Very-low-energy electron-diffraction analysis of oxygen on Cu(001) (original) (raw)
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Physical Review B, 1991
The surface-potential barrier shape for the (001) face of copper was determined by an analysis of lowenergy-electron-diffraction fine-structure measurements. The fitting of the fine-structure spectra was performed with a precise knowledge of the incident diffraction conditions of the experimental data (incidence angle, azimuthal angle, and contact-potential difference). This precision is necessary to allow a consistent barrier shape to be determined. For three different angles of incidence, it was found that a good match between theoretical and experimental I-V spectra was obtained when the image plane was located 2.5 a.u. from the topmost layer of atoms.
A LEED Fine Structure Study of Oxygen Adsorption on Cu(001) and Cu(111)
Australian Journal of Physics, 1990
LEED fine structure features are due to an interference between the measured beam (usually the specular) and a pre-emergent beam. This pre-emergent beam is internally reflected at the surface potential barrier and is subsequently diffracted by the substrate into the same direction as the beam under observation. As a result of the long-range image nature of the barrier potential, a rydberg-like series of peaks, converging on the emergence energy of the pre-emergent beam, is produced. Fine structure features, or threshold effects, occur at very low incident beam energies (typically <40 eV) and are extremely sensitive to the surface order of the crystal. The changes that occur to the fine structure features when atoms are adsorbed onto the surface contain information regarding the nature of the chemisorption process. In some cases it is possible to infer adsorption sites. In this work measurements are made of the fine structure features for the and surfaces of copper as a function of oxygen exposure. Analysis of these data shows that oxygen adsorption on (u(111) takes place in a disordered manner and results in a roughening of the surface, while for (u(OOl) the adsorption produces an ordered overlayer with oxygen atoms in the 2-fold bridge sites.
The structure of oxygen on Cu (1 0 0) at low and high coverages
Surface science, 2001
The local adsorption structure of oxygen on Cu(1 0 0) has been studied using O 1s scanned-energy mode photoelectron diffraction. A detailed quantitative determination of the structure of the 0.5 ML (√2×2√2)R45°-O ordered phase confirms the missing-row ...
Normal photoelectron diffraction of O/Cu(001): A surface-structural determination
Physical Review B, 1982
This report was done with support from the Department of Energy. Any conclusions or opinions expressed in this report represent solely those of the author(s) and not.necessarily those of The Regents of the •university of California, the Lawrence Berkeley Laboratory or the Department of Energy. Reference to a company or product name does not imply approval or recommendation of the product by the U hiversity of California or the U.S. Department of Energy to the exclusion of others that may be suitable.
Critical Importance of van der Waals Stabilization in Strongly Chemically Bonded Surfaces: Cu(110):O
Journal of Chemical Theory and Computation, 2013
We provide strong evidence that different reconstructed phases of the 10 oxidized Cu(110) surface are stabilized by the van der Waals (vdW) interactions. These 11 covalently bonded reconstructed surfaces feature templates that are an integral part of the 12 65 surface is the presence of additional copper atoms in every 66 second row, known as "super" copper atoms, 19,20 which are 67 bound between two oxygen atoms. As a result, the oxygen 68 atoms bonded to them are raised slightly out of plane and are 69 buckled in toward the super-Cu atoms, acquiring the names 70 "high" 19 or "buckled" 20 oxygen atoms. These high oxygen 71 atoms are bonded to the super-Cu atoms to form "super" CuO 2 72 molecules (or units) on the surface. The c(6 × 2) structure 73 (henceforth referred to as AS-c(6 × 2)) represents the tiling of 74 the surface with Cu−O templates resulting in a c(6 × 2) A dx.doi.org/10.1021/ct400813d | J. Chem. Theory Comput. XXXX, XXX, XXX−XXX slw00 | ACSJCA | JCA10.0.1465/W Unicode | research.3f (R3.6.i4:4180 | 2.0 alpha 39) 2013/10/21 02:46:00 | PROD-JCAVA | rq_2925327 | 11/11/2013 13:54:20 | 7 | JCA-DEFAULT 75 arrangement of the "super" CuO 2 units. Examples of other 76 possible variations of this building principle are depicted in 77 Figure 1(b−e). 78
On-surface and sub-surface oxygen on ideal and reconstructed Cu(100)
Surface Science, 2005
In order to understand the first steps of the Cu(1 0 0) oxidation we performed first principles calculations for on-surface and sub-surface oxygen on this surface. According to our calculations, the adsorption energies for all on-surface site oxygen atoms increase, whereas the energies of the sub-surface atoms decrease with the increasing oxygen coverage. At coverage 1 ML and higher on the reconstructed surface, structures including both on-and sub-surface atoms are energetically more favourable than structures consisting only of on-surface adsorbates. On the ideal (1 0 0) surface this change can be perceived at coverage 0.75 ML.
2009
Atomic oxygen embedment into a Cu(1 0 0) surface is studied by density functional theory calculation and the nudged elastic band method. As the oxygen coverage increases on the unreconstructed surface from 0.25 monolayer (ML) to 0.75 ML, the energy barrier for oxygen embedment decreases and an energetically favorable sub-surface site is found at 0.75 ML coverage. At a fixed oxygen coverage of 0.5 ML, the oxygen embedment energetics vary with the surface morphology and the embedment is found to be more probable for reconstructed structures compared to the bare surface. On the missing-row reconstructed surface, we find that the energy barrier for atomic oxygen embedment is smaller through the missing-row compared to other paths, suggesting a mechanism for the formation of sub-surface oxygen structures that are consistent with a recent experiment. The energy barrier for sub-surface oxygen diffusion is predicted to be less than that for on-surface diffusion.
Determination of the surface structure of CeO2(111) by low-energy electron diffraction
The Journal of Chemical Physics, 2013
We determine the atomic structure of the (111) surface of an epitaxial ceria film using low-energy electron diffraction (LEED). The 3-fold-symmetric LEED patterns are consistent with a bulk-like termination of the (111) surface. By comparing the experimental dependence of diffraction intensity on electron energy (LEED-I(V) data) with simulations of dynamic scattering from different surface structures, we find that the CeO2(111) surface is terminated by a plane of oxygen atoms. We also find that the bond lengths in the top few surface layers of CeO2(111) are mostly undistorted from their bulk values, in general agreement with theoretical predictions. However, the topmost oxygen layer is further from the underlying cerium layer than the true bulk termination, an expansion that differs from theoretical predictions.
Oxygen-induced missing-row reconstruction of Cu(001) and Cu(001)-vicinal surfaces
Physical Review B, 1990
We have used x-ray-diffraction analysis to examine the structure of flat and vicinal Cu(001) surfaces under the influence of oxygen chemisorption. The initial electropolished vicinal surface consists of a fairly regular array of steps and terraces that preferentially orient the oxygen-induced reconstruction. Prolonged annealing leads to a hill-and-valley morphology with large (001) facets, upon which the preferential orientation is lost, just as for the flat surface. We find evidence for only one ordered phase as a function of oxygen coverage, which has 2&2X&2 symmetry. Crystallographic analysis of the diffraction data shows this to be a "missing-row" structure with 25% of the Cu sites vacant and large relaxations in the top layer. The oxygen site is not uniquely determined, however, with two distinct possibilities. This Cu(001)/0 structure has a surprising similarity to that proposed for Cu(110)/O. In fact both surfaces can be decomposed into the same basic structural element, which is a Cu-0-Cu chain oriented along bulk [100]directions.