Search

La spectroscopie de Résonance Paramagnétique Electronique (RPE), c’est-à-dire l’étude de la structure électronique des centres paramagnétiques, est de plus en plus utilisée pour des applications qui vont bien au-delà de celles imaginées initialement par les physiciens. La RPE permet d’obtenir des informations sur l’évolution de propriétés dans le temps (datation) et dans l’espace (traçage). Avec plus d’investissement, elle rend possible l’identification d’une molécule et la détermination de niveaux d’énergie. Cela concerne la physique, la chimie mais aussi les sciences de la Terre et de l’univers, celles de l’environnement, de la vie et de la santé. Cet ouvrage collectif présente une grande variété d’applications. Certaines ne nécessitent pas un bagage théorique important pour être comprises. Pour d’autres, il est possible de se référer à l’ouvrage La spectroscopie de RPE - Fondements dans la même collection ou à certains compléments de fin de chapitre. Des annexes sur des méthodes ou techniques sont proposées de façon indépendante en fin d’ouvrage. Enfin, pour chaque application, des références sont proposées à ceux qui veulent approfondir. L’ouvrage est accessible à des étudiants de master 1 de physique, de chimie, de chimie physique, de biophysique et de biochimie. Il sera utile aux professionnels qui utilisent la technique de spectroscopie RPE, aux chercheurs mais aussi aux enseignants du supérieur et des classes préparatoires qui pourront ainsi élargir leurs connaissances de façon très concrète et illustrée.

Longtemps apanage des physiciens, la RPE, Spectroscopie de résonance paramagnétique électronique, est aujourd'hui utilisée pour élaborer de nouveaux matériaux, pour la datation en archéologie, dans les biotechnologies, en médecine, pour doser les rayonnements ionisants, dans la chimie de l'environnement… L'objectif de ce livre, le premier sur ce sujet en français, est d'exposer les bases de la spectroscopie RPE pour permettre de l'utiliser dans ces contextes si différents. Pour atteindre ce but, les deux premiers chapitres restent d'un niveau licence avec des «points importants pour les applications», des exercices simples corrigés et des termes définis dans un glossaire. Le lecteur peut choisir entre plusieurs stratégies d'appropriation : des parties peuvent être évitées dans une première approche (calculs détaillés, points plus développés) ; des annexes plus techniques sont proposées en fin d'ouvrage. De nombreuses figures, spectres originaux permettent une jonction directe avec les résultats expérimentaux. L'ouvrage est destiné aux professionnels et chercheurs des nombreux secteurs cités précédemment et aux étudiants de niveau Master 1 de Physique, Chimie, Chimie physique, Biochimie et Biophysique.

This feature article is focused on the application of secondary ion mass spectrometry (time-offlight SIMS) to the chemical and structural study of plasma-treated organic surfaces and plasma polymer films. After a brief historical perspective and a presentation of the recent developments of SIMS, illustrative case studies involving plasma-treated polymer surfaces and plasma polymers are presented. Beyond surface analysis by static SIMS, we show the potential of molecular depth-profiling by low-energy Csþ ions and large Arn þ clusters for the in-depth chemical characterization of plasma-modified samples. Together with SIMS data processing by multivariate analysis, molecular depth-profiling could provide a step change for the analysis of films treated or polymerized with plasmas.

This feature article is focused on the application of secondary ion mass spectrometry (time-of-flight SIMS) to the chemical and structural study of plasma-treated organic surfaces and plasma polymer films. After a brief historical perspective and a presentation of the recent developments of SIMS, illustrative case studies involving plasma-treated polymer surfaces and plasma polymers are presented. Beyond surface analysis by static SIMS, we show the potential of molecular depth-profiling by low-energy Cs+ ions and large Arn+ clusters for the in-depth chemical characterization of plasma-modified samples. Together with SIMS data processing by multivariate analysis, molecular depth-profiling could provide a step change for the analysis of films treated or polymerized with plasmas., SCOPUS: ar.j, FLWIN, info:eu-repo/semantics/published

Thin films of insulating polymers are sometimes analyzed by secondary ion mass spectrometry (SIMS) or by X-ray photoelectron spectroscopy (XPS) without the use of an electron gun. In this work, both SIMS and XPS have been used to study the chemical and structural modifications due to the charge effect during Cs+ sputtering of a thin film of polyvinyl chloride (PVC). The kinetic energy distribution study shows that at a small primary fluence ∼1015 Cs+ ions/cm2, the dielectric breakdown voltage of the PVC film is reached, i.e. the minimum voltage that causes a portion of an insulator to become electrically conductive. XPS study indicates that the conducting phase created in the PVC film after energetic Cs+ bombardment consists of graphitized carbon and metallic cesium clusters. After the dielectric breakdown of the film, the positive charge, previously accumulated on the surface, is neutralized through the conductive regions, which are created in the insulating film. During Cs+ sputtering of a PVC film, the chemical structure of the analyzed surface is completely modified and some ionic bonds such as CsC and CsCl are also created. © 2013 Elsevier B.V.

Surface preparation with gas cluster ion beam (GCIB) sputtering was performed on paint cross-sections, which belong to the collection of the Royal Institute for Cultural Heritage (KIKIRPA), Brussels, Belgium. Superficial cleaning of cross sectionswith residual embedding resin surface contamination was studied with different sputtering times in order to obtain a gain in the spectral and imaging mode. Sputtering was made directly through the Time-of-Flight-SIMS apparatus. It was thus demonstrated that GCIB sputtering for a short periodwas very efficient for the superficial decontamination of cultural heritage cross-sections without visible damage on the valuable samples. The GCIB sputtering time and dose can be highly decreased when combined with a monoatomic argon ion beam preparation techniques such as the ion milling systems.

The goal of this Ph.D. work was to gain a deeper understanding of the modifications of the physico-chemical properties of the surface of insulating polymeric thin films in the transitory phase of sputtering, before a steady-state is reached. For this purpose, polymer films were first bombarded by keV Cs+ ions and then investigated using both secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). At high impact energy (12.5 keV), it is shown that the SIMS signals of some elements with high electronic affinity exhibit an oscillatory behavior before attaining the equilibrium. Based on the comparison with data obtained from TRIDYN calculations, this oscillation could be related to the variations of both the sputter yield and the cesium surface concentration, which highly perturbs the ionization probability of these elements. During Cs+ sputtering of an insulating polymeric thin film a positive electric charge accumulates on the film surface. Via the study of the kinetic energy distributions of secondary ions, it could be shown that the accumulated charge density induced a high electric field in the film, permitting to reach the dielectric breakdown voltage, i.e. the minimum voltage that causes a portion of an insulator to become electrically conductive. After the breakdown, this conducting phase neutralizes the surface charge created upon sputtering. The XPS study of the film surface also showed that the bombarded film contained a conducting phase, consisting mainly of carbon islands and of metallic cesium clusters. The improved understanding of these phenomena constitutes a valuable assistance for interpretation of polymer depth-profiling experiments carried out using atomic primary ions., Le but de ce travail de thèse est de mieux comprendre les modifications des propriétés physico chimiques induites à la surface d’échantillons de films minces de polymères isolants soumis au profilage ionique en spectrométrie de masse d’ions secondaires. En début d’opération, les signaux ioniques provenant de la surface subissent une variation transitoire avant d’atteindre un régime stationnaire. Cela signifie que l’information liée aux premières couches de la surface est compromise. La phase transitoire n’a jamais été considérée dans les analyses, alors que les modifications structurales et chimiques apportées aux échantillons organiques, durant cette phase transitoire, influent sûrement sur les informations obtenues pendant l’analyse dans le régime stationnaire. La comparaison des résultats expérimentaux avec des données obtenues par la simulation TRIDYN montre un comportement ondulatoire dans la phase transitoire lors de la pulvérisation des matériaux organiques par des ions de césium à haute énergie d’impact (12,5 keV). L’étude des distributions énergétiques des ions secondaires prouve que l’accumulation de la charge électrique à la surface des échantillons provoque le claquage diélectrique des films minces de polymères isolants bombardés avec des ions de césium. Les résultats obtenus par la spectroscopie de photoélectrons X montrent la création d’une phase conductrice dans le film de polymère isolant bombardé. Cette phase permet ultérieurement la neutralisation de la charge électrique au cours de la pulvérisation ionique de polymère., (FSA 3) -- UCL, 2013

Although nowadays the use of cluster ion sources seems to enhance the secondary ion emission for nearly all materials, the technique of metal-assisted SIMS can still give further insights in the secondary ion emission process. In this study, the metallization for static SIMS analysis was performed in situ. The combination of a detailed morphology study by SEM, TEM and the secondary yield enhancements in time-of-flight SIMS allows to develop a model explaining the secondary yield enhancement in metal-assisted SIMS. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd.

The performance of Cs+, C60 + and Ar n + (with n ≈ 1700) sputtering ions have been compared for depth profiling multilayer films made from three evaporated phenylalanine layers sandwiched between four thicker evaporated tyrosine layers. Using Cs +, the ion signals and depth resolution degrade with depth and were significantly affected beyond a 200-nm depth. The depth profiling quality was more successful using C60 +. However, in this case, the depth resolution and the layer width values still degrade with the sputtered depth and are particularly poor after reaching a depth of about 400 nm. When Ar1700 + clusters were used, a depth resolution as low as 6 nm was obtained, and this value never exceeds 9 nm. Moreover, the experimental layer width is found to be of the same order of magnitude as the real value. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd.

Molecular semiconductor devices, such as light-emitting diodes and photovoltaic cells, have recently received considerable attention because of their compatibility with flexible substrates and large-area applications. Because of the importance of the interfacial properties for the performance of the devices, these organic (multi)layers constitute an important field of application for molecular depth profiling by SIMS. In this contribution, we investigate the use of C60 n+ and Ar 1000-2000 + cluster projectiles at different energies (ranging from 2.5 to 20 keV) as sputter ions for the organic depth profiling of fullerene-based films and heterojunctions. The bilayers consist of C 60 fullerenes on tin phthalocyanine (SnPc), deposited on silicon substrates. Our preliminary results showed that C60 films could not be successfully profiled using C60 n+ ions in regular analysis conditions (room temperature). In contrast, with Ar clusters, the depth profiling is successful (except for 20 keV Ar1000) and the sputtered volume shows a linear relationship with the Ar cluster energy. Surprisingly, for a given total energy of the projectiles, Ar2000 sputters approximately two times more than Ar1000. The observations are tentatively explained as being the result of a balance between the sputtering and the cross-linking efficiency for the different bombardment conditions, larger clusters being expected to naturally induce less cross-linking than smaller clusters with the same total energy. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd.

Cluster secondary ion mass spectrometry is now widely used for the characterization of nanostructures. In order to gain a better understanding of the physics of keV cluster bombardment of surfaces and nanoparticles (NPs), the effects of the atomic masses of the projectile and of the target on the energy deposition and induced sputtering have been studied by means of molecular dynamics simulations. 10 keV C60 was used as a model projectile and impacts on both a flat polymer surface and a metal NP were analyzed. In the first case, the mass of the impinging carbon atoms was artificially varied and, in the second case, the mass of the NP atoms was varied. The results can be rationalized on the basis of the different atomic mass ratios of the projectile and target. In general, the emission is at its maximum, when the projectile and target have the same atomic masses. In the case of the supported NP, the emission of the underlying organic material increases as the atomic mass of the NP decreases. However, it is always less than that calculated for the bare organic surface, irrespective of the mass ratio. The results obtained with C60 impacts on the flat polymer are also compared to simulations of C60 and monoatomic Ga impacts on the NP.

With the recent developments in secondary ion mass spectrometry (SIMS), it is now possible to obtain molecular depth profiles and 3D molecular images of organic thin films, i.e. SIMS depth profiles where the molecular information of the mass spectrum is retained through the sputtering of the sample. Several approaches have been proposed for "damageless" profiling, including the sputtering with SF5(+) and C60(+) clusters, low energy Cs(+) ions and, more recently, large noble gas clusters (Ar500-5000(+)). In this article, we evaluate the merits of these different approaches for the in depth analysis of organic photovoltaic heterojunctions involving poly(3-hexylthiophene) (P3HT) as the electron donor and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as the acceptor. It is demonstrated that the use of 30 keV C60(3+) and 500 eV Cs(+) (500 eV per atom) leads to strong artifacts for layers in which the fullerene derivative PCBM is involved, related to crosslinking and topography development. In comparison, the profiles obtained using 10 keV Ar1700(+) (∼6 eV per atom) do not indicate any sign of artifacts and reveal fine compositional details in the blends. However, increasing the energy of the Ar cluster beam beyond that value leads to irreversible damage and failure of the molecular depth profiling. The profile qualities, apparent interface widths and sputtering yields are analyzed in detail. On the grounds of these experiments and recent molecular dynamics simulations, the discussion addresses the issues of damage and crater formation induced by the sputtering and the analysis ions in such radiation-sensitive materials, and their effects on the profile quality and the depth resolution. Solutions are proposed to optimize the depth resolution using either large Ar clusters or low energy cesium projectiles for sputtering and/or analysis.

In the present study, the feasibility of synthesizing chlorinated films by a dielectric barrier discharge at atmospheric pressure is assessed. Two different liquid monomers (hexachlorobuta-1,3-diene C4Cl6 and 1,1,1,2-tetrachloroethane C2H2Cl4) are tested and results show that organic coatings rich in chlorine can be deposited. The correlation and complementarity of water contact angle, X-ray photoelectron spectroscopy, secondary ion mass spectrometry and ellipsometry techniques have provided information to compare the properties of the perchlorinated layers built up from monomers with different Cl/C ratios and hydrogen concentrations. The bond dissociation energies of C-Cl2, C-Cl and C-C/CC/C-H are used to provide an explanation for the differences in films structure recorded by X-ray photoelectron spectroscopy and secondary ion mass spectrometry. Finally, dynamic-secondary ion mass spectrometry complemented by ellipsometry is used to calculate a deposition rate ranging from 40 to 70 nm/min depending on the plasma conditions. These measurements also show a good homogeneity of the film throughout its thickness. © 2013 Published by Elsevier Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published

Methods for molecular analysis and imaging of solid surfaces are important for the development of materials science, biology and medical sciences. As an alternative to matrix-assisted laser desorption ionization (MALDI), we investigate the influence of a thin layer of gold (1-15 nm) condensed on the surface of a series of pure organic materials, without the use of a MALDI matrix, in the laser ablation using a 355 nm wavelength light. The evolution of the characteristic fragment ion intensities with increasing thickness of the gold overlayer has been recorded. For all the investigated materials, the largest signals of characteristic ions are measured after metallization with 4-8 nm of gold. The observed effects can be tentatively explained by the increased laser absorption by the gold nanoparticles in this wavelength range and, as suggested by surface potential measurements, by an increase of the ionization probability. Our results suggest that metal-assisted LDI provides an interesting alternative to MALDI for the surface analysis and, potentially, imaging of certain classes of materials, when a minimal perturbation of the surface structure is desired. The technique is not suitable to get high mass molecular signals in most cases, but intense signals of characteristic fragment ions are detected for all the tested samples. Because of the preservation of the sample surface and the controlled size of the gold islands (<100 nm), the application of the method to micrometer-scale or even submicrometer-scale surface chemical imaging is envisioned. © 2012 Elsevier B.V. All rights reserved.

For different fields of applications, the knowledge of the exact morphology of ultra thin metal layers deposited on polymers is of interest. In this work, gold metallization of polymers was carried out in high vacuum by evaporation at room temperature. The evaporation flux was measured by a quartz crystal microbalance. By dint of XPS measurements, it is shown that the condensation coefficient of gold onto the different polymers is far below unity. A detailed study of the gold deposit structure was accomplished by SEM and TEM measurements. The evolutions of various morphology parameters of the gold islands are shown as a function of the evaporated gold quantity, confirming a heterogeneous Volmer-Weber growth. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd.

An easy procedure to build up membrane-electrode assemblies for applications dedicated to miniaturized PEMFC using H2 or CH 3OH by a two-steps atmospheric plasma process is reported. Firstly, catalyst nanoparticles are grafted on carbon substrates by spraying a Pt colloidal solution in the post-discharge of an RF atmospheric plasma torch. In the second step, the resulting decorated electrodes are covered by plasma synthesized polymeric membranes in the discharge of a DBD. The sulfonated polystyrene membranes are synthesized by injecting simultaneously styrene and trifluoromethanesulfonic acid monomers, in the presence of a carrier gas (Ar or He). The membranes are chemically characterized by XPS, ToF-SIMS, and FTIR (IRRAS) and their deposition rate is investigated by SEM. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA., SCOPUS: ar.j, FLWIN, info:eu-repo/semantics/published

In static secondary ion mass spectrometry (s-SIMS), several more or less sample-restraint methods of secondary ion yield enhancement have been proposed. One of those methods is called Metal-Assisted SIMS (MetA-SIMS) and consists in a deposition of a small amount of noble metal onto the organic sample in order to enhance the characteristic secondary ion fragment intensities. In contrast to other MetA-SIMS studies, the metallization of the high-mass polymers was carried out in a preparation chamber, which is directly connected to the ToF-SIMS. This in situ metallization allows reducing the surface contamination and atmospheric influences to a minimum during sample manipulation/transportation. Beyond the secondary ion yield enhancement measured in ToF-SIMS, the exact deposited gold quantity was determined by XPS and a detailed characterization of the sample surface was accomplished by SEM and TEM. The aim of this work was two folded: From a purely analytical point of view, it was tried to find out the optimal conditions for the metallization of various and widely used polymers in order to maximize the secondary ion intensities in MetA-SIMS. A more theoretical aspect was to get further fundamental insights in the secondary ion emission process in MetA-SIMS. By dint of the morphology results, a model explaining the observed yield enhancement of the characteristic polymer fragments during atomic primary ion bombardment for low gold coverage was developed. The model takes into account that the polymer quantity at the sample surface diminish due to the deposited gold and suggests that the secondary ion yield enhancement mainly occurs near the polymer/gold interface. However for larger gold coverage, additional factors need to be determined in order to completely describe the yield enhancement in ToF SIMS., (FSA 3) -- UCL, 2011

A new method allowing the simultaneous and automatic determination of potentiometric and impedimetric characteristics of an electrochemical cell is presented. This method is based on a computerized or micro-controlled feedback loop that conditions a potentiostat input signal as a function of its output signal. The embedding of this method in a portable sensor prototype is used to evaluate the versatility and usefulness of this new approach. As this method is active, it is used both for the electrochemical preparation of polyaniline coated electrodes and for their subsequent evaluation in pH-linked sensors such as an antibiotic sensor.