The reconstruction and relaxation of lr(110) and Au(110) surfaces

We have applied medium-energy ion scattering using channeling and blocking to study the Au( 110) and Ir( 110) surfaces. Both surfaces are composed of rows of close-packed atoms which, when atomically clean, exhibit (1X2) reconstructions, i.e., a doubling of the unit cell in the direction perpendicular to the rows. We find that the Au( 110) reconstruction corresponds to a missing row structure with a large contraction of the first interplanar spacing. We directly show that the contraction is accompanied by deep, multilayer distortions of the surface. The clean Ir( 110) surface is similar to Au( 110), characterized by a missing row reconstruction but with a smaller contraction of the first interplanar spacing. We have also examined the phase transition on Ir (110) from a (1X 2) structure to an oxygen stabilized (lXl) structure. For the two phases, the yield of backscattered ions shows drastic differences only observable in the blocking directions, differences that could not have been observed in a conventional ion channeling experiment.