Morphology of copper nanoparticles in a nitrogen atmosphere: A first-principles investigation

We perform first-principles density-functional-theory calculations to determine the stability and associated physical and electronic properties of different adsorption phases of N on Cu (100) and Cu (110) substrates for coverages ranging from 0.125 to 1 monolayer (ML). For N on Cu (100), we consider adsorption in fourfold hollow sites while for N on Cu (110), we consider various adsorption sites including N-induced missing-row surface reconstructions and the surface nitridelike, "pseudo-(100)" reconstruction. We report the atomic and electronic structure and compare with analogous results for N/Cu (111). By combining results from our previous study of the N/Cu (111) system with the current investigations, we predict the possible morphology of a Cu crystal in different nitrogen environments by performing a Wulff construction at appropriate chemical potentials of nitrogen. We also find that all low-energy N/Cu surface structures-namely, Cu (100) -c (2×2) -N and the surface nitrides found on Cu (110) and Cu (111)-share a common geometric feature: i.e., surface nanopatterns resembling 1 atomic layer of Cu3 N (100). These nanopatterned structures exist for a narrow range of nitrogen chemical potentials before the onset of bulk Cu3 N, unless kinetically hindered. This qualitative behavior of the predicted formation of thin-surface nitridelike structures prior to the bulk nitride material is very similar to that for transition-metal surfaces in an oxygen atmosphere, where surface oxidelike structures are predicted to be thermodynamically stable prior to bulk oxide formation.