Showing papers in "Surface Review and Letters in 1995"
TL;DR: In this paper, a model oxide-supported metal catalysts have been prepared by evaporating a metal (e.g., Cu, Pd) onto an oxide (SiO2, Al2O3) thin film, which, upon annealing, form small metallic clusters on the oxide surface whose sizes are dependent upon the initial metal film thickness.
Abstract: Model oxide-supported metal catalysts have been prepared by evaporating a metal (e.g., Cu, Pd) onto an oxide (SiO2, Al2O3) thin film (~100 A) which, in turn, is supported on a refractory metal (Mo, W, Ta) surface. The deposited metal films, upon annealing, form small metallic clusters on the oxide surface whose sizes are dependent upon the initial metal film thickness. The surface structures and particle morphologies have been characterized using scanning probe microscopies, temperature programed desorption, X-ray and ultraviolet photoemission, and high-resolution electron energy-loss spectroscopy/infrared reflection-absorption spectroscopy of adsorbed carbon monoxide. The catalytic properties of these particles have also been investigated with respect to several reactions including CO/O2 and CO/NO. The chemical and electronic properties of the metal particles with respect to size are compared to the analogous properties of extended single-crystal surfaces.
120 citations
TL;DR: In this paper, a density-functional-theory analysis of adsorbate-substrate interaction on close-packed metal surfaces is discussed. But the authors focus on the coverage-dependent stable and metastable adorability and phase transitions of the adsorbates.
Abstract: Results of recent density-functional-theory calculations for alkali-metal adsorbates on close-packed metal surfaces are discussed. Single adatoms on the (111) surface of Al and Cu are studied with the self-consistent surface Green-function method by which the pure adsorbate-substrate interaction may be analyzed. Higher coverage ordered adlayers of K on Al(111), Na on Al(111), and Na on Al(001) are treated using the ab initio pseudopotential plane-wave method which affords the prediction of coverage-dependent stable and metastable adsorbate geometries and phase transitions of the adsorbate layers. Together, these studies give insight and understanding into current key issues in alkali-metal adsorption, namely, the nature of the adsorbate-substrate bond at low coverage and the occurrence of hitherto unanticipated adsorbate geometries, and the associated electronic properties.
59 citations
TL;DR: In this article, the electronic, chemical, and structural properties of metal/oxide and oxide/oxide interfaces which are formed via ultrathin film growth on oxide single-crystal surfaces are discussed.
Abstract: This article reviews aspects of the electronic, chemical, and structural properties of metal/oxide and oxide/oxide interfaces which are formed via ultrathin film growth on oxide single-crystal surfaces. The interactions at the interfaces are classified based on the nature of the reaction products, thermodynamic predictions of interfacial reactions, and wetting and adhesion. Then, properties of single-crystal oxide substrates and limitations and difficulties in studying these ceramic systems are discussed. The remainder of the article presents experimental observations for several systems involving both metal and oxide ultrathin film growth on stoichiometric NiO(100), TiO2(110), and surfaces including a discussion of interdiffusion, chemical and electronic interactions, thermal stability, and interfacial impurity effects.
56 citations
TL;DR: In this article, the authors used a scanning tunneling microscope (STM) to study the local properties of low-dimensional electrons and found that Fe adatoms strongly scatter the surface states and are good building blocks for constructing atomic-scale barriers to confine the surface state electrons.
Abstract: Electrons occupying surface states on the close-packed faces of noble metals form a two-dimensional (2-d) nearly free electron gas. Because this system is accessible to the scanning tunneling microscope (STM), it provides a unique opportunity to study the local properties of low-dimensional electrons. On Cu(111) we have observed standing wave patterns in the surface local density of states due to the quantum mechanical interference of surface state electrons scattering off of step edges and adsorbates. We find that Fe adatoms strongly scatter the surface state and, as a result, are good building blocks for constructing atomic-scale barriers (“quantum corrals”) to confine the surface state electrons. The barriers are constructed by individually positioning Fe adatoms using the tip of a cold (4 K) STM. Tunneling spectroscopy performed inside of the corrals reveals discrete resonances, consistent with size quantization. A more quantitative understanding is obtained by accounting for the multiple scattering of surface state electrons with the corrals’ constituent adatoms. This scattering is characterized by a complex phase shift which can be extracted from the electronic density pattern inside a quantum corral.
45 citations
TL;DR: In this paper, a review of surface reactions due to spillover species when reacting with the surface of a solid distinct from the donors is presented, including acceleration of the nucleation steps in the reduction of oxides, control of the nature of active sites on sulfides (e.g., MoS2), and the adequate oxide-reduction state of the surface active in selective oxidation.
Abstract: Transition metals can dissociate hydrogen to a surface mobile species called spillover hydrogen (H-so). Similarly, oxides like alpha-Sb2O4, BiPO4, Bi2O3 (donors) can dissociate molecular oxygen to a mobile surface species (O-so). These metals or oxides are conveniently called donors. This article reviews effects which are due to spillover species when reacting with the surface of a solid distinct from the donors: (i) acceleration of the nucleation steps in the reduction of oxides, (ii) control of the nature of active sites on sulfides (e.g., MoS2), and (iii) control of the adequate oxide-reduction state of the surface of the oxides active in selective oxidation. Atomic interpretations of the surface reactions explaining these effects will be given. It will be shown that all these phenomena are caused by the special reactivity of spillover species. Fundamental questions which could be solved by surface science approaches will be outlined.
37 citations
TL;DR: In this paper, very low energy electron diffraction (VLEED) intensities from a clean Cu(111) surface have been measured in detail in the energy range 15-100 eV by low-energy electron microscope (LEEM).
Abstract: Very-low-energy electron diffraction (VLEED) intensities from a clean Cu(111) surface have been measured in detail in the energy range 15–100 eV by low-energy electron microscope (LEEM). This enabled the elimination of possible disturbances due to stray magnetic fields. Corresponding theoretical I–V curves have been obtained in good agreement with experimental data when an image-type surface barrier and anisotropy of the electron attenuation were taken into account. The reliability factor analysis indicates a slight expansion of the topmost interatomic spacing of Cu(111) relative to its bulk value.
27 citations
TL;DR: In this article, the A-and B-type CrSi2 epitaxial films were grown by means of the template technique and the results showed that nucleation conditions and the type of surface phases determine the azimuthal orientation of the epitaxia relative to Si(111) under their nucleation.
Abstract: The literature data and new data on investigation of the Si(111)-Cr system were systematized to the diagram of structural phase transitions. The ranges on this diagram give the formation conditions of various phases and reflect the mechanism of the Cr/Si(111) and CrSi2/Si(111) interface formation during room-temperature Cr deposition following annealing. The proofs of the multilayer surface phase formation and the data about transitions between the multilayer surface phases and bulk silicides during formation of the Cr/Si(111) and CrSi2/Si(111) interfaces were presented. The investigation of A- and B-type CrSi2 templates formation was carried out. It was discovered that nucleation conditions and, in particular, the type of surface phases determine the azimuthal orientation of the epitaxial CrSi2 islands relative to Si(111) under their nucleation. The A- and B-type CrSi2 epitaxial films were grown by means of the template technique. The A-type CrSi2 semiconductor film with low concentration and high mobility of holes was obtained.
19 citations
TL;DR: In this paper, most of the experimental results for the submonolayer adsorption of alkali metals on copper and nickel surfaces are reviewed, with emphasis on the structural findings.
Abstract: This paper reviews most of the experimental results for the submonolayer adsorption of alkali metals on copper and nickel surfaces, with emphasis on the structural findings. Where possible, comparisons are made between the overlayers on copper and those on nickel. The goal is to point out some of the most interesting recent structural results and to move toward a general understanding of these systems. The few structural results of coadsorption of gases with alkali metals are also described.
16 citations
TL;DR: In this article, a real-time technique of measuring the adsorbate-induced surface stress has been applied to the oxidation reaction of CO on Pt(111) to investigate in-situ catalytic reactions on single-crystal surfaces.
Abstract: A new method to investigate in-situ catalytic reactions on single-crystal surfaces is introduced. The real-time technique of measuring the adsorbate-induced surface stress has been applied to the oxidation reaction of CO on Pt(111). The adsorption of each of the reactants, CO and oxygen, on Pt(111) induces a compressive stress which increases nonlinearly with the coverage. The stress-coverage dependence of CO and oxygen is explained by an ansatz, which considers the net charge transfer for an isolated adsorbate atom and the contribution of the wave-function overlap of adjacent atoms to the induced surface stress. The adsorbate-induced change of the total surface stress which is obtained during the surface reaction as a function of the time, is well reproduced by a Monte-Carlo simulation which regards the CO diffusion as well as the activation energy for the Langmuir-Hinshelwood reaction.
16 citations
TL;DR: In this paper, angle-resolved photo-emission spectroscopy (ARUPS) was used to study the electronic structure effects induced by potassium adsorption up to one monolayer on a nearly stoichiometric TiO2(110) surface.
Abstract: Electronic structure effects induced by potassium adsorption up to one monolayer (ML) on a nearly stoichiometric TiO2(110) surface has been studied by means of angle-resolved photoemission spectroscopy (ARUPS and ARXPS) from valence states and core levels. In agreement with the observations on K/TiO2(100) [P.J. Hardman et al., Surf. Sci.269/270, 677 (1992)], potassium adsorption at room temperature leads—due to K-to-substrate charge transfer—to the reduction of surface Ti ions (to nominally Ti3+ ions), evidenced by lowered Ti2p core-level binding energy (ΔBE=–1.6 eV) and occupation of Ti3d-like band-gap states centered at 0.9 eV BE. The gap-state intensity exhibits a pronounced maximum at 0.37 ML coverage, where the work function has a weak minimum. This behavior is in agreement with a ionic-to-neutral transition of the K-substrate bonding with increasing K coverage, as suggested recently [Souda et al., Surf. Sci.285, 265 (1993)]. Annealing of a surface precovered with 0.27 ML potassium up to 1000 K results in metallization of the surface, evidenced by (i) the occupation of a second gap-state centered at 0.4 BE and with a considerable state-density at the Fermi energy, and (ii) Ti2p core-levels lowered by 3.2 eV in BE (nominally “Ti2+” ions). This dramatic reduction of the surface is healed out with complete desorption of potassium. A discussion in terms of desorption of KOx species and oxygen diffusion from the bulk to the surface is given.
16 citations
TL;DR: In this paper, the interfacial chemistries of a 65-A film prepared by depositing zirconium in an oxidizing environment onto a methane-pretreated 11-A thick ZIRconium oxide film, which initially was deposited onto a gold substrate, were studied.
Abstract: X-ray photoelectron spectroscopy (XPS) has been used to study the interfacial chemistries of a 65-A film prepared by depositing zirconium in an oxidizing environment onto a methane-pretreated 11-A thick zirconium oxide film, which initially was deposited onto a gold substrate. The second metal deposition results in an outermost region composed of a mixed zirconium oxide, while below there is metallic zirconium followed by zirconium carbide and carbon on top of the first zirconium oxide film, which is itself in contact with the gold. The carbide component showed no changes on heating to 425°C, on treating with a hydrogen plasma at room temperature, or on heating the resulting film to 425°C. The oxide layers do show characteristic changes, and this also contrasts with earlier observations for a zirconium sulphide film. The zirconium carbide Zr3d5/2 component has a binding energy of 180.6 eV.
TL;DR: From crystal orbital calculations, benzene is found to chemisorb with nearly equal binding energy on a hollow site and on a bridge site of the Pt(111) face in agreement with experiment.
Abstract: From crystal orbital calculations, benzene is found to chemisorb with nearly equal binding energy on a hollow site and on a bridge site of the Pt(111) face. The chemisorption is stronger and involves larger molecular distortions than on palladium and rhodium surfaces in agreement with experiment. On the hollow site, the benzene molecule undergoes a Kekule distortion. On the bridge site found experimentally (with or without coadsorbed CO), the benzene molecule undergoes a local C2v distortion with long and short C-C bonds also in qualitative agreement with experiment. The favored azimuthal orientation of pure benzene coincides with that found experimentally only in the presence of CO. According to calculations, CO adsorption is found to weaken the benzene adsorption and reduce its metal-induced distortions but preserved the same orientation.
TL;DR: The results of recent photoelectron-diffraction investigations of structures formed upon alkali-metal adsorption on metal surfaces are presented in this article, where a variety of unexpected phenomena that are in contrast to earlier beliefs is found to occur for many systems.
Abstract: The results of recent photoelectron-diffraction investigations of structures formed upon alkali-metal adsorption on metal surfaces are presented A variety of unexpected phenomena that are in contrast to earlier beliefs is found to occur for many systems Photoelectron diffraction, in its angle-scanned or energy-scanned mode, is found to provide a powerful and direct tool for the identification and investigation of unanticipated adsorbate geometries such as ontop adsorption, substitutional adsorption, and surface alloy formation
TL;DR: In this article, the formation of the Schottky barrier is studied in weakly ionic semiconductors with a special emphasis on AMs on the surface of the semiconductor, and two regimes are clearly differentiated for the deposition of AMs: in the high-coverage limit, it is shown that for not very defective interfaces, the Fermi energy is pinned by the metallic density of states at the position determined by the charge neutrality level.
Abstract: Alkali metals deposited on weakly ionic semiconductors are neither reactive nor form large three-dimensional islands, offering an ideal system in which Schottky junctions can be analyzed. In this paper, the alkali-metal-semiconductor interface is reviewed with a special emphasis on the formation of the Schottky barrier. Two regimes are clearly differentiated for the deposition of AMs on a semiconductor: in the high-coverage limit the Schottky barrier is shown to depend, for not very defective interfaces, on the semiconductor charge neutrality level. For low coverages, different one- and two-dimensional structures appear on the semiconductor surface presenting an insulating behavior. For depositions around a metal monolayer, a Mott metal-insulator transition appears; then, the interface Fermi energy is pinned by the metallic density of states at the position determined by the semiconductor charge neutrality level. This situation defines the Schottky barrier height of a thick-metal overlayer.
TL;DR: In this article, the surface core-level shifts for the 4D transition metals and silver in the initial-state model and in the full-impurity formulation were obtained, giving an unambiguous separation into initial state and screening terms.
Abstract: Ab initio calculations based on density-functional theory were used to obtain surface core-level shifts for the 4d transition metals and silver in the initial-state model and in the full-impurity formulation, giving an unambiguous separation into initial state and screening terms. This shows that the screening of the core hole is substantially better at the surface than in the bulk for a transition metal. For Ag, an opposite and even larger effect is found, showing the central role of d-electron screening in the surface core-level shift of the transition metals.
TL;DR: In this paper, the structural properties of the ordered overlayers of Li, Na, K, Rb, and Cs on Ru(0001) are summarized, and it is shown that the adsorption site depends on the coverage while the hard-sphere radii of the alkali-metal atoms do not change (if corrected for different numbers of coordination).
Abstract: The structural properties of the ordered overlayers of Li, Na, K, Rb, and Cs on Ru(0001) are summarized. The major result is that the adsorption site depends on the coverage while the hard-sphere radii of the alkali-metal atoms do not change (if corrected for different numbers of coordination). This comparison also emphasizes the singular behavior of Cs for which adsorption takes place over single Ru atoms at a Cs coverage of 0.25. While on other close-packed substrate surfaces potassium and rubidium occupy ontop positions at low temperatures, this has not been found with Ru(0001). This finding points towards the important role of the substrate. For the ontop adsorption to be favored, an inward displacement of the substrate atoms directly underneath the alkali-metal atoms by a substantial amount is necessary which results in the formation of a quasisevenfold-coordinated bond geometry in connection with a reduction of the dipole-dipole repulsion. The stiffness of the substrate determines the energy cost for this local reconstruction, and consequently ontop adsorption on the hard Ru(0001) substrate has only been observed for the biggest alkali metal Cs where the energy difference between various adsorption sites [on the unrelaxed Ru(0001) surface] is assumed to be small. In order to force potassium to reside in the ontop position, the Ru(0001) surface has to be “softened” which task was accomplished by adding CO molecules to the K-(2×2) overlayer.
TL;DR: In this paper, an imitation model of CO oxidation reaction on platinum metals was constructed and studied, and the model takes into account oxygen dissociative adsorption, monomolecular adaption and desorption of carbon monoxide, active oxygen transformation into a less active oxygen of the second type, adsorbed CO reaction with the two types of oxygen, and CO diffusion over the surface.
Abstract: We constructed and studied an imitation model of CO oxidation reaction on platinum metals The model takes into account oxygen dissociative adsorption, monomolecular adsorption and desorption of carbon monoxide, active oxygen transformation into a less active oxygen of the second type, adsorbed CO reaction with the two types of oxygen, and CO diffusion over the surface We found that adsorbate coverages and reaction rate undergo self-oscillations attended by the autowave behavior of adsorbates on the surface With respect to oxygen partial pressures the interval of oscillations splits into three parts: nonregular relaxation oscillations, regular oscillations, and chaos, when the period and amplitude of adsorbate concentration oscillations change stochastically The model shows that nonuniform distribution of the less active second type oxygen on the surface and the difference in the orders of reagents adsorption kinetics is the reason of oscillations We suggest as well the reasons for the autowaves formation and development on the catalyst surface
TL;DR: In this paper, the reaction of O2 with Li and Cs films is accompanied by the emission of electrons and the variations of the initial yields with the velocity of the impinging molecules are exploited to access the dynamics of the adsorption process.
Abstract: The reaction of O2 with Li and Cs films is accompanied by the emission of electrons. The variations of the initial yields with the velocity of the impinging molecules is exploited to access the dynamics of the adsorption process. The data are analyzed in terms of a model where chemisorption proceeds via an intermediate species. This state readily dissociates while the de-excitation of the resulting O− into O2− may cause electron emission. From a comparison with experimentally observed electron yields the reaction time and velocity uptake of the products is accessed.
TL;DR: In this article, single-crystal films of permalloy (Ni80Fe20) were grown on Cu(001) seed layers oriented epitaxially with Si(001).
Abstract: Single-crystal films of permalloy (Ni80Fe20) were grown on Cu(001) seed layers oriented epitaxially with Si(001). The microstructural properties were measured using in-situ reflection high-energy electron diffraction, and ex-situ transmission electron microscopy, x-ray diffraction, and atomic force microscopy, whereas the magnetic properties were probed using in-situ magneto-optic Kerr effect and ex-situ vibrating sample magnetometry. Anisotropic magnetoresistance and resistivity for some of the samples were also measured. The coercivity for thinner (≤5 nm) Ni80Fe20 was significantly higher (10–20 Oersteds) than polycrystalline films deposited on SiO2/Si, and was also higher than films deposited on lattice-matched CuxNi1–x alloys. These magnetic properties were explained using a theoretical model involving interaction of domain walls with defects such as misfit dislocations and coherent islands, due to the mismatch between Ni80Fe20 and Cu.
TL;DR: In this article, a quantitative analysis of low-energy electron diffraction intensities has been carried out to investigate the superstructures of fcc-Fe films, and it has been shown that the reconstruction of layers always entails an increased atomic volume available for iron atoms involved in the reconstruction.
Abstract: By epitaxial growth of iron on Cu(100) phases of fcc-Fe can be stabilized at room temperature and below. Dependent on coverage the films show various superstructures which we investigate by quantitative analysis of low-energy electron diffraction intensities. There are three coverage regimes, whereby in the first one (Θ≤4 ML) all iron layers are considerably reconstructed and are fcc(100) layers only on average. Upon further iron deposition (5 ML<Θ<10 ML) subsurface iron layers flatten and only the top layer is reconstructed. Simultaneously, the epitaxial growth seems to change from pseudomorphic to nonpseudomorphic. At about 10 ML there is a 1. order phase transition fcc(100)⇒bcc(110), the latter phase being stable at higher coverages. It turns out that the reconstruction of layers always entails an increased atomic volume available for iron atoms involved in the reconstruction. In turn this is consistent with magnetic properties known for the iron films from the literature, i.e., bulk ferromagnetism in the first coverage regime and only surface ferromagnetism in the second. So, magnetic and structural properties are shown to be closely related.
TL;DR: In this paper, the time-of-flight (TOF) distributions of CO2 molecules desorbing after the oxidation of CO on Pt(111) were investigated at various desorption angles for surface temperatures Ts in the range 550-800 K.
Abstract: Time-of-flight (TOF) distributions of CO2 molecules desorbing after the oxidation of CO on Pt(111) were investigated at various desorption angles ϑ for surface temperatures Ts in the range 550–800 K. The Pt(111) surface was exposed to a continuous flow of O2 from a doser and to a chopped CO nozzle beam. Surface residence-time effects proved to be unimportant or were elucidated. Bimodal TOF distributions composed of two parts were obtained: molecules with a Maxwellian velocity distribution corresponding to Ts appeared in a cosine-shaped angular distribution and molecules with appreciably higher kinetic energies (mean kinetic energy normal to the surface ⊥≈9kTs) were observed in a narrow angular distribution proportional to cos8 ϑ. The partition of the total desorbing CO2 flux to these two channels depended on Ts and ϑ and the total oxygen dose d0 accumulated during an experiment. With increasing d0 the Maxwellian component markedly increased at the expense of the fast component. The observed trends suggest almost only fast desorption from clean Pt(111). We therefore assume Maxwellian desorption to occur mainly from surface sites gradually produced under the influence of oxygen.
TL;DR: In this article, the first clear evidence of electron emission arising directly from a quantized two-dimensional electron channel from the InAs(110) surface covered by a few Cs atoms was presented.
Abstract: We present the first clear evidence of electron emission arising directly from a quantized two-dimensional electron channel from the InAs(110) surface covered by a few Cs atoms (≈ 0.01 Cs ML). Spectral features observed by photoemission spectroscopy using synchrotron radiation reveal discrete-energy electronic states resulting from quantization in the direction normal to the surface. The electron photoemission originates from the vicinities of points in the first and second surface Brillouin zones corresponding to the bottom of the conduction band. These findings are in agreement with self-consistent theoretical energy-level calculations using a jellium-like model.
IBM1
TL;DR: In this paper, He-beam diffraction data evaluated for clean Rh(311) yield a best-fit corrugation, which shows a pronounced Corrugation amplitude along the (100)-microfacets and a practically vanishing amplitude along (111)-micro facets in agreement with expectation, but in contrast to Ni(311), where the reverse situation was found.
Abstract: He-beam diffraction data evaluated for clean Rh(311) yield a best-fit corrugation, which shows a pronounced corrugation amplitude along the (100)-microfacets and a practically vanishing amplitude along the (111)-microfacets in agreement with expectation, but in contrast to Ni(311) where the reverse situation was found. Hydrogen adsorption leads to a sequence of c(1×1), c(1×3), p(1×1), c(1×3), and p(1×1)REC phases. The fact that the c(1×1) phase was observed with He-diffraction, but not in previous LEED studies, again proves the exceptional sensitivity of He scattering for adsorbed hydrogen. Surface charge density calculations were performed to reproduce the shape and amplitude of the best-fit corrugation function of the c(1×1)H-phase. In this way we found that the H atoms occupy places between the topmost bridge sites and the adjacent threefold hollow sites on the (111)-microfacets; the H-Rh bond length amounts to 1.92±0.1 A.
TL;DR: In this article, the atomic structure of a clean (010) surface of the ordered binary alloy TiAl (with tetragonal bulk structure of the CuAu I type) was studied with quantitative low-energy electron diffraction (QLEED).
Abstract: The atomic structure of a clean (010) surface of the ordered binary alloy TiAl (with tetragonal bulk structure of the CuAu I type) is studied with quantitative low-energy electron diffraction (QLEED). Two different surface phases are found depending on the preparation procedure. After a cleaning step in vacuo by means of Ar-ion bombardments, anneals at 750−850°C produce a 2×1 surface and anneals at about 900° C produce a 1×1 surface. A QLEED intensity analysis of the 1×1 structure reveals the occurrence of chemical reconstruction, whereby the Ti atoms in the first layer exchange places with the Al atoms in the second layer. Thus, while any bulk (010) plane contains 50% Al and 50% Ti, the top atomic layer of a (010) surface contains 100% Al and the second atomic layer contains 100% Ti. Both layers are slightly buckled and the first interlayer distance is compressed about 7.1% while the second interlayer spacing is expanded about 7.4% with respect to the bulk value.
TL;DR: In this paper, the use of high-resolution core-level photoemission spectroscopy for investigating the geometrical aspects of alkali adsorption on aluminum surfaces is reviewed.
Abstract: The use of high-resolution core-level photoemission spectroscopy for investigating the geometrical aspects of alkali adsorption on aluminum surfaces is reviewed. Examples are given of the use of the technique for studies of the submonolayer growth modes of alkali overlayers, of the geometry of the strongly reconstructed ordered overlayer structures, and of temperature-induced phase transformations between metastable and stable alkali-induced structures.
TL;DR: The atomic structure of the surface formed by depositing a single-atomic layer of cobalt on Pt(111) has been investigated using low-energy electron diffraction (LEED) crystallographic analysis.
Abstract: The atomic structure of the surface formed by depositing a single-atomic layer of cobalt on Pt(111) has been investigated using low-energy electron diffraction (LEED) crystallographic analysis. Cobalt grows at room temperature on the Pt(111) surface forming islands a single-atomic layer thick. The layer is ordered and it forms a 1×1 epitaxial phase where cobalt atoms are in an fcc registry with respect to the substrate.
TL;DR: In this article, a density-functional method was used to calculate the ionization energies for adsorbed CO in the atop and bridge sites of the Ni(100) surface.
Abstract: Starting from the observed chemical shift of C-1s and O-1s ionization potentials (IP), reported in the literature for the adsorption of CO on Ni(100), and correlated to the different CO adsorption sites at different coverages, we have carried out a theoretical investigation, using a first-principle density-functional method, to calculate ionization energies for adsorbed CO in the atop and bridge sites. In our approach, the Ni(100) surface was simulated with clusters of up to nine metal atoms of different geometry, in order to test the two adsorption sites. For each cluster, the CO adsorption geometry was optimized and the O-1s and C-1s ionizations were calculated. The main result was that the (O-1s–C-1s) difference was very well reproduced even with clusters of modest size, thus confirming the possibility to use this value as a structure-sensitive parameter.
TL;DR: In this article, the Pb/Si(113) system has been studied with LEED, AES, EELS, and QKLEED calculations, and the atomic structure of the 1×1Pb surface of the intermixed phase has been determined with QK-LEED and there is one ordered Pb atom in each unit cell.
Abstract: In the present work the Pb/Si(113) system has been studied with LEED, AES, EELS, and QKLEED calculations. The interface is very reactive rather than abrupt as previously concluded. As a result, a specific intermixed phase, which is very similar to that in the Pb/Si and Pb/Ge systems studied earlier, forms at the interface even at room temperature. The atomic structure of the 1×1Pb surface of the intermixed phase has been determined with QKLEED and there is one ordered Pb atom in each unit cell. Primary results indicate that Pb atoms are likely to randomly occupy the interstitial sites in the intermixed phase.
TL;DR: In this article, the potentially extractable information carried by photoelectron spectromicroscopy data is analyzed and the results are used into finding practical optimization rules for different types of photoemission spectroscopy, microscopy, and spectromethylscopy experiments.
Abstract: The potentially extractable information carried by photoelectron spectromicroscopy data is analyzed. The results are used into finding practical optimization rules for different types of photoemission spectroscopy, microscopy, and spectromicroscopy experiments.