Title Details

GREG HAUGSTAD, PhD, is a technical staff member and Director of the Characterization Facility in the College of Science and Engineering at the University of Minnesota. He has collaborated with industry professionals on such technologies as medical X-ray imaging media, lubrication, inkjet printing, and more recently on biomedical device coatings. He teaches undergraduate and graduate AFM courses, as well as short professional courses, and has trained over 600 AFM users.

Acknowledgments xxi

1. Overview of AFM 1

1.1. The Essence of the Technique, 1

1.2. Property Sensitive Imaging: Vertical Touching and Sliding Friction, 6

1.3. Modifying a Surface with a Tip, 13

1.4. Dynamic (or “AC” or “Tapping”) Modes: Delicate Imaging with Property Sensitivity, 16

1.5. Force Curves Plus Mapping in Liquid, 21

1.6. Rate, Temperature, and Humidity-Dependent Characterization, 24

1.7. Long-Range Force Imaging Modes, 28

1.8. Pedagogy of Chapters, 30

References, 31

2. Distance-Dependent Interactions 33

2.1. General Analogies and Types of Forces, 33

2.2. Van der Waals and Electrostatic Forces in a Tip–Sample System, 38

2.2.1. Dipole–Dipole Forces, 38

2.2.2. Electrostatic Forces, 41

2.3. Contact Forces and Mechanical Compliance, 44

2.4. Dynamic Probing of Distance-Dependent Forces, 51

2.4.1. Importance of Force Gradient, 51

2.4.2. Damped, Driven Oscillator: Concepts and Mathematics, 56

2.4.3. Effect of Tip–Sample Interaction on Oscillator, 60

2.4.4. Energy Dissipation in Tip–Sample Interaction, 64

2.5. Other Distance-Dependent Attraction and Repulsion: Electrostatic and Molecular Forces in Air and Liquids, 67

2.5.1. Electrostatic Forces in Liquids: Superimposed on Van der Waals Forces, 67

2.5.2. Molecular-Structure Forces in Liquids, 69

2.5.3. Macromolecular Steric Forces in Liquids, 72

2.5.4. Derjaguin Approximation: Colloid Probe AFM, 76

2.5.5. Macromolecular Extension Forces (Air and Liquid Media), 78

2.6. Rate/Time Effects, 83

2.6.1. Viscoelasticity, 84

2.6.2. Stress-Modified Thermal Activation, 85

2.6.3. Relevance to Other Topics of Chapter 2, 86

References, 88

3. Z-Dependent Force Measurements with AFM 91

3.1. Revisit Ideal Concept, 91

3.2. Force-Z Measurement Components: Tip/Cantilever/Laser/Photodetector/Z Scanner, 93

3.2.1. Basic Concepts and Interrelationships, 93

3.2.2. Tip–Sample Distance, 96

3.2.3. Finer Quantitative Issues in Force–Distance Measurements, 99

3.3. Physical Hysteresis, 106

3.4. Optical Artifacts, 109

3.5. Z Scanner/Sensor Hardware: Nonidealities, 113

3.6. Additional Force-Curve Analysis Examples, 118

3.6.1. Glassy Polymer, Rigid Cantilever, 118

3.6.2. Gels, Soft Cantilever, 123

3.6.3. Molecular-Chain Bridging Adhesion, 126

3.6.4. Bias-Dependent Electrostatic Forces in Air, 129

3.6.5. Screened Electrostatic Forces in Aqueous Medium, 131

3.7. Cantilever Spring Constant Calibration, 133

References, 135

4. Topographic Imaging 137

4.1. Idealized Concepts, 138

4.2. The Real World, 143

4.2.1. The Basics: Block Descriptions of AFM Hardware, 143

4.2.2. The Nature of the Collected Data, 149

4.2.3. Choosing Setpoint: Effects on Tip–Sample Interaction and Thereby on Images, 156

4.2.4. Finite Response of Feedback Control System, 162

4.2.5. Realities of Piezoscanners: Use of Closed-Loop Scanning, 167

4.2.6. Shape of Tip and Surface, 180

4.2.7. Other Realities and Operational Difficulties—Variable Background, Drift, Experimental Geometry, 182

References, 186

5. Probing Material Properties I: Phase Imaging 187

5.1. Phase Measurement as a Diagnostic of Interaction Regime and Bistability, 189

5.1.1. Phase (and Height, Amplitude) Imaging as Diagnostics, 189

5.1.2. Comments on Imaging in the Attractive Regime, 200

5.2. Complications and Caveats Regarding the Phase Measurement, 202

5.2.1. The Phase Offset, 202

5.2.2. Drift in Resonance Frequency, Phase Offset, Quality Factor, and Response Amplitude, 207

5.2.3. Change of Phase and Amplitude During Coarse Approach, 211

5.2.4. Coupling of Topography and Phase, 214

5.2.5. The Phase Electronics and Its Calibration, 221

5.2.6. Nonideality in the Resonance Spectrum, 230

5.3. Energy Dissipation Interpretation of Phase: Quantitative Analysis, 234

5.3.1. Variable A/A0 Imaging, 235

5.3.2. Fixed A/A0 Imaging, 240

5.3.3. Variable A/A0 via Z-Dependent Point Measurements, 243

5.4. Virial Interpretation of Phase, 247

5.5. Caveats and Data Analysis Strategies when Quantitatively Interpreting Phase Data, 248

References, 255

6. Probing Material Properties II: Adhesive Nanomechanics and Mapping Distance-Dependent Interactions 258

6.1. General Concepts and Interrelationships, 259

6.2. Adhesive Contact Mechanics Models, 261

6.2.1. Overview and Disclaimers, 261

6.2.2. JKR and DMT Models, 263

6.2.3. Ranging Between JKR and DMT: The Transition Parameter l, 266

6.2.4. The Maugis–Dugdale Model, 270

6.2.5. Other Formal Relationships Relevant to Adhesive Contact Mechanics, 273

6.2.6. Summary Comments and Caveats on Adhesive Contact Mechanics Models, 274

6.3. Capillarity, Details of Meniscus Force, 277

6.3.1. Framing the Issues, 278

6.3.2. Basic Elements of Modeling the Meniscus, 280

6.3.3. Mathematics of Meniscus Geometry and Force, 283

6.3.4. Experimental Examples of Capillarity, 287

6.3.5. Capillary Transfer Phenomena: Difficulties and Opportunities, 293

6.4. Approach–Retract Curve Mapping, 296

6.4.1. Motivation and Background, 296

6.4.2. Traditional Force-Curve Mapping, 298

6.4.3. Approach–Retract Curve Mapping in Dynamic AFM, 306

6.4.4. Approach–Retract Curve Mapping of Liquidy Domains in Complex Thin Films, 313

6.5. High-Speed/Full Site Density Force-Curve Mapping and Imaging, 315

6.5.1. Liquidy Domains in Complex Thin Films, 317

6.5.2. PBMA/PLMA Blend at Variable Ultimate Load, 319

6.5.3. PBMA/Dexamethasone Mixture at Variable Temperature, 320

6.5.4. Arborescent Styrene–Isobutylene–Styrene Block Copolymer Plus Drug Rapamycin, 322

6.5.5. Comments on “Force Modulation” Mode, 323

References, 324

7. Probing Material Properties III: Lateral Force Methods 330

7.1. Components of Lateral Force Signal, 330

7.2. Application of Lateral Force Difference, 336

7.3. Calibration of Lateral Force, 343

7.4. Load-Dependent Friction, 346

7.4.1. Motivations, 346

7.4.2. Load Stepping and Ramping Methods, 347

7.5. Variable Rate and Environmental Parameters in AFM Friction and Wear, 352

7.5.1. Motivations, 352

7.5.2. Interplay of Rate, Temperature, Humidity, and Tip Chemistry in Friction, 354

7.5.3. Wear Under Variable Rate and Temperature, 359

7.5.4. Musings on the Spectroscopic Nature of Friction and Other Measurements, 362

7.6. Transverse Shear Microscopy (TSM) and Anisotropy of Shear Modulus, 364

7.7. Shear Modulation Methods, 366

7.7.1. Motivations and Terminology, 366

7.7.2. Shear Modulation During 1D Lateral Scanning, 368

7.7.3. Diagnostics of Sliding Under Shear Modulation, 371

7.7.4. Complementarity of Shear Modulation Methods to TSM, 372

7.7.5. Shear Modulation Within Force Curves: Material Creep, 373

References, 375

8. Data Post-Processing and Statistical Analysis 379

8.1. Preliminary Data Processing, 379

8.2. 1D Roughness Metrics, 383

8.3. 2D-Domain Analysis, 385

8.3.1. Slope and Surface Area Analysis, 385

8.3.2. 2D-Domain Fourier Methods for Spatial Analysis, 386

8.3.3. Fourier Methods for Time-Domain Analysis, 391

8.3.4. Grain or Particle Size Analysis, 394

8.4. “Lineshape” Fitting, 396

References, 398

9. Advanced Dynamic Force Methods 400

9.1. Principles of Electronic Methods Utilizing Dynamic AFM, 401

9.1.1. Shifted Dynamic Response due to Force Gradient, 402

9.1.2. Interleave Methods for Long-Range Force Probing, 405

9.1.3. Interleave-Based EFM/KFM on Different Metals and Silicon, 408

9.1.4. KFM of Organic Semiconductor, Including Cross-Technique Comparisons, 412

9.2. Methods Using Higher Vibrational Modes, 414

9.2.1. Mathematics of Beam Mechanics: The Music of AFM, 414

9.2.2. Probing Tip–Sample Interactions via Multifrequency Dynamic AFM, 419

9.2.3. Contact Resonance Methods, 425

9.2.4. Single-Pass Electric Methods, 429

References, 433

Appendices 437

Appendix 1: Spectral Methods for Measuring the Normal Cantilever Spring Constant K, 437

A1.1 Plan-View/Resonance Frequency Method, 438

A1.2 Sader Method, 441

A1.3 Thermal Method, 442

Appendix 2: Derivation of Van der Waals Force–Distance Expressions, 443

Appendix 3: Derivation of Energy Dissipation Expression, Relationship to Phase, 447

Appendix 4: Relationships in Meniscus Geometry, Circular Approximation, 449

References, 450

Index 453