We present a density-functional theory study addressing the energetics and electronic structure properties of isolated oxygen adatoms at the SrTiO3(001) surface. Together with a surface lattice oxygen atom, the adsorbate is found to form a peroxide-type molecular species. This gives rise to a non-trivial topology of the potential energy surface for lateral adatom motion, with the most stable adsorption site not corresponding to the one expected from a continuation of the perovskite lattice. With computed modest diffusion barriers below 1 eV, it is rather the overall too weak binding at both regular SrTiO3(001) terminations that could be a critical factor for oxide film growth applications.
Silicene monolayers grown on Ag(111) surfaces demonstrate a band gap that is tunable by oxygen adatoms from semimetallic to semiconducting type. By using low-temperature scanning tunneling microscopy, it is found that the adsorption configurations and amounts of oxygen adatoms on the silicene surface are critical for band-gap engineering, which is dominated by different buckled structures in R13xR13, 4x4, and 2R3x2R3 silicene layers. The Si-O-Si bonds are the most energy-favored species formed on R13xR13, 4x4, and 2R3x2R3 structures under oxidation, which is verified by in-situ Raman spectrosc…
Manganites are technologically important materials, used widely as solid oxide fuel cell cathodes: they have also been shown to exhibit electroresistance. Oxygen bulk diffusion and surface exchange processes are critical for catalytic action, and numerous studies of manganites have linked electroresistance to electrochemical oxygen migration. Direct imaging of individual oxygen defects is needed to underpin understanding of these important processes. It is not currently possible to collect the required images in the bulk, but scanning tunnelling microscopy could provide such data for surfaces.…
Large magnetic anisotropy energy (MAE) is desirable and critical for nanoscale magnetic devices. Here, using ligand-field level diagrams and density functional calculations, we well explain the very recent discovery [I. G. Rau et al., Science 344, 988 (2014)] that an individual Co adatom on a MgO (001) surface has a large MAE of more than 60 meV. More importantly, we predict that a giant MAE up to 110 meV could be realized for Ru adatoms on MgO (001), and even more for the Os adatoms (208 meV). This is a joint effect of the special ligand field, orbital multiplet, and significant spin-orbit in…
Adsorption of carbon, nitrogen, and oxygen on the (111) surface of delta-Plutonium has been studied within the framework of density functional theory using the full-potential linear augmented plane wave plus local basis (FP-LAPW+lo) method. All adatoms prefer to bind at the higher coordinated hollow sites, with the chemisorption energies for C, N, and O being 6.539 eV, 6.714 eV, and 8.2 eV respectively. The work function and the surface Pu magnetic moments respectively increased and decreased in all cases upon chemisorption. The partial charges inside the muffin tins spheres, difference charge…
Si(111) and Ge(111) surface formation energies were calculated using density functional theory for various biaxial strain states ranging from -0.04 to 0.04, and for a wide set of experimentally observed surface reconstructions: 3x3, 5x5, 7x7 dimer-adatom-stacking fault reconstructions and c(2x8), 2x2 and \sqrt{3}x\sqrt{3} adatoms based surfaces. The calculations are compared with scanning tunneling microscopy data obtained on stepped Si(111) surfaces and on Ge islands grown on a Si(111) substrate. It is shown that the surface structure transformations observed in these strained systems are acc…
Metal deposition on oxide surfaces usually results in adatoms, clusters, or islands of the deposited material, where defects in the surface often act as nucleation centers. Here an alternate configuration is reported. After the vapor deposition of Fe on the In$_2$O$_3$(111) surface at room temperature, ordered adatoms are observed with scanning tunneling microscopy. These are identical to the In adatoms that form when the sample is reduced by heating in ultrahigh vacuum. Density functional theory (DFT) calculations confirm that Fe interchanges with In in the topmost layer, pushing the excess I…
Nickel vapor-deposited on the SrTiO$_3$(110) surface was studied using scanning tunneling microscopy, photoemission spectroscopy (PES), and density functional theory calculations. This surface forms a (4 $\times$ 1) reconstruction, composed of a 2-D titania structure with periodic six- and ten-membered nanopores. Anchored at these nanopores, Ni single adatoms are stabilized at room temperature. PES measurements show that the Ni adatoms create an in-gap state located at 1.9 eV below the conduction band minimum and induce an upward band bending. Both experimental and theoretical results suggest …
The nature of the magnetism brought about by Fe adatoms on the surface of the topological insulator Bi2Se3 was examined in terms of density functional calculations. The Fe adatoms exhibit strong easy-axis magnetic anisotropy in the dilute adsorption limit due to the topological surface states (TSS). The spin exchange J between the Fe adatoms follows a Ruderman-Kittel-Kasuya-Yosida (RKKY) behavior with substantial anisotropy, and the Dzyaloshinskii-Moriya (DM) interaction between them is quite strong with |D/J|~0.3 under the mediation by the TSS, and can be further raised to ~0.6 by an external…
We carry out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom (Tiad) migration on, and descent from, TiN <100>-faceted epitaxial islands on TiN(001) at temperatures T ranging from 1200 to 2400 K. Adatom-descent energy-barriers determined via ab initio nudged-elastic-band calculations at 0 Kelvin suggest that Ti interlayer transport on TiN(001) occurs essentially exclusively via direct hopping onto a lower layer. However, AIMD simulations reveal comparable rates for Tiad descent via direct-hopping vs. push-out/exchange with a Ti island edge atom for T >= 1500 K. W…
Even something as conceptually simple as adsorption of electronegative adatoms on metal surfaces, where repulsive lateral interactions are expected for obvious reasons, can lead to unanticipated behavior. In this context, we explain the origin of surprising lateral interactions between electronegative adatoms observed on some metal surfaces by means of density functional theory calculations of four electronegative atoms (N, O, F, Cl) on 70 surfaces of 44 pristine metals. Four different scenarios for lateral interactions are identified, some of them being unexpected: (i) they are repulsive, whi…
Density-functional calculations on the polar TiX(111) (X = C, N) surfaces show (i) for clean surfaces, strong Ti3d-derived surface resonances (SR's) at the Fermi level and X2p-derived SR's deep in the upper valence band and (ii) for adatoms in periods 1-3, pyramidic trends in atomic adsorption energies, peaking at oxygen (9 eV). A concerted-coupling model, where adatom states couple to both kinds of SR's in a concerted way, describes the adsorption. The chemisorption versatility and the general nature of the model indicate ramifications and predictive abilities in, e.g., growth and catalysis.
The structure and dynamics of atomic oxygen adsorbed on Ag(410) and Ag(210) surfaces have been investigated using density functional theory. Our results show that the adsorption configuration in which O adatoms decorate the upper side of the (110) steps forming O--Ag--O rows is particularly stable for both surfaces. On Ag(210), this arrangement is more stable than other configurations at all the investigated coverages. On Ag(410), adsorption on the terrace and at the step edge are almost degenerate, the former being slightly preferred at low coverage while the latter is stabilized by increasin…
We present density functional theory calculations of the binding energies of one, two and three fluorine adatoms on the same side of monolayer graphene. We show that fluorine dimers on graphene in a spin-singlet state are stable against dissociation into isolated fluorine adatoms, suggesting that there is a tendency for fluorine adatoms on a single side of graphene to cluster. Our results suggest that fluorination develops by successive bonding of fluorine atoms to neighbouring carbon atoms on different sublattices, while the spins are arranged to reduce the total magnetisation of the ground s…
The atomic structure of well-ordered single steps on the Si(111)-\sqrt{3}\times\sqrt{3}-Sn surface and the dynamics of Sn adatoms in the vicinity of these steps was studied. The work was performed using low-temperature scanning tunneling microscopy (STM) and ab initio calculations based on the density-functional theory. The STM tip was used to record the tunneling current versus time on top of oscillating adatoms, keeping the feedback loop turned off. The dynamics of adatoms, detected as the telegraph noise present in the tunneling current, was registered near the steps at 80 K. The atomic str…
We show that an individual adatom on a magnetic surface can exhibit a noncollinear spin density. Using density functional theory we study Co and Ir adatoms on a Mn monolayer on the W(110) surface which possesses a noncollinear canted spin structure. Due to hybridization with the nearest and next-nearest Mn atoms of the monolayer the spin direction of the underlying substrate is encoded into the orbitals of the adatom. This explains recent scanning tunneling microscopy experiments showing a spin sensitive shape asymmetry of adatoms [Serrate \emph{et al.}, Phys. Rev. B \textbf{93}, 125424 (2016)…
The self-consistent charge density functional tight-binding (DFTB) theory study of carbon adatoms using tuned Hubbard U parameters
Institute of Atomic and Molecular Physics, Jilin University（吉林大学原子与分子物理研究所）；Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University)（吉林大学应用原子分子光谱学吉林省重点实验室）
Phosphorene is emerging as a promising 2D semiconducting material with a direct band gap and high carrier mobility. In this paper, we examine the role of the extrinsic point defects including surface adatoms in modifying the electronic properties of phosphorene using density functional theory. The surface adatoms considered are B, C, N, O and F with a [He] core electronic configuration. Our calculations show that B and C, with electronegativity close to P, prefer to break the sp3 bonds of phosphorene, and reside at the interstitial sites in the 2D lattice by forming sp2 bonds with the native a…
Alkali metal atoms (Li, Na, K, Rb, Cs), dimers and (2$\times$2) monolayers on a graphite (0001) surface have been studied using density functional theory, pseudopotentials, and a periodic substrate. The adatoms bind at the hollow site (graphite hexagon), with Li lying closest to (1.84 Å) and Cs farthest (3.75 Å) from the surface. The adsorption energies range between $0.55-1.21$ eV, and the energy ordering of the alkali adatoms is Li$>$Cs$\ge$Rb$\ge$K$>$Na. The small diffusion barriers (0.02-0.21 eV for the C-C bridge) decrease as the atom size increases, indicating a flat potential energy sur…
Ab initio total energy calculations within the framework of density functional theory have been performed for atomic hydrogen and oxygen chemisorption on the (0001) surface of double hexagonal packed americium using a full-potential all-electron linearized augmented plane wave plus local orbitals method. Chemisorption energies were optimized with respect to the distance of the adatom from the relaxed surface for three adsorption sites, namely top, bridge, and hollow hcp sites, the adlayer structure corresponding to coverage of a 0.25 monolayer in all cases. Chemisorption energies were computed…
Using density-functional theory in combination with a thermodynamic formalism we calculate the relative stability of various structural models of the polar O-terminated (000-1)-O surface of ZnO. Model surfaces with different concentrations of oxygen vacancies and hydrogen adatoms are considered. Assuming that the surfaces are in thermodynamic equilibrium with an O2 and H2 gas phase we determine a phase diagram of the lowest-energy surface structures. For a wide range of temperatures and pressures we find that hydrogen will be adsorbed at the surface, preferentially with a coverage of 1/2 monol…
The local environment of metal-oxide supported single-atom catalysts plays a decisive role in the surface reactivity and related catalytic properties. The study of such systems is complicated by the presence of point defects on the surface, which are often associated with the localization of excess charge in the form of polarons. This can affect the stability, the electronic configuration, and the local geometry of the adsorbed adatoms. In this work, through the use of density functional theory and surface-sensitive experiments, we study the adsorption of Rh1, Pt1, and Au1 metals on the reduce…
We investigate the effect of oxygen vacancies and hydrogen dopants at the surface and inside slabs of LaAlO3, SrTiO3, and LaAlO3/SrTiO3 heterostructures on the electronic properties by means of electronic structure calculations as based on density functional theory. Depending on the concentration, the presence of these defects in LaAlO3 slab can suppress the surface conductivity. In contrast, in insulating SrTiO3 slabs already very small concentrations of oxygen vacancies or hydrogen dopant atoms induce a finite occupation of the conduction band. Surface defects in insulating LaAlO3/SrTiO3 het…
Calculations of the diffusion of a Au adatom on the dimer reconstructed Si(100)-2x1 surface reveal an interesting mechanism that differs significantly from a direct path between optimal binding sites, which are located in between dimer rows. Instead, the active diffusion mechanism involves promotion of the adatom to higher energy sites on top of a dimer row and then fast migration along the row, visiting ca. a hundred sites at room temperature, before falling back down into an optimal binding site. This top-of-row mechanism becomes more important the lower the temperature is. The calculations …
We have demonstrated that the island nucleation in the initial stage of epitaxial thin film growth can be tuned by substrate surface charge doping. This charge effect was investigated using spin density functional theory calculation in Fe-deposition on graphene substrate as an example. It was found that hole-doping can apparently increase both Fe-adatom diffusion barrier and Fe inter-adatom repulsion energy occurring at intermediate separation, whereas electron-doping can decrease Fe-adatom diffusion barrier but only slightly modify inter-adatom repulsion energy. Further kinetic Monte Carlo si…
Controlling the bandgap of carbon nanostructures is key to the development and mainstream application of carbon-based nanoelectronic devices. We report density functional theory calculations of the effect of silicon impurities on the electronic properties of carbon nanotubes (CNTs). We have found that Si adatoms open up a bandgap in intrinsically metallic CNTs even when the linear density of Si atoms is low enough that they do not create a bonded adatom chain. The bandgap opened in metallic CNTs can range between 0.10 eV and 0.47 eV, depending on adsorption site, linear density of Si adatoms, …
Ordered configurations of hydrogen adatoms on graphene have long been proposed, calculated and searched for. Here we report direct observation of several ordered configurations of H adatoms on graphene by scanning tunneling microscopy. On the top side of the graphene plane, H atoms in the configurations appear to stick to carbon atoms in the same sublattice. A gap larger than 0.6 eV in the local density of states of the configurations was revealed by scanning tunneling spectroscopy measurements. These findings can be well explained by density functional theory calculations based on double side…
Although atomic diffusion on metal surfaces under high electric fields has been studied theoretically and experimentally since the 1970s, its accurate and quantitative theoretical description remains a significant challenge. In our previous work, we developed a theoretical framework that describes the atomic dynamics on metal surfaces in the presence of an electric field in terms of the local polarization characteristics of the surface at the vicinity of a moving atom. Here, we give a deeper analysis of the physics underlying this framework, introducing and rigorously defining the concept of t…
Low-temperature scanning tunneling microscopy is used here to study dynamic bonding of gold atoms on surfaces under low coordination conditions. In the experiments, using an atomically-sharp gold tip, a gold adatom is deposited onto a gold surface with atomic precision either on the first hollow site near a step edge, or far away from it. Classical molecular dynamics simulations at 4.2 K and density functional theory calculations serve to elucidate the difference in the bonding behavior between these two different placements, while also providing information on the crystalline classification o…
The results of a density-functional-theory study of the formation energies of (100)- and (111)-faceted steps on the Pt(111) surface, as well as of the barrier for diffusion of an adatom on the flat surface, are presented. The step formation energies are found to be in a ratio of 0.88 in favour of the (111)-faceted step, in excellent agreement with experiment; the equilibrium shape of islands should therefore clearly be non-hexagonal. The origin of the difference between the two steps is discussed in terms of the release of stress at the surface through relaxation. For the diffusion barrier, we…
The roles of oxygen vacancies on the electronic and magnetic properties of Ni doped In$_2$O$_3$ have been studied by first-principles calculations based on hybrid functional theory. Our results predict that the Ni-doped In$_2$O$_3$ system displays a ferromagnetic semiconducting character. However, the presence of oxygen vacancies results in antiferromagnetic coupling between the neighboring Ni pair bridged by an oxygen vacancy. The antiferromagnetic coupling is found to arise from the predominant role of superexchange due to the strong Ni 3d-O 2p hybridization. Consequently, the oxygen vacanci…
Point defects in diamond are of high interest as candidates for realizing solid state quantum bits, bioimaging agents, or ultrasensitive electric or magnetic field sensors. Various artificial diamond synthesis methods should introduce oxygen contamination in diamond, however, the incorporation of oxygen into diamond crystal and the nature of oxygen-related point defects are largely unknown. Oxygen may be potentially interesting as a source of quantum bits or it may interact with other point defects which are well established solid state qubits. Here we employ plane-wave supercell calculations …
We present density-functional results on the lifetime of the (111) surface state of the noble metals. We consider scattering on the Fermi surface caused by impurity atoms belonging to the 3d and 4sp series. The results are analyzed with respect to film thickness and with respect to separation of scattering into bulk or into surface states. While for impurities in the surface layer the overall trends are similar to the long-known bulk-state scattering, for adatom-induced scattering we find a surprising behavior with respect to the adatom atomic number. A plateau emerges in the scattering rate o…
Heterogeneous catalysts based on sub-nanometer metal clusters often exhibit strongly size-dependent properties, and the addition or removal of a single atom can make all the difference. Identifying the most active species and deciphering the reaction mechanism is extremely difficult, however, because it is often not clear how the catalyst evolves in operando. Here, we utilize a combination of atomically resolved scanning probe microscopies, spectroscopic techniques, and density functional theory (DFT)-based calculations to study CO oxidation by a model Pt/Fe3O4(001) single-atom catalyst. We de…
We present a systematic study of the atomic and electronic structure of the Si(111)-(5x2)-Au reconstruction using first-principles electronic structure calculations based on the density functional theory. We analyze the structural models proposed by Marks and Plass [Phys. Rev. Lett.75, 2172 (1995)], those proposed recently by Erwin [Phys. Rev. Lett.91, 206101 (2003)], and a completely new structure that was found during our structural optimizations. We study in detail the energetics and the structural and electronic properties of the different models. For the two most stable models, we also ca…
We propose a practical approach to spin-polarized systems within the van der Waals density functional (vdW-DF). The method was applied to a gas phase oxygen molecule and a parallel (H-type) pair of oxygen molecules. It was found that vdW-DF improves the equilibrium distance and binding energy. In particular, one type of vdW-DF can describe such systems reasonably well. The van der Waals interaction has been confirmed to have an energy comparable to the magnetic one, while emerging at a distance rather longer than the latter.
Density functional calculations with a large unit cell have been conducted to investigate adsorption, segregation and magnetization of Mn monomer on GaAs(110). The Mn adatom is rather mobile along the trench on GaAs(110), with an energy barrier of 0.56 eV. The energy barrier for segregation across the trenches is nevertheless very high, 1.67 eV. The plots of density of states display a wide gap in the majority spin channel, but show plenty of metal-induced gap states in the minority spin channel. The Mn atoms might be invisibl in scanning tunneling microscope (STM) images taken with small bias…
We recently proposed a new structural model for the Si(331)-(12x1) surface reconstruction containing silicon pentamers as elementary structural building blocks. Using first-principles density-functional theory we here investigate the stability of a variety of adatom configurations and determine the lowest energy configuration. We also present a detailed comparison of the energetics between our model for Si(331)-(12x1) and the adatom-tetramer-interstitial model for Si(110)-(16x2), which shares the same structural building blocks.
Atomic oxygen adsorption on the Mo(112) surface has been investigated by means of first-principles total energy calculations. Among the variety of possible adsorption sites it was found that the bridge sites between two Mo atoms of the topmost row are favored for O adsorption at low and medium coverages. At about one monolayer coverage oxygen atoms prefer to adsorb in a quasi-threefold hollow sites coordinated by two first-layer Mo atoms and one second layer atom. The stability of a structural model for an oxygen-induced $p(2\times 3)$ reconstruction of the missing-row type is examined.
Oxygen vacancies at the SnO2(110) and (101) surface and subsurface sites have been studied in the framework of density functional theory by using both all-electron Gaussian and pseudopotential plane-wave methods. The all-electron calculations have been performed using the B3LYP exchange-correlation functional with accurate estimations of energy gaps and density of states. We show that bulk oxygen vacancies are responsible for the appearance of a fully occupied flat energy level lying at about 1 eV above the top valence band, and an empty level resonant with the conduction band. Surface oxygen …
Electronic and atomic structures of the clean, and As and Te covered Si(211) surface are studied using pseudopotential density functional method. The clean surface is found to have (2 X 1) and rebonded (1 X 1) reconstructions as stable surface structures, but no π-bonded chain reconstruction. Binding energies of As and Te adatoms at a number of symmetry sites on the ideal and (2 X 1) reconstructed surfaces have been calculated because of their importance in the epitaxial growth of CdTe and other materials on the Si(211) surface. The special symmetry sites on these surfaces having the highest b…
It has been well established that nitrogen coordinated transition metal, TM-N$_{4}$-C (TM$=$Fe and Co) moieties, are responsible for the higher catalytic activity for the electrochemical oxygen reduction reaction. However, the results obtained using density functional theory calculations vary from one to another, which can lead to controversy. Herein, we assess the accuracy of the theoretical approach using different class of exchange-correlation functionals, i.e., Perdew-Burke-Ernzerhof (PBE) and revised PBE (RPBE), those with the Grimme's semiempirical dispersion correction (PBE+D3 and RPBE+…
Thin films of transition metal oxides open up a gateway to nanoscale electronic devices beyond silicon characterized by novel electronic functionalities. While such films are commonly prepared in an oxygen atmosphere, they are typically considered to be ideally terminated with the stoichiometric composition. Using the prototypical correlated metal SrVO$_3$ as an example, it is demonstrated that this idealized description overlooks an essential ingredient: oxygen adsorbing at the surface apical sites. The oxygen adatoms, which persist even in an ultrahigh vacuum environment, are shown to severe…
Large scale first-principles calculations based on density functional theory (DFT) employing two different methods (atomic orbitals and plane wave basis sets) were used to study the energetics, geometry, the electronic charge redistribution and migration for adsorbed atomic and molecular oxygen on defect-free SrTiO3(001) surfaces (both SrO- and TiO2-terminated), which serves as a prototype for many ABO3-type perovskites. Both methods predict substantial binding energies for atomic O adsorption at the bridge position between the oxygen surface ions and an adjacent metal ion. A strong chemisorpt…
We present a Density Functional Theory (DFT) study of the structural and electronic properties of bare rutile VO$_{2}$(110) surfaces and its oxygen-rich terminations. We discuss the performance of various DFT functionals, including PBE, PBE+U (U = 2 eV), SCAN and SCAN+rVV functionals with non-magnetic and ferromagnetic spin ordering. We predict the presence of a ring-like termination that is electronically and structurally related to a V$_{2}$O$_{5}$(001) monolayer and shows a higher stability than pure oxygen adsorption phases. Despite the fact that the calculated phase stabilities depend on …
We present a density-functional theory study addressing the on-surface adsorption of oxygen at the Pd(11N) (N =3,5,7) vicinal surfaces, which exhibit (111) steps and (100) terraces of increasing width. We find the binding to be predominantly governed by the local coordination at the adsorption site. This leads to very similar bonding properties at the threefold step sites of all three vicinal surfaces, while the binding at the central fourfold hollow site in the four atomic row terrace of Pd(117) is already very little disturbed by the presence of the neighboring steps.
We report an experimental refinement of the local charge density at the Si (111) 7x7 surface utilizing a combination of x-ray and high energy electron diffraction. By perturbing about a bond-centered pseudoatom model, we find experimentally that the adatoms are in an anti-bonding state with the atoms directly below. We are also able to experimentally refine a charge transfer of 0.26(4) e- from each adatom site to the underlying layers. These results are compared with a full-potential all-electron density functional DFT calculation.
We present ab initio local-density-functional electronic structure calculations for the (111) and (-1-1-1) surfaces of cubic BN. The energetically stable reconstructions, namely the N adatom, N3 triangle models on the (111), the (2x1), boron and nitrogen triangle patterns on the (-1-1-1) surface are investigated. Band structure and properties of the surface states are discussed in detail.
We investigate the behavior of oxygen vacancies in three different metal-oxide semiconductors (rutile and anatase TiO2, monoclinic WO3, and tetragonal ZrO2) using a recently proposed hybrid density-functional method in which the fraction of exact exchange is material-dependent but obtained ab initio in a self-consistent scheme. In particular, we calculate charge-transition levels relative to the oxygen-vacancy defect and compare computed optical and thermal excitation/emission energies with the available experimental results, shedding light on the underlying excitation mechanisms and related m…
We show that Pb and Bi adatoms and dimers have a large tunneling anisotropic magnetoresistance (TAMR) of up to 60% when adsorbed on a magnetic transition-metal surface due to strong spin-orbit coupling and the hybridization of 6p orbitals with 3d states of the magnetic layer. Using density functional theory, we have explored the TAMR effect of Pb and Bi adatoms and dimers adsorbed on a Mn monolayer on W(110). This surface exhibits a noncollinear cycloidal spin spiral ground state with an angle of 173$^\circ$ between neighboring spins which allows to rotate the spin quantization axis of an adat…
Oxygen vacancies in two-dimensional metal-oxide structures garner much attention due to unique conductive, magnetic and even superconductive functionalities they induce. Ferroelectric domain walls have been a prominent recent example because they serve as a hub for topological defects that enable unusual symmetries and are relevant for low-energy switching technologies. However, owing to the light weight of oxygen atoms and localized effects of their vacancies, the atomic-scale electrical and mechanical influence of oxygen vacancies has remained elusive. Here, stable individual oxygen vacancie…
To help provide insight into the remarkable catalytic behavior of the oxygen/silver system for heterogeneous oxidation reactions, purely sub-surface oxygen, and structures involving both on-surface and sub-surface oxygen, as well as oxide-like structures at the Ag(111) surface have been studied for a wide range of coverages and adsorption sites using density-functional theory. Adsorption on the surface in fcc sites is energetically favorable for low coverages, while for higher coverage a thin surface-oxide structure is energetically favorable. This structure has been proposed to correspond to …
Stable oxygen sites on a PdO film over a Pd(100) thin structures with a (sqrt{5} times sqrt{5}) R27^circ surface-unit cell are determined using the first-principles electronic structure calculations with the generalized gradient approximation. The adsorbed monatomic oxygen goes to a site bridging two 2-fold-coordinated Pd atoms or to a site bridging a 2-fold-coordinated Pd atom and a 4-fold-coordinated Pd atom. Estimated reaction energies of CO oxidation by reduction of the oxidized PdO film and N_2O reduction mediated by oxidation of the PdO film are exothermic. Motion of the adsorbed oxygen …
Solar water splitting has attracted much attention as a clean and renewable route to produce hydrogen fuel. Since the oxygen evolution half-reaction (OER) requires high overpotentials, much research has focused on finding catalyst materials that minimize this energy loss. Oxynitrides with a layered perovskite structure have the potential to combine the superior photocatalytic properties of layered perovskite oxides with enhanced visible-light absorption caused by the band gap narrowing due to less electronegative nitrogen ions. In this paper, we study the OER on the (001) and (100) surfaces of…
Pd(111) has recently been shown to exhibit a propensity to form a sub-nanometer thin surface oxide film already well before a full monolayer coverage of adsorbed O atoms is reached on the surface. Aiming at an atomic-scale understanding of this finding, we study the initial oxygen incorporation into the Pd(111) surface using density-functional theory. We find that oxygen incorporation into the sub-surface region starts at essentially the same coverage as formation of the surface oxide. This implies that the role of sub-surface oxygen should be considered as that of a metastable precursor in th…
