Advantages of laser absorption measurements

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Table of contents

I. Introduction
I.1 Plasma-surface interactions: historical overview
I.2 Context of the study
I.3 Organization of the thesis
1. Chapter I: Surface reactivity in N2/O2 plasmas
1.1 Interaction of radicals with surfaces: basic concepts
1.1.1 Adsorption
1.1.1.1 Physisorption
1.1.1.2 Chemisorption
1.1.2 Mechanisms of surface reactions
1.1.3 Surface reactions: thermodynamic viewpoint
1.2 Modelling of surface reactivity in plasmas
1.3 Mesoscopic modelling of atomic recombination on surfaces
1.3.1 Surface kinetics in N2/O2 mixtures
1.3.2 Role of plasma exposure
1.4 Surface reactions in N2/O2 plasmas: review of experimental studies
1.4.1 Recombination of O and N atoms on surfaces
1.4.2 Molecule production/conversion on surfaces
1.5 Research questions
1.6 Research strategy
1.7 Definitions and notations
2. Chapter II: Experimental setup and diagnostic techniques
2.1 Discharge setup
2.1.1 Reactor and gas system
2.1.2 Pulsed discharge systems
2.1.2.1 Direct current glow discharge
2.1.2.2 Radiofrequency capacitive discharge
2.2 Diagnostics employed
2.2.1 Tuneable diode laser absorption spectroscopy in mid-infrared range
2.2.1.1 Principles of laser absorption spectroscopy
2.2.1.2 Advantages of laser absorption measurements
2.2.1.3 Pitfalls of laser absorption measurements
2.2.1.4 Diode laser spectrometer
2.2.1.5 Three-channel quantum cascade laser spectrometer
2.2.2 Time resolved emission and absorption spectroscopy in UV-Vis range.
2.2.2.1 Optical emission spectroscopy for gas temperature determination
2.2.2.2 OES setup and data treatment.
2.2.2.3 Time resolved measurements of ozone concentration
2.2.3 TALIF measurements of atomic oxygen.
2.2.3.1 Principles and calibration of O TALIF measurements.
2.2.3.2 Laser setup
2.2.4 Mass spectrometric gas analysis
2.2.5 XPS surface diagnostics
2.2.6 Summary on used diagnostics
3. Chapter III: Adsorption and reactivity of N atoms on silica surface under plasma exposure
3.1 Introduction
3.1.1 Experimental procedures
3.2 Determination of the coverage of Nads: XPS study
3.2.1 Dynamics of N adsorption on SiO2
3.2.2 Species responsible for nitridation: ions or neutrals?
3.2.3 Reactivity of SiOxNy under plasma exposure
3.2.4 Conclusions on XPS study
3.3 Reactivity of Nads: Isotopic study
3.3.1 Experimental details
3.3.2 Characterization of the discharge: measurements of N2 dissociation degree
3.3.2.1 Dissociation of N2 in pulsed dc discharge
3.3.2.2 Dissociation in pulsed rf discharge
3.3.2.3 Estimation of atomic nitrogen exposure on the surface
3.3.3 14N adsorption on SiO2 under 28N2 plasma exposure
3.3.4 Reactivity of grafted 14N atoms under 30N2 plasma exposure
3.3.4.1 Evidence for a distribution of reactivity of Nads
3.3.4.2 Do Nads participate in surface recombination of N atoms?
3.3.5 Conclusions on the isotopic study
3.4 Recombination of Nads with O atoms
3.4.1 Experimental details
3.4.2 Kinetics of NO production on the surface
3.4.2.1 Proof of recombination mechanism Nads + O → NO
3.4.2.2 Kinetics of NOx in the probe discharge
3.4.2.3 Estimation of the coverage of Nads that produce NO
3.4.2.4 NO production on the surface under continuous O2 plasma exposure
3.4.3 Investigation of adsorption and reactivity of N using measurements of NO production on the surface
3.4.3.1 Kinetics of adsorption
3.4.3.2 Are Nads * active for recombination of N on the surface?
3.5 Discussion and conclusions
3.5.1 Summary and conclusions on used diagnostics
4. Chapter IV: Adsorption and reactivity of oxygen atoms on oxide surfaces under plasma exposure
4.1 Introduction
4.1.1 Experimental procedures
4.2 Chemisorption of O on silica-like surfaces: isotopic study
4.2.1 Experimental details
4.2.2 Do O atoms of the material participate in surface reactivity?
4.2.3 16O adsorption on the surface under 32O2 plasma exposure
4.2.4 Conclusions on the isotopic study
4.3 Adsorption of atomic oxygen on Pyrex and related reactivity towards NO
4.3.1 Experimental details
4.3.2 Evidence of NO oxidation by adsorbed O atoms
4.3.3 Determination of the surface coverage of adsorbed O atoms
4.3.4 Evidence of a distribution of reactivity adsorbed O atoms
4.3.5 Conclusions on the study of Oads reactivity on Pyrex
4.4 On the role of Oads for VOC oxidation
4.4.1 Context of the study: influence of the chemical nature of the surface on the reactivity of Oads
4.4.2 C2H2 oxidation by adsorbed oxygen atoms on TiO2
4.4.2.1 Experimental details
4.4.2.2 Kinetics of C2H2 destruction on pretreated TiO2 surface
4.4.2.3 Oxidation of adsorbed reaction intermediates
4.4.3 Discussion and conclusions on the study of Oads reactivity on TiO2
4.5 Investigation of ozone formation on surfaces
4.5.1 Experimental details
4.5.2 Ozone production in bare silica tube
4.5.3 Ozone production in the presence of high specific surface material
4.5.3.1 Influence of gas pressure and surface pretreatment
4.5.4 Modelling of ozone production in bare silica tube
4.5.5 Conclusions on the ozone production study
4.6 Conclusions
5. Chapter V: Study of surface vibrational relaxation of N2
5.1 Introduction
5.2 Kinetics of vibrationally excited nitrogen
5.2.1 Role played by N2(v) in nitrogen containing plasmas
5.2.2 Electron impact excitation/de-excitation of N2(v)
5.2.3 Vibrational relaxation of N2(v) in the gas phase
5.2.4 Vibrational relaxation on surfaces: motivation of the study
5.3 Study of N2(v) relaxation using infrared titration
5.3.1 Principles of the infrared titration technique
5.3.2 Experimental procedure
5.3.3 Validity of the diagnostics
5.3.3.1 Gas temperature and its influence on the relaxation measurements
5.3.3.2 Dissociation and re-association of titrating molecules
5.3.3.3 Vibrational excitation of titrating molecules
5.4 Modeling of vibrational kinetics in N2-CO2
5.4.1 Relevant relaxation processes
5.4.2 Model description
5.4.2.1 Gas phase processes
5.4.2.2 Heterogeneous processes
5.4.2.3 Numerical solution
5.4.3 Validation of the model
5.4.4 On the possibility of experimental determination of N2 dependence on v
5.4.5 Modeling results in N2 – CO2 mixtures
5.4.6 Determination of N2 for silica. The influence of CO2 admixture
5.4.7 Conclusions on the study of the N2 – CO2 system
5.4.8 Data analysis using characteristic relaxation times
5.5 Application of the IR titration for  determination on catalytic and plasmapretreated surfaces
5.5.1 The effect of plasma pretreatment
5.5.2 Vibrational relaxation on TiO2.
5.5.3 Vibrational relaxation on other catalytic surfaces
5.5.4 Vibrational relaxation on silica surface in air plasma.
5.6 Infrared titration as a plasma diagnostics tool: determination of the vibrational temperature of N2
5.6.1 Formulation of the method and its application to the N2 – CO2 system
5.6.2 On the vibrational temperature measurements in N2 – N2O and N2 – CO
5.7 Conclusions
6. Chapter VI: General conclusions and outlook
6.1 General conclusions
6.2 Summary of the main results
6.3 Implication for modelling of surface recombination
6.4 Future work
6.5 New diagnostic techniques
7. References