NEAR-FIELD OPTICS

NEAR-FIELD OPTICS THEORY, INSTRUMENTATION, AND APPLICATIONS

MICHAEL A. PAESLER North Carolina State University Raleigh, North Carolina

PATRICK J. MOYER Brooklyn College of The City University of New York Brooklyn, New York

® AWiley-lnterscience Publication

JOHN WILEY & SONS, INC.

New York • Chichester • Brisbane • Toronto • Singapore

CONTENTS

FOREWORD xi

PARTI. THEORY AND INSTRUMENTATION 1

1 INTRODUCTION TO NEAR-FIELD OPTICS 3

1.1 Imaging / 3 1.2 Spatial Resolution / 5 1.3 The Development of Near-Field Microscopy / 8

1.3.1 The Near-Field Scanning Optical Microscope / 9 1.3.2 Optical Tunneling Microscopes / 15

1.4 Definition of Near-Field Optics / 16 1.5 Outline of the Volume / 16

1.5.1 Theory and Instrumentation / 17 1.5.2 Near-Field Microscopy in Practice / 17 1.5.3 Applications / 17 1.5.4 Related Instruments and Conclusions / 18 References / 18

2 IMAGING 21

2.1 Microscopic Imaging / 21 2.2 Classical Treatment of Imaging / 22

2.3 The NSOM as a Scanned Image Microscope / 24 2.3.1 Illumination Mode / 25 2.3.2 Collection Mode / 26

2.4 The Scanning Process / 27 2.5 Spatial Resolution and NSOM Imaging / 29

References / 31

v

CONTENTS

THE TAPERED OPTICAL FIBER AND OTHER 33 SENSING ELEMENTS

3.1 The Sensing Element as the Heart of the NSOM / 33 3.2 Optics of the Tapered Optical Fiber / 34

3.2.1 NSOM Fiber-Optics / 35 3.2.2 NSOM Taper Optics / 46 3.2.3 Dark-Field NSOM Optics / 53

3.3 Taper Fabrication / 55 3.3.1 Heating-and-Pulling / 55 3.3.2 Etching / 57

3.4 Alternative Probes / 59

3.4.1 Other Waveguides / 60 3.4.2 The AFM Cantilever / 61 3.4.3 Semiconducting Structures / 62 References / 63

NSOM THEORY 67

4.1 General Theoretical Issues / 67 4.2 NSOM Imaging Theory / 69 4.3 The Near-Field Profile / 79

4.3.1 Near-Fields of Simple Structures / 80 4.3.2 Near-Fields of NSOM-Related Structures / 81

4.4 Prospects for the Future Developments in Near-Field Theory / 93 References / 94

NSOM INSTRUMENTATION 97

5.1 Introduction to NSOM Instrumentation / 97 5.2 General SPM Instrumentation / 98

5.2.1 Vibration Isolation / 99 5.2.2 Scanners / 103 5.2.3 Control Electronics and Image Analysis / 106

5.3 NSOM Instrumentation / 108 5.3.1 Light Sources / 108 5.3.2 Collection Optics / 111 5.3.3 Detection / 113

5.3.4 Scanner Design / 114 5.4 Feedback / 117 5.5 Coarse and Fine Tip Approach / 125

CONTENTS vii

5.6 Spectroscopy in the Near-Field / 127 5.7 Additional Design Considerations / 132

5.7.1 Inverted Microscope Design / 133 5.7.2 Dual Transmission/Reflection NSOM / 135 5.7.3 Low-Temperature NSOM / 137 References /140

6 OPTICAL TUNNELING MICROSCOPES 143

6.1 Optical Tunneling Microscopes as Near-Field Instruments / 143 6.2 The Development of Photon Tunneling in Optical Research / 144 6.3 Theory of Operation of the PTM / 146 6.4 Intrumentation and Operation of the PTM / 154

6.4.1 The Transducer and Sample Stage / 154 6.4.2 Illuminator and Objective / 156 6.4.3 Signal Detection, Calibration, and Imaging / 157 6.4.4 Sample Preparation / 158

6.5 Applications, Results, and Conclusions / 158 References / 160

PART II. PRACTICE 163

7 CONTRAST 165

7.1 The Notion of Contrast / 165 7.2 Infomation Transfer for Far-Field Incoherent Illumination / 166 7.3 Information Transfer for the NSOM / 169 7.4 Modulation and Contrast Mechanisms / 172

References / 174

8 INTENSITY 175

8.1 Introduction to Intensity Measurements / 175 8.2 Early Demonstrations of Super Resolution Imaging / 176 8.3 The Tip-Sample Interaction / 186

8.4 Resolution: A Reprise / 192 8.5 Conclusion / 201

References / 201

CONTENTS

9 POLARIZATION 203

9.1 Introduction / 203

9.2 Polarization in the Near-Field / 203 9.3 Obtaining a Linear Polarized State with a Near-Field Probe / 205 9.4 Reflection Mode Polarization NSOM / 207 9.5 Transmission Mode Polarization NSOM / 212 9.6 Conclusion / 217

References / 2 1 8

10 WAVELENGTH 219

10.1 What is Wavelenth Spectroscopy? /219 10.1.1 Optical Spectroscopy of Chemical Systems / 221 10.1.2 Optical Spectroscopy of Solid-State Materials / 222 10.1.3 Optical Spectroscopy of Biological Systems / 223

10.2 Near-Field Spectroscopy Effects / 223 10.3 Early Demonstrations of NSOM Spectroscopy / 224 10.4 Summary / 230

References / 230

11 AMPLITUDE AND PHASE 231

11.1 Amplitude and Phase Measurements / 231 11.2 Interferometric Imaging / 231

11.3 Experimental Setup / 234 11.4 Amplitude and Phase Contrast Images / 234

References / 237

12 TIME 239

12.1 Time as a Contrast Mechanism / 239

12.2 Carrier Lifetimes in Semiconductors / 241 12.3 Single-Molecule Dynamics / 245 12.4 Single-Molecule Lifetimes / 247 12.5 Temporal Effects of Near-Field Fiber Probes / 247

References / 248

13 PLASMONS 249

13.1 The Use of a Plasmon Resonance to Increase Contrast / 249 13.2 Plasma Oscillations and Plasmons / 249

CONTENTS

13.3 Surface Plasmon Resonances of Small Features / 250 13.3.1 Protrusions on a Film / 250 13.3.2 The Tetrahedral Tip / 251

13.3.3 The Magneto-Optic Kerr Effect NSOM / 252 13.4 Surface Plasmon Resonances of Films / 253

References / 254

PART III. APPLICATIONS 257

14 SURFACE CHEMISTRY 259

14.1 Introduction / 259 14.2 Liquid Crystals / 260 14.3 Single-Molecule Detection / 264

14.3.1 Instrumentation for Single-Molecule Detection / 266 14.3.2 Interaction of NSOM Aperture with Molecular

Electric Dipole / 268 14.3.3 Dynamic Investigations of Single Molecules / 269 14.3.4 Spectroscopy of Single Molecules / 276

14.4 Fluorescence of Polymer Films / 282 14.5 Summary / 284

References / 285

15 BIOLOGY

15.1 Introduction /287 15.2 Early Biological Near-Field Imaging / 289

15.3 NSOM Imaging of Single Proteins and Photosynthetic Membranes / 291

15.4 NSOM Chemical Fiber Sensors /293 References / 295

16 MATERIALS SCIENCE

16.1 Materials Science and NSOM / 297 16.2 Low-Temperature NSOM / 297 16.3 Self-Luminous Device and Waveguide Analysis

Using NSOM / 304 16.4 Photoconductivity Measurements Using NSOM / 309

References /311

287

297

CONTENTS

17 INFORMATION STORAGE 313

17.1 NSOM Data Storage / 313 17.2 Magneto-Optics Data Storage / 313 17.3 Solid Immersion Lens / 318

References / 321

18 NONVISIBLE WAVELENGTH INSTRUMENTS 323

18.1 Broadening the Perspective / 323 18.2 Microwave / 324 18.3 Infrared / 325 18.4 Ultraviolet / 331 18.5 x-Rays / 331

References / 3 3 3

PART IV. RELATED TECHNIQUES AND 335 CONCLUSION

19 RELATED TECHNIQUES AND UNUSUAL 337 CONFIGURATIONS

19.1 Complementary Developments / 337

19.2 Unusual NSOM Configurations / 338 19.2.1 The Tunnel NSOM / 338 19.2.2 Vibrating Metallic Tip NSOM / 339 19.2.3 The Wiener Fringe Microscope / 340

19.3 Related Techniques / 341 19.3.1 Near-Field Acoustic Microscopy / 341 19.3.2 Scanning Near-Field Ellipsometric Microscope / 343 19.3.3 The Trapped-Particle Optical Microscope / 344 References / 344

20 CONCLUSIONS AND FUTURE DIRECTIONS 347

INDEX 351