STRUCTURE DETERMINATION OF NI(110)-(2X3)-N BY USE OF SEXAFS MEASUREMENTS - ON-SURFACE AND SUBSURFACE SITES ON A PSEUDO-(100) RECONSTRUCTED SURFACE

Surface-extended X-ray-absorption fine-structure measurements have been performed on the Ni(110)-(2 x 3)-N system. The data are consistent with a model in which nitrogen chemisorbs on a pseudo-(100) reconstructed and largely corrugated surface with a nearest-neighbour N-Ni bond length of 1.86 +/- 0.03 Angstrom. The corrugation results in two raised and two lowered [110] Ni rows which are not uniformly distributed in the [001] direction. Nitrogen chemisorbs in four-fold hollow sites slightly (0.19 Angstrom) above the lowered Ni rows and in pseudo-four-fold hollow sites slightly (0.38 Angstrom) below the plane defined by a raised and a lowered Ni row. In both sites N is equidistantly bonded to Ni atoms in the second layer. Structural models with long-bridge adsorption sites can be safely excluded.