Search

International audience; In this paper, synchrotron radiation photoemission techniques are used to unravel the pending nature of the two Ba 4d components, also observed on Ba 3d lines, and commonly named Ba(α) and Ba(β). Investigations were carried out on the (001) surface of epitaxial very thin (≤ 20 nm) films combined with DFT calculations. Photoelectron diffraction experiments reveal different behaviors for Ba(α) and Ba(β) components. While six well defined diffraction features corresponding to the BaTiO$_3$ bulk structure are observed for the Ba(α) component, no feature really appears in the diffraction pattern of Ba(β). This observations reveal the absence of forward scattering processes, hence this component comes mostly from surface BaO plane. Supporting these results, DFT calculations demonstrate a shift to lower binding energy (BE) only for the Ba 4d peak from the topmost BaO layer with respect to the photoelectron peak stemming from bulk layers. Hence, only one peak (the Ba(α) one) should be observed for a sample with a complete TiO$_2$ termination. This hypothesis is supported by photoemission measurements carried out at low photon energy in grazing angle emission, in order to enhance the signal from topmost layers with respect to the bulk. For each sample, the Ba(β)/Ba(α) intensity ratio is well reproduced by a model where the Ba(β) signal is only coming from the topmost surface BaO plane.

International audience; We report the high capacity of recycling of a technologically simple, easily recoverable, Ru@Fe3O4 magnetic nanocatalyst, efficient in the release of H2 from ammonia-borane (AB) solvolysis, using H2O or methanol at room temperature (25 °C). The initially oxidized Ru small nanoparticles (2–4 nm) are well-dispersed on an iron oxide support (i. e. super paramagnetic iron oxide of spinel structure, SPIO, as aggregates of 20 nm to a few μm). As nanocatalyst, this composite achieved short-time (

Diamondoids, sp3 -hybridized nanometer-sized diamond-like hydrocarbons (nanodiamonds), difunctionalized with hydroxy and primary phosphine oxide groups, enable the assembly of the first sp3 -C-based chemical sensors by vapor deposition. Both pristine nanodiamonds and palladium nanolayered composites can be used to detect toxic NO2 and NH3 gases. This carbon-based gas sensor technology allows reversible NO2 detection down to 50 ppb and NH3 detection at 25-100 ppm concentration with fast response and recovery processes at 100 °C. Reversible gas adsorption and detection is compatible with 50 % humidity conditions. Semiconducting p-type sensing properties are achieved from devices based on primary phosphine-diamantanol, in which high specific area (ca. 140 m2 g-1 ) and channel nanoporosity derive from H-bonding.

International audience; Diamondoids, sp3-hybridized nanometer-sized diamond-like hydrocarbons (nanodiamonds), difunctionalized with hydroxyl and primary phosphine oxide groups enable the assembly of the first sp3-C-based chemical sensors by vapor deposition. Both pristine nanodiamonds and palladium nanolayered composites can be used to detect toxic NO2 and NH3 gases. This carbon-based gas sensor technology allows reversible NO2 detection down to 50 ppb and NH3 detection at 25–100 ppm concentration with fast response and recovery processes at 100 °C. Reversible gas adsorption and detection is compatible with 50% humidity conditions. Semiconducting p-type sensing properties are achieved from devices based on primary phosphine-diamantanol, in which high specific area (ca. 140 m2 g–1) and channel nanoporosity derive from H-bonding.

MICROSCOPIE+MEME+FCA:EEH:LBU:TEP; International audience; The di-block copolymer inverse micelle method, where an amphiphilic di-block copolymer dissolved in toluene creates a system of inverse micelles, is a rather simple method to obtain well controlled supported metallic nanoparticles once the micelle core is charged with metallic salts. Supported metallic catalysts can be obtained in this way on both flat (model catalysts) and powder (realistic catalysts) supports [1]. Our main interest deals with applications of bimetallic catalyst systems that we investigate from extended catalytic surfaces [2] to realistic catalysts [3]; the idea being to isolate and understand the role of important physico-chemical parameters on the catalytic behaviour of these systems in the shape of model catalytic surfaces and try to extrapolate them to realistic catalysts. This is very important for the controlled design of catalysts with specific properties. In this way we can, not only spend less active material (often rare and expensive), but also avoid unnecessary poisoning while keeping high activity (stability) and finely tune the selectivity to avoid deleterious unwanted products; these are important points to be able to achieve environmentally friendly and sustainable catalytic processes. Self-organized nanoparticles on flat surfaces is an intermediate configuration between extended catalytic surfaces and realistic catalysts and a necessary step to better extrapolate results between model and realistic systems. We have thus extended the di-block copolymer method to the synthesis of bimetallic catalysts [4]. In our presentation we will deal with a PdAu system, obtained from a PS-b-P2VP copolymer micellar solution that we transfer by spin-coating to a surface of a SiNx eletron-transparent films on dedicated microchips than are heated in Wildfire sample holder (DENS Solutions) within an objective lens aberration-corrected environmental TEM (Titan ETEM G2 80-300 kV from ThermoFisher Scientific) so that we can study in situ the behaviour of such a system in variable temperature and gas pressure. We observed the formation of the individual particles from the seeds within the core of the micelles in the presence of oxygen in variable temperature; sintering of the seeds within the micelle cores starts at 350°C and is completed at 500°C, temperatures that correspond, respectively, to the onset of the copolymer decomposition and to its quasi-completed decomposition [5]. We also observed that the network of nanoparticles is stable under oxygen up to 900°C and that, above this temperature, the network is modified only by the decomposition of the nanoparticles (when we approach their melting point).The authors acknowledge the French Microscopy and Atom probe network (METSA) and the Consortium Lyon – St-Etienne de Microscopie (CLYM) for supporting this work.References:[1] B. Roldan Cuenya, Accounts of Chemical Research 46 (2013) 1682.[2] MC Saint-Lager et al., ACS Catalysis 9 (2019) 4448.[2] B. Pongthawornsakun et al., Applied Catalysis A: General 549 (2018) 1.[4] E. Ehret et al., Nanoscale 7 (2015) 13239.[5] T. Orhan Lekesiz et al., Journal of Analytical and Applied Pyrolysis 106 (2014) 81.

MICROSCOPIE+MEME+EEH:TEP:MAO:LBU:FCA; International audience; We used self-assembled block copolymer templates to generate arrays of bimetallic nanoparticles. In this approach, a block copolymer consisting of hydrophilic and hydrophobic blocks is dissolved in a selective solvent such as toluene in order to obtain inverse micelles. The core of such inverse micelles can then be functionalized with metal precursors ligated by complexation or protonisation to the inner polymer block. The reverse micelles can then be transferred from the solution to the substrate by using, for instance, standard spin or dip coating techniques. The obtained layer exhibits a rather high degree of hexagonal order, reflecting the packing of spherical micelles.We present results on the formation of arrays of both PdAg and PdAu nanoparticles obtained by this method. For the latter a specific study on the stability of the array at high temperatures under oxygen pressure was performed within an objective-lens aberration-corrected environmental transmission electron microscope (Titan ETEM G2 80-300 kV from ThermoFisher Scientific).

MICROSCOPIE+MEME+EEH:FCA:LBU:TEP; International audience; Systems of self-organized nanoparticles (NPs) are useful in many domains such as, for instance, optics, nanostructure growth and, the domain of most interest in our case, catalysis. It is indeed a way to control the classic characteristics of catalysts (size, dispersion, chemical phase, …) and add a new tunable parameter, often poorly controlled, which is the long-distance ordering and, thus, the inter-nanoparticle distance. Well-controlled physicochemical properties of the catalysts lead to better correlation between these properties, their possible evolution, and their catalytic performance (activity, selectivity, stability). Among self-assembly techniques, the use of di-block copolymer method, where an amphiphilic di-block copolymer dissolved in toluene yields a system of inverse micelles, is a rather simple method to obtain well controlled supported NPs which can be used as supported metallic catalysts on both flat (model catalysts) and powder (realistic catalysts) supports [1]. After formation of the micellar solution, we can indeed charge the core with metal salts that can then be deposited on flat surfaces by dip or spin coating for instance. Our main interest deals with applications of bimetallic catalysts that we study in the form of both realistic catalysts [2] and extended catalytic surfaces [3]; self-organized NPs on flat surfaces is an intermediate configuration between these two approaches which is useful to better extrapolate results between model and realistic systems. With this in mind we have extended the di-block copolymer method to the synthesis of bimetallic catalysts [4]. For these systems composed of metals with different characteristics, several questions remain unanswered such as the evolution of the pre-formed bimetallic seeds (Fig. 1b-d) with temperature, the temperature formation of unique NPs at the micellar core or the stability of the network of bimetallic NPs (Fig. 1a) at high temperature in presence of reactive gases.An objective lens aberration-corrected Environmental TEM (Titan ETEM G2 from FEI/ThermoFisher Scientific), operated at 300kV and capable of gas pressure up to 20 mbar, is a well-adapted tool to study those phenomena. An Au-rich AuPd core-metallized PS-b-P2VP micellar solution was synthesized and deposited by spin-coating on dedicated heating microchips containing a silicon nitride electron transparent (discrete) film capable of reaching temperatures up to 1300°C within a WildFire support holder (DENS solutions). Special care was taken to minimize/prevent any influence of the electron beam on the observed events. In order to observe both the formation of the individual NPs, together with the elimination of the copolymer, and the high-temperature stability of the network we have worked under oxygen pressure (up to 2 mbar). We observed that the seeds within the micellar cores (Fig. 2a-left) begin to sinter around 350°C (Fig. 2a-center) which is consistent with the temperature onset at which the copolymer (associated to a metal) begins to decompose [5]; unique NPs are formed around 500°C (Fig. 2a-right), when the copolymer is almost completely gasified [5]. The network is remarkably stable up to 900°C (Fig. 2b); finally, around 1000°C, close to the melting temperature of Au (1064°C), the NPs begin to decompose (Fig. 2b). At 1100° C, unique Au-rich NPs (Fig. 3a) begin to shrink and yield smaller satellite NPs (Fig. 3b); then the facetted NP (Fig. 3c) becomes spherical (Fig. 3d) and finally disappears to leave only the satellite NPs that grow on the surface (Fig. 3e). The volume ratio between the satellite NPs and the initial Au-rich NP indicate that only the Au within the NP has disappeared and that the remaining satellite NPs are pure Pd. The stability of the network seems to depend only on the intrinsic properties of the chosen metals [6].References:[1] B Roldan Cuenya, Accounts of Chemical Research 46 (2013) 1682.[2] B Pongthawornsakun et al, Applied Catalysis A: General 549 (2018) 1.[3] MC Saint-Lager et al, ACS Catalysis 9 (2019) 4448.[4] E Ehret et al, Nanoscale 7 (2015) 13239.[5] T Orhan Lekesiz et al, Journal of Analytical and Applied Pyrolysis 106 (2014) 81.[6] The authors acknowledge the French Microscopy and Atom probe network (METSA) and the Consortium Lyon – St-Etienne de Microscopie (CLYM) for supporting this work.

We studied the growth of epitaxial ferroelectric layers BaTiO3/Pt(001) in the framework of solar water splitting. The stoichiometry, i.e. the Ti/Ba ratio, appears as a crucial parameter not only for the crystallographic structure but also for the photocurrent generation when the sample is used as photoanode. We established an electrochemical poling method using a modulated potential, without altering the sample to control the electric polarization. Importantly, we show that the photoanode efficiency is improved when the polarization of the film is oriented towards the substrate. We demonstrate that this improvement is only due to the electrical field created by screening charges, which allows the separation of photo-generated charges.

The pollution of waste water due to organic dyes used in textile and chemical industries is an important environmental issue. Inverse opals (IO) offer a great potential for increasing the efficiency of semiconductor photocatalysts as TiO2 by the synergy of high specific surface and photonic crystal properties. In this work, we report the synthesis of both IO and planar TiO2 films by Atomic Layer Deposition and a comparative study of their photocatalytic activity for the degradation of methylene blue in water under UV irradiation. The porosity of planar TiO2 films was modified by a pre-treatment of the substrate to analyze its effect on the photocatalytic activity. A rutile single-crystal was also used for comparison. The kinetics of the MB degradation process was studied for long times to investigate the eventual effect of the progressive increase of degradation products in the solution. A degradation percentage about 90% was obtained after 10 h using IO films, and only about 60% by using planar and dense films. A first-order reaction kinetics was shown in the case of IO films. For the other catalysts, a slowing-down of the reaction kinetics was shown above 8 h. The adsorption of the degradation products at the catalyst surface was addressed to explain this effect. The results highlight the potential of IO films synthesized by ALD for photocatalytic applications.

Titanium tetraisopropoxide (TTIP) molecules have been deposited on the copper substrate Cu(111) with monolayer coverage at cryogenic, room and elevated temperatures and studied by variable temperature scanning tunneling microscope (STM), X-ray photoelectron spectroscopy (XPS), low electron energy diffraction (LEED) and X-ray absorption near edge structure (XANES) spectroscopy using the synchrotron radiation. Adsorption and irregular assembling of entire molecules are observed at low temperatures. At room temperature, STM reveals an agglomeration of TTIP molecular fragments. The XPS analysis confirms presence of ligand groups bonded to molecular center, indicating a partial decomposition process up to 670 K. TTIP molecules start to decompose completely on copper surface at elevated temperatures, higher than 800 K. Hexagonal surface oxide structure is formed after TTIP monolayer thermal decomposition at 870 K, as it is proved by LEED and STM.

The influence of water on the out-of-plane polarization of ${\mathrm{BaTiO}}_{3}$ (BTO) ultrathin films is studied by means of density functional theory calculations. The adsorption is investigated for different coverages on both terminations of BTO with, for each case, all possible states of polarization, namely, paraelectric, polarized upward, and polarized downward. We thus demonstrate different behavior as a function of the termination. While ${\mathrm{H}}_{2}\mathrm{O}$ adsorbs only dissociatively on the BaO termination, with a reinforced interaction compared to BTO without out-of-plane polarization, only molecular adsorption is observed on the ${\mathrm{TiO}}_{2}$ termination. In addition, the presence of water is able to switch the polarization. Whatever the initial state of polarization is, water induces a downward state on the BaO termination and an upward polarization on the ${\mathrm{TiO}}_{2}$ one. A detailed analysis of this phenomenon is given.

The research was devoted to studying unlubricated tribological behaviors of γ-TiAl-based coatings in the temperature range 25–400 °C. These γ-TiAl-based intermetallic coatings alloyed with Fe or Mn were formed on CP-Ti workpieces using a non-vacuum electron beam deposition. The microstructure, phase and elemental analyses proved the formation of γ-TiAl and appearance of the ternary phases (Laves and G-phases). It was shown that friction coefficients obtained for three materials were barely different but their fluctuations were strongly dependent on surface oxidation and the phase composition. It was found that the Ti-45Al-8Mn (at.%) coatings consisting mainly of γ and α2 phases had lower wear resistance in comparison with the Ti-42Al-7Fe (at.%) and Ti-57Al-13Fe (at.%) coatings. Whereas the Ti-57Al-13Fe (at.%) coating contained γ and G phases possessed better wear resistance as compared to that of Ti-42Al-7Fe (at.%) coating with the structure represented by the γ matrix and a eutectic (α2 + Laves phases). The microprobe analysis, scanning electron and optical microscopy, and XPS measurements revealed the formation of highly oxidized mechanically mixed layers after the sliding tests. The Ti-45Al-8Mn (at.%) coating subsurface consisted of Al2O3, Al, TiO2, and Ti sub-oxides, whereas for both Ti-Al-Fe coatings the formation of an initial oxide film consisted of a titanium dioxide (rutile structure), alumina, and a low amount of iron oxide (hematite structure) was revealed. Thermal softening of the counter body provoked the iron oxide growth in the wear traces of the coatings alloyed with Fe. Tribooxidation behaviors of Ti-Al-Fe coatings may be interpreted as an example of adaptation the as-deposited structure and phases to high-temperature sliding condition and therefore these coatings can be recommended for protection of the titanium alloy components.

Density functional theory calculations are performed to study the out-of-plane polarisation in BaTiO3 (BTO) thin films epitaxially grown on platinum. Prior to any polarisation calculation, the stability of the Pt(001)/BaTiO3(001) structure is thoroughly discussed. In particular, the nature of the Pt/BTO and BTO/vacuum interfaces is characterised. The growth of BTO is shown to start with a TiO2 layer while the nature of the surface termination does not broadly modify the stability. Therefore both upper terminations are considered when describing the ferroelectric behaviour in Pt/BTO interfaces. The geometric and electronic effects of the substrate on the polarisation are investigated. To isolate the electronic influence of platinum, the out-of-plane polarisation in Pt/BTO systems is compared to the one in isolated BTO slabs constrained to the same lattice mismatch induced by the epitaxial growth on platinum. The ferroelectric phase is favoured as soon as the thickness is larger than 23 A, both for isolated and deposited BTO, for the smallest width. The Pt substrate will modify the size of polarisation domains, while an upper BaO layer through the use of asymmetric [TiO2/BaO] systems will induce an increase of the polarisation. One could take advantage of this experimentally.

In this study, we report a direct deposition of three-dimensional freestanding nanostructures of platinum-doped ceria films on holey carbon coated copper transmission electron microscopy (TEM) grid by direct liquid injection chemical vapor deposition (DLI-CVD). TEM was then directly performed on the pristine thin films, without any kind of mechanical or ion thinning. High-resolution TEM reveals that highly porous and crystallized layers were deposited over the whole membrane. The existence of platinum in the ceria grains was confirmed by Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS). Moreover, the substitution of carbon membrane by Pt-CeO2 layer was highlighted by Electron Energy Loss Spectroscopy (EELS), showing that the Pt-CeO2 nanofilms are freestanding. These results are very promising and represent an important step for performing specific nanoscale TEM analyses necessary for the study of the growth mechanism of nanofilms on substrates.

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.

Nanocomposite films composed of gold nanoparticles (AuNPs) embedded in a TiO 2 matrix have been prepared by direct liquid injection chemical vapor deposition process, using preformed nanoparticles and titanium isopropoxide as precursors. The spherical AuNPs about 4.1 nm in diameter were synthesized by using gold (III) chloride trihydrate and stabilized by thiol ligands. The depositions were carried out by performing at first oxide deposition, then gold nanoparticle one and capping with oxide. The morphology, structure; the chemical state and optical properties of nanocomposite films were characterized by scanning electron microscopy, Raman, X-ray photoelectron and UV–Vis absorption spectroscopies, respectively. The stability of the films upon thermal annealing up to 800 °C was studied.

Porous cerium oxide thin films were grown by pulsed direct liquid injection metal organic chemical vapor deposition (DLI-MOCVD) on silicon substrate, using cerium tetrakis (1-methoxy-2-methyl-2-propanolate) dissolved in cyclohexane as precursor as well as oxygen as oxidant agent. The chemical and morphological characteristics of the films were investigated by XPS, SEM and TEM. The influence of the growth conditions on the morphological features of the thin films and the cerium chemical states are reported and discussed. The decrease of the oxygen and/or alkoxide flow rate induces the decrease of both the film thickness and the porosity of the layer. Moreover, the growth of silicate at the interface between the silicon substrate and the grown film is evidenced.

Nanostructured Pt–TiO 2 composite thin films were synthesized by direct liquid injection metal organic chemical vapor deposition process, using trimethyl(methylcyclopentadienyl)platinum and titanium isopropoxide as precursors. Surface and cross-sectional morphologies obtained by scanning electron microscopy and transmission electron microscopy evidenced the uniform distribution of platinum nanoparticles in the TiO 2 matrix. At higher Pt content, the X-ray diffraction analysis showed that the face-centered cubic phase of platinum appeared together with an anatase TiO 2 structure. In addition, as far as the platinum chemical state is concerned, the co-deposition of TiO 2 and Pt allowed obtaining Pt 2 + or Pt°, in a ratio strongly dependent on the Pt content. Indeed, X-ray photoelectron spectroscopy characterization evidenced the presence of only Pt 2 + for lower Pt content and only Pt° for higher one. The variation of platinum content in the TiO 2 films resulted in a change of the chemical state of platinum.

Deposition of tungsten carbide (WC) films was investigated by radio-frequency reactive sputtering using a tungsten target and methane gas. The effect of some processing parameters (pressure, power, CH 4 -to-Ar gas flow ratio) upon the chemical and structural properties of the films has been investigated. The evolution of the chemical composition has been analyzed by photoemission, the microstructure has been studied through electron microscopy techniques and the crystallographic structure was investigated by X-ray diffraction as well as Raman spectroscopy. This study demonstrates that the formation of tungsten carbide is highly dependent on the deposition conditions: thin films are composed of either metallic tungsten or carbon for a total gas pressure of 0.5 Pa while for higher total gas pressure (5 Pa), tungsten carbide films are deposited for a large power range (50–180 W) but a narrow range of methane flow rate (2–8%). In this latter case, no changes are observed in microstructure and crystallography of tungsten carbide films with processing parameters: all films present a columnar growth and are mainly formed of cubic sub-stoichiometric WC 1 − x nanocrystallites embedded in amorphous carbon. However, as function of process parameters, a strong variation in chemical composition of the films is revealed and is attributed to the defective structure of cubic sub-stoichiometric WC 1 − x phase.

Thin films of Pt-doped CeO 2 were grown by direct liquid injection chemical vapor deposition on silicon wafer covered by native oxide at 400 °C using Ce(IV) alkoxide and organoplatinum(IV) as precursors. X-ray photoelectron spectra evidenced that the platinum oxidation state is linked to the deposition way. For platinum deposited on top of cerium oxide thin films previously grown, metallic platinum particles were obtained. Cerium and platinum codeposition allowed obtaining a Pt 0 and Pt 2 + mixture with the Pt 2 + to Pt ratio strongly dependent on the platinum flow rate during the deposition. Indeed, the lower the platinum precursor flow rate is, the higher the Pt 2 + to Pt ratio is. Moreover, surface and cross-sectional morphologies obtained by scanning electron microscopy evidenced porous layers in any case.

International audience; Nanocrystalline tungsten oxide (WO 3) thin films synthesized by thermal oxidation of tungsten substrates were exposed to low energy helium ions (energy: 80 eV; flux: 1.4-1.7×10 20 m-2 s-1) at room temperature and at 673 K. The structure and morphology changes of the oxide were studied using Raman spectroscopy and electron microscopy. Due to the low ion energy, no erosion is observed at room temperature. On the contrary, at 673 K, a colour change is observed and a significant erosion is measured (~ 70 nm for a fluence of ~ 4×10 21 m-2) due to a synergetic effect between ion bombardment and heating. We show that erosion processes and structural changes strongly depend on the ion fluence and in particular the higher the fluence, the lower the erosion yield, most likely due to oxygen depletion in the oxide near-surface layers.

The thermal behavior of the titanium–tungsten adhesive layer (30–70 at.%) deposited on a SiO2 substrate followed by a thicker Pt layer was investigated. The resulting Pt/TiW/SiO2 planar system was annealed under air or vacuum. Morphological and chemical characterizations at different stages of the annealing, as a function of several parameters such as treatment atmosphere, annealing temperature and thickness of the Pt film were performed through surface science analyses. When annealing under air, even at mild temperature (773 K), the whole interlayer oxidizes while a low amount of tungsten diffuses through platinum film. This phenomenon is related to tungsten oxidation which acts as the driving force leading to WO3 ultra thin overlayer. On the obtained WO3/Pt/TiO2–WO3/SiO2 system, whatever subsequent vacuum annealing conditions are, the reduction process of surface tungsten oxide is revealed leading to WOx

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.

The thermal stability of Pt/Ti–W/SiO2 system was studied after annealing under air or vacuum in the present work. A Ti–W adhesive film (30 at. % Ti) was deposited on a SiO2 substrate followed by a thicker Pt layer. Depositions were performed using DC magnetron sputtering. The whole as-deposited films are metallic with a columnar growth of platinum deposit which totally wets the substrate. Whatever the atmosphere is, annealing at 500 °C for 12 h does not change the platinum state but modifies the morphology of platinum particles, the lateral average size of which increasing from less than 10 nm up to ca. 75 nm. Besides, a noticeable diffusion of metallic tungsten through Pt film is revealed for annealing carried out under vacuum. When annealing under air, oxygen diffusion through the Pt layer causes an oxidation of the whole Ti–W interlayer, inducing an important volume increase and degraded interfaces. Such an oxidation process comes with the migration of WO3 species through Pt-grain boundaries, up to the Pt surface. As the width of Ti–W interlayer is increased, a higher amount of WO3 reaches the surface, ultimately leading to discontinuities of the Pt layer.

The surface of Cu(111) was exposed to molybdenum hexacarbonyl Mo(CO)6 with monolayer coverage at temperature 160 K and studied by a Scanning Tunneling Microscope. The monolayer structure has a hexagonal arrangement and forms a (√7 × √7) R19 superlattice on the copper (111) plane. Upon repeated scanning the monolayer is transformed into a (1 × 2) superstructure with 3-fold oriented domains. The domains of (1 × 2) superstructure can change orientation under scanning according to 3-fold surface symmetry. From analysis of the domain mobility, it follows that CO groups of carbonyl fragments are organized in the (1 × 2) superstructure conditioning the domain reorientation. The observed structure transformation under scanning is a result of stimulated dissociation of molybdenum hexacarbonyl on the copper surface.

In this study, the characterization of nanostructured Pt-doped CeO2 films with low platinum content and porous structure is reported, deposited on silicon substrate by direct liquid injection chemical vapor deposition. The platinum localization and concentration in the nanocomposite are determined by scanning transmission electron microscopy associated with energy dispersive X-ray spectroscopy. Films are made of approximate to 3 nm diameter CeO2 particles and platinum is homogeneously dispersed through the layers. X-ray photoelectron spectroscopy (XPS) also shows that platinum is mainly in an ionic Pt2+ state. After diffusion through the preformed porous structure of ceria films, the platinum precursor decomposes at the surface of each ceria particle forming the films, producing a homogeneous platinum-doped CeO2 nanocomposite. This result is supported by synchrotron radiation XPS experiment, where the measured relative Pt concentration demonstrates that platinum is decomposed only at the surface of ceria particles. Finally, when the saturation of Pt2+ sites at the surface of ceria particles is reached, metallic nanoclusters are formed from platinum excess.

Barium was deposited at room temperature on a thermal silicon oxide layer and the interfacial reaction was monitored by synchrotron induced photoemission (both core level and valence band). The first step of the growth consists of an interfacial reaction which leads to the formation of an interfacial silicate layer. The next step consists in formation of barium oxide while metallic barium occurs subsequently. The deposit can be also homogenized by annealing above 575 K. This results in the formation of several layers of silicate by consumption of silicon oxide. In the case of fractional coverage, subsequent annealing at 975 K induces the decomposition of barium silicate. However, such a decomposition process is strongly dependent on the initial film thickness. It can be avoided for deposits thicker than 3 eqML.

Nickel was deposited on stoichiometric TiO2(1 1 0) surface in the 0.02–2.1 equivalent monolayer (eqML) range and analyzed by means of photoemission and resonant photoemission. In the case of very low coverage (lower than 0.1 eqML), deposited nickel reacts with the surface through an electronic transfer from nickel atoms towards titanium ions. This exchange caused the filling of unoccupied Ti3d states leading to the increase of a peak in the TiO2 band gap. These states can be better characterized through resonant photoemission experiments at the Ti 3p → 3d absorption edge: for very low coverage, these states in the TiO2 band gap have resonant behavior of Ti3d electrons rather than Ni3d ones, confirming the filling of Ti3d states and thus electron transfer between nickel and titanium. For coverage higher than 0.14 eqML, nickel peaks (both Ni3p core level and valence band) should be related to the presence of metallic nickel in small clusters.

International audience; WO3 nanorods are grown by a simple vapor deposition method on a mica substrate and characterized by Selected Area Electron Diffraction and Energy Dispersive X-rays Spectroscopy. Experimental results show the clear evidence of an unexpected WO3 hexagonal structure as well as an epitaxial growth on the mica substrate. Besides, potassium is evidenced inside the nanorods. It is thus deduced that a metastable WO3 hexagonal phase is stabilized by epitaxy through a tungsten bronze interlayer having same hexagonal structure.

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.

In situ chemical surface analyses using X-ray photoelectron spectroscopy (XPS), completed by ex situ atomic force microscopy (AFM) analyses, were performed in order to compare the initial stages of MOCVD growth of TiO 2 thin films on two different surface types. The first type was a silicon native oxide free hydrogen terminated surface and the second one was a silicon dioxide surface corresponding to a thin layer of 3.5 nm thick in situ thermally grown on silicon substrate. Si(100) was used as substrate, and the growths of TiO 2 thin films were achieved with titanium tetraisopropoxide (TTIP) as precursor under a temperature of 675 °C, a pressure of 0.3 Pa and a deposition time of 1 h. Whatever the surface is, the deposited titanium amount was globally the same in the two cases. On the contrary, the deposit morphology was different: a covering layer composed of a SiO 2 and TiO 2 phases mixture on the hydrogen terminated surface, and small TiO 2 clusters homogeneously spread on the SiO 2 surface.

The rutile TiO 2 (1 1 0) surface is a highly anisotropic surface exhibiting “channels” delimited by oxygen rows. In previous experimental and theoretical DFT works we could identify the molybdenum adsorption sites. They are located inside the channels. Moreover, experimental studies have shown that during subsequent annealing after deposition, special molybdenum nano structures can be formed, especially two monolayer high pyramidal chains of atoms. In order to better understand the dynamics of nano structure formation, we present a kinetic Monte Carlo study on diffusion and adsorption of molybdenum atoms on a TiO 2 (1 1 0) surface. A quasi one-dimensional lattice gas model has been used which describes the possible adsorption sites of a Mo atom in a single channel of the surface. The atomic positions of a 1.5 monolayer thick Mo film formed of pyramidal chains define the lattice sites of the model. Thereby the formation of three-dimensional clusters could be studied. Here we have studied the cluster formation as a function of parameters that can be controlled in a growth experiment by physical vapor deposition: deposition and annealing temperature, flux and total amount of deposited Mo. Good qualitative agreement with recent experiments is obtained.

Small amounts of molybdenum (from 0.03 to 1.3 eqML) were deposited on non-stoichiometric TiO 2 (1 1 0) surface. The deposits were investigated by means of LEED and X-ray/UV photoemission using synchrotron radiation. For the smallest coverage (

The interfacial reaction between deposited molybdenum and three different TiO2(1 1 0) substrates (a bulk and surface stoichiometric TiO2; a bulk stoichiometric and surface reduced crystal; a bulk and surface slightly reduced crystal) was investigated by means of X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). While the interfacial reaction is not a function of the substrate at room temperature (in any case, molybdenum layers grow with oxygen dissolved in), this study clearly reveals a strong effect of the substrate bulk stoichiometry on the chemical state of the deposit after annealing up to 750 °C whereas the substrate surface stoichiometry plays a minor role. Indeed, annealing carried out on deposits performed on bulk stoichiometric TiO2 (whatever the initial surface stoichiometry is) leads to MoO3 formation whereas annealing carried out on layers which grew on bulk non-stoichiometric TiO2 involves metallic molybdenum overlayers. These results, as well as others previously published on the same system, are discussed from a new model based on thermodynamical considerations including entropic effect.

Molybdenum has been deposited at room temperature on stoichiometric TiO 2 (1 1 0) surfaces with two deposition rates: 0.1 equivalent monolayer (eqML) and 1.5 eqML min −1 . X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy studies clearly reveal an effect of the deposition rate upon the growth mode and the interfacial reaction. Indeed, whereas a strong interfacial reaction between Mo and TiO 2 involves a Stranski–Krastanov growth mode with the formation of amorphous molybdenum oxide monolayers for the lowest deposition rate, no reaction can be observed for the highest deposition rate. Moreover in this latter case, the growth mode seems to be a 3D one. These differences are discussed from a pure kinetics point of view.

The coupled synthesis and sintering of Fe2NiO4 can be carried out from the calcination under air at high temperatures (>1200 °C) of precompacted (under 12 MPa) pellets of different mixtures: NiO/α-Fe2O3; NiO/α-Fe2O3/Fe; NiO/α-Fe2O3/Ni. The densest material is obtained at 1200 °C only from the following mixture: NiO (40 mol%), α-Fe2O3 (50 mol%) and Ni (10 mol%). Because the metallic nickel is very ductile, it is used as an internal binder in order to enhance the precompacting of the samples. Moreover, the role of nickel is to enhance the sintering reaction. This route leads to a final material of relative density close to 98±2%.

Traditional industrial cleaning processes of titanium and titanium alloys use solvents which are potentially toxic and environmentally harmful. Carbon dioxide, which is nontoxic, nonflammable, recyclable, and available on a large scale, is a potential substitute for these solvents. Indeed, the zero surface tension of supercritical CO2 (SC-CO2) provides a significant advantage over liquid and aqueous solutions, and facilitates the access to small structures, while a high diffusion coefficient allows a fast rate of mass transfer. Moreover, its viscosity and density can be adjusted by tuning pressure and temperature. In this study, the performances of solvent-assisted SC-CO2 process are compared to traditional TA6V alloy cleaning processes. The efficiency of residual oil removal from a TA6V surface has been investigated by several techniques such as x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). While XPS gives a measure of the so-called r...

MICROSCOPIE+ATARI+EEH:GMA:TBG:NSP:MAO; International audience; The self-assembly technique provides a highly efficient route to generate well-ordered structures on a nanometer scale. In this paper, well-ordered arrays of PdAg alloy nanoparticles on flat substrates with narrow distributions of particle size (6-7 nm) and interparticle spacing (about 60 nm) were synthesized by the block copolymer micelle approach. A home-made PS-b-P4VP diblock copolymer was prepared to obtain a micellar structure in toluene. Pd and Ag salts were then successfully loaded in the micellar core of the PS-b-P4VP copolymer. A self-assembled monolayer of the loaded micelles was obtained by dipping the flat substrate in the solution. At this stage, the core of the micelles was still loaded with the metal precursor rather than with a metal. Physical and chemical reducing methods were used to reduce the metal salts embedded in the P4VP core into PdAg nanoparticles. HRTEM and EDX indicated that Pd-rich PdAg alloy nanoparticles were synthesized by chemical or physical reduction; UV-visible spectroscopy observations confirmed that metallic PdAg nanoparticles were quickly formed after chemical reduction; XPS measurements revealed that the PdAg alloy nanoparticles were in a metallic state after a short time of exposure to O-2 plasma and after hydrazine reduction.

Excess electrons profoundly affect the properties of oxide surfaces. The present review deals with excess charges on rutile and anatase. These much studied titania polymorphs open with strong prospects regarding (photo)catalysis and dye-sensitized solar cells. In the complex landscape of the mechanisms of electron trapping and electron transfer toward adsorbates, excess electrons open with flexible model systems which are the focus of an extensive research effort.

Molybdenum films were deposited at room temperature on rutile TiO2(1 1 0) surfaces having different stoichiometries, surface roughnesses and crystallinities. The film structures and compositions and the substrate–film interfaces were investigated by X-ray diffraction, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. Different substrate pretreatments resulted in markedly different film and interface structures. Under the growth conditions studied, no amorphous molybdenum oxide interlayers were formed upon deposition in contrast to previous studies. Preferred (1 1 0) textured Mo films grew on both air-annealed and oxygen-bombarded substrates. While sharp substrate–film interfaces were observed in the air-annealed samples, oxygen bombardment led to a rough interface. Epitaxial growth was achieved on argon-bombarded substrates, and a single crystal TiO interlayer was present as a result of the substrate pretreatment. The orientation relationship among three crystalline layers was: Mo(2 0 0)[0 0 1]//TiO(2 0 0)[0 1 1]//TiO2(1 1 0)[0 0 1]. Even though the growth was epitaxial, the argon bombardment resulted in a rough interface between the substrate and the TiO interlayer and between TiO and the Mo film. The results are compared with previous data on thin Mo film growth ( 6 3 ML) on rutile TiO2(1 1 0), and the structural evolution is discussed. � 2002 Published by Elsevier Science B.V.

Catalytic systems containing an ansabiscyclopentadienyllanthanide core and lithium and/or magnesium salts are obtained by reaction of the chloride precursors with allyllithium. These allyl complexes lead to the same active species which polymerises 1,3-dienes, copolymerises 1,3-dienes and α-olefin or α,ω-dienes or allows the controlled diblock polyisoprene/polycaprolactone copolymerisation. The exact nature of this active species and of the allyl precursors is investigated here.

Dynamic segregation phenomena were revealed by XPS during the oxidation of some ferrites (Fe 2.5 Ti 0.5 O 4 , Fe 2.5 Ni 0.5 O 4 , Fe 2 CrO 4 and FeCr 2 O 4 ). This kind of phenomenon induces, at a low temperature (below room temperature), drastic changes in the cationic composition of the most external layers. Dynamic segregation is a function of the cationic composition, the oxidation capability and the morphology of these ferrites. Although dynamic segregation seems to be a quite frequent phenomenon that often can be observed during ferrite oxidation, there are materials in existence where it does not appear, such as molybdenum ferrite.

Multi-cationic spinel compounds are solids that exhibit polar faces. X-ray Photoelectron spectroscopy revealed the main phenomena allowing the stabilization of these faces, carried out as a function of the material treatment, particularly the cooling rate after thermal treatment at a high temperature (1200°C). This study showed that, whatever the cooling rate, each sample is subject to a significant hydroxylation that reduces the polarity. Nevertheless, it appears that the hydroxyl group content at the surface is a strong function of the cooling rate. Indeed, whereas quenched materials are subject to high levels of hydroxylation, slowly cooled samples are sparingly hydroxylated. This phenomenon corresponds to the fact that, during a slow cooling down, a change of the cationic composition in the topmost layers of the solids is able to occur, inducing a decrease of the polarity. Moreover, this segregation comes with a change of the grain surface morphology, leading to less polar faces. Copyright © 2002 John Wiley & Sons, Ltd.

Thin films of TiNxOy were deposited by d.c. magnetron sputtering on glass substrates using an (Ar+,N2) plasma and Ti target. The N2 partial pressure was changed from 2.3 × 10−4 mbar to 4.6 × 10−3 mbar in order to obtain films with increasing nitrogen contents. X-ray photoelectron spectroscopy was used to determine the as-deposited composition. The presence of oxygen, which is probably due to contamination from the residual atmosphere in the vacuum chamber, is always detected, both in the surface layers and in the bulk of the films, confirming the formation of TiNxOy. When the nitrogen partial pressure was increased, a maximum for the nitrogen content in the films was reached, corresponding to a TiN0.8O0.4 film composition. The nitrogen content of the films did not increase further for higher N2 partial pressures. X-ray diffraction showed that each deposited layer had a rock salt structure, isomorphic to that for TiN, in which some nitrogen atoms would seem to be substituted by oxygen atoms in the anionic sub-lattice. Moreover, this crystalline TiNxOy phase is super-stoichiometric with this deposition method. To the best of our knowledge such results have already been observed on TiN films but it is the first time that they have been presented for TiNxOy thin layers. Copyright © 2002 John Wiley & Sons, Ltd.