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In this study, we report transmission electron microscopy and electron energy loss spectroscopy study of cerium oxide thin layer grown on graphite foil substrate by direct liquid injection chemical vapour deposition. Transmission electron microscopy experiments have revealed the porous morphology of the deposited layer. Energy electron loss spectroscopy measurements were also performed in scanning mode to study the evolution of the cerium valence. In addition to Ce 4+ inside the layer, the presence of reduced cerium oxide with Ce 3+ valence is pointed out at the layer surface and at the surface of the porosity developed by the layer. Besides, studies of high resolution images coupled to electron energy loss spectroscopy have indicated the presence of crystallized ceria nanoparticles, and the absence of cerium carbide.

In this study, we report transmission electron microscopy and electron energy loss spectroscopy study of cerium oxide thin layers deposited on silicon substrate. Transmission electron microscopy experiments have revealed the flat morphology of the deposited layers. In addition, studies of high resolution images have indicated the presence of mainly ceria crystallized nanoparticles. Energy electron loss spectroscopy measurements were also performed in scanning mode to study the evolution of the cerium valence. In addition to Ce4+ inside the layer, the presence of amorphous cerium silicate with valence +3 is pointed out at the vicinity of the substrate.

The present work investigated the thermal stability of tungsten–titanium diffusion barrier layers intercalated between SiO 2 substrate and platinum thin film. The resulting structures were annealed under air in the temperature range 400–600 °C for annealing times up to 100 h. Chemical and structural characterizations at different stages of the treatment evidenced several phenomena occurring during annealing under air, especially the complete oxidation of the adhesive layer, the diffusion of tungsten oxide through platinum film at particle boundaries as well as the sublimation process of tungsten oxide. The results of film surface chemistry and microstructure were correlated with diffusion phenomena.

Accepted manuscript, Direct current reactive magnetron sputtering was implemented to successfully deposit dark Ti(C,O,N) thin films on silicon substrates. A titanium target was sputtered while a mixture of oxygen and nitrogen was injected into the deposition chamber, independently from an acetylene source. The deposition parameters were chosen as a function of pre-existing knowledge about sputtered Ti–O–N and Ti–C–O films. Tuning the oxygen/(nitrogen+carbon) ratio allowed obtaining a large spectrum of properties. In particular, the colour of the films was characterized by spectral reflectance spectroscopy, and expressed in the CIE 1976 L*a*b* colour space. An accurate control of the reactive gas mixture flow rate allowed obtaining intrinsic, stable and attractive dark colour for decorative applications. Surprisingly, the coatings with the lowest content of carbon and the highest content of oxygen presented the darkest tones. Composition analysis by electron probe microanalysis was done to quantify the titanium and metalloid concentrations in the films. X-ray diffraction experiments revealed the evolution of the film structure from a fcc structure for the lowest (O2+N2) flow rates to an amorphous one for the highest flow rates., Fundação para a Ciência e Tecnologia (FCT) - SFRH/BPD/27114/2006 and PTDC/CTM/69362/2006. CRUP (Acção Integrada Luso-francesa No. F-2307). GRICES/CNRS collaboration (Proc. 4.1.1 França)

The combination of photoelectron diffraction, density functional theory, and multiple scattering calculations is used for a quantitative analysis of the widely debated structure of ${\mathrm{TiO}}_{2}$ (011). The modeling of the diffraction patterns for different surface reconstructions allows one to discriminate the key structural constraints required or, on the contrary, prohibited in the reconstruction of this termination. In particular, photodiffraction rules out previously proposed reconstructions while it evidences the key feature of the ${\mathrm{TiO}}_{2}$ (011) termination: an oxygen splitting induced by missing rows.

Palladium and its alloys have been extensively studied because of their faculty to store reversibly hydrogen isotopes. Here, the substitution of palladium with platinum is investigated. Thermodynamical studies have shown an anomalous behaviour regarding to the classical models. This original behaviour is explained by the study of the electronic structure of the binary solid solutions. The drastic decrease of the hydrogen solubility in the Pd–Pt alloys is accounted for by the filling up of the palladium conduction band by the valence electrons of platinum. The anomalous decrease of the stability of the hydride is explained by the large broadening of the valence band due to the substitution.

The ratio of the two components of the L 23 M 23 V Auger transition is currently used to determine the stoichiometry of titanium oxides. The reduction of Ti manifests itself by a relative increase (decrease) in intensity of the Auger component lying at high (low) kinetic energy, which is assigned to an intraatomic (interatomic) transition involving Ti 3d (O 2p) valence electrons. The LMV Auger transition is herein revisited via its resonant behaviour at the Ti L 23 absorption edge in TiO 2 . Resonances of the high energy component occurs exclusively at the L 2 edge, while resonances of the other component are seen at the L 3 edge, but also at the L 2 edge. The latter being attributed to a L 2 L 3 V Coster–Kronig transition, the low- and high-lying LMV are identified as L 3 MV (including those following CK) and L 2 MV transitions, respectively, at variance with the previous assignment.

International audience; WOx and MoOx nano phases were prepared on TiO2(1 1 0) surfaces by a CVD procedure consisting of adsorption and decomposition of W(CO)(6) or Mo(CO)(6) precursors followed by annealing under UHV. Metal amount involved in each elaborated sample is in the fractional range from 0.1 to 0.35 equivalent monolayer (eqML) of W or Mo. Evolution of sample stoichiometry as a function of subsequent treatment is followed by valence band and core level photoemission as well as work function measurement. In each case, exposure of samples to molecular oxygen at room temperature induces an increase of sample work function in a range of several tenth of eV. Such a work function change is related to oxidation of sample involving both titanium and tungsten (or molybdenum) ions. Such an oxidation is reversible through an annealing under UHV at 470 K for molybdenum oxide and 670 K for tungsten oxide. Several cycles of exposure/annealing are possible without changes in work function or stoichiometry. (C) 2011 Elsevier B.V. All rights reserved.

The evolution of the nanoscale structure and the chemical bonds formed in Ti–C–N–O films grown by reactive sputtering were studied as a function of the composition of the reactive atmosphere by increasing the partial pressure of an O2+N2 gas mixture from 0 up to 0.4 Pa, while that of acetylene (carbon source) was constant. The amorphisation of the films observed by transmission electron microscopy was confirmed by micro- Raman spectroscopy, but it was not the only effect associated to the increase of the O2+N2 partial pressure. The chemical environment of titanium and carbon, analysed by X-ray photoemission spectroscopy, also changes due to the higher affinity of Ti towards oxygen and nitrogen than to carbon. This gives rise to the appearance of amorphous carbon coexisting with poorly crystallized titanium oxynitride. The evolution of the films colour is explained on the basis of these structural changes., Fundação para a Ciência e a Tecnologia (FCT) - PTDC/CTM/69362/2006, SFRH/BPD/27114/2006, CRUP (Acção Integrada Luso-francesa N° F-2307) and the GRICES/CNRS collaboration (Proc. 4.1.1 França)

Laser treatment of a titanium surface at certain conditions initiates the formation of titanium oxide layers as well as micro (nano) scale powder ejected from the surface of the substrate. The resultant morphology of the surface as well as the size and the structure of the particles are all strongly dependent on the treatment parameters (laser fluence, pulse frequency, overlap parameter, etc.). In this study, titanium substrates were treated with an industrial pulsed Nd:YAG laser in air, with varying parameters. Surface layers and ejected materials were compared using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The rutile phase of TiO(2) dominates in the surface layers, while the ejected powder is mainly formed of anatase nanoparticles. (C) 2008 Elsevier B. V. All rights reserved.

International audience; Incorporation of oxygen into TiN lattice results in formation of titanium oxynitrides, TiOxNy that have become particularly interesting for photocatalytic applications. Elaboration as well as characterization of TiN and in situ oxygen-doped thin films is the subject of this paper. Thin films, 250–320nm in thickness, have been deposited by dc-pulsed magnetron reactive sputtering from Ti target under controllable gas flows of Ar, N2 and O2. Optical monitoring of Ti plasma emission line at = 500nm has been implemented in order to stabilize the sputtering rate. Scanning electron microscopy (SEM), X-ray diffraction in grazing incidence (GIXRD), micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), optical spectrophotometry and four-point probe electrical resistivity measurements have been performed in order to follow evolution of film physical parameters as a function of the oxygen flow rate O2 at which the films were deposited. The relationship between O2 expressed in standard cubic centimetres per minute, sccm and the nitrogen/oxygen content in thin films has been established by means of the analysis of the XPS spectra. GIXRD studies indicate that incorporation of oxygen results in a progressive loss of preferential orientation in 111 direction, a change in the grain size from 16nm for TiN to about 3 nmfor films deposited at O2 = 1.32 sccm and a decrease in the lattice constant. A systematic shift of all X-ray diffraction (XRD) lines towards higher diffraction angles is consistent with substitution of oxygen for nitrogen. Micro-Raman investigations indicate amorphisation of thin films upon oxidation. Binding energies determined fromfitting of the XPS results concerning the N1s and Ti2p lines give evidence of the presence of TiOxNy compound. Red-shift of the plasma reflectance edge upon TiN oxidation is correlated with a decreased carrier concentration. Metal–semiconductor transition can be expected on the basis of the electrical conductivity decrease and development of the fundamental absorption across the forbidden band of TiO2 upon increase in the oxygen flow rate. Additional absorption feature in the visible range, being a consequence of coexistence of free-electron and interband absorption within almost the same spectral range ( = 400–600 nm) seems to be very promising for photocatalytic applications of titanium oxynitride thin films.

International audience; Homogeneous collections of Pd−Ni core−shell nanoparticles have been prepared by decomposition of metal−organic compounds and studied by several electron microscopy techniques: transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), energy-filtered microscopy (EFTEM), and by X-ray photoelectron spectroscopy (XPS). The physical and chemical properties of the Pd shell are supposed to depend on its electronic properties, which are influenced by the presence of the Ni core and by the deformation in the Pd lattice. Here, the interfacial structure of Pd/Ni and the lattice deformations in the core and the shell are studied in detail. The catalytic properties of the pure metal and the bimetallic particles, toward CO oxidation, have been investigated.

International audience; The ability to determine the nature and the occurrence of defects is a central need of ceramic surface chemistry. In titanium oxides, the Ti-LMV Auger decays line shape is very sensitive to the titanium degree of oxidation, and has long been empirically used as a qualitative probe of the stoichiometry. In the present work, resonant Auger and resonant valence-band measurements at the Ti-L2,3 edges in TiO2, TiO2–x and metallic titanium provide a clear evidence that the evolutions of the Ti-LMV Auger line shape are due to drastic changes in the valence-band profile and in the probability of L2L3V Coster-Kronig decay processes when a fraction of titanium ions is reduced. Both are shown to be consequences of the filling of Ti-3d states near the Fermi level on defects sites. These conclusions are confirmed by Auger-photoelectron coincidence experiments.

International audience; We report the percolation behaviour of the conductivity of titanium oxynitride films grown by low-pressure metal-organic chemical vapour deposition, composed of TiNxOy mixed with TiO2. The usual DC parameters (t, s and Φc), obtained from the effective media theory equations, are compared to the universal values (s = sun while t < tun because of the film anisotropy). This is the first example of an electrical continuum percolation applied to columnar films with chemically similar conducting and insulating units (non-heterogeneous percolation) whose mixing is based upon the growth temperature during the film growth.

Physical review letters 88(24), 243001 (2002). doi:10.1103/PhysRevLett.88.243001, Published by APS, College Park, Md.

not Available.

The structure and stability of different crystallographic phases of tungstentrioxide and the effect of potassium doping have been studied using ab initiocalcuations, both in the bulk and at the surface. The study was motivatedby experimental works on the growth of WO3 nanorods on a mica substrate.The nanorods adopt a hexagonal phase, which is metastable in bulk WO3.The first part of the manuscript reports the study of bulk WO3. For thehexagonal and monoclinique phase, the atomic structure is deterimined andcompared with different models that have been proposed in the experimentalliterature. The relative stability of the two phases is calculated as a functionof potassium doping. From this an approximate phase diagram of KxWO3is obtained which shows that the the hexaongal phase is stable for x between3 and 35%. It is also shown that the WO3 lattice distortions disappearfore sufficient K concentration. These results explain the stabilization of thehexagonal phase in the nanorods through insertion of K atoms from the micasurface.In the second part of the manuscript, a sytematic study of the surfaces ofWO3 in the monoclinic and hexagaonal phase is presented. For each phase,the three surface orientations of lowest Miller indices are considered. All nonreconstructedterminations and several types of reconstructions are analysedin terms of polarity, stability and atomic structure. In the monoclinic phase,the (010) surface with a c(2x2) reconstruction is most stable, in agreementwith experiment. For the hexagonal phase, the surface with lowest energy(0.02 eV/Å2) is c(1x1)O2(1120). It is found that the stability of the differentorientations is very sensitive to potassium doping. For hexagonal KxWO3with x = 13 , the (0001) surface is most stable with a KO3 termination and asurface energy of 0.05 eV/Å2., Nous avons étudié par calcul ab initio la structure et la stabilité de différentes phases cristallographiques du trioxyde de tungstène en volume et ensurface, ainsi que l'effet du dopage par le potassium. L'étude a été motivéepar des travaux expérimentaux sur la croissance de nano-bâtonnets WO3 surun substrat de mica ; ces nanostructures adoptent la phase hexagonale, mé-tastable dans le WO3 massif. La première partie du manuscrit est consacrée àl'étude du volume. Les structures atomiques des phases hexagonales et monocliniquessont déterminées et comparées aux différents modèles proposés dansla littérature expérimentale. La stabilité relative de ces deux phases est calculée en fonction du taux de potassium permettant d'obtenir un diagrammede phase approximatif de KxWO3 montrant que la phase hexagonale est stablepour x compris entre 3 et 35%. Par ailleurs, les distorsions disparaissentpour des concentrations de K suffisamment élevées. Ces résultats expliquentla stabilisation de la phase hexagonale dans les nano-bâtonnets par l'insertiond'atomes de K de la surface du mica. Dans la seconde partie, une étudesystématique des surfaces, en phase monoclinique et hexagonale, est présentée. Pour chaque phase, les trois orientations de surface de plus faibles indicesde Miller sont considérées. Toutes les terminaisons non-reconstruitesainsi que plusieurs types de reconstructions ont été analysées en terme depolarité, stabilité et structure atomique. Pour la phase monoclinique, l'orientation(010) avec reconstruction c(2x2) est la surface la plus stable, enaccord avec des données expérimentales. Quant à la phase hexagonale, c'estla surface c(1x1)O2(1120) qui a la plus petite énergie de surface (0.02 eV/Å2).Nous trouvons que la stabilité des différentes orientations est très sensible audopage par le potassium. En effet, pour KxWO3 avec x = 13 , c'est l'orientation (0001) qui est la plus stable, avec une terminaison KO3 et une énergiede surface de 0.05 eV/Å2.