Real-Space Observation of the 2×1 Structure of Chemisorbed Oxygen on Ni(110) by Scanning Tunneling Microscopy

We present the first real-space observation of well defined single adsorbates: oxygen atoms forming the 2×1 structure on Ni(110). The sawtooth model is consistent with all experimental results. The structure consists of domains, separated in the $\left[1\mathrm{}\overline{1}0\right]$ direction by uncovered Ni ribbons 1½ surface unit cells wide. Such domain walls appear responsible for the $\theta =0.35\mathrm{}$ coverage of the saturated chemisorption structure.