Nitrogen adsorption and thin surface nitrides on Cu(111) from first-principles

Experimental studies of nitrogen adsorbed on a Cu(111) surface show that the surface layer undergoes a reconstruction to form a pseudo-(100) structure. We use ab initio techniques to demonstrate the theoretical stability of this reconstructed surface phase over a range of conditions. We systematically investigate the chemisorption of N on the Cu(111) surface, frorn 0.06 to 1 ML coverage. A peculiar atomic relaxation of N atoms for 0.75 ML is identified, which results in the formation of a (metastable) N-trimer cluster on the surface. We have also investigated surface nitride formation, as suggested from experiments. A surface nitride-like structure similar to the reported pseudo-(100) reconstruction is found to be highly energetically favored. Using concepts from ab initio atomistic thermodynamics, we predict that this surface nitride exists for a narrow range of nitrogen chemical potential before the formation of bulk CU3N. (c) 2007 Elsevier B.V. All rights reserved.