Written for readers interested in non-thermal gas discharge plasmas and their applications, this book is focused on microwaves and microwave generated plasmas which can be used in a number of applications. Even within the engineering community, there is a very little knowledge about different plasma systems and applications even though there is now growing interest in such technology for new plasma chemical processes. This book includes detailed descriptions, explanations and recommendations in three parts of the technology: (1) the microwave power and components, (2) the plasma properties and generation principles, (3) selected applications. Chapter 1 is devoted to microwave systems starting with descriptions and explanations of parts and components in microwave power lines, which can be used not only in laboratory experiments but also in industrial devices. Chapter2 contains fundamentals of gas discharge plasma and differences between plasmas generated at different kinds of power, with particular emphasis to microwave power. Chapter 3 is devoted to plasma processing and explanations of plasma interactions with solid surfaces and gases, particularly at reduced and low pressures. Chapter 4 is focused on different microwave plasma systems, including novel and non-conventional ones developed and tested in different processing applications at reduced pressures. Chapter 5 covers microwave plasma systems and applications at atmospheric and higher pressures, including plasmas inside liquids and plasma interactions with the combustion flames. Chapter 6 describes new trends in microwave discharges with future perspectives of the microwave plasma and its applications.

Ladislav Bardos, PhD, is Professor at the Department of Electrical Engineering at Uppsala University. He received his PhD from the Institute of Plasma Physics at the Czech Academy of Sciences in 1978 and DrSc from the Charles University Prague in 1995. He was awarded the Plasma Physics Innovation Prize 2019 by the European Physical Society.

Hana Barankova is a Professor at the Department of Electrical Engineering, Uppsala University. She received her PhD from the Institute of Radio Engineering and Electronics at the Czech Academy of Sciences in 1981. She was awarded the Plasma Physics Innovation Prize 2019 by the European Physical Society. She is Secretary of the Board of Directors at the Society of Vacuum Coaters in the US.

Foreword from the Authors ix

1 Basic Principles and Components in the Microwave Techniques and Power Systems 1

1.1 History in Brief – From Alternating Current to Electromagnetic Waves and to Microwaves 1

1.2 Microwave Generators 3

1.3 Waveguides and Electromagnetic Modes in Wave Propagation 5

1.3.1 The Cut-off Frequency and the Wavelength in Waveguides 7

1.3.2 Waveguides Filled by Dielectrics 9

1.3.3 Wave Impedance and Standing Waves in Waveguides 10

1.3.4 Coaxial Transmission Lines 12

1.3.5 Microwave Resonators 14

1.4 Waveguide Power Lines 14

1.4.1 Magnetron Tube Microwave Generator 16

1.4.2 Microwave Insulators 16

1.4.3 Impedance Tuners 17

1.4.4 Directional Couplers 19

1.4.5 Passive Waveguide Components – Bends, Flanges, Vacuum Windows 20

1.4.6 Tapered Waveguides and Waveguide Transformers 22

1.4.7 Power Loads and Load Tuners 23

1.4.8 Waveguide Phase Shifters 25

1.4.9 Waveguide Shorting Plungers 25

1.4.10 Coupling from Rectangular to Circular Waveguide: Resonant Cavities for Generation of Plasma 26

1.5 Microwave Oven – A Most Common Microwave Power Device 28

References 33

2 Gas Discharge Plasmas 37

2.1 Basic Understanding of the Gas Discharge Plasmas 37

2.2 Generation of the Plasma, Townsend Coefficients, Paschen Curve 40

2.3 Generation of the Plasma by AC Power, Plasma Frequency, Cut-off Density 43

2.4 Space-charge Sheaths at Different Frequencies of the Incident Power 50

2.5 Classification of Gas Discharge Plasmas, Effects of Gas Pressure, Microwave Generation of Plasmas 55

2.5.1 Classification of Gas Discharge Plasmas 55

2.5.2 Effects of the Gas Pressure on Particle Collisions in the Plasma 58

2.5.3 Microwave Generation of Plasmas 61

References 64

3 Interactions of Plasmas with Solids and Gases 67

3.1 Plasma Processing, PVD, and PE CVD 67

3.2 Sputtering, Evaporation, Dry Etching, Cleaning, and Oxidation of Surfaces 72

3.3 Particle Transport in Plasma Processing and Effects of Gas Pressure 75

3.3.1 Movements of Neutral Particles 76

3.3.2 Movements of Charged Particles 77

3.3 Effect of the Gas Pressure on the Plasma Processing 79

3.4 Afterglow and Decaying Plasma Processing 81

References 83

4 Microwave Plasma Systems for Plasma Processing at Reduced Pressures 85

4.1 Waveguide-Generated Isotropic and Magnetoactive Microwave Plasmas 85

4.1.1 Waveguide-Generated Isotropic Microwave Oxygen Plasma for Silicon Oxidation 87

4.1.2 ECR and Higher Induction Magnetized Plasma Systems for Silicon Oxidation 93

4.2 PE CVD of Silicon Nitride Films in the Far Afterglow 105

4.3 Microwave Plasma Jets for PE CVD of Films 111

4.3.1 Deposition of Carbon Nitride Films 115

4.3.2 Surfajet Plasma Parameters and an Arrangement for Expanding the Plasma Diameter 119

4.4 Hybrid Microwave Plasma System with Magnetized Hollow Cathode 122

References 129

5 Microwave Plasma Systems at Atmospheric and Higher Pressures 135

5.1 Features of the Atmospheric Plasma and Cold Atmospheric Plasma (CAP) Sources 136

5.2 Atmospheric Microwave Plasma Sources Assisted by Hollow Cathodes 140

5.2.1 Applications of the H-HEAD Plasma Source in Surface Treatments 144

5.3 Microwave Treatment of Diesel Exhaust 151

5.4 Microwave Plasma in Liquids 154

5.5 Microwave Plasma Interactions with Flames 157

5.6 Microwave Plasmas at Very High Pressures 161

References 162

6 New Applications and Trends in the Microwave Plasmas 169

References 176

7 Appendices 181

7.1 List of Symbols and Abbreviations 181

7.2 Constants and Numbers 188

Index 189