Submonolayer adsorption of Na onto the Cu(110) surface: Structure and vibrational properties
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Submonolayer Adsorption of Na onto the Cu(110) Surface: Structure and Vibrational Properties G. G. Rusinaa,b,*, S. D. Borisovaa,b,**, and E. V. Chulkovc,d a
Institute of Strength Physics and Materials Science, Russian Academy of Sciences, Siberian Branch, Akademicheskii pr. 2/4, Tomsk, 634021 Russia b Tomsk State University, pr. Lenina 36, Tomsk, 634050 Russia c St. Petersburg State University, St. Petersburg, 198504 Russia d Departamento de Física de Materiales, San Sebastián, 20080 Spain *e-mail: [email protected] **e-mail: [email protected] Received December 23, 2016
Abstract—The submonolayer adsorption of Na onto the Cu(110) surface is studied. At small Na coverages (Θ = 0.16–0.25 ML), the substrate surface subjected to missing-row reconstruction (1 × 2) is shown to be most stable dynamically. When the coverage increases to Θ = 0.5 ML, the unreconstructed substrate surface with a c(2 × 2) sodium adlayer becomes dynamically stable. For an analysis, we used data on the equilibrium atomic configuration, the adsorption energy, the phonon spectra, the local density of phonon states, and the polarization of localized vibrational modes. All calculations were performed using the interatomic potentials obtained in terms of the embedded-atom method. The calculated frequencies of localized vibrational modes agree well with the existing experimental data. DOI: 10.1134/S1063776117080179
1. INTRODUCTION The adsorption of alkali metals (AMs) onto metallic substrates has long attracted the attention of researchers. The simplicity of an electronic structure of an AM makes it possible to use it as a model system to study the influence of adsorbates on the processes occurring on the substrate surface. For fcc metals, the basic data on the type of chemical bond, atomic and electronic structures, work function, electron–electron and electron–phonon interactions, catalytic and photochemical reactions, and charge and energy transfer over a surface were obtained during the adsorption of an AM on the close-packed (111) and (100) substrate surfaces [1–13]. The (110) surface has received little attention [14–18]. The geometry of this surface, which is determined by the absence of close packing along one row, makes it possible to perform reconstruction (under an external action) for the surfaces that are stable in a pure state [19]. An experimental support of the reconstruction of surface Cu(110), Ag(110), Ni(110), or Pt(110) during AM (Li, Na, K, Cs) adsorption was obtained using low-energy electron diffraction [20], photoemission [21], and lowenergy electron spectroscopy [22]. Structural investigations showed that local missing-row surface reconstruction (1 × 2) appears even at ultralow degrees of adsorption of about 0.04 AM atom monolayer (ML)
onto the Cu(110), Ag(110), or Ni(110) surface. In this case, adatoms reject the atoms of the surface layer on a substrate from every second close-packed row along [ 1 10] [23–27]. At the same time, using the adsorption of Na, K, and Cs onto the Cu(110) surface as an example, the
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