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

Abstract

The adsorption of bromine on Ni(110) has been studied by scanning tunnelling microscopy (STM). At low bromine coverage ‘butterfly’ structures are observed in STM, built up from ‘pairs of pairs’ of greyscale maxima. Two alternative 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-saturated surface to 200°C for 1 h leads to formation of a well-ordered p(3×2) reconstruction that produces sharp superstructure spots in LEED. The superstructure involves alternating rows with atomic sequences Ni–Br–Br–Ni–Br–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 allow facile manipulation with the tip of the STM.