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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.

In this work stable non-thermal ac high voltage atmospheric pressure microplasma jet (APMJ) device was used for optical and electrical characterizations. It enables the generation of low power (~5W) microplasma jet at frequency of 60Hz. The jet has a visible radial diameter of approximately 1.5 mm. Optical emission spectroscopy was used as a diagnostic tool to determine the gas discharge parameters as the modes temperature. The rotational temperature of OH radicals at the exit nozzle varies from 325 to 525K for different gases where the electrical input power ranged from 3 to 10W. Both the electronic (0.5 - 0.7eV) and vibrational temperatures (0.35 - 0.58eV) were estimated at the same power conditions for Ar, He, N2, air and O2 + 1%Ar flow rates. The highly reactive species as OH, O, N2 + and the energetic photons produced between the electrodes extent along the plasma plume, both in radial and axial direction from the exit of the APMJ.

An atmospheric pressure ac microplasma jet device with Cu spiral-torsion-spring type electrodes was developed. This electrode geometryenables the generation of low power and stable micro plasma jet operated in Ar, He, O2, N2 and air at flux rates ranging from 2 to 12 L/min, applying an ac high voltage at 60Hz frequency. Moreover, the device is absent of dielectric parts which prevents contamination of the plasma. To observe the outflow pattern a Schlieren photography system was used, resulting in broaden and continuous laminar gas flow. Optical emission spectroscopy measurements allow us to infer the mean gas temperature of plasma jet from the outer electrode along its axial position. A temperature decrease of 110℃ to 40℃ was observed up to 5 mm and beyond this gas temperature the plasma jet reaches room temperature, so enabling it to use in treatment of heat-sensitive surfaces such as biomaterials and polymers like polyethylene.

Gas discharge parameters of a direct current Ar+2%H2 non-thermal microplasma operated at atmospheric pressure were measured in this work. The microplasma was investigated in the normal and abnormal glow regimes, for current ranging from 10 to 130 mA, at ~ 160 - 250 V of applied voltage for a cathode formed with Cu+Mo+Fe foils, covered with mica at front face Cu foil. The microplasma goes through an opening hole traversing the dielectric and metal foils and emerging on open air. Both OH (A 2 Σ + , ν = 0 → X 2 Π, ν ' = 0) and N2(C 3 ∏u , ν = 0 → B 3 ∏g, ν ' = 2) bands were used to estimate the gas temperature, which ranges from 450 to 800 K. The electron number densities, ranging from 3.0 × 10 14 to 8.0 × 10 14 cm -3 , were determined by the Hβ line. Excitation temperatures were measured from three methods: from two Cu I and Mo I spectral lines ratio (Texc = 2 700 K) and from Boltzmann-plot of both Fe I and He I transitions (Texc = 3 000 K). The vibrational temperature was carried out from the second positive system N2 (C 3 ∏u → B 3 ∏g) for Δν = -2 and it was in the range 2500 - 3000 K for a current varying from 20 to 100 mA.

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.

A low energy electron diffraction (LEED) investigation of the structure of the surface of an FeO(0 0 1) thin film grown on Ag(0 0 1) is presented. The results show that this surface has an almost bulk termination structure with a very small rumple on the first layer, which agrees with the structure found in other studies carried out on the (0 0 1) surface of oxides that have rock-salt structure. Evidences that may support a linear behaviour of the topmost layer rumple with the oxide lattice constant are also discussed.

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.

We perform a systematic study on the evolution of the magnetic spin moment (${m}_{s}$) of epitaxial [100]- and [111]-magnetite films of increasing thickness. The ultrathin films are characterized by low-energy electron diffraction, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD). By employing sum rules on the XMCD spectra we obtain ${m}_{s}=3.6$ ${\ensuremath{\mu}}_{B}$/f.u. for samples of around 35 \AA{}. This is considered a bulk value and has been reported only for films more than 10 times thicker. Moreover, we show that even 10-\AA{}-thick magnetite already presents a significant magnetic moment. For both grown directions the moment increases similarly with the thickness. The ferromagnetic behavior for each iron ion site (${\mathrm{Fe}}_{\mathrm{octa}}^{2+}$, ${\mathrm{Fe}}_{\mathrm{octa}}^{3+}$, ${\mathrm{Fe}}_{\mathrm{tetra}}^{3+}$) of ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ is measured by monitoring XMCD peaks. The deduced hysteresis curves (per ion, per site) exhibit a coercive field of 300 Oe. Our results show that both the ferrimagnetic order and the bulk moment value are preserved at room temperature around the thickness of 2 unit cells.

C${}_{60}$ monolayers grown on Ag(111) at room temperature form incommensurate lattices that convert into a commensurate (2$\sqrt{3}$ \ifmmode\times\else\texttimes\fi{} 2$\sqrt{3}$)R30\ifmmode^\circ\else\textdegree\fi{} phase upon annealing. The C${}_{60}$ molecules in the commensurate phase have been observed to exist in three different states on Ag(111), namely bright, dim, and superbright (SB). All three species are in dynamical equilibrium at 280 $T$ 440 K. The bright and dim species were the subject of an earlier low-energy electron diffraction study that determined their geometries on the surface and the dynamics of the switching between those two states. The study presented here takes a closer look at the SB molecules, which appear and disappear at temperature-dependent rates with a measured activation barrier of 1.5 eV. The SB molecules in the commensurate phase comprise about 0.5% of the molecules and have a spatially random distribution. The evidence suggests that the formation of the three different states of C${}_{60}$ on Ag(111) is a result of stress imposed by the substrate as the C${}_{60}$ adopts the commensurate spacing that is slightly smaller than its natural spacing. In the incommensurate phases, there is no bright-dim contrast, but SB C${}_{60}$ molecules form and organize into ordered arrays that appear to correspond to the moir\'e patterns that are produced by the mutually incommensurate lattices. This suggests that the substrate responds to the nonuniform forces imposed by the C${}_{60}$ molecules by producing raised islands of Ag atoms at the vertices of the moir\'e structure. A similar island structure may account for the SB molecules in the commensurate phase.

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.

Details of the growth and of the surface structure of 1, 2, and 3 monolayers of Au on Pd(100) have been investigated by reflection high-energy electron diffraction (RHEED), quantitative low-energy electron diffraction (LEED)-I(V) analysis and density-functional theory calculations (DFT). Despite the 4.7% misfit between Au- and Pd-lattice parameters, no change on the lateral lattice parameter was observed up to a thickness of 10 ML by RHEED, evidencing pseudomorphous growth. Up to 3 ML a ($1\ifmmode\times\else\texttimes\fi{}1$) LEED pattern is observed, while at higher coverages a ($7\ifmmode\times\else\texttimes\fi{}1$) superstructure is formed. The interlayer distances of the last atomic layers of $n$-ML-Au/Pd(100) ($n=1$, 2, 3) as determined by quantitative LEED and DFT calculations are compared and show only a reasonable agreement. However, DFT results indicate that surface alloying is energetically favorable, and a better match with the experimentally determined interlayer distances is obtained with surface alloy formation.

In this work we report on a low-energy electron diffraction (LEED) study of $\mathrm{MnO}(100)$ thick films grown on $\mathrm{Ag}(100)$ in order to determine their surface geometry. The LEED results indicate a topmost layer rumple of $(4.8\ifmmode\pm\else\textpm\fi{}2.0)%$ with the oxygen ions moving towards the vacuum side. These results are in line with other surface structure determinations carried out on the (100) surface of different oxides having rock-salt structure but are in disagreement with MEIS results reported in the literature for the $\mathrm{MnO}(100)$ using a $\mathrm{MnO}$ single crystal.