Adsorbate-induced Surface Reconstruction Research Articles

Pd4O3 Subsurface Oxide on Pd(111) Formed during Oxygen Adsorption-Induced Surface Reconstruction and Its Activity toward Formate Oxidation Reactions

Pd₄O₃ Subsurface Oxide on Pd(111) Formed during Oxygen Adsorption-Induced Surface Reconstruction and Its Activity toward Formate Oxidation Reactions

Quantitative and Atomic-Scale View of CO-Induced Pt Nanoparticle Surface Reconstruction at Saturation Coverage via DFT Calculations Coupled with in Situ TEM and IR.

Atomic-scale insights into how supported metal nanoparticles catalyze chemical reactions are critical for the optimization of chemical conversion processes. It is well-known that different geometric configurations of surface atoms on supported metal nanoparticles have different catalytic reactivity and that the adsorption of reactive species can cause reconstruction of metal surfaces. Thus, characterizing metallic surface structures under reaction conditions at atomic scale is critical for understanding reactivity. Elucidation of such insights on high surface area oxide supported metal nanoparticles has been limited by less than atomic resolution typically achieved by environmental transmission electron microscopy (TEM) when operated under realistic conditions and a lack of correlated experimental measurements providing quantitative information about the distribution of exposed surface atoms under relevant reaction conditions. We overcome these limitations by correlating density functional theory predictions of adsorbate-induced surface reconstruction visually with atom-resolved imaging by in situ TEM and quantitatively with sample-averaged measurements of surface atom configurations by in situ infrared spectroscopy all at identical saturation adsorbate coverage. This is demonstrated for platinum (Pt) nanoparticle surface reconstruction induced by CO adsorption at saturation coverage and elevated (>400 K) temperature, which is relevant for the CO oxidation reaction under cold-start conditions in the catalytic convertor. Through our correlated approach, it is observed that the truncated octahedron shape adopted by bare Pt nanoparticles undergoes a reversible, facet selective reconstruction due to saturation CO coverage, where {100} facets roughen into vicinal stepped high Miller index facets, while {111} facets remain intact.

Calculations of Oxygen Adsorption-Induced Surface Reconstruction and Oxide Formation on Cu(100)

The energetics and kinetics of the missing-row reconstruction (MRR) and missing-row island formation on the Cu(100) surface are investigated using density functional theory calculations. We find that copper ejection from the c(2 × 2) surface is made energetically possible by the presence of surface-adsorbed O2 molecules. The barrier for MRR formation via this ejection mechanism is calculated to be 0.96 eV, consistent with the experimentally observed formation temperature of 400 K. The reaction pathways between Cu and O2 result in the formation of Cu–O chains on the c(2 × 2) surface, which can grow from the −O–Cu–O– trimer at least up to the −Cu–O–Cu–O–Cu– pentamer. Remarkably, these chains can both diffuse rapidly and change their orientation on the surface, allowing them to assemble into longer Cu–O chains. Facile diffusion of the Cu–O chains occurs via a collective mechanism which limits the number of broken Cu–O bonds. Perpendicular to the Cu–O rows, the chains hop first at one end and then the other. ...

Adsorbate-induced surface stress, surface strain and surface reconstruction: CH3S on Cu(100) and Cu(111)

Adsorbate-induced surface stress, surface strain and surface reconstruction: CH3S on Cu(100) and Cu(111)

Contributions of dispersion forces to R-3-methylcyclohexanone physisorption on low and high Miller index Cu surfaces

The physisorption of R-3-methylcyclohexanone on low and high Miller index Cu surfaces is studied with temperature programmed desorption (TPD) and density functional theory (DFT). The DFT calculations are performed with D2, vdW-optB86b, and vdW-optB88 dispersion corrected methods. The adsorption energies calculated by the dispersion corrected methods are more comparable to the TPD results than those calculated without dispersion corrections, although, the former methods have a tendency to overbind the surface adsorbates. The implementation of dispersion corrected methods also indicates a possible adsorbate induced surface reconstruction on Cu(110).

Large perpendicular magnetic anisotropy at Fe/MgO interface

A large perpendicular magnetic anisotropy (PMA) of 1.4 MJ/m3 was observed from ultrathin Fe/MgO(001) bilayers grown on Cr-buffered MgO(001). The PMA strongly depends on the surface state of Fe prior to the MgO deposition. A large PMA energy density of 1.4 MJ/m3 was achieved for a 0.7 nm thick Fe layer having adsorbate-induced surface reconstruction, which is likely to originate from oxygen atoms floating up from the Cr buffer layer. This large magnitude of PMA satisfies the criterion that is required for thermal stability of magnetization in a few tens nanometer-sized magnetic memory elements.

The Role of Reducible Oxide–Metal Cluster Charge Transfer in Catalytic Processes: New Insights on the Catalytic Mechanism of CO Oxidation on Au/TiO2 from ab Initio Molecular Dynamics

To probe metal particle/reducible oxide interactions density functional theory based ab initio molecular dynamics studies were performed on a prototypical metal cluster (Au20) supported on reducible oxides (rutile TiO2(110)) to implicitly account for finite temperature effects and the role of excess surface charge in the metal oxide. It is found that the charge state of the Au particle is negative in a reducing chemical environment whereas in the presence of oxidizing species coadsorbed to the oxide surface the cluster obtained a net positive charge. In the context of the well-known CO oxidation reaction, charge transfer facilitates the plasticization of Au20, which allows for a strong adsorbate induced surface reconstruction upon addition of CO leading to the formation of mobile Au-CO species on the surface. The charging/discharging of the cluster during the catalytic cycle of CO oxidation enhances and controls the amount of O2 adsorbed at oxide/cluster interface and strongly influences the energetics of all redox steps in catalytic conversions. A detailed comparison of the current findings with previous studies is presented, and generalities about the role of surface-adsorbate charge transfer for metal cluster/reducible oxide interactions are discussed.

Scanning Tunneling Microscopy and Density Functional Theory Studies of Adatom-Involved Adsorption of Methylnitrene on Copper(110) Surface

In this study, we used scanning tunneling microscopy (STM) and density functional theory (DFT) to examine the bonding structure of CH3N adsorbed on the Cu(110) surface. A previous study [Chin. J. Phys.2005, 43, 212–218] shows the adsorbed CH3N aggregate to form a zigzag structure with a p(2 × 3) unit cell, without considering the possibility of adsorbate-induced surface reconstruction. Here, we propose a revised adsorption structure, with the key feature of bonding each CH3N with two Cu adatoms in a tetrahedral manner. Three structure models (double-row, dimer, and alternative-dimer) are examined by ab initio calculations. We find that the most energetically favorable model is the double-row model with CH3N bonding alternatingly along either side of double added rows from Cu adatoms.

Adsorbate-induced surface stress, surface strain and surface reconstruction: S on Cu(100) and Ni(100)

Density functional theory (DFT) calculations have been applied to investigate the known difference in behaviour of S adsorption on Cu(100) and Ni(100). Both surfaces form a 0.25ML (2×2) adsorption phase, but while at higher coverage a 0.5ML c(2×2) phase forms on Ni(100), on Cu(100) only a reconstructed 0.47ML (√17×√17)R14° structure occurs. Calculations of the energy, structure, and surface stress of (2×2) and c(2×2) phases on both substrates show there is an energy advantage on both surfaces to form the higher coverage phase, but that both surfaces show local surface strain around the S atoms in the (2×2) phase, a phenomenon previously investigated only on Cu(100). More than forty different structural models of the Cu(100)(√17×√17)R14°-S phase have been investigated. The pseudo-(100)c(2×2) structure previously proposed, containing 16 Cu adatoms per unit mesh in the reconstructed layer, is found to be less energetically favourable than many other possible structures, even after taking account of local structural relaxations. Significantly more favourable is a structure with 12 Cu adatoms per (√17×√17)R14° unit mesh, previously proposed on the basis of scanning tunnelling microscopy (STM), and found to yield simulated STM images in good agreement with experiment. This model has all S atoms in local 4-fold coordinated hollows relative to the Cu atoms below, half being located above Cu adatoms with the remainder lying above the underlying outermost substrate layer. However, an alternative model with only 4 Cu adatoms and with half the S atoms at 3-fold coordinated sites on the periphery of the Cu adatom cluster, has an even lower energy and gives simulated STM images in excellent agreement with experiment.

Structures of Dense Glycine and Alanine Adlayers on Chiral Cu(3,1,17) Surfaces

Density Functional Theory calculations have been used to predict the structures of dense glycine and alanine adlayers on Cu(3,1,17)(S). Facets of this chiral Cu surface result from adsorbate-induced surface reconstruction when glycine or alanine are adsorbed and annealed on Cu(100). We have calculated the surface energy changes associated with this surface reconstruction. Our results allow the enantiospecificity of this reconstruction following adsorption of enantiopure or racemic alanine on Cu(100) to be discussed. The overall stability of glycine and alanine adlayers on Cu(3,1,17)(S) arises from an interplay between the formation of chemical bonds with the Cu surface, deformations in the adsorbed molecules during adsorption, and intermolecular hydrogen bonds within the adlayer; none of these factors individually dominates.

Anion Adsorption Induced Surface Reconstruction

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Diffusion of particles on a heterogeneous surface: A case of adsorption-induced surface reconstruction

The influence of surface reconstruction on diffusion of particles adsorbed on the surface is investigated in the framework of symmetrical four-position model. The analytical expressions for free energy and diffusion coefficients are obtained assuming the lateral interaction between particles is negligibly small. The critical behavior of the system is described by the Ising spin model. The coverage dependencies of the tracer, jump and chemical diffusion coefficients are calculated for some representative temperatures. The dependencies show clearly strong influence of the surface reconstruction on the thermodynamic and kinetic phenomena: diffusion coefficients become anisotropic on the reconstructed surface. To check the analytical results we have used Monte Carlo simulations of the diffusion on this lattice.

Kinetic Monte Carlo modeling of CO desorption and adsorption on Pd(110) surface

Desorption and adsorption of carbon monoxide on Pd(110) is modeled and simulated, aiming at gaining atomic level understanding of experimentally observed rates. The model parameters are fitted to reproduce the temperature programmed desorption spectra and molecular beam surface scattering data. Desorption turns out to be best described as thermally activated, the activation energy depending on the detailed nearest neighbor site occupation configuration. For a good fit, the adsorption induced surface reconstruction needs to be included in the model. Also, desorption needs to be modeled with a precursor state included. However, surface diffusion was not found to be essential. With these ingredients the coverage dependent sticking coefficient can be successfully simulated in the temperature range from 300 to 500 K. Furthermore, the experimentally observed saturation coverage—temperature dependence is correctly predicted from the balance between simultaneous adsorption and desorption.

Electronic structure studies of adsorbate-induced surface reconstructions: oxygen on Rh(1 0 0)

Solid-state Fenske–Hall band structure calculations have been used to study the electronic structure and bonding that occur on an “asymmetric” clock reconstructed Rh(1 0 0) surface with a half-monolayer of O atom adsorbates. The displacement of the top-layer Rh atoms on reconstructed O/Rh(1 0 0) is similar to that observed when a half-monolayer of C or N atoms adsorb onto clean Ni(1 0 0). Unlike the five-coordinate C or N adsorbates that adsorb into effectively coplanar sites on the Ni(1 0 0) surface, however, O atoms sit well above the Rh surface plane and occupy three-coordinate adsorption sites. The results of these calculations show that the asymmetric clock reconstruction of O/Rh(1 0 0) increases the negative charge localized on the highly electronegative O atoms and strengthens the O–Rh bonding relative to an unreconstructed surface. This suggests that, in contrast to the C(N)/Ni(1 0 0) clock, which appears to be driven primarily by the restoration of metal–metal bonding, the asymmetric O/Rh(1 0 0) clock reconstruction is driven by the optimization of the O atom bonding environment. Comparisons of the O/Rh(1 0 0) and C(N, O)/Ni(1 0 0) surfaces further indicate that the electronegativity and electron count of the adsorbed species, as well as the electron count and physical size of the metal, all play a role in determining the preferred atomic geometries of these adsorbate-covered transition metal surfaces.

Phase transitions in adsorption-induced reconstruction model

In this work we analyze a simple model of adsorption-induced surface reconstruction, which is developed in the framework of the lattice gas model. The critical behavior of the substrate atoms is obtained by monitoring the specific heat and the fluctuations in the fraction of unreconstructed surfaces, where the critical temperature is calculated by using finite size scaling techniques. The phase diagram (critical temperature as a function of surface coverage) of the system is obtained for different conditions. Two different behaviors are obtained depending on the structures of the adsorbed gas. In fact, if the adsorption process favors the island formation, two critical regions appear, characterized by two critical temperatures, however, if the adsorbed particles do not form island there is only one critical region with one critical temperature. The mechanism of island formation is also discussed.

In situ STM study of the anodic oxidation of Cu(0 0 1) in 0.1 M NaOH

In situ electrochemical scanning tunneling microscopy measurements of the anodic oxidation of Cu(001) in 0.1 M NaOH are reported. Adsorption-induced surface reconstruction is observed in the underpotential range of oxidation with the formation of dimers of superimposed Cu atoms ejected from the substrate and stabilized by adsorbed OH groups, presumably in bridging positions. The reconstruction causes the reorientation of the substrate step edges and the formation of holes and ad-islands of monoatomic height. The dimers of superimposed Cu atoms are alternatively aligned along the 〈100〉 directions to form zig-zag arrangements. Long range ordering is observed in areas of limited lateral extension with c(2×6) and c(6×2) domains. In the potential range of Cu(I) oxide formation, a facetted Cu2O layer grows with a Cu2O(001)[11̄0]∣∣Cu(001)[100] epitaxial relationship. The 45° rotation between the close-packed directions of the oxide lattice and metal lattice results from the orientation of the dimers of superimposed Cu atoms in the precursor adsorbed OH layer. The surface of the oxide layer is facetted due to a tilt of ∼3% between oxide and metal lattices. Its (001) terraces have an identical chemical termination and are presumably hydroxylated.

Low energy electron diffraction structure determination of the Ni [formula omitted]c(2×2)–CN surface phase

The structure of the Ni(1 1 0)c(2×2)–CN surface phase has been determined by quantitative low energy electron diffraction (LEED). Contrary to earlier suggestions that relatively intense fractional order LEED beams imply that adsorbate-induced Ni surface reconstruction occurs, the results confirm previous findings by scanned-energy mode photoelectron diffraction and medium energy ion scattering that no significant reconstruction occurs. The C–N axis is oriented along an open-packed 〈1 0 0〉 azimuth, with the molecule lying above a second layer Ni atom; the intramolecular axis is tilted by 23.7±4.5° relative to the surface plane. The adsorption does lead to a substantial (9±4%) outward relaxation of the outermost Ni layer spacing and small distortions of the outermost layers of the Ni substrate.

Properly interpreting scanning tunneling microscopy images: the Cu( [formula omitted])-c(2×2)N surface revisited

Recent scanning tunneling microscopy (STM) and photoelectron diffraction studies of the Cu(1 0 0)-c(2×2)N system have led to the proposal of a “new type of adsorbate-induced surface reconstruction” involving the movement of Cu atoms perpendicular to the surface. Claims were made that images from prior STM studies were misinterpreted. We present STM images that clearly contradict these claims. We discuss the role of tip structure in the imaging process and demonstrate how tips with asymmetric apexes can result in STM images that can easily be misinterpreted.

Formation of surface oxides on Pt(100) during CO oxidation in the millibar pressure range

CO oxidation on Pt(100) at oxygen pressures of 9.0×10 −2 mbar was studied. An unusual decrease in catalytic activity with time was observed, which has not been observed at lower pressures. Post-reaction Auger and thermal desorption spectroscopy measurements showed the formation of a surface oxide species, which deactivated the catalyst. The surface oxide is compared to subsurface oxygen and to surface oxide studied previously on low index Pt single crystal surfaces. An adsorbate induced surface reconstruction is proposed as a possible driving force for oxide formation.

Imaging and chemical probing on the atomic scale: reconstruction and dynamics of the systems O2/Rh and NO2–H2/Pt

This paper presents two case studies of adsorbate-induced surface reconstruction, on the one hand, and dynamical reaction imaging along with local chemical probing, on the other hand. The first one deals with the oxygen-induced reshaping of 3D Rh crystals. Field ion microscopy (FIM) was applied to image in real-space the change from a nearly hemispherical shape in the absence of oxygen toward a polyhedral one in the presence of oxygen. Shape transformation occurs at temperatures of 380–550 K and is associated with the appearance of facets with {111} and {001} orientation. The only high-index planes present in the polyhedral form are of {137} symmetry. (1×2) and (1×3) missing-row reconstructions appear in the {113} and {011} planes. The polyhedral form has also been imaged under in situ conditions of the oxygen–hydrogen reaction on Rh at 505 K. The second case study deals with kinetic non-linearities occurring in the NO2 reaction with hydrogen on the surface of a 3D Pt crystal reconstructed to a top- and edge-truncated pyramid. The reaction was found to ignite in the {012} corner planes of the crystal. One-dimensional wavefronts were subsequently observed to move along the 〈211〉 zone lines. These studies were performed by video-FIM and could be correlated with a local chemical analysis by time-of-flight mass spectrometry of ionised species. The mass spectrum provided information on water product (H2O+ and H3O+) and NO intermediate formation. Strong fluctuations in the NO2+ current indicated the occurrence of NO2 surface diffusion. These species are most likely responsible for the field ion image formation.