SURFACE PERIODICITY OF IR(110) FROM TIME-OF-FLIGHT SCATTERING AND RECOILING SPECTROMETRY (TOF-SARS)

The surface periodicity of the Ir(110) surface in both the clean reconstructed (1 x 3) and oxygen stabilized unreconstructed (1 x 1) phases have been investigated using time-of-flight scattering and recoiling spectrometry (TOF-SARS). A pulsed 4 keV Ar+ ion beam is directed at a grazing incident angle to the surface and the scattered neutral plus ion flux is monitored as a function of beam exit angle and crystal azimuthal angle. It is demonstrated that either maxima or minima are obtained in the scattered flux along the low-index crystallographic directions depending on whether near-specular or off-specular scattering conditions, respectively, are used. These scattering intensity patterns as a function of crystal azimuthal angle provide a direct measure of the surface periodicity. These intensity variations are explained in terms of the Lindhard critical angle, semichannel focusing effects, and trajectory simulations.