Oxygen on Ni(111): A multiple-scattering analysis of the near-edge x-ray-absorption fine structure

Oxygen chemisorption and oxide formation on a Ni(111) surface have been monitored by using the near-edge x-ray-absorption fine-structure technique. The adsorption site of oxygen in the p(2×2) and (√3 × √3 )R30° superstructures has been determined by a multiple-scattering analysis. In both structures the oxygen occupies a threefold-coordinated fcc site with a nearest-neighbor O-Ni bond length of 1.85±0.05 Å on a Ni(111) surface relaxed outwards by ∼0.15 Å

Electronic structure of Ca1−x_{1-x}Srx_xVO3_3: a tale of two energy-scales

We investigate the electronic structure of Ca$_{1-x}$Sr$_x$VO$_3$ using photoemission spectroscopy. Core level spectra establish an electronic phase separation at the surface, leading to distinctly different surface electronic structure compared to the bulk. Analysis of the photoemission spectra of this system allowed us to separate the surface and bulk contributions. These results help us to understand properties related to two vastly differing energy-scales, namely the low energy-scale of thermal excitations (~$k_{B}T$) and the high-energy scale related to Coulomb and other electronic interactions.Comment: 4 pages and 3 figures. Europhysics Letters (appearing

A Nexafs Study of Nitric Oxide Layers Adsorbed from a nitrite Solution onto a Pt(111) Surface

NO molecules adsorbed on a Pt(111) surface from dipping in an acidic nitrite solution are studied by near edge X-ray absorption fine structure spectroscopy (NEXAFS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) techniques. LEED patterns and STM images show that no long range ordered structures are formed after NO adsorption on a Pt(111) surface. Although the total NO coverage is very low, spectroscopic features in N K-edge and O K-edge absorption spectra have been singled out and related to the different species induced by this preparation method. From these measurements it is concluded that the NO molecule is adsorbed trough the N atom in an upright conformation. The maximum saturation coverage is about 0.3 monolayers, and although nitric oxide is the major component, nitrite and nitrogen species are slightly co-adsorbed on the surface. The results obtained from this study are compared with those previously reported in the literature for NO adsorbed on Pt(111) under UHV conditions

Missing-row reconstruction in the system (2×1)O/Ag(110): A surface extended x-ray-absorption fine-structure study

Oxygen K-edge surface extended x-ray-absorption fine-structure studies on the (2×1)O/Ag(110) system confirm the long-bridge adsorption site with a nearest-neighbor O-Ag bond length of 2.05±0.03 Å. They show that oxygen adsorbs close to the surface inducing a reconstruction of the missing-row type. Structural similarities of the (2×1)O phases on Ni(110), Cu(110), and Ag(110) are discussed

Molecular states of polyacenes grown on noble metal surfaces

Here we present a combined photoemission (UPS), metastable deexcitation (MDS) and optical absorption (NEXAFS) at C K-edge study of molecular states of polyacenes grown on Ag(111) and Au(111), from submonolayer to multilayer thicknesses. We focus on the evolution of the HOMO and LUMO molecular states induced by the adsorption from submonolayer to monolayer thickness and we find a different redistribution of these states in the various systems formed at RT: while a strong redistribution of the molecular states takes place in Pn/Ag(111) and Tc/Ag(111) interface, a weaker interaction is indicated for Tc/Au(111)

Real examples of surface reconstructions determined by direct methods

In this work the modulus sum function is briefly introduced and its applicability to the automated interpretation of projections of reconstructed surfaces shown. The selected real examples have been arranged according to the interpretation complexity of the respective two-dimensional Patterson maps and correspond to the most common types of surface reconstructions represented by: (i) a shift of the surface atoms from their ideal positions. This type of reconstruction is often found on (001) semiconductor surfaces and its most characteristic structural feature is the pairing of neighbouring surface atoms forming dimers, e.g., the In0.04Ga0.96As(001)-p(4 × 2) reconstructed surface. (ii) Different atom types occupying the surface sites. This type of reconstruction can be induced by both the adsorption of deposited atoms onto the surface, e.g. Sb/Ge(113)-c(2 × 2), or a new structural arrangement of the substrate caused by the adsorption of external molecules onto the surface, e.g. C60/Au(110)-p(6 × 5) reconstructed surface

Influence of steps on the tilting and adsorption dynamics of ordered Pn films on vicinal Ag(111) surfaces

Here we present a structural study of pentacene (Pn) thin films on vicinal Ag(111) surfaces by He atom diffraction measurements and density functional theory (DFT) calculations supplemented with van der Waals (vdW) interactions. Our He atom diffraction results suggest initial adsorption at the step edges evidenced by initial slow specular reflection intensity decay rate as a function of Pn deposition time. In parallel with the experimental findings, our DFT+vdW calculations predict the step edges as the most stable adsorption site on the surface. An isolated molecule adsorbs as tilted on the step edge with a binding energy of 1.4 eV. In addition, a complete monolayer (ML) with pentacenes flat on the terraces and tilted only at the step edges is found to be more stable than one with all lying flat or tilted molecules, which in turn influences multilayers. Hence our results suggest that step edges can trap Pn molecules and act as nucleation sites for the growth of ordered thin films with a crystal structure similar to that of bulk Pn.Comment: 4 pages, 4 figures, 1 tabl