Adsorption of Bromobenzene on Periodically Stepped and Nonstepped NiO(100)

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Abstract
Periodically stepped NiO(100) surfaces were prepared and characterized with low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). Two vicinal NiO(100) single-crystal samples were cut, oriented, and polished with regular, repeating monatomic steps in six-atom or seven-atom terrace widths. LEED diffraction patterns showed characteristic spot-splitting that corresponded to the appropriate terrace and step height. The nonstepped and stepped NiO(100) surfaces were exposed to bromobenzene at 130 K first to produce a molecularly adsorbed monolayer species and then, with increased exposure, a multilayer adsorbate. An additional adsorbate species, observed only on the stepped surfaces, was found to desorb at 145 K by two competing pathways. One pathway, which saturates at low coverages, leaves bromine behind on the substrate and results in dehalogenation. The other pathway yields molecular desorption at 145 K, but is only observed in detectable amounts after the dehalogenation pathway is saturated. On both stepped and nonstepped NiO(100) substrates, adsorbed bromine resulting from dehalogenation processes appears as nickel bromide, determined by the Br 3p XPS data.