Pr. Marie-Paule Delplancke

• CHIM-H-419 Surface treatment : processing and analysis
• CHIM-H-316 Matériaux et chimie inorganique : mise en oeuvre et analyse
• CHIM-H-412 Microstructural design and characterization of inorganic materials
• CHIM-S-201 Industrial applications of chemistry

Articles dans des revues avec comité de lecture

2024

Sulfur Mortar Goes to Infinity: Mechanical Performance and Characterization of Sulfur Mortar Composed of Different Aggregates During Heating Cycles, Exploring Potential Sustainability, Recyclability, and Circularity

Sulfur mortar hardens quickly, shows a high chemical resistance, and can be recycled, making it ideal for construction and rehabilitation in extreme environments. Despite its potential for sustainability, current research lacks sufficient characterization of sulfur mortar's performance during recycling, particularly regarding the physical and chemical changes when iron oxide is introduced. This study investigates the replacement of conventional siliceous sand with high-iron-content sand in sulfur mortar, through a series of five break-recast cycles. The results demonstrate an 11% increase in compressive strength and a 26% increase in flexural strength after five recasting cycles. Optical microscopy and scanning electron microscopy (SEM) revealed that recasting improved the distribution of the sulfur binder, while the formation of iron sulfates filled the gaps between aggregates and the binder. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the presence of iron sulfates, and differential scanning calorimetry (DSC) showed that high-iron-content sulfur mortar narrowed the phase change temperature range, preventing uneven solidification within the samples. This study sheds light on the strengthening mechanisms that occur during the recycling process, enhancing the material's durability and recyclability. This aligns with circular economy principles, contributes to resource efficiency, and supports sustainable construction practices.

2023

Postplasma Catalytic Model for NO Production: Revealing the Underlying Mechanisms to Improve the Process Efficiency

2022

Effusion nozzle for energy-efficient NOx production in a rotating gliding arc plasma reactor

2020

Advanced characterisation of the early age behaviour of bulk hydrophobic mortars

Over the last 15 years, bulk hydrophobic treatment of cementitious materials with silanes and siloxanes is in the scientific focus. They are beneficial in terms of reducing water uptake by capillarity, however, this is often followed by an impact on cement hydration leading to the decrease in structural properties of cement matrix. The aim of this paper is to study the influence of different incorporation modes of a silicone-based hydrophobic agent used for the bulk hydrophobic treatment of mortars, and to evaluate their effect on cement hydration and the early age properties. Two different incorporation modes are compared: an emulsion of silane and silicone resin and microencapsulation of silicone resin. Each of these is incorporated in mortars prepared with CEM I and CEM III/A. Based on the combined measurement of isothermal calorimetry, electrical resistivity, ultrasonic pulse velocity, compressive strength, thermal expansion coefficient and autogenous deformation at early age, it is shown that the emulsion, as a delivery method of hydrophobic agent, affects the early age mechanical behavior of cement-based systems, for both types of cements. The microencapsulation on the other hand, prevents these effects from occurring, and is therefore suitable for bulk hydrophobic treatment.

Hydrogen chloride removal from hydrogen gas by adsorption on hydrated ion-exchanged zeolites

Hydrogen chloride is found in important hydrogen gas streams of the chemical industry and needs to be removed for safety and environmental concerns. Here, a systematic study is presented on HCl removal from hydrogen gas by adsorption on zeolites, including cation free and high cation loaded materials, as well as ion-exchanged zeolites (with alkali, alkaline earth and transition metal ions). The HCl removal performance was studied by a fixed-bed breakthrough method under high gas velocities (>0.3 m/s), at high pressures (30 bar) and at room temperature, and with low HCl concentrations (<200 ppm). The zeolite screening indicated that the 13X zeolite outperforms the other tested materials. The ion-exchanged X zeolites were extensively characterized via SEM-EDX, XRD, ATR-FTIR, TGA and argon adsorption isotherms. The results revealed that the ion-exchange was successfully achieved with expected tendencies in XRD and ATR-FTIR spectra, and porosities. The breakthrough experiments demonstrated that the hydration of the zeolite prior HCl adsorption improves the hydrogen gas purification performance. The characterization after HCl adsorption supports the hypothesis that HCl is taken up by the material by forming salt molecules within the zeolite cavities by reaction with the cations and, which is, moreover, enhanced by the presence of pre-adsorbed water. The type of cation present in the zeolite framework structure notably affected the HCl removal adsorption capacity as well as uptake rate. Among the ion-exchanged zeolite samples, the Zn2+ form exhibited the highest adsorption capacity at saturation, attributed to the over-exchange of the zeolite cations. The investigation revealed important parameters such as cation radius, atomic mass and electronegativity, which played a noteworthy role in defining the HCl removal performance of ion-exchanged zeolites.

2019

N-Doped TiO2 Photocatalyst Coatings Synthesized by a Cold Atmospheric Plasma

This work presents a simple, fast (20 min treatment), inexpensive, and highly efficient method for synthesizing nitrogen-doped titanium dioxide (N-TiO2) as an enhanced visible light photocatalyst. In this study, N-TiO2 coatings were fabricated by atmospheric pressure dielectric barrier discharge (DBD) at room temperature. The composition and the chemical bonds of the TiO2 and N-TiO2 coatings were characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The results indicate that the nitrogen element has doped the TiO2 lattice, which was further confirmed by Raman spectroscopy and grazing incidence X-ray diffraction (GIXRD). The doping mechanism was investigated using OES to study the plasma properties under different conditions. It suggests that the NH radicals play a key role in doping TiO2. The concentration of nitrogen in the N-TiO2 coatings can be controlled by changing the concentration of NH3 in the plasma or the applied power to adjust the concentration of NH radicals in the plasma. The band gap of N-TiO2 was reduced after NH3/Ar plasma treatment from 3.25 to 3.18 eV. Consequently, the N-TiO2 coating showed enhanced photocatalytic activity under white-light-emitting-diode (LED) irradiation. The photocatalytic degradation rate for the N-TiO2 coating was about 1.4 times higher than that of the undoped TiO2 coating.

Highly Robust MOF Polymeric Beads with a Controllable Size for Molecular Separations

Shaping metal-organic frameworks (MOFs) into robust particles with a controllable size is of large interest to the field of adsorption. Therefore, a method is presented here to produce robust MOF beads of different sizes, ranging from 250 μm to several millimeters, which, moreover, preserve the adsorption properties of the unformulated MOF. A simple, mild, and flexible method is demonstrated with the zeolitic imidazolate framework-8 (ZIF-8)/polyvinyl formal composite material. The properties of the composite material are determined via optical imaging, scanning electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, X-ray diffraction, mercury intrusion, argon porosimetry and pycnometry as well as thermogravimetric analysis/differential scanning calorimetry, crush strength tests, and immersion experiments. The proposed method allows the production of resistant particles with a high MOF loading (up to 85 wt %) and remarkable structural and textural properties required for adsorptive separation processes, including a preserved ZIF-8 crystalline structure, microporosity, and a narrow macropore size distribution (1.27 μm average). The particles show a spherical shape with an average aspect ratio of 0.85. The stability tests demonstrated that the composite MOF material exhibits a high mechanical strength (3.09 N/Pc crushing strength) almost equivalent to that of a widely used commercial zeolite material. Furthermore, the material remains stable up to 200 °C and in most solvents. The adsorption properties are explored via static and dynamic experiments in the vapor and liquid phases. The results show that the adsorption capacities are only reduced in proportion to the binder content compared with the pristine material, indicating no binder intrusion in the ZIF-8 pores. Fixed-bed experiments demonstrate the remarkable separation performance in the vapor phase, whereas mass transfer limitations arise in the liquid phase with increasing flow rate. The mass transfer limitations are attributed to the diffusion in the macropores or through the ZIF-8 crystal outer layer.

2018

Study of the early growth stages of chemically deposited ZnS thin films from a non-toxic solution

ZnS thin films grown by the chemical bath deposition method have been under intense investigation due to their applications in solar cells. In this work, the early growth stages of ZnS thin films deposited by means of a non-toxic solution are studied by measuring the morphological, chemical and optical properties of the films obtained at different deposition time (5,10,20,30,60,90 and 120 min). From the atomic force microscopy (AFM) studies, it was seen that the substrate surface is not fully covered before 20 min, and the growth exponential value changed from 0.5 to 1.8. The x-ray photoelectron spectroscopy (XPS) measurements revealed the presence of the Zn-O bond and the absence of the S-Zn bond at the earliest deposition time. Additionally, from XPS analysis, a shift in the signals for O1s and Zn2p3/2 for the sample grown at 30 min was observed due to the formation of Zn(OH)2. Finally, the UV-Vis spectrophotometry measurements showed that all samples have a high transmittance (>80%) and that the band gap value decreased as the deposition time increased.

Dynamic behaviors of inorganic all-solid-state electrochromic device: Role of potential

Applied potential plays a significant role in the properties of electrochromic devices (ECDs), for example, cyclic property, optical modulation, and response rate. In this study, inorganic all-solid-state ECDs with the multilayer structure of Glass/ITO/NiOx/Ta2O5/LiNbO3/Ta2O5/WO3/ITO were prepared by magnetron sputtering. The potential dependence of charges dynamic behaviors in the ECDs were analyzed on the basis of cyclic voltammograms (CVs), chronoamperograms (CAs), multi-potential steps, and in-situ optical transmittance at 550 nm. Results demonstrated that the trapping of Li+ ions in NiOx layer and in WO3 layer were responsible for the degradation of electrochromic properties of the ECDs operated at different potential ranges. Besides, the dynamic behavior of Li+ ions in WO3 layer, acting as the primary electrochromic layer in the ECDs, had a crucial influence on the response characteristics of the ECDs. Excellent optical memory effects at randomly electrochromic extent were observed and the corresponding open-circuit potential was relevant to the chemical potential of the ECDs.

Charge-transfer kinetics and cyclic properties of inorganic all-solid-state electrochromic device with remarkably improved optical memory

Optical memory effect plays a critical role in energy-saving coefficient of electrochromic devices (ECDs). Due to the finite electron-blocking capacity of ions electrolyte layer and the weak interfacial energy between the ions electrolyte layer and electrochromic layers, typically five-layer inorganic all-solid-state ECDs generally suffer from poor optical memory. A seven-layer inorganic ECD with significantly improved optical memory is designed by means of the embedment of Ta2O5 layers between ions conductive layer and electrochromic layers. Compared with the typical five-layer ECD-1 (ITO/NiOx/LiNbO3/WO3/ITO), the seven-layer ECD-2 with the structure of ITO/NiOx/Ta2O5/LiNbO3/Ta2O5/WO3/ITO presents much less leakage current, larger optical modulation and higher coloration efficiency during electrochemical cycling. The further analyses reveal that the embedded Ta2O5 layers greatly increase the energy barrier between NiOx, WO3 and LiNbO3, imposing restrictions on the transfer kinetics of electrons contributing to the leakage current and enlarging the threshold potential available to ECD-2, which gives rise to a high coloration efficiency up to 98.0 cm2 C−1. Furthermore, the seven-layer ECD-2 maintains a stable optical modulation of approximately 52.5% for over 10,000 cycles, even though there is a compromise in response characteristic due to the Li+-ion trapping in electrochromic layers, which provides a further insight into the electrochromic degradation of inorganic all-solid-state complementary ECDs.

Atmospheric pressure dielectric barrier discharge synthesis of morphology-controllable TiO2 films with enhanced photocatalytic activity

Atmospheric plasma technology is a promising next-generation alternative for replacing thermal chemical vapor deposition or wet chemical processes for the deposition of functional coatings. In this work, TiO2 films with various morphologies and thicknesses are synthesized in a controllable way by atmospheric Dielectric Barrier Discharges (DBD) under argon/oxygen ambient conditions. This method allows varying the density of the deposited coatings, from low density powders to dense compact anatase layers simple tuning of the parameters. The surface morphology and cross section of the as-synthesized films are observed by scanning electron microscopy (SEM). It is demonstrated that the total flow rate together with the absorbed power have a significant effect on the morphology of the film, which changes from granular to compact film by increasing the total flow rate or decreasing the power. In other words, changing the energy density (Ed) in the plasma allows to control the morphology of the TiO2 films. A deposition mechanism is proposed to explain the effect of the synthesis parameters on the formed films. The chemical and phase composition of these films before and after annealing for 2 h in air at 673 K are comparatively studied. The photocatalytic activities and the reusability of the TiO2 films is investigated by degrading a methylene blue (MB) solution under Ultra-Violet (UV) light. It is compared to the activity of a P25 film, deposited by drop-casting. The photocatalytic rate of the annealed TiO2 film synthesized at a total flow rate of 2.5 slm turns out to be about 2 and 15 times higher than the one of P25 and as-synthesized TiO2 films, respectively. The annealed TiO2 film were shown to be reusable for at least three cycles, without significant loss of photocatalytic activity.

Electrochemical synthesis of copper(I) dicyanamide thin films

The electrochemical behaviour of Cu(II) ions has been investigated in acidic aqueous solutions in the presence ofdicyanamide (dca), an anion frequently used as bridging agent in coordination polymers. The cyclic voltammogramsrecorded at a gold electrode have revealed two consecutive one electron transfer processes indicatingthat Cu(I) is stabilized by the dicyanamide anion at the electrode surface. The formation of an insoluble film afterreduction of Cu(II) to Cu(I) was evidenced by EQCM measurements and imaged by scanning electron microscopy.XRD and infrared reflection spectroscopy data have confirmed the formation of a Cu(I)-dca film.

In situ electrochromic efficiency of a nickel oxide thin film: Origin of electrochemical process and electrochromic degradation

Electrochromic nickel oxide (NiOx) thin films are one of the most promising anodic colored materials. However, there is lack of accurate description of their electrochemical process and degradation mechanism. In this study, a novel approach involving in situ electrochromic efficiency is proposed to reveal the electrochemical origin of an electrochromic NiOx thin film cycled in a Li+-ion electrolyte. The results indicate that the coloring process of the NiOx thin film refers to the oxidation reactions of Ni2+ to Ni3+ and Ni2+ to Ni4+ (in two forms of Ni3O4 and Ni2O3), and the bleaching process is associated with the reduction reactions of Ni4+ to Ni2+, Ni4+ to Ni3+, and Ni3+ to Ni2+. The irreversible reduction of Ni4+ to Ni3+ plays a dominant role in the activation procedure of NiOx. It is deduced that the Li+-ion trapping in the bleaching process along with the reduction reactions of Ni4+ to Ni3+ and Ni3+ to Ni2+ causes the degradation of the electrochromic properties. This study provides a further insight into the electrochromic mechanism and is conducive to the improvement of the long-term cyclic durability for Li+-based electrochromic NiOx. Moreover, the study significantly establishes a direct connection between an electrochemical process and a variation in the optical absorbance of materials.

2017

Plasma-catalytic conversion of CO2 and CO2/H2O in a surface-wave sustained microwave discharge

The conversion of CO2 and CO2/H2O mixtures on a TiO2 supported NiO catalyst in a pulsed surface-wave sustained microwave discharge has been investigated. The influence of the catalyst preparation method (conventional calcination (in air or Ar) vs. Ar plasma-assisted decomposition) on the CO2 conversion and its energy efficiency has been studied. The results demonstrate that the Ar plasma-treated catalyst is more active compared to the conventional calcined one. The plasma-treated catalyst increases the CO2 conversion and its energy efficiency almost by a factor of two, compared to the plasma only assisted CO2 dissociation, while the conventional calcined catalysts affect the CO2 conversion rather insignificantly. The conversion of CO2 is found to be about 45% at 70 Torr in pure CO2 with Ar plasma-treated catalyst, having an energy efficiency of 56%. In the case of CO2/H2O mixture, the CO2 conversion efficiency reaches 42% (energy efficiency is 52%) at 60 Torr. The catalyst characterization shows that Ar plasma treatment may result in a higher density of oxygen vacancies and a comparatively uniform distribution of NiO on the TiO2 surface. The dissociative electron attachment of CO2 at the catalyst surface enhanced by the oxygen vacancies and plasma electrons may explain the increase of conversion and energy efficiencies in this case. A mechanism of plasma-catalytic conversion of CO2 at the catalyst surface in CO2/H2O mixture is proposed.

Understanding Microwave Surface-Wave Sustained Plasmas at Intermediate Pressure by 2D Modeling and Experiments

An Ar plasma sustained by a surfaguide wave launcher is investigated at intermediate pressure (200-2667 Pa). Two 2D self-consistent models (quasi-neutral and plasma bulk-sheath) are developed and benchmarked. The complete set of electromagnetic and fluid equations and the boundary conditions are presented. The transformation of fluid equations from a local reference frame, that is, moving with plasma or when the gas flow is zero, to a laboratory reference frame, that is, accounting for the gas flow, is discussed. The pressure range is extended down to 80 Pa by experimental measurements. The electron temperature decreases with pressure. The electron density depends linearly on power, and changes its behavior with pressure depending on the product of pressure and radial plasma size.

Effect of different complexing agents on Pb-Co thin-film electrodeposition

Lead (Pb)-cobalt (Co) films have been studied by several researchers regarding their electrocatalytic activity when used as anodes in oxygen evolution reactions. Although several authors have suggested that the electrodeposition technique is the best alternative to Pb-Co film deposition, the process is complex. In many cases, the use of complexing agents facilitates the electrodeposition of multi-element coatings; but this performance has not been reported in the literature for Pb-Co electrodeposition. In this work, the effect of three different complexing agents (tartaric acid, sodium citrate, and ascorbic acid) on Pb-Co electrodeposition was studied. Speciation diagrams and polarization curves have been used to determine the reduction potentials of Pb2+ and Co2+ ions in the different systems studied. Speciation diagram predictions were incapable of revealing all species present in solution and for an accurate prediction of the actual electrochemical functioning of the system; the information given by the speciation diagrams and polarization curves must be considered together. Additionally, electrodeposition of Pb-Co films was achieved without complexing agent and using the three complexing agents. Morphological and chemical properties of these coatings are shown and discussed in terms of the electrochemical functioning of each system. Finally, the electrocatalytic ability of the Pb-Co films was investigated by means of polarization curves.

Deposition of photocatalytic anatase titanium dioxide films by atmospheric dielectric barrier discharge

In this study, TiO2 films are easily deposited in a single-step process from titanium tetraisopropoxide (TTIP) using a dielectric barrier discharge (DBD) device under atmospheric pressure at room temperature. The surface morphology of the as-deposited TiO2 films is observed by scanning electron microscopy (SEM). The as-deposited TiO2 films exhibit nanometer-sized particles with a lot of agglomerates. The cross section images indicate that the deposition rate of TiO2 films can reach about 70 nm·min− 1, which is much faster than that of conventional low pressure chemical vapor deposition (CVD) (typically < 4 nm·min− 1). In order to confirm the structure composition and optical properties of the films, glancing incidence X-ray diffraction (GIXRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) are employed. The as-deposited TiO2 films are partly crystalline which show a good photocatalytic activity in the degradation of methylene blue under UV irradiation. After annealing at 673 K, the TiO2 films are in the anatase phase and composed by homogeneous nanoparticles. The photocatalytic degradation rate of methylene blue of the TiO2 films after annealing (~ 0.6 h− 1) is almost 4 times higher than that of the as-deposited TiO2 films (~ 0.16 h− 1). The photocatalytic degradation rate of the TiO2 film after annealing is the same as the one of the commercial anatase TiO2 spin coated film when the error bar is taken into account. The TiO2 films show excellent photocatalytic stability during 3 recycling photocatalytic measurements.

An overview of CO2 conversion in a microwave discharge: The role of plasma-catalysis

An overview of the recent progress on plasma-assisted CO2 conversion in microwave discharges is given. Special attention is devoted to the results obtained using plasma catalysis, which are compared to the plasma-only CO2 decomposition cases. The effects of plasma operating conditions, catalyst preparation methods, nature of plasma activation gas, gas mixture, as well as the NiO content on the TiO2 surface on CO2 conversion and its energy efficiency are discussed. A significant improvement in CO2 conversion is obtained with a NiO/TiO2 catalyst activated in Ar plasma, when the NiO content is about 10 wt.%. The catalyst characterization data show that Ar plasma treatment results in a higher density of oxygen vacancies and a comparatively more uniform distribution of NiO on the TiO2 surface, which strongly influence CO2 conversion and its energy efficiency. The dissociative electron attachment of CO2 at the catalyst surface enhanced by the oxygen vacancies and by plasma electrons may also explain the increase in conversion and energy efficiencies. A mechanism for the plasma-catalytic CO2 conversion at the surface of an Ar plasma-threated catalyst is proposed.

Sol-gel hot injection synthesis of ZnO nanoparticles into a porous silica matrix and reaction mechanism

Despite the enormous interest in the properties and applications of porous silica matrix, only a few attempts have been reported to deposit metal and metal oxide nanoparticles (NPs) inside the porous silica matrix. We report a simple approach (i.e. sol-gel hot injection) for insitu synthesis of ZnO NPs inside a porous silica matrix. Control of the Zn:Si molar ratio, reaction temperature, pH value, and annealing temperature permits formation of ZnO NPs (≤ 10 nm) inside a porous silica particles, without additives or organic solvents. Results revealed that a solid state reaction inside the ZnO/SiO2 nanocomposites occurs with increasing the annealing temperature. The reaction of ZnO NPs with SiO2 matrix was insignificant up to approximately 500 °C. However, ZnO NPs react strongly with the silica matrix when the nanocomposites are annealed at temperatures above 700 °C. Extensive annealing of the ZnO/SiO2 nanocomposite at 900 °C yields 3D structures made of 500 nm rod-like, 5-7 μm tube-like and 3-5 μm needle-like Zn2SiO4 crystals. A possible mechanism for forming ZnO NPs inside porous silica matrix and phase transformation of the ZnO/SiO2 nanocomposites into 3D architectures of Zn2SiO4 are carefully discussed.

Electrodeposition of lead-cobalt anodes: The effect of electrolyte pH on film properties

Electrodeposited lead (Pb)-cobalt (Co) coatings are an effective electrocatalyst in the oxygen-evolution reaction. We studied the effect of an electrolytic bath pH on the electrodeposition of Pb-Co coatings, and the coating properties were analyzed. The pH was varied from 1 to 6 for a solution without and with ascorbic acid as complexing agent. Cathodic polarization curves show that the deposition conditions have a greater effect on the reduction potential of Co2+ than the reduction potential of Pb2+. Energy-dispersive X-ray spectrometer analysis shows that a pH higher than 4 promotes Co deposition and yields a [Pb]/[Co] film ratio lower than 1. Scanning electron micrographs showed that samples grown at a pH higher than 2 were covered with Co dendrites, and that the sample grown with ascorbic acid at pH 1 exhibited a compact morphology. Anodic polarization curves showed that Pb-Co-coated anodes grown at pH 1 with a complexing agent evolved oxygen at c.a. 1.6 V vs. normal hydrogen electrode, which lead to a 40% reduction in the required overpotential (η) for the oxygen-evolution reaction compared with conventional Pb-Ca-Sn anodes.

2016

Electrolytes-relevant cyclic durability of nickel oxide thin films as an ion-storage layer in an all-solid-state complementary electrochromic device

NiOx thin films approximately 300 nm thick were deposited on indium tin oxide (ITO)-coated glass substrates by magnetron sputtering. Their electrochromic properties were tested in a 1 M potassium hydroxide (KOH) aqueous solution and in a 1 M lithium perchlorate dissolved in propylene carbonate (LiClO4-PC) anhydrous electrolyte, respectively. The evolution of the lattice structure, surface morphology, chemical composition, optical transmittance modulation, cyclic voltammograms, inserted and extracted charge capacities of NiOx thin films was evaluated as a function of the number of cycles. Even though the cyclic voltammograms and the charge capacity present a similar variation tendency during 1000 cycles, significant differences between cycling in 1 M KOH and 1 M LiClO4-PC were observed. In 1 M KOH, X-ray diffraction (XRD) results showed that the lattice planes (111) and (200) had a larger shift toward higher diffraction angles, and SEM images exhibited that cracks emerged more quickly from the surface of NiOx thin film during the cycling process. More importantly, the optical modulation varying from 58.5% to 32.9% presented an obvious degradation after 1000 cycles. On the contrary, in 1 M LiClO4-PC, NiOx thin films presented a better cyclic durability and a stable optical modulation approximating 41%. In a second step, an all-solid-state complementary electrochromic device with an ITO/WO3/LiClO4-PC-PMMA/NiOx/ITO structure was assembled. The device had an average optical modulation of 51.7% in the visible region and an excellent cyclic durability (over 50,000 times). In situ optical transmittance spectra showed that, in the initial cycles, the response time was 4.5 s for the coloring process and 1.7 s for the bleaching process. After 1000 cycles, both were delayed to 5.0 s and 2.9 s, respectively. In addition, open circuit memory of the device was characterized by the optical transmittance variation plotted against time after disconnection of the external circuit.

Comprehensive study of growth mechanism and properties of low Zn content Cd1-xZnxS thin films by chemical bath

Cd1-xZnxS thin films have been studied extensively as window layers for solar cell applications. However, a mismatch between the Cd1-xZnxS and copper-indium-gallium-selenide absorber layers increases with Zn film concentration, which reduces the device eficiency. In this work, Cd1-xZnxS thin films with low Zn concentrations were analyzed. The effect of the addition of different molar Zn concentrations to the reaction mixture on the growth mechanism of Cd1-xZnxS thin films and the influence of these mechanisms on structural, optical and morphological properties of the films has been studied. Cd1-xZnxS thin films were synthesized by chemical bath deposition using an ammonia-free alkaline solution. Microstructural analysis by X-ray diffraction showed that all deposited films grew with hexagonal structure and crystallite sizes decreased as the Zn concentration in the film increased. Optical measurements indicated a high optical transmission between 75% and 90% for wavelengths above the absorption edge. Band gap value increased from 2.48 eV to 2.62 eV, and the refractive index values for Cd1-xZnxS thin films decreased as the Zn increased. These changes in films and properties are related to a modification in growth mechanism of the Cd1-xZnxS thin films, with the influence of Zn(OH)2 formation being more important as Zn in solution increases.

Plasma assisted catalytic decomposition of CO2

In this research, conversion of carbon dioxide in the presence of TiO2 supported NiO catalyst has been investigated in a pulsed surface-wave sustained microwave discharge. The catalyst is prepared by combination of impregnation and plasma-treatment methods. The decomposition of TiO2 supported nickel nitrate was done by plasma, induced in three different gases (O2, Ar, CO2). NiO/TiO2 catalysts were formed. The supplied gas has a prominent effect on the chemical and physical properties of the prepared catalysts. The catalyst prepared with an Ar plasma increases almost by a factor of 2 the CO2 conversion and energy efficiencies, while the O2 or CO2 plasma prepared catalysts show little effect on the CO2 conversion in comparison with catalyst-free plasma assisted dissociation. The results from the catalyst characterization by different techniques demonstrated that Ar plasma pre-treatment resulted in formation of oxygen vacancies. Dissociative electron attachment of CO2 at the catalyst surface enhanced by oxygen vacancies and plasma electrons could explain the improved conversion and energy efficiency. A constant catalytic activity was observed indicating continuous catalyst regeneration under reactor conditions. A mechanism of plasma-catalysis synergy is proposed.

Growth and characterization of WSe2 single crystals usingTeCl4 as transport agent

The growth of WSe2 single crystals, using TeCl4 as transport agent was performed successfully from slowly cooled polycrystalline powders as precursors. The resulting single crystals were characterized by X-ray diffraction (XRD) and their surfaces examined by scanning electron microscopy (SEM) presented fewer defects than single crystals prepared from air-quenched polycrystalline powders. Energy Dispersive X-ray microanalysis (EDX), inductively coupled plasma (ICP) spectroscopy and X-ray photoelectron spectroscopy (XPS) revealed that the single crystals are homogeneous and stoichiometric. Electrical conductivity and photocurrent measurements have confirmed the semiconducting character of the single crystals and a photocurrent of 75 mA cm^(-2) has been reached. In addition, single crystals with areas in the 25-100 mm2 range can be obtained under the reported growth conditions.

2015

Fs- and ns-laser processing of polydimethylsiloxane (PDMS) elastomer: Comparative study

Medical grade polydimethylsiloxane (PDMS) elastomer is a widely used biomaterial as encapsulation and/or as substrate insulator carrier for long term neural implants because of its remarkable properties. Femtosecond (λ = 263 and 527 nm) and nanosecond (266 and 532 nm) laser processing of PDMS-elastomer surface, in air, is investigated. The influence of different processing parameters, including laser wavelength, pulse duration, fluence, scanning speed and overlapping of the subsequent pulses, on the surface activation and the surface morphology are studied. High definition tracks and electrodes are produced. Remarkable alterations of the chemical composition and structural morphology of the ablated traces are observed in comparison with the native material. Raman spectra illustrate well-defined dependence of the chemical composition on the laser fluence, pulse duration, number of pulses and wavelength. An extra peak about ∼512-518 cm-1, assigned to crystalline silicon, is observed after ns- or visible fs-laser processing of the surface. In all cases, the intensities of SiOSi symmetric stretching at 488 cm-1, SiCH3 symmetric rocking at 685 cm-1, SiC symmetric stretching at 709 cm-1, CH3 asymmetric rocking + SiC asymmetric stretching at 787 cm-1, and CH3 symmetric rocking at 859 cm-1, modes strongly decrease. The laser processed areas are also analyzed by SEM and optical microscopy. Selective Pt or Ni metallization of the laser processed traces is produced successfully via electroless plating. The metallization process is not sensitive with respect to the time interval after the laser treatment. DC resistance is measured to be as low as 0.5 Ω mm-1. Our results show promising prospects with respect to use such a laser-based method for micro- or nano-fabrication of PDMS devices for MEMS and NEMS.

Influence of electrolyte composition on the formation of mixed oxide nanotube arrays for solar fuel production

Water splitting using sunlight is an important process for future energy supplies. TiO2 is widely used as photoanode, but has a limited light absorption range. Here, ternary Ti-Mo-Ni mixed oxide nanotube arrays were fabricated via electrochemical anodization of Ti-Mo-Ni alloy in formamide-ethylene glycol-based electrolytes, to extend the absorption range into visible light. The electrolyte composition and anodization time were found crucial in controlling the structural features of the nanotubes. By tuning these parameters, arrays of thin walled (∼9 nm) and ∼8 μm long nanotubes were obtained. In photoelectrochemical water splitting, the mixed oxides showed incident photon conversion efficiency (IPCE) up to 65% for wavelengths from 300 nm to 450 nm. This enhancement in the IPCE of the mixed oxide nanotubes, compared with pure titania, can be related to synergistic effects of Mo and Ni oxides as well as to the unique structural properties of the fabricated mixed oxide nanotubes.

Simultaneous dissociation of CO2 and H2O to syngas in a surface-wave microwave discharge

In this research, conversion of carbon dioxide and water vapor into value-added chemicals has been investigated in a pulsed surfacewave sustained microwave discharge operating under different conditions. Formation of syngas (CO/H2) was observed. The influence of the gas mixture ratio, the specific energy input (SEI), Espec, and the feed flow rate on H2 and CO production, was studied. It is found that syngas with a ratio close to 1 can be produced when CO2 - H2O ratio in the gas mixture is 50:50. The optimum SEI for H2 and CO formation for this gas mixture ratio is 1.6 eV/mol. Experiments carried out with Ar/H2O showed that the presence of CO2 supports the H2 formation at low SEI. Increasing the feed flow rate, i.e. reducing the residence time, hinders the H2 yield while the CO yield initially decreases and reaches a stable level. The highest energy conversion efficiency is calculated to be at low SEI and low flow rate. Optical emission spectroscopy measurements show that comparatively high dissociation rates correspond to low gas temperatures.

A green, simple chemical route for the synthesis of pure nanocalcite crystals

A new, simple chemical route was developed for the synthesis of pure nanocalcite crystals by controlling the reaction of an aqueous solution of CaO and CO2 gas. Results revealed formation of well-defined and pure nanocalcite crystals with controlled crystallite and particle size, without additives or organic solvents. The crystallite and particle size can be controlled, and smaller sizes are obtained by decreasing the CaO concentration and increasing the CO2 flow rate. The decrease of crystallite and particle size below a certain threshold provides the nanocalcite crystal signature characteristics that can be clearly observed in XRD patterns, TEM images, FTIR spectra, Raman spectra, XPS spectra, and thermal stability measurements.

Silicone rubber encapsulation for an endoscopically implantable gastrostimulator.

Gastrointestinal stimulator implants have recently shown positive results in treating obesity. However, the implantation currently requires an invasive surgical procedure. Endoscopy could be used to place the gastric stimulator in the stomach, hence avoiding the riskier surgery. The implant then needs to go through the oesophagus and be located inside the stomach, which imposes new design constraints, such as miniaturization and protecting the electronic circuit against the highly acidic environment of the stomach. We propose to protect the implant by encapsulation with silicone rubber. This paper lists the advantages of this method compared to the more usual approach of a hermetic enclosure and then presents a method to evaluate the underwater adhesive stability of six adhesive/substrate couples, using repeated lap-shear tests and an elevated temperature to accelerate the ageing process. The results for different adhesive/substrate couples tested, presented on probability plots, show that FR4 and alumina substrates with MED4-4220 silicone rubber are suitable for a first implantable prototype. We then compare these with the predicted lifetimes of bonds between historical standard silicone rubber DC3140 and different substrates and describe the encapsulation of our gastrostimulator.

2014

Influence of the processing temperature on the compressive strength of Na activated lateritic soil for building applications

The present study investigates the suitability of alkali activation of a lateritic soil for building applications. Lateritic soil was found to contain kaolinite, associated with quartz and hematite minerals. Both the processing temperatures and the amount of NaOH used were found to influence the development of compressive strength which was in the range of 12-51 MPa and 2-23 MPa respectively for dry and wet specimens. The synthesized products were thermally more stable, containing crystalline and amorphous phases mainly resulting from the dissolution of kaolinite. The XRD, FTIR, SEM and TG/DTA analyses showed an incomplete dissolution of the starting minerals. © 2014 Elsevier Ltd. All rights reserved.

Effect of the water saturation of aggregates on the shrinkage induced cracking risk of concrete at early age

This work consists in studying the effect of the water saturation of aggregates on the development of shrinkage and the potential cracking risk of early age ordinary concrete. Different concretes were obtained from a given concrete mixture by changing only the initial degree of saturation of limestone aggregates. Three degrees of saturation were studied, namely: 0% (dry aggregates), 50% (partially saturated aggregates) and 100% (saturated aggregates). From the experimental results, the early age behaviour and the mechanical properties of the concrete strongly depend on the water saturation of aggregates. A relative cracking risk was estimated from a stress-based approach and experimentally assessed parameters. The potential risk of cracking of these different concretes was shown to be different. Even if the total water content is kept constant, the water remaining in the cement paste actually depends on the initial water saturation of aggregates. The early age behaviour of concrete and the development of its early age properties depend on the amount of added water during the mixing. © 2014 Elsevier Ltd. All rights reserved.

Influence of temperature on oxidation mechanisms of fiber-textured AlTiTaN coatings

The oxidation kinetics of AlTiTaN hard coatings deposited at 265 °C by DC magnetron sputtering were investigated between 700 and 950 °C for various durations. By combining dynamic secondary ion mass spectrometry (D-SIMS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) investigations of the different oxidized coatings, we were able to highlight the oxidation mechanisms involved. The TEM cross-section observations combined with XRD analysis show that a single amorphous oxide layer comprising Ti, Al, and Ta formed at 700 °C. Above 750 °C, the oxide scale transforms into a bilayer oxide comprising an Al-rich upper oxide layer and a Ti/Ta-rich oxide layer at the interface with the coated nitride layer. From the D-SIMS analysis, it could be proposed that the oxidation mechanism was governed primarily by inward diffusion of O for temperatures of ≥700 °C, while at ≤750 °C, it is controlled by outward diffusion of Al and inward diffusion of O. Via a combination of structural and chemical analysis, it is possible to propose that crystallization of rutile lattice favors the outward diffusion of Al within the AlTiTa mixed oxide layer with an increase in the temperature of oxidation. The difference in the mechanisms of oxidation at 700 and 900 °C also influences the oxidation kinetics with respect to oxidation time. Formation of a protective alumina layer decreases the rate of oxidation at 900 °C for long durations of oxidation compared to 700 °C. Along with the oxidation behavior, the enhanced thermal stability of AlTiTaN compared to that of the TiAlN coating is illustrated. © 2014 American Chemical Society.

Influence of the chemical and mineralogical composition on the reactivity of volcanic ashes during alkali activation

The influence of chemical and mineralogical compositions on alkali activation of four natural volcanic ashes was investigated. NaOH was used as the sole alkaline activator. The reactivity of the systems was studied with Differential Scanning Calorimetry. The X-ray spectra of reacted materials showed a mixture of amorphous and crystalline phases. The SEM micrographs showed that the dissolution of larger particles is incomplete while smaller particles dissolved in the activating solution forming the glassy aluminosilicate matrix. The infrared spectra showed a broad absorbance at 820-1250 cm-1and 480-600 cm-1 assigned to internal vibration of Si3O3Si and Si3O3Al in both raw volcanic ash and resulting inorganic polymers. The reactivity of the volcanic ashes was found to correlate with their amorphous fraction. The dry compressive strength of synthesized products from all the ashes were in the range 14-63 MPa, suggesting their possible utilization as building materials. However, the strength was found to decrease (1-28 MPa) after specimens' immersion overnight in water, but was partly or totally recovered after overnight drying at 90 C. © 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Corrosion product identification at the cut edge of aluminum-rich metal-coated steel

The formation of corrosion product at the cut edge of aluminum-rich metalcoated steel is reported in the present work. Painted metal-coated steel samples with different amounts of Al in the metal coating, were immersed in a 0.05M NaCl solution. The ex situ analysis of the corrosion products formed was carried out by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), Raman and Fourier transform infrared (FT-IR) spectroscopy. The role of these products is discussed along with the influence of Al content in the metal coating. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Temperature-dependent wear mechanisms for magnetron-sputtered AlTiTaN hard coatings

Preparation and characterization of ultra-hydrophobic calcium carbonate nanoparticles

Anionic surfactants based on fatty acids are usually used to modify the particle surface properties of CaCO<inf>3</inf> with the aim to enhance its dispersion and compatibility with polymer matrices. In this study sodium oleate was used for the preparation of ultrahydrophobic CaCO<inf>3</inf> nanoparticles using a wet carbonation route. The effect of sodium oleate on the characteristics, particle size, morphology, surface potential, thermal decomposition and hydrophobicity of CaCO<inf>3</inf>, was investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), Zeta potential, thermogravimetric analysis (TGA) and water contact angle measurement (WCA). The results showed that the addition of 2 wt% sodium oleate helps in reducing the particle size from 2 μm length scalenohedral particles to 45 nm rhombohedral particles and modifying of the hydrophobic property of CaCO<inf>3</inf>.

2013

Fast-scanning calorimetry of electrospun polyamide nanofibres: Melting behaviour and crystal structure

This paper discusses the melting behaviour and crystal structure of electrospun (polymorphous) polyamide (PA) fibres and presents the importance of the heating rate used for their study by thermal analysis. A case study of PA6, PA46 and PA69 nanofibres is performed using a Rapid Heat-Cool DSC (RHC), a fast-scanning calorimeter capable of controlled heating rates above 1000 K min-1. Thermal lag becomes significant at scan rates above 500 K min-1 and the ideal scan rate for analysis of the crystal structure depends on the PA type. Measurements at the most suitable heating rate indicate that the thermal stability of the crystals is higher for nanofibres compared to bulk material. Additionally, more stable crystals are favoured in finer nanofibres. This is especially the case for PA6 nanofibres, having an increasing fraction of stable α-crystal phase with decreasing fibre diameter, as shown by both thermal analysis and X-ray diffraction. © 2013 Elsevier Ltd. All rights reserved.

Structural and mechanical characterization of nanostructured titanium oxide thin films deposited by filtered cathodic vacuum arc

Titanium oxides are interesting materials, because they can be used for photocatalytic, optical and gas sensing purposes. In a variety of applications, the present phases and film structure have an influence on the effectiveness of the coating function: for this reason, deposition parameter control plays a fundamental role in the formation of coatings with the wished features. In this work, titanium oxide films are deposited by filtered cathodic vacuum arc (FCVA) operated in a pulse mode. FCVA is a versatile deposition system appreciated both in research and industry for its high deposition rate, for the possibility to control the ion energy and for the production of nearly fully ionized plasma. A pure titanium cathode is used as ion source, and depositions are carried out in an oxygen reactive atmosphere. The effects of substrate temperature and substrate bias on film properties, structure and composition are investigated. Bragg-Brentano X-ray diffraction, and electron and atomic force microscopy are used to assess the deposited film structure, while nanoindentation is used to study film mechanical properties. Phases, roughness, hardness and reduced Young's modulus are studied as a function of the deposition parameters. Correlation between deposition conditions and structure of synthesized films is discussed, taking into account the features of plasma produced by a filtered cathodic arc system. © 2013 Elsevier B.V.

Growth and characterization of large, high quality MoSe2 single crystals

MoSe2 single crystals were grown by chemical vapor transport using TeCl4 as transport agents in the temperature gradient 1020-980°C. They were characterized by scanning electron microscopy (SEM), optical microscopy, image analysis coupled with SEM, microanalysis by SEM-EDX, X-ray fluorescence, inductively coupled plasma (ICP), X-ray photoelectron spectroscopy (XPS) and electrical conductivity. The characterizations showed that single crystals are perfectly homogeneous, stoichiometric and have very few defects and clean surfaces with areas in the range of 35-100 mm2. Single crystals grown by TeCl4 showed a high electrical conductivity. Their properties were highly dependent on the quality of the polycrystalline powders used for the growth. © 2012 Elsevier B.V. All rights reserved.

Impact of silane and siloxane based hydrophobic powder on cement based mortar

Impact of the addition of silane and siloxane based hydrophobic powders on cement based mortar was studied. Effect of powder addition on mechanical properties and water absorption of cement based mortar is described. Impact of accelerated ageing, including UV radiation, and rain-sun cycles on hydrophobic performance was assessed, demonstrating excellent durability of silane-based hydrophobic performance. © (2013) Trans Tech Publications, Switzerland.

Influence of the activating solution composition on the stability and thermo-mechanical properties of inorganic polymers (geopolymers) from volcanic ash

The influence of the activating solution composition on the stability and thermo-mechanical properties of geopolymers made from a Cameroonian volcanic ash is investigated. NaOH, KOH solutions and silicate solutions with low modulus were tested. The samples are cured at 90 C and the mechanical strength increases up to 21 days. With NaOH the strength development is faster, with a dry and wet compressive strength respectively around 40 MPa and 20 MPa at 21 days. The largest particles only act as reactive filler while smaller particles dissolve in the activating solution as seen by SEM. Pure volcanic ash and synthesized materials consisted of mostly X-ray amorphous material with some newly formed crystalline phases. KOH specimens were found to be thermally more stable, shrinking less than 3% after heating till 1000 C. The obtained results suggest the possible use of the synthesized materials for building applications and low temperature refractories up to 700-800 C. © 2013 Elsevier Ltd. All rights reserved.

The effect of roughness on nanoindentation results

Instrumented Indentation Technique (IIT) or nanoindentation is widely used to measure mechanical properties on nano to macro scales. Due to the simple testing procedure and the continuously increasing sensor sensitivity there exists practically no limitation on application scale and specimen size. One of the most important sources of error in IIT test is the inevitable roughness of the tested surface. The nanoindentation test is more sensitive for the roughness of the sample as the conventional hardness test because of its shallower penetration in the sample, especially in the case of thin films' characterization, when the indentation depth is limited by the film thickness. The question, what an effect the roughness on the value of hardness has, was not studied in detail yet. In this study we applied specially roughened samples in tests, carried out with different indenter tips and by various instruments to determine experimentally the effect of roughness. Other parameters (as indenter rounding and shape, penetration depth, wavelength of the roughness) do have some effect on test results. The initial theoretical findings were confirmed by a considerable accuracy in the experiments. Copyright © 2013 American Scientific Publishers. All rights reserved.

2012

Microstructural and chemical characterization of nanostructured Tialsin coatings with nanoscale resolution

Nanoscale resolution electron microscopy analysis combined with ion beam assisted techniques are presented here, to give answers to full characterization of morphology, growth mode, phase formation, and compositional distribution in nanocomposite TiAlSiN coatings deposited under different energetic conditions. Samples were prepared by magnetron sputtering, and the effects of substrate temperature and bias were investigated. The nanocomposite microstructure was demonstrated by the formation of a face-centered cubic (Ti,Al)N phase, obtained by substitution of Al in the cubic titanium nitride (c-TiN) phase, and an amorphous matrix at the column boundary regions mainly composed of Si, N (and O for the samples with higher oxygen contents). Oxygen impurities, predicted as the principal responsible for the degradation of properties, were identified, particularly in nonbiased samples and confirmed to occupy preferentially nitrogen positions at the column boundaries, being mainly associated to silicon forming oxynitride phases. It has been found that the columnar growth mode is not the most adequate to improve mechanical properties. Only the combination of moderate bias and additional substrate heating was able to reduce the oxygen content and eliminate the columnar microstructure leading to the nanocomposite structure with higher hardness (>30 GPa). ©2012 Microscopy Society of America .

2011

Effect of autogeneous deformation on the cracking risk of slag cement concretes

Special issue featuring articles arising from the 11th High-Tech Plasma Processes Conference

Endurance of TiAlSiN coatings : effect of Si and bias on wear and adhesion

In this work, the endurance of TiAlSiN nanocomposite thin films subjected to tribological solicitation is studied. These coating were deposited on M2 steel substrate by magnetron sputtering. Dry sliding experiments were conducted at ambient temperature against WC-Co ball. Coefficients of friction, wear rates and endurances were correlated with the composition, microstructure, mechanical properties, residual stress and adhesion of the coatings. The hardness and elastic modulus were found dependent not only on the composition but also on the residual stress induced by the deposition process. Friction coefficient was found to be independent on Si content while the wear rate is strongly reduced for higher Si contents. The formation of a nanocomposite microstructure, the amount of amorphous Si-based phase and both, wear resistance and adhesion are shown as the critical factors to determine the endurance of the coating. © 2011 Elsevier B.V.

Titanium oxide thin film deposition by pulsed arc vacuum plasma

The experimental study of effects of deposition conditions and plasma parameters on the structure of titanium oxide films is presented. The films are deposited by reactive deposition from a plasma generated by a pulsed cathodic vacuum arc source. The effects of deposition time and substrate bias voltage are studied, the films being deposited at different substrate temperatures. Bragg-Brentano X-ray diffraction and electron microscopy were used to investigate the structure of deposited films. Correlation between plasma parameters, deposition conditions and structure of synthesized films are established.

Study of bronze porous alloy Cu-Sn worked out by metallugy of the powders

Porous bronzes take popularity in various fields of technology. Their development is based on the metallurgy of powders. The samples, in the present study, are worked out by pressure sintering pressure. We used various techniques of characterization: density, hardness, optical and electronic microscopy and diffraction of x-rays. We showed that in the temperature and pressure range or field swept the density believes linearly with these two parameters. The secondary phase was identified. By microscopy, we proved that the structure is not homogeneous. © 2011 Published by Elsevier B.V.

2010

Mechanical and tribological properties of Ti-containing carbon nanocomposite coatings deposited on TiAlV alloys

Ti-doped carbon coatings were deposited on TiAlV alloys by reactive dc-magnetron sputtering in Ar/CH4 mixed gas. When Ar flow increases the incorporation of Ti into films raises while the concentration of C decreases. The formed nanometric TiC crystals were more noticeable for coatings deposited with higher Ar flows. Hardness (H) and elastic modulus (E) of coatings were measured by nanoindentation. H values were in the range of 8.8-15.9 GPa and E of 53.4-113.7 GPa. Higher values for H and E were obtained for films containing larger amount of TiC-phase. The presence of TiC crystals increased the coefficient of friction (COF) from 0.07 to 0.28 in scratch tests. Tribological experiments were carried out by using a pin-on-disk apparatus in air and in liquid. COF values ranged from 0.10 to 0.50 for tests in air. Despite of presenting higher COF, tests performed in liquid resulted in less pronounced wear tracks.

Influence of mixing and solid concentration on sodium bicarbonate secondary nucleation rate in stirred tank

This work aims to investigate the influence of the solid concentration in suspension on the contact secondary nucleation rate of sodium bicarbonate crystallization in a stirred tank crystallizer and to show the necessity of a local description of the mixing for a nucleation rate influence study. Experiments and computational fluid dynamics (CFD) simulations are realized. Crystallization kinetic parameters are extracted from experimental data using a mass distribution fitting approach. CFD and the experimental results allow identifying that a mixing property correlated with the measurements of the secondary nucleation rate in the stirred tank crystallizer appears to be the turbulent dissipation rate on the edge of the impeller. Its influence and the influence of the solid concentration in the suspension on the secondary nucleation rate are estimated by the evaluation of their exponents in a kinetic law. The obtained exponent values are then discussed qualitatively.

Mechanical properties of face-centered cubic supercrystals of nanocrystals

We report the first nanoindentation studies of well-ordered nanocrystal supercrystals composed of 7 nm lead sulfide nanocrystals stabilized with oleic acid ligands as a model system. Their modulus and hardness were found to be similar to hard polymers at 1.7 GPa and 70 MPa, respectively, and the fracture toughness was 40 KPa/m1/2, revealing the brittle nature of these materials. The mechanical properties are dominated by the organic capping agents surrounding the inorganic cores. The close-packed structure distributes stress evenly increasing the modulus and hardness. The relatively short ligands are not likely to be highly interdigitated leading to low dissipation during crack propagation and a low-fracture toughness value. © 2010 American Chemical Society.

Corrosion behavior of hybrid coatings: Electroless Ni-Cu-P and sputtered TiN

Protective coatings for mild steel (MS) are prepared by combining two techniques: electroless (autocatalytic) deposition of a Ni-Cu-P layer and reactive DC sputtering of TiN/Ti atop. These hybrid coatings are designated to provide corrosion protection together with wear resistance and hardness. The corrosion behavior of the system Ni-Cu-P/MS is compared with the conventional Ni-P/MS and its superiority is demonstrated by the weight loss method. This justified the choice of the ternary coating as intermediate amorphous layer, aiming to improve the impermeability of the inherently porous TiN/Ti. The structure of the hybrid TiN/Ti/Ni-Cu-P/MS is studied by TEM of thinned cross-sections prepared by the focused ion beam (FIB) technique. Electrochemical characterization (via potentiodynamic polarization curves) of TiN/Ti/MS and hybrid TiN/Ti/Ni-Cu-P/MS in two model media: 5% NaCl and 0.5M H2SO4 shows the outperformance of the hybrid coatings. SEM-EDS study of the local corrosion areas is conducted on FIB prepared sections. The role of internal stress in corrosion destruction process is discussed. The importance of bias voltage applied to the substrate during sputtering is considered. The advantage and prospects are outlined of MS finishing with hybrid TiN/Ti/Ni-Cu-P coating to ensure reliable corrosion protection joint with the excellent mechanical properties of TiN. © 2010 Elsevier B.V.

SiOxNy thin films with variable refraction index: Microstructural, chemical and mechanical properties

In this work amorphous silicon oxynitride films with similar composition (ca. Si0.40N0.45O0.10) were deposited by reactive magnetron sputtering from a pure Si target under different N2-Ar mixtures. Rutherford backscattering (RBS) studies revealed that the coatings presented similar composition but different density. The mechanical properties evaluated by nanoindentation show also a dependence on the deposition conditions that does not correlate with a change in composition. An increase in nitrogen content in the gas phase results in a decrease of hardness and Young's modulus. The microstructural study by high resolution scanning electron microscopy (SEM-FEG) on non-metalized samples allowed the detection of a close porosity in the form of nano-voids (3-15 nm in size), particularly in the coatings prepared under pure N2 gas. It has been shown how the presence of the close porosity allows tuning the refraction index of the films in a wide range of values without modifying significantly the chemical, thermal and mechanical stability of the film. © 2010 Elsevier B.V. All rights reserved.

Mechanical Properties of Face-Centered Cubic Supercrystals of Nanocrystals

We report the first nanoindentation studies of well-ordered nanocrystal supercrystals composed of 7 nm lead sulfide nanocrystals stabilized with oleic acid ligands as a model system Their modulus and hardness were found to be similar to hard polymers at 17 GPa and 70 MPa, respectively, and the fracture toughness was 40 KPa/m(1/2), revealing the brittle nature of these materials The mechanical properties arc dominated by the organic capping agents surrounding the inorganic cores The close-packed structure distributes stress evenly increasing the modulus and hardness The relatively short ligands are not likely to be highly interdigitated leading to low dissipation during crack propagation and a low-fracture toughness value

Corrosion behavior of hybrid coatings: Electroless Ni-Cu-P and sputtered TiN

Protective coatings for mild steel (MS) are prepared by combining two techniques: electroless (autocatalytic) deposition of a Ni-Cu-P layer and reactive DC sputtering of TiN/Ti atop. These hybrid coatings are designated to provide corrosion protection together with wear resistance and hardness. The corrosion behavior of the system Ni-Cu-P/MS is compared with the conventional Ni-P/MS and its superiority is demonstrated by the weight loss method. This justified the choice of the ternary coating as intermediate amorphous layer, aiming to improve the impermeability of the inherently porous TiN/Ti. The structure of the hybrid TiN/Ti/Ni-Cu-P/MS is studied by TEM of thinned cross-sections prepared by the focused ion beam (FIB) technique. Electrochemical characterization (via potentiodynamic polarization curves) of TiN/Ti/MS and hybrid TiN/Ti/Ni-Cu-P/MS in two model media: 5% NaCl and 0.5 M H2SO4 shows the outperformance of the hybrid coatings. SEM-EDS study of the local corrosion areas is conducted on FIB prepared sections. The role of internal stress in corrosion destruction process is discussed. The importance of bias voltage applied to the substrate during sputtering is considered. The advantage and prospects are outlined of MS finishing with hybrid TiN/Ti/Ni-Cu-P coating to ensure reliable corrosion protection joint with the excellent mechanical properties of TiN. (C) 2010 Elsevier B.V. All rights reserved.

Une cachette d'objets de valeur des années 260 apr. J.-C. dans une villa de la cité des Nerviens (Merbes-le-Château, Belgique)

La villa gallo-romaine de Merbes-le-Château (Belgique) est implantée en bordure de Sambre, à l'extrémité orientale de la cité des Nerviens. Elle comportait, aux IIe et IIIe siècles de notre ère, un imposant corps de logis et plusieurs bâtiments à fonctions économique et ornementale. Le site a également livré un dépôt d'objets précieux, découvert à l'intérieur du bâtiment principal, dans une petite pièce semi-enterrée. Il se compose de deux chaudrons en alliage de cuivre et d'un petit coffret contenant deux cuillères en argent, une bourse de 122 antoniniens en argent, une fiole en verre ainsi que quatre sesterces usés posés sur une plaque dédiée aux « Cavaliers Danubiens ». Cette plaquette en alliage de cuivre étamée apparaît exceptionnelle tant par sa rareté dans les Provinces Occidentales que par la qualité technique de son décor. L'originalité du dépôt, dont l'enfouissement est daté des années 260 de notre ère, tient dans sa composition hétéroclite, mêlant des objets de la vie courante, des biens précieux et une pièce à caractère religieux.

Simple filtered repetitively pulsed vacuum arc plasma source

A very simple design of cathodic filtered vacuum arc plasma source is proposed. The source without filter has only four components and none of them require precise machining. The source operates in a repetitively pulsed regime, and for laboratory experiments it can be used without water cooling. Despite the simple construction, the source provides high ion current at the filter outlet reaching 2.5% of 400 A arc current, revealing stable operation in a wide pressure range from high vacuum to oxygen pressure up to more than 10 -2 mbar. There is no need in complicated power supply system for this plasma source, only one power supply can be used to ignite the arc, to provide the current for the arc itself, to generate the magnetic field in the filter, and provide its positive electric biasing without any additional high power resistance. © 2010 American Institute of Physics.

2009

Electrostatic forces in micromanipulation: Experimental characterization and simulation including roughness

Manipulation by contact of objects between 1 μm and 1 mm are often disturbed by adhesion between the manipulated object and the gripper. Electrostatic forces are among the phenomena responsible for this adhesive effect. Analytical models have been developed in the literature to predict electrostatic forces. Most models have been developed within the framework of scanning probe microscopy, i.e. for a contact between a conducting tip and a metallic surface. In our study, we developed a simulation tool based on finite elements modeling. The strength of this model lies in the fact that it integrates roughness parameters. Measurements of electrostatic forces in function of roughness were conducted by atomic force microscopy. The experimental results were compared with the simulation results showing very good correlation. This demonstrates the influence of surface topography on electrostatic forces, especially for very small separation distances and proves the utility of the simulation tool in designing surfaces with controlled adhesion. Some application fields to which these results can be applied are drug delivery devices and micromanipulation tools. © 2009 Elsevier B.V. All rights reserved.

Infrared reflectivity spectra of thin porous aluminum oxide films

Combination of instrumented nanoindentation and scanning probe microscopy for adequate mechanical surface testing

Structural and mechanical study of nanocomposite Ti-Zr-C-H coatings prepared by reactive magnetron sputtering

Nanocomposite structures formed by small crystallites embedded in a lubricant matrix present moderate-high hardness, good toughness, and low values of friction coefficient and wear rate, and they are a promising alternative for protective tasks. In this study, we have prepared Ti-Zr-C-H films as potential candidates as protective layers for biocompatible applications. The constituting elements were selected due to their proven good biocompatibility at the macroscale. The films were prepared by reactive dc magnetron sputtering, and further characterized by X-ray photoelectron spectroscopy and X-ray diffraction. Mechanical and tribological properties were also evaluated. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Study of the rate-dependent behavior of pure nickel in conical nanoindentation through numerical simulation coupled to experiments

The use of specific metallic materials in micro-mechanical systems is promising for surgical applications due to their bio-compatibility and interesting mechanical and wear properties compared to the widely used material, silicon. Nanoindentation is one of the methods used to investigate the mechanical properties of materials at the nano-scale. Numerical simulation tools are useful in the understanding of the nanoindentation experiment. In this paper, the results of numerical simulations coupled to nanoindentation experiments conducted at various indentation depths and at different load rates on pure nickel are presented. The study parameters are carefully chosen to ensure the closest possible conditions between the experiments and the numerical simulations. It is shown that a good agreement between the experimental and the numerical results can be obtained for both the load levels and the creep indentation phase (displacement-time curves in the holding period) when taking into account a simple model with rate-dependent material behavior, and using a material parameter set that is in the acceptable domain for metals. © 2008 Elsevier Ltd. All rights reserved.

2008

The structure of niobium-doped MoSe2 and WSe2

Polycryst. niobium-doped molybdenum and tungsten diselenides were synthesized in silica tubes sealed under secondary vacuum. They were characterized by SEM, electron diffraction, X-ray diffraction, chem. compn. and EDX analyses. The morphol. of niobium-doped molybdenum solid solns. was shown to depend strongly on the conditions of synthesis, whereas the structural characterization did not.

Vibrational polaritons in thin oxide and nitride films

Angular dependencies of infrared reflectivity spectra of thin silicon oxinitride amorphous films on silicon and porous aluminum oxide films on aluminum had been measured. These spectra show vibrational bands and strong interference bands allowing film thickness and dielectric function calculation and providing useful information on the bonding struc-ture of the coatings. Angular dependencies of these bands give the dispersion of vibrational and interference polariton modes in the films. The intersection of vibrational and interference polaritons has been observed for silicon oxinitride film. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

2005

Influence of calcium ions on the crystallization of sodium bicarbonate

In industrial crystallization of sodium bicarbonate (sodium hydrogenocarbonate), the presence of calcium ions in solutions is unavoidable due to the production process. The understanding of the Ca2+ role in NaHCO3 crystallization would be helpful for improving the quality of the final products. The influence of calcium ions on NaHCO3 crystallization was investigated in a 5-l mixed suspension mixed product removal crystallizer under controlled conditions. A density meter was used for continuous supersaturation monitoring. After a steady state had been reached, different CaCl2 amounts were added at a constant flow rate. It was found that limited calcium ion levels in the system reduce drastically the nucleation frequency of NaHCO3 and has a limited influence on crystal growth rate. The supersaturation measurements and other methods confirmed this phenomenon. The relationship between the Ca2+ influence on NaHCO 3 crystallization, the calcium carbonate solubility and its metastable zone in concentrated NaHCO3 solution was established. In fact, Ca2+ has a maximum effect on NaHCO3 crystallization kinetics when the saturation of calcium carbonate in NaHCO3 solution has been reached, and the effect is constant in the metastable zone. The excess of Ca2+ precipitates in NaHCO3 solution as CaCO 3, as observed by energy dispersive X-ray and X-ray diffraction. This explained why an increasing Ca2+ concentration in the solution has a limited influence on NaHCO3 crystal size distribution and habit, but decreases the crystal purity. It is also confirmed that an impurity as Ca 2+ has no influence on the equilibrium NaHCO3-Na 2CO3. © 2004 Elsevier B.V. All rights reserved.

Investigation of crystallization kinetics of sodium bicarbonate in a continuous stirred tank crystallizer

In our previous work [J. Crystal Growth 263 (2004) 459], a supersaturation determination method using a high-precision densimeter was designed and developed for monitoring sodium bicarbonate supersaturation in the sodium carbonate-bicarbonate system, a two-component solution in equilibrium. In the present paper, we apply this method to the study of sodium bicarbonate continuous crystallization. It gives us access to the sodium bicarbonate supersaturation evolution. The sodium bicarbonate supersaturation evolution and their crystallization kinetics obtained in a continuous stirred tank crystallizer are investigated under different operational conditions, such as residence time, initial supersaturation and seeding. The induction time determined by density measurements is discussed. Mathematical modeling is used to interpret the supersaturation evolution. It is shown that measuring the density gives satisfying performances for studying the crystallization of a two-component solution in equilibrium, such as the sodium carbonate-bicarbonate system. © 2005 Elsevier B.V.

2004

Active carbon production from used tire in two-stage procedure: Industrial pyrolysis and bench scale activation with H2O-CO2 mixture

In the present study active carbons have been prepared from used tires and their characteristics were investigated. A two-stage activation procedure (pyrolysis at 800 °C in N2 atmosphere during 45 min in an industrial pyrolyser with a capacity of 1 t/h, followed by CBp activation with steam in the presence of CO2 at 970 °C in a bench scale reactor) was used for the production of activated samples. Gas (He/N2) phase adsorption and SEM techniques were used to characterize the produced active carbons. Comparison of surface area of the obtained activated carbons with others reported in the literature and the commercial carbon NORIT® GL 50 has also been performed. © 2004 Elsevier B.V. All rights reserved.

Application of density meter in the supersaturation determination of the two-component equilibrium systems

In industrial crystallization, a successful concentration measurement technique helps controlling the supersaturation, and thus obtaining the desired crystal size distribution will be possible. But for a two-component solution in equilibrium, a rapid concentration determination could be difficult. During the crystallization of sodium hydrogenocarbonate (sodium bicarbonate), in solution, there is an equilibrium between NaHCO3, Na2CO3 and CO2. In this study, a supersaturation determination method has been devised and developed for the sodium carbonate-bicarbonate system. The objective is to relate the density variation of the solution to the supersaturation of NaHCO3, so that the evolution of the supersaturation can be followed during the crystallization process. The method is to measure the density variation between the original solution and the solution after a desaturation or a saturation step, while minimizing the Na 2CO3 influence. The desaturation and saturation steps are carried out in a glass tube filled with NaHCO3 crystals. This supersaturation determination method has been successfully applied, and the validity of the method was confirmed on NaHCO3 saturated solutions, where the Na2CO3 is controlled by CO2 partial pressure. This methodology could be interesting not only for the study of the crystallization in two-component systems but also for solutions containing impurities. © 2003 Elsevier B.V. All rights reserved.

2003

In situ measurement of stresses in diamond-like carbon films

In situ determination of stresses in thin films can be used as an important tool to assist process development as well as to understand the thermodynamics of film formation. A simple technique for the measurement of stresses in growing films is described here. The technique consists of measuring the displacement of a laser beam reflected from the film surface. Displacement is induced by changes in the radius of the curvature of the substrate resulting from stresses in the film. The detector sensitivity at the used wavelength (635 nm) is approximately 12 mV μm-1, for which our experimental set-up is equivalent to 4 mV μrad -1. The actual data collected consist of the reflected beam displacement vs. time, and provides at any instant the value of the average stress. By knowing the deposition rate, time is directly correlated with film thickness, and the local stress can be determined. Examples of measurement of stresses in tetragonally bonded amorphous carbon films prepared by filtered cathodic arc are presented, as well as how this technique can be used to design the deposition process to virtually eliminate intrinsic stresses. © 2003 Elsevier B.V. All rights reserved.

Study of the solubility and the metastable zone of 1,3-dihydroxyacetone for the drowning-out process

The 1,3-dihydroxyacetone (DHA) is an important raw material in the cosmetic industry for its skin pigmentation property. The DHA is highly soluble in water, which leads to a very important viscosity value and a huge metastable zone width. In addition, the DHA is a heat-sensitive substance. The drowning-out process (water-out or salting-out) is then necessary to reduce the solubility and to favor the mobility of the molecular species in solution. In this work, the solubility curves of DHA in different water/ethanol mixtures have been established experimentally. The turbidimetric method is used successfully to study the metastable zone in the water/ethanol mixture. The results show that the metastable zone is large, both the dissolution and the crystallization of DHA are time consuming, which could be due to the low diffusivity in the high-concentration solutions and at low temperatures. © 2003 Elsevier B.V. All rights reserved.

Boron carbide coatings prepared by cathodic arc deposition

Boron carbide films are attractive materials for use as tribologcal coatings for low and high operating temperatures, especially for applications that require high hardness. The properties of boron carbide films prepared by cathodic arc using a heated B4C cathode are investigated. The B:C ratio in the film was about 3, and the only detected impurity was oxygen with a content below 5%. The effect of substrate bias on the film characteristics was studied. A direct correlation between hardness and elastic modulus and bias voltage applied to the substrate was observed for bias voltages in the interval of 0-500 V. Microstructure and chemistry of the films were investigated using X-ray diffraction, electron microscopy and X-ray absorption spectroscopy. © 2003 Kluwer Academic Publishers.

An international round-robin experiment to evaluate the consistency of nanoindentation hardness measurements of thin films

We conducted an international round-robin experiment to determine the consistency of nanoindentation hardness measurements of thin films among six different laboratories, using three different samples. These samples were chosen to present a challenge of indenting at small loads (μN range). They were: 250-nm-thick TiNx, 700-nm-thick TiC, and 500-nm-thick TiB2/TiC multilayer coatings (each layer being 3-nm thick), prepared at Northwestern University using magnetron sputtering on silicon (0 0 1) substrates. Each research team was free to use whatever nanoindentor and analysis methods at its disposal. This round-robin experiment demonstrates that for the hardness range of interest (15-35 GPa) and using well-documented procedures and analysis methods, the reported results from all laboratories are essentially the same, allowing for a statistical spread of approximately ± 14%. For consistent hardness measurements, four precautions must be observed: (i) proper tip-area function calibration, (ii) using sharp indenters, (iii) performing nanoindentation measurements with minimal thermal drift and with drift correction, (iv) using smooth samples, and (v) measuring the full hardness-maximum penetration curve. © 2002 Elsevier Science B.V. All rights reserved.

Investigation of non-hydrogenated DLC:Si prepared by cathodic arc

Non-hydrogenated diamond-like carbon (DLC) films (also referred as ta-C) have been extensively studied and are used for a variety of wear related applications. Alloying DLC with refractory metals and other elements have been shown to be promising techniques to overcome some of the problems associated with pure DLC, such as excessive level of intrinsic stresses and hightemperature stability. The microstructure of DLC:Me in general consists of crystalline metal carbides dispersed in a DLC matrix. In contrary, DLC:Si has an amorphous structure. We have used filtered cathodic arc to prepare DLC:Si up to 6% Si, and have characterized their structure and bonding using transmission electron microscopy and X-ray absorption spectroscopy. The effect of Si in changing the bonding configuration of the C network is discussed. The microstructure is then correlated to hardness and friction measured by nano-indentation and micro-wear. 002 Elsevier Science B.V. All rights reserved.

Engineering properties of superhard films with ion energy and post-deposition processing

Recent developments in plasma synthesis of hard materials using energetic ions are described. Metal plasma immersion ion implantation and deposition (MePIIID) was used to prep. several hard films: from diamond-like C (DLC) to carbides, from nitrides to oxides. The energy of the depositing species is controlled to maximize adhesion as well as to change the phys. and chem. properties of the films. Adhesion is promoted by the creation of a graded interface between the film and the substrate. The energy of the depositing ions is also used to modify and control the intrinsic stresses and the microstructure of the films. The deposition is carried out at room temp., which is important for temp. sensitive substrates. A correlation between intrinsic stresses and the energetics of the deposition is presented for the case of DLC films, and means to reduce stress levels are discussed.

2002

Vacuum arc deposited DLC based coatings

The great interest in the use of diamond-like carbon (DLC) films as a coating material is justified by the superior wear resistance and hardness, chem. inertness, and very low friction coeffs. of these coatings. Vacuum arc deposition is well suited to prep. superhard films with high sp3/sp2 ratios. However, the high level of internal stresses originating during growth prevents the deposition of thick films, and their hardness makes it difficult for DLC layers to comply with substrate deformations. To overcome these limitations, different approaches are possible. Multilayer structures are one means to maintain the surface mech. properties of the DLC while relieving the internal stresses. Another possibility is to dope the DLC films to reduce the internal stress and to stabilize the desirable sp3 bonds to higher temps. At higher doses of dopants, the formation of nanocrystals is possible and the properties of the coatings change drastically. All these approaches were investigated on films prepd. by cathodic arc and a synthesis of the results is presented here.

Nitrogen rich carbon nitride thin films deposited by hybrid PLD technique

Highly nitrogenated CNx, films were created by pulsed laser deposition (PLD), combined with radiofrequency (RF) and hollow cathode (HC) discharges. The N/C ratio higher than 1 was measured. Deposition set- up and results of optical measurement are discussed.

2001

Preparation of nitrogen-rich CNx films with inductively coupled plasma CVD and pulsed laser deposition

Nitrogen-rich amorphous carbon nitride films with N/(N + C) ≥ 0.5 have been deposited with three different methods, namely: (i) inductively coupled plasma CVD utilizing chemical transport reactions (ICP-CTR); (ii) inductively coupled plasma CVD with gaseous precursors (ICP-GP) and (iii) pulsed laser deposition (PLD) with additional r.f. plasma discharge. By means of plasma diagnostic measurements it is shown that in each case high concentrations of active radical species (e.g. CN' and N') are necessary to obtain high nitrogen concentrations. On the other hand, these nitrogen-rich films turned out to be mainly sp2 bonded having rather low densities of 1.8-2.0 g cm-3 only, irrespective of the method. From a comparison of the three techniques, and of further literature data, conclusions are drawn regarding the conditions necessary to obtain high N/(N + C) ratios, and regarding the deposition of superhard, crystalline sp3 bonded carbon nitride modifications. © 2001 Elsevier Science B.V. All rights reserved.

Depth resolved comparative investigation of phase formation and stress build-up in cubic boron nitride films

Cubic boron nitride films have been deposited by means of ion beam assisted deposition (IBAD) and electron cyclotron resonance plasma CVD. Specially designed silicon cantilever substrates were used which allow precise stress measurements. After deposition, the films were etched back in steps of approximately 5-20 nm by Ar ions. After each step, the stress, the thickness and also FTIR spectra were measured. By this means, the stress distribution, the development of the c-BN content and also the thicknesses of the h-BN nucleation layer and the transition layer h-BN --> c-BN could be determined. Major differences were found between the two types of layers: IBAD films possess a nucleation layer with a thickness of 15-20 nm and a stress of approximately 3 GPa. After c-BN nucleation, a transition region of approximately 20 nm is observed in which the c-BN content rapidly increases to the final value, which can exceed 90%. However, the c-BN top layer possesses a high compressive stress with values up to 20 GPa. In contrast, for ECR films the transition from the h-BN nucleation layer to the c-BN top layer is much more gradual (nucleation layer thickness approx. 50 nm). Simultaneously, the c-BN content of the top layer is limited to approximately 70% while its stress is much lower (2-3 GPa). The reasons for these differences in phase formation and stress build-up are discussed in terms of the differences between the two techniques. (C) 2001 Elsevier Science B.V. All rights reserved.

Mechanical and optical properties of c-BN films deposited by ECR-microwave PECVD

Mechanical and optical properties of CNx films with high N/C ratio

Nitrogen-rich carbon nitride films were prepared by three different deposition methods on fused silica, stainless steel and silicon cantilever substrates. Their optical properties were studied by spectroscopic ellipsometry and UV spectrometry. Mechanical properties such as plastic and Vickers microhardness, Young's modulus, adhesion and film stress were also tested. The results were compared with the properties of films with lower nitrogen concentrations.

Comparative characterization of nitrogen-rich CNx films prepared by different ICP-CVD techniques

Thin amorphous nitrogen-rich CNx films (N/(C+N) ≥ 0.5) have been prepared by two inductively coupled plasma chemical vapour deposition (ICP-CVD) techniques: using transport reactions from a solid carbon source and from CCl4/NH3/Ar and CCl4/N2/H2/Ar gas mixtures. Optical emission spectroscopy (OES) and quadrupole mass spectrometry were used to derive information about the plasma properties. The composition of the films was investigated by Anger electron spectroscopy (AES), wavelength dispersive X-ray (WDX) and elastic recoil detection (ERD) analyses, and the chemical bonding structure by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. In addition, several application relevant properties (mechanical, optical, electrical) of the nitrogen-rich CNx films were studied. The results of both deposition methods were compared and discussed on the base of the specificities of the processes.

2000

Investigation of the thermal stability of nitrogen-rich amorphous carbon nitride films

The thermal stability of nitrogen-rich amorphous carbon nitride films (N/C≥1) is investigated from room temperature up to 600 °C. The films were deposited by three different methods, namely pulsed laser deposition (PLD), inductively coupled plasma chemical vapour deposition (ICP-CVD) with gaseous precursors, and ICP-CVD utilizing transport reactions. As-deposited and annealed films were characterized with respect to their thickness, composition and bonding structure by a variety of methods including wavelength dispersive X-ray analysis (WDX), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). Annealing at 200 °C leads to desorption of surface contaminants while in the range between 200 and 400 °C a significant densification is observed. Above 400 °C a drastic loss of film material, especially nitrogen-rich groups, sets on, leading to the total destruction of the films at 600-700 °C. These observations are compared with the annealing behaviour of films with lower nitrogen content.

Structural characterization of epitaxial Bi2Sr2CuO6+δ thin films deposited on SrTiO3 substrates using inverted cylindrical magnetron sputtering

High quality c-axis oriented epitaxial Bi2Sr2CuO6+δ thin films were deposited on 0° and 6° vicinal SrTiO3 (100) substrates using an inverted cylindrical magnetron sputtering method. Their structural properties, regarding the orientation, epitaxy, surface morphology, composition, and surface microstructure, were studied by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The influences of the deposition parameters and substrate surface structure on the structural properties of these epitaxial Bi2Sr2CuO6+δ thin films are studied. A metal-insulator transition is observed with a variation of the Sr deficiency. It is demonstrated that films on 0° and 6° vicinal substrates grow in the two-dimensional and step-flow modes, respectively. Optimal deposition conditions were obtained leading to an extremely smooth film surface and high epitaxial quality.

Physical properties of carbon nitride films synthesized using atomic transport reactions

Inductively coupled plasma chemical vapour deposition (ICP-CVD) has been used for the preparation of thin CNx films from a solid carbon source (at floating potential) and a nitrogen plasma. Volatile CN species generated via atomic transport reactions are the film forming particles. The deposited layers have a rather smooth surface; their deposition rate and thickness, respectively, depend on the substrate position due to a gradient in the precursor species concentration. The nitrogen fraction is at about 50% and exhibits almost no dependence on the deposition parameters. Emphasis was placed on a detailed study of the bonding structure by different analytical techniques. Based on these investigations, a probable structure of the CNx films is proposed. Since no identification of tetragonally bonded carbon atoms was found, it is supposed that the bonding network is composed of imine-like units and only to a small part of nitrile-type elements. The films are insulating with resistivity of up to 1011Ωcm. © 2000 Elsevier Science S.A.

Formation of cubic boron nitride thin films using ECR plasma enhanced CVD

Cubic boron nitride containing thin films were deposited on (100) Si and steel substrates using electron cyclotron resonance plasma enhanced chemical vapor deposition. The deposition chamber is designed for large area coatings. Dynamic properties of the ECR plasma were studied using a Langmuir probe. A uniform ion density of the order of 5×1011 cm-3 over the heater surface, which has a diameter of 18 cm, was obtained. A systematic optimization of the deposition parameters was carried out. The films were characterized using Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and ellipsometry. Under optimal conditions, homogeneous cubic boron nitride containing thin films were obtained on large area with a diameter of 12 cm. It was found that the films deposited on steel substrates have a long-term stability when compared with the films on Si substrates. © 2000 Elsevier Science S.A.

1999

Application-relevant characterization of magnetron-sputtered carbon nitride films

Carbon nitride (CNx) films were deposited onto Si substrates by radio frequency magnetron sputtering at nitrogen pressures up to 0.3Pa (the resulting nitrogen concentration ranged from 32 to 41%). Their optical properties, structure and bonding were characterized by spectroscopic ellipsometry, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. The films exhibit a behavior typical for disordered systems, and no known C3N4 structure was identified. A pronounced effect of the nitrogen partial pressure is found for the low pressure region. The presence of various types of C-N bond, as well as of hydrogen and oxygen, is revealed. The complementarity of information inferred from Raman and IR spectra is discussed. © 1999 Elsevier Science S.A.

Inductively coupled plasma and laser-induced chemical vapour deposition of thin carbon nitride films

Thin CNx films have been deposited on silicon substrates by inductively coupled plasma chemical vapour deposition (ICP-CVD) and by laser-induced chemical vapour deposition (LCVD) utilizing the focused beam of a copper bromide vapour laser. Different gas mixtures were used: CH4/N2 and CCl4/N2/H2 for ICP-CVD, and CCl4/NH3 for LCVD. Plasma properties (electron temperature, electron and ion densities, plasma potential) were studied by Langmuir probe and optical emission spectroscopy. The growth rates ranged up to 80nmmin-1 for ICP-CVD and 700μmmin-1 for LCVD. The surface morphology was studied using atomic force microscopy for ICP-CVD, and scanning electron microscopy for LCVD. Beside carbon and nitrogen, silicon and oxygen for LCVD and chlorine for ICP-CVD (in the case of the CCl4/N2/H2 system) was detected by Auger electron spectroscopy. Fourier transform infrared (FTIR) spectroscopy was used to determine the chemical bonding structure. Bands assigned to C=C and C=N (graphite-like domains) and to C-H bonds were detected in the films deposited by both processes. In addition, different bands attributed to other types of carbon nitride bonds or to due to the presence of impurity atoms were observed in the FTIR spectra of the CNx films deposited by the ICP-CVD and LCVD. The results of both deposition techniques were compared and discussed on the base of the processes peculiarities. © 1999 Elsevier Science S.A.

Characterization of magnetron sputtered carbon nitride films

Influences of thermal annealing and humidity exposure on surface structure of (100) single-crystal MgO substrate

We studied the influence of thermal annealing on the surface structure of (100) single-crystal MgO substrates by atomic force microscopy (AFM). By annealing MgO substrates at various temperatures for 4 h in flowing oxygen, we showed that the surface reconstruction could be explained by considering surface diffusion, surface evaporation, and condensation. At an annealing temperature of 1473 K, a stepped structure was formed with screw dislocations acting as step sources. The influence of humidity on the surface morphology of MgO substrates was also studied by exposing them to a constant humidity of 40 and 80% for different times. After an exposure time of 1.5 h in 80% humidity, the substrate surface was already covered by reaction products. For the 40% humidity, the corresponding time is 10 h. The major reaction product was identified as Mg(OH)2 by x-ray diffraction.

Tungsten-containing amorphous carbon films deposited by pulsed vacuum arc

Amorphous carbon (a-C) films with a wide range of W concentrations have been produced by mixing C+ and Wn+ plasma streams originated in filtered cathodic arc plasma sources. Adhesion of these films to silicon substrates was very high, and was achieved by atomically mixing the film and the Si at the interface. The deposition of the tungsten-doped amorphous carbon films was carried out at room temperature, and the energy of the depositing ions was in the range of 100-6 keV. The films were characterized by TEM, XRD, XPS, RBS and Raman spectroscopy. Small additions of W to amorphous carbon significantly decrease the magnitude of the compressive stresses that are present in these films. The corresponding decrease in hardness with increasing W content was not nearly as significant. Film hardness varied between 63 GPa (with 1 at.% W) and 20 GPa (the bulk value for WC) and depended not only on the W content but also on the depositing ion energy. At W contents between 20 and 50 at.%, the film consisted of crystalline WC dispersed in an amorphous C matrix. At W content below 20 at.%, the WC present in the film was amorphous, and the film consisted then of mixtures of a-WC and a-C.

1998

Wear behavior of diamond-like carbon/metal carbide multilayers

The high level of stress in hard diamond-like carbon (DLC) films limits their maximum thickness and their compliance with substrate deformation. Multilayer films are one approach to overcome these disadvantages. We have prepared multilayers of DLC/TiC, and DLC/WC(x) by filtered cathodic vacuum arc, then investigated and compared their wear properties at room temperature. The films were deposited on polished, oil-hardened AISI 01 tool steel substrates. The number and thickness of layers within the films were varied while the total thickness was approximately constant. Friction coefficients and wear were measured as a function of the atmosphere and load in ball-on-disk tests. Tests were performed in dry nitrogen and in air with relative humidity of 50%. Initial Hertzian contact pressures of 0.8 and 1.4 GPa were used with alumina balls. For all films showing good wear resistance, both the layer in immediate contact with the steel and the topmost layer were DLC. The failure mechanism and the wear resistance were found to be highly dependent on the type of carbide, on the atmosphere during the wear test and on the thickness and number of individual layers.

Residual stress evolution by the ex-situ annealing of TiN thin films deposited on steel substrates

1997

Synthesis and characterization of thin films of WCx produced by mixing W and C plasma streams

WCx coatings have been synthesized by filtered cathodic arc deposition at room temperature. Repetitively pulsed W and C plasma streams were mixed, and the duration of the pulse of each stream was used to vary the film composition. The energy of the incident ions was controlled by applying a pulsed bias voltage at the substrate, and was used for enhancing the adhesion as well as for modifying the microstructure of the film. The films with low W content (less than 20 at.%) consisted of regions of amorphous WC dispersed in an amorphous carbon matrix. At higher W content, nano-crystalline WC was observed. Internal stresses in the as deposited films ranged between 500 and 4500 MPa, depending on the W content and the applied bias voltage. Film hardness varied between 63 GPa and 30 GPa, and strongly depended on the W content and also on the applied bias voltage. © 1997 Elsevier Science S.A.

Preparation of extremely smooth YBa2Cu3O7-δ thin films on the annealed MgO substrates

Extremely smooth YBa2Cu3O7-δ thin films (Tc = 88 K and a Jc > 2 × 106 A cm-2 at 77 K) were deposited on annealed (100) MgO substrates. X-ray diffractions of these films reveal that they are c-axis oriented with a high quality of epitaxy. A flat surface free of outgrowths is observed by scanning electron microscopy. Atomic force microscopy study shows that the average surface roughness of these films is less than 1 nm. It is found that the surface steps, induced by the thermal annealing on MgO substrates are essential for the preparation of epitaxial YBa2Cu3O7-δ thin films with an extremely smooth surface. These steps are interpreted as the preferential nucleation and rapid growth sites which lead to a controlled growth and a smooth surface. © 1997 Elsevier Science Ltd.

Deposition of titanium carbide films from mixed carbon and titanium plasma streams

Dual source metal plasma immersion ion implantation and deposition was used to deposit TixCy films over a wide range of Ti:C composition. This technique is well adapted for this purpose and allows one to tailor the microstructure and properties of the films. We investigated the variation of the composition, bonding states, and structure as functions of the deposition conditions. Excess carbon and contamination oxygen are incorporated in the TiC lattice interstitially and substitutionally, respectively. The wear mechanism of a stoichiometric TiC film was investigated and compared to that of a diamondlike carbon film. TiC fails by wear and microcrack propagation. © 1997 American Vacuum Society.

Atomic force microscopy study of the surface microstructure of YBa2Cu3O7-δ thin films on MgO substrates

The surface microstructure of c-axis oriented epitaxial YBa2Cu3O7-δ thin films (Tc=88 K, ΔTc=0.2-1 K, Jc≥2×106 A cm-2 at 77 K) deposited on MgO substrates was studied by atomic force microscopy (AFM) operating in air at room temperature. Polished MgO substrates were annealed at 1200°C for 2 h in flowing oxygen and the induced modification on the surface microstructure was detected by AFM. Steps and screw dislocation loops, observed for the substrates annealed at 1200°C, were found to act as preferential nucleation sites for YBa2Cu3O7-δ thin film growth and lead to a controlled growth with a surface roughness lower than 10 Å. We propose a film growth model to describe the controlled epitaxial film growth on the substrates with steps on the surface. Within this model, thin films grown on substrates with surface-steps will have a smoother surface when compared with the films deposited on substrates without steps. This is in agreement with our experimental observations. © 1997 Elsevier Science S.A.

Structural properties of c-axis oriented epitaxial YBa2Cu3O7-δ thin films

C-axis oriented epitaxial YBa2Cu3O7-δ thin films ( Tc of 88 K and Jc of 107A/cm2 at 77K) were deposited on (100) MgO and SrTiO3 substrates using magnetron sputtering. Their structural properties, studied by x-ray diffraction, scanning electron microscopy, atomic force microscopy, Rutherford backscattering, and transmission electron microscopy, will be reported. The TEM study indicates a high density of nanometer-sized Y2O3 precipitates in these films, which can act as effective pinning centers and lead to the very large critical current densities observed in these films.

Deposition and properties of doped diamondlike carbon films produced by dual-source vacuum arc plasma immersion

Diamond-like C films with mech. properties approaching those of diamond were consistently produced by cathodic vacuum arc based techniques. These films were successfully used in applications where enhanced hardness and wear resistance are required. Such DLC films have two major drawbacks that prevent their application in other area: a high level of internal stresses, which promotes failure by spallation of thick films; and the loss of mech. properties at temps. >300°. The authors describe the effect of doping elements on the room-temp. mech. properties and on the thermal stability of DLC films upon annealing in air. The effect of the presence of W and Ti was studied and compared to pure DLC. The films were produced by dual-source metal plasma immersion ion implantation and deposition with magnetic filtering to remove macro impurities from the plasma; dopant content was controlled by varying the relative pulse duration of the two plasma sources. Microstructural and chem. characterization of the films are presented.

Preparation of TiC and TiC/DLC multilayers by metal plasma immersion ion implantation and deposition: relationship between composition, microstructure and wear properties

We have used pulsed vacuum arc deposition to prepare TixCy films and multilayer structures of TixCy / diamondlike carbon (DLC) in a dual plasma source set-up. The composition of the monolithic films was controlled by varying the pulse duration of each plasma gun. During the deposition, a repetitively pulsed bias voltage was applied to the substrate in order to improve the adhesion to the substrate and between the individual layers. For the multilayers, the carbon and Ti guns were synchronously pulsed during deposition of the TixCy, and the Ti gun was not operated during the DLC deposition. Multilayers with different periodicities were synthesized. The deposited films were analyzed by various techniques including XPS, AES, TEM, EELS, and XRD to characterize the composition, bonding states, and microstructure. Special attention was given to the interface thickness in relation to the applied bias voltage. Tribological properties such as friction coefficient and wear resistance were measured, and correlated to the composition and microstructure of the films.

1996

Glow discharge sputtering deposition of thin films of Ag, Cr, Cu, Ni, Pd, Rh and their binary alloys onto NaCl and MgO

The experimental conditions to condense epitaxial films of Ag, Cr, Cu, Ni, Pd, Rh, AgPd, CuPd and CuRh on MgO(100) and NaCl(100) by glow discharge sputtering are reported. The films are characterized by THEED, RHEED, SAD, TEM, ICP and AES. The effect of the substrate, the temperature and the target composition on the films obtained is examined and discussed. Perfect parallel epitaxy ((001)[110]d (100)[110]s) was observed for all systems studied, except for Ag/MgO.

1995

Comparison of the properties of BN films synthesized by inductively coupled r.f. and microwave plasmas

hin films of boron nitride are synthesized by two plasma-enhanced chemical vapour deposition techniques: inductively coupled r.f. plasma (13.56 MHz) and microwave plasma (2.45 GHz). We study the composition (impurity level, B N ratio), the proportion of c-BN phase in the films and other properties of those films as a function of various process parameters. Two boron and two nitrogen precursors are compared: trimethyl borazine and diborane, dini trogen and ammonia, respectively. The advantages and disadvantages of each combinations are presented. The deposition process is followed by optical emission spectroscopy. Adhesion is one of the main problems encountered for films containing c-BN. © 1995.

Diamond-like coatings

Non-hydrogenated diamond-like carbon films have been prepared by Dual Ion Beam Sputtering and Ion Beam Assisted Magnetron. The assistance parameters -ion energy, ion mass, ion flux/atom flux- have been systematically varied and their effect on the microstructure of the films studied. The films have been characterised by Rutherford Backscattering Spectroscopy (RBS), High Resolution Transmission Electron Microscopy (HRTEM), Electron Energy Loss Spectroscopy (EELS), Positron Annihilation Spectroscopy (PAS), and Raman Spectroscopy (RS). RBS and PAS results showed that the density and the degree of disorder of the films go through a maximum with ion energy, and that the void concentration goes through a minimum. EELS and RS show that the films are mostly sp(2) bonded, with a maximum concentration of sp(3) bonding of about 16% for the largest values of density. The evolution of density with ion flux and energy is consistent with a combined effect of atomic displacements in the film leading to densification, and with damage buildup leading to progressive graphitisation as the energy is increased.

Structure of galvanostatic anodic TiO2 films: comparison of microscopies

The galvanostatic anodization of titanium substrates at high current density (higher than 50 A/m2 at room temperature) tends to the formation of a thin oxide film with preferential conducting channels inside a homogeneous non conducting matrix. The purpose of this paper is to compare the results obtained by different microscopies (optical microscopy, scanning electron microscopy, scanning transmission electron microscopy at high resolution with electron diffraction and atomic force microscopy) in order to identify the structure and the composition of these channels. These channels are formed by the contact of a small number (10 to 20) of submicronic (100 to 500 nm) crystals. All these crystals present the same crystallographic orientation perpendicular to the substrate. The aggregates are protruding from the relatively flat oxide surface. The different microscopies provide complementary results.

Structure and composition of hydrogenated Ti<inf>x</inf>C<inf>y</inf> thin films prepared by reactive sputtering

1994

Physical properties of nitrogenated amorphous carbon films produced by ion-beam-assisted deposition

Carbon films with up to 32 at.% N (a-C:N) have been prepared using an ion-beam-assisted magnetron, with an N2 + beam at energies between 50 and 300 eV. The composition and density of the films vary strongly with the deposition parameters. Electron energy loss spectroscopy shows that these a-C:N films are mostly graphitic with up to 20% C sp3 bonding. Rutherford backscattering spectroscopy and neutron depth profiling show that the density goes through a maximum as the average deposited energy per unit depth increases. X-ray photoelectron spectroscopy shows that nitrogen is mostly combined with carbon in triple (C≡N) and double (C=N) bonds. Positron annihilation spectroscopy shows that the void concentration in the films goes through a minimum with deposited energy. These results are consistent with a densification induced by the collisions at low deposited energy, and damage-induced graphitization at high deposited energy values. © 1994.

Microstructural evolution of non-hydrogenated amorphous carbon under ion beam assistance

Amorphous carbon films have been deposited by ion beam assisted techniques and characterized by high resolution transmission electron microscopy, electron energy loss spectroscopy, and positron annihilation spectroscopy. It was found that the momentum transfer of bombardment has a strong influence on coating properties such as density, void concentration and sp3 content. The results can be explained by an ion pinning effect at low ion energies and a damage-induced graphitization at high ion energies. © 1994.

Surface segregation study of Ib-VIII single-crystal alloys

Surface segregation of AgPd, CuPd and CuRh single crystals was studied by AES. The samples were either massive alloys or epitaxial thin films deposited on MgO. A weak surface segregation of silver was detected in AgPd alloys while the surfaces of CuPd and CuRh alloys were enriched in copper. The diffusion of copper and silver to the surface during heat treatments can be easily shown by looking at the behaviour of the Auger low-energy peaks. Our results were compared with previously published data and with theoretical models. The element with the lower surface energy segregates but not as strongly as suggested by the ideal solution model. © 1994.

Microstructural development at Ti-based alloy/coated SiC interfaces

The kinetics of formation of reaction layers at the interface between a Ti-based alloy (β-21s) and graphite blocks coated first, by CVD techniques, with a 100 μm layer of SiC and then either TiC or C were detd. The rate controlling step for reaction at 900° and 10 MPa for up to 6 h was carbon diffusion through the reaction layer. The behavior was consistent with that of composite systems for prolonged heat treatment and the same growth behavior was exhibited by both systems. Incubation times of 0.42 and 0.9 h were detd. for reaction layer growth in the TiC- and C-coated systems resp. The reaction layer/Ti-alloy bond strength was good but all couples failed readily, esp. if any C layers remained. The growth conditions of TiC coatings by reactive magnetron sputtering were detd. for two different types of gas mixts.: CH4/Ar and C2H2/Ar. The compn. and structure of the films were extensively studied.

Physical properties of A-C:N films produced by ion beam assisted deposition

Carbon films with up to 32 at.% of nitrogen have been prepared with ion beam assisted magnetron, using a N2+/N+ beam at energies between 50 and 300 eV. The composition and density of the films vary strongly with the deposition parameters. EELS, SXS, XPS, and IR studies show that these a-C: N films are mostly graphitic and have up to 20% sp3 bonding. Nitrogen is mostly combined with carbon in nitrile (C = N) and imine (C = N) groups. It is shown by RBS and NDP that density goes through a maximum as the average damage energy per incoming ion increases. Positron annihilation spectroscopy shows that the void concentration in the films goes through a minimum with average damage energy. These results are consistent with a densification induced by the collisions at low average damage energy values and induced graphitization at higher damage energy values. These results are similar to what is observed for Ar ion assisted deposition of a-C films. The mechanical properties of these films have been studied with a nanoindenter, and it was found that the hardness and Young's modulus go through a maximum as the average damage energy is increased. The maximum of mechanical properties corresponds to the minimum in the void concentration in the film. Tribological studies of the a-C:N show that the friction coefficient obtained against diamond under dynamic loading decreases strongly as the nitrogen composition increases, this effect being more pronounced at low loads.

Effect of ion beam assistance on the microstructure of nonhydrogenated amorphous carbon

Nonhydrogenated diamondlike carbon films have been prepared by dual ion beam sputtering and ion-beam-assisted magnetron. The assistance parameters - ion energy, ion mass, ion flux/atom flux - have been systematically varied, and the films have been characterized by Rutherford backscattering spectroscopy, high-resolution transmission electron microscopy, electron energy loss spectroscopy, positron annihilation spectroscopy, Raman spectroscopy, and nanoindentation. It was found that the density and the degree of disorder of the films go through a maximum with ion energy, and the void concentration goes through a minimum. Microstructure analysis shows that the films are mostly sp2 bonded, with a maximum of about 16% concentration of sp 3 bonding from the largest values of density. The evolution of density with ion flux and energy is consistent with a combined effect of atomic displacements in the film leading to densification, and damage buildup leading to progressive graphitization as the energy is increased. The large hardness/elastic modulus ratios obtained should lead to excellent friction properties.

Surface segregation study of Ib-VIII single-crystal alloys

Microstructural evolution of non-hydrogenated amorphous carbon under ion beam assistance

1993

Deposition by Glow Discharge Sputtering of Thin Epitaxial Films of I Alloys (AgPd, CuPd, CuRh)

Thin films of CuRh, CuPd, and AgPd were deposited by glow discharge sputtering onto (100) magnesium oxide single crystals. The rhodium and palladium content ranged from 0% to 100% of precious metal and the film thickness was usually between 10 and 100 nm. The composition, epitaxial relationship, crystallinity, and phase diagram were investigated as a function of substrate temperature and target composition. A comparison of the three systems was realized. Conditions of epitaxy were determined for the pure metals and their alloys. The temperature of epitaxy of the alloys, even at very low precious metal concentrations, is close to that of the group VIII elements. The parallel epitaxial relationship between the deposit and the substrate is identical for the three systems, namely (001)[110]d

1991

Solidification of copper-rhodium alloy single crystals

Preparation of copper-rhodium alloy single crystals by the vertical Bridgman method is described in this paper. Dendritic structures are formed during the solidification process of 1.5, 4, 8.75 and 15 at.% Rh alloys. Various methods (microindentation, electron microprobe and scanning Auger microscopy) are used to characterize the solute distribution. A study of the formation conditions and of the thermal stability of the structures is also presented. The results are in agreement with existing models. © 1991.

Preparation of SixCyHz films from methylsilane by plasma-enhanced chemical vapor deposition

Hydrogenated amorphous silicon carbide (SixCyHz) films were synthesized by plasma-enhanced chemical vapor deposition using monomethylsilane (CH3SiH3) as the precursor. Silicon (100) wafers and gold foils were employed as substrates. A mass spectrometric analysis of the plasma showed that the advantage of using monomethylsilane relative to a silane-hydrocarbon mixture is that the majority of the Si-C bonds were preserved in the CH3SiH3 plasma. The composition and the morphology of the SixCyHz films was studied via X-ray photoelectron spectroscopy, Auger electron spectroscopy, and scanning electron microscopy as a function of the substrate temperature, composition of the ion flux bombarding the surface, and kinetic energy of these ions. The oxygen content of the films was found to decrease monotonically with increasing substrate temperature. © 1991.

Preparation and characterization of amorphous SiC:H thin films

Silicon carbide films were deposited by plasma enhanced chemical vapor deposition utilizing monomethylsilane (CH3 SiH3). Silicon (100) and polycrystalline gold were used as substrates. A mass spectrometric analysis of the monomethylsilane plasma showed that the majority of the Si-C bonds were preserved in the gas phase. The composition, the density and morphology of the amorphous SiC:H (a:SiC:H) films were studied as a function of substrate temperature, composition of the ion flux bombarding the surface and the kinetic energy of these ions. The surface science techniques utilized for these investigations include x-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning electron microscopy, Fourier transform infrared, and Raman spectroscopies. © 1991, American Vacuum Society. All rights reserved.

1990

Surface characterization of rhodium-copper alloys

This paper presents the results of a surface analysis of copper-rhodium alloys by Auger electron spectroscopy during heat treatments under vacuum. It is shown that copper segregation takes place in the first atomic layer at every rhodium concentration. Special attention is given to the influence of diffusion rate on the composition of the surface region. The results are compared with theoretical models. A segregation enthalpy is determined for a 1.5 at.% Rh alloy at 873 K.

1989

Electrodéposition de métaux et non-métaux en milieux organiques

Ce travail présente une synthèse bibliographique des travaux réalisés dans le domaine de l'électrodéposition des métaux (et non métaux) en milieux organiques. La diversité des conditions d'obtention des dépôts nous a conduit à présenter ces conditions sous la forme de deux tableaux, le premier centré sur les couples «métalsolvant», et le second sur les couples «électrolytes-solvants» (55 références)

1986

Structure and purity of epitaxial films of copper and rhodium deposited onto MgO single-crystal substrates by glow discharge sputtering

The structure and surface purity of epitaxial films of rhodium deposited by thermal evaporation and ion sputtering onto MgO(100), air cleaved and chemically polished, and onto epitaxial films of Cu(100) are compared. The orientation (100)d//(100)s (where d indicates deposit and s indicates substrate) is always predominant and only this orientation occurs on the (100)Cu//(100)MgO substrate. Electron diffraction and Auger spectroscopy show that the best results are obtained by glow discharge sputtering onto the last substrate. © 1986.

Preliminary study of the formation and characterization of Rh alloys with an element of the 1B group

The catalytic importance of rhodium in the industry implies an increased knowledge of its surface composition and of the alloying effect on the surface properties of this metal. For this reason, we selected the Cu-Rh system. Massive single crystals of dilute Cu-Rh alloys were prepared by the Bridgman method (fusion and unidirectional solidification). They were characterized by x-ray back reflexion and optical microscopy. All our samples (1. 5, 2, 8 and 15 at% Rh) showed cellular-dendritic structures. Their elimination was obtained by heating at 1000 degree C in hydrogen at atmospheric pressure (to limit the copper loss). The surface composition of the crystals is determined by auger electron spectroscopy but a quantitative analysis requires a measure of the rhodium relative sensitivity factor. This value was obtained by two methods: (a) the internal standard method by scraping the samples surface; (b) the use of elemental sensitivity factors.

Communications publiées lors de congrès ou colloques nationaux et internationaux

2017

Cement paste setting and early age hydration in presence of encapsulated and emulsified siloxane

Influence of silanes on the setting time and early age hardening of bulk hydrophobic mortars

Influence of silane on the setting time and early age hardening of bulk hydrophobic mortars

Comparison of the effect of microencapsulated and emulsified siloxane on setting and early age hydration of CEMI

2016

Apport des analyses élémentaires et structurales à l'interprétation des dispositifs pariétaux de la grotte d'El Castillo (Cantabrie).

2014

Non-ionic silane emulsion as integral water repellent - impact on cement hydration process

Silanes or siloxanes have been used as post treatment water repellents for a long time. They are capable of chemically reacting with the pore surfaces thus protecting the cementitious matrix from water penetration. The study evaluates the combination of a non-ionic emulsion of a silane monomer with a silicone resin used as integral water repellent. Detailed analyses of cement hydration process were carried out by means of isothermal calorimetry, setting time measurements, and SEM investigation. It was possible to show that the hydrophobic agent introduced as integral water repellent influences the cement hydration process. Mercury porosimetry analysis showed that porosity and pore structure in cement matrix does not change due to the presence of silane emulsion. Reduction of water uptake by this emulsion was also assessed as well as its impact on the mechanical properties.

Continuous monitoring of the setting and early age hardening of mortars with novel integral water repellent

Bulk hydrophobic treatments of cement-based materials have an excellent industrial application potential. According to the design process of the hydrophobic cement-based material, the hydrophobic agent can be incorporated as admixture, neat emulsion or powder. In this study, a non-ionic water based emulsion of silane monomer and silane resin is used as “integral water repellent” treatment of mortar. The setting and early age hardening of mortars with water/cement ratio of 0.5 and two types of cement (CEMI and CEMIII) were assessed by means of isothermal calorimetry, penetration resistance tests and ultrasonic transmission measurements. The use of ultrasonic measurements allows the continuous monitoring of the evolution of the p- and s- wave velocity through mortars and consequently, a whole picture of the early age elastic properties development of mortars. A decrease in the Young's elastic modulus amplitude evolution was noticed when the silane emulsion is used. Furthermore, with the addition of water repellent, the penetration resistance tests have also shown that the setting time is retarded. These results are correlated with the data obtained with the ultrasound device as well as those of the isothermal calorimetry campaign.

2010

Growth kinetics and controlled auto-assembly of gold nanoparticles

2009

Early age properties development of concrete with different slag contents

Copper Solvent Extraction by Ultrasound-Assisted Emulsification

2008

Hydratation process and microstructure development of integral water repellent cement-based materials

2007

Recent developments in Vacuum arc surface treatments

Correlation between properties and microstructure in Si-O-N nanostructured coatings obtained by magnetron sputtering

2005

Sodium bicarbonate crystallization: a fundamental study of the production process

2004

Stress development and relaxation in nanostructured films deposited by cathodic vacuum arc

2003

Development of stress in DLC based coating deposited by filtered cathodic vacuum arc

Vacuum arc deposited DLC based coatings

Ultra-hard DLC-based coatings

2002

Engineering properties of superhard films with ion energy and post-deposition processing

Vacuum Arc Deposited Super-Hard Coatings

Characteristics of boron carbide films prepared by cathodic arc deposition

Reverse fabrication process for organic light emitting device

2001

Contrôle et caractérisation fine de multicouches minces

Cubic boron nitride thin films deposited on steel substrates with different interlayers

2000

Effect of structure and interface thickness on mechanical properties of thin hard coatings

Deposition of nitrogen-rich CNx films with inductively coupled plasma CVD and pulsed laser ablation

Deposition and characterization of nitrogen-rich amorphous carbon nitride films

Optical and mechanical properties of CNx films with high N/C ratio

1999

Study of CNx films deposited by ICP-CVD from N2/CCl4/H2 precursors

Thin CNx films were deposited on silicon substrate by inductively coupled r.f. plasma chem. vapor deposition (ICP-CVD). A mixt. of N2/CCl4/H2 was used. Influence of deposition parameters on film quality and plasma properties was studied. Nature of gaseous species, electron temp. and plasma d. were obtained by optical emission spectroscopy and Langmuir probe measurements. Pressure, ratio of H2 to CCl4, substrate temp. and injected r.f. power were varied in the following ranges: p = 15-200 Pa, H2/CCl4 = 1-10, Ts = 100-400 °C, and P = 15-300 W. Film compn. was studied by AES before and after in-situ Ar ion sputtering. The N/C ratio varied in the range of 0.5-0.7. Chlorine contamination of the deposits was detected but could be reduced by optimizing the deposition conditions. Decrease of both nitrogen and chlorine concn. was obsd. after sputtering. Fourier transform IR spectroscopy (FTIR) was used for the detn. of chem. bonding. Presence of Hydrogen was confirmed by N-H stretching vibrational band at 3350 cm-1 and weak C=CH stretching band at 3050 cm-1. A group assigned to C=C and C=N was detected around 1650 cm-1 as well as a nitril C≡N group at 2220 cm-1. The surface morphol. of the films was studied by at. force microscopy.

Characterization of high nitrogen containing CNx films

Mechanical properties of cubic boron nitride thin films synthesized by ECR PECVD: Influence of deposition conditions

Formation of cubic boron nitride thin films using ECR plasma enhanced CVD

1998

Characterization of magnetron sputtered carbon nitride films

1997

Properties and microstructure of DLC/DLC:Me multilayers prepared by cathodic arc deposition

Synthesis and characterization of thin films of WCx produced by mixing W and C plasma streams

Study of the role of activation before the phosphating process on aluminum substrates by means of AFM and TOF-SIMS

Correlation between microstructure and mechanical properties of TiC films produced by vacuum arc deposition and reactive magnetron sputtering

1996

Preparation of TiC and TiC/DLC multilayers by metal immersion and implantation: relationship between composition, microstructure and wear properties

1994

Metal-ceramic reactions in Ti-alloy/C and Ti-alloy/TixC couples

1993

Analysis of gaseous species during plasma enhanced chemical vapour deposition of boron nitride thin films

Plasma enhanced chemical vapour deposition (PECVD) of boron nitride thin films: analysis of gaseous species

1991

Characterization of a-SiC:H thin films deposited by plasma enhanced chemical vapor deposition

1989

Surface properties of rhodium and rhodium-copper alloys.

1986

Auger study of surface segregation on massive single crystalline CuRh alloys

Divers

2010

Introduction to arc technology

2006

Cathodic arc evaporation and its applications to thin film synthesis

2005

Cathodic arc evaporation and its applications to thin film synthesis

Stress generation and relaxation in thin DLC coatings

Synthesis of superhard nanocomposite coatings

Cathodic arc evaporation and its applications to multiplayer synthesis

2001

Arc cathodique filtré sous vide