S. Surnev

CO adsorption on Pd(1 1 1): a high-resolution core level photoemission and electron energy loss spectroscopy study

By combining high-resolution X-ray photoelectron and electron energy loss spectroscopies a comprehensive analysis of the adsorption of CO on Pd(1 1 1) at 300 K has been performed. The characteristic fingerprints for various CO‐ Pd(1 1 1) bonding configurations have been identified from the decomposition analysis of the adsorbate C 1s and the substrate Pd 3d5=2 core-level photoemission spectra obtained after CO adsorption at 120 K. The cO4 2U structure at 0.5 monolayer (ML) and theO2 2U-3CO structure at 0.75 ML formed at low temperature have been used for calibration purposes. The core-level results are consistent with CO adsorbing in a mixture of fcc and hcp threefold hollow sites in the cO4 2U structure and of hollow and on-top sites in theO2 2U structure, as reported in the literature. For CO adsorption at 300 K, a diAerent site occupation is evidenced by the presence of two components in the C 1s and Pd 3d5=2 core-level and C‐O stretching vibration lineshapes. At coverages up to 0.1 ML only fcc threefold hollow sites in a O AAA

Low-dimensional oxide nanostructures on metals: Hybrid systems with novel properties

Oxide nanostructures in low dimensions on well-defined metal surfaces form novel hybrid systems with tremendous potential and impact in fundamental research and for the emerging nanotechnologies. In contrast to bulk materials low-dimensional oxide nanostructures not only involve a large number of undercoordinated atoms but their interaction with the metal substrate also provides constraints on their structure and morphology and often yields elastic strain and/or uncompensated charge. These factors modify significantly the physical and chemical properties of the nanophases as compared to bulk oxides. In this review the authors will examine critically the available data with respect to structure-property relationships of metal-supported oxide nanostructures in reduced dimensions. The connection between structure, elastic strain, and charge transfer on the one hand, and electronic and magnetic behavior on the other one, will be discussed. The novel chemical properties of the oxide-metal nanostructure systems will provide another focus of this review.

Nature, growth, and stability of vanadium oxides on Pd(111)

Thin films of vanadium oxides grown on a Pd(111) single crystal surface have been studied using high resolution x-ray photoelectron spectroscopy (XPS), near edge x-ray absorption fine structure (NEXAFS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). The vanadium oxides have been prepared by reactive evaporation of vanadium in pO2=2×10−7 mbar at 250 °C from submonolayer to 5 monolayer (ML) coverages. As observed on other substrates, the stoichiometry of the oxide phase varies as a function of the coverage, VO/VO2-like at low coverages to V2O3 for thicker oxide layers as indicated by XPS V 2p core level spectra and the characteristic NEXAFS fingerprints at both V 2p and O 1s edges. The V2O3 oxide phase grows epitaxially on the Pd(111) surface in the form of small three-dimensional (3D) islands as revealed by LEED and STM. The thermal stability of the oxides is also coverage dependent: the decomposition onset temperatures range from 300 °C for submonolayer coverage to ⩾500 ...

The structure of the indium-Si(111) (7 × 3) monolayer surface

Abstract The structure of the ordered indium overlayer which forms at around one monolayer (ML) coverage at elevated temperature on Si(111)7 × 7 surfaces has been investigated by scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS) and low energy electron diffraction (LEED). The surface is characterised by a | 2 −1 1 2 | unit cell, designated in the following as ( 7 × 3 ), but two different local atomic configurations are observed to coexist at the same sample surface in atomically resolved STM images: a quasi-hexagonal arrangement with a local coverage of exactly 1 ML, and a quasi-rectangular arrangement with a local coverage of 1.2 ML. Both surface structures are metallic and reveal a very similar electronic structure in the STS spectra. The structures are discussed in terms of a close-packed In(001)-type overlayer and a straindashinduced distortion of a pseudomorphic overlayer.

Vanadium oxide nanostructures: from zero- to three-dimensional

A fluid and elastomer device for isolating dynamic loading between members connected to the device, the fluid and elastomer device comprising: an inner member that defines a compliance chamber; an outer member that defines an outer housing chamber; an elastomeric element flexibly interconnecting said inner member relative to said outer member; a passageway located in the compliance chamber and flow connecting the compliance chamber with a primary working chamber; a secondary compliance member joined to the passageway in the compliance chamber; a volume compensator located in the housing chamber the volume compensator comprising spring means, piston member at one spring end and a diaphragm member that overlies the piston; a member located between the compliance and housing chambers, the member being moveable with the outer housing, the moveable member in combination with the diaphragm defining a compensator chamber; and a volume of working fluid in said chambers and passageway.

Metal Tungstates at the Ultimate Two-Dimensional Limit: Fabrication of a CuWO4 Nanophase

Metal tungstates (with general formula MWO4) are functional materials with a high potential for a diverse set of applications ranging from low-dimensional magnetism to chemical sensing and photoelectrocatalytic water oxidation. For high level applications, nanoscale control of film growth is necessary, as well as a deeper understanding and characterization of materials properties at reduced dimensionality. We succeeded in fabricating and characterizing a two-dimensional (2-D) copper tungstate (CuWO4). For the first time, the atomic structure of an ultrathin ternary oxide is fully unveiled. It corresponds to a CuWO4 monolayer arranged in three sublayers with stacking O-W-O/Cu from the interface. The resulting bidimensional structure forms a robust framework with localized regions of anisotropic flexibility. Electronically it displays a reduced band gap and increased density of states close to the Fermi level with respect to the bulk compound. These unique features open a way for new applications in the field of photo- and electrocatalysis, while the proposed synthesis method represents a radically new and general approach toward the fabrication of 2-D ternary oxides.

Structural and vibrational properties of two-dimensional MnxOy layers on Pd(100) : Experiments and density functional theory calculations

Using different experimental techniques combined with density functional based theoretical methods we have explored the formation of interface-stabilized manganese oxide structures grown on Pd(100) at (sub)monolayer coverage. Amongst the multitude of phases experimentally observed we focus our attention on four structures which can be classified into two distinct regimes, characterized by different building blocks. Two oxygen-rich phases are described in terms of MnO(111)-like O-MnO trilayers, whereas the other two have a lower oxygen content and are based on a MnO(100)-like monolayer structure. The excellent agreement between calculated and experimental scanning tunneling microscopy images and vibrational electron energy loss spectra allows for a detailed atomic description of the explored models.

The metal–insulator transition in V2O3(0001) thin films: surface termination effects

Epitaxially grown V2O3(0001) thin films have been prepared with different surface terminations, as evidenced by atomically resolved scanning tunnelling microscopy and high-resolution electron energy loss spectroscopy (HREELS) phonon spectra. The spectral changes observed in valence band photoemission spectra and HREELS on cooling the V2O3 samples from 300 to 100 K have been associated with the metal–insulator transition (MIT) in the bulk of the V2O3 film. The reconstructed surface regions per se do not display the MIT, but affect the MIT signature observed with surface sensitive techniques, depending on the thickness of the reconstructions. Whereas the thermodynamically stable (1 × 1) vanadyl V = O surface termination allows the observation in photoemission and HREELS of a clear signature of the MIT, the latter is screened on a surface formed by V = O defect structures. Doping of the surface with small amounts of adsorbed water restores reversibly the MIT spectral fingerprints. These observations are discussed in terms of the different geometrical and electronic structures of the different surface terminations.

Interplay between magnetic, electronic, and vibrational effects in monolayer Mn3O4 grown on Pd(100)

The surface stabilized MnO(100)-like monolayer, characterized by a regular c(4 x 2) distribution of Mn vacancies, is studied by hybrid functionals and discussed in the light of available scanning tunneling microscopy and high-resolution electron energy loss spectroscopy data. We show that the use of hybrid functionals is crucial to account for the intermingled nature of magnetic interactions, electron localization, structural distortions, and surface phonons. The proposed Pd(100) supported Mn(3)O(4) structure is excellently compatible with the experiments previously reported in literature.

Modification of overlayer growth kinetics by surface interlayers: The Si(111)√7×√3‐indium surface

The growth of thin films of In on bare Si(111)‐type substrate surfaces and on the so‐called (√7×√3)–In monolayer structure on Si(111) as an interlayer surface has been studied comparatively by scanning tunneling microscopy (STM), Auger electron spectroscopy, and low‐energy electron diffraction (LEED). The In uptake and the morphology of In islands formed on the two surfaces are remarkably different, and a nonwetting behavior of In on the (√7×√3) surface is observed. Due to the very high mobility of In adatoms on the (√7×√3)–In surface very few, but large, In islands are observed; they cover only a minor portion of the surface area, whereas on bare Si(111) surfaces the In islands are more uniformly distributed over the surface, indicating a more limited diffusion rate of In atoms. Epitaxially ordered In islands with In–In distances close to those in bulk In, as revealed by atomically resolved STM images and by LEED, are observed to grow at room temperature on Si(111) surfaces. On the (√7×√3)–In surface met...