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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.

Sol-gel x TiO 2 (100 − x )SiO 2 nanocomposite thin films with x = 0, 25, 50, 75 and 100 mol % were dip-coated on glass and silicon substrates. The influence of the composition on structure, morphology and optical properties was studied by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electronic microscopy, monochromatic ellipsometry at λ = 632.8 nm and ultraviolet–visible absorbance spectroscopy. The optical properties were discussed on the basis of the microstructure. After annealing at 500 °C, results showed high pure materials, homogenous crack-free surfaces with good adherence and high optical qualities. The 100% TiO 2 crystallizes in the anatase phase and exhibits nanograins of 6 to 10 nm in size. However, all the other compositions are amorphous with comparable grains around 4 nm in size. The averaged transmittance decreases with increasing the TiO 2 content but remains higher than 90%. Whatever the composition, the coating thickness increases linearly as the withdrawal speed increases from 10 to 54 mm/minute. The relationship between refractive index and composition was analyzed by fitting the experimental data to different theoretical models for the refractive index of mixed films. Results showed that depending on the withdrawal speed, the data can properly fit either the Drude or the linear models. Thus, the film thickness can be adjusted by the control of the withdrawal speed. However, the control of the composition allows easily the tuning of the refractive index from 1.48 to 2.18 at λ = 632.8 nm to achieve optimum anti-reflection characteristics. Different anti-reflection designs of both single and double layers were experimentally examined. Gains (assigned to the reduction of reflection losses) up to 54 and 63% were predicted with 75% TiO 2 single-coating and SiO 2 /TiO 2 double-coatings respectively.

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.

We studied in this work the influence of the wavelength (532 vs. 1064 nm) on the insertion of nitrogen in titanium targets by surface laser treatments in air. The laser pulses were of 5 ns and the irradiance was lower than 25 × 10 12 W/m 2 . Results obtained using a frequency-doubled Nd:YAG laser at 532 nm were compared with those previously reported for laser treatments at 1064 nm. Nuclear reaction analysis and micro-Raman spectroscopy were used for determining the composition and the structure of the surface layers, respectively. Results showed the lower efficiency of irradiation at 532 nm for nitrogen insertion, which is possible only above threshold conditions depending on both the laser irradiance and the number of cumulated impacts per point. This was explained as being due to a higher ablative effect in the visible range. The insertion of oxygen giving rise to the growth of titanium oxynitrides was also discussed.

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.

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.

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

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 (

Undoped TiO 2 and Ag–TiO 2 (up to 23 at.% Ag) cermet thin films and polycrystalline powders have been prepared by sol–gel process. Their structure, composition, surface morphology and optical properties have been investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and ultraviolet–visible spectroscopy (UV–VIS spectroscopy). It has been observed that while Ag does not form a solid solution with TiO 2 , it promotes the anatase to rutile phase transformation. The transformation temperature decreases from 827 °C for undoped TiO 2 to about 650 °C for 23 at.% Ag-doped TiO 2 . SIMS analyses show that Ag is mostly present on the surface of the films. XPS studies confirm that these Ag are in the Ag 0 state. Optical analyses show that with increasing Ag content, the refractive index ( n ) increases and the optical absorption behavior of the cermet films is modified, but the band gap of the anatase TiO 2 is not influenced.

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.

The adsorption site of sodium on the TiO2(1 1 0)–(1 × 1) surface was studied by extended X-ray absorption fine structure. For coverage ranging between 0.25 and 0.5 ML, we find that sodium is on an ‘in-between' site where it is bound to two bridging oxygen atoms at 2.25 Å and one in-plane oxygen atom at 2.40 Å, in full agreement with DFT calculations. At higher coverage the site becomes an hollow site where the sodium atom is equidistant to the three oxygen atoms at 2.30 Å, while metallic sodium clusters are also formed at the surface.

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.

Resonant spectroscopies offer a new opportunity to get more insight into excited electronic states by studying line shapes and intensities of decay processes. For photon excitations in the pre-K-edge region, the Ti KL 2,3 L 2,3 Auger spectra in TiO 2 show additional peaks when an electron is promoted in localized d-like states via a quadrupolar transition. This resonant process is used to unravel the respective contributions of quadrupolar and dipolar transitions to the absorption edge prepeaks.

TiO 2 thin films were deposited on (100) GaAs substrates by LP-MOCVD with deposition temperatures ( T d ) ranking from 450 to 750 °C. The structure of these layers was studied by X-ray diffraction (XRD) and Raman spectroscopy. The growth of the TiO 2 anatase phase was observed for T d T d >600 °C. Finally, X-ray photoelectron spectrometry (XPS) and secondary ion mass spectroscopy (SIMS) experiments showed the presence of small quantities of Ga and As through the whole film thickness, slightly increasing at the surface of the layers. This result was related to the SEM observations and explained by considering the growth conditions.

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.

TiO2/TiNxOy superlattices were grown by Low Pressure-Metal-Organic Vapor Phase Epitaxy (LP-MOVPE) technique at deposition temperatures ranking from 650 to 750°C. The growth was performed on top of TiO2(110) rutile substrates. Intense peaks observed in the X-rays rocking curves and θ-2θ diffraction patterns show the presence of crystalline epilayers. The TiNxOy layers were grown in a (200) cubic structure on the (110) quadratic TiO2 epilayer structure. Transmission electron microscopy confirmed the XRD results and showed the formation of periodic and well structured epilayers.

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

TiN(O)–TiO 2 thin films were prepared on Si(1 0 0) by the low pressure organo metallic chemical vapor deposition (LP-OMCVD) method, using ammonia and titanium isopropoxide as precursors. In order to complete previous characterizations, an Ar + bombardment/XPS coupled study was carried out. This method is based on the fact that the behavior of a compound towards an ion bombardment is a function of its composition. In particular, Ar + bombardment of TiO 2 (whatever its form) leads to a preferential sputtering of oxygen atoms with subsequent reduction of titanium and formation of Ti 3+ and Ti 2+ easily detectable by XPS from a significant broadening of the Ti 2p lines. In the opposite, no broadening of the Ti 2p lines is observed for an Ar + bombardment of TiN. Then, with this method, we succeed in showing that films obtained at high temperature (≥700°C) contain only a TiN x O y phase which is isomorphic to TiN. In the coatings, synthesized at low temperatures (≤650°C) amorphous TiO 2 has been evidenced.

TiNxOy/TiO2 multilayers have been grown by LP-MOCVD using titanium isopropoxide (TIP) precursor during the whole growth, but with an ammonia flow interrupted for the TiO2 layers. The one step growth process used to grow these structures allowed to stack the conducting and insulating layers without any growth breakdown. SIMS and TEM analyses showed the presence of an alternated insulating/conducting layers structure. Moreover, electrical measurements allowed to measure the dielectric part of insulating TiO2 stacked in these structures, whose permittivity was found to be about 80 for a MOS structure. Thus, such multilayers may lead to very promising applications in the microelectronics field.

Titanium oxinitride thin films have been grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) using titanium isopropoxide, Ti(OCH(CH 3 ) 2 ) 4 (TIP) and NH 3 precursors in a growth temperature range from 450 to 750°C on sapphire substrates. The electrical behaviour of these films was studied between 400 and 173 K, revealing three different behaviours, ranking from a hopping conductivity (450–500°C) to a conducting one (700–750°C), with a dual behaviour for the intermediate growth temperatures. Moreover, at room temperature, both conductimetry and impedance spectroscopy highlighted a percolation behaviour, interpreted in terms of continuum percolation. The effective media theory equations led to the usual percolation parameters ( s , t , Φ c ) and the difference between the values thus obtained and the expected ones was explained in terms of anisotropic percolation occurring in the columnar film structure.

Exposures to oxygen at room temperature and annealings under vacuum were carried out on deposits obtained from molybdenum interacting with (1 1 0) TiO 2 surfaces in order to obtain molybdenum oxide ultra thin films. Exposures to oxygen at room temperature show that the interfacial molybdenum oxide layers resulting from the TiO 2 /Mo interactions are inactive towards oxygen whereas the metallic molybdenum clusters, which grew on top of the interfacial layers, oxidise into MoO 3 . Besides, during annealings under vacuum, substrate oxygen anions can diffuse into the deposit. Thus, between 400 and 500°C, molybdenum oxide layers are progressively oxidised into MoO 2 . Moreover, from the annealing temperature, it is possible to control the film oxidation and to select its stoichiometry. At higher temperatures, MoO 2 layers oxidise, leading to MoO 3 clusters which sublimate restoring a clean TiO 2 surface. As concerns the metallic clusters, if they are exposed to air and then oxidised in MoO 3 prior to annealing, they sublimate below 300°C.

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.

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.

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.

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.

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.

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.

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; 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; 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.