MOLECULAR PLASMONICS. D Agostino. Della Sala HANDBOOK OF

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sensing, optoelectronics, medical diagnosis, optical communications, nanoscience, and energy.

surface-enhanced Raman scattering, and from optical microscopy to the synthesis of metal nanoparticles, filling the gap in the literature of this emerging field.

1 Prof. Lucio C. Andreani University of Pavia, Italy Molecular plasmonics is a rapidly growing interdisciplinary science that aims at investigating the coupling, at the nanometer scale, between emitting molecules and metallic nanostructures. This metal molecule electromagnetic interaction involves the excitation of localized and/or delocalized surface plasmons and is of great interest for a variety of research disciplines such as sensing, optoelectronics, medical diagnosis, optical communications, nanoscience, and energy. This handbook presents a comprehensive overview on the physics of the plasmon emitter interaction, ranging from electromagnetism to quantum mechanics, from metal-enhanced fluorescence to surface-enhanced Raman scattering, and from optical microscopy to the synthesis of metal nanoparticles, filling the gap in the literature of this emerging field. It is useful for graduate students as well as researchers from various fields who want to enter the field of molecular plasmonics. The text allows experimentalists to have a solid theoretical reference at a different level of accuracy and theoreticians to find new stimuli for novel computational methods and emerging applications. Stefania D Agostino is a postdoc fellow and assistant lecturer in the Department of Physics, University of Pavia, Italy. Her research interests focus on computational solid-state physics, nanoscience, photonics, and molecular plasmonics. V148 ISBN Della Sala D Agostino Fabio Della Sala leads the theoretical and computational division of the National Nanotechnology Laboratory of CNR, Lecce, Italy. He is an expert in density functional theory methods, computational material science, organic and inorganic optoelectronics, and computational nano-plasmonics. HANDBOOK OF This is a well-conceived and well-organized book in the broad and highly active area of molecular plasmonics. It contains leading specialists contributions on theory and simulation, experimental techniques, and fabrication. Each chapter is structured in order that it can serve both as an introduction for a non-specialist reader and as a review reference for an active researcher in the field. The content achieves very good balance between tutorial and research aspects what can make the book an authoritative reference in the field for several years. edited by Fabio Della Sala MOLECULAR PLASMONICS This is a really complete book that covers topics ranging from the basics of light matter interaction through practical and theoretical methods to understand and characterize the optical response of nanoparticles and molecules, as well as their interaction and related surface enhancement effects. The theoretical description is complemented by experimental examples and applications. The book will be very useful to researchers entering the field of molecular plasmonics, particularly those who are less familiar with the basic concepts, which are usually skipped in more specialized books or reviews. Prof. Luis M. Liz-Marzán CIC biomagune, Spain Stefania D Agostino

2 H A N D B O O K O F MOLECULAR PLASMONICS

4 H A N D B O O K O F MOLECULAR PLASMONICS edited by Fabio Della Sala and Stefania D Agostino

5 Published by Pan Stanford Publishing Pte. Ltd. Penthouse Level, Suntec Tower 3 8 Temasek Boulevard Singapore editorial@panstanford.com Web: British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. Handbook of Molecular Plasmonics Copyright c 2013 Pan Stanford Publishing Pte. Ltd. All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the publisher. For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher. ISBN (Hardcover) ISBN (ebook) PrintedintheUSA

6 Contents Preface Acknowledgment xiii xvii 1 Foundations of Molecular Plasmonics 1 F. Della Sala 1.1 Electromagnetic Waves Propagation in a Homogeneous Medium Poynting vector Reflection and Transmission at an Interface Normal incidence Current and Charges as Sources of Fields Green s function Dielectric Function of Metals The Drude Model Noble Metals Linear Response Theory Delocalized Surface Plasmon Resonances The Surface Plasmon-Polariton Wavevector Propagation length Field-penetration depths Localized Surface Plasmon Resonances Nanosphere in the Quasi-Static Approximation Dipole Radiation Radiation Pattern Dissipated Power Classical Approach Scattering Theory Scattering Cross-Section Optical Theorem 54

7 vi Contents Rayleigh Scattering by a Nanosphere Radiative Damping Mie Scattering Dipole Radiation in Scattering Environments Forced Damped Oscillator Purcell s Effect Fluorescence Lifetime and Quantum Yield Fluorescence Emission Near a Metal Surface Fluorescence Emission Near a Metal Nanosphere The Gersten-Nitzan model The Carminati model 76 PART I THEORY AND COMPUTATIONAL METHODS 2 Computational Approaches for Plasmonics 83 M. A. Yurkin 2.1 Introduction Overview of Different Methods Finite Scatterers in Homogeneous Medium Periodic Scatterers Scatterers Near an Infinite Plane Surface Electric Permittivity Theory of the DDA General Framework Numerical Scheme Iterative methods to solve the linear system Block-Toeplitz structure and FFT acceleration Orientation averaging and repeated calculations Existing Formulations Interaction term Polarizability prescription Calculating measurable quantities Decreasing shape errors 112

8 Contents vii 2.5 Practical Aspects of DDA Simulations General Applicability System Requirements Free Parameters Available Codes Accuracy of the DDA Size and Shape Dependence of Localized Surface Plasmon Resonances 137 S. D Agostino 3.1 Introduction Size Dependence Small Nanoparticles and Surface Damping Large Nanoparticles and Higher-Order Modes Shape Dependence Radially Symmetric Nanoparticles Ellipsoids and spheroids Cylinders and disks Prisms and Finite-Number Facets Nanoparticles Cubes Triangular prisms Polyhedral Nanoparticles Truncated cubes Rounded, regular and marks decahedral nanoparticles Multi-Tips Objects Stars Urchins-like nanoparticles Void Nanoparticles Nanoshells Void cubes Conclusions Computational Molecular Photophysics 175 E. Fabiano 4.1 Introduction Electronic Excitations 177

9 viii Contents Electronic Absorption Spectrum Vibrational Contributions Photophysics Semiclassical Description of Internal Conversion and Inter-System Crossing Computational Methods for Excited States Configuration Interaction Time-Dependent Density Functional Theory Linear Response TD-DFT Metal Molecule Electrodynamic Coupling 213 S. Corni 5.1 Introduction The Quasi-Static Limit The Point-Dipole Model of the Molecule, and the Classical Metal Nanoparticle Light Absorption Light Emission Light Scattering The Dielectric Function of the Classical Metal Nanoparticle Toward an ab initio Molecular Plasmonics Coupling the ab-initio Description of the Molecule with a Continuous Metal Fully ab initio Description of the Molecule Metal Nanoparticle Systems 246 PART II APPLICATIONS AND EXPERIMENTAL ASPECTS 6 Near-Fields in Assembled Plasmonic Nanostructures 261 P. K. Jain and C. Deeb 6.1 Introduction Optical Properties of Metal Nanoparticles Nanoplasmonic Field Enhancement Tunability of the LSPR and Near-Field Optical Properties of Coupled Nanoparticles Nanoparticle Assemblies 268

10 Contents ix LSPR response of assemblies Field enhancement Plasmonic wave-guiding Polarization Dependence of Coupling in a Dimer Dipolar-Coupling Model Analogy to Exciton Coupling in Molecular Aggregates Bonding and Anti-Bonding of Plasmons Spatial Profile of the Near-Field Distance-Dependence of the Near-Field Size-Scaling of Near-Field Decay Direct Mapping of the Near-Field Applications of Near-Field Coupling Concepts Plasmon Ruler Metal Nanoshells Coupling in Larger Arrays Molecular Sensing Future Outlook Noble Metal Nanostructure Enhancement of Fluorescence 295 R. J. Phaneuf 7.1 Introduction Nanostructure Size, Shape and Spacing Dependence Role of Substrate Standing Wave Surface Plasmons Spacer Layer Effect Surface-Enhanced Raman Scattering 321 M. Sun 8.1 Introduction Electromagnetic Mechanism and Numerical Methods Chemical Mechanism and Visualization Method of Charge Transfer Synthesis and Experiment on SERS Remote-Excitation SERS Conclusions 346

11 x Contents 9 Parabolic Mirror Assisted Gap-Mode Optical Ultramicroscopy 355 D. Zhang and A. J. Meixner 9.1 Introduction Principles Instrumentation Optics layout PM Optics Tip-Sample Distance Control and Image Recording Different Types of Gap-Modes Gap-Mode of Metallic System Au tip and Au substrate Au tip and monolayer adsorbates/au substrate Au tip and single molecule/au substrate Gap-Mode of Metal-Organic Semiconductor System Au tip and diindenoperylene molecule Au tip and organic solar cell blends Gap-mode of metal-inorganic semiconductor system Conclusion Wet-Chemical Synthesis Techniques for Colloidal Plasmonic Nanostructures Assisted by Convective or Microwave Dielectric Heating 395 L. Carbone 10.1 Introduction Wet-Chemical Synthesis: Basic Principles Hybrid nanoarchitecture formation Synthesis under Conventional Convective Heating Hard-Templated Growth Precipitation-Promoted Growth Electrochemical and Shape-Controlled Growth 405

12 Contents xi Photochemical and Shape-Controlled Growth Galvanic Displacement-Mediated Growth Seed-Promoted Growth Homogeneous nucleation Heterogeneous nucleation Synthesis under Microwave Dielectric Heating Basic Principles of Microwave-Promoted Growth Mono-Metallic Nanostructures Bi-Metallic Hetero-Nanostructures Conclusions 440 Index 463

14 Preface The term molecular plasmonics refers to a rapidly growing interdisciplinary science which aims at investigating the coupling, at the nanoscale level, between emitting molecules and metallic nanostructures. Collective oscillations of the conduction electrons, named surface plasmons, can strongly enhance the electromagnetic field around metallic nanoparticles and nano-patterned surfaces: the optical responses (absorption, fluorescence, lifetime, and Raman scattering) of molecules close to the metal are thus strongly modified. Despite these effects have been known since the seventies, it is only with the recent progress in the synthesis and fabrication of nanosystems as well as innovations in the characterization procedures and spectroscopies that interest in molecular plasmonics has been boosted. Surface-enhanced Raman spectroscopy (SERS), localized surface plasmon resonance (LSPR) spectroscopy, and metalenhanced fluorescence (MEF) find large applications in biology, to realize plasmonic biosensors or to detect molecular-binding events, as well as in medicine, for molecular-specific imaging, detection, and photothermal therapy of cancer. Surface plasmons and MEF are also widely used in organic opto-electronics, photonics, and energy-conversion applications. In addition, different theoretical approaches and modeling tools have been developed in recent years to describe both organic molecules and metal nanoparticles as well as their interactions, with increased accuracy and efficiency. Molecular plasmonics thus has great interdisciplinary appeal, attracting researchers from fields as diverse as telecommunication engineering (as emitting molecules behave like electromagnetic antennas), inorganic chemistry (to synthesize metal nanoparticles), quantum mechanics (to describe optical properties of molecules and

15 xiv Preface metals), nano-photonics (to manipulate light at a length scale below the diffraction limit), and optical microscopy (to measure the nearfield around metallic objects). Handbook of Molecular Plasmonics is intended for a broad readership and contains both high-level specialized chapters and introductory chapters as well as theoretical and experimental reviews. The main idea underlying this project is to create a useful feedback between theory and experiments, giving a theoretical reference to experimentalists and, at the same time, new inputs to theoreticians for further developments. This handbook is organized in 10 chapters that reflect the current status of this evolving scientific field, discuss the most recent developments, and identify the directions of future research. Chapter 1 introduces the basic foundations of molecular plasmonics. It is a self-contained chapter, starting with Maxwell s equations and concluding with the derivation of the radiative and non-radiative decay rates of emitting molecules near metal surfaces and nanoparticles. After this introductory chapter, the handbook is subdivided in two parts: the first one describes the computational and theoretical methods of interest in molecular plasmonics, while the second is entirely dedicated to the most relevant applications and experimental techniques. Both parts contain precious contributions from international experts to ensure a plurality of points of view. Part I, Theory and Computational Methods, opens with a chapter by M. A. Yurkin (Russia) who describes in detail the Discrete Dipole Approximation (DDA) approach, which is an efficient method to study the absorption and scattering of metal nanoparticles of arbitrary shapes. This chapter will serve as an important reference for theoreticians to model metal nanoparticles. Chapter 3 reports DDA results for nanoparticles of different sizes and shapes. This systematic analysis, inspired by recent literature, should represent an important reference for both experimentalists and theoreticians to verify and compare the absorption and scattering spectra of different nanoparticles. While these first two chapters are completely dedicated to metal nanoparticles, Chapter 4 introduces the discussion about the molecular counterpart. In this chapter E. Fabiano (Italy) sheds light on the optical and photophysical

16 Preface xv properties of organic molecules as well as theoretical methods of quantum mechanics. The interaction between metals and organic molecules is then analyzed in detail in Chapter 5 by Stefano Corni (Italy). This chapter represents the synthesis of the concepts of all previous chapters. Part II, Applications and Experimental Aspects, starts with a chapter by P. K. Jain (Illinois) and C. Deeb (Illinois). They describe the coupling between two plasmonic nanostructures and concepts and applications of the optical near-field. This chapter serves as a link between theory and experiments. In Chapter 7, R. J. Phaneuf (Maryland) discusses recent results on MEF. Both localized and delocalized surface plasmon resonances are presented, including comparison between theory and experiments. Chapter 8 is dedicated to SERS, and M. Sun (China) gives special emphasis to theoretical calculations of charge-transfer effects and to experimental results on remote SERS excitation, a treatment which should be useful for both theoreticians and experimentalists. In Chapter 9, D. Zhang and A. J. Meixner (Germany) describe nearfield microscopy and the techniques based on the parabolic mirror confocal microscope. Different types of gap modes are discussed and relevant experimental images and results are presented. The last chapter is devoted to the colloidal synthesis of metal nanoparticles. L. Carbone (Italy) presents a complete review on different synthetic approaches, ranging from convective to microwave heating. This chapter should prove very useful not only to chemists but also to readers from other backgrounds as a reference for all types of nanoparticles that can be realized experimentally. It has been a great pleasure to work with all these leading scientists of this field, and we thank all of them for their support. We hope this handbook proves to be a helpful reference manual and a useful tool for both students and experts in this field, and we encourage readers to give their valuable comments/suggestions so that the book can be improved further. Fabio Della Sala Stefania D Agostino Summer 2013

18 Acknowledgment We would like to thank all our collegues of the National Nanotechnology Laboratory who have collaborated with us in the field of molecular plasmonics. F. D. S. thanks his wife Erika for her constant support and for proofreading the book. S. D. thanks the Photonics and Nanostructures group of the Physics Department of Pavia for the precious friendship and support received during the period of the project.

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