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Molydenum has been deposited at room temperature on (110) TiO2 surfaces with different stoichiometries, roughnesses and crystallinities. Whatever the substrate preparation is, in-situ Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) studies as well as ex-situ atomic force microscopy (AFM) and reflexion high-energy electron diffraction (RHEED) studies reveal a Stranski–Krastanov growth mode: the completion of three monolayers followed by islands growth is observed in every case. The three monolayers are always composed of amorphous molybdenum oxide with an oxidation state of molybdenum less than IV. The oxidation of the molybdenum layers generates Ti3+ and Ti2+ in the substrate, and induces a reconstruction of the surface: during the layer formation, the roughness of the material strongly decreases. Moreover, if the substrate is prereduced prior to the deposition, the reduction induced by molybdenum oxidation can easily migrate in the TiO2 bulk. In the case of an initial stoichiometric surface, the reduction is more located in the interfacial layers. After the growth of three layers, metallic BC islands without preferential orientation appear.

The interaction of cyanogen with (100) Ni surfaces at room temperature was studied using secondary ion mass spectrometry in a static mode, and photoemission spectroscopies (XPS and UPS). It has been shown that cyanogen is adsorbed on this nickel surface in a dissociative mode: atomic carbon and nitrogen are present on the surface as well as CN fragments. These adsorbed species have been characterized by XPS and UPS. Increasing the temperature in the 400 K range increases the rate of the dissociation reaction of CN into atomic carbon and nitrogen. Moreover carbon is found to dissolved into the bulk for temperatures as low as 475 K. No evidence has been found of a polymerized form of cyanogen molecules on this nickel surface, when the temperature is increased unlike the results obtained for the (111) Ni surface.

Titanium oxynitride (TiN x O y ) thin films were deposited by low-pressure metal-organic CVD (LP-MOCVD) on (100) silicon, sapphire, and polycrystalline alumina substrates. Titanium isopropoxide (TIP) and ammonia were used as precursors. The influence of the growth temperature, ranking from 450°C to 750°C, was investigated by scanning electron microscopy (SEM), and electrical DC measurements. Rutherford back-scattering (RBS) measurements were used to determine the N/O ratio in the films. The surface observations of the deposited films showed two morphological transitions. The resistivity decreased with the growth temperature, while the nitrogen content increased. Moreover, for the highest deposition temperatures, the temperature dependence of the resistivity revealed a transition from a semiconducting to a metallic behavior. Finally, these electrical properties were correlated with the two morphological transitions.

TiO 2 thin films have been grown on (100)GaAs and (111)GaAs substrates by low-pressure metal organic chemical vapour deposition (LP-MOCVD). Titanium(IV) isopropoxide, Ti{OCH(CH 3 ) 2 } 4 , was used as a precursor and TiO 2 films were obtained without an additional oxygen flux. Scanning electron microscopy (SEM) experiments have shown a well ordered rod-like crystallisation in the films grown on (100)GaAs. This ordered crystallisation was favoured by a high deposition temperature ( T d =700°C). By contrast, no distinct order was observed in the films grown on (111)GaAs substrates. X-ray diffraction patterns revealed a mainly rutile structure for the TiO 2 films deposited on (100)GaAs at 700°C. XPS results confirmed the TiO 2 stoichiometry of the surface of the films and revealed the presence of C, Ga and As as impurities.

This paper presents the growth and characterization of titanium oxinitride (TiN x O y ) films grown by low pressure metal organic chemical vapour deposition (LP-MOCVD). The film nitrogen content, obtained by Rutherford backscattering spectroscopy (RBS), increases as the growth temperature increases (from 23 at.% at 450°C to 46 at.% at 750°C). Below 550°C, the films do not show any X-ray diffraction pattern. Above 550°C, the deposited films present the (111) and (200) TiN textures. Films deposited on (100) Si exhibit a 2 θ shift to higher Bragg angles, depending on the N/O ratio. These shifts are explained by using a substitutional oxygen model. Moreover, the atomic structure of such materials is described from this behaviour in terms of lattice vacancies and N/O substitutions, leading to different titanium valencies confirmed by X-ray photoelectron spectroscopy (XPS) analysis.

Characterizations of ultra-thin iron films deposited on TiO 2 (110) surfaces with different stoichiometries, roughnesses and crystallinities have been carried out by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). For a high initial roughness of the substrate, a 2D growth mode is observed up to three monolayers. But, if the initial roughness is low, clusters grow on the TiO 2 surface. Whatever the initial surface stoichiometry, electronic exchanges occur between titanium and iron leading to a reduction of titanium and an oxidation of iron. This interaction between iron and titanium dioxide surface takes place only at the interface between the metal and the oxide surface: during the completion of the first layer for deposition on a non-stoichiometric and rough surface (2D growth) and at the base and periphery of the islands for 3D growth (in the case of deposition on a flat and stoichiometric surface). Moreover, the amount of electrons exchanged between titanium and iron is lower when the substrate oxide surface is prereduced. The interaction between the deposited metal and the oxide surface is related to the amount of available oxygen.

The deposition of ultra thin molybdenum films has been carried out on three different TiO 2 surfaces: a stoichiometric and flat one obtained after annealing, a non stoichiometric and rough surface made by Ar + bombardment and a stoichiometric and rough surface obtained by oxygen bombardment. Whatever the substrate preparation, in situ AES and XPS studies and ex situ AFM and RHEED characterizations have revealed a Stranski–Krastanov growth mode: the completion of three monolayers followed by island growth is observed in any case. The three monolayers are composed of amorphous molybdenum oxide with a molybdenum oxidation state between III and IV. The oxidation of the molybdenum layers generates a reduction of the substrate with the formation of Ti 3+ and Ti 2+ and induces a reconstruction of the surface: during the formation of the molybdenum oxide layers the roughness of the surface strongly decreases. After the growth of the three layers, the surface is flat whatever the initial roughness. Then, the molybdenum atoms can diffuse on the surface and generate clusters. The resulting islands are metallic (BC structure) but without preferential orientation.

Atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) was used to prepare iron doped titanium dioxide thin films. Thin films, between 40 and 150 nm thick, were deposited on Si, SiO 2 and Al 2 O 3 substrates using titanium tetra isopropoxide and ferrocene as metal organic precursors. TiO 2 iron doping was achieved in the range of 1–4 at.%. The film morphology and thickness, polycrystalline texture and doping content were studied using respectively scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The influence of growth temperature, deposition time, substrate type and dopant partial pressure were studied. Electrical characterizations of the films were also performed.

The cationic composition of three types of titanium ferrite Fe 2.5 Ti 0.5 O 4 has been analyzed by XPS during their oxidation in order to reveal dynamic segregation phenomena. These samples included two pulverised materials obtained by high energy ball milling followed by a thermal treatment under a well controlled reducing atmosphere (I) and by a ceramic process followed by grinding (II), as well as a compact material obtained by a ceramic process (III). In each case, under pure oxygen and under a linear increase of the temperature, the material was subject to oxidation in the cation deficient phase i.e. without phase transformation below 350°C. During this reaction, an important modification of the chemical composition of the near surface layers has been revealed: the titanium ferrite surface becomes richer in iron and poorer in titanium. For pulverised compounds, if the heating is extended above 400°C, the oxidation in a cation deficient phase can proceed and some titanium can move back to the surface. Then, from this temperature, the amount of titanium detected by XPS increases. For samples obtained by high energy ball milling, this phenomenon can lead to a homogeneous compound. This is not so for the samples obtained by the ceramic process. For these, a phase transformation of the compound appears which generates α-Fe 2 O 3 at the surface of the material. The segregation phenomenon has been interpreted on the basis of the different mobilities of the species Fe 2+ , Fe 3+ , Ti 4+ and cation vacancies present in the material.

Different mixed cobalt—iron molybdates Co1 − xFexMoO4 (0 ≤ x ≤ 1) have been prepared by means of a ceramic process. The oxidation of pulverulent samples leads to ferric molybdate Fe2(MoO4)3, spinelle Co3O4 and cobalt molybdate CoMoO4. After a strong grinding which reduces the grain size (about 0.1 μm) and induces crystallographic defects in the grains, the cobalt—iron molybdates can be partially oxidized into cation-deficient phases. This oxidation corresponds to an isostructural substitution of part of the Fe2+ and Co2+ ions by Fe3+ and Co3+ ions and the creation of cation vacancies. The concomitant presence of trivalent cations and associated cation vacancies in the lattice stabilizes the highest-temperature variety of the cobalt or iron molybdates, i.e., the a variety.

Compositional and chemical changes of titanium dioxide monocrystalline surfaces induced by bombardment with 4 keV argon and oxygen ions have been studied by AES, XPS and AFM. Argon ion bombardment induced strong changes in the composition and chemical state of the surface: loss of oxygen due to preferential sputtering occurred, and, related to this, Ti4+ species were reduced to Ti3+ and Ti2+. During oxygen bombardment, competition between preferential sputtering of oxygen ions of the oxide surface and oxygen implantation was observed. This phenomenon was found to be strongly dependent upon the incidence angle of the oxygen ions. Moreover, an oxygen bombardment with normal incidence of the surface that had been previously submitted to an argon ion bombardment led to a restoichiometrization of the surface: no further Ti3+ or Ti2+ was found by XPS, only Ti4+.

The metal organic chemical vapour deposition (MOCVD) method was used to prepare titanium dioxide thin films. Thin films of TiO2, about 100 nm thick, were deposited on (100)Si and (1102)Al2O3 sapphire substrates using titanium isopropoxide (Ti(OC3H7)4) as metal organic precursor. The morphology of the films and the presence of impurities on the thin films surfaces were studied using respectively, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The influence of the growth parameters such as the deposition temperature, the carrier gas (nitrogen) flow rate and the presence of an additional oxygen flow on the characteristics of the titanium dioxide films has been studied. The morphology of the deposits has been shown to be greatly influenced by the growth parameters (temperature, substrate and carrier gas flow rate). The main impurity of the layer, carbon, has been found by XPS to be a function of both the growth temperature and the nature of the substrate. Moreover, it has been evidenced that an additional oxygen flow is not essential to obtain stoichiometric titanium dioxide films.

The exposure of silver surfaces to oxygen under about 10 −6 mbar at room temperature was studied mainly by secondary ion mass spectrometry (SIMS) used in a static mode. No reactivity of oxygen appeared under these exposure conditions in accordance with previous works. No modifications in the AES spectra, but an unexpected and huge increase in the intensities of secondary ions such as CN − , CNO − , Ag(CN) − 2 , Ag 2 CN + were observed. Different experiments were performed in order to specify the origin of this unexpected reaction in presence of pure oxygen. Moreover, exposures to pure (CN) 2 and to a mixture of cyanogen and oxygen were performed in order to compare the reactivity of silver towards cyanogen when oxygen was present or not. It was shown that the presence of oxygen enhanced the quantity of adsorbed species and modified the adsorption mode of cyanide species on silver. It was also shown that when the temperature increased, these species rearranged on the surface to a polymerized form of cyanogen molecules.

The first stages of nickel deposition on a clean (110) TiO 2 surface were studied using surface extended X-ray absorption fine structure (EXAFS). Experiments were performed on two kinds of nickel deposits, one of 0.8 equivalent monolayers and another of 1.6 equivalent monolayers. Depositions were performed on well characterized TiO 2 (110)-p(1 × 1) surfaces. The correlation of Auger experiments with EXAFS results showed that no islands were present on the surface; only two-dimensional growth of nickel was observed. Moreover, it was shown, in the case of the thinner deposit, that a model with nickel atoms forming chains in the channels determined by oxygen atoms on the surface is consistent with the EXAFS data.

An in-depth study of the first steps of electron beam assisted growth of Mo from molybdenum hexacarbonyl on Cu(1 1 1) has been carried out exploiting the complementarity of X-ray photoemission and X-ray absorption spectroscopies. Frank van der Merwe (2D) growth mode has been observed for the completion of the two first monolayers of adsorbed molecules through a simple physisorption process. Irradiation of the Mo(CO)6 deposit by 1 keV electron beam induces a modification of molybdenum coordination, the average number of C-neighbors decreasing from 6 to 3. Decomposed molecules remain on the surface after annealing at 520 K and organize themselves, the molybdenum atoms moving in Cu(1 1 1) surface fcc hollow sites. After annealing at 670 K, metallic molybdenum growth begins, if the total amount of adsorbed Mo atoms exceeds 1.2 monolayers.

X-ray photoemission spectroscopy was used to study thin nickel deposits on monocrystalline titanium dioxide surfaces. These surfaces were submitted before deposition to different kinds of treatment in order to obtain samples with various fixed bulk as well as surface stoichiometries. The influence of these stoichiometries on the electronic structure of deposited nickel was studied. Reducing thermal treatments were also performed in situ and their consequences studied by XPS.

Titanium oxinitride thin film with a thickness equal to 250 nm is obtained at 700 °C by the LP-MOCVD method. Analysis by photoelectron spectroscopy and by X-ray diffraction show that the composition of the deposit is TiN 0 . 8 O 0 . 4 with a TiN structure. Morphological observation of the deposit, studied by scanning electron microscopy, indicated that the surface is rough with the presence of some fissures. Electrochemical study of samples in Ringer's solution (9g/l of NaCI) at 37°C, showed the role played by the surface state and imperfections on the corrosion acceleration.

International audience; A density functional theory study is reported on pure and potassium doped tungsten trioxide. The nature of lattice distortions in the hexagonal phase is analyzed and a new symmetry group is proposed. The structure and stability of cubic, monoclinic, and hexagonal phases is studied as a function of potassium doping and an approximate phase diagram is derived. KxWO3 undergoes a monoclinic to hexagonal phase transition at x similar to 3%.

The gap state that appears upon reduction of TiO2 plays a key role in many of titania's interesting properties but its origin and spatial localization have remained unclear. In the present work, the TiO2(110) surface is reduced in a chemically controlled way by sodium adsorption. By means of resonant photoelectron diffraction, excess electrons are shown to be distributed mainly on subsurface Ti sites strikingly similar to the defective TiO2(110) surface, while any significant contribution from interstitial Ti ions is discarded. In agreement with first principles calculations, these findings demonstrate that the distribution of the band gap charge is an intrinsic property of TiO2(110), independent of the way excess electrons are produced.

International audience; KxWO3 nanorods, interesting as gas sensors, were elaborated on mica muscovite substrate and characterized by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and mainly transmission electron microscopy. A combination of structural analyses allowed determining the morphology of these rods, and selected area electron diffraction experiments pointed out the simultaneous presence of the exotic hexagonal and stable monoclinic phases. Moreover, the presence of potassium inside the nanorods, coming from the mica substrate, was revealed. By combining all the observations, a growth model is proposed, consisting of the stacking of two different crystallographic structures. An interfacial hexagonal KxWO3 tungsten bronze grows in epitaxy on the mica substrate, followed by the growth of monoclinic trioxide tungsten. The stability of these nanometric objects was studied by annealing up to 870 K, indicating that the transformation of the presumed metastable hexagonal phase never occurred.

International audience; Molybdenum carbonyl Mo(CO)(6) was adsorbed on the Cu(111) surface at 160 K in the monolayer coverage range and studied by scanning tunneling microscopy. A well-ordered monolayer of hexacarbonyl molecules was observed experimentally for the first time. The monolayer has a hexagonal structure compatible with a (root 7 x root 7)R19 superlattice on the copper (111) plane. The arrangement and orientation of the molecules on the surface were determined by density functional theory calculations, including van der Waals interactions. The comparison of adsorption and cohesive energies reveals that the molecule-substrate interaction is stronger than the intermolecular one, which explains the observed two-dimensional growth.

International audience; Tunneling induced decomposition of Mo(CO)(6) from the gas phase was studied on TiO2(110) surface by scanning tunneling microscopy (STM) and spectroscopy (STS). The efficiency of the procedure was followed by measuring the dot volume as a proportional indicator of the amount of the decomposed precursor. It was found that below 1 x 10(-5) Pa background pressure of Mo(CO)(6), there is no measurable effect and above 1 x 10(-4) Pa, the nanodot size is too large compared to the curvature of the tip (20-40 nm). A threshold bias of +3.1(+/- 0.1) V on the sample was measured for the decomposition of Mo(CO)(6) in gas ambient. In the absence of the precursor, dot formation was observed only above +3.7(+/- 0.2) V, in good agreement with the results reported in our earlier work about nanolithography on clean TiO2(110) substrate (E. Krivan, A. Berko: J. Vac. Sci. & Tech. B 15(1) (1997)25). By applying voltages in the range of 3.1-3.5 V, a systematic enlargement of the created nanodots was found in the range of 2-20 s of duration and 0.01-1.0 nA of tunneling current. The I-V curves detected on the top of the nanodots have shown that the created features are of insulator character. This observation indicates that the decomposition of Mo(CO)(6) is also accompanied by oxidation of the deposited Mo species. (C) 2011 Elsevier Ltd. All rights reserved.

Import JabRef; International audience; Small angle x-ray scattering was used to probe in-situ the formation of nanoparticles in the plasma plume generated by pulsed laser irradiation of a titanium metal surface under atmospheric conditions. The size and morphology of the nanoparticles were characterized as function of laser irradiance. Two families of nanoparticles were identified with sizes on the order of 10 and 70 nm, respectively. These results were confirmed by ex-situ transmission electron microscopy experiments.

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)

The growth of thin cobalt films on (100) copper surfaces has been studied by Auger electron spectroscopy (AES) and static secondary-ion mass spectrometry (SIMS). The cobalt and copper SIMS intensities were recorded during the growth. It is shown that the growth is of a layer-by-layer type as has already been observed by AES but problems arise during the completion of the first layer. Moreover a modelization of the SIMS signals is proposed and the contribution coefficients of cobalt and copper are calculated for the different layers. It is shown that 80% of the secondary ionic intensities come from the two first atomic layers.

International audience; This study is concerned with the elaboration of barium silicate thin films by metal organic chemical vapor deposition (MOCVD) and in situ characterization by X-ray photoemission spectroscopy (XPS) with an apparatus connected to the deposition reactor. The difficulty to find an efficient metal organic precursor for barium is described. After characterizations of the selected reactant, Ba(TMHD)2tetraglyme, the development of an original specific vapor delivering source which allows reactant sublimation in the CVD reactor was performed. In the most optimized cases, including use of oxygen introduction during the deposition, barium silicate films were obtained. Moreover, non-negligible amounts of carbon and presence of barium oxide on the top of the layers were observed.

The interaction of TiO2(100) surfaces with hydrogen and water vapour has been studied using mainly secondary ion mass spectrometry (SIMS). The influence of the stoichiometry of the surface on its reactivity has been checked. The existence of two kinds of hydroxyl groups is pointed out. The behaviour of these hydroxyl populations with the temperature was studied. Moreover the ability of SIMS to distinguish different isotopes of the same element was used: exposure of TiO2(100) surfaces to isotope labelled molecules, D2 and H218O, was performed in order to specify the nature of these two hydroxyl groups.

International audience; Synchrotron based photoemission spectroscopy was used to study the adsorption of tungsten hexacarbonyl on SiO2 surfaces modified by potassium. Results were compared with the ones obtained when no potassium was present. Experiments using W4f and Si2p intensities variations show that, at 140 K, the tungsten hexacarbonyl growth proceeds via a simultaneous multilayer mode for the two kinds of surfaces but with differences in compositions of growing layers. Indeed, it is evidenced that, even at cryogenic temperatures, the presence of potassium induces decomposition of a significant part of tungsten hexacarbonyl molecules through a strong interaction between tungsten and potassium atoms in opposition to potassium-free surface cases where W(CO)6 molecules are simply physisorbed. Additional irradiation of adsorbed molecules with photons coming from 0-order synchrotron radiation, subsequent going back to room temperature and additional thermal treatments up to about 700 K were then used to induce further decomposition of the adsorbed precursor. It allows as well to get rid of carbon and, finally, to stabilize different W-based species on the surface. The state of tungsten remaining on the surface is then strongly influenced by presence of potassium. When potassium is present, highly oxidized tungsten species are observed, whereas reduced species are mainly detected for potassium-free surfaces. Moreover, as diffusion of potassium is revealed during formation of tungsten phase, one should guess that potassium plays a crucial role in tungsten oxidation mechanism.

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; Titanium oxynitride layerswere formed by surface laser treatment of Ti plates in air using a Nd:YAG laser source of short pulse duration about 5 ns. The cumulated laser fluence was varied in the 100–1200 J cm2 range and its influence on the composition and the structure of the formed layers was studied by different characterization techniques providing physico-chemical and structural information. It was shown that the laser treatment induces the insertion of light elements as O, N and C in the formed layer with the amount increasing with the laser fluence. The in-depth composition of the layers and the co-existence of different phases were also studied. The way in which the laser parameters such as fluence affect the insertion of nitrogen and oxygen was discussed in connection with the effects of the plasma plume formed above the target.

International audience; We report a first principles study on the structure and energetics of thin films of molybdenum on a (1 1 0) surface of rutile TiO2. Mo films with 1 × 1 epitaxy in the coverage range between 0.5 and 2 monolayer are investigated. The most stable structures are those which maximize the number of Mo–Mo bonds. This leads to two-dimensional structures with zigzag Mo–Mo coordination for 1 monolayer coverage and three-dimensional structures with approximately body-centered cubic coordination for higher coverage. For a coverage up to 1.5 monolayers, the interface Mo atoms preferentially occupy the so-called upper hollow adsorption site with three Mo–O bonds

The charge distribution of the defect states at the reduced ${\mathrm{TiO}}_{2}(110)$ surface is studied via a new method, the resonant photoelectron diffraction. The diffraction pattern from the defect state, excited at the $\mathrm{Ti}\mathrm{\text{\ensuremath{-}}}2p\mathrm{\text{\ensuremath{-}}}3d$ resonance, is analyzed in the forward scattering approach and on the basis of multiple scattering calculations. The defect charge is found to be shared by several surface and subsurface Ti sites with the dominant contribution on a specific subsurface site in agreement with density functional theory calculations.

International audience; A study on the field-induced tip–surface oxygen transfer at room temperature and its influence on the tunneling conditions for stable STM imaging of the TiO2(110) (1 1) surface is reported. A simple model of field-induced transfer is applied to tungsten and platinum–iridium tips. The oxygen transition rates from the sample to the tip or from the tip to the sample depend on the oxygen desorption barriers formed at tunneling distance. For stable imaging the applied bias voltage has to balance the oxygen transfer probabilities in both directions. In the case of Pt/Ir tips, the tunneling conditions for images with clear evidence of bridging oxygen point defects have been established.

International audience; Room temperature depositions of barium on a thermal silicon oxide layer were performed in ultra high vacuum (UHV). In-situ X-ray photoelectron spectroscopy (XPS) analyses were carried out as well after exposure to air as after subsequent annealings. These analyses were ex-situ completed by secondary ion mass spectrometry (SIMS) profiles and transmission electron microscopy (TEM) cross-sectional images. The results showed that after air exposure, the barium went carbonated. Annealing at sufficient temperature permitted to decompose the carbonate to benefit of a barium silicate. The silicate layer was formed by interdiffusion of barium with the initial SiO2 layer.

International audience; TiO2 thin films were deposited on soda–lime glass substrates by reactive direct current magnetron sputtering in a mixture of pure argon and oxygen. The influence of both the deposition time, td, and the post-annealing treatments on the films morphology, composition and structure was analyzed by scanning electron microscopy, ellipsometry, X-ray photoelectrons spectroscopy, X-ray diffraction (XRD) and Raman spectroscopy. Amorphous TiO2 was obtained for the shortest deposition time, td=15 min. Increasing td up to 30 min, poorly crystallized anatase and rutile phases were formed together with amorphous TiO2, as was revealed by complementary XRD patterns and Raman spectra. For longer td, the growth of the anatase phase dominates that of the rutile phase. The post-annealing treatment of the films in air at 450 °C. induced the complete crystallization of the films leading to mainly anatase films for all the deposition times. All these results show the feasibility to fabricate stoichiometric TiO2 thin films with amorphous to crystalline structures by means of soft fabrication conditions: low substrate temperature and moderate annealing treatment.

International audience; Tungsten oxide nanorods are grown at atmospheric pressure and low temperature (360 1C), by sublimation of WO3 and condensation on mica substrates. The nanorods are characterized by atomic force microscopy, high-resolution electron microscopy, energy-dispersive X-ray spectroscopy and high energy electron diffraction. The experimental results evidence the formation of a hexagonal tungsten bronze at the nanorod–substrate interface. The epitaxial relationships of the nanorods on mica are determined and the role of epitaxial orientation of the interfacial bronze in the nanorod growth and morphology are discussed.

Synchrotron-based photoemission spectroscopies were used to study the adsorption of tungsten hexacarbonyl on (1 1 0) TiO 2 surfaces: experiments using W4f and Ti2p intensities variations show that, at 140 K, the hexacarbonyl growth proceeds via a layer-by-layer mode. Moreover, it was evidenced using both core levels and valence band experiments that, after back to room temperature, W(CO) 6 desorbs without significant decomposition. However, low energy (500 eV) ion (Ar + ) irradiation can allow partial decomposition of tungsten hexacarbonyl molecules leading to sub-carbonyl tungsten molecules. The bonding of sub-carbonyl species to the TiO 2 surface was then stronger than the one of hexacarbonyl: these chemisorbed species do not desorb when going back to room temperature allowing a higher amount of metal to remain on the surface. Subsequent annealing gets rid of remaining carbonyl groups. This phenomenon leaves tungsten atoms at the TiO 2 surface. The annealing organizes these W atoms in the 400–600 K temperature range leading to WO x phases, which are almost free of carbon. The oxidation degree of these phases is strongly related to tungsten amount remaining at the surface.

K-wire migration after internal fixation of the clavicle has rarely been reported to cause spinal cord injuries. A 30-year-old man presented with progressive paraparesis, hypaesthesia under a Th4 level and electric pain in the neck and arms. CT of the spine revealed a migrated K-wire from a one-year-old clavicle osteosynthesis, penetrating the spinal canal through the Th2 nerve root foramen, and perforating the spinal cord with a transversal trajectory. Surgical removal of the K-wire was performed after exposing both ends. Laminectomy allowed visual control of the entry point and correction of cerebrospinal fluid leakage. The pain disappeared and the patient recovered a normal gait after 6 weeks. The use of two incisions is advocated in such cases: one lateral to allow wire removal, and one medial for dural repair and early intradural bleeding control. Regular follow ups, K-wire removal after fracture healing as well as bending the wire end in a walking stick shape should minimise the risk of migration.

International audience; In situ Angle Resolved X-ray Photoemission Spectroscopy (ARXPS) characterizations of TiO2 thin films grown on silicon by Metal Organic Chemical Vapour Deposition were performed in order to get information on interfacial reactions at the first stages of the growth, one of the aims being to understand the influence of deposition conditions. Thickness measurements were also carried out from ARXPS analyses. As the real structure of the films was shown to be a double layer system such as TiO2/SiO2/Si, an ARXPS model of thickness and surface coverage determination was applied to each layer independently. However, the application of this model to very thin films underestimates the surface coverage of the interfacial layer. A “Double Layer” model taking into account the attenuation of the silicon oxide and substrate signals by the external layer was also developed.

Molybdenum was deposited in two steps (3 eq. ML and 1 eq. ML) on the light blue rutile TiO2 10) (1 x 1) surface at room temperature, each Mo deposition cycle being followed by an annealing up to 950-1000 K. This procedure was found to lead to formation of separated clusters having a size in very wide range (1-20 nm). Scanning tunneling microscopy showed a dependence of the cluster morphology as a function of the size. The scanning tunneling spectra of Mo clusters was studied as a function of cluster dimensions and discussed in comparison with photoelectron spectroscopy results previously obtained for homogeneous Mo films. The dI/d V curves do not display the valence band structure of deposited material, which could be explained by the Schottky barrier formation. (C) 2007 Elsevier B.V. All rights reserved.

International audience; The adsorption and decomposition of molybdenum hexacarbonyl on (110) TiO2 surfaces were studied using both core levels and valence band photoemission spectroscopies. It was found that after an adsorption at 140 K, when going back to room temperature, only a small part of molybdenum compounds, previously present at low temperature, remained on the TiO2 surface. This indicates that the desorption temperature on such a surface is lower than the decomposition one. The use of photon irradiation to decompose the hexacarbonyl molecule was also studied. It was shown that during such a decomposition molecular fragments were chemisorbed on the surface allowing a higher amount of metal to remain on the surface. It was also shown that it was possible to get rid of adsorbed subcarbonyl groups and to organize the metal atoms by thermal treatments at temperatures as low as 400 K, i.e. much lower than the one needed to obtain the same structures using physical vapour deposition (PVD). Moreover, due to lower used temperatures, this chemical way of deposition allows a better control of the interface than during PVD growth.

The cationic composition of a titanium ferrite (Fe 2.5 Ti 0.5 O 4 ) has been followed by XPS during its oxidation in cation deficient phases (without crystallographic transformation) in order to reveal a dynamic segregation phenomenon. Indeed, during this oxidation, an important modification of the chemical composition of the first layers of the material has been revealed: below 350 °C, the titanium ferrites surface becomes richer in iron and poorer in titanium. But, if the reaction is extended above 400 °C, some titanium can move to the surface. This phenomenon has been interpreted on the basis of the differences of mobility of the different ions which are present in the material. Finally, at 450 °C, on the surface of the spinel, the α –Fe 2 O 3 phase begins to appear and hides the ferrite.

International audience; Reactivity of deposited tungsten towards TiO2(1 1 0) surface was studied using synchrotron radiation photoemission spectroscopy (both core levels, valence band and resonant photoemission) on Materials Science Beamline at ELETTRA. W depositions carried out at room temperature on TiO2(1 1 0) surface give rise to an interfacial reaction which leads to a metastable situation due to kinetic limitations. Annealing induces chemical changes which are function of the initial coverage; for fractional coverage, annealing induces completion of oxidation of deposit whereas reduction to metallic tungsten occurs for highest coverage. These results demonstrate that interaction of W with TiO2(1 1 0) surface is, as the one of molybdenum, driven by a balance between W–O interactions and W–W depending on tungsten atoms density on TiO2 surface.

We report photoelectron diffraction (PED) experiments of weakly sub-stoichiometric TiO 2 (100) rutile surfaces. Apart from standard core-level PED from the Ti-2p3/2 line, we have studied valence band PED from the defect induced Ti-3d states in the insulating band gap. For maximum yield, the latter were resonantly excited at the Ti-2p absorption edge. The PED patterns have been analyzed within the forward scattering approximation as well as by comparison with simulated PED patterns obtained in multiple scattering calculations. The analysis shows that the defect induced Ti-3d charge is mainly located on the second layer Ti atoms. © 2007 Elsevier B.V. All rights reserved.

Molybdenum was deposited at room temperature on the ${\mathrm{TiO}}_{2}(110)$ surface in the 0--1.3 equivalent monolayer (eqML) range and was then annealed at $400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ in order to reach a kind of equilibrium state. A threshold was found in the behavior of the deposit: below 0.2 eqML, substitutional molybdenum occurs in titanium sites located under the bridging oxygen atoms of the ${\mathrm{TiO}}_{2}(110)$ surface. In this position, molybdenum atoms are in a structural and chemical ${\mathrm{MoO}}_{2}$-like environment. Density-functional theory calculations show that this molybdenum site is actually the most stable one in the case of isolated molybdenum atoms. Angle-scanned photoelectron diffraction data are in perfect agreement with such a hypothesis. For deposits higher than 0.2 eqML, the increased amount of molybdenum atoms raises the probability of $\mathrm{Mo}\text{\ensuremath{-}}\mathrm{Mo}$ interactions during the annealing at $400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, taking to a reduction process of the deposit. However, such annealing does not allow the deposit to become fully metallic: molybdenum clusters formed during the annealing are in strong interaction with the substrate, and metallic molybdenum can be obtained only depositing a film thicker than $1\phantom{\rule{0.3em}{0ex}}\mathrm{ML}$.

International audience; This study is concerned with the chemical characterization of metallic gallium droplets, obtained on silicon (1 0 0) substrates with a single growth step, by the LP-MOCVD technique with TMGa like precursor. These structures are characterized by SIMS, XPS and TEM. The analyses results lead to a structure proposition for the droplets. The core is composed of metastable metallic gallium with a non-negligible carbon quantity probably coming from incomplete precursor decomposition. The outer part, composed of gallium oxide maintains the structure stability. Covering of the substrate by a thin gallium layer of gallium compounds is observed.