Second layer rumpling in Ni()c(2×2)–S

Medium energy ion scattering (MEIS) using 100 keV H+ ions has been used to study the structure of Ni(110)c(2×2)–S. Blocking curves in two of the three principal azimuths have been measured in order to determine the atomic positions in both the surface and sub-surface layers. The MEIS data indicate that S lies 0.90±0.06 Å above the plane of the first layer Ni. The average distance of 1.39±0.04 Å found for the first to second nickel layer spacing corresponds to an expansion of 12% when compared to the bulk layer spacing and we find a rumpling of 0.18±0.07 Å in the second layer. The polarity of rumpling is such that Ni atoms capped by S lie closer to the surface.