Phthalocyanine–titanate nanotubes: a promising nanocarrier detectable by optical imaging in the so-called imaging window

International audience; TiONts-phthalocyanine nanohybrids combining an efficient optical probe and a promising nanovector have been developed in a step-by-step approach and were thoroughly characterized. Each 150 nm long TiONts-Pc bear ca. 450 Pc. Three nanohybrids were prepared including three different linkers in quest for the best stability.

Scale composition and oxidation mechanism of the Ti–46Al–8Nb alloy in air at 700 and 800 °C

It is known that the oxide scale formed on TiAl alloys is generally composed of a mixture of alumina (Al2O3) and titania (TiO2). The presence of niobium changes the activities of Ti and Al and influences the kinetics of oxidation and oxide layer composition. In this work, the Tie46Ale8Nb alloy was subjected to cyclic oxidation in air at 700 � C (for 2 and 24 h) and 800 � C (for 300 h). Scale composition was analyzed by means of different techniques including X-ray photoelectron spectroscopy, X-ray diffraction and secondary ion mass spectroscopy. The scale consisted of several layers. The outer layer was built of alumina (amorphous or with very fine grains), whereas the inner layer e mainly …

Tuning of interfacial charge transport in polyporphine/phthalocyanine heterojunctions by molecular geometry control for an efficient gas sensor

Abstract Owing to high interfacial conductivity, organic heterostructures hold great promises to augment the electrical performances of electronic devices. In this endeavor, the present work reports fabrication of novel polyporphine/phthalocyanine heterostructures and investigates the modulation of charge transport induced by structural change of polyporphine and its implication on ammonia sensing properties. Polyporphines materials are electrosynthesized by oxidation of zinc(II) porphine monomer that corresponds to the fully unsubstituted porphyrin. At less-positive anodic potential, low conducting meso,meso-singly-linked type-1 polymer (pZnP-1) is formed in which a monomer unit stays orth…

Flash annealing influence on structural and electrical properties of TiO2/TiO/Ti periodic multilayers

Abstract Multilayered structures with a 40 nm period composed of titanium and two different titanium oxides, TiO and TiO 2 , were accurately produced by DC magnetron sputtering using the reactive gas pulsing process. These multilayers were sputtered onto Al 2 O 3 sapphire to avoid substrate compound diffusion during flash annealing (ranging from 350 °C to 550 °C). Structure and composition of these periodic TiO 2 /TiO/Ti stacks were investigated by X-ray diffraction, X-ray photoemission spectroscopy and transmission electronic microscopy techniques. Two crystalline phases α-Ti and fcc-TiO were identified in the metallic-rich sub-layers whereas the oxygen-rich ones were composed of a mixture…

Enhancement of visible light photoelectrocatalytic activity of ZnO(core)/TiO2(shell) composite by N-doping and decorating with Au0 nanoparticles

Abstract The composites consisting of ITO-supported ZnO nanorods covered with TiO2 shell were doped with nitrogen and decorated with gold nanoparticles in order to improve their photocatalytic activity under visible light. N-doped TiO2 (TiO2(N)) was prepared under mild conditions through a simple sol-gel synthesis in the presence of NH4Cl. Such procedure results in formation of a highly porous shell of TiO2(N) on the ZnO nanorods. The gold nanoparticles (AuNPs) of the size 7–25 nm were grafted onto the surface of TiO2 as well as TiO2(N) by a photodeposition method from aqueous solution of [AuCl(4-x)(OH)x]− precursor at pH 6.7. The composition and microstructure of the prepared samples were …

Electroactive polymeric material with condensed structure on the basis of magnesium(II) polyporphine

International audience; Previous publication of the authors presented evidences that electroch emical oxidation of Mg(II) porphine (fully unsubstituted porphyrin, MgP) in acetonitrile (AN) at a very low potential leads to deposition of films at electrode surface corresponding to typical electroactive polymers, with their reversible transition betwee n the electronconducting and insulating states depending on the electrode potential/oxidation level ("film of type I"). It is demonstrated in the actual publication that these films in contact with a monomer-free solution are subject to an irreversible transformation to quite a different material ("film of type II") under the influence of a high…

Nitrogen plasma pressure influence on the composition of TiNxOy sputtered films

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 …

Adsorption of gelatin during electrodeposition of copper and tin-copper alloys from acid sulfate electrolyte

International audience; An acid Cu–Sn deposition bath was developed, and copper and copper–tin coatings were electrodeposited on polycrystalline platinum. The effect of gelatin on copper and copper–tin electrodeposition from acid sulfate solutions has been investigated by a variety of electrochemical methods (voltammetric studies and electrochemical quartz crystal microbalance) as well as by morphologic technique (scanning electron microscopy). The electrochemical results have shown that the overpotential is required when gelatin is added, indicating the presence of interaction between the additive and the coating. From the results of X-ray photoelectron spectroscopy, PM-IRRAS and cyclic vo…

Magnesium(II) polyporphine: The first electron-conducting polymer with directly linked unsubstituted porphyrin units obtained by electrooxidation at a very low potential

Abstract Electrooxidation of magnesium(II) porphine, a totally unsubstituted porphyrin, in acetonitrile solution under potentiostatic or potentiodynamic regime leads to a polymer film at the electrode surface. Polymer deposition takes place at extremely low potential, several hundred mV less positive even compared to the deposition potential for pyrrole or EDOT (at identical monomer concentrations) in the same solvent. Film thickness can be controlled by the passed deposition charge. This material and its THF-soluble fraction have been characterized by various electrochemical methods as well as by UV–visible and IR spectroscopies, XPS, XRD and MALDI-TOF techniques. This analysis has allowed…

Structure and chemical bonds in reactively sputtered black Ti–C–N–O thin films

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 nitro…

Chemical characterization of gallium droplets grown by LP-MOCVD.

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

Improve the dielectric properties of PrSrNi0.8Mn0.2O4 compounds by longer mechanical milling

Abstract Structural and dielectric properties of PrSrNi 0.8 Mn 0.2 O 4 ceramics elaborated by a rapid method combining mechanical milling and heat treatment were studied for the first time. The raw materials are milled at different times ( t mil  =  0, 5, 10, 20 and 30 h) and annealed at 1300 °C for 8 h to produce a revealed PrSrNi 0.8 Mn 0.2 O 4 single phase, exhibiting tetragonal structure with space group I 4/ mmm . This result was confirmed by using the TEM/ED pattern for sample milled at 30 h using the [001] orientation. The corresponding lattice images show a well-ordered compound, indicating the absence of stacking faults and the growth of the crystallites. Giant dielectric response …

Estimation of band alignment at CdS/Cu 2 ZnSnS 4 hetero‐interface by direct XPS measurements

The Role of Zr in the High-Temperature Oxidation of Fe<sub>3</sub>Al

The paper describes an examination of the effect of the addition of zirconium as a third element on the heat-resisting properties and explains the high temperature oxidation mechanism of Fe3Al intermetallic compounds. The Fe3Al and Fe3Al-0,05Zr specimens have been isothermally oxidized in the temperature range of 1173-1473 K in synthetic air for 100 hrs. The formed oxide layer, about 1,5-2 μm thick, was Al2O3. An examination of the cross-sectioned scales by SEM-EDS showed that the alumina layer consisted of a small inner columnar layer and an outer equiaxed grain layer. Additionally, very fine (50-150 nm) oxide grains rich in Zr, further identified as ZrO2, were found across the alumina sca…

Characterization of [Cu]-MCM-41 by XPS and CO or NO adsorption heat measurements

We report the characterization of copper doped MCM-41 prepared by original direct synthesis by XPS and adsorption calorimetry of CO and NO, which are selective molecular probes for Cu(I) and Cu(II) respectively. Investigation of the nature of the copper ions in this particular calcined Cu-MCM-41 by NO adsorption calorimetry shows that two types of energetically distinct adsorption sites exist, meaning the presence of two populations of Cu(II) species differently coordinated to the silica surface in quasi-equimolar concentration, as ascertained by XPS data. A small amount of Cu(I) was also detected, probably stemming from a partial reduction upon the successive vacuum treatments. The respect…

Impact of optical and structural aging in As_2S_3 microstructured optical fibers on mid-infrared supercontinuum generation

We analyze optical and structural aging in As2S3 microstructured optical fibers (MOFs) that may have an impact on mid-infrared supercontinuum generation. A strong alteration of optical transparency at the fundamental OH absorption peak is measured for high-purity As2S3 MOF stored in atmospheric conditions. The surface evolution and inherent deviation of corresponding chemical composition confirm that the optical and chemical properties of MOFs degrade upon exposure to ambient conditions because of counteractive surface process. This phenomenon substantially reduces the optical quality of the MOFs and therefore restrains the spectral expansion of generated supercontinuum. This aging process …

A multi-step mechanism and integrity of titanate nanoribbons.

A one-step hydrothermal treatment of TiO2 powders under strongly basic conditions has been used to synthesize titanate nanoribbons. The nanoparticles were thoroughly characterized using several methods including transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectrometry (XPS) to determine their morphological, structural and chemical characteristics. The influence of the nature and size of the TiO2 precursor and of the reaction duration on the formation of the nanoribbons was investigated. The conditions required to obtain only titanate nanoribbons with a width ranging from 100 to 200 nm and several tens of micrometers in length w…

A glassy carbon electrode modified by a triply-fused-like Co( ii ) polyporphine and its ability for sulphite oxidation and detection

This article presents a Co(II) polyporphine conductive polymer easily and rapidly obtained (less than 2 h 30 min) on the surface of a glassy carbon electrode from the transformation of an initial Mg(II) porphine solution in a four-step process (including electrochemical and chemical stages). The intimate molecular structure is argued on the basis of the electrochemical response of the modified electrode, as well as its surface characterization. Owing to its apparent stability in water over potential cycling and its high density in active Co(II) centers, the electrosynthesized film shows its ability to catalyze sulphite oxidation in aqueous solutions. The mechanism of this molecular catalysi…

Surface modifications induced by nanosecond pulsed Nd:YAG laser irradiation of metallic substrates

International audience; Substrate surface preparation is a key step in coating deposition process. In recent years, pulsed laser cleaning has emerged as a possible technique to challenge the traditional preparation methods (based on degreasing and eventually grit-blasting). The laser operated at short-pulse mode offers high cleaning efficiency and therefore has been largely used. In a specific process named PROTAL®, a nanosecond pulsed laser is introduced to prepare the surface simultaneously to thermal spraying, with the purpose of eliminating the contaminants and generating favorite surface conditions for coating deposition. This study aims at clarifying some fundamental aspects of nanose…

Nanodiamond‐Palladium Core–Shell Organohybrid Synthesis: A Mild Vapor‐Phase Procedure Enabling Nanolayering Metal onto Functionalized sp 3 ‐Carbon

Effect of surface finishing on the oxidation behaviour of a ferritic stainless steel

Abstract The corrosion behaviour and the oxidation mechanism of a ferritic stainless steel, K41X (AISI 441), were evaluated at 800 °C in water vapour hydrogen enriched atmosphere. Mirror polished samples were compared to as-rolled K41X material. Two different oxidation behaviours were observed depending on the surface finishing: a protective double (Cr,Mn) 3 O 4 /Cr 2 O 3 scale formed on the polished samples whereas external Fe 3 O 4 and (Cr,Fe) 2 O 3 oxides grew on the raw steel. Moreover, isotopic marker experiments combined with SIMS analyses revealed different growth mechanisms. The influence of surface finishing on the corrosion products and growth mechanisms was apprehended by means o…

Electrochemistry of methylene blue at an alkanethiol modified electrode

International audience; Gold surfaces were derivatized with decanethiol. The electrochemistry of methylene blue at these modified electrodes was investigated in function of the gold cleaning process and compared with the results obtained at a bare gold electrode. Cyclic voltammetry at low methylene blue concentrations (c(MB) <= 16 mu M) yielded surface behavior data. The properties of the film vary with the electrode pretreatment. Without electrochemical cleaning step, the standard potential at a gold electrode modified with 1-decanethiol is nearly the same as on a bare gold electrode. On the other hand, when the electrode is electrochemically cleaned before adsorption of the alkanethiols, …

Inverse growth transport in thermal chromia scales on Fe–15Cr steels in oxygen and in water vapour and its effect on scale adhesion

Chromia scales of near equivalent thickness were thermally grown on Fe–15Cr steels in 16O2 followed by 18O2 and in H216O followed by H218O. SIMS oxygen isotope profiles showed that oxidation in oxygen proceeded by outward chromium transport, whereas oxidation in H2O involved inward transport of hydroxide species. Adhesion measurements using room temperature tensile testing could quantify adhesion energy: 20 J m−2 for O2-grown scales and 80 J m−2 for scales formed in H2O, a result of this mass transport inversion.

Sources d'hétérogénéité d'un assemblage par soudage par diffusion homogène de tôles en acier austénitique inoxydable

Ce document presente un apercu des heterogeneites de microstructure aux interfaces qui peuvent etre rencontrees lors du soudage par diffusion homogene d'un assemblage de toles. Un assemblage homogene a finalement ete realise avec l'obtention de proprietes mecaniques tres satisfaisantes. Pour finir, une piste de reflexion est apportee afin d'ameliorer les proprietes des assemblages.

Perovskite thin films grown by direct liquid injection MOCVD

Abstract The continuous scaling down of devices dimensions, in silicon technology, imposes to replace silicon dioxide. Among the potential candidates for new capacitors, some perovskite structure materials (such as titanate or zirconate) show interesting characteristics. The first way to develop perovskite films is to use a mixture of two β-diketonates by varying the solution's cationic ratio. However, our previous results on SrZrO3 showed that a wide parametric study had to be carried on. Another way is to design novel heterometallic precursors that contain both cations on the same molecule. The ligands could be chosen so that peculiar evaporation and decomposition temperatures could be ob…

Structural and in depth characterization of newly designed conducting/insulating TiN O /TiO2 multilayers obtained by one step LP-MOCVD growth

Abstract 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 microelectroni…

Influence of the dissolution of MnS inclusions under free corrosion and potentiostatic conditions on the composition of passive films and the electrochemical behaviour of stainless steels

Abstract The influence of the dissolution of MnS inclusions at the OCP value and 400 mV versus SCE on the chemical composition of passive films and the electrochemical behaviour of resulfurized austenitic stainless steel was studied in 1 M NaClO 4 , pH 3, solution using SIMS, XPS, electrochemical impedance spectroscopy and the electrochemical microcell technique. The electrochemical dissolution (at 400 mV versus SCE) of inclusions occurred uniformly along the interface and this process was almost complete after 25 min immersion. A small amount of sulfur was detected on the matrix that exhibited a wide passive range. By contrast, the dissolution process under free corrosion was not uniform a…

Influence de la composition chimique du film passif et des contraintes résiduelles sur le comportement micro-électrochimique des aciers inoxydables duplex en milieux contenant des ions chlorure

Le comportement micro-electrochimique d’aciers inoxydables duplex a ete determine dans des milieux contenant des chlorures, a l’aide de la technique de la microcellule electrochimique (capillaires de 30 µ m). Les resultats obtenus ont ete analyses en considerant la composition chimique du film passif. Des relations quantitatives entre les parametres electrochimiques et la distribution en chrome et fer dans la couche passive ont ete trouvees. Comme les deux phases ont des proprietes mecaniques differentes, un champ de contraintes residuelles heterogene est genere a la surface de l’alliage. Une methode thermo-mecanique basee sur la simulation numerique par elements finis a ete utilisee pour c…

Improving the high temperature oxidation resistance of pure titanium by shot-peening treatments

International audience; Shot-peening (SP) treatments have shown their capacity to improve the oxidation resistance of titanium and zirconium thanks to the large compressive stresses and the surface hardening induced by this mechanical process. However, shot-peening treatments can produce a surface chemical deposit, which can modify the high temperature oxidation resistance. Here, we study pure titanium samples shot-peened with different type of balls: tungsten carbide, alumina or glass. The oxidation behavior was studied at 700 °C in dry air by thermo gravimetric analysis for short isotherm oxidation periods up to 100 h. Also, long oxidation tests (3000 h) at 700 °C were performed with an i…

Passive properties of lean duplex stainless steels after long-term ageing in air studied using EBSD, AES, XPS and local electrochemical impedance spectroscopy

Abstract Passivity of duplex stainless steel was studied after long-term ageing in air using local electrochemical impedance spectroscopy, AES, XPS and EBSD. After mechanical polishing, the passive film was homogeneous and had a capacitive behaviour described by the CPE. After long-term ageing, a small thickening was detected and O2−/OH− was significantly higher in the austenite than in the ferrite. Austenite behaved as a blocking electrode whereas two capacitive loops were observed in the ferrite (low value of O2−/OH). The loop at high frequencies was related with the oxygen reduction and the loop at low frequencies was connected with the passive film.

Comparison of different methods for evaluating the transmission function of a two-stage cylindrical mirror analizer in XPS applications

Three different evaluations of the energy dependence of the transmission-detection function of a two-stage cylindrical electron analyzer have been obtained by resorting to three established procedures. Their relative merits have been tested as follows. First they have been used to correct raw XPS spectra of clean Cu, Ag and Au surfaces. Next, the secondary electron background has been subtracted using Tougaard's method. Finally, the primary electron spectra so obtained have been reanalyzed by peak area measurement in the frame of the modern formalism for quantitative XPS analysis. Ideally a constant residual value should thus be obtained. The variability of these residuals with peak energy …

Low Conductive Electrodeposited Poly(2,5-dimethoxyaniline) as a Key Material in a Double Lateral Heterojunction, for Sub-ppm Ammonia Sensing in Humid Atmosphere

We present a new device called a double lateral heterojunction (DLH) as an ammonia sensor in humid atmosphere. It combines polyaniline derivatives in their poor conducting state with a highly conductive molecular material, lutetium bisphthalocyanine, LuPc2. Polyaniline and poly(2,5-dimethoxyaniline) are electrodeposited on ITO interdigitated electrodes, leading to an original device that can be obtained only by electrochemistry and not by other solution processing techniques. Both polymers lead to highly conducting materials that require a neutralization step before their coverage by LuPc2. While the device based on polyaniline shows ohmic behavior, the nonlinear I- V characteristics of the…

Investigation on sol–gel synthesized Ag-doped TiO2 cermet thin films

Abstract 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 fo…

Influence of the Chemical Dissolution of MnS Inclusions on the Electrochemical Behavior of Stainless Steels

Immersion of stainless steel containing a well-controlled density of MnS inclusions in 1 M NaCI, pH 3 leads to the chemical dissolution of these heterogeneities. This process was studied using in situ atomic force microscopy and the dissolution rate of MnS inclusions was estimated between 0.01 and 0.19 μm 3 /min. The effects of MnS dissolution on the chemical composition and the local electrochemical behavior of the specimen surface were investigated using secondary ion mass spectroscopy, X-ray photoemission spectroscopy, and the electrochemical microcell technique. It was shown that stable CrS and unstable FeSO 4 were formed. The size of the areas around MnS inclusions affected by the pres…

Changes in surface stress, morphology and chemical composition of silica and silicon nitride surfaces during the etching by gaseous HF acid

Abstract HF acid attack of SiO2 and Si3N4 substrates is analyzed to improve the sensitivity of a sensor based on microcantilever. Ex situ analysis of the etching using XPS, SIMS and AFM show significant changes in the anisotropy and the rate of the etching of the oxides on SiO2 and Si3N4 surface. Those differences influence the kinetic evolution of the plastic bending deflection of the cantilever coated with SiO2 and Si3N4 layer, respectively. The linear dependence between the HF concentration and the Si3N4 cantilever bending corresponds to a deep attack of the layer whereas the non-linear behavior observed for SiO2 layer can be explained by a combination of deep and lateral etching. The ca…

Surface modifications induced by pulsed-laser texturing—Influence of laser impact on the surface properties

Abstract Laser cleaning technology provides a safe, environmentally friendly and very cost effective way to improve cleaning and surface preparation of metallic materials. Compared with efficient cleaning processes, it can avoid the disadvantages of ductile materials prepared by conventional technologies (cracks induced by sand-blasting for example) and treat only some selected areas (due to the optical fibers). By this way, laser technology could have several advantages and expand the range of thermal spraying. Moreover, new generations of lasers (fiber laser, disc laser) allow the development of new methods. Besides a significant bulk reduction, no maintenance, low operating cost, laser f…

Grafting and characterization of dodecylphosphonic acid on copper: Macro-tribological behavior and surface properties

International audience; Thin film of n-dodecylphosphonic acid (DDPA) was prepared on a copper oxide substrate via a molecular self-assembly process. The composition, structure, organization, surface energy, morphology, and electrochemical behavior of the DDPA filmwere characterized bymeans of X-ray photoelectron spectroscopic analysis (XPS), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), contact angle measurement v(CAM), microscopic observations, and electrochemistry. The friction behavior of the DDPA film adsorbed on copper oxide substrate sliding against a Si3N4 ball was examined on a linear reciprocating tribological tester. Worn surfaces of the DDPA film…

Auto-assembly of nanometer thick, water soluble layers of plasmid DNA complexed with diamines and basic amino acids on graphite: Greatest DNA protection is obtained with arginine.

Abstract We have investigated the ability of diamines as well as basic amino acids to condense DNA onto highly ordered pyrolytic graphite with minimum damage after re-dissolution in water. Based on a bibliographic survey we briefly summarize DNA binding properties with diamines as compared to basic amino acids. Thus, solutions of DNA complexed with these linkers were drop-cast in order to deposit ultra-thin layers on the surface of HOPG in the absence or presence of Tris buffer. Atomic Force Microscopy analyses showed that, at a fixed ligand-DNA mixing ratio of 16, the mean thickness of the layers can be statistically predicted to lie in the range 0–50 nm with a maximum standard deviation ±…

Improvement of photocatalytic and photoelectrochemical activity of ZnO/TiO2 core/shell system through additional calcination: Insight into the mechanism

Abstract ZnO/TiO2 composites were prepared by sol-gel deposition of TiO2 on ZnO nanorods hydrothermally grown on electrically conductive indium tin oxide substrate (ITO). It has been shown that the ZnO/TiO2 interface plays a key role in enhancement of photodecomposition of methylene blue (MB) used as a model test pollutant, under monochromatic light irradiation (400 nm). The increase of photocatalytic activity was attributed to the shift of absorption edge of ZnO/TiO2 towards visible light in comparison with bare TiO2. Further enhancement of photocatalytic activity of ZnO/TiO2 was achieved through its additional calcination at 450 °C for 3 h. This treatment brings 40% increase in the rate o…

Effect of Reaction Parameters on Composition and Morphology of Titanate Nanomaterials

International audience; In the present article, we report the synthesis of titanate nanotubes and nanoribbons with controlled morphology, structure, and chemical composition depending on the main parameters of the synthesis. Hydrothermal processing time, grain size of the precursor, type of agitation, and acid treatment were investigated, and the principal controversies mentioned in the literature such as nanotube crystallographic structure, their chemical composition, and acid treatment impact are discussed. These controversies may be due to the heterogeneities present in all the samples and are rarely considered in the literature. These nanostructures were characterized by Raman spectrosc…

Influence of modification time and high frequency ultrasound irradiation on self-assembling of alkylphosphonic acids on stainless steel : electrochemical and spectroscopic studies

International audience; Self-assembly of alkylphosphonic acids on stainless steel was investigated under different conditions. Four different alkylphosphonic acids exhibiting alkyl chain of various size were synthesized and studied: butylphosphonic acid (C4P), octylphosphonic acid (C8P), decylphosphonic acid (C10P), and hexadecylphosphonic acid (C16P). Electrochemistry experiments were extensively carried out in order to determine electrochemical surface blocking of adsorbed layers in function of grafting time. In term of surface blocking, an 8h modification time was optimal for all alkylphosphonic acids. Longer immersion times lead to degradation of adsorbed layers. For the first time, gra…

Investigation of absorber and heterojunction in the pure sulphide kesterite

This paper aims to study the properties of the absorber layer and the heterojunction in kesterite solar cells. The Cu2ZnSnS4 (CZTS) thin films were layered on a glass substrate from a colloidal solution of metal salts and thiourea dissolved in a mixture of water and ethanol and deposited by spin coating technique. The samples were then heat treated in a furnace, in the presence of sulphur powder and under a nitrogen gas flow. The results revealed the formation of homogeneous layers of a pure kesterite phase of CZTS crystallites after heat treatment with correct stoichiometry and oxidation states. The optical transmission measurements indicate an energy band-gap of 1.4 eV and an absorption c…

Low Temperature H2S Removal with Metal-Doped Nanostructure ZnO Sorbents: Study of the Origin of Enhanced Reactivity in Cu-Containing Materials

Sulfidation of pure and metal-doped ZnO nanostructure sorbents (M0.03Zn0.97O, M = Fe, Co, Ni, Cu) was studied in order to clarify the effect of metal on the transformation kinetics at 200−350 °C. The solids were prepared by coprecipitation from metal nitrate solution followed by calcination at 400 °C. Reaction with H2S was studied by thermal gravimetric analysis (TGA) using a gas mixture containing 0.2 vol % H2S in equimolar H2−N2. It was found that at 350 °C the TGA sulfidation profiles of all studied samples are similar, with the interface reaction being the main rate-determining step. After lowering the temperature to 250 °C the transformation of Cu0.03Zn0.97O continues to be controlled …

Interface reactivity study between La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode material and metallic interconnect for fuel cell

Abstract Interface reactivity between La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode material and metallic interconnect (Crofer22APU) was investigated in laboratory air at 700 °C. Due to the interconnect geometry, two interfaces have been analysed: (i) interconnect rib/cathode interface (physically in contact); (ii) the interface under the channel of interconnect. In both cases, formation of a parasite phase was observed after various ageing treatments (20 h, 100 h and 200 h). However, the growth of the determined SrCrO4 parasite phase depends on interface type and on ageing time. Two different mechanisms have been established in function of interface type: (i) SrCrO4 phase was formed after solid …

Electrocatalytic properties of manganese and cobalt polyporphine films toward oxygen reduction reaction

International audience; Novel member of polymetalloporphines, namely manganese polymetalloporphine of type I (pMnP-I) obtained by ion exchange from magnesium polyporphine of type I (pMgP-I) is reported for the first time and compared to its cobalt analogue (pCoP-I). Both polymer films have been obtained via two-step procedure: demetaladon of the pMgP-I electrode film via its exposure to trifluoroacetic acid solution, resulting in formation of the metal-free polyporphine of type I (pH(2)P-I) followed by electrochemically induced incorporation of Co or Mn ions from the acetonitrile solution of cobalt and manganese perchlorates. A further oxidative transformation of pCoP-I, polymer films has l…

Synthesis and Characterization of Palladium Nanoparticle/Polypyrrole Composites

In this work, a simple non-template one-step method for the synthesis of 2.0−2.5 nm palladium nanoparticles encapsulated into a polypyrrole shell via direct redox reaction between palladium(II) acetate and pyrrole in acetonitrile medium is described. Palladium nanoparticles are found to be able to self-organize into spherical Pd/PPy composites. The size of the Pd/PPy composite particles and Pd content in the composite depend strongly on the concentration of the palladium salt component. The combination of elemental CHNS and thermogravimetric (TGA) analysis was used to determine a high (∼40 wt %) content of palladium, which is in a good agreement with EDX data. The process of Pd/PPy composit…

Comprehensive Study of Poly(2,3,5,6-tetrafluoroaniline): From Electrosynthesis to Heterojunctions and Ammonia Sensing.

In this work, we report for the first time on a comprehensive study of poly(2,3,5,6-tetrafluoroaniline) (PTFANI). Contrary to the nonfluorinated polyaniline (PANI) or its analogues bearing one fluorine atom, PTFANI is a poorly conductive material. We present a comprehensive study of the electrosynthesized PTFANI from its monomer in an acidic aqueous medium. PTFANI was fully characterized by a potential-pH diagram, spectroelectrochemistry, and electrochemical quartz crystal microbalance (EQCM) measurements, as well as by a morphological study. Combined with the X-ray photoelectron spectroscopy (XPS) analysis, it allowed us to understand the redox properties of this polymer compared to those …

Elaboration and characterization of barium silicate thin films.

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

Phase mixture in MOCVD and reactive sputtering TiOxNy thin films revealed and quantified by XPS spectra factorial analysis

International audience

The use of local electrochemical probes and surface analysis methods to study the electrochemical behaviour and pitting corrosion of stainless steels

Abstract In this paper, the electrochemical microcell technique is combined with ex situ (SIMS and XPS) and in situ (SVET) techniques to study the electrochemical behaviour and pitting corrosion of inclusion-contaning stainless steels. Dissolution of metallurgical heterogeneities, depassivation and pitting mechanisms are first discussed in 1 M NaClO4, pH 3, and 1 M NaCl, pH 3, by considering the chemical composition and morphology of inclusions. The influence of the chemical composition of passive films on the electrochemical reactions and the microgalvanic coupling processes occurring at the corrosion potential is also investigated on the same specimen microstructure.

Electrochemical behaviour of copper-nickel alloys as immobilisation matrices for the storage of fission products in CO2-enriched synthetic groundwater

International audience; The surface properties of nickel and copper alloys exposed to simulated French Callovo-Oxfordien ground-water (aerated and CO2-saturated solutions) have been evaluated from electrochemical impedance spectroscopy in conjunction with X-ray photoelectron spectroscopy. The kinetic reactions and physical properties of the layers grown on the alloy's surfaces, change versus the Ni content in the alloys and the presence of CO2 in the solution. Nickel alloys retain favourable passive properties in such environments, whereas oxide products on copper alloys are insufficiently protective when formed in the absence of dissolved oxygen in the electrolyte. A maximum addition of 30…

Mechanism of co-pyrolysis of coal-tar pitch with polyacrylonitrile

Abstract Co-pyrolysis of coal-tar pitch with polyacrylonitrile (PAN) and PAN oxidized in air at 300 °C was studied as a possible way of manufacturing of carbonaceous materials enriched in nitrogen. The thermal behaviour of components and blends was evaluated by thermogravimetry and optical microscopy of solid residues. The transformation of nitrogen functional groups on co-treatment was monitored using elemental analysis, infrared spectroscopy and X-ray photoelectron spectroscopy. Oxidized polymer behaved as an inert during co-pyrolysis. In contrast, strong interactions of unoxidized PAN with pitch could be deduced from enhanced residue yield and extensive deterioration of the optical textu…

Detection of gas trace of hydrofluoric acid using microcantilever

Abstract Microcantilevers have been used as a gas sensor in order to detect Hydrofluoric acid (HF) in the concentration range of 0.26–13 ppm. Silicon derived elements (Si 3 N 4 , SiO x ) were chosen to serve as chemical sensitive layer. Cantilever deflection and frequency shift were analyzed and compared as a function of the flow rate and the concentration of the HF molecules. The stoichiometry and roughness of the sensitive layer were found to be of major importance. Results show that the most appropriate signal at the lowest concentration ( x surface by HF. The frequency shift that is mainly governed by the loss in cantilever mass can be used at higher concentration.

Influence of the passive film properties and residual stresses on the micro-electrochemical behavior of duplex stainless steels

In the present paper, the chemical composition of passive films formed on both phases of two types of duplex stainless steels (UNS S31803 and UNS S32304) is determined at the micro-scale using Auger electron spectroscopy (AES). Samples were either mechanically polished (down to diamond pastes) or electrochemically etched in acidic solutions. The micro-electrochemical behavior of samples was then determined in sodium chloride media by means of the electrochemical micro-cell technique (capillary diameters of 30 μm). The results obtained were analyzed considering the passive film chemical composition. Quantitative relationships between electrochemical parameters and the distribution of chromiu…

Which tool to distinguish transient alumina from alpha alumina in thermally grown alumina scales?

International audience; Alumina scales constitute excellent protective barriers when they form on alumina-forming steels. If they keep tightly adherent to the underlying substrate, they isolate it from the surrounding aggressive atmosphere at high temperature. The protectiveness of the alumina scale is highly dependant upon its growth mechanism. The nucleation and transformation of transient alumina (mainly g-Al2O3 and y-Al2O3) is known to play an important role on alumina scale formation. It is therefore fundamental to characterise these transient alumina especially during the early stages of the oxidation process. The morphology of the transient alumina was observed by scanning electron m…

Influence of magnesium content on the corrosion resistance of the cut-edges of Zn–Mg-coated steel

Abstract The ability of Zn–Mg coatings (with magnesium content between 5.8 and 15.5 wt.%) to protect steel sheets has been evaluated with local electrochemical techniques (scanning vibrating electrode technique, microcapillary electrochemical cell) and rotating disk electrode, and compared with the corrosion protection afforded by a pure zinc coating. From immersion tests of coated steel cut-edges, it is observed that alloying zinc with magnesium leads to a decrease of the galvanic current between the coating and the steel surface, and to an improvement of the steel corrosion resistance after a drying period, due to the presence of magnesium in the corrosion products.

One pot microwave assisted synthesis of bisphosphonate alkene capped gold nanoparticles

International audience; A new synthetic pathway for the direct synthesis of water soluble gold nanoparticles (GNPs) already possessing terminal alkene functional groups was developed. This is achieved by using synthesized (1-hydroxy-1-phosphonopent-4-enyl)phosphonic acid (HMBPene), presenting advantages of the well known bisphosphonate coating applied to colloidal gold instead of metal oxides. The proposed protocol allowed an accurate control of the particle size in the 13–20 nm diameter range with a high spherical uniformity, which is a crucial point for these colloids' properties. We have shown that it is possible to synthesize a functionalized nanoplatform in a one-pot one-phase process …

Detection of Indoor Air Pollutants Using Reactive Sputtering/GLAD of Tin Oxide Thin Films

-

Nanocatalysts for High Selectivity Enyne Cyclization: Oxidative Surface Reorganization of Gold Sub-2-nm Nanoparticle Networks

International audience; Ultrasmall gold nanoparticles (NPs) stabilized in networks by polymantane ligands (diamondoids) were successfully used as precatalysts for highly selective heterogeneous gold-catalyzed dimethyl allyl(propargyl)malonate cyclization to 5-membered conjugated diene. Such reaction usually suffers from selectivity issues with homogeneous catalysts. This control over selectivity further opened the way to one-pot cascade reaction, as illustrated by the 1,6-enyne cycloisomerization–Diels–Alder reaction of dimethyl allyl propargyl malonate with maleic anhydride. The ability to assemble nanoparticles with controllable sizes and shapes within networks concerns research in sensor…

Influence of the chemical dissolution of MnS inclusions on the composition of passive films and the local electrochemical behaviour of stainless steels

Abstract Immersion of stainless steel containing MnS inclusions in aqueous electrolytes leads to the chemical dissolution of these heterogeneities. Chemical dissolution of MnS inclusions in 1M NaCl, pH=3 was studied using in-situ AFM and the dissolution rate of MnS was estimated between 0.04 and 0.19 μm 3 /min. The local electrochemical measurements reveal that the chemical dissolution of MnS inclusions promotes pitting corrosion. Similary, chemical dissolution of MnS inclusions in IM NaClO 4 , pH=3 solution modified the surface close to the inclusions by the presence of FeSO 4 in the passive film.

Atomic Layer Deposition of Au-TiO2 inverse opals for the visible light photocatalysis of dyesdegradation

The pollution of waste water due to organic dyes used in the textile and chemical industries is an important environmental issue. Inverse opals (IO) offer a great potential for increasing the efficiency of their degradation by semiconductor photocatalysts such as TiO2 by the synergy of high specific surface and photonic crystal properties [1]. Doping TiO2 with gold nanoparticles is another possible strategy to enhance its photocatalytic activity by increasing its optical absorption in the visible range [2].This work reports the synthesis of Au-TiO 2 IO films by Atomic Layer Deposition and the study of their visible-light photocatalytic activity for the degradation of methylene blue in water…

Functionalized Fe3O4 nanoparticles: influence of ligand addition sequence and pH during their continuous hydrothermal synthesis

In this study we report various new efficient ways to synthesize and modify in situ magnetite (Fe3O4) iron oxide nanoparticles (NPs). Thanks to an apparatus especially developed for this new method of grafting, the NPs have been synthesized and functionalized by 3,4-dihydroxyhydrocinnamic acid (DHCA) or 3,4-dihydroxy-L-phenylalanine (LDOPA) in one step and under hydrothermal conditions using varying concentration ratios ([organic molecules]/[ferrous and ferric ions]). The organic molecules were added before or after the NP synthesis. The addition of these organic molecules modifies the structure, the morphology, the oxidation degree and the growth of the crystallites. Adding the organic mol…

Structure and properties of GaNxOy films grown by nitridation of GaAs (100) substrates

GaAs (100) substrates have been heat-treated in a metal-organic chemical vapor deposition reactor under flows of NH 3 and an oxygen organo-metallic precursor at temperatures between 650°C and 750°C. Yellowish films formed at the surface of all the samples. Gallium, nitrogen and oxygen were detected by EDX analysis of the films. The oxygen content was estimated in the range of at 5-10 at% depending on the heat-treatment temperature. X-ray diffraction and HRTEM results indicate that the structure of the films corresponds to the hexagonal wurtzite phase of GaN with an expanded unit cell. Raman spectra show hands corresponding to the Raman active GaN modes as well as disorder-activated broad ba…

Thermal effects on the growth by metal organic chemical vapour deposition of TiO2 thin films on (100) GaAs substrates

Abstract 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.

Phase mixture in MOCVD and reactive sputtering TiOxNy thin films revealed and quantified by XPS factorial analysis.

Abstract Titanium oxynitride thin films have been deposited by low-pressure metalorganic chemical vapour deposition and reactive sputtering. The growth temperature for chemical vapour-deposited films and water vapour partial pressure for sputter-deposited films have been used to modulate the chemical composition. Both series have been analysed using X-ray photoelectron spectroscopy (XPS) in order to describe the structure of the materials using a factorial analysis approach. Titanium and metalloid concentrations have also been determined and compared to an elemental analysis performed using Rutherford backscattering spectroscopy and nuclear reaction analysis. The two deposition methods led …

Influence of long-term ageing in solution containing chloride ions on the passivity and the corrosion resistance of duplex stainless steels

Abstract The influence of long-term ageing in NaCl on the passivity and the electrochemical behavior of UNS S32304 is studied. The passive film thickness, the Cr/Fe ratio and the chloride content were significantly increased after ageing. The chloride distribution depends on residual stresses, sample microstructure and surface preparation. Local electrochemical measurements revealed that pitting potentials are between 250–550 mV vs. SCE after electropolishing. The higher the chloride content, the lower the local pitting potential. It was also shown that the presence of chloride was balanced by the enrichment in chromium after ageing. Then no pitting potential could be measured.

Study of titanium alloy Ti6242S oxidation behaviour in air at 560°C: Effect of oxygen dissolution on lattice parameters

Abstract High temperature oxidation of titanium alloy Ti6242S was studied in air at 560 °C up to 10000 h. Oxidation kinetics obeys a parabolic law (kp = 8.7 × 10−15 g². cm−4.s-1). Oxygen dissolution in the metal was found to represent between 80 and 90% of the total mass gain. Thin oxide scales are mainly composed of TiO2, in top of which some alumina is present. Titanium nitride was detected as a very thin layer at the outer part of the metallic substrate. Underneath, the oxygen dissolution area was found to reach the maximum brittleness after 1000 h of oxidation.

Influence of the microstructure on the corrosion behaviour of low-carbon martensitic stainless steel after tempering treatment

Abstract The microstructure of grade X4CrNiMo16.5.1 stainless steel was studied at different scales. The chemical composition of the native passive film formed on the different phases was then determined at the microscale. The degree of homogeneity of the native passive film is discussed. Subsequently, the susceptibility to pitting corrosion of X4CrNiMo16.5.1 was quantified using the electrochemical microcell technique. The nature of precursor sites and the morphology of pits were investigated by combining scanning electron microscopy with Electron BackScatter Diffraction and potentiostatic pulse tests. The role of the microstructure and the cold-worked layer generated by polishing in pitti…

XPS and SIMS study of aluminium native oxide modifications induced by Q-switched Nd:YAG laser treatment

Publié suite au congrès ECASIA: 11th European Conference on Applications of Surface and Interface Analysis, 25-30 September 2005, Vienna, Austria; International audience; During laser cleaning of aluminium in ambient atmosphere, modifications of the metal surface can be induced by transient thermal effects. This work aims to characterize the modification of the aluminium oxide layer on pure aluminium for a wide range of power per area using a Q-switched Nd :YAG (1064 nm) laser with two pulse durations, 10 and 180 ns. Experiments were carried out with single laser shots in ambient air at fluences (e.g. energy per area) below the ablation regime. For 10-ns pulses with fluences between 0.7 and…

Amorphous TiO2 in LP-OMCVD TiNxOy thin films revealed by XPS

Abstract 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…

Pulsed laser growth and characterization of thin films on titanium substrates

Abstract Colored layers were obtained by laser surface treatment of Ti substrates with a pulsed Nd:YAG Q-switched laser. The changes in the morphology, structure and chemical composition of the layers were studied by SEM, EDS, XPS, SIMS and Raman spectroscopy as a function of the laser fluence in the 4–60 J cm −2 . For laser fluences lower than 25 J cm −2 , the layers are colorless or yellow. Their surface is smooth, but they display cracks which increase when the fluence increases. The O/Ti ratio, determined by XPS analysis, varies from 0.7 (colorless layers) to 1.3 (yellow layer). Moreover, XPS spectra evidence non-negligible amounts of nitrogen and carbon in these layers. Raman spectra s…