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Hexaniobate nanosheets derived from the parent compound K 4 Nb 6 O 17 have been decorated with CeO 2 nanoparticles by ion exchange with aqueous cerium (IV) solution. Very homogeneous CeO 2 nanoparticle decoration of the hexaniobate sheets can be achieved by this method and the resulting composites may absorb visible light. HRTEM images show that ∼3.0 nm diameter CeO 2 nanoparticles adhere to hexaniobate nanosheets that are exfoliated and then restacked prior to Ce deposition. The interfacial interaction between CeO 2 nanoparticles and nanosheets would be due to an electrostatic attraction mechanism. Raman and XRD measurements have given strong evidence that CeO 2 nanoparticles have fluorite structure. EDS, FTIR and XPS results suggest almost complete exchange of TBA + and K + by Ce 4+ . Cerium ion exchange on the acid exchanged parent compound, H 2.9 K 1.1 Nb 6 O 17 , revealed that the extent of Ce ion exchange is much greater in case of nanosheets, which may be rationalized by the larger surface area available after exfoliation. XPS measurements show that the ratio of Ce 4+ /Ce 3+ is around 4.4, in agreement with the formation of fluorite structure (CeO 2 ). Thus, these CeO 2 nanoparticle/nanosheet composites may be useful for catalytic processes.

The production and characterization of ultra-thin iron oxide films grown on an atomically clean Ag(100) surface by molecular beam epitaxy (MBE) is presented. The goal of this work was to prepare ultra-thin FeO(100) with excellent crystallographic quality. The films were prepared with high purity 57 Fe and O 2 and afterwards analyzed in situ by means of Low Energy Electron Diffraction (LEED), X-Ray Photoelectron Spectroscopy (XPS) and Conversion Electron Mossbauer Spectroscopy (CEMS). During preparation the evaporation rate, the O 2 partial pressure, film thickness and annealing procedures were varied. The analysis of the various samples showed that in general a mixture of FeO and Fe 3 O 4 phases is obtained. We determined the best conditions to produce the desired oxide (FeO). Besides the paramagnetic phase, the antiferromagnetic phase of the FeO films was characterized by low temperature Mossbauer spectra.

The structural properties of graphene/Ni(111) are investigated by a combination of low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), angle-scanned photoelectron diffraction (PED), and first-principles calculations. XPS data indicate that graphene interacts strongly with the topmost Ni layer. Diffraction data show that graphene is deposited commensurably with the underlying Ni surface atoms. Twelve different graphene preparations were analyzed by LEED and one by PED. Considering the relative position between the carbon and Ni atoms, five experimental sets indicate a top-fcc structure, three show a bridge-top structure, and four have a mixed structure. The analysis of the PED experiment suggests the top-fcc termination. Our first-principles calculations show that the total energies of the top-fcc and bridge-top structures are nearly degenerate, which corroborates the observed bistability of those phases. Moreover, by comparing the structural parameters obtained by the three methods (LEED, PED, and ab initio calculations), excellent agreement is achieved.

The intercalation of different metals underneath the graphene sheet has opened the possibility of preparing new low-dimensional structures that could present quantum-size effects. Knowing the surface crystallograpy of these low-dimensional systems is mandatory for a complete understanding of their physical and chemical properties. In this work, we present a combined low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy, and first-principles calculations study of the structural properties of graphene-protected Fe films on Ni(111). The results indicate that graphene interacts strongly with the topmost Fe atoms, similar to graphene on Ni(111). For one and two Fe monolayer films, the Fe is isostructurally deposited on Ni (fcc on fcc), and graphene is deposited commensurably with the underlying Fe surface atoms. For one Fe monolayer case, the LEED data indicate the coexistence of two types of crystalline domains, named top-fcc and bridge-top structures. Our first-principles calculations show that for the graphene/Fe/Ni system, the total energies of the the top-fcc and bridge-top structures are nearly degenerate, consistent with the observed bistability.

Metallic nanoparticles (NPs) supported on oxides thin films are commonly used as model catalysts for studies of heterogeneous catalysis. Several 4d and 5d metal NPs (for example, Pd, Pt and Au) grown on alumina, ceria and titania have shown strong metal support interaction (SMSI), for instance the encapsulation of the NPs by the oxide. The SMSI plays an important role in catalysis and is very dependent on the support oxide used. The present work investigates the growth mechanism and atomic structure of Rh NPs supported on epitaxial magnetite Fe3O4(111) ultrathin films prepared on Pd(111) using the Molecular Beam Epitaxy (MBE) technique. The iron oxide and the Rh NPs were characterized using X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction and photoelectron diffraction (PED). The combined XPS and PED results indicate that Rh NPs are metallic, cover approximately 20 % of the iron oxide surface and show height distribution ranging 3–5 ML (monolayers) with essentially a bulk fcc structure.