Small Ni-S bond lengths in a c(2 × 2) overlayer of sulfur on Ni (001)

We conclude from the close agreement between low-energy electron diffraction calculations and experiment that sulfur adsorbed in a c (2 × 2) structure on Ni (001) is located 1.30 ± 0.1 Å above the surface in a four- fold coordinated bonding site. This location corresponds to a Ni-S bond length which is smaller than occurs in several bulk compounds or than suggested in a previous calculation by Duke et al.