Atomic Force Microscopy: Understanding Basic Modes and Advanced Applications

This book enlightens readers on the basic surface properties and distance-dependent intersurface forces one must understand to obtain even simple data from an atomic force microscope (AFM). The material becomes progressively more complex throughout the book, explaining details of calibration, physical origin of artifacts, and signal/noise limitations. Coverage spans imaging, materials property characterization, in-liquid interfacial analysis, tribology, and electromagnetic interactions. “Supplementary material for this book can be found by entering ISBN 9780470638828 on booksupport.wiley.com”

Table of Contents:
Preface xiii 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 4.2.5. 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

About the Author :
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.