The authors report the first observation of surface reconstruction in an hexagonal close-packed metal. Above about 610K low-energy electron diffraction patterns from the (11•0) face of yttrium metal have twofold symmetry and were characteristic of the ideal surface. Below this temperature the patterns comprise two principal and congruent sets of diffraction spots, each with sixfold symmetry, rotated by 30° with respect to each other. They suggest that the transition, which was accompanied by substantial changes in ultra-violet photo-emission spectra, corresponds to the formation of terraces of close-packed atoms on the surface, involving a approximately 60% increase in atom density.

Surface Reconstruction of Y(11•0). S.D.Barrett, R.G.Jordan, A.Begley: Journal of Physics F, 1987, 17[8], L145-50