Cathodic Arcs (eBook)

André Anders is a Senior Scientist and the Leader of the Plasma Applications Group at Lawrence Berkeley National Laboratory in Berkeley, California. He published his first paper on discharges in vacuum in 1984 and has worked in related fields ever since, first with his mentors Burkhard Jüttner and Erhard Hantzsche in East Berlin, Germany, and since 1992 in Berkeley, California. With over 200 publications in refereed journals, he contributed to the field of cathodic arcs and arc-based coatings by extensive measurements of arc plasma properties and the development of miniaturized filtered arc systems for diamond-like carbon, which are today used by the magnetic storage industry. He currently serves in many committees, most notably as the Chairman of the Permanent International Scientific Committee of the Symposia on Electrical Insulation and Discharges in Vacuum.

Springer Series on atomic, optical, and plasma physics 2
Preface 7
Contents 10
Introduction 18
A Brief History of Cathodic Arc Coating 24
2.1 Introduction 24
2.2 Cathodic Arcs in the Eighteenth Century 25
2.2.1 The Capacitor: Energy Storage for Pulsed Discharges 25
2.2.2 Priestley’s Cathodic Arc Experiments 27
2.2.3 Experiments Leading to the Electrochemical Battery 32
2.3 Cathodic Arcs in the Nineteenth Century 34
2.3.1 Improvements to the Voltaic Pile 34
2.3.2 Davy’s Observation of Pulsed Discharges 35
2.3.3 Petrov’s Observation of Continuous Arc Discharges 36
2.3.4 Davy’s Work on Continuous Arc Discharges 39
2.3.5 Electromagnetic Induction 41
2.3.6 Rühmkorff Coil and Pulsed Discharges 41
2.3.7 Discharge Experiments in Gases and ‘‘In Vacuo’’ 43
2.3.8 Faraday’s Deflagrator 45
2.3.9 Optical Emission Spectroscopy 47
2.3.10 Maxwell 47
2.3.11 Wright’s Experiments: Coatings by Pulsed Glow or Pulsed Arc? 47
2.3.12 Lecher’s Arc Experiments: Discontinuous Current Transfer 48
2.3.13 Goldstein’s Canal Rays 50
2.3.14 Edison’s Coating Patents 50
2.3.15 Cathodic Arc Ion Velocity Measurements 51
2.3.16 Early Probe Experiments in Arc Plasmas 52
2.4 Cathodic Arcs in the Twentieth Century 53
2.4.1 Around the Year 1905: Einstein, Weintraub, Stark, and Child 53
2.4.1.1 The Mercury Arc in Vacuum 54
2.4.1.2 From Mercury to Cathodic Arcs of Other Materials 55
2.4.1.3 Chopping Current 56
2.4.1.4 Spot Steering 57
2.4.1.5 Arc Voltage 58
2.4.1.6 Probes, Potential Distribution, and Sheaths 58
2.4.1.7 Plasma Transport Along Magnetic Field Lines 59
2.4.1.8 Arc Modes 60
2.4.1.9 Role of Oxides on Cathodes 61
2.4.1.10 Cathode Erosion, Gettering Effect, and Coatings 61
2.4.2 The Decades Until WWII 62
2.4.3 Secret Work During WWII 63
2.4.4 The Quest for the ‘‘Correct’’ Current Density and Cathode Model 64
2.4.5 Ion Velocities: Values and Acceleration Mechanism 66
2.4.6 Cathodic Arc Deposition Is Emerging as an Industrial Process 67
2.4.6.1 Coatings of Refractory and Transition Metals 67
2.4.6.2 Coatings of Ferrites 68
2.4.6.3 From Pump Research to Coatings 69
2.4.6.4 Hard and Decorative Coatings in the Soviet Union 69
2.4.6.5 From Soviet Union to America 71
2.4.7 Large-Scale Industrial Use in the 1980s and 1990s 72
2.4.8 Macroparticle Filtering: Enabling Precision Coating for High-Tech Applications 73
2.5 Cathodic Arcs at the Beginning of the Twenty-First Century 76
2.5.1 Advances in Diagnostics and Modeling of Arc Plasma Processes 76
2.5.2 Improvements of Coating Quality and Reproducibility, Enabling High-Tech Applications 77
2.5.3 Cathodic Arcs for Large-Area Coatings 78
2.5.4 Multilayers and Nanostructures of Multi-component Materials Systems 79
References 79
The Physics of Cathode Processes 92
3.1 Introduction 93
3.2 Theory of Collective Electron Emission Processes: Steady-State Models 96
3.2.1 Thermionic Emission 96
3.2.2 Field-Enhanced Thermionic Emission 99
3.2.3 Field Emission 101
3.2.4 Thermo-field Emission 103
3.3 Refinements to the Electric Properties of Metal Surfaces 104
3.3.1 Jellium Model and Work Function 104
3.3.2 The Role of Adsorbates 107
3.3.3 The Role of Surface Roughness 111
3.4 Theory of Collective Electron Emission Processes: Non-stationary Models 112
3.4.1 Ion-Enhanced Thermo-field Emission 112
3.4.2 The Existence of a Critical Current Density 115
3.4.3 The Tendency to Non-uniform Emission: Cathode Spots 115
3.4.4 Energy Balance Consideration for Cathodes 116
3.4.4.1 Heat Conduction Equation 116
3.4.4.2 Joule Heat 116
3.4.4.3 Ion Bombardment Heating 117
3.4.4.4 Ion Emission Cooling 117
3.4.4.5 Atom Evaporation Cooling 118
3.4.4.6 Atom Condensation Heating 119
3.4.4.7 Electron Emission Cooling 119
3.4.4.8 Heating by Returning Electrons 120
3.4.4.9 Radiation Cooling 120
3.4.4.10 Radiation Heating from Plasma 121
3.4.5 Stages of an Emission Center 121
3.4.6 Plasma Jets, Sheaths, and Their Relevance to Spot Ignition and Stages of Development 123
3.4.7 Explosive Electron Emission and Ecton Model 126
3.4.8 Explosive Electron Emission on a Cathode with Metallic Surfaces 128
3.4.9 Explosive Electron Emission on a Cathode with Non-metallic Surfaces 130
3.5 Fractal Spot Model 131
3.5.1 Introduction to Fractals 131
3.5.2 Spatial Self-Similarity 133
3.5.3 Temporal Self-Similarity 135
3.5.4 Fractal Character and Ignition of Emission Centers 139
3.5.5 Spots, Cells, Fragments: What Is a Spot, After All? 143
3.5.6 Cathode Spots of Types 1 and 2 145
3.5.7 Cathode Spots on Semiconductors and Semi-metals: Type 3 148
3.5.8 Arc Chopping and Spot Splitting 149
3.5.9 Random Walk 150
3.5.10 Self-Interacting Random Walks 152
3.5.11 Steered Walk: Retrograde Spot Motion 154
3.5.12 But Why Is the Cathode Spot Moving in the First Place? 162
3.6 Arc Modes 163
3.7 The Cohesive Energy Rule 166
3.7.1 Formulation 166
3.7.2 Other Empirical Rules 167
3.7.3 Experimental Basis 167
3.7.4 Physical Interpretation 168
3.7.5 Quantification 170
3.7.6 Related Observations: Ion Erosion and Voltage Noise 170
3.8 Cathode Erosion 172
3.9 Plasma Formation 175
3.9.1 Phase Transitions 175
3.9.2 Non-ideal Plasma 176
3.9.3 Ion Acceleration 179
References 180
The Interelectrode Plasma 192
4.1 Plasma Far from Cathode Spots 192
4.2 Special Cases of Plasma Expansion 195
4.2.1 Plasma Expansion into Vacuum 195
4.2.2 Plasma Expansion Dominated by an External Magnetic Field 196
4.2.3 Plasma Expansion for High-Current Arcs 197
4.2.4 Plasma Expansion into Background Gas 198
4.3 Ion Charge State Distributions 199
4.3.1 Experimental Observations 199
4.3.2 Local Saha Equilibrium: The Instantaneous Freezing Model 200
4.3.3 Partial Saha Equilibrium: The Stepwise Freezing Model 203
4.3.4 Plasma Fluctuations 206
4.3.5 Effect of an External Magnetic Field 209
4.3.6 Effect of Processing Gas 212
4.4 Ion Energies 214
4.4.1 Ion Energy Distribution Functions for Vacuum Arcs 214
4.4.2 Ion Energies in the Presence of Magnetic Fields 220
4.4.3 Ion Energy Distribution Functions for Cathodic Arcs in Processing Gas 223
4.5 Neutrals in the Cathodic Arc Plasmas 224
4.5.1 Sources and Sinks of Neutrals 224
4.5.2 The Effects of Metal Neutrals on the Ion Charge States 225
4.5.3 The Effects of Gas Neutrals on the Ion Charge States 231
4.5.4 The Effects of Neutrals on the Ion Energy 234
References 235
Cathodic Arc Sources 243
5.1 Continuous Versus Pulsed: Advantages and Disadvantages of Arc Switching and Pulsing 243
5.2 DC Arc Sources 245
5.2.1 Random Arc Sources 245
5.2.2 Steered Arc Sources 248
5.2.3 Sources with Challenging Cathodes 255
5.2.4 Sources with Multiple Cathodes 259
5.3 Pulsed Arc Sources 259
5.3.1 Miniature Sources 259
5.3.2 High-Current Pulsed Arc Sources 260
5.3.3 Sources with Multiple Cathodes 264
5.4 Arc Triggering 266
5.4.1 Contact Separation 266
5.4.2 Mechanical Trigger 266
5.4.3 High-Voltage Surface Discharge 267
5.4.4 Low-Voltage and ‘‘Triggerless’’ Arc Ignition 268
5.4.5 Laser Trigger 269
5.4.6 Plasma Injection 270
5.4.7 Trigger Using an ExB Discharge 271
5.5 Arc Source Integration in Coating Systems 271
5.5.1 Batch Systems 271
5.5.2 In-Line Systems 274
References 276
Macroparticles 280
6.1 Macroparticle Generation of Random Arcs 280
6.2 Macroparticle Generation of Steered Arcs 289
6.3 Macroparticle Generation of Pulsed Arcs 292
6.4 Macroparticles from Poisoned Cathodes 293
6.5 Macroparticle-Plasma Interaction 294
6.5.1 Plasma Effects on Macroparticles 294
6.5.2 Mass Balance 295
6.5.3 Energy Balance 298
6.5.3.1 Energy Fluxes Related to Electron Currents 298
6.5.3.2 Energy Fluxes Related to Ion Currents 300
6.5.3.3 Energy Fluxes Related to Atom Fluxes 302
6.5.3.4 Energy Fluxes Related to Radiation 303
6.5.4 Momentum Balance 303
6.6 Interaction of Macroparticles with Surfaces 305
6.7 Defects of Coatings Caused by Macroparticles 306
6.8 Mitigation Measures 308
References 310
Macroparticle Filters 314
7.1 Introduction to Macroparticle Filtering 314
7.2 Figures of Merit 315
7.2.1 Filter Efficiency 315
7.2.2 System Coefficient 316
7.2.3 Particle System Coefficient 316
7.2.4 Attenuation Length 317
7.2.5 Normalized Macroparticle Reduction Factor 319
7.3 Theory of Plasma Transport in Filters 320
7.3.1 Motion of Charged Particles and Plasma Models 320
7.3.2 Magnetization and Motion of Guiding Center 320
7.3.3 Existence of an Electric Field in the Magnetized Plasma 323
7.3.4 An Over-Simplified but Intuitive Interpretation of Ion Transport in Curved Filters 324
7.3.5 Kinetic Models: Rigid Rotor Equilibria 326
7.3.6 Plasma Optics 329
7.3.7 Drift Models 333
7.3.8 Magneto-hydrodynamic Models 335
7.4 Experimental and Industrial Filter Designs 340
7.4.1 Filters of Closed and Open Architecture 340
7.4.2 Filters for Circular and Linear Plasma Source Areas 341
7.4.3 Straight Filter 342
7.4.4 Straight Filter with Axial Line-of-Sight Blockage 343
7.4.5 Straight Filter Combined with Annular-Cathode Plasma Source 344
7.4.6 Straight Filter with Off-Axis Substrate 344
7.4.7 Classic 90 Duct Filter 345
7.4.8 Modular Filter 346
7.4.9 Knee-Filter 346
7.4.10 Large-Angle, Omega- and S-Duct Filters 347
7.4.11 Off-Plane Double Bend Filter 348
7.4.12 Duct Filter for Linear Arc Source 350
7.4.13 Rectangular S-Filter for Linear Arc Source 350
7.4.14 Dome Filter 351
7.4.15 Magnetic Reflection Configuration 351
7.4.16 Bi-directional Linear Filter 352
7.4.17 Radial Filter 352
7.4.18 Annular Cathode Apparatus 354
7.4.19 Annular Venetian Blind Filter 354
7.4.20 Linear Venetian Blind Filter 355
7.4.21 Open, Freestanding 90 Filter 356
7.4.22 Open, Freestanding S-Filter 357
7.4.23 Twist Filter 357
7.4.24 Stroboscopic Filter 359
7.4.25 Rotating Blade Filter 359
7.4.26 Parallel Flow Deposition 360
7.5 Filter Optimization 361
7.5.1 Biasing 361
7.5.2 Arc Source-Filter Coupling 364
7.6 Effects of Filtering on Ion Charge State and Energy Distribution 365
7.7 Plasma Density Profile and Coating Uniformity 366
References 371
Film Deposition by Energetic Condensation 378
8.1 Energetic Condensation and Subplantation 379
8.2 Secondary Electron Emission 384
8.3 Neutrals Produced by Self-Sputtering and Non-sticking 386
8.4 Film Properties Obtained by Energetic Condensation 389
8.4.1 Structure Zone Diagrams 389
8.4.2 Stress and Stress Control 391
8.4.3 Preferred Orientation 396
8.4.4 Adhesion 398
8.4.5 Hall-Petch Relationship 399
8.5 Metal Ion Etching 400
8.6 Metal Plasma Immersion Ion Implantation and Deposition (MePIIID) 402
8.7 Processing with Bipolar Pulses - The Use of Ions and Electrons 405
8.8 Substrate Biasing Versus Plasma Biasing 407
8.9 Arcing and Arc Suppression 408
8.10 Case Study: Tetrahedral Amorphous Carbon (ta-C) 409
References 414
Reactive Deposition 423
9.1 Arc Operation in Vacuum and Gases: Introduction 423
9.2 Cathode ‘‘Poisoning’’: Effects on Spot Ignition and Erosion Rate 424
9.3 Cathode ‘‘Poisoning’’: Hysteresis 428
9.4 Interaction of the Expanding Spot Plasma with the Background Gas 430
9.5 Nucleation and Growth 432
9.6 Water Vapor and Hydrogen Uptake 436
9.7 Arcs in High-Pressure Environments 439
References 440
Some Applications of Cathodic Arc Coatings 443
10.1 Overview 443
10.2 Nitride Coatings for Wear Applications 448
10.2.1 TiN and Other Binary Nitrides 448
10.2.2 Ti1-xAlxN 450
10.2.3 Other Ternary and Quaternary Nitrides, Carbides, and Nanocomposites 451
10.2.4 Multilayers, Nanolayers, and Nanolaminates 454
10.2.5 Replacement of Hexavalent Chromium 455
10.2.6 Carbides 456
10.2.7 Multi-Element Coatings on Turbine Blades 457
10.2.8 Cubic Boron Nitride and Boron-Containing Multi-Component Coatings 457
10.2.9 Tetrahedral Amorphous Carbon (ta-C) 459
10.2.10 Hydrogen, Nitrogen, and Metal-Doped Tetrahedral Amorphous Carbon 461
10.3 Decorative Coatings 464
10.3.1 Appearance of Color 464
10.3.2 Color by Interference 465
10.3.3 Color by Spectrally Selective Absorption 466
10.3.4 The L*a*b* Color Space 469
10.3.5 Example: Color of Nitrides 471
10.4 Optical Coatings 472
10.5 Transparent Conductor, Solar Energy, Electronic, and Photocatalytic Applications 475
10.6 Field Emission Applications 478
10.7 Metallization 480
10.7.1 Ultrathin Metal Films 480
10.7.2 Metallization of Integrated Circuits 481
10.7.3 Metallization of Superconducting Cavities 483
10.7.4 Metallization for Specialty Brazing 485
10.7.5 Metallization Using Alloy Cathodes 486
10.8 Bio-compatible Coatings 486
10.8.1 Carbon-Based Materials 487
10.8.2 Titanium-Based Materials 489
10.9 Surface Cleaning by Arc Erosion and Ion Etching 490
References 491
Plasmas and Sheaths: A Primer 505
Plasmas 505
Sheaths 508
References 511
Periodic Tables of Cathode and Arc Plasma Data 512
References 530
Index 531