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- Herausgeber: Wiley-VCH GmbH
- Kategorie: Fachliteratur
- Sprache: Englisch
- Veröffentlichungsjahr: 2024
This book focuses on plasmonic nanostructures and their applications, for instance, in catalyis, sensing, spectroscopy, thin-film analysis and optoelectronics.
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
Preface
I Introduction of This Book
I.1 Human Beings Never Stop Exploring Light
I.2 Charming Metal Color
I.3 Natural Development of Plasmonics
I.4 About This Book
Part I: Fundamental and Latest Development in the Plasmonics
1 Theoretical Backgrounds and Advances of Plasmonics
1.1 Introduction
1.2 Drude Model for Free Electron Gas
1.3 Dielectric Function of the Free Electron Gas
1.4 Surface Plasmon Polaritons
1.5 Plasmon at Metal‐Vacuum Interface
1.6 Excitation and Detection of SP
1.7 Surface Plasmon Effects
1.8 Summary of this Chapter
References
2 Dielectric Modification and Fundamental of Plasmonic Nanostructure
2.1 Introduction
2.2 Drude–Lorentz Model of Metal Nanoparticles
2.3 Dielectric Properties of Complex Nanostructures
2.4 Optical Property Analysis of Isolated Nanoparticles
2.5 Numerical Simulation of Optical Properties
2.6 Coupling Nanostructure Assembly with High Sensitivity
2.7 Conclusion
References
3 Advanced Characterizations for Plasmonic Nanostructures
3.1 Introduction
3.2 Optical Property Characterization Technology
3.3 Electron Microscopy
3.4 Conclusion
References
Part II: Precise Preparation of Plasmonic Nanostructures
4 Core–Shell and Porous Nanorods with Hot Spots
4.1 Introduction
4.2 One‐Dimensional Au Nanostructures
4.3 Core–Shell Nanostructures
4.4 Alloy Au/Ag Nanorods
4.5 Porous Nanorods
4.6 Yolk–Shell Nanostructures
4.7 Conclusion and Remarks
References
5 Nanowires for Conductive Films and Electromagnetic Shielding
5.1 Introduction
5.2 One‐Dimensional Metal Nanowires
5.3 Conductive Films
5.4 Conclusion and Remarks
References
6 Normal and Novel Nanoplates for Understanding Growth Mechanism
6.1 Introduction
6.2 General Considerations for fcc Nanoplates
6.3 Au Nanoplates with Novel and Well‐Defined Shapes
6.4 Summary of this Chapter
References
7 Hollow and Open Nanostructures with Enhanced Activity
7.1 Introduction
7.2 Hollow Nanostructures
7.3 Open Nanostructures
7.4 Properties of Au NBP‐Embedded Nanostructures
7.5 Conclusion and Remarks
References
8 Metal–Semiconductor Nanocomposite
8.1 Introduction
8.2 Metal Decorated Semiconductor
8.3 Core–Shell Structure and Properties Modulation
8.4 Conclusion
References
Part III: Applications of Plasmonic Nanostructures
9 Hot Electron Effect on Optoelectronic Device
9.1 Introduction
9.2 Light‐Emitting Device and Modulation
9.3 Hot‐Electron Transfer Induced by Plasmon
9.4 Hot‐Electron Photodetection
9.5 Conclusion
References
10 Applications in Catalysis and Energy
10.1 Introduction
10.2 Electrocatalysis
10.3 Photocatalysis
10.4 Solar Vapor Generation
10.5 Conclusions and Outlook
References
11 Applications in SERS and Sensor
11.1 Introduction
11.2 Typical SERS Substrates
11.3 SERS for Detection and Sensor
11.4 Conclusion and Outlook
References
Index
End User License Agreement
List of Tables
Chapter 3
Table 3.1 Interaction of a light beam with matter and corresponding spectral...
Table 3.2 Interaction of an electron beam with a matter and corresponding el...
Chapter 6
Table 6.1 Density‐functional theory calculations of the surface energy of di...
Chapter 11
Table 11.1 Values of
N
surf
,
I
SERS
,
N
vol
, and
I
NRS
for Au NBP, Au NBP‐embedde...
List of Illustrations
Introduction of This Book
Figure I.1 Concept map for the linear propagation of light through the small...
Figure I.2 Bulk Au, Ag and their nanometer‐sized materials in colloidal stat...
Figure I.3 Cognition attitude towards the plasmonics field.
Chapter 1
Figure 1.1 Dispersion of light in free space (a) and metals (b).
Figure 1.2 Dispersion of transverse electric TE mode and transverse magnetic...
Figure 1.3 Dispersion of SPP at a dielectric‐metal interface. Also plotted i...
Figure 1.4 Schematic diagram and simulation diagram for SPP propagation in m...
Figure 1.5 SP excitation configurations: (a) Kretschmann geometry, (b) two‐l...
Figure 1.6 (a) Wave vector dispersion in the Kretschmann geometry. (b) Typic...
Figure 1.7 (a, b) Scanning electron microscopy (SEM) image of the structures...
Figure 1.8 The schematic diagram of electrically driven plasmonic laser base...
Figure 1.9 (a) Schematic diagram of the working principle of bright visible ...
Figure 1.10 (a) EEL intensity mapping of an Ag particle (energy window: 3.3–...
Figure 1.11 (a) Pictorial sketch of the hot‐carrier generation in an Au/TiO
2
Figure 1.12 (a) Overview of CO
2
methanation.(b) Schematic diagrams of ph...
Figure 1.13 The timescales and mechanism and energy conversion process of LS...
Figure 1.14 (a) Mechanistic representation of H
2
dissociation on the Au nano...
Figure 1.15 Schematic of the integrated dual‐functions of an Ag‐based plasmo...
Figure 1.16 Metal‐to‐semiconductor charge‐separation pathways. (a) Conventio...
Chapter 2
Figure 2.1 Dielectric functions of plasmonic metals. (a) The imaginary part ...
Figure 2.2 The Lorentz sphere scheme applied to cluster matter.
Figure 2.3 The calculated real (a) and imaginary (b) parts of the dielectric...
Figure 2.4 (a) The normalized extinction spectra of AuBP@AuxAg1−x...
Figure 2.5 (a) Theoretical optical absorption spectra of Au NRs using Gans e...
Figure 2.6 (a) Difference grids in FDTD discretization and (b) Yee cell.
Figure 2.7 (a–c) Simulated optical absorption spectra of Au NRs with differe...
Figure 2.8 (a) FDTD calculations of the absorption spectra for Ag nanocubes ...
Figure 2.9 (a) Schematic representation of the nanoparticle dimensions and m...
Figure 2.10 Near‐field two‐photon excitation images of Au nanosphere dimers....
Figure 2.11 (a) SEM images of the core/satellite nanostructures on the Si su...
Figure 2.12 (a, b) SEM images of Au nanoprisms (diameter 150 nm, height 17 n...
Figure 2.13 (a) Enhanced SHG spectra of diffractively coupled periodic array...
Figure 2.14 Change in the LSPR scattering spectra of single AuNS (a) and AuN...
Figure 2.15 TEM images of mono‐dispersed Au NRs (a) for end‐to‐end assembly ...
Figure 2.16 Pictures for Au NRs dispersed in H
2
O and tetrahydrofuran (THF), ...
Figure 2.17 (a) Digital picture of four cycles of end‐to‐end assembly and di...
Figure 2.18 (a) Experimental spectra for side‐by‐side assembly of Au NRs wit...
Figure 2.19 (a) Scattering spectra of nanorod‐nanoparticle bend trimers havi...
Figure 2.20 (a) Experimental and (b) simulated results for the plasmon coupl...
Figure 2.21 (a) Schematic illustration of DNA‐assisted assembly of satellite...
Figure 2.22 (a) Surface charge distribution and electric‐field enhancement o...
Chapter 3
Figure 3.1 Schematic diagram of the optical path for Lambert’s law.
Figure 3.2 Diagram of dual beam UV–vis–NIR spectrophotometer.
Figure 3.3 (a) UV–Vis–NIR spectrum of the typical AgInS
2
flowerlike nanoarch...
Figure 3.4 Some typical colloid photos of Ag and Au nanostructures, and the ...
Figure 3.5 Molecular vibrations and scattering.
Figure 3.6 Energy level diagram of Rayleigh and Raman scattering.
Figure 3.7 Schematic illustration of the difference between normal Raman and...
Figure 3.8 (a) Raman signal of molecules; (b) Raman signal of molecules adso...
Figure 3.9 (a) Tip‐enhanced Raman spectra of brilliant cresyl blue (BCB) dis...
Figure 3.10 (a) SEM and high‐resolution TEM images of Au@SiO
2
and Au@Al
2
O
3
s...
Figure 3.11 Two possible Raman enhancement possesses.
Figure 3.12 SERS applications in different areas.
Figure 3.13 Typical TEM of different ages for observation of Au, Ag nanopart...
Figure 3.14 (a) Diagram of TEM equipment. (b) Bragg diffraction of incident ...
Figure 3.15 One typical SAED pattern of Au nanoplate, showing the fractional...
Figure 3.16 (a) An elephant shadow formed in the sun by three children. (b) ...
Figure 3.17 (a) Diagram of SEM instrument, Formation of secondary electrons ...
Figure 3.18 Arrangement of two detectors and signal operation modes for diff...
Figure 3.19 Element and morphology diagrams of polished aluminum alloy (a, b...
Figure 3.20 Structural and compositional analyses of the [email protected] icosahedr...
Figure 3.21 39 pm STEM resolution demonstrated on GaN[212]; Taken at 300 kV ...
Figure 3.22 Crystal structures of the layered nickelates in the Nd
6
Ni
5
O
16
Ru...
Figure 3.23 Schematic of EELS acquisition in STEM equipped with a Wien‐type ...
Figure 3.24 (a) Dark‐field STEM image of the initial Au@Ag core–shell nanoro...
Figure 3.25 Schematic view of the liquid‐cell setup for
in‐situ
AC‐STE...
Figure 3.26 (a) Schematic of the experimental setup and SEM image of one Au ...
Figure 3.27 Sketch of the experiments and light spectra for a single‐molecul...
Figure 3.28 (a) Sketch of the experiments in which acceptor and Donor pairs ...
Chapter 4
Figure 4.1 HRTEM images and schematic diagrams of ultrafine Au seeds with (a...
Figure 4.2 The preparation process of Au NRs, including three steps: (1) pre...
Figure 4.3 Schematic representation of the proposed key steps of the symmetr...
Figure 4.4 TEM images and photograph of the corresponding aqueous dispersion...
Figure 4.5 (a–e) TEM images of Au NBPs with different aspect ratios. (f) The...
Figure 4.6 Schematic illustration of the synthetic route of Au NR‐ and Au NB...
Figure 4.7 (a, b) Schematic illustration for axial and ending growth of Ag n...
Figure 4.8 TEM images and UV–Vis–NIR spectra of Au NR‐supported core–shell N...
Figure 4.9 TEM images and EDX mapping of fusiform and dumbbell‐shaped Au NR@...
Figure 4.10 TEM images and corresponding UV–vis–NIR spectra of fusiform‐shap...
Figure 4.11 TEM images and UV–Vis–NIR spectra of Au NR@SiO
2
with different (
Figure 4.12 TEM images (a–d) and UV–Vis–NIR spectra (e, f) of different Au N...
Figure 4.13 Schematic illustration of the synthetic route of stable Au NR‐ba...
Figure 4.14 TEM images of Au NRs (a) and Au@Ag core–shell nanocuboids (b) wi...
Figure 4.15 STEM images and elemental maps of Au, Ag, Si, and O of one (Au@A...
Figure 4.16 (a–j) TEM images of Au NBP@Ag NRs with different aspect ratios....
Figure 4.17 UV–Vis–NIR spectra of (a) Au NBPs and the products in the presen...
Figure 4.18 TEM images of Au NBP@Au
x
Ag
1−
x
NRs with different component ...
Figure 4.19 TEM images of (a) Au NBP, and Au NBP@Au
0.4
Ag
0.6
NRs with differen...
Figure 4.20 UV–vis–NIR of (a) Au NBP@Au
x
Ag
1−
x
NRs with different compo...
Figure 4.21 UV–Vis–NIR spectra of Au NBP@Au
x
Ag
1−
x
NRs with different c...
Figure 4.22 Morphology and structural characterization of ultrathin AuAg wav...
Figure 4.23 Schematic illustration showing (a) atoms distribution in thermal...
Figure 4.24 TEM images of (a) Au NRs‐ and Au NBPs‐ supported core–shell NRs,...
Figure 4.25 (a) HAADF‐STEM images of Au NR‐ and Au BP‐supported core–shell N...
Figure 4.26 (a) TEM image of the products by annealing Au NR‐supported core–...
Figure 4.27 TEM images and corresponding UV‐vis‐NIR spectra of core–shell Au...
Figure 4.28 EDX images of alloyed Au–Ag NR obtained by annealing at 400 °C a...
Figure 4.29 Schematic illustration of the synthetic route of P‐AuAg NRs nano...
Figure 4.30 (a) Extinction spectra of Au@Ag NRs (A) and UT‐AuAg NRs (B) and ...
Figure 4.31 (A) Aberration‐corrected HAADF‐STEM image of alloyed P‐AuAg NRs ...
Figure 4.32 Extinction spectra of (a) alloyed AuAg NRs and (c) core–shell Au...
Figure 4.33 Yolk–shell nanostructures and their biomedical applications.
Figure 4.34 (a) Schematic illustration of the generation process of AuNR@
TiO
...
Chapter 5
Figure 5.1 (a) The number of publications containing the keyword “nanowire” ...
Figure 5.2 Solution‐phase synthesis of Ag NWs. (a) SEM image of a random ass...
Figure 5.3 Schematic diagram illustrating the fabrication of the Ag NWs.
Figure 5.4 (a) Diameter histogram and (b–e) SEM images of the products obtai...
Figure 5.5 Schematic illustration of NW evolution from the 1D Ag NWs.
Figure 5.6 (a) Schematic image of the formation mechanism of Cu nanowires wh...
Figure 5.7 Schematic of the formation mechanism of Cu nanowires. The Ni
2+
...
Figure 5.8 Schematic illustration of NW evolution from the Cu NWs and typica...
Figure 5.9 Schematic illustration of NW evolution from the Cu NWs.
Figure 5.10 Schematic illustration of NW evolution from the 1G Cu NWs.
Figure 5.11 (a, b) TEM images of Au UNWs and the synthesis scheme of the ori...
Figure 5.12 (a) A bent Cu NWs film completing an electrical circuit with a b...
Figure 5.13 Photographs of Ag NW‐based films prepared through (a) Mayer‐rod ...
Figure 5.14 (a) Schematic diagram illustrating the fabrication of PET/Ag NW/...
Figure 5.15 Plot of the sheet resistance versus time for films of Ag NWs, Cu...
Figure 5.16 (a) Optical transmittance spectra of the PET/Ag NW/PMMA FTCFs wi...
Figure 5.17 (a) Schematic illustrating the synthetic process of Au NBP@AgPt ...
Figure 5.18 (a) SE
R
and SE
A
of the PET/Ag NW/PMMA FTCFs at different Ag NW a...
Figure 5.19 Thermal IR images (left) and photographs (right) of gloves fabri...
Chapter 6
Figure 6.1 (a) Calculation of anisotropicity value (α was defined in the ins...
Figure 6.2 (a–e) TEM images of Au nanoplates with increasing edge lengths. (...
Figure 6.3 (a–f) TEM images of the triangular Ag nanoplates with different e...
Figure 6.4 Au and Ag nanoplates were obtained by the hydrothermal method. (a...
Figure 6.5 The bimodal growth and schematic illustration of the photochemica...
Figure 6.6 Proposed growth mechanisms and schematic illustration for the for...
Figure 6.7 Schematic illustration for the formation of (a) triangular nanosh...
Figure 6.8 The general view of Au NRs and nanoplates is obtained in the abse...
Figure 6.9 Characterization of Au nanoplate with a nanopore structure. (a) T...
Figure 6.10 Primary chemical reactions involved in the photochemical synthes...
Figure 6.11 The size‐controlled Ag nanoplates by the incident light waveleng...
Figure 6.12 Structural characterization of the triangular Ag nanoplates. (a)...
Figure 6.13 (a) Schematic illustrating how intrinsic stacking faults along [...
Figure 6.14 (a) Schematic illustrating the growing process through atom migr...
Figure 6.15 (a) TEM image and intense plasmon resonances of Cu nanoplates vi...
Figure 6.16 FE‐SEM images of Au nanoplates obtained from different polyol pr...
Figure 6.17 TEM images of the obtained Au nanoplates show the new and well‐d...
Figure 6.18 UV/Vis–NIR absorption spectra of (a) samples during the preparat...
Figure 6.19 (a) XRD patterns of the Au nanoplates with hexagonal and star‐li...
Figure 6.20 (a) Atoms arrangement and growth directions of (111) plane. (b) ...
Figure 6.21 TEM images for two kinds of shape transformations from shield‐li...
Chapter 7
Figure 7.1 Model of a nanocube, nanobox, nanocage, and nanoframe in three di...
Figure 7.2 Schematic illustration of two protocols that rely on the carving ...
Figure 7.3 Schematic illustration showing the fabrication of cubic nanoframe...
Figure 7.4 Schematic illustration showing the formation of an A–B alloy nano...
Figure 7.5 Schematic illustration showing the fabrication of nanoframes made...
Figure 7.6 Schematic illustration showing the use of a preformed metal nanof...
Figure 7.7 (a) Schematic illustration of the structure evolution based on th...
Figure 7.8 (a) The three major steps involved in the synthesis of Pd‐Rh core...
Figure 7.9 Summary of bimetallic nanoframe structures via solvothermal route...
Figure 7.10 Schematic diagram of the synthesis of open nanostructures.
Figure 7.11 (a) Schematic synthesis procedure for Au/Ag alloy YS NPs, (b) TE...
Figure 7.12 Structure and composition analysis of the Au/PdAg yolk/shell nan...
Figure 7.13 Au NBP‐embedded ultrathin metal (Au, Pd, Pt) nanoframes. (a) Sch...
Figure 7.14 (a) TEM image of Au NBP@AgPd nanostructure samples. (b) Extincti...
Figure 7.15 (a) Schematic illustrating the synthetic process of Au NBP@AgPt ...
Figure 7.16 (a–f) TEM images of the Au NBP‐embedded Au NFs and Au NF@Pd arra...
Figure 7.17 (a) HRTEM image of Pd arrays on Au NFs. (b) SAED image of the co...
Figure 7.18 Shape evolution with the pH values. (a, f, k) TEM images of the ...
Figure 7.19 Schematic illustrating the proposed deposition mechanism of Au a...
Figure 7.20 Some typical colloid photos of Ag and Au nanostructures, and the...
Figure 7.21 (a) UV–Vis spectra taken from aqueous suspensions of the structu...
Figure 7.22 (a) Extinction spectrum of (up to bottom: A–D) 55.5 ± 6.3 nm Pd ...
Figure 7.23 FDTD simulations. (a) Schematics of the simulation models. (b) S...
Figure 7.24 FDTD simulations. (a) Schematics of the models used in the simul...
Chapter 8
Figure 8.1 Schematic unit cell of TiO
2
polymorphs: (a) Rutile, (b) Anatase, ...
Figure 8.2 Schematic illustrating the hybrid structure and TEM images. (a, b...
Figure 8.3 (a) Schematic image of the fabrication of an arrays of ZnO nanoro...
Figure 8.4 Crystal structures of orthorhombic (a) and cubic (b) metal halide...
Figure 8.5 (a) Illustration of the synthetic strategy to modulate the crysta...
Figure 8.6 (a) Schematic of formation process of Ag‐CsPbBr
3
hybrid NCs. (b) ...
Figure 8.7 (a–c) The CsPbBr
3
QDs synthesized with different solvent. (d) The...
Figure 8.8 (a–c) TEM, high‐resolution TEM and FFT image of the CsPbBr
3
QDs. ...
Figure 8.9 (a) Schematic illustration of the
in‐situ
synthesis and ass...
Figure 8.10 (a) Schematic representation of the synthetic procedures for the...
Figure 8.11 (a) Synthetic Process of Pd@Ag@sSiO
2
@mSiO
2
‐DihBen/DOX Nanocompos...
Figure 8.12 (a) The diagram of the synthesis process of the AuNBP‐Pt@TiO
2
na...
Figure 8.13 (a) TEM images of Au@TiO
2
and Au@TiO
2
‐Au core‐shell structure. (...
Chapter 9
Figure 9.1 (a) SEM image of the device; (b) schematic diagram of tunneling j...
Figure 9.2 (a) Schematic diagram of four devices; (b, c) the light emitted i...
Figure 9.3 (a) Schematic diagram of nanorod arrays; the evolution of emissio...
Figure 9.4 (a) The emission micrograph; (b) emission spectrum of intraband t...
Figure 9.5 (a, b) Schematic diagram of charge separation under different mec...
Figure 9.6 (a) SEM image of grating and cone fabricated on an octagonal pyra...
Figure 9.7 (a) TEM image of Au/Cu‐doped ZnO nanowire inserted with HRTEM ima...
Figure 9.8 (a) Micrographs of bright visible light emitting from an electric...
Figure 9.9 (a) Schematic illustrating the cross section of the laser device ...
Figure 9.10 (a) Schematic diagram of hot electron generation and interaction...
Figure 9.11 (a) Optical microscope image of the device; (b) photoresponse of...
Figure 9.12 (a) Schematic of the chiral plasmonic metamaterial; SEM images o...
Figure 9.13 (a) Schematic diagram of the device architecture; (b) transient ...
Figure 9.14 (a) Schematic diagram of the planar hot‐electron photodetector; ...
Figure 9.15 (a) Schematic illustration, SEM image and photocurrent image of ...
Figure 9.16 (a) Schematic illustration, energy band diagram and cross‐sectio...
Figure 9.17 Schematic diagram (a) and SEM image (b) of the gold grating; (c)...
Chapter 10
Figure 10.1 Size effects on nanoparticle‐based electrocatalysts. (a) Mass‐sp...
Figure 10.2 Crystalline structure effects on nanoparticle‐based electrocatal...
Figure 10.3 Electrochemical characterizations by RDE in 0.1 M HClO
4
of Pt
x
Ni
Figure 10.4 Influence of surface morphology and electronic surface propertie...
Figure 10.5 Performance evolution of shaped PtNi nanoparticles.
Figure 10.6 Nanostructure effects on activity and selectivity of Au catalyst...
Figure 10.7 CV curves of commercial Pd/C, Au NBP@Pd array, Au NF@Pd and Au N...
Figure 10.8 Simulated mass‐transport corrected Tafel plots for a rotating di...
Figure 10.9 Excitation and decay mechanisms of LSPR on the metal surface: (a...
Figure 10.10 (a–c) Metal‐to‐semiconductor charge‐separation pathways.(d)...
Figure 10.11 (a) Photocatalysis schematic diagram and energy band diagram; (...
Figure 10.12 Plasmon‐driven O
2
dissociation and oxidation reactions. (a) SEM...
Figure 10.13 (a) Plasmon‐driven N
2
fixation over AuRu catalyst. (b) STEM and...
Figure 10.14 (a) Temperature gradient model of the catalyst bed and the equa...
Figure 10.15 (a) Schematic of flexible thin‐film black gold membrane consist...
Figure 10.16 (a) Schematic of hybridized plasmonic structure to enhance sola...
Figure 10.17 (a) Schematics of the self‐floated solar evaporator based on th...
Chapter 11
Figure 11.1 (a) Schematic of the SERS study using Ag nanocubes hierarchical ...
Figure 11.2 (a) Raman spectra of 2‐MPy on Au nanostars, nanorods and Au nano...
Figure 11.3 (a) Schematic representation of the SERS working principle for a...
Figure 11.4 (a) Raman spectra of MBA‐labeled multilayered Au nanoshells and ...
Figure 11.5 Schematic illustration on the synthesis process of P‐AuAg NRs (i...
Figure 11.6 (a) TEM images of the prepared Au NC‐AuNS dimers, (b) UV–Vis ext...
Figure 11.7 (a) Typical Raman spectrum of defect‐containing graphene measure...
Figure 11.8 (a) Schematic illustration of detection of organic molecule by u...
Figure 11.9 Raman spectra of 4‐NTP attached on Au@Ag core‐shell NR, solid Au...
Figure 11.10 (a) Schematic diagram for the reduction of 4‐NTP to 4‐ATP. (b) ...
Figure 11.11 (a) schematic illustrating of the oxidation of TMB by H
2
O
2
and ...
Figure 11.12 (a) The normalized extinction spectra of AuBP@Au
x
Ag
1
x
NRs (
x
: 0....
Figure 11.13 Two Au colloidal methods for home pregnancy test and 2019‐ncov ...
Guide
Cover
Table of Contents
Title Page
Copyright
Preface
I Introduction of This Book
Begin Reading
Index
End User License Agreement
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Plasmonic Metal Nanostructures
Preparation, Characterization, and Applications
Caixia Kan
Author
Prof. Caixia KanNanjing University of Aeronautics and Astronautics29 Yudao StreetQinhuai DistrictNanjingChina210016
Cover Image: Courtesy of Caixia Kan
All books published by WILEY‐VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
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Preface
In nanophotonics, plasmonics are primarily concerned with the manipulation of light at the nanoscale based on the properties of propagating and localized surface plasmons. Plasmons can turn impossibility into reality through modulating the energy flow, trapping light, and injecting hot electrons for semiconductors. Rich phenomena related to plasmonics have inspired practical uses in many technologies. You may find out why colloidal gold is more precious than bulk pretty gold. You will understand that nanogold does not glitter but that its future looks bright.
This book is mainly focused on noble metal nanostructures. Nanometer‐sized particles have existed more than 15 centuries, decorated in historical art of the Lycurgus glass cup, although people could not recognize them at that time. Mie’s electromagnetic theory, derived from Maxwell’s equations 100 years ago, can be applied to explain the color of colloidal metals. The term plasmon was initially proposed by Pines and Bohm in 1952. After a period of tepid development, plasmonics got a mighty rebirth after the demonstration of surface‐enhanced Raman scatting (SERS) in the 1990s. As a “hot” academic direction, plasmonics has expanded and penetrated into various interdisciplinary research fields in the past two decades, involving materials science, optoelectronics, analytical chemistry, energy, and biomedicine. For the methodology and material fabrication, the advanced characterization, precise growth, and tunable properties of plasmonic metal nanostructures have also attracted tremendous attention.
There are many outdated and latest reviews about the precise preparation, characterization, and application of plasmonic nanostructures. To contribute to plasmonics, we need many references to go beyond our research work. I’m extremely grateful to all the members of our group for their contribution to the chapters of this book One striking feature of the book is that more than half of the chapters come from our recent research work.
Plasmonic nanostructures provide the fundamental basis and practical device for rapid sensing and detection of chemical and biological objects, such as colloidal gold, which is applied in pregnancy tests in family planning and the 2019 novel coronavirus infection. Many of the techniques and concepts described in this book will come true in the near future. Ideally, readers will be inspired to improve the methods described here or even to develop fundamentally new methods.
This book was compiled with a lot of newly published references and books. There are inevitably some improper descriptions and errors; any criticism and corrections are welcome.
Basely, Jun. 2023Nanjing
Caixia Kan
IIntroduction of This Book
I.1 Human Beings Never Stop Exploring Light
As an important branch of physics, optics is an important foundation for the development of science and technology. According to the historical records in the ancient Chinese book, Mozi did the first small hole imaging experiment about 2500 years ago and explained the inverted standing image using the linear propagation of light, as indicated by Figure I.1 for the concept map.
Throughout the history of the Nobel Prize over one hundred years, there have been more than 40 achievements, about 40% of physics Awards, related directly or indirectly to light. Since the 1960s, the development of laser technology has brought great changes to industries such as industry and medical treatment. Optics brings new development opportunities to other fields. Particularly, two Nobel Prizes in chemistry (1999 and 2014) are also related to optics. They are breakthrough contributions of femtosecond spectroscopy used in chemical reactions and super‐resolution optical microscopes.
According to the diffraction of light in Optics, we know that the resolution of optical instruments is dependent on the size of the circular screen and circular hole. When the focal length of the lens and the size of the lens are in the same order, the energy of Airy spot produced by parallel light diffracted by the convex lens is focused on the size equivalent to wavelength scale, let alone the fact that the focal length of the lens is usually larger than the size of the lens. Therefore, in the field of optical imaging, the diffraction limit of light limits the size of the focusing region when we focus the light field with a convex lens, which in turn limits the imaging accuracy and resolution of optical microscopy.
How can we improve the resolution of imaging? There are two extreme directions, radio telescope and electron microscope, in improving the imaging resolution from the Optics principles. They are now being used respectively to observe distant stars and study the structure of tiny substances such as viruses and atoms. Microscope and telescope are two expensive imaging technologies, enabling us to know the world to the boundless large and infinitesimal region.
In the Nano Era, nanotechnology has penetrated many fields of national economic and social development. With the development of electron microscopy and micromachining, understanding of the material properties and device construction are also in the advance of micro direction. Internationally, a series of basic research projects and major engineering plans have been carried out in the design and development of new photoelectric devices with high performance and high integration. With the development of nano‐optics and optoelectronics, significant progress has been made on the nanometer‐sized devices with the assistance of electron microscopy and micromachining. At the same time, the development of high‐performance micro devices also depends on the preparation of new functional structures and modification of existing materials. Nowadays, materials with desired properties are in great demand, and they are more or less related to the optical properties of materials in small sizes. For example, information and data storage require the medium to meet larger storage density and higher transmission speed. In the biomedicine field, it is required that bacteria and viruses can be quickly detected with high efficiency. And drug molecules can load and release intelligently under irradiation. In terms of energy, we should make full use of solar radiation as much as possible and effectively produce new clean energy sources.
Figure I.1 Concept map for the linear propagation of light through the small hole.
What new effects and phenomena will be discovered during the interaction between light and matter or materials on the microscopic scale? Here, we will start the story of the interaction between light and matter from the color of metals in different sizes.
I.2 Charming Metal Color
Do you know the color of gold (Au)? Yes, of course, we do know the glitter of BRICs wealth, as shown in Figure I.2. We are very familiar with some metals with specific colors, such as golden gold and silvery silver (Ag). Can you imagine the Au BRICs are the same materials as the red colloidal matter dispersed in the inserted two flasks? Do you believe the Ag coin is the same as the black powder on the plate? Moreover, it is known that the row of colored dispersions are the Au/Ag mixing particles of various ratios. Why do the metals present so many puzzling colors?
Figure I.2 Bulk Au, Ag and their nanometer‐sized materials in colloidal states.
Source: The colloid product is from the website: Zhongke Keyou/https://www.zhongkekeyou.cn//last accessed July 14, 2023.
The optical properties of materials are related to the basic principles of solid‐state physics, including the energy band structure inter‐ and intra‐band transition. Here, we briefly describe the color of the bulk metals. There are a large number of electrons that can move freely in metals, forming an electron sea. The collective electrons, titled plasma, respond to the electromagnetic field, resulting in a plasma frequency far greater than that of visible light. Therefore, bulk metals can reflect visible light and form metallic luster. From the view of energy band theory, metals are zero band gaps due to the overlap of valence and conduction bands. The electrons excited by light absorption jump to higher unoccupied energy levels above the Fermi surface, generating photocurrent, which rapidly discharges to emit photons of the same wavelength. As a result, the absorbed light is immediately emitted to the metal surface. That is why a thin metal coating has high reflection. Due to the special electron arrangement of d‐orbit relative to the outer s‐orbit for Au and Cu metals, they can selectively absorb green light, exhibiting golden and red colors.
As for the metals in small nanometer sizes, their physical and chemical properties are different from those of the bulk metals and atomic states. The photoelectric characteristics can be described by the property of the dispersive medium, absorbing and scattering electromagnetic waves of specific bands. Therefore, different colors can be achieved if they strongly absorb specific visible light.
There is a legendary story about one magic Lycurgus cup collected in the British Museum from ancient Rome related to the Au and Ag nanoparticles. Actually, the history of Au nanoparticles can be dated back to the sixteenth century. It is said that Paracelsus (1493–1541) a Swiss chemist, prepared “drinking gold” to treat mental illness. Then, in 1857, Faraday (1791–1867), a British scientist, studied the wonderful color of ultrathin gold leaf under light and also discovered that colorless liquid turned to red when extremely thin Au tablets were dispersed in water. As an experimental physicist, Faraday did many experiments to reduce gold chloride precursor solution with phosphorus and obtain ruby‐colored liquid. In the case of the matter state in a colored liquid, he found a clear beam through the liquid by irradiating the liquid with a beam of light. This effect is known as the Dindal phenomenon for colloids with light irradiation, which is an experimental method for directly distinguishing colloids from solution. Then, 50 years later, the scattering theory of light by small particles was established by Mie by solving Maxwell’s equations. The color of Au nanoparticles colloid is theoretically explained by low reflection and strong absorption for light in different visible bands due to the dielectric properties of nanometer‐sized metals. With the development of colloidal chemistry and optical characterization technology, it is well known that the response wavelength and intensity of particles to light are closely related to their morphology, size, composition, aggregation state, and environmental medium. You can achieve various colorful metal nanoparticle colloids.
I.3 Natural Development of Plasmonics
Unlike conventional optics, plasmonics enables unrivaled concentration of optical energy well beyond the diffraction limit of light. The physical mechanism behind this striking functionality is the excitation of surface plasmon polaritons. Along with the ongoing efforts and development of scientific technologies, it is important to find and synthesize better plasmonic materials. Another strategy relies on hybrid photonic‐plasmonic devices by coupling plasmonic nanostructures to resonant optical elements. It is confirmed that nanostructures and newly developed plasmonics are two effective methods for light diffraction limitation. Plasmonics is a scientific branch of photonics involving the study of the localization, propagation and guidance of surface plasmons to manipulate light in desired structures of different dimensions. For the nanometer‐sized metals, such as Au, Ag, Cu, and Al, they are also titled “plasmonic metals” in many reports. Surface plasmons can realize a series of unique optical properties. Based on the resonance effect of surface plasmon, the electromagnetic field can be localized in the subwavelength scale, forming a booming new field in nanophotonics. It is widely studied and applied in the fields of information transmission, optical sensing, photoelectric detection, display and so on. It is highly evaluated that “Nanogold does not glitter, but its future looks bright.”
Surface plasmon involves conducting surface plasmon and local surface plasmon. Their properties are both closely related to materials, in which the concentration of free electrons (carrier of semiconductor), mobility and the damping by interband transition are three main factors. Although conducting surface plasmon can be used to fabricate novel subwavelength waveguides, the transverse propagation distance is not only determined by the electron’s Ohmic loss, but also limited by the dispersive property. It cannot be directly excited by light incident on the metal surface because of wave vector mismatch. In order to excite the surface plasmon, additional structures or devices must be applied to achieve the wave vector matching conditions.
Compared with conducting surface plasmon, it is relatively easy to excite the localized surface plasmon of metal nanostructures. In fact, we know that a convex lens can focus sunlight for local heating. Similarly, if the light energy is focused on a scale much smaller than the wavelength, it can not only produce a strong field but also greatly improve the resolution of an optical microscope. On the other hand, this localization can significantly enhance the interaction between light and matter, which is similar to the nonlinear effect of macro media under laser irradiation. The nonlinear optical effect of strong field will induce many unique physicochemical properties. How do we further focus the light field in the microscopic size? Surface plasmon provides an effective solution.
Localized surface plasmonic nanostructures can efficiently collect light propagating in free space and converge it to nanoscale hotspots in the near field region, enabling efficient excitation of molecules. Conversely, spectra information about molecules in the hotspots can be broadcast to far fields. This process is accompanied by the enhancement of light absorption, radiation, scattering, light force resonance migration and photo‐thermal effects. The rich phenomena associated with localized surface plasmonic nanostructures have resulted in a series of applications in many fields. At the same time, the complexity of its behavior also brings challenges to physics. Thus, confronting this reality spurred many new directions in the field of plasmonics; research on plasmonics involves several development stages, like the Kubler‐Ross grief cycle.
Figure I.3 Cognition attitude towards the plasmonics field.
I.4 About This Book
The book is compiled in a combination of teaching work with the research of the authors’ group in the past two decades. Based on the plasmonic metal nanostructures, the optical effects of plasmon, precise preparation, properties, and applications of different plasmonic nanostructures will be presented. We first arrange the progress in surface plasmon physics to understand the common problems of plasmon nanostructures and updated characterization technologies. The second feature of this book focused on the frontier progress in plasmonics with emphasis on the structure‐dependent performance and applications in photoelectron, sensor and energy issues Chapter 9 highlights the application of the plasmon hot electron effect in semiconductor micro and nanodevices that were carried out in our research group in recent years.
There are many physical laws or mechanisms to be revealed in the optoelectronic research of metal nanomaterials. So far, there is no reliable physical explanation for many problems and effects in the complex optical response and interaction in the nanometer‐size region. The observed significant enhancement and modulation processes of various transitions under a strong light field need to be further discussed comprehensively and systematically.
Some of the chapters were collaborated by the members from author’s research group. Prof. Shuiyan Cao collaborated Chapter 3. Chapter 4 was co‐authored by Dr. Yuan Ni, Dr. Shanlin Ke, and Prof. Haiying Xu. Prof. Xingzhong Zhu and Dr. Juan Xu completed Chapter 5 and Chapter 7. Dr. Changshun Wang collaborated Chapter 6. Dr. Tingcha Wei collaborated Chapter 8. Prof. Junfeng Lu contributed to Chapter 9. Chapter 10 and Chapter 11 were collaborated by Dr. Yuan Ni and Dr. Juan Xu.
In the process of editing this book, a large number of references and literature have been cited. We only list the main references and books with great thanks. With the never‐ending research proceeding, some viewpoint descriptions and conclusions also need to be revised. Thanks to the readers. We apologize for errors and would be thankful for suggestions and corrections if any.
Part IFundamental and Latest Development in the Plasmonics
1Theoretical Backgrounds and Advances of Plasmonics
The field of nanoplasmonics is young but rich in phenomena that have inspired practical uses in physics, biomedicine, environmental monitoring, and national security
1.1 Introduction
When light irradiates on a solid materials, two kinds of electrons excitation will be formed in the materials. One is electron‐hole pair excitation, which is called exciton. The other is the collective oscillation of electrons, which is known as plasmon. In physics, plasmon is a quantum of plasma oscillation that can be considered as a quasiparticle. Thus, plasmons are collective (a discrete number) oscillations of the free electron gas density [1, 2]. As a new type of exciton formed by the interaction between light and condensed matter, plasmon‐related topic has become focus research in the frontier fields of micro‐nano photonics. Ideally, plasmon is easy to excite without decay. However, all the materials exist in a certain medium environment, particularly for the low dimensional structure with rich surface and interfaces. When the dimensions of materials is comparable to the mean path of free electrons, Landau damping becomes the dominant loss source in plasmonics.
For the well‐known metals, such as gold (Au) and silver (Ag), plasmons of these metals have significant spatial confinement and propagation loss due to the strong Landau damping effect and the scattering between plasmon and phonon [3]. In this chapter, some basic theory and experimental advances about plasmon will be presented, involving an overview of plasmon, dielectric function, propagation behavior, excitation and applications of surface plasmon.
1.2 Drude Model for Free Electron Gas
As one of the most basic models of solid physics, Drude (Drude‐Lorentz) model described that the electrons in the metal are free around the fixed ion solid and dispersed in the whole space of the metal, forming the so‐called free electron gas [4]. The physical significance of the excitation at ωp can be understood by considering the collective longitudinal oscillation of the conduction electron gas versus the fixed positive background of the ion cores in a plasma slab. To visualize a plasmon oscillation, it can be imagined that a metal was placed in an external electric field. A collective displacement of the electron cloud by a distance x leads to a surface charge density σ = ± neex at the slab boundaries (ne is number density of electrons). This establishes a homogeneous electric field E. Thus, the displaced electrons experience a restoring force, and their movement can be described by the equation of Newtonian motion. If the electric field is removed, electrons oscillate back and forth at the plasma frequency until the energy is lost in some kind of resistance or damping. Inserting the expression for the electric field, we get the motion function (ε0 is electric permittivity or dielectric constant of vacuum).
Equation (1.1) can also be expressed by , in which plasmon vibrates at the same plasma frequency (ωp) with . ωp is the plasma frequency of bulk materials. It exists in metals, semiconductors and insulators. But it cannot be excited nor can be observed by transverse light wave.
The plasma frequency ωp can thus be recognized as the natural frequency of a free oscillation of the electron sea. The quanta of these charge oscillations are called plasmons (or volume plasmons) to distinguish them from surface and localized plasmons, which will be discussed in the next part. For most metals, the ωp is in the ultraviolet regime (∼1016 Hz), depending on details of the electrons density (ne) and band structure. Light with frequencies less than ωp will be reflected by the metals because the electrons in the metals screen the electric field of the light. If the light with frequencies above ωp, the light will be transmitted through the metals because the electrons in the metals cannot respond fast enough to screen it. For most metals, the ωp is in the ultraviolet region, making them shiny (reflective) in the visible range. Some metals, such as Cu and Au, have electronic interband transitions in the visible range, whereby specific light energies (colors) are absorbed, yielding their distinct color.
Due to the longitudinal nature of the excitation, volume plasmons do not couple to transverse electromagnetic waves. Plasmons can only be observed when high‐speed electrons pass through a metal film or photons are reflected on the surface of the film. Another consequence is that their decay occurs only via energy transfer to single electrons, a process known as Landau damping.
Although Drude model is one classical free electron theory with Boltzmann distribution law under four approximations of independent electron, free electron, collision hypothesis and relaxation time, it can be well applied to explain the physical mechanism of surface plasmon and many experimental phenomena. Then the revised Drude‐Sommerfeld model was proposed by taking Fermi‐Dirac distribution law of quantum mechanics into Drude model.
1.3 Dielectric Function of the Free Electron Gas
For the materials in bulk, film or low dimensions, dielectric function is one important parameter in describing the photoelectronic properties of these structures. For some of the noble metals, interband effects already start to occur for energies of 1 eV. As examples, the real part (εr) and the imaginary part (εi) of the dielectric function for Au and Ag and Drude model fits to the data [5]. Clearly, this model is not adequate for describing either εr or εi at high frequencies. For the case of Au, its validity breaks down at the boundary between the near‐infrared and the visible region.
With introduction of damping coefficient (γ), electron movement under the irradiation of electric field (ω) can be described by the equation of motion:
According to the polarization of dielectric D = ε0(1 + χ)E = ε0εE, the polarization can be achieved.
P describes the electric dipole moment per unit volume inside the material, caused by the alignment of microscopic dipoles with the electric field. The linear relationship between D and E is often implicitly defined using the dielectric susceptibility χ, particularly in quantum mechanical treatments of the optical response. The linear relationship between D and E via:
Here the dielectric property as a function of frequency can be described as:
Then we can get real and imaginary parts of dielectric functions , . Therefore, the refractive index of electrolyte is expressed in the form of . Here, n is refractive index coefficient, indicating the permittivity εr = n2 − k2. k is extinction coefficient related to the conductivity of the medium (2nk = σ/ωε0). k presents the material loss during the relaxation (or Landau damping), in which the polarization cannot keep up with the change of external high‐frequency electric field. Under the conditions that ω ≫ γ or weak damping γ = 0, Eq. (1.6) can be written:
It can be taken as the dielectric function of the undamped free electron plasma. γ > 0 leads to damping of transmitted wave.
In general, ε(ω) = εr (ω) + εi (ω) complex‐valued functions of frequency ω. ε can be experimentally determined for example via reflectivity studies and the determination of the complex refractive index . As defined , is imaginary for ω < ωp. A material with negative dielectric permittivity does not support propagation of electromagnetic waves; instead the electromagnetic field decays inside the materials with a certain depth and most of the incident energy is reflected. This behavior is the characteristic of metals, where the depth is typically around tens of nanometers. For this case, there is a strong interaction between metal and incident electromagnetic wave, known as absorption and scattering in the following parts of this chapter and Chapter 2.
Reflectivity of metal can be expressed by , showing that metals have high reflectivity. Then is positive for ω > ωp, and metal is only a conventional dielectric material for incident light.
For transverse waves, K · E = 0, yielding the generic dispersion relation:
From Eqs. (1.7) and (1.8), we can get the dispersion relation of volume plasmon . It is clear that this value is always larger than that in free space, as shown in Figure 1.1.
Figure 1.1 Dispersion of light in free space (a) and metals (b).
As it is discussed above, is real in value for ω > ωp, while is imaginary for ω < ωp, and , leading to rapid decay of electromagnetic waves in the material. The skin depth is defined as , which determines whether the electromagnetic wave can propagate through the medium. For example, in the ionosphere (50–500 km) above our ground, the plasmon density in the order of 1012 – 15/m3, and the cut‐off frequency (∼10 MHz) is less than the TV band. Therefore, the TV electromagnetic signal can penetrate into this ionosphere and spread signal from the satellites. The free electrons in metals can also be regarded as plasmon. However, the frequency of visible light (∼10 THz) is less than ωp of metals (>100 THz), and visible light cannot penetrate most metals. As a result, most metals are silvery white for high reflectivity of visible light. In the metal‐medium (or vacuum) system, the plasmons are confined strongly with light to surfaces, resulting in a surface polariton.
Actually, the electrons of metals are not free as described in the Drude model. The electrons have inherent frequency ω0 and form restoring force that depends on the existing space or local structure. Therefore, the electron movement was revised into Eq. (1.9)
We can get Eq. (1.10)
For practical purpose, the advantage of the Drude model is that it can easily be incorporated into time‐domain based numerical solvers for Maxwell’s equations. Its inadequacy in describing the optical properties of Au and Ag at visible frequencies can be overcome by replacing Eq. (1.6) with Eq. (1.10). Here, the interband transitions are thus described using the classical picture of a bound electron with resonance frequency ω0.
In the Drude model for free electrons, the collective electrons vibration is a longitudinal wave mode due to the electrons vibration caused by electrostatic field force. The electric field caused by surface plasmons decays quickly after penetrating the interface, localizing in the range of a few nanometers on the surface.
1.4 Surface Plasmon Polaritons
Similar to the complex wave of water surface caused by liquid surface tension, there will be rich physical phenomena on the interface between metal and medium due to the breaking of symmetry. Surface plasmon is a special mode of plasmon due to the special boundary conditions on the surface.
Since plasmon was proposed as the quantization of classical plasma oscillation from a Hamiltonian for the long‐range electron–electron correlations, most of their properties can be derived directly from Maxwell’s equations [6]. When electromagnetic wave incidents on the interface between metal and medium, the coupling between collective electron vibration and incident light leads to the formation of near‐field electromagnetic wave propagating along the metal surface. And resonance will occur if these two frequencies are the same. Under the resonance state, the energy of electromagnetic field is effectively transformed into the collective vibration energy of free electrons on the metal surface. That is the well‐known surface plasmon resonances (SPR).
There are also two modes of surface plasmon. One is longitudinal surface plasmon wave mode caused by electron oscillation, and the other one is confined to the surfaces that can interact with light to form propagating surface plasmon polaritons (SPPs). Polariton is the elementary excitation of the coupling vibration of photons and other quasiparticles. SPP has two excitation motions, charge motion (plasmon) and electromagnetic waves decayed at surface.
The electromagnetic field of SPP at a dielectric‐metal interface is obtained from the solution of Maxwell’s equations and the associated boundary conditions. To introduce the main characteristics of SPP, we consider a system consisting of a dielectric material, characterized by an isotropic dielectric constants ε2 (real and positive), in the half‐space z > 0, and a metal in the half‐space z < 0, characterized by complex dielectric function ε1(ω) = εr(ω) + εi(ω).
Using the continuity of electric field at the interface, we can get the electromagnetic field of SPP at the dielectric‐metal interface with the polarization direction of the incident light parallel to the incident plane. From the Maxwell’s electromagnetic field theory, we can obtain the following equations:
Then we can get the s‐polarized wave (TE mode) with
We then consider a p‐polarized (transverse magnetic or TM) wave in this structure that propagates in the x‐direction.
Figure 1.2 Dispersion of transverse electric TE mode and transverse magnetic TM mode on the dielectric‐metal interface.
For the TE case, k1 and k2 are wave vectors in metal and medium along z direction. We now consider an s‐polarized (transverse electric or TE) wave in the structure depicted in Figure 1.2. In a wave of this polarization, it is the electric vector that is perpendicular to the plane of incidence. The solutions of Maxwell’s equations that are wavelike in the x‐direction localized to the interface can be written as:
The continuity of the tangential components of the electric (Ey) and magnetic fields (Hx) across the interface z = 0 yields the pair of equations.The solution of this equation is A1 = A2 = 0. Thus an s‐polarized SPP (TE mode) cannot exist in the structure depicted.
Therefore, we only consider a p‐polarized (transverse magnetic or TM) wave in this structure that propagates in the x direction. In a wave of this polarization the magnetic vector is perpendicular to the plane of incidence – the plane defined by the direction of propagation and the normal to the surface. The solutions of Maxwell’s equations that are wavelike in the x direction and whose amplitudes decay exponentially with increasing distance into each medium from the interface z = 0 can be written as:
The boundary conditions at the plane z = 0 yield the pair of equations:
Here we can write wave vector in the x direction.
In the region of z < 0, kz determines the decay of the electromagnetic field with increasing distance from the surface.
Surface plasmon occurs at the interface of a material exhibiting positive part in a dielectric constant (such as vacuum, air, glass, and other dielectrics) and a metal (or heavily doped semiconductor) whose real part of permittivity is negative at the given frequency of light. The dispersions of bulk plasmon, SPP at a dielectric‐metal interface, light in air and in the dielectric medium is shown in Figure 1.3. In addition to opposite sign of the real part of the permittivity, the magnitude of the real part of the permittivity in the negative permittivity region should typically be larger than the magnitude of the permittivity in the positive permittivity region, otherwise the light is not bound to the surface (i.e. the surface plasmons do not exist).
For the existence of surface plasmon wave, the wave vector must be a positive value. Due to the facts of ε1 < 0,ε2 > 0, and ⌊ε1⌋ > ε2, it can be seen that the surface wave vector Kx is always larger than K for the incident light of any frequency. Kz must be an imaginary number, and electromagnetic field of the SPP decays exponentially in the z direction into the dielectric medium in contact with the metal. Consequently, the SPP cannot radiate light into the dielectric medium, and cannot be excited with conventional illumination from the adjacent dielectric. Moreover, the frequency of the surface plasmon is also the limiting frequency of the SPP with Kx → ∞.
Thus, the existence of SPs depends entirely on the fact that dielectric function ε(ω) has a negative real part (ε1 < 0). The SPs are well pronounced as resonances when the losses are small enough, i.e. ⌊ε1⌋ ≫ ε2. This is the well‐known property of a good plasmonic metal. We will define the substance as a good plasmonic metal if these two properties are satisfied simultaneously.
Figure 1.3 Dispersion of SPP at a dielectric‐metal interface. Also plotted is the dispersion of light in air and in the dielectric medium, and the corresponding surface plasmon frequency.
1.5 Plasmon at Metal‐Vacuum Interface
For the metal‐vacuum interface with , when Kx ⟶ ∞ , ε1 + ε2 = 0, we can see the relation between the bulk plasmon and SPP in the Drude model Eq. (1.7)
For the metal‐dielectric interface, in dielectric, and . This wave vector k0 equals to one value of SPP.
