Nonthermal Plasmas for Materials Processing

Jörg Florian Friedrich is a chemist at the Technical University of Berlin. He has worked in the fields of plasma chemistry, polymer chemistry, and polymer and surface analytics since 1972 and has published several books on these topics. His special interest is the clarification and explanation of chemistry in plasma and at the surface of polymers.Jürgen Meichsner is a physicist at the University of Greifswald. He has worked in the field of low-temperature plasma physics and plasma surface interaction, e.g., plasma polymerization and polymer surface modification/functionalization since 1977. He has published numerous articles in peer-reviewed journals and a few book contributions. His special interest is the diagnostics of molecular low-temperature plasmas and the analysis of thin organic films and surfaces.

• Preface xiii1 Introduction 1References 152 Basic Principles of the Plasma State of Matter 172.1 Characteristics and Physical Properties of Plasmas 172.1.1 Ionization Degree, Energy Content and Classification 172.1.2 Quasi-Neutrality, Debye Shielding Length, Plasma Frequency 192.1.3 Ambipolar Diffusion 242.1.4 High-Frequency Conductivity and Permittivity of Non-Thermal Plasmas 262.1.5 Charged Particles in External Magnetic Field 302.1.6 Thermal and Non-Thermal Plasmas 342.1.7 Plasma Kinetics and Transport Equations 40References 562.2 Elementary Processes and Collision Cross Section 572.2.1 Classification of Collision Processes in Non-Thermal Plasmas 572.2.2 The Collision Cross Section 64References 772.3 Interaction of Non-Thermal Plasmas with Condensed Matter 792.3.1 Stationary Plasma Boundary Sheath and Bohm Criterion 802.3.2 Plasma Boundary Sheath in Front of the Floating Surface 832.3.3 Generalized Bohm Sheath Criterion 842.3.4 High-Voltage Plasma Sheath 842.3.5 Non-Stationary Plasma Sheaths 88References 932.4 Non-Thermal Plasmas of Electric Gas Discharges 942.4.1 Overview 942.4.2 The Electric Breakdown in Gases 952.4.3 The Glow Discharge 1012.4.4 Glow Discharges at Harmonic Electric Fields, RF and MW Plasmas 1092.4.5 High-Voltage Breakdown at Atmospheric Pressure, Corona and Barrier Discharge 115References 1183 Plasma Diagnostics 1193.1 Introduction 1193.2 Overview of Diagnostic Methods Used for the Characterization of Non-Thermal Plasmas 1193.3 Analysis of Charged and Neutral Plasma Particles in Non-Thermal Plasmas 1193.3.1 Electric Probe Measurements 1193.3.2 Special Case for Single Electric Probe Measurements in Radio-Frequency (RF) Plasmas 1333.4 Microwave Interferometry 1363.4.1 Microwave Propagation in Non-Magnetic Plasmas 1363.4.2 Heterodyne Microwave Interferometry at 160 GHz 1383.4.3 Electron Density Analysis in CCP and ICP with Argon and Oxygen as Processing Gas 1403.5 Mass Spectrometry 1433.5.1 Principle of Mass Spectrometry 1433.5.2 Quadrupole Mass Spectrometry 1433.5.3 Analysis of Low-Pressure Plasmas by Quadrupole Mass Spectrometry 145References 1553.6 Plasma and Laser-Induced Optical Emission Spectroscopy 1573.6.1 Spectral Analysis of Plasma Emission (VUV, UV-vis-NIR) 1573.6.1.1 Optical Emission Spectroscopy (OES) of Low-Pressure Plasmas – Examples 1593.6.1.2 Determination of the Rotation Temperature from Atmospheric O2 A Band, PP and PQ Branch 1613.6.1.3 Determination of Ground State Particle Density from Plasma Emission Spectrum 1643.6.1.4 Abel Inversion 1653.6.1.5 Phase Resolved Optical Emission Spectroscopy (PROES) of RF Plasmas 1663.6.2 Laser-Induced Fluorescence (LIF) Spectroscopy 1693.7 IR Broadband and IR Laser Absorption Spectroscopy 1723.7.1 Fourier Transform Infrared (FTIR) Spectroscopy for Gas Phase Analysis 1723.7.1.1 Principle of FTIR Spectroscopy 1723.7.1.2 FTIR Gas Phase Spectroscopy of RF Plasma with Precursor Ethylenediamine and Argon 1783.7.2 Infrared Tunable Diode Laser Absorption Spectroscopy (IR-TDLAS) 1803.7.2.1 Configuration of the IR-TDLAS Experiment 1803.7.2.2 Principle Procedure for Measuring Single Absorption Lines 1813.7.2.3 IR-TDLAS of Fluorocarbon Radicals and Reaction Products in CF4 or CF4+H2 RF Plasmas 183References 1854 Methods of Polymer and Polymer Surface Analysis 1874.1 Introductory Remarks 1874.2 Photoelectron Spectroscopy (XPS) or Electron Spectroscopy for Chemical Analysis (ESCA) 1884.3 Secondary Ion Mass Spectrometry 1934.4 NEXAFS – Use of Synchrotron Radiation 1944.5 Infrared Reflection Absorption Spectroscopy (IRRAS) 1954.6 Size-Exclusion Chromatography (SEC)/Gel Permeation Chromatography (GPC) and Field-Flow-Fractionation (FFF) 1964.7 Matrix-Assisted Laser/Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-ToF-MS) 1974.8 Electrospray Ionization Time-of-Flight Mass Spectrometry (ESI-ToF-MS) 1994.9 Overview of Methods 200References 2025 Chemical Interactions Between Polymer and Plasma 2035.1 Introduction 2035.2 General Conflict Between High Plasma Energies and Low Dissociation Energies of Bonds in Polymers 2035.3 Chemical Bonds and Functional Groups in Polymers 2065.4 Response of Different Types of Polymers to Plasma Exposure 208References 2146 Polymer Surface Functionalization 2176.1 Important Properties of Polymers 2176.2 Why Pretreatment? 2176.3 Chemical and Structural Problems of Polymers Provoked by Plasma Pretreatment 2206.4 Inevitability of Simultaneous Functionalization and Polymer Degradation 2216.5 Physical and Chemical Attacks of the Plasma to Polyolefin Surfaces 2236.6 Chemical Grafting onto Plasma-Exposed Polymer Surfaces 2246.7 Oxidation of Polymers by Exposure to the Oxygen Low-Pressure Plasma 2256.7.1 Introduction of O-Functional Groups Onto Polymer Surfaces 2256.7.2 Nature of Oxygen-Plasma Introduced Functional Groups 2266.7.3 Identification of O-Functional Groups Bonded Onto the Topmost Polymer Surface Layer 2266.7.4 Fit Strategy of O-Functional Groups as Introduced by D. T. Clark 2326.7.5 Other Surface-Sensitive Analytical Methods 2336.7.6 Derivatization of O-Functional Groups 2346.7.7 Identification of Radicals by Chemical Labeling or ESR Spectroscopy 2366.7.8 Physical Characterization of Oxygen Plasma 2376.7.9 Use of Plasma Afterglow for Polymer Modification 2386.7.10 Surface Oxidation and Etching (see also the special section on etching) 2396.7.11 Changes in Supermolecular Structure in Subsurface Layers Upon Exposure to Oxygen Plasma 2406.7.12 Changes in Polymer Structure Generated by Exposure to the Vacuum UV Radiation of the Oxygen Plasma 2456.7.13 Depth of Modification 2486.7.14 Accelerated Artificial Aging of Polymers by Exposure to Low-Pressure Oxygen Plasma 2516.7.15 Kinetics of Crosslinking 2536.7.16 Time-Dependence of Oxygen Introduction 2576.7.17 Reaction Details of Poly(ethylene terephthalate) Upon Exposure to Oxygen Plasma 2646.7.18 Optimum Time of Exposure to Oxygen Plasma for Formation of O-Functional Groups and Preventive Avoidance of Structural Degradation and Decomposition 2696.7.19 Dependence of Oxygen Introduction on Plasma Parameters 2726.7.20 Behavior of Molecular Orientation and Chain Structure Upon Exposure to Oxygen Plasma 272References 2797 Sensitivity of Polymer Units and Functional Groups Towards Exposure to Oxygen Plasma 2917.1 Introductory Remarks 2917.2 Behavior of Polymer Structure Upon Exposure to Oxygen Plasma 2917.3 Etching Behavior of Polymers Upon Exposure to Oxygen Plasma 2947.4 Classification of Polymers with Similar Degradation Behavior on Exposure to Oxygen Plasma 2997.5 Stability of Surface Functionalization and Superposition with Post-Plasma Effects upon Exposure to Air 3027.6 Surface Oxidation of Polyolefins Using Atmospheric-Pressure Plasmas (DBD, APGD or Corona Discharge, Spark Jet, etc.) 3087.6.1 Dielectric Barrier Discharge 3087.6.2 Plasma-Assisted and Plasma-Less Spraying of Intact High-Molecular-Weight Polymers at Atmospheric Pressure 3147.7 Oxidation of Carbon Nanomaterials 3207.7.1 Graphene 3207.7.2 Oxidation of Carbon Fibers 3217.8 Generation of Monosort O-Functional Groups at Polyolefin Surfaces as Anchor Points for Grafting of Molecules 3237.8.1 OH Groups 3237.8.2 COOH Groups 3327.8.3 CHO Groups 3337.8.4 Super-Acidic Groups via Oxyfluorination 3347.8.5 Functionalization of Fluorine-Containing Polymers with O-Functional Groups 3377.9 Post-Plasma Chemical Grafting of Molecules, Oligomers or Polymers Onto OH-Groups 3397.10 Course of Oxidation from Virgin Polymer to Oxidized Polymer and Finally to CO2 3427.10.1 Problems of Depth Profiling of Oxidation at Polymer Surface 3427.10.2 Binding Energies of Covalent Bonds in Polyolefins 3437.10.3 Analogy Between Thermal Oxidation and Auto-Oxidation of Paraffins 3447.10.4 Decarboxylation and Emission of CO2 3457.10.5 Formation of Gaseous Low-Molecular-Weight Etch Products by Oxygen Plasma Treatment 3457.10.6 Introduction of Oxygen-Containing Groups at Surface of Polyolefins as a Forerunner of Gasification/Etching 3477.10.7 Formation and Characterization of Low-Molecular-Weight Oxidized Material (LMWOM) 3507.10.8 LMWOM Formation by Re-Deposition of Etched Fragments 3517.10.9 Depth Profiling of O/C from Surface to Bulk 3527.10.9.1 Angle-Resolved XPS 3537.10.9.2 Dynamic SIMS 3547.10.9.3 Sputtering 3547.10.9.4 Post-Plasma Oxidation 3547.10.10 Tentative Mechanism 355References 3598 Ammonia and Bromine Plasmas 3718.1 Generation of Monosort NH2 Groups 3718.1.1 Brief History of Plasma-Induced Introduction of Primary Amino Groups Into the Surface of Polyolefins 3718.1.2 Ways to Produce Amino Groups at Polymer Surfaces 3728.1.3 Ammonia, Nitrogen-Hydrogen and Hydrazine Plasmas 3738.1.4 Carbon Fibers Exposed to Ammonia Plasma 3768.1.5 Oxygen Post-Plasma Introduction After Ammonia Plasma Exposure 3808.1.6 Invalidity of Le Chatelier’s Principle in Low-Pressure Plasma 3818.1.7 Time Dependence of N and NH2 Introduction on Exposure of the Ammonia Plasma into Polyolefin Surfaces 3838.1.8 Hydrogenation Effect of NH3 Plasma 3858.1.9 Modification of Polyolefin Within a 2μm-Deep Surface Layer 3868.1.10 Bulk Analysis by NMR 3898.1.11 Summary of All Attempts to Increase the Yield in NH2 Groups 3918.1.12 Ammonia Plasma – Undesired Side and Post-Plasma Reactions 3928.1.13 Deposition of Plasma Polymers Carrying Amino Groups as an Alternative to Ammonia Plasma Treatment 3938.1.14 Chemical Labeling and Protection of NH2 Groups 3948.1.15 Post-Plasma Chemical Grafting Onto NH2-Groups 3968.1.16 Amino Groups at Polymer Surfaces – A Summary 3998.2 Bromine Plasma 3998.2.1 Chemical Aspects 3998.2.2 Theoretical Considerations of the Plasma Process Using Bromine 4048.2.3 Comparison of Halogen Chemistry 4068.2.4 Behavior of Plasma-Brominated Surface Layers in Solvents 4088.2.5 Plasma Polymerization of Vinyl and Allyl Bromide 4108.2.6 Attempts to Increase Br Concentration in the Plasma Polymer Layers by Admixture of Br2 to Allyl Bromide or Bromoform 4128.2.7 Dependence of Bromine Introduction Onto Polyolefin Surfaces on Plasma Parameters 4128.2.8 Electron Temperature in the Bromoform Plasma 4158.2.9 Yields in Introduction of Other Halogens 4158.2.10 Plasma Bromination of Other Polymers 4178.2.11 Chemical Post-Plasma Synthesis of New Monosort Functional Groups by Conversion of Plasma-Introduced Bromine Groups 4188.2.12 Grafting of Molecules onto Br Groups by Nucleophilic Substitution 4198.2.13 Grafting Density at Polyolefin Surfaces 4228.2.14 Comparison of Surface Bromination of Polyolefins with Other Processes 4268.2.15 Plasma Bromination of Graphitic and Carbon Surfaces 4278.2.16 Efficiency in Bromination and Grafting of Carbon in Comparison to Polyolefins 4418.2.17 Conclusions to Plasma Bromination 445References 4469 Noble Gas Plasmas 4579.1 Characterization of Noble Gas Plasmas 4579.2 Polymer Crosslinking Caused by Noble Gas Plasmas 4589.3 Vacuum-Ultra Violet Radiation Emitted by Noble Gas Plasmas 460References 46410 Plasma Polymerization 46710.1 Introduction 46710.2 Milestones in History 47010.3 General Features of Plasma Polymers 47310.4 Mechanisms of Plasma Polymerization 47510.4.1 Absence of Often Proposed Plasma-Induced Radical Chain-Growth Polymerization to Linear Macromolecules? 47710.4.2 Radical Polymerization of Allyl Monomers 48010.4.3 Ion-Molecule Reactions 48210.4.4 Role of Polymerizing Intermediates 48310.4.5 Crosslinking 48310.4.6 Polymerization in Continuous-Wave Plasma 48610.4.7 Pulsed Plasma Polymerization 49110.4.8 Pressure- and Plasma-Pulsed Discharge 50010.5 Special Aspects of Plasma Polymerization 50610.5.1 Fragmentation-(poly)Recombination 50610.5.2 Atomic Polymerization 50610.5.3 Rearrangement and Crosslinking of the Already Deposited Plasma Polymer Layer by Plasma Particle Bombardment and Vacuum-UV Irradiation 50710.5.4 Formation of Unsaturations 50810.5.5 Formation of CH3 Groups 51010.5.6 H/C Ratio in Plasma Polymers and “Quasi-Hydrogen-Plasma” 51110.5.7 Hydrogen Exchange Between Plasma and Polymer Deposit 51610.5.8 Existence of Crystalline and Supermolecular Structures in Plasma Polymers 51710.5.9 Influence of Monomer or Precursor Type 51810.5.10 Role of Pressure and Flow Rate 51810.5.11 Role of Energy Dose 52010.5.12 Plasma Polymerization of n-Hexane and Other Hydrocarbons 52010.5.13 Dependence of Deposition Rate on Position of Sample in the Plasma Zone 52410.5.14 Retention of Monomer Structure in Plasma Polymer –Changes in Aromaticity and Substitution 52510.5.15 Molecular Weight Distribution 52710.5.16 Energetic Balancing 52910.6 Locus of Plasma Polymerization 53010.6.1 Adsorption or Gas Phase? 53010.6.2 Powder Formation 53110.6.3 Redeposition of Etched Products as Layer 53210.6.4 Special Effects of Irradiation of Growing Polymer Layer by Vacuum-UV Radiation from Plasma 53310.6.5 Formation of a “Polymer Skin” 53510.6.6 Graft Polymerization 53510.7 Plasma Polymers with Monosort Functional Groups 53710.7.1 OH Groups 54010.7.2 COOH Groups 54410.7.3 NH2 Groups 54810.8 Attempts to Increase the Yield of Functional Group 55610.8.1 Optimization of Plasma Conditions for Generation of NH2 Groups 55610.8.2 Attempts to Increase the Concentration of NH2 Groups by Addition of Ammonia to Allylamine Plasma Polymerization 55610.8.3 Alternative Methods 56410.8.4 Plasma-Produced Amino Groups for Promotion of Adhesion 56410.9 Plasma Copolymerization 56610.9.1 General Remarks on the Background of Copolymerization and Its Definition 56610.9.2 Copolymers with Allyl Alcohol 56910.9.3 Copolymers with Acrylic Acid 57510.9.4 Allylamine Copolymers 57610.10 Grafting Onto Plasma Polymers as Special Case of ‘Graft-Copolymerization’ 58010.10.1 General Aspects 58010.10.2 Direct Grafting Onto Radical Sites 58210.10.3 Grafting Onto Peroxy Radicals/Hydroperoxides 58210.10.4 Reactions with OH Groups 58310.10.5 Reactions with COOH Groups 58410.10.6 Reactions with NH2 Groups 58410.10.7 Reactions with Br Groups 58510.10.8 Other Methods 58510.11 Significant Side Reactions 58510.11.1 Details of the IR Bands at 2200 cm-1 58810.11.2 DSC Results 59010.11.3 Post-Plasma Oxidation 59110.11.4 Attempts to Eliminate Post-Plasma Oxidations 59610.12 Plasma Polymers Deposited by Atmospheric-Pressure Plasmas 597References 59811 Technical Applications 62111.1 Introduction 62111.2 Adhesion Promotion 62211.2.1 Polymer Surface Modification 62411.2.2 Combination of Plasma Pretreatment and Wet-Chemical Post-Plasma Treatment 62811.2.3 Deposition of Adhesion-Promoting Polymer Films 62911.2.3.1 Direct Grafting 62911.2.3.2 Grafting via Peroxy Route 63011.2.3.3 Co-Evaporation or Sputtering of Metals During Plasma Polymerization 63011.2.3.4 Plasma Polymer Coating 63111.3 Cleaning 63311.4 Wettability 63511.5 Etching of Polymers 63711.5.1 Preparation and Excavation of Supermolecular Structures of Polymers for Their Characterization by Electron Microscopy 63711.5.2 Ashing 63811.6 Barrier Layers or Barrier Formation 63811.6.1 Organic and Inorganic Barrier Layer for Limiting Diffusion 63811.6.2 Fluorination of Polymers 63911.7 Anti-Fouling Layers 64111.8 Sterilization 64211.9 Water Purification and Desalination 64311.10 Flame Protection 64311.11 Textile Modification 64411.12 Modification of Carbon Fibers and Nanotubes 64411.13 Silent Discharge and Excimer Radiation 64511.14 Conducting Films 64611.15 Scratch-Resistant Coatings 64611.16 Underwater Plasma 647References 650Index 671