Scattering of Hyperthermal Argon Atoms from Clean and D-covered Ru(0001) Surfaces

Hyperthermal Ar atoms were scattered from a Ru(0001) surface held at temperatures of 180, 400 and 600 K, and from a Ru(0001)-(1×1)D surface held at 114 and 180 K. The resultant angular intensity and energy distributions are complex. The in-plane angular distributions have narrow (FWHM£10°) near-specular peaks and additional off-specular features. The energy distributions show an oscillatory behaviour as a function of outgoing angle. These features, which are most visible when scattering from the clean surface at 180 K and from the Ru(0001)-(1×1)D surface, are consistent with rainbow scattering. The measured TOF profiles of the scattered atoms contain two scattered components whose relative intensities vary as a function of the outgoing angle. This suggests two significantly different site and/or trajectory dependent energy loss processes at the surface. In comparison, scattered Ar atoms from a Ag(111) surface exhibits a broad angular intensity distribution and an energy distribution that qualitatively tracks the binary collision model. The results are interpreted in terms of the stiffness of the surface and highlight the anomalous nature of the apparently simple hcp(0001) ruthenium surface.