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Surface-confined polymerization via Ullmann coupling is a promising route to create one- and two-dimensional covalent π-conjugated structures, including the bottom-up growth of graphene nanoribbons. Understanding the mechanism of the Ullmann reaction is necessary to provide a platform for rationally controlling the formation of these materials. We use fast X-ray photoelectron spectroscopy (XPS) in kinetic measurements of epitaxial surface polymerization of 1,4-dibromobenzene on Cu(110) and devise a kinetic model based on mean field rate equations, involving a transient state. This state is observed in the energy landscapes calculated by nudged elastic band (NEB) within density functional theory (DFT), which assumes as initial and final geometries of the organometallic and polymeric structures those observed by scanning tunneling microscopy (STM). The kinetic model accounts for all the salient features observed in the experimental curves extracted from the fast-XPS measurements and enables an enhanced understanding of the polymerization process, which is found to follow a nucleation-and-growth behavior preceded by the formation of a transient state.

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Cation-deficient nickel oxides have been investigated by X-ray photoelectron spectroscopy. The high-binding-energy features in the O( 1 s), Ni(2p) X.P.S. of defective NiO are described as multielectron final states, induced by defective sites. These sites are described as (Ni0,)9-molecular clusters because of the d hole. The energy shift between the main peak and the satellite, in both the O(1s) and Ni(2p) X.P.S. spectra, is due to a change in the ionic charge and in the oxygen coordination induced by cation vacancies.

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