Kelvin Probe Force Microscopy (eBook)

Sascha Sadewasser has been the Principal Investigator of the Laboratory for Nanostructured Solar Cells at INL - International Iberian Nanotechnology Laboratory (Portugal) since 2011. In 1999, he received his PhD from Washington University in St. Louis (USA). After a post-doc at Hahn-Meitner Institut Berlin and a Ramón y Cajal fellowship at the CNM in Barcelona (Spain), he was a group leader at the Helmholtz-Zentrum Berlin (Germany). Sascha’s research focuses on the development of nanostructures for and of chalcopyrite materials for the improvement of solar cells. He is an expert on scanning probe microscopy, and specifically Kelvin probe force microscopy, applied to semiconductor and solar cell research. His work has provided important insights into the physics of grain boundaries in polycrystalline Cu(in,Ga)Se2 thin-film solar cells. He has published over 80 peer-reviewed papers and 5 book chapters, and has been granted 3 patents. He is also a member of several scientific committees and evaluation boards. Thilo Glatzel is leader of the force microscopy group which is part of the research group from Prof. E. Meyer at the University of Basel. He is co-author of 115 international publications, contributed several book chapters, co-edited the first volume of the book on Kelvin probe force microscopy (KPFM), and has more than 100 contributions to international scientific conferences. During his dissertation at the Helmholtz-Zentrum Berlin he investigated interfaces and surfaces of chalcopyrite thin film solar cells based on Cu(Ga,In)(S,Se)2 absorber materials by KPFM. His work is now focused on the development of instruments and measurement techniques for high resolution scanning probe microscopy and the analysis of molecules and insulating and semiconducting surfaces at the nanometer scale. The expertise of the group is clearly focused on the nanoscale analysis and preparation of highly ordered surfaces down to the molecular and atomic scale, however with a focus on optoelectronic processes. 

Foreword 6
Preface 7
Contents 9
Contributors 17
Abbreviations 20
Experimental Methods and Technical Aspects 24
1 Experimental Technique and Working Modes 25
1.1 Introduction 25
1.2 Non-contact Atomic Force Microscopy 26
1.3 Electrostatic Force Microscopy 30
1.4 Kelvin Probe Force Microscopy 32
1.4.1 AM-KPFM 33
1.4.2 FM-KPFM 34
1.4.3 Technical Realization 35
1.4.4 Other Modes and Additional Experimental Options 38
1.5 Additional Remarks 40
References 42
2 Dissipation Modulated Kelvin Probe Force Microscopy Method 45
2.1 Introduction 46
2.2 Theory 48
2.2.1 Review of Theory of Frequency Modulation Atomic Force Microscopy 48
2.2.2 Analysis of Electrostatic Force with AC Bias Voltage 50
2.3 Experimental 56
2.4 Results and Discussion 57
2.4.1 Validation of D-KPFM Theory 57
2.4.2 Illustrative Example of D-KPFM Imaging 60
2.4.3 Comparison of Different KPFM Techniques 62
2.4.4 Dynamic Response of D-KPFM 66
2.5 Conclusion 67
References 68
3 Dynamic Modes in Kelvin Probe Force Microscopy: Band Excitation and G-Mode 70
Abstract 70
3.1 Introduction 71
3.2 Principles of EFM and KPFM 72
3.3 Classic KPFM Methods 76
3.4 Dynamic KPFM Without DC Bias Feedback 77
3.5 Band Excitation KPFM 80
3.5.1 Open Loop BE-KPFM 81
3.5.2 Half Harmonic BE-KPFM 84
3.5.3 Photothermal BE-KPFM 86
3.5.4 Force Volume BE-KPFM 88
3.6 Time Resolved KPFM 91
3.7 G-Mode KPFM 94
3.7.1 Classical Analysis Approach: Digital Heterodyne Detection 96
3.7.2 Physics Based Analysis: Recovery of Force-Voltage Dependence 101
3.7.3 Information Based Analysis: Data Mining 102
3.7.4 General Dynamic Mode 103
3.8 KPFM Spectroscopies 106
3.8.1 Contact KPFM 107
3.9 Outlook 114
Acknowledgement 115
References 115
4 Practical Aspects of Kelvin Probe Force Microscopy in Liquids 121
Abstract 121
4.1 Introduction 121
4.2 Electric Double Layer 122
4.3 Capacitive Force 125
4.4 Electrostatic Force 128
4.5 Surface Charge Measurement by Force Mapping 132
4.6 Summary 136
References 137
5 Time-Resolved Electrostatic and Kelvin Probe Force Microscopy 139
Abstract 139
5.1 Introduction 139
5.2 Time-Resolved Electrostatic Force Microscopy 141
5.2.1 Real-Time Measurements After Bias Pulsing 141
5.2.2 Real-Time Measurements After Light Pulses 144
5.2.3 Improved Time Resolution by Analysis of the Cantilever Oscillation 146
5.3 Time-Resolved Kelvin Probe Force Microscopy 148
5.3.1 Real-Time Measurements After Light Pulsing 148
5.3.2 Real-Time Measurements After Bias Pulsing 151
5.3.3 Intensity-Modulated KPFM 152
5.3.4 Bias-Modulated KPFM 155
5.3.5 Pump-Probe KPFM 156
5.4 Conclusion and Outlook 160
References 160
Data Interpretation and Theoretical Aspects 164
6 Imaging Static Charge Distributions: A Comprehensive KPFM Theory 165
6.1 Introduction 166
6.2 Electrostatic Description 167
6.3 KPFM Detection 173
6.4 The KPFM Signal 179
6.4.1 Excursus: Measuring Spectral Components 180
6.4.2 AM-KPFM 181
6.4.3 FM-KPFM 182
6.4.4 Summary of the KPFM Modes 184
6.5 The Weight Function for Charges 185
6.6 Conclusions and Outlook 186
References 187
7 Interpretation of KPFM Data with the Weight Function for Charges 189
7.1 Introduction 190
7.2 The Weight Function for Charges 191
7.2.1 The Void Tip-Sample System 192
7.3 Properties of the Weight Function for Charges 193
7.4 KPFM Signal for Relevant Charge Distributions 195
7.4.1 Imaging a Single Point Charge 196
7.4.2 Lateral Resolution for Imaging Charges with KPFM 201
7.4.3 Imaging Dipoles 205
7.4.4 Surface Charge Distribution 206
7.5 Conclusions and Outlook 210
References 217
8 Precise Modeling of Electrostatic Interactions with Dielectric Samples in Kelvin Probe Force Microscopy 219
8.1 Introduction 219
8.2 Analytic Approach 220
8.2.1 Spherical Tip Against Semi-infinite Dielectric 221
8.2.2 Dielectric Slab 229
8.2.3 Spherical Tip Atop Grounded Dielectric Slab 232
8.3 Numerical Approach 235
8.3.1 Numerical Image Charges Method 236
8.3.2 Real Space Discretization 236
8.3.3 Conductive Probe-Dielectric Sample Electrostatics 239
8.4 Concluding Remarks 242
References 243
9 Quantitative Analysis of Kelvin Probe Force Microscopy on Semiconductors 245
9.1 Introduction 245
9.2 Fundamentals of KPFM Measurements on Semiconductors 247
9.3 The Work Function of Semiconductors 250
9.4 Surface Charge on Semiconductors 251
9.5 Model Calculations for pn-Junctions 254
9.6 Comparison with Selected Experiments 258
9.7 KPFM and Surface Photovoltage 262
References 264
Application to Device Characterization 266
10 Nanoscale Transport Imaging of Active Lateral Devices: Static and Frequency Dependent Modes 267
Abstract 267
10.1 Introduction 267
10.2 Techniques 269
10.2.1 DC Transport by KPFM 273
10.2.2 Frequency and Time Dependent Transport Imaging 278
10.2.3 Non-linear Transport Imaging via Scanning Probe Microscopy 287
10.2.3.1 Non-linear SIM 287
10.2.3.2 Scanning Frequency Mixing Microscopy 290
10.2.4 Time-Resolved and Pump-Probe KPFM Methods 294
10.2.5 Gating Probes 299
10.3 Tip Calibration and Imaging Artefacts 301
10.3.1 Tip Calibration in Electrostatic SPMs 301
10.3.2 Imaging Artifacts and Some Considerations on Invasiveness 304
10.3.3 Invasiveness 307
10.4 Applications to Non-invasive Electronic Transport 307
10.5 Voltage Modifications in Lateral Devices 321
10.6 Light Effects 329
10.7 Transport Imaging in Liquids 332
10.8 Perspectives 334
10.8.1 New Techniques 334
10.8.2 Probes and Controlled Environments 336
10.8.3 Data Analysis and Knowledge Extraction 337
10.8.4 Towards Community Science 338
Acknowledgements 338
References 338
11 Kelvin Probe Force Microscopy Characterization of Organic and Hybrid Perovskite Solar Cells 346
Abstract 346
11.1 Introduction 346
11.1.1 Organic Solar Cells 346
11.1.2 Hybrid Perovskites Solar Cells 349
11.1.3 Using KPFM for Local Investigations of Solution Processed Solar Cells 352
11.2 KPFM Investigations of Donor-Acceptor Interfaces 353
11.3 KPFM Investigations of Hybrid Perovskite Thin Films 363
11.4 Cross-Sectional KPFM Investigations 365
11.5 Time-Resolved Surface Photo-Voltage Measurements 372
11.6 Summary and Outlook 376
References 377
12 KPFM of Nanostructured Electrochemical Sensors 381
12.1 Introduction 381
12.1.1 Nanostructured Chemical Sensors 382
12.1.2 Principles of Operation of Electrochemical Transducers 383
12.1.3 Effect of Surface Adsorption on the Work Function 384
12.2 Molecular Gate 385
12.2.1 CPD Map of a Multiple Gate FET Sensor 385
12.2.2 CPD Changes Following Chemical Modification 387
12.2.3 Coupling Between Front and Back Gate Potentials 391
12.2.4 Molecular Gating of a Multiple Gate FET Sensor 393
12.3 KPFM as a Tool to Evaluate Sensor Selectivity and Sensitivity on a Nanoscale 395
12.3.1 Multiple Gate FET-based Sensor Surface After Analyte Adsorption 395
12.3.2 Recent Examples for KPFM of Nanostructured Sensors 397
12.3.3 Sensor Surface Recovery and Degradation 399
12.4 Summary and Perspective 400
References 401
13 Applications of KPFM-Based Approaches for Surface Potential and Electrochemical Measurements in Liquid 404
Abstract 404
13.1 Introduction 404
13.2 Understanding Electrostatic Forces in Liquid 406
13.2.1 Standard EDL Models 406
13.2.1.1 The Diffuse EDL 406
13.2.1.2 EDL Dynamics 408
13.2.1.3 Poisson-Nernst-Planck Equation 410
13.2.2 Practical Implementations of VM AFM 414
13.3 Applications of EFM in Liquid 416
13.3.1 Bias-Free Approaches 417
13.3.2 Applications Utilizing Constant Voltage 418
13.3.3 Applications Utilizing Voltage Modulation 420
13.4 Applications of KPFM in Liquid 426
13.4.1 Macroscopic Kelvin Probe in Liquid 427
13.4.2 Applications of Classical KPFM in Non-polar Liquid 427
13.4.3 Breakdown of Classical KPFM in Polar Liquid 430
13.4.4 Applications of Open Loop-KPFM in Liquid 432
13.5 Bias and Time Resolved Approaches 436
13.5.1 Electrochemical Force Microscopy 436
13.6 Conclusions and Outlook 441
Acknowledgements 443
References 443
Atomic Scale Experiments 447
14 Kelvin Probe Force Microscopy with Atomic Resolution 448
Abstract 448
14.1 Introduction 449
14.2 Stray Capacitance Effect in Kelvin Probe Force Microscopy 449
14.2.1 Theoretical Comparison of FM-, AM- and Heterodyne AM-KPFM 450
14.2.1.1 FM-KPFM 452
14.2.1.2 AM-KPFM 453
14.2.1.3 Heterodyne AM-KPFM 456
14.2.2 Experimental Results of FM-, AM-, and Heterodyne AM-KPFM 457
14.2.2.1 Stray Capacitance Effect 457
14.2.2.2 Surface Potential Measurements 458
14.3 Surface Potential Measurement of TiO2(110) by FM-KPFM 460
14.3.1 Topography and Local Contact Potential Difference Image of TiO2(110) 461
14.3.2 Model to Explain the Origin of the Surface Potential of TiO2 (110) 464
14.4 Simultaneous Measurement of Topography, Tunneling Current, and Surface Potential 467
14.4.1 Theory of FM-KPFM Without Bias Voltage Feedback 467
14.4.2 Experimental AFM/STM/KPFM System 469
14.4.3 Multiple Images with Atomic Resolution on a TiO2(110) Surface 470
14.5 Conclusions 472
Acknowledgements 472
References 473
15 The Electrostatic Field of CO Functionalized Metal Tips 475
15.1 Introduction 475
15.2 The Dipole of CO Molecules in Gas Phase 477
15.3 The Electric Field of Metallic Tips 479
15.4 The Electric Field of Metal-CO Tips 481
15.5 A Theoretical Model to Simulate HR-AFM Imaging with Metal-CO Tips 484
15.5.1 Description of the Tip-Sample Interaction Potential 484
15.5.2 Cl Vacancy on a NaCl/Cu(100) Surface 486
15.5.3 CO Tilting: DFT Versus Model Calculations 487
15.6 Experimental Validation of the Electric Field Created by a Metal-CO Tip: Cl Vacancy on a NaCl Bilayer 488
15.6.1 Experimental Results 488
15.6.2 Simulation Results 490
15.6.3 Determination of the Dipole that Describes the Metal Tip in the Experiment 493
15.6.4 Interplay Between CO and Metallic Tip Electrostatic Interactions 494
15.6.5 Can a Single Dipole Mimic a CO Molecule on a Tip? 496
15.7 AFM Imaging of the CO Molecule as an Adsorbate 497
15.8 Conclusions 502
References 505
16 Imaging Charge DistributionWithin Molecules by Scanning ProbeMicroscopy 508
16.1 Introduction 508
16.2 Atomic Resolution in Kelvin Probe Force Microscopy 510
16.2.1 Detection of Charge States 514
16.2.2 Mapping Charge Distribution Within Molecules 515
16.3 High-Resolution AFM/STM Imaging 518
16.3.1 Impact of the Electrostatic Interaction on the High-Resolution AFM/STM Imaging 518
16.3.2 Mapping Electrostatic Potential Using High-Resolution Imaging 521
16.4 Conclusions 525
References 525
Index 528