Table of Contents

1 Optical Properties of Plasmonic Materials

1.1 Electromagnetic Waves Propagating through Materials

     1.1.1 Fundamental equations of electromagnetic waves

     1.1.2 Constitutive equations of inhomogeneous media

     1.1.3 Isotropic and anisotropic media

     1.1.4 Constitutive equations of dielectric media

1.2 Electromagnetic Properties of Materials

     1.2.1 Permittivity and permeability

     1.2.2 Loss tangent

     1.2.3 Penetration depth and skin depth

1.3 Optical Properties of Metals

     1.3.1 Free electrons and interband transitions

     1.3.2 Harmonic oscillator model

     1.3.3 Drude model and Lorentz model

     1.3.4 Drude-Lorentz model

1.4 Optical Properties of Dielectric Materials

     1.4.1 Dielectric function of dielectric media

     1.4.2 Kramers-Kronig relation

     1.4.3 Obtaining optical functions from physical observables

1.5 Effective Medium Approach for Composite Nanostructures

     1.5.1 Effective medium theory

     1.5.2 Topologies of metal-dielectric composites

     1.5.3 Lorentz cavity model

     1.5.4 Maxwell-Garnett theory

     1.5.5 Bruggeman medium theory

References

2 Surface Plasmon Polaritons at Planar Interfaces

2.1 Surface Plasmon Polaritons

     2.1.1 Concepts

     2.1.2 Dispersion relation

     2.1.3 Requirements

     2.1.4 Momentum mismatch

     2.1.5 Dispersion relations in special cases

2.2 SPP Propagation Characteristics

     2.2.1 Surface plasmon wavelength

     2.2.2 Surface plasmon propagation length

     2.2.3 Surface plasmon penetration depth

2.3 Excitation of Surface Plasmon Polaritons

     2.3.1 Evanescent waves

     2.3.2 Prism excitation

     2.3.3 Corrugated grating excitation

     2.3.4 Near-field excitation

     2.3.5 Coupling to integrated photonic elements

References

3 Localized Surface Plasmon Resonances

3.1 Localization of Electromagnetic Waves in Nanocavities and Nanoparticles

3.2 Nanoparticles in a Quasi-Static Approximation

     3.2.1 Quasi-static approximation

     3.2.2 Potentials inside the particle and the surrounding medium

     3.2.3 Electric fields inside a particle and surrounding medium

     3.2.4 Resonance surface modes

     3.2.5 Damping the plasmon resonance

3.3 Extinction Efficiency of Nanoparticles

     3.3.1 Extinction efficiency in Mie theory

     3.3.2 Electromagnetic normal modes in Mie resonances

     3.3.3 Extinction efficiency for small spherical particles

     3.3.4 Extinction coefficient for large spherical particles

3.4 Spectral Properties of Localized Surface Plasmons

     3.4.1 Beyond the quasi-static approximation

     3.4.2 Spectrum shifting due to surrounding medium

     3.4.3 Shape-dependent plasmon extinction spectra

3.5 Surface Plasmon Resonance Affinity Biosensors

     3.5.1 Fluorescence enhancement by metal nanoparticles

     3.5.2 Localized surface plasmon resonance sensing

References

4 Extraordinary Transmission through Subwavelength Apertures

4.1 Extraordinary Optical Transmission

     4.1.1 Diffraction through subwavelength apertures

     4.1.2 Extraordinary optical transmission phenomena

     4.1.3 Fano resonance in hole arrays

4.2 Transmission through a Single Aperture

     4.2.1 Transmission properties of an isolated circular aperture

     4.2.2 Polarization transmission of an isolated rectangular hole

     4.2.3 Field distribution inside isolated rectangular aperture

4.3 Transmission through Aperture Arrays

     4.3.1 Transmission spectrum of circular aperture arrays

     4.3.2 Shape and size dependence

     4.3.3 Influence of material properties

     4.3.4 Effective optical properties in homogenous anisotropic films

4.4 Aperture Surrounded by Periodic Corrugations

     4.4.1 Slit aperture surrounded by a groove structure

     4.4.2 Directional emission of an aperture surrounded by slit grooves

     4.4.3 Aperture surrounded by concentric grooves

     4.4.4 Other geometrical aperture arrays

References

5 Surface Plasmon Polariton Waveguides

5.1 Guided Modes in Dielectric and Metal Waveguides

     5.1.1 Plasmonic waveguides

     5.1.2 Symmetric and antisymmetric SPP modes

     5.1.3 General description for a multiple-layer interface

5.2 Dispersion Relation for Plasmonic Waveguides

     5.2.1 Dispersion relation of TM modes

     5.2.2 Plasmon dispersion in insulator-metal-insulator

     5.2.3 Plasmon dispersion in metal-insulator-metal

     5.2.4 Channel plasmon polariton waveguides

5.3 Examples of SPP Waveguides

     5.3.1 Figures of merit for surface plasmon waveguides

     5.3.2 SPP modes in a metallic stripe

     5.3.3 SPP modes in nanowires

References

6 Optical Nanoantennas

6.1 Elements of Optical Antenna Theory

     6.1.1 Radio and optical antennas

     6.1.2 Near field and far field

     6.1.3 Engineering spontaneous emission

     6.1.4 Power dissipation of a quantum dipole

     6.1.5 Reciprocity theorem

6.2 Properties of an Optical Antenna

     6.2.1 Efficiency, directivity, and gain

     6.2.2 Purcell effect and field enhancement

     6.2.3 Strong and weak coupling

     6.2.4 Wavelength scaling

6.3 Examples of Optical Antennas

     6.3.1 Spherical nanoparticle

     6.3.2 Ellipsoid nanoparticle optical antennas

6.4 Field Enhancement Due to Resonance Effects

     6.4.1 Local field enhancement of a nanorod antenna

     6.4.2 Bowtie nanoantennas for strong field enhancement

     6.4.3 Yagi-Uda nanoantennas for radiation emission control

6.5 Nanoantennas for Photodetection and Photovoltaics

     6.5.1 Photon absorption enhancement by plasmonic nanoantennas

     6.5.2 Photodetection with active optical antennas

     6.5.3 Multiple-band plasmonic absorber

6.6 Optical Antenna for Nanoscale Sensor Imaging

     6.6.1 Metallic tip antennas for nanoscale imaging

     6.6.2 Tip-enhanced Raman scattering

References

7 Nanostructure Fabrication and Optical Characteristics

7.1 Fabrication Techniques for Metallic Nanostructures

     7.1.1 General process

     7.1.2 Electron-beam lithography

     7.1.3 Focused ion-beam milling

     7.1.4 Ion-beam etching and reactive ion etching

     7.1.5 Atomic layer deposition

7.2 Large-Scale Nanofabrication

     7.2.1 Nanosphere lithography

     7.2.2 Nanoimprint lithography

7.3 Chemical Synthesis for Metal Nanostructures

     7.3.1 Polyol synthesis process

     7.3.2 Seed-mediated growth

     7.3.3 Light-mediated synthesis

7.4 Optical Nanostructure Characterization

     7.4.1 Near-field optical microscopy

     7.4.2 NanoFTIR for chemical identification in nanostructures

     7.4.3 STEM and electron-energy loss spectroscopy (EELS)

References

Preface

Plasmonic optics - an emerging research field - combines electronics and photonics with nanostructures. It studies the interactions between electromagnetic waves and matter at the nanoscale. The prominent feature of plasmonic optics is the coupling of electromagnetic waves into collective electron oscillations. This peculiar feature enables the localization and enhancement of electromagnetic energy in a novel family of nanodevices, nanoelectronics, and nanosensors. Plasmonics involves many subjects, such as optics, physics, materials, and even chemistry. So far, it has favorable applications in chemical sensors, high-resolution microscopy, photovoltaic cells, biological detection, communication, and medical diagnosis. Each achievement plays a significant role in improving the future.

Federico Capasso, while receiving his 2013 SPIE Gold Medal Award, said, "You can't go wrong becoming a very strong optical scientist because you can work in many different fields." Plasmonics is one such field. Many researchers have devoted themselves to it over the last few decades because it provides a compelling risk and promise. That is what makes science so attractive: we are eager to understand the unknown. In fact, we are attracted by the risk to find the next achievement around the corner.

To fulfill the promise offered by plasmonic optics, this book presents a brief introduction to the theory and applications. The first chapter introduces the optical properties of materials. An elementary description of electromagnetic theory is provided. Noble metals, dielectric materials, and semiconductors are frequently used in plasmonic optics; their optical properties are described in terms of the Drude and Lorentz theories. Although the effective optical properties of nanostructures deviate from those of bulk materials, the penetration depths and skin depths play a crucial role in defining plasmonic properties. The end of the chapter discusses the effective medium theory for composite materials.

Surface plasmon polariton (SPP) is a recurring term that requires a clear definition. In this book, SPPs refer to a collective electron oscillation and the associated wave fields that propagate along a metal-dielectric planar interface. Surface plasmon modes are sometimes used to describe the resonance cases of SPPs. When the electron oscillations occur on the curved surface of nanoparticles, these phenomena are called local surface plasmon resonances (LSPRs) because, in most cases, only the resonance conditions of oscillating charges in nanoparticles are considered. Chapters 2 and 3 address the physical concept and typical applications of SPPs and LSPRs. The scattering and absorption properties of nanoparticles with various geometries are discussed in terms of the Mie theory.

The concepts of SPPs and LSPRs are applied to a series of unusual optical properties/devices: extraordinary optical transmission (OET) through a single aperture or hole arrays (Chapter 4), the waves guiding and confined by the metal-insulator-metal (MIM) and insulator-metal-insulator (IMI) nanostructures (Chapter 5), the radiation/emission enhancement, and the perfect absorption achieved by an optical antenna from visible to infrared wavelengths (Chapter 6). These chapters discuss nanostructures with various geometries for the purpose of achieving plasmonic sensors, including chemical sensors, biosensors, and surface-enhanced spectroscopy.

Chapter 7 briefly introduces the nanofabrication techniques aiming at plasmonic devices. Top-down material-removal methods for elaborate nanostructures, bottom-up synthesis for self-growing nanoparticles, and solution phase methods for assembly geometries are introduced. The optical characterizations of plasmonic nanostructures are briefly reviewed; characterization methods benefit from the significant progress of plasmonic optics and advance its progress in return.

A vast number of applications and various geometries for SPP-enhanced sensing are referenced throughout the text. There is extensive literature contributing to this field. References were selected because of their descriptions of a particular effect or their suitability for a beginner. I would like to thank the authors of the literature cited in this book.

I had to omit a few topics associated with plasmonics due to the scope of this book. These topics include but are not limited to plasmonic cloaking and transformation optics, plasmonic lasers, electromagnetically induced transparency, metamaterials, and metasurfaces; the latter two are huge areas that could be covered in their own texts. Numerical simulation methods are not provided in this book, but interested readers can find them in various available commercial and free software. This Tutorial Text should provide a readable introduction to plasmonic optics with distinct concepts, typical applications, and comprehensive knowledge. A modest amount of primary background knowledge in electromagnetism is sufficient to understand the concepts discussed here. I very much hope that more graduate students and young researchers pursue careers in this fascinating area. Their participation would further enhance the field and help plasmonic optics improve our future life.

Any comments and suggestions are very much appreciated.

Yongqian Li
November 2016