OBSERVATION OF A (7 X-1) SURFACE RECONSTRUCTION ON Y(1120)

A study of the surface reconstruction of Y(112BAR0) has shown a sixfold-symmetric low-energy electron diffraction pattern in contrast to the twelvefold-symmetric pattern reported earlier. This indicates that only one orientation of close-packed atoms exists on the surface; the collapse of the surface unit cell is uniaxial along the [0001] direction. This produces the same commensurate surface structure as found previously for the (112BAR0) (7 X 1) reconstructions of Ho and Er. Why the earlier study of Y showed a two-domain reconstruction has not been determined, but we suggest that this structure was influenced by the presence of surface defects, inducing the collapse of the unit cell along the [101BAR0] direction to form an incommensurate domain with approximately equal probability to that of the commensurate (7 X 1) domain.