Interaction of bromine with Ni(110) studied by scanning tunnelling microscopy

The adsorption of bromine on Ni(110) has been studied by scanning tunnellin g microscopy (STM). At low bromine coverage 'butterfly' structures are obse rved in STM, built up from 'pairs of pairs' of greyscale maxima. Two altern ative models for the butterflies are discussed, the most plausible of which involves location of dissociated Br atoms in two-fold hollow sites flanked by pairs of Ni adatoms. At higher coverages the discrete butterfly structure breaks down and adatom pairs form a disordered arrangement on the surface. Annealing a Br-saturat ed surface to 200 degrees C for Ih leads to formation of a well-ordered p(3 x2) reconstruction that produces sharp superstructure spots in LEED. The s uperstructure involves alternating rows with atomic sequences Ni-Br-Br-Ni-B r-Br-Ni and Br-Ni-Ni-Br-Ni-Ni-Br. The binding of Br butterflies to Ni(110) at low coverage is too strong to a llow facile manipulation with the tip of the STM. (C) 1999 Elsevier Science B.V, All rights reserved.