Tesi sul tema "Characterization of plasmas"

Particle contamination in plasma processing is a serious and challenging issue for the semiconductor industry. In this work, Laser Doppler Velocimetry, Laser Light Scattering, and Optical Emission Spectroscopy are used to elucidate the physical behavior of particles trapped in a plasma. Coulomb theory is used to describe the motion of particles. The theory agreed very well with experimental data and was explored to evaluate conditions for which particle agglomeration is likely. Finally, it was observed that particles may fall out of the particle trap during plasma ignition and subsequently contaminate the substrate.

The use of plasmas in aerodynamics has become a recent topic of interest. In particular, over the last ten years, plasma actuation has received much attention as a promising active method for airflow control. Flow control consists of manipulating the properties of a generic moving fluid with the aim of achieving a desired change, but flow dynamics in proximity of a solid object is usually considered, being a consistent and significant issue in many engineering applications, such as engine, automobile or airplane design. Plasma control of airflows along surfaces has been the subject of several experimental studies whose aim was to reduce turbulence, to decrease drag, to enhance airfoil lift or to prevent flow detachment. The fast temporal response and the absence of moving parts are the most promising features from which plasma actuators could benefit. Different types of plasma sources are currently studied as good candidates for plasma actuation, but Dielectric Barrier Discharges (DBDs) are usually preferred, being characterized by the presence of an insulating barrier between the electrodes. This allows the generation of a non-thermal plasma at atmospheric pressure and prevents the discharge from collapsing into an arc. Surface Dielectric Barrier Discharges (SDBDs) are particularly suitable for these kinds of applications, since plasma is created by ionizing a thin portion of air nearby the surface of the dielectric barrier and this can effectively influence the local properties of the boundary layer associated to an external flow. This thesis deals with SDBDs in an asymmetric configuration where one electrode is glued into an insulating material and to other one is exposed to air, so that plasma is created in correspondence of just one side of the dielectric barrier. The buried electrode is connected to the ground, whereas a sinusoidal high-voltage is applied to the exposed one. It has been noticed that, when these discharges are operated in quiescent air, an airflow of several metres per second is observed above the dielectric sheet and near the plasma region. This is usually called ionic wind because the main mechanism responsible for its generation is believed to be momentum transfer from the ions drifting in the discharge electric field to the surrounding fluid, by particle-particle collisions. When the electric field imposed by the voltage difference between the electrodes is sufficiently high, plasma is created and electrical charges are transported through the gap and accumulated on the insulating surfaces. This charge accumulation generates an electric field that locally weakens the external one. When the total electric field falls below the threshold necessary for plasma ignition, the discharge extinguishes. If the voltage imposed to the fed electrode is increased, the discharge can be locally initiated again, and that is the reason why a sinusoidal high-voltage supply is adopted instead of a continuous one. Consequently, the presence of the insulating barrier usually leads to a regime where charge is mainly transported in sub-millimetre regions consisting of current filaments with temporal duration limited to a few tens of nanoseconds. These plasma microdischarges are concentrated into two phase intervals of the sinusoidal voltage supply, when the modulus of the applied voltage difference is high enough and is increasing in time. These two phases of plasma activity are often called Backward Stroke (BD) and Forward Stroke (FD), depending if the high-voltage signal is rising from its minimum to its maximum or decreasing from its maximum to its minimum. This thesis is motivated by the fact new studies focusing on plasma properties and dynamics are required in order to get better and better aerodynamic results, to understand which parameters mainly affect the actuator performances and to validate numerical models trying to forecast the aerodynamic effects induced by the discharge. This has brought to a scientific collaboration between the Centre of Excellence PlasmaPrometeo of University of Milano-Bicocca and the Aerodynamics and Wind Tunnel Department of the aerospace company Alenia Aermacchi. During these years I have studied the properties of these discharges by means of electrical and optical diagnostics (mainly Rogowski coils, capacitive probes, a photomultiplier tube and a thermal camera). With some of them a temporal resolution high enough for studying several characteristics of plasma microdischarges has been achieved. This is important because these strokes manifest as series of current and light pulses, lasting tens of nanoseconds and a few nanoseconds respectively. I have first of all carried out a detailed investigation of the properties of these events and of their evolution in space and time in the course of the FD and BD. It has been pointed out that there are several analogies between the BD and FD, but that not all plasma properties are identical for the two semi-cycles, because of the asymmetrical configuration adopted. These investigations let think that light and current signals give insights about different microdischarge properties. Light is presumably ascribable to electrons that excite nitrogen immediately after the passage of the ionizing wave that initiates the microdischarge. In contrast, the current signal is due to the movement of charges into the plasma channel and thus reflects the microdischarge temporal evolution, rather than its formation. In the following experiments I have thus focused mainly on the electrical properties of plasma microdicharges, with the aim of better understanding which plasma characteristics are responsible for the ionic wind generation and properties. Several SDBDs with different geometrical configurations and operating parameters have been considered. It has been found that both the discharge and ionic wind characteristics are mainly affected by the dielectric thickness, whereas other properties of the SDBD are less decisive. These studies are of practical interest because optimizations of SDBD characteristics are still needed for adopting these discharges as plasma actuators for active flow control. In particular, it has been found that at first the speed of the induced wind increases quite linearly with the voltage amplitude, but then this velocity and thus the aerodynamic effects induced by the discharge tend to saturate. This is particularly evident when thin panels are adopted as dielectric barriers. I thus focused on this topic and I found that an asymmetry in the total charge transported by plasma microdischarges during the backward and forward strokes is favourable for obtaining a ionic wind with a greater velocity, and that the velocity saturation at the highest voltages is associated to a change in discharge regime, which is visible first of all because a pattern of plasma filaments appears superimposed to the more homogeneous plasma. I have thus characterized how this regime transition affects the dynamics of the backward and forward strokes. Three groups of microdischarges have been identified, depending on their temporal duration, and results let think that they don't contribute equally to the electric wind generation. These studies pave the way to a better understanding of the discharge peculiarities and ionic wind formation, with the aim of understanding if an intrinsic limit exists in plasma actuator potentialities or if new optimization strategies are possible. Eventually, I proposed to implement the Background Oriented Schlieren (BOS) technique for the visualization and characterization of the airflow induced by the discharge. The potentialities of this technique have been evaluated in relation to the specifics of the available scientific equipment. The technique has then been proved to be able to visualize density changes induced by plasma. A spatial characterization of the air near the discharge was made in stationary wall jet conditions as well as in the transient period following the discharge ignition when a starting vortex is generated.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 161-167).
Low-frequency fluctuations of plasma density, floating potential, ion saturation current, visible light intensity, and edge magnetic field are routinely observed in the Levitated Dipole Experiment (LDX). For the purposes of this thesis, we define low-frequency as W << Wbe where Wbe is the electron bounce frequency. These fluctuations in a laboratory dipole confined plasma lead to turbulence mixing that maintain peaked density profiles. The relationship between the different types of low-frequency fluctuations and plasma density transport is considered. Two 16-channel photodiode arrays were designed and constructed to study the spatial and temporal structure of these fluctuations as part of this dissertation. In addition to the photodiode arrays, a four-channel microwave interferometer is used to estimate the density profile and to measure density fluctuations in the plasma. Several electrostatic probes, including a 24-channel floating probe array, measure fluctuations at the plasma edge and eight Mirnov coils measure magnetic fluctuations. The fluctuations fall into three general categories: broadband, turbulent fluctuations observed during nearly all plasma conditions; quasi-coherent fluctuations with low azimuthal mode numbers and peak frequencies on the order 1 kHz observed during discharges with low neutral pressure; and coherent fluctuations with zero toroidal mode number and peak frequencies on the order of 100 Hz, observed during discharges with moderate neutral fueling. The relationship between time-averaged fluctuation characteristics and plasma parameters are explored. The spatial structure of the fluctuations for several representative shots are discussed. The turbulent fluctuations and concurrent density profiles are compared to quasilinear diffusion of interchange mixing in dipolar plasmas for cases where the fluctuations are random. I show that the quasilinear diffusion equation agrees well with the experimental observations of random fluctuations, supporting the conclusion that interchange mixing is causing inward transport that results in peaked density profiles. For other cases, where nonlinear effects appear to dominate the plasma dynamics, the saturated fluctuation amplitudes are compared to the plasma density profiles.
by Jennifer L. Ellsworth.
Ph.D.

The work deals with electron tempearature and transport analysis in RFP plasams; in particular the following topics are discussed: - the commissioning of the edge Thomson Scattering in RFX-mod for temperature evaluation; - the commissioning of the laser blow-off system in RFX-mod for impurity transport characterization -the analysis of RFP helical states in term of electron temperature, diffusivity and confinement on the experiments RFX-mod (Padua) and MST (madison, WI).
Il presente lavoro sviluppa una caratterizzazione dei plasmi RFP dal punto di vista termico e di trasporto; in particolare vengonodiscussi i seguenti punti: -lo sviluppo della diagnostica di Thomson Scattering di bordo per la misura della temperaturea elettronica; -lo sviluppo del sistema di laser blow off per l'iniezione di impurezze e lo studio del loro trasporto -l'analisi degli stati elicoidali negli RFP, in termini di caratteristiche termiche e di confinamento, negli esperimenti RFX-mod(Padova) e MST(Madison-WI)

Thesis (Ph. D.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

La modification de surface par plasma est une technique largement utilisée pour améliorer les propriétés de surface de polymères par le greffage de différents groupes fonctionnels. Dans ce projet de recherche, différentes méthodes pour améliorer les techniques de caractérisation de décharge micro-ondes de N2 et N2-H2 ont été étudiées dans le but d’optimiser le procédé de traitement de surface par plasma. Tout d'abord, un certain nombre de paramètres du plasma ont été mesurés à différentes conditions de traitement. Pour déterminer les paramètres du plasma, la spectroscopie d'émission optique a été utilisée dans la région l’ultraviolet, du visible et l’infrarouge (rarement utilisée dans la littérature scientifique). L’utilisation de la spectroscopie d'émission dans cette dernière région spectrale est avantageuse car elle permet d'éliminer les forts chevauchements entre les transitions atomiques et moléculaires et de pallier la faible intensité du signal observée dans la région de l’ultraviolet et du visible. Par la suite, la composition chimique de surface du PTFE a été analysée par XPS pour déterminer les concentrations en carbone, fluor, azote et des groupements amine suite à un traitement par plasma. Les résultats mentionnés ci-dessus ont été utilisés pour corréler les conditions de traitement et les paramètres de décharge micro-ondes à la composition chimique du PTFE modifié, dans l’objectif de mettre en évidence les paramètres expérimentaux du plasma et les espèces présentes dans le plasma qui jouent un rôle clé pour maximiser la fonctionnalisation de surface du polymère avec des groupements amine. En outre, un modèle mathématique a été développé en utilisant la technique de régression PLS. Pour construire ce modèle, un ensemble de données de variables d'entrée contenant les conditions de traitement et les paramètres spectroscopiques du plasma et une matrice de réponse contenant les propriétés de surface du polymère ont été générées. La base de données obtenue a été utilisée pour établir la relation entre les paramètres du plasma, les conditions de traitement et la chimie de surface du film. Cela a finalement permis de prédire la composition chimique de la surface à partir d’informations relatives au plasma, sans avoir à effectuer des analyses de surface après le traitement.
Plasma surface modification is a widely used technique for improving the surface properties ‎of ‎polymers through the introduction of different functional groups. In ‎the current research project, ‎different methods to improve the characterization techniques of ‎N2 and N2-H2 microwave discharge ‎were investigated with the aim of optimizing the ‎plasma surface process. First of all, a number of plasma parameters were measured at ‎different process conditions. To determine the plasma ‎parameters, optical emission spectroscopy was used ‎not only within the well-documented ‎UV-Visible region but also within the rarely ‎studied infrared zone. Using infrared optical emission ‎spectroscopy is advantageous as it ‎eliminates the strong overlap between atomic and molecular ‎transitions as well as the low ‎intensity UV-Visible emission spectroscopy limitations. In the next step, the PTFE surface chemical composition was analyzed via XPS to quantify the ‎concentrations of carbon, fluorine, and nitrogen after a plasma treatment in a N2-H2 gaseous ‎environment. The XPS analyses were also performed after chemical derivatization to quantify the ‎surface concentration of amino groups (%NH2) at different process conditions. The above-mentioned results were used to correlate process conditions and microwave N2-‎H2 ‎discharge‏ ‏parameters‏ ‏to the chemical composition of the modified ‎PTFE. The purpose was ‎to ‎determine the external plasma parameters and species present within the plasma ‎which ‎‎play a key ‎role in the introduction of amino groups to the polymer surface. ‎Furthermore, a mathematical model was developed using ‎the Partial Least Squares ‎Regression, ‎‎(PLSR) ‎using custom scripts written in MATLAB. A data set of ‎input variables including the process conditions ‎and plasma ‎parameters for each experiment ‎were generated along with the corresponding response ‎matrix which in turn contained the ‎surface ‎properties of the film.‎ ‎The resulting database was used to ‎build the relationship ‎between the plasma parameters, ‎process condition and the resulting film ‎surface chemistry. ‎This ultimately enabled to predict the PTFE surface chemistry from data originating ‎from the plasma, without having to proceed to post-plasma surface characterization.

Cette thèse porte sur l’étude d’un jet de plasma d'hélium à pression atmosphérique alimenté par des impulsions positives unipolaires à une fréquence de l’ordre du kHz. Des expériences sont effectuées pour caractériser la dynamique de propagation, la structure de l'écoulement et la température dans un jet en expansion libre, ainsi que l'influence d'une cible métallique sur le plasma.La spectroscopie à polarisation Stark indique un champ électrique axial d'environ 10 kV/cm dans le capillaire du jet et une augmentation jusqu'à 20 kV/cm dans le panache, qui est constante pour différentes amplitudes et durées de l'impulsion de tension appliquée. La diffusion Thomson et la diffusion Raman rotationnelle sont utilisées pour déterminer la densité électronique et la température électronique, à différentes positions axiales et radiales, ainsi que la température du gaz et la densité de N2 et O2 de l'air environnant qui sont mélangés dans le flux d’hélium.La comparaison quantitative de ces résultats expérimentaux avec les résultats d'un modèle fluide 2D montre une bonne concordance et permet une meilleure compréhension des résultats obtenus, à savoir que le champ électrique dans le front d'ionisation augmente avec la quantité d’air intégré au flux d’hélium au lond de la propagation. L'imagerie Schlieren révèle l'apparition de structures turbulentes à des débits élevés et lors de l'application des impulsions de tension. On constate que la température du gaz, mesurée par une sonde de température, augmente d'environ 12 C quand le plasma est allumé et d'environ 25 C lorsqu'une cible métallique est placée devant le jet
This thesis studies an atmospheric pressure helium plasma jet that is powered by positive, unipolar pulses at a kHz frequency. Experiments are performed that focus on the propagation dynamics, flow structure and temperature in a freely expanding jet, as well as the influence of a metallic target on the plasma.Stark polarization spectroscopy yields an axial electric field of around 10 kV/cm in the capillary of the jet and an increase up to 20 kV/cm in the plume, which is constant for different amplitudes and durations of the applied voltage pulse. Thomson and rotational Raman scattering are used to determine the electron density and electron temperature, at different axial and radial positions, as well as the gas temperature and the density of N2 and O2 that are mixed into the helium from the surrounding air.Quantitative comparison of these experimental results with results from a 2D fluid model show a good agreement and allow for a better understanding of the obtained results, namely that the electric field in the ionization front depends linearly on the flow composition at that location. Schlieren imaging shows the onset of turbulent structures at high applied flow rates and at the application of the voltage pulses. The gas temperature, as measured by a temperature probe, is found to increase by around 12 C when the plasma is ignited and by around 25 C when a metallic target is placed in front of the jet

The 'high-pressure' atmospheric (TIG) arc plasma is studied by means of a multi-Langmuir probe system. In order to determine the appropriate regime of operation, definitions of the plasma parameters for the description of the argon arc are considered and evaluations are presented. A description of the probe basic techniques is followed by an in-depth discussion of the different regimes of probe operation. The emphasis is put on atmospheric and flowing (arc) regimes. Probe sheath theories are compared and “Nonidealities” like cooling due to plasma-probe motion and probe emission mechanisms are then described. The extensive literature review reveals that the existing probe theories are inappropriate for a use in the TIG arc, because of ‘high’ pressure (atmospheric), broad range of ionization across the arc, flowing conditions, and ultimately, to the uncertainty about onset of Local Thermodynamical Equilibrium. The Langmuir probe system is built to operate in floating and biased conditions. The present work represents the first extensive investigation of electrostatic probes in arcs where the experimental difficulties and the primary observed quantities are presented in great detail. Analysis methodologies are introduced and experimental results are presented towards a unified picture of the resulting arc structure by comparison with data from emission spectroscopy. Results from different measurements are presented and comparison is made with data on TIG arcs present in literature. Probe obtained temperatures are lower than the values obtained from emission spectroscopy and this ‘cooling’ is attributed to electron-ion recombination. However, it is believed that probes can access temperatures regions not attainable by emission spectroscopy. Only axial electric potential and electric field are obtained because of the equipotential-probe requirement. Estimations of the sheath voltage and extension are obtained and a qualitative picture of the ion and electron current densities within the arc is given.

Growth of semiconducting Si~based quantum-confined (QC) nanoparticles (NPs) in non~thermal atmospheric pressure plasmas with potential application in photovoltaic cells is studied in this project. The attractive optoelectronic properties of QC NPs in combination with the advantages of Si-based materials make Si-based QC NPs promising candidates for a range of applications including photovoltaic cells, light emitting devices and biomarkers. Novel radio-frequency microplasma reactors suitable for growth of small NPs with diameter < 10 nm were developed. The work includes extensive materials characterization and specifically TEM analysis of Si, SiC and SiSn NPs. It is demonstrated that the developed plasma reactors are excellent tools for producing QC Si-based NPs with possibility of control over NPs properties; e.g. control over the size and optical properties (i.e. band-gap) of NPs was achieved by changing the precursor concentration. Significant impact of the reactors design on the plasma parameters and also NPs properties such as crystalline/amorphous structure, size and optical properties are observed and analysed. Study of the link between the plasma parameters and NPs properties was possible with the aid of optical emission spectroscopy (OES) of the plasmas. Specifically NPs crystallization has been studied with a theoretical model that describes NPs heating in atmospheric pressure plasmas coupled with the results from OES and NPs characterization. It is found that the growth of crystalline NPs can occur in non-thermal atmospheric pressure plasmas well below the crystallization temperature of Si NPs due to the ion-collision enhanced heating ofNP in this type of plasmas. A noticeable outcome of this work is the development of a plasma reactor for high rate synthesis of NPs in atmospheric pressure plasmas. The reactor design allows scaling-up without any impact on the NPs properties and also it allows deposition of thin film of NPs with potential application in fabrication of solar cell devices. Synthesis of Si and SiC NPs with tunable size and intense photoluminescence has been demonstrated in this reactor. Accurate control over the size of SiC QC NPs in the range of ~ 1-5 nm allowed the study of quantum confinement in these materials; the red shift in the PL peak with increasing size was observed for SiC QC NPs.

Lors des manoeuvres d'entrée ou d'aérocapture dans l'atmosphère de Titan, une quantité importante d'énergie est émise sous forme de radiation dans la couche de choc présente autour du véhicule spatial. Le dimensionnement du bouclier thermique du véhicule demande une évaluation précise de la quantité d'énergie qu'il reçoit sous forme radiative. Nous proposons dans cette étude une analyse du rayonnement émis par un plasma dont la composition est représentative de l'atmosphère de Titan, et ceci dans l'intervalle de longueur d'onde compris entre 350 et 1000 nm. Le plasma analysé est produit dans un tunnel plasma à couplage inductif (ICP). Des mesures par spectroscopie d'émission sont effectuées pour deux pressions différentes, 300 et 23 mbar. Le cas à haute pression favorise l'équilibre thermodynamique local dans l'écoulement, tandis que le cas à basse pression permet d'étudier un plasma hors équilibre. La modélisation de l'émission radiative du plasma est effectuée pour des conditions d'équilibre thermodynamique et montre un bon accord, sur une échelle absolue de l'émission, avec le spectre mesuré à haute pression. L'application du modèle développé à l'analyse du cas basse pression démontre l'obtention de conditions hors équilibre thermique. Des limitations liées à l'implémentation des mesures sont néanmoins observées. Elles sont liées aux fluctuations du plasma étudié
During entry or aero-capture in the atmosphere of the Saturn’s satellite Titan, largeamounts of radiation are produced in the shock layer of a spacecraft. The design of theheat shield of this vehicle requires a precise assessment of the radiative heat flux impingingon it. We propose in this study an analysis of the radiation emitted in the spectral range350-1000 nm by a high temperature gas mixture with a composition representative of theTitan atmosphere composition. The plasma is produced in an Inductively Coupled Plasmawind tunnel. Emission spectroscopy measurements are performed for two different pressureconditions, 300 and 23 mbar, in order to produce equilibrium and non-equilibrium plasmas. The modelling of the plasma emission at equilibrium is performed and shown to agree tothe measured spectra on a absolute scale for the high-pressure case. The use of the samemodel for the analysis of the low-pressure case provides evidence of departure from equilibrium. Limitations of the implemented procedure are observed. They are due to unresolved fluctuations of the plasma source

Afin de mettre à profit les propriétés des plasmas pour développer des fonctions hyperfréquences originales, le milieu plasma doit d’abord être caractérisé dans cette gamme de fréquence car son expansion et sa densité, supposée homogène, sont des paramètres mal maîtrisés. Une méthode de mesure de la constante diélectrique du plasma a donc été développée pour déterminer une permittivité relative complexe moyenne dans les conditions d’utilisation et d’excitation. A partir d’un modèle basé sur une méthode modale, et de la mesure de fréquence de résonance d’un résonateur, on caractérise un milieu plasma (permittivité, fréquence de coupure plasma) généré au sein d’une ligne microruban multicouches. Cette thèse, à l’intersection entre deux disciplines, plasmas et micro-ondes, valide l’utilisation de plasma localisé au sein d’une technologie planaire multicouches pour dimensionner des lignes d’impédance et/ou longueur de ligne variables. Elle met également en avant les difficultés rencontrées en termes de réalisation, pour générer des plasmas reproductibles et stables.

An atmospheric pressure radio frequency capacitively coupled plasma (CCP) has been developed and characterized for applications in atomic emission spectrometry (AES), atomic absorption spectrometry (AAS) and gas chromatography (GC). The CCP torch was initially designed as an atom reservoir for carrying out elemental analysis using atomic absorption. Functionally, the device consists of two parts, the CCP discharge tube and the tantalum strip electrothermal vaporization sample introduction system. The torch design provides for very effective energy transfer from the power supply to the plasma by capacitive coupling. Therefore, the plasma can be generated at atmospheric pressure with a flexible geometry. The plasma can be operated at very low rf input powers (30-600 W) enabling optimal conditions for atom resonance line absorption measurements. Absorption by the analyte takes place within the plasma discharge which is characterized by a long path length (20 cm) and low support gas flow rate (0.2 L/Min). Both of these characteristics ensure a relatively long residence time. The device exhibits linear calibration plots and provides sensitivities in the range of 3.5-40 pg. A preliminary measurement gave a Fe I excitation temperature of approximately 4000 K for the discharge. At this temperature, potential chemical interferences are likely to be minimal. Chemical interferences for Fe, Al, As, Ca, Co, Cd, Li, Mo and Sr were negligible in the determination of silver. Chloride interference, which is prevalent in GF-AAS, was not found. The amount of Ag found in a SMR#1643b (NIST) water sample was 9.5 ± 0.5 ng/g which fell in the certified range of 9.8 ± 0.8 ng/g. Spikes of 30 ng/g and 60 ng/g of silver were added to the SRM and recoveries were found to be in a range from 105 % to 96.2 %. The RSD obtained for 7 replicates of 270 pg silver was 4.6 %. The results for the CCP AES are even more promising. The interferences of thirteen elements are negligible in the determination of silver. The chloride interference was not found. The detection limits for Ag, Cd, Li, Sb and B are 0.7, 0.7, 2, 80 and 400 pg respectively. The amount of silver found in a SRM#1643b (NIST) water sample was 9.3 ± 0.5 ng/g which also fell in the certified range of 9.8 ±0.8 ng/g. Spikes of 30 ng/g and 60 ng/g of silver were added into the SRM#1643b (NIST) samples; the recoveries were found to range from 97 % to 104 %. The RSD obtained for 7 analyses of 270 pg silver were 1.5 % for CCP-AES. It was also found that the signal to noise ratios (S/N) are higher in the AES mode than those in the AAS mode in the same CCP atomizer. In order to exploit advantages inherent in both GF-AAS and I CP-AES, an atmospheric pressure capacitively coupled plasma sustained inside a graphite furnace was developed. This source combines the high efficiency of atomization in furnaces and the high efficiency of the excitation in atmospheric pressure plasmas. In general, plasma sources are able to effectively excite high-lying excited states for most metals and non-metals and can also ionize vaporized elements. Therefore the possibility exists of using non-resonance lines to avoid the effects of self-absorption at high analyte concentrations. Ion lines may also be used in cases where they provide better sensitivity or freedom from spectral interferences. This source also offers the ability to independently optimize vaporization and excitation. However, the most important aspect of this new source is that it can be used for simultaneous, multielement determinations of small sized samples in a graphite furnace atomizer, a design which has been proven to be effective over many years of use. Preliminary quantitative characteristics of this new atmospheric pressure plasma emission source have been studied. The detection limit for Ag of 0.3 pg is lower than the value of 0.4 pg reported for GF-AAS. Variants of the CCP, including a gas chromatography (GC) detector, combinations of laser ablation - CCP, rf sputtering - CCP direct solid analysis, and its application as an intense spectral lamp have been developed and are reported in this dissertation.
Science, Faculty of
Chemistry, Department of
Graduate

Le dioxyde de carbone, principal gaz à effet de serre lié aux activités humaines, est considéré comme l’un des gaz les plus problématiques pour notre environnement ces dernières années, principalement à cause du réchauffement climatique qu’il engendre. C’est pour cette raison que l’augmentation de sa teneur dans l’atmosphère nous concerne tous quant aux conséquences futures pour notre planète. Afin de limiter l’émission de CO2, sa conversion en composés à valeur ajoutée présente un grand intérêt et est possible notamment via des procédés plasmas. Plus particulièrement, les décharges à barrière diélectrique (DBD) sont utilisées depuis quelques années pour générer des plasmas froids opérant à pression atmosphérique, principalement pour des applications en traitement de surface, mais également pour le traitement d’effluents gazeux.Lors de cette thèse, nous nous sommes focalisés sur le processus de dissociation du CO2 en CO et O2 via un réacteur DBD à flux continu et avons analysé sa conversion et son efficacité énergétique via différentes études. Celles-ci ont été réalisées grâce à plusieurs méthodes de diagnostic, comme par exemple la spectrométrie de masse utilisée pour déterminer la conversion et l’efficacité du processus, la spectroscopie d’émission optique, l’oscilloscope pour une caractérisation électrique, etc. afin d’avoir une meilleure compréhension du comportement des décharges CO2.Dans un premier temps, nous avons réalisé une étude détaillée d’un plasma CO2 pur où nous avons fait varier différents paramètres, tels que le temps de résidence, la fréquence, la puissance, la pulsation de la haute tension et l’épaisseur et la nature du diélectrique. Le CO2 donne lieu généralement à une décharge filamentaire, consistant en de nombreuses microdécharges réparties au niveau de la zone du plasma. Celles-ci constituent la principale source de réactivité dans une DBD. Un aperçu détaillé de l’aspect physique de ces microdécharges a été réalisé grâce à la caractérisation électrique, permettant de mieux comprendre les propriétés électriques de la décharge et des microdécharges. En effet, nous avons pu déterminer l’importance de la tension présente au niveau du plasma, de l’intensité du courant plasma, du nombre de microdécharges et de leur temps de vie sur l’efficacité du processus de dissociation de CO2.Ensuite, nous avons conclu ce travail avec des études combinant le CO2 en phase plasma avec de l’eau ou du méthane afin de produire des molécules à valeur ajoutée telles que les syngas (CO et H2), mais aussi des hydrocarbures (C2H6, C2H4, C2H2 et CH2O) dans le cas de l’ajout du méthane. A travers ces études, nous avons obtenu une meilleure connaissance de la chimie et de la physique qui ont lieu dans ce type de plasma.
Carbon dioxide appears as one of the most problematic gases for the environment, mostly because it is responsible for global warming. This is why its increasing concentration into the atmosphere, mainly due to anthropogenic activities, is a real concern for planet Earth. In order to prevent the release of large amounts of CO2, its conversion into value-added products is of great interest. In this context, plasma-based treatments using dielectric barrier discharges (DBDs) are nowadays more and more used for the conversion of this gas. In this thesis, we investigated the CO2 splitting process into CO and O2 via a flowing cylindrical DBD and we studied its conversion and energy efficiency by means of several diagnostic methods, such as mass spectrometry to determine the conversion and energy efficiency of the process, optical emission spectroscopy for gas temperature measurements, and an oscilloscope for electrical characterization, in order to obtain a better understanding of the CO2 discharge itself.First, we focused on an extensive experimental study of a pure CO2 plasma where different parameters were varied, such as the gas residence time, the operating frequency, the applied power, the pulsation of the AC signal, the thickness and the nature of the dielectric. CO2 discharges typically exhibit a filamentary behavior, consisting of many microdischarges, which act as the main source of reactivity in a DBD. A detailed insight in the physical aspects was achieved by means of an in-depth electrical characterization, allowing more insight in the electrical properties of the discharge and more specifically in the microdischarges, which are spread out throughout the active zone of the plasma. It was found throughout this work that the plasma voltage, which reflects the electric field and thus determines how the charged particles are accelerated, the plasma current, which reflects the electron density, but also the number of microdischarges and their average lifetime, play an important role in the efficiency of the CO2 dissociation process. It was revealed that the microdischarge number is important as it represents the repartition of the locations of reactivity. Indeed, as the microfilaments are more spread out in the same discharge volume, the probability for the CO2 molecules to pass through the reactor and interact with at least one microdischarge filament becomes more important at a larger number of microfilaments.The second part of the thesis was dedicated to discharges combining CO2 and H2O or CH4, both being hydrogen source molecules. The combined CO2/H2O or CO2/CH4 conversion allows forming value-added products like syngas (CO and H2), but also hydrocarbons (C2H6, C2H4, C2H2 and CH2O), at least in the presence of methane. Throughout this study, we tried to obtain a better knowledge of the chemistry and physic behind these conversion processes.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Le risque de colonisation bactérienne sur des surfaces abiotiques pose des défis importants dans plusieurs domaines de la science. Dans cette optique, des revêtements anti-bactériens ont été développés à l'aide de différents matériaux. La modification de surface des polymères améliore ses propriétés, ce qui facilite le développement de matériaux ayant des réponses biologiques optimales adaptées ou adaptables à l'environnement dans lequel ils sont implantés. Le chitosane est un biopolymère avec activité anti-microbienne inhérente qui peut être utilisé dans une grande variété d'applications de soins de santé et de l'industrie, ce qui rend particulièrement intéressant pour le développement et l'application de nouveaux matériaux fonctionnalisés, ou avec des propriétés antibactériennes. Ce polymère est utilisé pour une grande variété d'applications dans les soins de santé et l'industrie, ce qui le rend particulièrement intéressant pour le développement et l'application de nouveaux matériaux fonctionnalisés. Dans cette étude, différents types de chitosane ont été caractérisés en fonction de leur degré de déacétylation (DDA) et de leur poids moléculaire (Mw) par des techniques telles que la Résonance Magnétique Nucléaire (¹³C-RMN) et la Chromatographie d'exclusion par taille (SEC). Les résultats obtenus à partir de ces analyses révèlent de l'importance d’une caractérisation complète des biopolymères, puisque leurs propriétés peuvent varier en fonction des méthodes de production, ce qui peut influencer par la suite son utilisation et l’application. Ensuite, la méthodologie utilisée pour la modification de traitement et la surface en utilisant des techniques de plasma pour la fonctionnalisation de surfaces et le greffage de molécules a été validée. Dans un premier temps, les films en PTFE (polytétrafluoroéthylène) ont été utilisés pour vérifier l'efficacité de la méthodologie proposée pour le traitement et la modification des surfaces. Trois bras d'ancrages l'anhydride glutarique (GA), le poly (éthylène glycol) bis (carboxyméthyl) (PEGb) et le poly (anhydride éthylène-alt-maléique) (PA) ayant des caractéristiques différentes ont été utilisés dans le but de créer des liens covalents entre le recouvrement de chitosane et des surfaces aminées PTFE. Chaque étape du traitement de surface a été vérifiée par Spectrométrie Photoélectronique par Rayons-X (XPS), avec les changements de la composition chimique, ainsi que par des mesures d'angle de contact et par colorimétrie. Les changements topographiques et de rugosité après le greffage ont également été observés par la Microscopie Électronique à Balayage (MEB) et par la profilométrie. Ces résultats ont démontré que le type de bras d'ancrage a une plus grande influence sur le processus de production des revêtements que le poids moléculaire des différents types de chitosane. Pour vérifier la réponse antibactérienne des différents types de revêtements obtenus, les tests ont d'abord été réalisés avec Xylella fastidiosa et ont révélé le potentiel de ces substrats recouverts de chitosane. Des tests utilisant des bactéries pathogènes telles que Escherichia coli, Pseudomonas aeruginosa et Staphylococcus aureus ont été réalisés, confirment l'activité antibactérienne des échantillons de PTFE-plasma-PA-CHIMW. Ces résultats ont amené l'application de cette méthodologie sur une surface de PET (polytéréphtalate d’éthylène), un polymère largement utilisé dans le domaine des textiles conventionnels ainsi que dans la production de biomatériaux hospitaliers. Ainsi, les méthodologies par plasma et par greffage développées dans cette étude pour la production de revêtements de chitosane, peuvent être appliquées à la production de surfaces pour lesquelles l'activité antibactérienne est souhaitée.
The risk of bacterial colonization on abiotic surfaces poses important challenges in various fields of science. In this scenario, antibacterial coatings were developed, using a large number of materials. The surface modification of polymeric materials allows to improve surface properties, facilitating the development of optimized materials with biological responses adapted or adaptable to the environment in which they will be implanted. Chitosan is a biopolymer with inherent antimicrobial activity which can be used in a wide variety of health care and industrial applications, making it particularly interesting for the development and application of novel functionalized materials, i.e. antibacterial properties. In this study, different types of chitosan were characterized according to their degree of deacetylation (DDA) and molecular weight (Mw), using Nuclear Magnetic Resonance (¹³C NMR) and Size Exclusion Chromatography (SEC), among others. The results obtained through these analyses revealed the great importance of the characterization of biopolymers since their properties can vary according to the production methods, which can influence its use as an application. Afterward, the methodology applied for the treatment and modification of surfaces using plasma, for the surface functionalization and grafting of molecules was validated. Initially, PTFE (poly(tetrafluoroethylene)) films were used to verify the efficiency of the proposed methodology for the treatment and surface modification. Three spacer molecules glutaric anhydride (GA), poly (ethylene glycol) bis (carboxymethyl) (PEGb) and poly (ethylene-alt-maleic anhydride) (PA), with different characteristics were used to covalently attach the chitosan coating to the aminated PTFE surfaces. Each step of the surface treatment was verified by X-ray Photoelectron Spectroscopy (XPS), through changes in chemical composition, by contact angle measurements and by colorimetry. The topographic and roughness changes after grafting were also observed by Scanning Electron Microscopy (SEM) and profilometry. These results demonstrated that the type of anchors has a greater influence on the coating process than the molecular weight of the different types of chitosan. To verify the antibacterial response of the different types of coatings obtained, tests were initially carried out using Xylella fastidiosa and revealed the potentiality of the substrates covered with chitosan. Tests using pathogenic bacteria such as Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were performed confirming the antibacterial behavior of PTFE-plasma-PA-CHIMW samples. These results encouraged the application of this methodology in PET (polyethylene terephthalate) substrate, a polymer widely used in the field of conventional textiles as well as in the production of hospital textiles and biomaterials. Thus, the plasma-grafting methodology developed in this study, for the production of chitosan coatings, can be applied to the production of surfaces where antibacterial activity is desired.
O risco da colonização bacteriana em superfícies abióticas impõe desafios importantes para os diversos campos da ciência. Neste cenário, revestimentos antibacterianos têm sido desenvolvidos, usando um grande número de diferentes materiais. A modificação da superfície de polímeros permite melhorar as suas propriedades, com vistas ao desenvolvimento de materiais com respostas biológicas adaptadas ou adaptáveis ao ambiente onde serão implantados. A quitosana é um biopolímero com atividade antimicrobiana o qual pode ser utilizado numa ampla variedade de aplicações de cuidados de saúde e industriais, tornando-a particularmente interessante para o desenvolvimento e aplicação de novos materiais funcionalizados, ou seja, com propriedades antibacterianas. Neste estudo, diferentes tipos de quitosana foram caracterizadas de acordo com o seu grau de desacetilação (DDA) e massa molar (Mw), através de técnicas como ressonância magnética nuclear (¹³C RMN) e cromatografia de exclusão de tamanho (SEC), entre outras. Os resultados obtidos através dessas análises revelaram a grande importância da caracterização de biopolímeros, uma vez que suas propriedades podem variar de acordo com os métodos de produção, o que pode influenciar no seu uso como aplicação. Em seguida, a metodologia aplicada para o tratamento e modificação de superfícies empregando as técnicas de plasma, para a funcionalização de superfícies e o grafting para a imobilização do recobrimento de quitosana foi validada. Inicialmente, filmes de PTFE (politetrafluoretileno) foram utilizados para verificar a eficácia da metodologia proposta para o tratamento e modificação de superfície. Três moléculas “ancoradoras” com diferentes características anidrido glutárico (GA), poli(etileno glicol) bis(carboximetil) (PEGb) e poli(anidrido etileno-alt-maleico) (PA), foram utilizadas visando ligar covalentemente o recobrimento de quitosana às superfícies de PTFE aminadas. Cada etapa do tratamento da superfície foi verificada por espectroscopia de fotoelétrons de raios-X (XPS), por medições de ângulo de contato e colorimetria sendo evidenciada as mudanças na composição química da superfície e sua molhabilidade. As alterações topográficas e de rugosidade após o grafting também foram observadas por microscopia eletrônica de varredura (MEV) e perfilometria. Esses resultados demonstraram que o tipo de molécula ancoradora tem uma influência primária no processo de produção dos recobrimentos seguido pela massa molecular dos diferentes tipos de quitosana. Para verificar a resposta antibacteriana dos diferentes tipos de recobrimentos obtidos, testes foram inicialmente realizados empregando a Xylella fastidiosa e revelaram a potencialidade dos substratos recobertos com quitosana. Assim, testes utilizando bactérias patogênicas como, Escherichia coli, Pseudomonas aeruginosa e Staphylococcus aureus foram realizados confirmando o comportamento antibacteriano das amostras PTFE-plasma-PA-CHIMW. Esses resultados encorajaram a aplicação desta metodologia em um substrato de PET (polietileno tereftalato), um polímero muito usado no ramo de têxteis convencionais como também na produção de têxteis hospitalares e biomateriais, demonstrando assim, que a metodologia de plasma-grafting aplicada neste estudo, para a produção de recobrimentos de quitosana, pode ser usada para a produção de superfícies onde a atividade antibacteriana é desejada, ou seja, esses revestimentos podem fornecer uma barreira adicional e complementar à transmissão de patógenos, enquanto podem atuar combinados com procedimentos normais de limpeza e desinfecção.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Neste trabalho são apresentados os efeitos da diluição da atmosfera precursora de metano por três gases nobres (Ar, Ne e He) nas propriedades mecânicas e na microestrutura de filmes de carbono amorfo hidrogenado (a-C:H). Tanto a influência da diluição da atmosfera precursora de metano (para Vb=-350 V), como da variação da tensão de autopolarização (Vb) são estudadas. A influência da temperatura do substrato também é estudada para três temperaturas do substrato (250 K, 300 K e 420 K) em filmes depositados em atmosferas de 100% CH4 e 2% CH4+98% Ar. Os filmes foram depositados utilizando a técnica de Deposição Química na Fase Vapor Assistida por Plasma (PECVD). As propriedades mecânicas e estruturais foram investigadas com o uso das técnicas nucleares (retroespalhamento Rutherford e detecção de íons de recuo elástico), espectroscopia de absorção no infravermelho, espectroscopia Raman, microscopia de força atômica, medidas de ângulo de contacto, medidas de tensão interna (por perfilometria) e medidas da dureza (por nanoindentação). Os resultados obtidos mostraram que a diluição da atmosfera precursora de metano por gases nobres não induz modificações substanciais à microestrutura do filme ou às propriedades mecânicas. Pelo contrário, os resultados mostraram que tanto a composição, como a microestrutura e as propriedades mecânicas dos filmes são fortemente dependentes da energia de bombardeamento dos íons. Também foi observada uma dependência das propriedades mecânicas e estruturais dos filmes em função da temperatura do substrato. Resultados experimentais importantes e originais foram obtidos a partir da medida da rugosidade dos filmes usando microscopia de força atômica que sugerem uma transição nos mecanismos de formação dos filmes de a-C:H de predominantemente por adsorção/difusão para a predominância dos processos balísticos.
In this work, the effects of the dilution of the precursor methane atmosphere by three noble gases (Ar, Ne and He) on the mechanical properties and the microstructure of hydrogenated amorphous carbon films (a-C:H) are presented. The influence of the precursor atmosphere (for Vb=-350 V) and the variation of the self-bias voltage (Vb) are studied. The influence of the substrate temperature also is studied for three temperatures 250 K, 300 K and 420 K for films deposited in atmospheres of 100% CH4 and 2% CH4 + 98% Ar. The films were deposited by Plasma Enhance Chemical Vapor Deposition (PECVD). The mechanical and structural properties were investigated with the use of the nuclear techniques (Rutherford backscattering and elastic recoil detection analysis), infrared and Raman spectroscopies, atomic force microscopy, contact angle measurements, internal stress and hardness measurements. The results shown that the precursor atmosphere dilution by noble gases did not induce substantial modifications in the microstructure or in the mechanical properties of the films. On the other side, the results shown that the composition, the microstructure and the mechanical properties of the films are strongly dependent on the ion bombardment regime. The dependence of the mechanical and structural properties of the films as a function of the substrate temperature was also investigated. Experimental results had been obtained from the film roughness measurements using atomic force microscopy. These results suggest the transition from predominantly adsorption/diffusion mechanisms to the predominance of the ballistic processes in the formation mechanisms of the a- C:H films.

Les transformateurs piézoélectriques se positionnent aujourd'hui comme une alternative technologique séduisante face aux solutions classiquement utilisées pour la génération des plasmas froids. Leur haute permittivité, leur faible tension d’alimentation et leur capacité de miniaturisation en font une solution sérieuse et originale pour de nombreuses applications faibles puissances, notamment dans le domaine biomédical pour la stérilisation, le traitement de surface et la décontami-nation des instruments médicaux. Dans le cadre d'un fonctionnement en générateur plasma, la conversion électromécanique au sein du transformateur s’accompagne de pertes mécaniques et diélectriques, souvent converties en chaleur. À ces effets s'ajoute l’influence proprement dite de la décharge sur le comportement électrique du dispositif. L’évolution dynamique et fortement non-linéaire de la décharge entraine un comportement méconnu des grandeurs électriques. Par conséquent, l’étage d’alimentation du transformateur constitue un sujet d’étude au même titre que le transformateur lui-même. De plus, étant donné la configuration du processus de génération, qui positionne le matériau piézoélectrique comme source et siège de la décharge plasma, il devient nécessaire d’analyser la viabilité du dispositif. L’ionisation du milieu gazeux environnant le générateur provoque des effets électroniques complexes, susceptibles d’entrainer des dépôts de matière à la surface du matériau ou d’en éroder la surface. C’est dans ce cadre, à l’interface entre le génie électrique et la science des matériaux, que s’articule cette thèse. Une première partie est destinée au développement d’un outil de commande numérique du générateur par une boucle de verrouillage de phase, assurant sa continuité de fonctionnement face aux variations des conditions opératoires. Par la suite, une modélisation du générateur plasma dans des configurations proches des décharges à barrières diélectriques est effectuée ;des simulations permettent une estimation de la puissance de décharge à partir d’une identification expérimentale des paramètres du modèle. Dans un deuxième temps, nous cherchons à établir une corrélation entre la structure du matériau et ses propriétés électriques en s’appuyant sur une méthodologie de caractérisation multi-échelle, avant et après décharge plasma. L'étude se focalise principalement sur l'évolution en surface de la structure cristalline et la composition chimique, en liaison avec les propriétés fonctionnelles du transformateur après génération de la décharge. Enfin, une étude en température porte sur l’investigation des effets d’auto-échauffement du générateur dans ce mode de fonctionnement
Due to intensive development efforts during the past decade, piezoelectric transformers havebecome an attractive alternative solution compared to the con-ventionally used technologies forcold plasma generation. Their high efficiency, thin-shaped dimensions and low voltage supplymake them serious and original candidates for numerous low power applications, particularly inbiomedical field. Operating as a plasma generator, the electromechanical conversion within thetransformer is accompanied by mechanical and dielectric losses, often converted into heat. On topof these effects, the discharge is likely to influence the electrical behavior of the device. Thedynamic and highly non-linear evolution of the dis-charge leads to an unknown behavior ofelectrical properties. Consequently, the transformer supply stage is an active research subject inthe same way as the trans-former itself. Moreover, considering the configuration of the generationprocess, which positions the piezoelectric material as the source and the spot of the plasmadischarge, it becomes necessary to consider the viability of the device. The ioniza-tion of thegaseous environment surrounding the generator causes complex elec-tronic effects, which canlead to material deposition on the surface of the generator and thus modify or even degrade it. It iswithin this framework, at the interface between electrical engineering and material science, thatthis thesis is articulated. A first part is intended to develop a setup for numerical control of thedevice using a digital phase-locked loop to ensure its continuous operation in different operatingconditions. Subsequently, a model of the plasma generator in configurations close to dielectricbarrier discharges is proposed; Simulations allow an estimation of the discharge power from anexperimental identification of the model parameters. In a second part, we seek to establish acorrelation between the material structure and its electrical properties based on a multi-scalecharacterization methodology, before and after plasma discharge. The study focuses mainly onthe surface evolution in terms of the crystalline structure and the chemical composition, related tothe over-all properties of the piezoelectric transformer before and after discharge generation.Finally, a temperature study that concerns the investigation of the effects of self-heating of thegenerator in this operating mode is performed

Nous avons développé une décharge transportée fonctionnant à la pression atmosphérique. Le générateur fonctionne en mode alternative avec une fréquence d’excitation variant entre 1 et 10kHz. Grace à une forme d'onde en dents de scie, il a été possible de transporter la décharge à l’intérieur d’un tube sur une longueur qui pourrait atteindre 200cm. L’influence des différents paramètres tels que la forme de la tension appliquée, le diamètre du tube et la configuration d’électrode, sur la formation de la décharge a été étudié. La nature des espèces excitées à l’intérieur et extérieur du tube a été identifié par Spectroscopie Optique d’Emission. La propagation de la décharge dans un système multi jets et un jet unique de la même section a été comparée. L’influence de ces deux types de jets transportés exposés aux bactéries de type E. coli a été étudiée et les résultats montrent que la zone d’inactivation des bactéries augmente significativement.De plus le potentiel de cette décharge pour le traitement de surface et dépôt des couches minces de polymère a été investigué aussi bien à l’extérieur qu’à l’intérieur du tube capillaire pour la première fois. Nous avons employé deux types de précurseurs: le TEOS, et le DEGME. Sous certaines conditions, les couches de type PEG présentant des propriétés antiadhésives des cellules ont été déposées sur le PS. Afin d’étudier les modifications de surface créées sur les polymères par cette décharge. Les résultats obtenus par des méthodes d’analyse différentes montrent qu’à part l’oxydation de la surface du UHMWPE nous pouvons déceler une insaturation de la surface qui est souvent accompagnée de la réticulation de la surface
We have developed a transporting discharge source that can operate at atmospheric pressure. The device is working by using AC power supply with a frequency ranging between 1 to 10 kHz. The sawtooth waveform enabled the transport of discharge as long as 200 cm. The different parameters that affect the plasma delivery such as voltage of the waveforms, tube diameter and electrode configuration were investigated. The electronically excited and active species inside and outside of the plasma channel were characterized by Optical Emission Spectroscopy. The electrical and temporal characteristics of the plasma, discharge power and charges on the sample were investigated. The propagation of transporting discharge with multi-jets and a single jet with the same cross-sectional area has been compared. Also, E.coli bacteria were exposed to the transporting discharge multijets and single jet for different time durations.The potential of the transported discharge for the surface treatment of polymers and deposition of thin films has been investigated. Two different precursors namely TEOS, and DEGME have been employed for the elaboration of thin organic coatings by introducing the precursors inside and at the exit of the capillary tube. The PEG like coatings obtained in the case of DEGME on PolyStyrene films showed for particular operating conditions nonadhesive coatings with respect to Ovary Carcinoma Celles. In order to study the surface modification effects of the discharge, the Ultra High Molecular Weight PolyEthylene was used as the substrate in the two different configurations. The results show that besides the oxydation of the UHMWPE, crosslinking takes place

Il presente lavoro di tesi ha come obiettivo principale lo studio di materiali innovativi per lo sviluppo di componenti ottici nella regione spettrale dell’estremo ultravioletto (EUV) e dell’ultravioletto da vuoto (VUV). I campi di applicazione sono molteplici e spaziano dalla litografia EUV all’esplorazione spaziale. Questo tipo di ricerca richiede contemporaneamente l’utilizzo e la messa a punto di adeguati metodi di caratterizzazione, che permettano una completa analisi delle proprietà nella regione spettrale di interesse. Il risultato più interessante presentato è sicuramente l’analisi ottica e strutturale di strati di grafene (singolo e triplo) depositati su silicon oxide, nella regione spettrale dell’ultravioletto da vuoto. Lo studio è stato affrontato combinando diverse tecniche sperimentali e partendo dalle proprietà ottiche dell’ossido di silicio depositato su silicio (SiO2/Si), che costituisce il substrato. Il SiO2/Si è stato caratterizzato alla hydrogen Lyman-alpha (121.6 nm) utilizzando un riflettometro dedicato alla riflettometria nell’ultravioletto e recentemente implementato per misure polarimetriche (CNR-IFN Padova). Sono stati determinati i parametri ellissometrici, ratio (ρ) and phase shift (), le costanti ottiche e le proprietà polarimetriche del silicon oxide. Il SiO2 si comporta effettivamente come una lamina di ritardo introducendo una differenza di fase tra le componenti s- e p- della radiazione incidente. La differenza di fase introdotta varia dai 18° ai 160° e dipende dall’angolo di incidenza. Successivamente, lo stesso tipo di analisi sperimentale è stata completata per i campioni con uno strato di grafene depositato sull’ossido di silicio (1LG/SiO2/Si). E’ stato osservato che, nonostante il sottile spessore, il singolo strato di grafene migliora la riflettività del substrato. Dall’analisi polarimetrica, non si può invece affermare che il grafene introduca un ritardo di fase osservabile. Le costanti ottiche del singolo e triplo strato di graphene cresciuto su SiO2/Si sono state studiate alla hydrogen Lyman-alpha utilizzando misure in riflettometria in polarizzazione s- e p- acquisite utilizzando luce di sincrotrone (ELETTRA Trieste, BEAR beamline). Si notano differenze misurabile nella riflettività dei campioni. Le differenze dipendono dal numero di strati di graphene. Queste misure sono state utilizzate per ricavare le costanti ottiche. E’ stata inoltre sperimentalmente osservato una anisotropia ottica con asse di simmetria quasi perpendicolare alla superficie e coerentemente correlata all’orientamento degli orbitali π. Le costanti ottiche efficaci sono state ricavate simulando l’interazione della radiazione elettromagnetica con la struttura del campione. Inoltre, l’attendibilità delle costanti ottiche trovate è stata qualitativamente testata ricavando la “surface differential reflectance (SDR)” dalle misure di riflettività. Un altro effetto molto interessante indotto dal grafene è lo spostamento dell’angolo di pseudo-Brewster rispetto a quanto osservato per il substrato. Lo spostamento, che cresce in valore assoluto con il numero di strati, induce un downshift contrariamente a quanto osservato in altre regioni spettrali. La qualità della superficie, la morfologia e il numero di layer sono stati caratterizzati con misure di microscopia a forza atomica e spettroscopia Raman. Per quanto ne sappiamo, questi risultati relativi allo studio delle proprietà ottiche del grafene nel VUV sono assolutamente nuovi. L’ultima parte della tesi riguarda lo studio dello strato di stagnazione che si forma sul fronte di collisione di due plasmi collidenti. La tecnica utilizzata è una spettroscopia risolta in tempo. Il tempo di evoluzione e le dinamiche dei plasmi collidenti di Al-Al e Al-Si sono stati studiati con tecniche spettroscopiche risolte in tempo. È stato osservato che nel caso di un "wedge target" lo strato di ristagno produce uno spettro più luminoso e in precedenza sono comparsi stati di ionizzazione più elevati con un'intensità relativamente più elevata di un "flat target". Il tempo di evoluzione della densità elettronica è stato studiato e confrontato nel caso delle due configurazioni con i target diversi e una densità elettronica relativamente più alta è stata osservata nel caso di “wedge target”.
The aim of this research is to investigate and explore new innovative material(s) and techniques regarding development and improvement of vacuum ultraviolet (VUV) and extreme ultraviolet (EUV) optics and sources; for the advancement of EUV and VUV technological areas like space exploration (e.g. observation and spectroscopic diagnostics of the solar corona) and EUV lithography (e.g. advancement and minimization of integrated electronic circuits (ICs)). The research work was primarily focused on the investigations of the optical and structural properties of graphene (mono and few-layer) deposited on SiO2/Si substrate in VUV spectral region by exploiting different diagnostic techniques, based on reflection and polarimetric measurements. The study was addressed starting from silicon dioxide deposited on silicon (SiO2 / Si), which works as the substrate for graphene samples. The optical properties of SiO2/Si were thoroughly investigated at the hydrogen Lyman–alpha line (121.6 nm) by employing the tabletop EUV-VUV polarimetry facility located at CNR-INF Padova. An approach based on the combined use of reflectometry with polarimetry technique was used to find out the reliable values of the optical constants. The results show the potential of the approach and it was demonstrated in this study that the optical constants retrieved by using ellipsometric parameters; ratio (ρ), and phase shift (), are more reliable than the retrieved one using least square fitting of the reflectivity. Moreover, it was found that SiO2 behaves as a phase retarder by introducing a phase difference between the s- and p- polarization components of the incoming light. The phase differences observed was 18° to 160° depending on the incidence angle. Using the similar experimental technique, the ellipsometric parameters (phase shift (ϕ), ratio (ρ)) of graphene (1LG/SiO2/Si) sample were also investigated and compared with that of SiO2/Si to see the effect of the graphene as capping layer. It was found that 1LG on top of SiO2 improves optical throughput and despite having atomic thickness it affects the polarimetric properties of the underlying substrate. Further, detailed optical properties of mono (1L) and tri-layer (3L) of commercial graphene grown on (SiO2/Si) substrate were studied at hydrogen Lyman alpha by using laboratory based (at CNR-IFN, Padova) and synchrotron light-based (at BEAR beamline, Elettra synchrotron) EUV-VUV reflectometer setups. Angular reflectance measurements of graphene samples along with bare substrate were performed by taking into account the light polarization. Distinguishable optical performance was observed for both samples (1LG and 3LG) in spite of the ultra-thin thickness of the films. Optical anisotropy with the axis of symmetry nearly perpendicular to the surface and coherently related to the p-orbitals structural orientation has been experimentally demonstrated. Anisotropic “effective optical constants” corresponding to “effective thickness” were retrieved by simulating the interaction of the electromagnetic wave with the structure of the sample. Furthermore, the reliability of the derived optical constants was tested qualitatively by deducing surface differential reflectance (SDR) from the reflectance measurements. Another very interesting effect induced by graphene is the shift of the pseudo-Brewster angle with respect to what was observed for the substrate. The downshift of the pseudo-Brewster angle was observed for both samples 1LG (-1.5°), and 3LG (-5°), with larger shift for an increasing number of layers. However, in literature an upshift in the Brewster angle is reported but for different spectral region. AFM, XPS and Raman spectroscopies were used to study surface morphology, quality of graphene coatings, and to estimate the thickness/ number of layers. To the best of our knowledge, these remarkable optical properties of graphene at VUV spectral region was determined for the first time and results are of considerable interest for VUV optics advancement. The last part of the thesis is about the study of the stagnation layer formed at the collision front of two colliding plasmas by employing time resolved spectroscopic technique. Time evolution and dynamics of the Al-Al, Al-Si colliding plasmas studied and compared in the case of flat and wedge targets. It was observed that in case of wedge target the overall emission from stagnation layer was more intense and higher ionization states of (Al and Si) appeared earlier in time having higher intensity compared to the flat target. The time evolution of the electron number density was also studied and it was observed that wedge target results in a relatively higher electron number density

In this thesis, we focused on the understanding of the synthesis and texturization processes of hydrophobic and (super)hydrophobic fluorinated surfaces by atmospheric plasmas.

First, we focused on the surface modifications of a model surface, the polytetrafluoroethylene (PTFE), by the post-discharge of a radio-frequency plasma torch. The post-discharge used for the surface treatment was characterized by optical emission spectroscopy (OES) and mass spectrometry (MS) as a function of the gap (torch-sample distance), and the helium and oxygen flow rates. Mechanisms explaining the production and the consumption of the identified species (N2, N2+, He, O, OH, O2m, O2+, Hem) were proposed.

The surface treatment was then investigated as a function of the kinematic parameters (from the motion robot connected to the plasma torch) and the gas flow rates. Although no change in the surface composition was recorded, oxygen is required to increase the hydrophobicity of the PTFE by increasing its roughness, while a pure helium plasma leads to a smoothing of the surface. Based on complementary experiments focused on mass losses, wettability and topography measurements coupled to the detection of fluorinated species on an aluminium foil by XPS, we highlighted an anisotropic etching oriented vertically in depth as a function of the number of scans (associated to the treatment time). Atomic oxygen is assumed to be the species responsible for the preferential etching of the amorphous phase leading to the rough surface, while the highly energetic helium metastables and/or VUV are supposed to induce the higher mass loss recorded in a pure helium plasma.

The second part of this thesis was dedicated to the deposition and the texturization of fluorinated coatings in the dielectric barrier discharge (DBD). The effects of the nature of the precursor (C6F12 and C6F14), the nature of the carrier gas (argon and helium), the plasma power, and the precursor flow rate were investigated in terms of chemical composition, wettability, topography and crystallinity by SIMS, XPS, WCA, AFM and XRD. We showed that hydrophobic surfaces with water contact angles (WCA) higher than 115° were obtained only in the presence of argon and were assumed to be due to the roughness created by the micro-discharges. Plasma-polymerized films in helium were smooth and no WCA higher than 115° was observed. We also studied the impact of the deposition rate and the layer thickness in the hydrophobic properties as well as the polymerization processes through the gas phase characterization.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Dans cette thèse de doctorat, des simulations numériques basées sur un modèle fluide 2D sont utilisées pour caractériser des jets de plasma d’Hélium pulsés. Le modèle pour les jets de plasma d’Hélium est développé pour décrire des jets qui s’écoulent dans des atmosphères de N2 et O2 et interagissent avec des cibles. La dynamique de la décharge dans les jets d’Hélium impactant une cible métallique à la masse est analysée pour des polarités positive et négative de la tension appliquée. Les évolutions temporelles et spatiales de champ électrique associées au premier front d’ionisation et au front de rebond sont en bon accord qualitatif avec des mesures récentes de champ électrique. Puis, l’interaction plasma cible entre une décharge positive et une cible diélectrique en BSO est examinée en détail et les résultats sont directement comparés aux expériences. Un bon accord est obtenu entre les simulations et les expériences sur les évolutions temporelles et spatiales de champ électrique. Des valeurs maximales de champ électrique dans la cible de 5 kV.cm−1 ont été obtenues expérimentalement et numériquement. Le champ électrique dans le plasma de l’ordre de quelques dizaines de kV.cm−1 est fortement diminué par le changement de permittivité de la cible. Le champ électrique dans la cible est presque exclusivement dû aux fortes valeurs de charges de surface déposées sur la surface de la cible. Finalement, l’influence des évolutions de champ électrique sur la production d’espèces actives près des cibles est évaluée. On démontre qu’avec des cibles métalliques la synergie entre le premier front et le front de rebond augmente la production d’espèces près de la cible
In this PhD thesis numerical simulations based on a 2D fluid model are used to characterize pulsed Helium plasma jets. The model for He plasma jets is developed to describe He jets flowing in N2 and O2 atmospheres and interacting with targets. The discharge dynamics in He jets impacting a grounded metallic target is analyzed with both positive and negative polarities of applied voltage. The temporal and spatial evolutions of electric field associated to the first and rebound ionization fronts are in good qualitative agreement with recent electric field measurements. Then, the plasma-target interaction occurring between a positive discharge and a BSO dielectric target is investigated in detail and results are directly compared with experiments. A good agreement is obtained between simulations and experiments concerning the temporal and spatial profiles of electric field. Maximum values of electric field inside the target of 5 kV.cm−1 are found. The high electric field in the plasma of the order of dozens of kV.cm−1 is severely depleted by the change of permittivity. As a result, the electric field experienced inside the target is almost exclusively originated by the high values of surface charge deposited on the target surface. Finally, the influence of the electric field evolutions on the production of chemically active species close to the targets is evaluated. It is shown that with metallic targets the synergy between the first and rebound fronts increases species production close to the target

Ce travail de thèse de doctorat propose et évalue différentes solutions pour caractériser, avec des outils optiques et électromagnétiques non intrusifs, les nanoparticules et agrégats observés dans différents systèmes physiques : suspensions colloïdales, aérosols et plasma poussiéreux. Deux types de modèles sont utilisés pour décrire la morphologie d'agrégats fractals (p. ex. : suies issues de la combustion) et agrégats compacts (qualifiés de « Buckyballs » et observés dans des aérosols produits par séchage de nano suspensions). Nous utilisons différentes théories et modèles électromagnétiques (T-Matrice et approximations du type dipôles discrets) pour calculer les diagrammes de diffusion (ou facteur de structure optique) de ces agrégats, de même que leurs spectres d'extinction sur une large gamme spectrale. Ceci, dans le but d'inverser différentes données expérimentales. Différents outils numériques originaux ont également été mis au point pour parvenir à une analyse morphologique quantitative de clichés obtenus par microscopie électronique. La validation expérimentale des outils théoriques et numériques développés au cours de ce travail est focalisée sur la spectrométrie d'extinction appliquée à des nano agrégats de silice, tungstène et silicium
This Ph.D. work provides and evaluates various solutions to characterize, with optical/electromagnetic methods nanoparticles and aggregates of nanoparticles found in suspensions, aerosols and dusty plasmas. Two main models are introduced to describe the morphology of particle aggregates with fractal-like (for particles in plasmas and combustion systems) and Buckyballs-like (aerosols, suspensions) shapes. In addition, the author proposes various solutions and methods (T-Matrix, Rayleigh type approximations) to calculate the scattering diagrams (optical structure factors) of fractal aggregates as well as algorithms to inverse extinction spectra. As a reference case for the performed analysis, several tools to describe the morphology of fractal aggregates from electron microscopy images have been also developed. The experimental validation carried out with the Light Extinction Spectrometry (LES) technique (for nano silica beads, tungsten, dusty plasma and silicon aggregates) clearly proves the validity of the algorithms developed as well as the potential of the LES technique

Les chalcogénures sont des matériaux très prometteurs pour des applications dans divers domaines, comme l’enregistrement et la transmission des données, l’optique intégrée, les capteurs ou la médecine. Ceci est dû à leurs propriétés exceptionnelles, en termes de transparence dans l’infrarouge, effets photo-induits, grande solubilité pour les terres rares, ou contraste élevé des paramètres électriques et optiques lors d’un changement de phase. Pour beaucoup de ces applications, les chalcogénures doivent se présenter sous forme de couches minces. Une méthode efficace et flexible pour obtenir de telles couches est le dépôt par ablation laser (PLD).Dans cette thèse nous avons entrepris une étude systématique sur l’influence de divers paramètres, comme la longueur d’onde, la durée de l’impulsion ou la fluence du laser, la pression de dépôt et la distance cible-substrat, sur les propriétés des couches minces déposées. Deux familles de composés ont été étudiées : (GeTe)x(Sb2Te3)1-x (avec x = 0, 1/3, 1/2, 2/3, 1) et GaLaS (pur ou dopé avec des terres rares – Er et Pr). Une étude en spectroscopie optique d’émission a été également effectuée afin d’explorer la dynamique et l’énergétique du plasma créé par ablation laser. Les propriétés des couches minces ont été caractérisées par microscopie optique et électronique, profilométrie, diffraction de rayons X, spectroscopie Raman, ellipsométrie etc. Les principaux résultats indiquent de meilleures propriétés pour les couches déposées à faible longueur d’onde, courte durée d’impulsion et fluence modérée. Ils ouvrent la voie vers l’optimisation du processus PLD pour la croissance de couches minces de chalcogénures de manière contrôlée
Chalcogenides are among the most promising materials for applications in various fields, like data storage and transmission, integrated optics, bio- and chemical-sensing, or medicine. This is due to their outstanding properties, in terms of wide infrared transparency, photo-induced effects, high rare-earth solubility or high contrast in electrical and optical parameters upon phase transformation. For many of these applications, processing of chalcogenides in form of thin films with required chemical composition and appropriate physical properties is necessary. Pulsed Laser Deposition (PLD) is one of the most efficient and flexible methods for the preparation of such multicomponent layers.In this thesis we performed a systematic study on the influence of various PLD parameters, like laser wavelength, pulse duration and fluence, background pressure and target-substrate distance, on the properties of deposited thin films. Two families of chalcogenide compounds were explored: (GeTe)x(Sb2Te3)1-x (with x = 0, 1/3, 1/2, 2/3, 1) and GaLaS (pure or doped with Er and Pr rare earths). Additionally, a time- and space-resolved optical emission spectroscopy study was performed in order to characterize the dynamics and energetics of the laser ablation plasma plume. The properties of the thin films were investigated by specific methods, as optical and electronic microscopy, profilometry, X-ray diffraction, Raman spectroscopy, ellipsometry etc. The main results indicate better properties for samples deposited at lower wavelength, short pulse duration and moderate fluence. They open the way for the optimization of the PLD process for chalcogenide thin film growth in a controlled manner

La spectroscopie de plasma induit par laser (En anglais LIBS: laser-induced breakdown spectroscopy) est une méthode analytique de spectroscopie d'émission optique qui utilise un plasma induit par laser comme source de vaporisation, d'atomisation et d'excitation. Bien que la LIBS ait démontré sa polyvalence et ses caractéristiques attrayantes dans de nombreux domaines, les aspects quantitatifs de la LIBS sont considérés comme son talon d'Achille. D'un point de vue fondamental, cela peut être dû à la nature complexe du plasma induit par laser comme source d'émission spectroscopique. La caractérisation temporelle et spatiale du plasma induit par laser est considérée comme l'un des points clés pour comprendre les fondements de la technique LIBS. D'autre part, la LIBS est habituellement caractérisée par l'utilisation d'une ablation laser directe, sans traitement préalable de l'échantillon. Cela pourrait être assez limitant en particulier pour certains types de matériaux tels que des poudres ou des liquides. Une préparation adéquate ou un traitement approprié de l'échantillon permettant le dépôt d'un film mince et homogène de l'échantillon sur une surface métallique pourrait grandement augmenter le potentiel de la LIBS en vue d'obtenir de meilleures performances analytiques, et notamment une meilleure sensibilité et un effet de matrice réduit. On parle alors de LIBS assistée par surface car la matrice métallique contribue à une augmentation de la température du plasma. Le présent travail de thèse est donc motivé par deux aspects importants de la technique LIBS: la connaissance du plasma induit par laser comme source d'émission spectroscopique, et de nouvelles méthodes de préparation des échantillons pour améliorer la performance analytique de la LIBS, notamment pour des échantillons comme poudres et liquides visqueux. La première partie de cette thèse (chapitre 2) est consacrée à la caractérisation du plasma induit sur des échantillons de verre, en fonction de la longueur d'onde du laser, infrarouge (IR) ou ultraviolet (UV), et du gaz ambiant, de l'air ou de l'argon. L'imagerie spectroscopique et la spectroscopie d'émission résolue en temps et en espace sont utilisées pour le diagnostic du plasma. La deuxième partie de cette thèse est de développer des méthodes de préparation d'échantillons, déposés sur des surfaces métalliques pour l'analyse LIBS de poudres ainsi que de vins comme exemples de liquide. Au chapitre 3, nous avons appliqué la LIBS pour l'analyse quantitative dans des poudres (exemples de poudres : cellulose, alumine ainsi que de la terre). Au chapitre 4, nous avons appliqué la LIBS pour la classification des vins français selon leurs régions de production. Deux modèles de classification basées sur l'analyse des composants principaux (PCA) et la forêt aléatoire (RF) sont utilisés pour la classification. A l'aide de ces applications, ce travail de thèse démontre l'efficacité de la méthode LIBS assistée par surface pour l'analyse de poudres (cellulose, alumine et sols) et de liquides (vins), avec une limite de détection dans l'ordre de ou sous la ppm et une réduction significative de l'effet de matrice
Laser-induced breakdown spectroscopy (LIBS) is an analytical method with optical emission spectroscopy that uses a laser pulse to vaporize, atomize, and excite a hot plasma as the spectroscopic emission source. Although LIBS has demonstrated its versatility and attractive features in many fields, the quantitative analysis ability of LIBS is considered as its Achilles’ heel. From a fundamental point of view, this can be due to the complex nature of laserinduced plasma as the spectroscopic emission source for LIBS application. The temporal and spatial characterization of laser-induced plasma is considered as one of the key points for the LIBS technique. On the other hand, from the analytical point of view, LIBS is usually characterized by direct laser ablation. This can be however quite limiting, especially for some types of materials such as powders or liquids. Proper sample preparation or treatment allowing the deposition of a thin homogeneous film on a metallic surface could greatly improve the analytical performance of LIBS for these types of materials. Since the metallic surface is expected to contribute to increase the temperature and the density of the plasma and, consequently, to a better overall sensitivity, we call this technique surface-assisted LIBS. The present thesis work is therefore motivated by two basic aspects of LIBS analysis: the need of an improved knowledge of laser-induced plasma as a spectroscopic emission source, and new methods to improve the analytical performance of LIBS, including a higher sensibility and a reduced matrix effect. The first part of this thesis (Chapter 2) is dedicated to an extensive characterization of the plasma induced on glass samples, as a function of the laser wavelength, infrared (IR) or ultraviolet (UV), and the ambient gas, air or argon. Both the spectroscopic imaging and time- and space-resolved emission spectroscopy are used for plasma diagnostics in this work. The second part of this thesis is to develop a surface-assisted LIBS method for the elemental analysis in powders, and in wines as examples of liquids. We applied the surface-assisted LIBS for the quantitative elemental analysis in cellulose powders, alumina powders, and soils (Chapter 3). Special attentions are paid on the figures-of-merit, matrix effects, and normalization approaches in LIBS analysis. We also used the surfaceassisted LIBS for the classification of French wines according to their production regions (Chapter 4). Two classification models based on the principal component analysis (PCA) and random forest (RF) are used for the classification. Through these applications, this thesis work demonstrates the efficiency of the surface-assisted LIBS method for the analysis of powders (cellulose, alumina and soils) and of liquids (wines), with ppm or sub-ppm sensitivities and a reduced matrix effect

Characterization of edge tokamak plasma instabilities by measuring emergent phenomena within a range of frequencies above the ion cyclotron frequency have been explored in two ways: using the inter-event waiting times of Edge Localized Modes (ELMs) occurrences in measured time series of JET plasmas and by performing 2D/3D simulations of filamentary structures dynamics using a hybrid model plasma description, i.e. kinetic ion particles and massless charge neutralizing electron fluid. The analysis of ELMs time series using characteristic emission lines Da of JET tokamak in otherwise similar plasmas was performed with only a minimal number of drivers such as the gas puffing rate. They have shown a key role in changing the underlying system mode cycle where a threshold value revealed its transition from single harmonic behaviour to a transitioning phase into a total lost of the state and born of a higher frequency resonant mode. Hybrid simulations of blobs/filaments are performed in 2D/3D to observe the kinetic evolution of these plasma structures over several ion gyroperiods. Novel 3D simulations represent the first kinetic simulations of these structures along the parallel direction using a kinetic description. We have investigated the evolution and the internal density currents which provide insight of the effects of finite Larmor radius in the blobs dynamics and evolution.

La structuration à l’échelle submicronique de la surface des aciers inoxydables permet de leur apporter de nouvelles fonctionnalités, par exemple pour des applications tribologiques et optiques. Cette thèse s’inscrit dans le cadre du projet ANR SPOT qui a pour objectif de structurer à l’échelle submicronique la surface d’aciers austénitiques et martensitiques par gravure sèche. Dans ce travail, nous avons développé un procédé plasma avec un mélange de chlore et d’argon pour la gravure des aciers inoxydables. La mise au point de ce procédé a été réalisée en se basant sur l’étude de la gravure des métaux principaux qui composent ces aciers, à savoir, le fer, le chrome et le nickel. En se basant sur des mesures de vitesses de gravure, ainsi que sur des techniques de diagnostics plasmas, nous avons montré que, dans un plasma de chlore et d’argon, le fer est l’élément qui se grave le plus, suivi du chrome puis du nickel. Les échantillons métalliques ainsi que les aciers inoxydables gravés ont été analysés par des techniques de caractérisation de surface notamment des analyses de spectrométrie photoélectronique X (XPS). Nous avons également étudié la variation des vitesses de gravures de ces métaux et de ces aciers en fonction de la température des substrats. Ces études nous ont permis d’établir les mécanismes mis en jeu en cours de la gravure des éléments métalliques. Nous avons montré que, dans un plasma de chlore et d’argon, le fer se grave principalement par un mécanisme chimique qui suit une loi d’Arrhenius. Ce mécanisme serait basé sur la formation de chlorures de fer volatiles. Dans le cas du chrome, la gravure nécessite une assistance ionique afin de désorber les chlorures de chrome non volatiles formés à la surface du matériau. Enfin, pour le nickel, nous avons observé que la vitesse de gravure diminue lorsque la température augmente. Dans ce cas, des observations au microscope électronique à balayage ont permis de mettre en évidence la formation de gonflements riches en chlore. Les analyses XPS de la surface gravée du nickel suggère que ces gonflements sont dus à la formation de chlorures de nickel non volatiles. Ces chlorures seraient à l’origine de la diminution de la vitesse de gravure du nickel dont la pulvérisation se trouverait bloquée par la présence de ces chlorures. La compréhension de ces mécanismes a permis de conclure que, dans un plasma chloré, l’élément bloquant dans la gravure des aciers inoxydables est le nickel
The structuring at sub-micronic scale of the surface of stainless steels allows to provide them with new functionalities, for example for tribological and optical applications. This thesis is part of the ANR SPOT project which aims to structure the surface of austenitic and martensitic steels on a submicronic scale by dry etching. In this work, we have developed a plasma process with a mixture of chlorine and argon for the etching of stainless steels. The development of this process was carried out based on the study of the etching of the main metals that make up these steels, namely, iron, chromium and nickel. Based on measurements of etching speeds, as well as on plasma diagnostic techniques, we have shown that, in a chlorine and argon plasma, iron is the most etched element, followed by chromium, then nickel. The metallic and the stainless steels etched samples were analyzed by surface characterization techniques, in particular X photoelectron spectrometry (XPS) analyzes. We have also studied the variation of the etching speeds of these metals and steels as a function of the temperature of the substrates. These studies have enabled us to establish the mechanisms involved in the etching of metallic elements. We have shown that in a plasma of chlorine and argon, iron is mainly etched by a chemical mechanism which follows an Arrhenius law. This mechanism would be based on the formation of volatile iron chlorides. In the case of chromium, the etching requires ionic assistance in order to desorb the non-volatile chromium chlorides formed on the surface of the material. Finally, for nickel, we observed that the etching speed decreases when the temperature increases. In this case, observations with a scanning electron microscope made it possible to highlight the formation of swellings rich in chlorine. XPS analyzes of the etched surface of nickel suggest that these swellings are due to the formation of non-volatile nickel chlorides. These chlorides would be at the origin of the decrease in the rate of etching of nickel, the sputtering of which would be blocked by the presence of these chlorides. Understanding these mechanisms led to conclude that, in a chlorinated plasma, the blocking element in the etching of stainless steels is nickel

Cette thèse s’inscrit dans le contexte des travaux visant à réduire la durée d’impulsion des lasers XUV générés dans des plasmas au domaine femtoseconde. La bande spectrale très étroite du milieu amplificateur limite la durée minimum accessible (limite de Fourier). Le milieu amplificateur des lasers XUV sont des plasmas denses et chauds qui peuvent être créés aussi bien par décharge électrique rapide que par différents types de lasers de puissance. Il existe ainsi 4 types de sources lasers XUV distinctes dont les paramètres du plasma (densité, température) dans la zone de gain diffèrent. Or, les propriétés spectrales et temporelles du rayonnement émis sont fortement liées à ces paramètres. L’ensemble des 4 types de lasers XUV opèrent en mode d'amplification de l'émission spontanée (ASE) et 2 d'entre eux peuvent opérer en mode « injecté ». Cette technique consiste à injecter une impulsion harmonique d'ordre élevé femtoseconde, résonante avec la transition laser, à l'une des extrémités du plasma amplificateur. L'important désaccord entre la largeur spectrale du plasma et celle de l'harmonique ne permet pas de conserver la durée fs de cette dernière au cours de l'amplification. Les simulations (code Bloch-Maxwell COLAX) montrent que l'amplification est fortement non-linéaire dans ces systèmes, avec notamment l'apparition d’oscillations de Rabi. La génération d'oscillations de Rabi dans des lasers XUV en mode injecté est actuellement considérée comme un moyen prometteur de produire des lasers XUV fs, mais la manifestation de ces dernières n’a toutefois encore jamais été mise en évidence expérimentalement. Ainsi, une méticuleuse caractérisation expérimentale des propriétés spectrales des 4 types de lasers XUV en relation avec les conditions du plasma, associée à une meilleure compréhension des mécanismes d’amplification sous différentes conditions plasma basée sur des études théoriques et des simulations, sont nécessaires pour atteindre notre objectif. Une large campagne expérimentale visant à caractériser spectralement l'ensemble des différents types de lasers XUV a été menée par notre groupe sur la dernière décennie. La résolution spectrale nécessaire n'étant pas accessible avec les spectromètres actuels, la méthode employée consiste à mesurer la cohérence temporelle du laser XUV par autocorrélation du champ électrique à l'aide d'un interféromètre à division de front d'onde, spécifiquement conçu pour ces mesures, à partir desquelles la largeur spectrale peut être déduite. Le dernier type de laser XUV (PALS, Prague) a été caractérisé dans le cadre de cette thèse. Le temps de cohérence mesuré est de 0,68 ps, significativement inférieur aux valeurs mesurées sur les autres types de lasers XUV. L'analyse de l'ensemble des mesures a fait apparaître un comportement différent suivant que la durée d’impulsion est longue devant le temps de cohérence ou proche de celui-ci. Dans le premier cas les largeurs spectrales déduites sont en bon accord avec les calculs, dans le second l’accord est moins bon et la forme des traces d'autocorrélation n'était pas comprise. Ces observations ont motivé une étude détaillée de l'influence des propriétés temporelles de l'émission ASE des lasers XUV sur la méthode interférométrique employée pour caractériser leur largeur spectrale. Cette étude, basée sur un modèle emprunté aux lasers à électrons libres, a révélé un effet de la cohérence temporelle partielle sur les mesures d'autocorrélation en champ de ces sources. Elle ouvre des perspectives sur l'utilisation de notre méthode pour une mesure simultanée de la largeur spectrale et de la durée d'impulsion de la source. Enfin, une étude basée sur un modèle Bloch-Maxwell a été réalisée pour tenter de mieux comprendre les conditions d'apparition des oscillations de Rabi au cours de l'amplification de l'harmonique dans le plasma de laser XUV. Deux régimes d'amplification, adiabatique et dynamique, autour d'un seuil d'inversion de population ont été mis en évidence
The work of this thesis was made in the context of the efforts made to reduce the pulse duration of plasma-based XUV lasers down to the femtosecond domain. The very narrow spectral width of the amplifier medium (~ 1E10 - 1E11 Hz) limits the minimum achievable pulse duration (Fourier limit). The amplifier medium of XUV lasers pumped by collisional excitation are dense and hot plasmas that can be created both by rapid electrical discharge and by different types of power lasers. There are thus 4 distinct types of XUV laser sources with different plasma parameters (density, temperature) in the gain region. Yet, the spectral and temporal properties of the emitted radiation are strongly linked to these parameters. All 4types of XUV lasers operate in amplification of spontaneous emission (ASE) mode, and 2 of them, for a few years, can operate in "seeded" mode. This technique consists in injecting a femtosecond high order harmonic pulse (the seed), resonant with the lasing transition, at one extremity of the plasma amplifier. Because of the major mismatch between the spectral width of the plasma and that of the seed the femtosecond duration of the latter is not preserved during amplification. Simulations (COLAX Maxwell-Bloch code) show that the amplification is highly non-linear in such systems, including the appearance of Rabi oscillations. Generating Rabi oscillations in seeded XUV lasers is currently considered a promising way to produce femtosecond XUV lasers. However Rabi oscillations have yet never been experimentally demonstrated. Thus, a meticulous experimental characterization of the spectral properties of the 4 types of XUV lasers in connection with the plasma conditions, combined with a better understanding of amplification mechanisms under different theoretical plasma conditions based on studies and simulations are needed to reach our goal. A wide experimental campaign aiming to spectrally characterize all different types of XUV lasers was conducted by our group over the past decade. The required spectral resolution is not available with the best current spectrometers, so the method we used consists on the measurement of the temporal coherence of the XUV laser through an electric field autocorrelation, using a wave front-division interferometer that was specifically designed for these measures, from which the spectral width can be deduced. The latter type of the four XUV laser types (PALS, Prague) was characterized during this thesis, closing this experimental campaign. The measured coherence time was 0.68 ps, which is significantly lower than the coherence times measured on the other XUV laser types. Analysis of the overall results revealed two different behavior whether the XUV laser has a long pulse duration compared to its coherence time or if the two durations are close. In the first case the inferred spectral widths are in good agreement with theoretical predictions, while in the second case the agreement was not as good and the shape of the electric field autocorrelation traces was not understood. This observation has prompted a detailed study of the influence of temporal properties of ASE XUV lasers on the interferometric methodology used to determine the spectral width of XUV lasers. The study, based on a model developed for X-free electron lasers, revealed an effect of partial temporal coherence in electric field autocorrelation measures of these sources. This study offers perspectives on a simultaneous measure of the spectral width and the duration of theses sources with our method. Finally, a study based on Maxwell-Bloch equations was carried out in order to understand better the conditions of apparition of Rabi oscillations. This study highlighted two amplification regimes, adiabatic and dynamic, around a population inversion threshold

Il est reconnu que la structure des semi-conducteurs organiques influence la sensibilité et la sensitivité des capteurs des gaz. Pour améliorer la compréhension des mécanismes sous-jacents dans les capteurs à base des transistors d’effet de champ organique (OFETs) cette thèse a exploré trois pistes différentes : L’utilisation de l’hystérésis des caractéristiques de transfert comme paramètre de détection des gaz est étudié. En ajoutant l’hystérésis aux paramètres standards, on améliore la sélectivité des OFETs à base de poly(3-hexylthiophène) aux gaz polaires. Des mesures transitoires de courant indiquent que la cinétique de piégeage et de piégeage des porteurs de charges est à l’origine de cette amélioration. Pour comprendre l’influence qu’à la structure moléculaire sur la sensibilité aux vapeurs d’éthanol, des polymères avec des chaînes latérales alcoxyle dont on fait varier la polarité ainsi que l’encombrement stérique, ont été étudiés. L’intensité de la réponse est corrélée avec la quantité d’analyte absorbée et le moment dipolaire des chaînes latérales. Pour permettre l’étude des mécanismes à l’échelle nanométrique, une partie de ce travail se concentre sur la fabrication de transistors avec une taille de canal réduite. En utilisant le nitrure de silicium comme couche diélectrique, on réduite les tensions de commande et les propriétés chimiques à l’interface
The molecular structure of organic semiconductors which can be tailored by the chemical synthesis influences the sensitivity and selectivity of gas sensor devices. To improve the understanding of the ongoing mechanisms in sensors based on organic field effect transistors (OFETs) this thesis follows three different tracks: The applicability of the hysteresis of the transfer characteristics as a gas sensing parameter is studied. As a complement to the standard transistor parameters the hysteresis improves the selectivity of poly(3-hexylthiophen-2,5-diyl) based OFETs to polar gases. Transient current measurements indicate the additional dependence on the detrapping kinetics as origin of the increased selectivity. To understand the influence of the molecular structure on the gas sensing behavior, polymers with alkoxy side chains, varying in polarity and steric hindrance, are used as gas sensing layer for ethanol vapor. The response strength correlates with the amount of absorbed analyte and the dipole moment of the side chains. To enable investigations of the mechanisms at the nanoscale, one part of this work focuses on the preparation of transistors with a reduced channel length. By using silicon nitride as dielectric layer, driving voltages decreased and interface properties could be improved

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.
Includes bibliographical references (p. 48).
by Dexter FitzGeoffreys Beals.
M.S.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada
During certain hypersonic flight regimes, shock heating of air creates a plasma sheath resulting in telemetry attenuation or blackout. The severity of the signal attenuation is dependent on vehicle configuration, flight trajectory, and transmission frequency. This phenomenon is investigated with a focus placed on the nonequilibrium plasma sheath properties (electron concentration, plasma frequency, collision frequency, and temperature) for a range of flight conditions and vehicle design considerations. Trajectory and transmission frequency requirements for air-breathing hypersonic vehicle design are then addressed, with comparisons made to both shuttle orbiter and RAM-C II reentry flights.

Orientador: Konstantin Georgiev Kostov
Resumo: Nos últimos anos, tem intensificado o emprego de plasmas em pressão atmosférica para diferentes aplicações. Com o desenvolvimento dos jatos de plasma em pressão atmosférica, alguns tratamentos precisos, como no campo biomédico ou em específicos processamentos de superfícies, tornaram-se mais frequentes. No entanto, a aplicação de plasma à objetos irregulares, dentro de tubos ou mesmo dentro de órgãos ocos é limitada quando se utilizam configurações convencionais de jatos de plasma. Portanto, essas limitações podem ser superadas com o desenvolvimento de jatos de plasma alongados ou gerados remotamente. Neste trabalho, duas configurações de jato de plasma longo visando diferentes campos de aplicação foram aperfeiçoadas e caracterizadas. Inicialmente foi desenvolvido um jato de plasma endoscópico (plasma endoscope) operando em configuração de descarga por barreira dielétrica (DBD) com dimensões milimétricas, versátil ao acoplamento em endoscópios típicos. Este jato de plasma pode operar com hélio ou neônio e conta com um canal externo e concêntrico de gás que permite a introdução de uma cortina de gás eletronegativo ao redor da pluma de plasma. A cortina de proteção a gás preserva a forma do jato de plasma quando operado dentro de cavidades fechadas. As dificuldades advindas do desenvolvimento deste foram investigadas quando diferentes gases foram testados como cortina de proteção dele, dentre estes, o dióxido de carbono se mostrou uma boa opção evitando a formação de descargas ... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The use of atmospheric pressure plasmas for different purposes has increased in recent years. With the development of atmospheric pressure plasma jets, some precise treatments such as in the biomedical field or specific surface processing became more often. However, the delivery of plasma to irregular shaped objects, inside tubes or even hollow organs is limited with the use of conventional plasma jet configurations. Therefore, those limitations can be surpassed with the development of elongated or remotely generated plasma jets. In this work, two extended plasma jet configurations aiming at different application fields were further developed and characterized. Firstly, an endoscopic plasma jet (plasma endoscope) operating with a dielectric barrier discharge (DBD) configuration in millimeter dimensions that can be coupled to a typical endoscope was developed. This plasma jet can operate with helium or neon and counts with an external concentric shielding gas channel that provides the introduction of an electronegative gas curtain around the plasma plume. The shielding gas allows the preservation of the plasma jet shape when operated inside closed cavities. The construction difficulties arisen from the use of different feed and shielding gases were explored. Carbon dioxide was proven to be a good option for the curtain gas around the plasma plume avoiding the formation of parasitic discharges inside the shielding gas tube and the endoscopic housing. When operated with neon, th... (Complete abstract click electronic access below)
Doutor

In plasma assisted thin film growth, control over the energy and direction of the incoming species is desired. If the growth species are ionized this can be achieved by the use of a substrate bias or a magnetic field. Ions may be accelerated by an applied potential, whereas neutral particles may not. Thin films grown by ionized physical vapor deposition (I-PVD) have lately shown promising results regarding film structure and adhesion. High power impulse magnetron sputtering (HIPIMS) is a relatively newly developed technique, which relies on the creation of a dense plasma in front of the sputtering target to produce a large fraction of ions of the sputtered material. In HIPIMS, high power pulses with a length of ~100 μs are applied to a conventional planar magnetron. The highly energetic nature of the discharge, which involves power densities of several kW/cm2, creates a dense plasma in front of the target, which allows for a large fraction of the sputtered material to be ionized. The work presented in this thesis involves plasma analysis using electrostatic probes, optical emission spectroscopy (OES), magnetic probes, energy resolved mass spectrometry, and other fundamental observation techniques. These techniques used together are powerful plasma analysis tools, and used together give a good overview of the plasma properties is achieved. from the erosion zone of the magnetron. The peak plasma density during the active cycle of the discharge exceeds 1019 electrons/m3. The expanding plasma is reflected by the chamber wall back into the center part of the chamber, resulting in a second density peak several hundreds of μs after the pulse is turned off. Optical emission spectroscopy (OES) measurements of the plasma indicate that the degree of ionization of sputtered Ti is very high, over 90 % in the peak of the pulse. Even at relatively low applied target power (~200 W/cm2 peak power) the recorded spectrum is totally dominated by radiation from ions. The recorded HIPIMS spectra were compared to a spectrum taken from a DC magnetron discharge, showing a completely different appearance. Magnetic field measurements performed with a coil type probe show significant deformation in the magnetic field of the magnetrons during the pulse. Spatially resolved measurements show evidence of a dense azimuthally E×B drifting current. Circulating currents mainly flow within 2 away cm from the target surface in an early part of the pulse, to later diffuse axially into the chamber and decrease in intensity. We record peak current densities of the E×B drift to be of the order of 105 A/m2. A mass spectrometry (MS) study of the plasma reveals that the HIPIMS discharge contains a larger fraction of highly energetic ions as compared to the continuous DC discharge. Especially ions of the target material are more energetic. Time resolved studies show broad distributions of ion energies in the early stage of the discharge, which quickly narrows down after pulse switch-off. Ti ions with energies up to 100 eV are detected. The time average plasma contains mainly low energy Ar ions, but during the active phase of the discharge, the plasma is highly metallic. Shortly after pulse switch-on, the peak value of the Ti1+/Ar1+ ratio is over 2. The HIPIMS discharge also contains a significant amount of doubly charged ions.

Bulk hydroxyapatite- and bioactive glass-based ceramics are produced in this work by Spark Plasma Sintering (SPS). The main results are briefly summarized in what follows. Densification and crystallization phenomena taking place when an innovative CaO-rich bioactive glass (BG_Ca/Mix) and conventional 45S5 Bioglass® are processed by SPS. Fully dense and wholly amorphous BG_Ca/Mix products are obtained at 730 °C after 2min dwell time. Temperatures equal or higher than 830 °C are needed to induce crystallization of CaSiO3 in the parent glass. Conversely, Na6Ca3Si6O18 crystals are formed in sintered 45S5 samples produced after 2 min at 550°C, although the glassy character is preserved. Products from BG_Ca/Mix powders display higher hardness and local elastic modulus. SPS was also employed to produce highly dense and bioactive composites from different mixtures of hydroxyapatite (HA) and BG_Ca/Mix glass. The produced samples are significantly denser with respect to the counterparts obtained by conventional sintering. Thanks to the low tendency to crystallize of BG_Ca/Mix, it was possible to reduce the devitrification of the glassy phase in the samples, with beneficial effects in terms of the resulting in vitro bioactivity. Detailed in-vitro experiments concerning SaOS-2 human osteoblasts cultivated on the surface of dense samples obtained by SPS from three different HA powders are finally carried out. The composition and microstructures characterizing the sintered products significantly affect the biological response of the cells. In particular, mineralization phenomena are observed to occur only in samples exclusively made of HA, particularly where submicrometer sized grains are involved. Correspondingly, an apatite layer with a trabecular-like microstructure was formed on the scaffolds surface. In contrast, mineralization is suppressed, and so does the formation of the apatite phase, when cells were seeded on specimens composed of β-TCP.

Plasma railguns are electromagnetic accelerators used to produce controlled high velocity plasma jets. This thesis discusses the design and characterization of a small coaxial plasma railgun intended to accelerate argon-helium plasma jets. The railgun will be used for the study of plasma shocks in jet collisions. The railgun is mounted on a KF-40 vacuum port and operated using a 90 kA, 11 kV LC pulse forming network. Existing knowledge of coaxial railgun plasma instabilities and material interactions at vacuum and plasma interfaces are applied to the design. The design of individual gun components is detailed. Jet velocity and density are characterized by analyzing diagnostic data collected from a Rogowski coil, interferometer, and photodiode. Peak line-integrated electron number densities of approximately 8 × 10¹⁵ cm^-2 and jet velocities of tens of km/s are inferred from the data recorded from ten experimental pulses.
Master of Science
Plasma is a gaseous state of matter which is electrically conductive and interacts with electric and magnetic fields. Plasmas are used in many everyday objects such as fluorescent lights, but some of the physics of plasmas are still not entirely understood. One set of plasma interactions that have not been fully explored are those which occur during high-velocity collisions between plasmas. Experiments aimed to further the understanding of these interactions require the generation of plasmas with specified properties at very high velocities. A device known as a plasma railgun can be used to produce plasmas which meet these experimental demands. In a plasma railgun, a short pulse of current is passed through a plasma located between two parallel electrodes, or "rails". This current generates a magnetic field which propels the plasma forward. The plasma is accelerated until it leaves the muzzle of the railgun. In coaxial plasma railguns, the electrodes are concentric. This paper discusses the design and testing of a small, relatively low power coaxial plasma railgun. Specific elements of the design are examined and the inherent physical and material difficulties of a coaxial design are explored. The experiment which was performed to confirm the properties of the plasma jets produced by the coaxial plasma railgun is explained. The results of this experiment confirm that the design succeeds in producing plasmas which meet targets for plasma properties.

A modified Tegal MCR-1 plasma etch system has been electrically characterized, and the plasma impedance has been measured at 13.56MHz. Important aspects of radio-frequency (RF) impedance measurements are addressed as they pertain to the measurement of the plasma impedance. These include: transmission line effects, magnitude and phase errors of the measurement probes, and the intrinsic impedance of the empty plasma chamber. Plasma harmonics are discussed, and a technique for measuring the plasma impedance at harmonic frequencies is presented. Transients in the plasma impedance are observed during the first 5 minutes after the plasma is initiated, and represent a decrease in the plasma impedance. Residual gas analysis (RGA) confirms the presence of H₂O in the plasma. The H₂O ion current measured by RGA shows a downward transient similar to the impedance transients, suggesting a possible relationship between H₂O and the impedance transients. A possible explanation for these impedance transients is presented.

Les thérapies anticancéreuses basées sur des principes physiques (radiofréquences, ultrasons, laser, électroporation...) ont considérablement augmenté lors de la dernière décennie. Leurs objectifs sont de détruire directement les cellules cancéreuses, de favoriser l'entrée ciblée de molécules thérapeutiques ou encore de stimuler le système immunitaire du patient afin d'éliminer la tumeur. Le plasma froid suscite l'intérêt dans le domaine de l'oncologie grâce à sa capacité à générer des espèces réactives oxygénées (ROS) et azotées (RNS) qui peuvent être génotoxiques et cytotoxiques pour les cellules cancéreuses. Deux approches d'utilisation du plasma sont étudiées : soit l'exposition directe de cellules au jet plasma, soit l'exposition indirecte via l'utilisation d'un Milieu Activé par Plasma (PAM). Le PAM étant plus facile à délivrer par injection dans la tumeur, c'est cette approche qui est choisie lors de ces travaux. Le travail de thèse présenté consiste à étudier l'effet génotoxique et cytotoxique du PAM, obtenu après exposition du milieu au jet de plasma d'hélium, sur des tumeurs in vitro et in vivo. Pour les études in vitro, nous avons choisi d'utiliser un modèle 3D : le sphéroïde (MCTS - MultiCellular Tumor Spheroid). Ce modèle présente des caractéristiques proches du modèle in vivo grâce à son organisation en sphéroïde. Les MCTS présentent en effet des gradients de pénétration d'oxygène, de nutriments et de prolifération cellulaire. La première partie de la thèse concerne l'identification et la quantification des espèces générées dans le PAM. Les méthodes d'analyses utilisées sont la résonance paramagnétique électronique, la fluorimétrie, la colorimétrie, la chromatographie en phase liquide et la spectrométrie de masse. Ces analyses ont mis en évidence que la toxicité du PAM était due à plusieurs facteurs : d'un côté la génération de ROS et RNS mais aussi à la dégradation des nutriments pour les cellules contenues dans le milieu via par exemple l'oxydation et la nitrosylation des acides aminés. La deuxième partie est dédiée à l'étude des effets du PAM sur les MCTS HCT-116 (cancer du côlon).[...]
Cancer therapies based on physical principles (radiofrequency, ultrasound, laser, electroporation...) have considerably increased in the last decade. Their objectives are to directly destroy cancer cells, to favor the targeted entry of therapeutic molecules or to stimulate the patient's immune system in order to eliminate the tumor. Cold plasma still arouses interest in the field of oncology through its ability to generate reactive oxygen species (ROS) and nitrogen species (RNS) which can be genotoxic and cytotoxic for cancer cells. Two approaches to the use of plasma are studied: either direct exposure of cells to the plasma jet, or indirect exposure via the use of a Plasma Activated Medium (PAM). The PAM being easier to deliver by injection into the tumor, this approach was chosen in this work. The work presented consists in studying the genotoxic and cytotoxic effects of PAM resulting from exposure of the medium to the helium plasma jet on in vitro and in vivo tumors. For in vitro studies, we chose to use a 3D model: the spheroid (MCTS - MultiCellular Tumor Spheroid). This model has similar characteristics to the in vivo model thanks to its spheroidal organization. The spheroids have indeed gradients of oxygen penetration, nutrients and cell proliferation. The first part of the thesis concerns the identification and quantification of the species generated in PAM. The analytical methods used are paramagnetic electronic resonance, fluorimetry, colorimetry, liquid chromatography and mass spectrometry. These analyses revealed that the toxicity of PAM was due to several factors: on the one hand to the generation of ROS and RNS and on the other hand to the degradation of cell nutrients contained in the medium via, for example, the oxidation and nitrosylation of the amino acids. The second part is dedicated to the study of the effects of PAM on HCT-116 (colon cancer) spheroids[...]

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Dr. Dennis W. Hess; Committee Member: Dr. Clifford L. Henderson; Committee Member: Dr. J. Carson Meredith; Committee Member: Dr. L. Andrew Lyon; Committee Member: Dr. Mark R. Prausnitz. Part of the SMARTech Electronic Thesis and Dissertation Collection.

ABSTRACT PLASMA SURFACE MODIFICATION AND CHARACTERIZATION OF PMMA FILMS Ö
zgen, Ö
zge M.Sc., Department of Polymer Science and Technology Supervisor: Prof. Dr. Nesrin Hasirci Co-supervisor: Prof. Dr. Vasif Hasirci December 2011, 114 pages Surface properties play an essential role for determining the behavior of a material for many applications such as coating, printing, adhesion and prosthesis implanting since the surface is the first part that comes in contact with the environment. Although the bulk properties of some materials are at the desired level, the surface may need to be modified for a better compatibility with its surrounding. Plasma treatment is one generally preferred technique because of its high potential to create various functional groups on the surface of the sample by changing the applied plasma parameters. Some molecules can be successfully immobilized onto these surfaces using these specific chemical functional groups created by plasma. The type of the functional group is important for intended purpose of covalent binding of different molecules on the surface of a material. Present study offers important routes for optimization of the surface functionality of (PMMA) films by changing the plasma parameters. For this purpose, solvent casted polymethylmetacrylate PMMA films were modified by, nitrogen, argon and oxygen plasma by using a radiofrequency (RF) generator
and with various powers (10W, 50W, 100W) for different periods (5min, 15min and 30min). The effects of these plasma parameters (gas type, applied power, plasma time) on hydrophilicity, surface free energy, surface chemistry, and surface topography were investigated. Also, the types of surface free radicals created with oxygen plasma treatment were analysed and the decay of these radicals were examined by Electron Spin Resonance Spectroscopy (ESR). In general, plasma treatment reduced the contact angle of PMMA films where the most hydrophilic surface was obtained for 100W 30 min argon plasma treated sample showing superhydrophilic character with the water contact angle value of ~10°
. Surface free energy measurements were carried out according to Geometric Mean, Harmonic Mean, Acid-Base approach and it was found that oxygen, nitrogen and argon plasma treatments increased the surface free energy for all samples by increasing the polar components and introducing functional groups on the surface. X-Ray Photoelectron Spectroscopy (XPS) analysis results revealed that free carbonyl and carbonate groups were formed by oxygen plasma treatment, whereas carboxylic acid and free carbonyl groups were formed after argon plasma treatment, and imine, primary amine, amide and nitrozo groups were formed by nitrogen plasma. Atomic Force Microscopy (AFM) analysis revealed that the roughness of the surface increased considerably from ~2 nm to ~75 nm for the 100W 30 min oxygen plasma treated samples. ESR analysis indicated the presence of peroxy radicals on the surface of the oxygen plasma treated PMMA and the intensity of these radicals increased with increasing plasma power. Decay study of the newly created radicals demonstrated that after 1 month under the atmospheric conditions there were still peroxy radicals on the surface of PMMA. This functionality is important in leading time for further process for binding of different molecules to the surface of the materials for specific purposes. As a result, RF plasma was found to be an effective tool for modification of surface properties of materials with product diversity for intended purposes.

This dissertation focuses on the microstructural and analytical characterization of plasma dissociated zircon (PDZ) which was produced by the South African Nuclear Energy Corporation (NECSA). The techniques used in the analysis of the material include scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy and wavelength dispersive X-ray spectrometry (EDS and WDS), infrared spectroscopy, Raman spectroscopy and X-ray diffraction (XRD). The differences in morphology of the zirconia (ZrO2) crystals observed in the PDZ are related to the thermal history of the material. Large zirconia crystals grow in a spherulitic manner and have the monoclinic crystal structure. Some smaller crystals formed via a rapid cooling process appear to retain the tetragonal or cubic crystal structures rather than relaxing to the monoclinic structure, and this may be because such nanocrystals are stabilised by small surface area or constraints from surrounding materials. Impurity distribution analysis of the PDZ showed that majority of the impurities present in zircon segregates to the silica phase during the dissociation process. The infrared and Raman spectroscopy analysis of the PDZ material indicated that the zirconia is present in the monoclinic and tetragonal polymorphs. X-ray diffraction revealed the presence of monoclinic, tetragonal and cubic zirconia phases. Rietveld refinement of the XRD patterns revealed zirconia to be predominantly found in the monoclinic polymorph followed by the tetragonal and cubic polymorphs. A Fourier transform infrared (FTIR) spectrometer equipped with an attenuated total reflectance (ATR) cell proved to be a viable method for determining the percentage dissociated zircon in PDZ.

The discovery of unique properties of graphene has led to the development of graphene for a variety of applications like integrated circuits, organic electronic devices, supercapacitors, sensors, and composite materials. Fluorination of graphene enables control of its physical, chemical, and electronic properties. Our initial studies demonstrated the viability of sulfur hexafluoride plasmas to fluorinate epitaxial graphene as a safer alternative to the commonly reported techniques of fluorination that include exposures to fluorine and xenon difluoride gas. Formation of carbon-fluorine bonds after SF6 plasma-treatment was confirmed by x-ray photoelectron spectroscopy. Raman spectroscopy and low-energy electron diffraction studies suggest that the framework of sp2-hybridized carbon atoms remains intact after the plasma-treatment. Increase in work function after the fluorination was determined by ultra-violet photoelectron spectroscopy. The findings of our subsequent investigation to controllably modify the work function of epitaxial graphene via plasma-fluorination indicate that the work function of fluorinated epitaxial graphene is controlled by the polarity of carbon-fluorine bonds. Further studies to investigate the effect of the surface topography of epitaxial graphene on the work function of plasma-fluorinated epitaxial graphene were performed using scanning Kelvin probe microscopy (SKPM). The results of SKPM characterization of plasma-fluorinated epitaxial graphene demonstrated that the increase in the work function of epitaxial graphene after plasma-treatment is independent of its surface topography, but non-uniform fluorination may result from non-uniformities in plasma density.