title: Formation of Two-Dimensional Copper Selenide on Cu(111) at Very Low Selenium Coverage.
abstract: Using scanning tunneling microscopy (STM), we observed that adsorption of Se on Cu(111) produced islands with a (√3×√3)R30° structure at Se coverages far below the structure's ideal coverage of 1/3 monolayer. On the basis of density functional theory (DFT), these islands cannot form due to attractive interactions between chemisorbed Se atoms. DFT showed that incorporating Cu atoms into the √3-Se lattice stabilizes the structure, which provided a plausible explanation for the experimental observations. STM revealed three types of √3 textures. We assigned two of these as two-dimensional layers of strained CuSe, analogous to dense planes of bulk klockmannite (CuSe). Klockmannite has a bulk lattice constant that is 11 % shorter than √3 times the surface lattice constant of Cu(111). This offers a rationale for the differences observed between these textures, for which strain limits the island size or distorts the √3 lattice. STM showed that existing step edges adsorb Se and facet toward ⟨12‾ 1⟩, which is consistent with DFT.
authors.affiliation: Department of Chemistry, Iowa State University, Ames, IA, 50011, USA.|Surface and Interface Science Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.
authors.forename: Holly
authors.initials: H
authors.lastname: Walen
authors.affiliation: Ames Laboratory of the USDOE, Ames, IA, 50011, USA.
authors.forename: Da-Jiang
authors.initials: DJ
authors.lastname: Liu
authors.affiliation: Surface and Interface Science Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.
authors.forename: Junepyo
authors.initials: J
authors.lastname: Oh
authors.affiliation: Surface and Interface Science Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.|University College London, London, WC1E 6BT, UK.
authors.forename: Hyun Jin
authors.initials: HJ
authors.lastname: Yang
authors.affiliation: Surface and Interface Science Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.
authors.forename: Yousoo
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Iowa State University, Ames, IA, 50011, USA. pthiel@iastate.edu.|Ames Laboratory of the USDOE, Ames, IA, 50011, USA. pthiel@iastate.edu.|Department of Materials Science & Engineering, Iowa State University, Ames, IA, 50011, USA. pthiel@iastate.edu.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Thiel
keywords: chalcogenides; copper; density functional theory; scanning tunneling microscopy; selenides