989 The American Physical Society.