The growth morphology and structure of ceria nano-islands on a stepped Au(788) surface has been investigated by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Within ...the concept of physical vapor deposition, different kinetic routes have been employed to design ceria-Au inverse model catalysts with different ceria nanoparticle shapes and arrangements. A two-dimensional superlattice of ceria nano-islands with a relatively narrow size distribution (5 ± 2 nm²) has been generated on the Au(788) surface by the postoxidation method. This reflects the periodic anisotropy of the template surface and has been ascribed to the pinning of ceria clusters and thus nucleation on the fcc domains of the herringbone reconstruction on the Au terraces. In contrast, the reactive evaporation method yields ceria islands elongated in 01-1 direction,
, parallel to the step edges, with high aspect ratios (~6). Diffusion along the Au step edges of ceria clusters and their limited step crossing in conjunction with a growth front perpendicular to the step edges is tentatively proposed to control the ceria growth under reactive evaporation conditions. Both deposition recipes generate two-dimensional islands of CeO₂(111)-type O-Ce-O single and double trilayer structures for submonolayer coverages.
The vanadium oxides can exist in a range of single and mixed valencies with a large variety of structures. The large diversity of physical and chemical properties that they can thus possess make them ...technologically important and a rich ground for basic research. Here we assess the present status of the microscopic understanding of the physico-chemical properties of vanadium oxide surfaces. The discussion is restricted to atomically well-defined systems as probed by surface techniques. Following a brief review of the properties of the bulk oxides the electronic and geometric structure of their clean single crystal surfaces and adsorption studies, probing their chemical reactivity, are considered. The review then focuses on the growth and the surface properties of vanadium oxide thin films. This is partitioned into films grown on oxide substrates and those on metal substrates. The interest in the former derives from their importance as supported metal oxide catalysts and the need to understand the two-dimensional overlayer of the so-called “monolayer” catalyst. On the single crystal metal substrates thin oxide layers with high structural order and interesting properties can be prepared. Particular attention is given to ultrathin vanadium oxide layers, so-called nano-layers, where novel phases, stabilised by the substrate, form.
(WO3)3 gas-phase clusters generated via vacuum sublimation are deposited under UHV and low temperature (<15 K) conditions on a Cu(110) stripe phase consisting of alternating Cu-O (2 × 1) and clean Cu ...regions. STM imaging shows that the clusters adsorb as intact units on both substrates, and the suggested adsorption geometries are confirmed by density-functional (DF) simulations. On the clean surface, the overall distortion is minor, and we are able to image the nodal structure of an individual molecular orbital in the STM at low bias, whereas on the Cu-O surface both the clusters and the substrate are significantly distorted due to the strong oxygen affinity of W atoms. On both surfaces, cluster and Cu electronic states are appreciably mixed, and the electron charge is donated by the surface to the cluster. The experimentally STS-determined DOS signature of the adsorption complex consists of two peaks across the Fermi energy and is well reproduced by the DF calculations.
The formation of nickel oxide nanolayers by oxidizing Ni overlayers on Rh(111) has been investigated and their structures are reported as a function of the nickel coverage and oxygen pressure. ...Scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and diffraction (XPD), and high-resolution electron energy loss spectroscopy (HREELS) have been applied to characterize the structure and stoichiometry of the nickel oxide nanolayers. Several different phases have been observed depending on the strain state of the metallic Ni overlayers. For the pseudomorphic Ni monolayer, two distinctly different oxide phases with (6×1)-Ni5O5 and (2√3×2)-Ni8O10 structures have been identified at oxygen-poor (p=5×10−8mbar) and oxygen-rich (p≥1×10−6mbar) conditions, respectively. Above one monolayer, where the Ni layers are relaxed, bulk-like NiO(100) films form at the O-rich conditions, whereas chemisorbed-type p(2×2)ONi(111) layers develop in the O-poor regime. X-ray photoelectron diffraction analysis has provided additional insight into the relaxation mechanism and the detailed atomic structure of the Ni-oxide nanolayers.
► Two monolayer oxide phases with (6×1)-Ni5O5 and (2√3×2)-Ni8O10 stoichiometries ► Above 1 ML a p(2×2) chemisorbed oxygen structure on Ni(111)-like layers forms. ► Under oxygen-rich conditions the NiOx films converge to bulk-like NiO(100) phases.
Doping of tungsten trioxide (WO3) and molybdenum trioxide (MoO3) materials with alkali atoms, leading to the formation of the so-called sodium bronzes, is a viable approach to achieve a precise ...control of their electronic, optical, and magnetic properties via electron band structure engineering. Driven by the ongoing trend for thickness reduction and the resulting new functionalities at the nanoscale, using a combination of state-of-the-art experimental and computational techniques, we investigate here the interaction of two isostructural two-dimensional (2D) WO3 and MoO3 layers, grown epitaxially onto a Pd(100) surface, with Na dopants. We identify two interaction regimes as a function of the Na coverage: a low-coverage regime up to 0.3 ML, which we describe in terms of doping interactions, and a reaction regime, where at higher Na coverages, the 2D WO3/MoO3 lattices become destroyed and several ordered 2D bronze-type phases form upon thermal activation. In the doping regime, Na initially decorates the oxide domain boundaries and later adsorbs in a (2 × 2) superstructure, filling the regular adsorption sites within the oxide domains. Further Na accommodation in the 2D oxide lattice is unfavorable due to the poor lateral electrostatic screening and elastic strain increase. In the reaction regime, the most prominent and energetically stable phase is the hexagonal 2D bronze-like layer, whose atomic details are resolved in a density functional theory (DFT) analysis and compared with the structure of the bulk counterpart.
The radiation-induced chemistry in ultrahigh vacuum (UHV)-sublimated thin glycine films during continuous soft X-ray irradiation was investigated by X-ray photoelectron spectroscopy (XPS) and ...temperature-programmed desorption (TPD). The glycine films were irradiated with an Al Kα X-ray source (1486.6
eV) for over 360
min and XPS spectra were taken repeatedly every 60
min. TPD measurements of pristine and X-ray exposed glycine layers were also conducted. The results show that the glycine films are very sensitive to damage by X-ray illumination. The analysis of C 1s, N 1s and O 1s spectral regions together with TPD changes indicate that amino acid degradation occurs mainly
via dehydrogenation, decarboxylation, dehydration and deamination of pristine molecules. Among the decomposition products, H
2, CO
2, H
2O and NH
2 are identified. Enrichment of the X-ray exposed surface with hydrocarbon fragments is detected as well. The observed effects must be taken into account in studies of amino acids and peptides utilizing X-rays.
The interactions of glycine (Gly) with amorphous solid water (ASW) nanolayers (≤100ML), vapor-deposited on single crystalline AlOx surfaces at 100K, have been investigated by near-edge X-ray ...absorption fine structure spectroscopy (NEXAFS) at the oxygen K-edge, temperature-programmed thermal desorption (TPD), X-ray photoelectron spectroscopy (XPS), and temperature-dependent work function measurements. Gly-on-ASW, ASW-on-Gly, and Gly on top of ASW-on-Gly ultrathin films have been fabricated. In contrast to the uniform ASW films grown directly on the hydrophilic AlOx, water molecules adsorb on the hydrophobic Gly films in the form of 3D ASW clusters. This leads to significant differences in the NEXAFS and work function data obtained from ASW-on-AlOx and ASW-on-Gly films, respectively. Furthermore, these structural differences influence the chemical state of Gly molecules (neutral vs. zwitterionic) adsorbed on top of ASW films. N1s XPS measurements revealed an increased amount of neutral Gly molecules in the film top-deposited on the ASW-on-Gly structure in comparison to the neutral Gly in the films directly condensed on AlOx or grown on the ASW substrate. H2O TPD spectra demonstrate that the crystallization and desorption processes of ASW are affected in a different way by the Gly layers, top-deposited on to ASW-on-AlOx and ASW-on-Gly films. At the same time, Gly adlayers sink into the ASW film during crystallization/desorption of the latter and land softly on the alumina surface in the form of zwitterionic clusters.
► The interactions between glycine and ASW ultrathin films condensed at 100 K on to alumina surfaces were investigated. ► The hydrophobicity of the substrate (hydrophobic glycine film vs. hydrophilic alumina surface) influences the morphology of top-deposited water layers. ► ASW surface properties affect the chemical form of glycine adlayers.
We present results on the electrolyte additive acrylic acid nitrile (AAN), which allows the use of propylene carbonate (PC)-based electrolytes together with graphitic anodes. This report will focus ...on the basic electrochemical properties and on XPS results of the films formed in the presence of AAN. Further data on in situ investigations of AAN is presented in another paper of this proceedings. The combination of both reports gives strong evidence, that the initiative step for solid electrolyte interphase (SEI) formation is a cathodic, i.e. by reduction induced electro-polymerisation of the vinyl-group. It is concluded that this electro-polymerisation may also be a main reduction mechanism of other vinyl compounds such as vinylene carbonate (VC), vinylene acetate and others.
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