NEAR-FIELD NANO-OPTICS From Basic Principles to Nano-Fabrication and N ano-Photonics

LASERS, PHOTONICS, AND ELECTRO-OPTICS

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FUNDAMENT ALS OF LASER OPTICS Kenichi Iga

NEAR-FIELD NANO-OPTICS: From Basic Principles to Nano-Fabrication and Nano-Photonics Motoichi Ohtsu, and Hirokazu Hori

OPTICAL-THERMAL RESPONSE OF LASER-IRRADIATED TISSUE Edited by Ashley J. Welch and Martin J. C. van Gernert

THEORY AND APPLICATION OF LASER CHEMICAL VAPOR DEPOSITION Jyoti Mazurnder and Aravinda Kar

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NEAR-FIELD NANO-OPTICS From Basic Principles to Nano-Fabrication and N ano-Photonics

MOTOICHI OHTSU Tokyo Institute of Technology Yokohama. Japan

and

HIROKAZU HORI Yamanashi University Ko{u. Japan

SPRINGER SCIENCE+BUSINESS MEDIA, LLC

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A

AII

No or

Llbrary of Congress CataJoglng-ln-PubJlcatlon Data

Ohtsu, Motolchi. Near-field nano-optics , from basic principles to nani-fabrication

and nano-photonics I Motoichi Ohtsu and Hirokazu Hori. p. cm. -- ILasers, photonics, and electro-opticsl

Includes bibliographical references and index. ISBN 978-1-4613-7192-2 ISBN 978-1-4615-4835-5 (eBook) DOI 10.1007/978-1-4615-4835-5 1. Nanostructure materials. 2. Near-field microscopy. 3. Quantum

optics. 4. Photonics. 1. Hori, Hirokazu. II. Title. III. Series. TA418.9.N36038 1999 621.36--dc21 99-14419

ISBN 978-1-4613-7192-2

1999 Springer Science+Business Media New York Originally published by Kluwer Academic I Plenum Publishers 1999 Softcover reprint of the hardcover 1 st edition 19999

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PREFACE

Conventional optical science and technology have been restricted by the diffraction limit from reducing the sizes of optical and photoruc devices to nanometric dimensions. Thus, the size of optical integrated circuits has been incompatible with that of their counterpart, integrated electronic circuits, which have much smaller dimensions. This book provides potential ideas and methods to overcome this difficulty.

Near-field optics has developed very rapidly from around the middle 1980s after preliminary trials in the microwave frequency region, as proposed as early as 1928. At the early stages of this development, most technical efforts were devoted to realizing super-high-resolution optical microscopy beyond the diffraction limit. However, the possibility of exploiting the optical near-field, phenomenon of quasistatic electromagnetic interaction at subwavelength distances between nanometric particles has opened new ways to nanometric optical science and technology, and many applications to nanometric fabrication and manipulation have been proposed and implemented.

Building on this historical background, this book describes recent progress in near-field optical science and technology, mainly using research of the author's groups. The title of this book, Near-Field Nano-Optics-From Basic Principles to Nano-Fabrication and Nano-Photonics, implies capabilities of the optical near­field not only for imaging/microscopy, but also for fabrication/manipulation/proc­essing on a nanometric scale.

Although a variety of acronyms have been used for the near-field optical microscope/microscopy, e.g., NSOM, SNOM, and PSTM, this book employs the simplest and shortest one, NOM. Chapters 1, 2, 8, and 9 provide detailed theoretical intuitive models based on the concept of interaction-type measurements of short­range electromagnetic correlations by using a spatial/temporal-frequency resonant probe tip. Chapters 3-7 review experimental work.

v

vi PREFACE

We gratefully thank Drs. T. Saiki, R. Uma Mahewari, S. Mononobe, H.lto, K. Kurihara, M. Ashino, M. Naya, H. Fukuda, R. Micheletto, J. D. White (Kanagawa Academy of Science and Technology), M. Kourogi (Tokyo Institute of Technol­ogy), Drs. I. Banno and T. Inoue (Yamanashi University), and Prof. W. Jhe (Seoul National University) for their collaborations. We also extend a special acknowledg­ment to Drs. R. Uma Maheswari, J. D. White, Y. Takiguchi (Japan Science and Technology Corporation), S. Lathi, M. Lawrence, and S. Kasapi (Stanford Univer­sity) for their critical readings and comments on the manuscript. H.H. would like to express his gratitude to Profs. T. Yabuzaki and M. Kitano (Kyoto University) and Prof. K. Kitahara (Tokyo Institute of Technology) for their helpful discussions, and also to Profs. K. Shimoda, T. Sakurai and A. Shimizu for their encouragement. H. H. also thanks T. Matsudo, K. Tsuchiya, and Y. Ohdaira (Yamanashi University) for their assistance and Dr. K. Kobayashi (IBM Japan) for useful comments on the manuscript. Further, We wish to express our special thanks to Dr. L. Nagahara (Phoenix Corporate Research Laboratories, Motorola, Inc.) for his patient reading of the whole manuscript and valuable comments. Finally, we wish to express our gratitude to L. S. Marchand, A. McNamara, and the production staff of Kluwer Academic / Plenum Publishing Corporation for their guidance and suggestions throughout the course of preparation of this book.

Motoichi Ohtsu (Yokohama, Kanagawa)

Hirokazu Hori (Kofu, Yamanashi)

CONTENTS

Chapter 1. Introduction

1.1. Near-Field Optics and Photonics. . . . . . . . . . . . . . . . . . . . . . . .. . . 1 1.1.1. Optical Processes and Electromagnetic Interactions ...... 1

1.2. Ultra-High-Resolution Near-Field Optical Microscopy (NOM) . . . . 4 1.2.1. From Interference- to Interaction-Type

Optical Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2.2. Development of Near-Field Optical Microscopy

and Related Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3. General Features of Optical Near-Field Problems. . . . . . . . . . . . . 10

1.3.1. Optical Processes and the Scale of Interest . . . . . . . . . . . . . 10 1.3.2. Effective Fields and Interacting Subsystems. . . . . . . . . . . . 12 1.3.3. Electromagnetic Interaction in a Dielectric System. . . . . . . 15 1.3.4. Optical Near-Field Measurements. . . . . . . . . . . . . . . . . . . . 20

1.4. Theoretical Treatment of Optical Near-Field Problems. . . . . . . .. 25 1.4.1. Near-Field Optics and Inhomogeneous Waves .. . . . . . . . . 25 1.4.2. Field-Theoretic Treatment of Optical

Near-Field Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 28 1.4.3. Explicit Treatment of Field-MatterInteraction. . . . . . . . .. 32

1.5. Remarks on Near-Field Optics and Outline of This Book. . . . . .. 33 1.5.1. Near-Field Optics and Related Problems. . . . . . . . . . . . . .. 33 1.5.2. Outline of This Book ............................. , 34

1.6. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 35

vii

viii CONTENTS

Chapter 2. Principles of Near-Field Optical Microscopy

2.1. An Example of Near-Field Optical Microscopy. . . . . . . . . . . . . . 43 2.2. Construction of the NOM System . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.2.1. Building Blocks of the NOM System. . . . . . . . . . . . . . . . . 45 2.2.2. Environmental Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . 47 2.2.3. Functions of the Building Blocks. . . . . . . . . . . . . . . . . . . . 48

2.3. Theoretical Description of Near-Field Optical Microscopy. . . . . 50 2.3.1. Basic Character of the NOM Process. . . . . . . . . . . . . . . . . 50 2.3.3. Demonstration of Localization in the Near-Field

Interaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 2.3.4. Representation of the Spatial Localization of an

Electromagnetic Event. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 2.3.5. Model Description of a Local

Electromagnetic Interaction. . . . . . . . . . . . . . . . . . . . . . . . . 55 2.4. Near-Field Problems and the Tunneling Process. . . . . . . . . . . . . . 56

2.4.1. Bardeen's Description of Tunneling Current in STM. . . . . 57 2.4.2. Comparison of the Theoretical Aspects of

NOM and STM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 2.5. References........................................... 61

Chapter 3. Instrumentation

3.1. Basic Systems of a Near-Field Optical Microscope. . . . . . . . . . . . 63 3.1.1. Modes of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.1.2. Position Control of the Probe .......... " . . . . . . . . . . . 69 3.1.3. Mechanical Components. . . . . . . . . . . . . . . . . . . . . . . . . . . 74 3.1.4. Noise Sources Internal to the NOM. . . . . . . . . . . . . . . . . . 75 3.1.5. Operation under Special Circumstances. . . . . . . . . . . . . . . 78

3.2. Light Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 3.2.1. Basic Properties of Lasers . . . . . . . . . . . . . . . . . . . . . . . . . . 82 3.2.2. Characteristics of CW Lasers. . . . . . . . . . . . . . . . . . . . . . . 84 3.2.3. Additional Noise Properties of CW Lasers. . . . . . . . . . . . . 88 3.2.4. Short-Pulse Generation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 3.2.5. Nonlinear Optical Wavelength Conversion. . . . . . . . . . . . . 97

3.3. Light Detection and Signal Amplification. . . . . . . . . . . . . . . . . . . 98 3.3.1. Detector... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 3.3.2. Signal Detection and Amplification. . . . . . . . . . . . . . . . .. 103

3.4. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 111

CONTENTS ix

Chapter 4. Fabrication of Probes

4.1. Sharpening of Fibers by Chemical Etching .................. 113 4.1.1. A Basic Sharpened Fiber. . . . . . . . . . . . . . . . . . . . . . . . . .. 114 4.1.2. A Sharpened Fiber with Reduced-Diameter Cladding. . .. 118 4.1.3. A Pencil-Shaped Fiber. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 119 4.1.4. A Flattened-Top Fiber ............................. 122 4.1.5. A Double-Tapered Fiber. . . . . . . . . . . . . . . . . . . . . . . . . . .. 127

4.2. Metal Coating and Fabrication of a Protruded Probe. . . . . . . . . .. 130 4.2.1. Removal of Metallic Film by Selective Resin Coating .... 132 4.2.2. Removal of Metallic Film by Nanometric

Photolithography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 135 4.3. Other Novel Probes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 139

4.3.1. Functional Probes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 139 4.3.2. Optically Trapped Probes. . . . . . . . . . . . . . . . . . . . . . . . . .. 141

4.4. References ........................................... 141

Chapter 5. Imaging Experiments

5.1. Basic Features of the Localized Evanescent Field . . . . . . . . . . . .. 143 5.1.1. Size-Dependent Decay Length of the Field Intensity ..... 143 5.1.2. Manifestation of the Short-Range Electromagnetic

Interaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 146 5.1.3. High Discrimination Sensitivity ofthe Evanescent Field

Intensity Normal to the Surface. . . . . . . . . . . . . . . . . . . . .. 149 5.2. Imaging Biological Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 152

5.2.1. Imaging by the C-Mode. . . . . . . . . . . . . . . . . . . . . . . . . . .. 152 5.2.2. Imaging by the I-Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 161

5.3. Spatial Power Spectral Analysis of the NOM Image. . . . . . . . . .. 170 5.4. References ............................................ 177

Chapter 6. Diagnostics and Spectroscopy of Photonic Devices and Materials

6.1. Diagnosing a Dielectric Optical Waveguide ................. 179

x CONTENTS

6.2. Spatially Resolved Spectroscopy of Lateral p-n Junctions in Silicon-Doped Gallium Arsenide. . . . . . . . . . . . . . . . . . . . . . . . .. 184 6.2.1. Photoluminescence and Electroluminescence

Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 185 6.2.2. Photocurrent Measurement by Multiwavelength NOM. .. 191

6.3. Photoluminescence Spectroscopy of a Semiconductor Quantum Dot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 196

6.4. Imaging of Other Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 201 6.4.1. Fluorescence Detection from Dye Molecules .......... 201 6.4.2. Spectroscopy of Solid-State Materials . . . . . . . . . . . . . . .. 205

6.5. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 207

Chapter 7. Fabrication and Manipulation

7.1. Fabrication of Photonic Devices. . . . . . . . . . . . . . . . . . . . . . . . . .. 209 7.1.1. Development of a High-Efficiency Probe. . . . . . . . . . . . .. 212 7.1.2. Development of a Highly Sensitive Storage Medium. . . .. 212 7.1.3. Fast Scanning of the Probe. . . . . . . . . . . . . . . . . . . . . . . .. 213

7.2. Manipulating Atoms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 213 7.2.1. Zero-Dimensional Manipulation. . . . . . . . . . . . . . . . . . . .. 214 7.2.2. One-Dimensional Manipulation. . . . . . . . . . . . . . . . . . . .. 216

7.3. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 231

Chapter 8. Optical Near-Field Theory

8.1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 235 8.2. Electromagnetic Theory as the Basis of Treating Near-Field

Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 237 8.2.1. Microscopic Electromagnetic Interaction and Averaged

Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 237 8.2.2. Optical Response of Macroscopic Matter. . . . . . . . . . . . .. 241 8.2.3. Optical Response of Small Objects and the Idea of System

Susceptibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 244 8.2.4. Electromagnetic Boundary Value Problem. . . . . . . . . . . .. 245

8.3. Optical Near-Field Theory as an Electromagnetic Scattering Problem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 255

CONTENTS xi

8.3.1. Self-Consistent Approach for Multiple Scattering Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 255

8.3.2. Scattering Theory in the Near-Field Regime Based on Polarization Potential and Magnetic Current. . . . . . . . . . .. 260

8.4. Diffraction Theory in Near-Field Optics. . . . . . . . . . . . . . . . . . . .. 275 8.4.1. Diffraction of Light from Subwavelength Aperture ....... 275 8.4.2. Kirchhoff's Diffraction Integral and Far-Field Theory . . .. 276 8.4.3. Small-Aperture Diffraction and Equivalent Problem. . . . .. 277 8.4.4. Magnetic Current Distribution and Self-Consistency . . . .. 278 8.4.5. Leviatan's "Exact" Solutions for the Aperture Problem ... 280

8.5. Intuitive Model of Optical Near-Field Processes. , ............ 281 8.5.1. Short-Range Quasistatic Nature of Optical Near-Field

Processes, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 281 8.5.2. Intuitive Model Based on Yukawa-Type

Screened Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 282 8.5.3. Application ofVrrtual Photon Model for Diffraction from

a Small Aperture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 285 8.5.4. Vrrtual Photon Model of NOM ...................... 288 8.5.5. Meaning of the Screened Potential Model and Physical

Meaning of the Virtual Photon. . . . . . . . . . . . . . . .. . . . . .. 292 8.6. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 297

Chapter 9. Theoretical Description of Near-Field Optical Microscope

9.1. Electromagnetic Processes Involved in the Near-Field Optical Microscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 300

9.2. Representation of the Electromagnetic Field and the Interaction Propagator ........................................... , 302 9.2.1. Spherical Representation of Scalar Waves .............. 302 9.2.2. Vector Nature of the Electromagnetic Field. . . . . . . . . . . .. 307

9.3. States of Vector Fields and Their Representations . . . . . . . . . . . .. 316 9.3.1. State of Vector Plane Waves. . . . . . . . . . . . . . . . . . . . . . . .. 316 9.3 .2. State of Vector Spherical Waves. . . . . . . . . . . . . . . . . . . . .. 318 9.3.3. State of Vector Cylindrical Waves .................... 319 9.3.4. Spatial Fourier Representation of Electromagnetic

Fields .......................................... 319 9.3.5. Multipole Expansion of Vector Plane Waves ........... 321

xii CONTENTS

9.4. Angular Spectrum Representation of Electromagnetic Interactions. . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . .. 324 9.4.1. Angular Spectrum Representation of Scattering

Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 325 9.4.2. Meaning of the Angular Spectrum Representation ...... 327 9.4.3. Angular Spectrum Representation of Scalar Multipole

Field and Propagator. . . . . . . . . . . . . . . . . . . . . . . . . . . . •. 329 9.4.4. Angular Spectrum Representation of Vector Multipole

Field and Propagator. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 332 9.4.5. Angular Spectrum Representation of Cylindrical

Field and Propagator.. .. .. . .. . .. .. .. . . .. . . . . . .. . .. 340 9.4.6. Transformation between Spherical and Cylindrical

Representations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 341 9.4.7. Summary: Representations of Electromagnetic Fields

and Transformations between Mode Functions ......... 343 9.5. Near-Field Interaction of Dielectric Spheres Near a Planar

Dielectric Surface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 347 9.5.1. Sample-Probe Interaction at a Dielectric Surface.. .. ... 348 9.5.2. Mode Description of Evanescent Waves of Fresnel . .. . .. 351 9.5.3. Multipolar Representation of Evanescent Modes. . . . . . .. 352 9.5.4. Near-Field Interaction of Dielectric Spheres at a

Planar Dielectric Surface. . . . . . . . . . . . . . . . . . . . . . . . . .. 359 9.6. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 379

Index ....................................................... 381