The structure of the clean ${\mathrm{Ni}}_3\mathrm{Al}\left(111\right)$ surface has been studied using surface x-ray diffraction. Analysis of the crystal truncation rods reveals that the clean surface contains an unexpected disorder while the bulk remains ordered. This surface-induced disorder extends down to the sixth layer and it decreases gradually with depth. The surface is, on the whole, stoichiometric and the maximum deviation per layer from the ideal $3_{\mathrm{Ni}}:1_{\mathrm{Al}}$ composition is less than 8%. There is a very small difference $(0.02\pm 0.01\mathrm{\AA })$ between the relaxations of the two different sites at the surface, and the interlayer distance between the outmost, second, and third layers is slightly reduced $(0.02\pm 0.01\mathrm{\AA })$ with respect to the bulk value.

• Received 1 June 2005

DOI:https://doi.org/10.1103/PhysRevB.72.195430