1

www.wiley-vch.de

Sau Rogach (Eds.)

Com

plex-shapedM

etal Nanoparticles

The past few years have witnessed the development of non-spherical metal nanoparticles with complex morphologies, which offer tremen-dous potential in materials science, chemistry, physics and medicine. Covering all important aspects and techniques of preparation and characterization of metal nanoparticles with controlled morphology and architecture, this book provides a sound overview from the basics right up to recent developments. Renowned research scientists from all over the world present the existing knowledge in the fi eld, covering theory and modeling, synthesis and properties of these nanomaterials. By emphasizing the underlying concepts and principles in detail, this book enables researchers to fully recognize the future research scope and the application potential of the complex-shaped metal nanopar-ticles, inspiring further research in this fi eld.

Tapan K. Sau is an associate professor at the International Institute of Information Technology, Hyderabad, India. After his PhD in chemistry, obtained from the Indian Institute of Technology in Kharagpur, he had worked as a postdoctoral fellow at the University of South Carolina-Columbia and Clarkson University, USA, and as an assistant professor at the Panjab University in Chandigarh, India. From 2007 to 2009 he was an Alexander-von-Humboldt Research Fellow at the Ludwig-Maximilians-Universitt, Mnchen, Germany. His research interests are in synthesis, spectroscopy and applica-tions of colloidal metal nanocrystals. He has authored over 50 publications including patents and book chapters.

Andrey L. Rogach is chair professor at the Department of Physics and Materials Science of City University of Hong Kong. After his PhD in chemistry, obtained from the Belarusian State University in Minsk, he had worked as a research scientist at the University of Hamburg, Germany (19952002), and as a lead staff scientist at the Photonics and Optoelectronics group of the Ludwig-Maximilians-Universitt Munich, Germany (20022009), where he completed his habilitation in experi-mental physics. His research is focused on synthesis, assembly, optical spectroscopy and applications of colloidal semiconduc-tor and metal nanocrystals, which has been extensively (over 12,000) times cited.

Edited by Tapan K. Sau andAndrey L. Rogach

Complex-shapedMetal NanoparticlesBottom-Up Syntheses and Applications

57268File AttachmentCover.jpg

Edited by

Tapan K. Sau and

Andrey L. Rogach

Complex-shaped Metal

Nanoparticles

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Edited byTapan K. Sau and Andrey L. Rogach

Complex-shaped Metal Nanoparticles

Bottom-Up Syntheses and ApplicationsWith a Foreword by Catherine J. Murphy

The Editors

Prof. Tapan K. SauInt. Inst. of Inform. Technol.Comput. Nat. Sc. & Bioinform.GachibowliHyderabad, AP 500032India

Prof. Andrey L. RogachCity University of Hong KongDept. of Physics & Mat. ScienceTat Chee Avenue 83KowloonHong Kong

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British Library Cataloguing-in-Publication DataA catalogue record for this book is available from theBritish Library.

Bibliographic information published bythe Deutsche NationalbibliothekThe Deutsche Nationalbibliothek lists this publica-tion in the Deutsche Nationalbibliografie; detailedbibliographic data are available on the Internet athtt p://dnb.d-nb .de.

# 2012 Wiley-VCH Verlag & Co. KGaA,Boschstr. 12, 69469 Weinheim, Germany

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Dedicated to our great families Kaberi and Oxana, Miteshand Janina, Michael, and Vital

V

Foreword

The brilliant colors of nanoscale metal particles are abundant in the art of the past stained glass windows and Italian Renaissance pottery are only two examples. Thescience of the past has allowed us to understand how the optical properties of suchmetal nanoparticles arise and has given us the notion that shape controls color.This book shows us that at the highest levels, the art of making unusually shapedmetal nanoparticles has become a science in its own right. The reader of this bookwill happily observe that at its best, science can become art in the form of thebeautiful structures, spectra, and calculational maps that are abundant throughoutits pages.

I am very happy to see the breadth of coverage in this book, which is edited by twooutstanding scholars in the field and contains contributions from over a dozenluminaries. Theory and experiment are well balanced. The fundamentals of crystalgrowth and assembly are also well balanced by the application space of thesematerials, which encompasses chemical sensing, photothermal therapy, and ther-moelectrics. The readers of this book will, I hope, be inspired to contribute to thescience of the future in the area of complex-shaped metal nanoparticles.

Enjoy!

University of Illinois at Urbana-Champaign Catherine J. MurphyUrbana, IL

VII

Contents

Foreword VIIPreface XVIIList of Contributors XIX

Metal Nanoparticles of Complex Morphologies:A General Introduction 1References 5

1 Colloidal Synthesis of Noble Metal Nanoparticles ofComplex Morphologies 7Tapan K. Sau and Andrey L. Rogach

1.1 Introduction 71.2 Classification of Noble Metal Nanoparticles 81.3 Synthesis Methodologies 91.3.1 Chemical Reduction Method 91.3.1.1 Spatially Confined Medium/Template Approach 101.3.1.2 Preformed Seed-Mediated Synthesis 151.3.1.3 High-Temperature Reduction Method 191.3.2 Chemical Transformation Method 191.3.2.1 Galvanic Displacement Method 191.3.2.2 Etching Method 211.3.3 Electrochemical Synthesis 221.3.4 Photochemical Method 231.3.5 Biosynthesis 241.3.6 Postpreparation Separation 251.4 Characterization 251.5 ThermodynamicKinetic Factors and Particle Morphology 291.5.1 Nucleation and Growth 291.5.1.1 Homogeneous and Heterogeneous Nucleations 291.5.1.2 Defects in Seed Crystal 371.5.1.3 Growth of Seed Crystal 411.5.2 Reaction Parameters 43

IX

1.5.2.1 Reactants and Their Concentrations 431.5.2.2 Additives/Impurities 481.5.2.3 Solvent, pH, and Temperature 501.6 Mechanisms of Morphology Evolution 511.6.1 One-Dimensional Nanoparticle Formation 521.6.1.1 Nanorod Formation 521.6.1.2 Nanobipyramid Formation 571.6.2 Two-Dimensional Nanoparticle Formation 571.6.3 Three-Dimensional Polyhedral Shape Evolution 621.6.4 Epitaxial/CoreShell/Heterodimer/Overgrowth Mechanism 641.6.5 Branched Nanoparticle Formation 671.6.6 Hollow/Porous Nanoparticle Formation 701.7 Conclusions and Outlook 72

References 73

2 Controlling Morphology in Noble Metal Nanoparticlesvia Templating Approach 91Chun-Hua Cui and Shu-Hong Yu

2.1 Introduction 912.2 Galvanic Replacement Method 922.2.1 Synthesis of Quasi-Zero-Dimensional Nanoparticles 932.2.2 Synthesis of One-Dimensional Nanostructures 972.3 Hard Template-Directed Method 992.3.1 Porous Membrane Template-Directed Method 1002.3.2 Pattern Template-Directed Method 1042.4 Soft Template-Directed Method 1062.4.1 Micelle Template-Directed Synthesis 1062.4.2 Selective Adsorption-Directed Synthesis 1092.5 Conclusions and Outlook 112

References 113

3 Shape-Controlled Synthesis of Metal Nanoparticles of HighSurface Energy and Their Applications in Electrocatalysis 117Na Tian, Yu-Hua Wen, Zhi-You Zhou, and Shi-Gang Sun

3.1 Introduction 1173.2 Fundamentals and Background 1193.2.1 Thermodynamics of Crystallization: Principles and Rules 1193.2.1.1 Equilibrium Shape of a Crystal 1193.2.1.2 Nucleation 1203.2.1.3 Three-Dimensional Growth of a Crystal on Substrate 1223.2.1.4 Two-Dimensional Nuclei Theory 1243.2.2 Correlation of the Shape of Crystal and Its Surface Structure 1253.3 Progress in Shape-Controlled Synthesis of Metal Nanoparticles of High

Surface Energy and Their Applications 1273.3.1 Electrochemistry Route 128

X Contents

3.3.1.1 Pt and Pd Nanoparticles 1283.3.1.2 Fe Nanoparticles 1373.3.2 Wet Chemistry Route 1373.3.2.1 Au Nanoparticles 1393.3.2.2 Pd and PdAu Nanoparticles 1413.3.2.3 Pt Nanoparticles 1443.4 Theoretical Simulations of Structural Transformation and Stability

of Metal Nanoparticles with High Surface Energy 1483.4.1 Brief Description of Theoretical Calculation Methods 1483.4.1.1 First-Principles Methods 1483.4.1.2 Molecular Dynamics Methods 1493.4.1.3 Predictions and Limitations of Theoretical Calculations 1493.4.2 Theoretical Study of Metal Nanoparticles of High Surface Energy 1503.4.2.1 Pt Nanoparticles 1513.4.2.2 Pd Nanoparticles 1533.4.2.3 Au Nanoparticles 1553.4.2.4 Fe Nanoparticles 1573.5 Conclusions 160

References 162

4 Shape-Controlled Synthesis of Copper Nanoparticles 167Wen-Yin Ko and Kuan-Jiuh Lin

4.1 Introduction 1674.1.1 Zero-Dimensional Nanostructures 1674.1.2 One-Dimensional Nanostructures 1684.1.3 Two-Dimensional Nanostructures 1694.1.4 Complex (3D) Nanostructures 1704.2 Metallic Copper 1724.2.1 Significance and Challenges 1724.2.2 Shape Control of Cu Nanoparticles 1724.3 Electrodeposition Method for Growth of Cu Nanoparticles

of Different Shapes 1744.3.1 Synthesis and Growth Mechanism of Tetrahedral Metallic Cu 1744.3.1.1 Synthesis 1744.3.1.2 Growth Mechanism 1774.3.2 Synthesis of Cu Nanoparticles of Cubic and Multipod Shapes 1794.4 Conclusions 179

References 181

5 Size- and Shape-Variant Magnetic Metal and Metal OxideNanoparticles: Synthesis and Properties 183Kristen Stojak, Hariharan Srikanth, Pritish Mukherjee, Manh-Huong Phan,and Nguyen T. K. Thanh

5.1 Introduction 1835.2 Synthesis of Size- and Shape-Variant Ferrite Nanoparticles 184

Contents XI

5.2.1 Thermal Decomposition 1845.2.1.1 Surface Functionalization 1855.2.1.2 Size and Shape Variance 1875.2.2 Chemical Coprecipitation 1895.2.3 Solvothermal Technique 1915.2.4 Microemulsion Technique 1925.3 Other Magnetic Nanoparticles: Synthesis, Size Variance,

and Shape Variance 1945.4 Magnetism in Ferrite Nanoparticles 1965.4.1 Crystal Structure and Spin Configuration 1965.4.2 Critical Size and Superparamagnetism 1975.4.3 Size-Dependent Magnetic Properties 1985.4.3.1 Static Magnetic Properties 1985.4.3.2 Dynamic Magnetic Properties 2035.4.4 Shape-Dependent Magnetic Properties 2055.5 Magnetic Nanoparticles for Biomedical Applications 2075.5.1 Targeted Drug Delivery 2075.5.2 Hyperthermia 2085.5.3 MRI Contrast Enhancement 2085.6 Concluding Remarks and Future Directions 210

References 212

6 Structural Aspects of Anisotropic Metal Nanoparticle Growth:Experiment and Theory 215Tulio C.R. Rocha, Herbert Winnischofer, and Daniela Zanchet

6.1 Introduction 2156.2 Atomic Packing on Metal NPs 2176.3 Structural Aspects in the Anisotropic Growth: The Silver

Halide Model 2216.4 Experimental Requisites to Produce Anisotropic NPs 2266.5 Concluding Remarks 234

References 235

7 Colloids, Nanocrystals, and Surface Nanostructures of Uniform Size andShape: Modeling of Nucleation and Growth in Solution Synthesis 239Vladimir Privman

7.1 Introduction 2397.2 Burst Nucleation Model for Nanoparticle Growth 2427.3 Colloid Synthesis by Fast Growth 2477.4 Improved Models for Two-Stage Colloid Growth 2517.5 Particle Shape Selection in Solution Synthesis 2547.6 Applications for Control of Morphology in Surface Structure

Formation 2617.7 Summary 263

References 264

XII Contents

8 Modeling Nanomorphology in Noble Metal Particles:Thermodynamic Cartography 269Amanda S. Barnard

8.1 Introduction 2698.2 Ab Initio Simulation of Small Gold Nanoclusters 2718.3 Ab Initio Simulation of Gold Nanoparticles 2728.4 Thermodynamic Cartography 2768.4.1 Size-Dependent Melting 2818.4.2 Mapping the Morphology of Nanogold 2828.5 Gold Nanorods and Dimensional Anisotropy 2858.5.1 Preferred Shape and Termination Geometry 2868.5.2 Aspect Ratio and Dependence on Temperature 2898.5.3 Twinning in Gold Nanorods 2918.6 Comparison with Platinum and Inclusion of Surface Defects 2948.7 Conclusions 298

References 300

9 Platinum and Palladium Nanocrystals: Soft Chemistry Approachto Shape Control from Individual Particles to Their Self-AssembledSuperlattices 305Christophe Petit, Caroline Salzemann, and Arnaud Demortiere

9.1 Introduction 3059.2 Influence of the Chemical Environment on the NC Shape 3069.2.1 How the Capping Agents Tune the Shape and the Size of Metal NCs:

A Comparison of Two-Liquid Synthesis Methods 3069.2.1.1 Effect of the Capping Agent on the Shape of Platinum NCs 3089.2.1.2 Effect of the Capping Agent on the Size of Platinum NCs 3109.2.1.3 Effect of the Capping Agent on the Size and Shape of Palladium

NCs Made in Reverse Micelles 3129.2.2 Role of the Strength of the Capping AgentMetal Bond 3159.2.3 Role of the Gas Dissolved in a Solvent 3189.3 Synthesis of Platinum Nanocubes 3219.4 Supercrystals Self-Assembled from Nonspherical NCs 3239.5 Conclusions 333

References 335

10 Ordered and Nonordered Porous Superstructures from MetalNanoparticles 339Anne-Kristin Herrmann, Nadja C. Bigall, Lehui Lu, and Alexander Eychmller

10.1 Introduction 33910.2 Metallic Porous Superstructures 34110.2.1 Ordered Porous Metallic Nanostructures 34110.2.1.1 Preparation 34210.2.1.2 Applications in Catalysis and as SERS Substrates 34510.2.2 Nonordered Porous Superstructures on Biotemplates 347

Contents XIII

10.2.3 Freestanding Nonordered Porous Superstructures 35110.3 Summary and Outlook 355

References 355

11 Localized Surface Plasmons of Multifaceted Metal Nanoparticles 361Cecilia Noguez and Ana L. Gonzlez

11.1 Introduction 36111.2 Light Absorption and Scattering by Metal NPs 36311.2.1 Light Absorption Mechanisms 36611.2.2 Surface Plasmon Resonances 36711.2.3 Dielectric Function of Metal NPs 36811.3 Spectral Representation Formalism 37111.3.1 General Trends of SPRs of Metal NPs in Vacuum 37311.3.2 General Trends of SPRs of Metal NPs in a Host Medium 37411.4 Spherical and Spheroidal NPs 37511.4.1 Nanospheres 37511.4.2 Nanospheroids 37811.4.3 Multishell NPs 37911.5 Discrete Dipole Approximation 38011.6 SPRs in Multifaceted Morphologies 38311.6.1 Cubic Morphology 38311.6.2 Decahedral Morphology 38511.6.3 Elongated NPs with Complex Morphologies 38811.7 Summary 390

References 391

12 FluorophoreMetal Nanoparticle Interactions and Their Applicationsin Biosensing 395Thomas A. Klar and Jochen Feldmann

12.1 Introduction 39512.2 Fluorescence Decay Rates in the Vicinity of Metal Nanostructures 39512.2.1 Physical Concept 39512.2.2 Oligonucleotide Sensing 40112.2.3 Protein Sensors 40412.2.3.1 Unspecific Protein Sensors 40512.2.3.2 Immunoassays 40512.2.3.3 Aptamer-Based Sensing 40712.2.4 Sensing Small Molecules (Haptens) 40912.2.5 Ion Sensing 41112.2.6 Fluorescence Enhancement Sensors 41112.3 Shaping of Fluorescence Spectra by Metallic Nanostructures 41212.4 Shaping of Extinction Spectra by Strong Coupling 41712.4.1 Physical Concept 41712.4.2 Biosensor Applications 419

XIV Contents

12.5 Specific Issues on the Interaction of Fluorophores with Complex-ShapedMetallic Nanoparticles 419

12.5.1 Spectral Tunability 42012.5.2 Encoding 421

References 422

13 Surface-Enhanced Raman Scattering Using Complex-ShapedMetal Nanostructures 429Frank Jckel and Jochen Feldmann

13.1 Introduction 42913.2 Basics 43013.2.1 Raman Scattering 43013.2.2 Surface-Enhanced Raman Scattering 43113.3 Modeling 43513.4 SERS Substrate Preparation 43713.5 Fundamental Studies 43913.5.1 Morphology Dependence 43913.5.2 SERS with Single Particles 44113.5.3 Single-Molecule SERS 44313.5.4 Enhancement Mechanism 44413.6 Applications 44713.7 Conclusions and Outlook 448

References 449

14 Photothermal Effect of Plasmonic Nanoparticlesand Related Bioapplications 455Alexander O. Govorov, Zhiyuan Fan, and Alexander B. Neiman

14.1 Introduction 45514.2 Theory of the Photothermal Effect for Single Nanoparticles

and for Nanoparticle Clusters 45814.2.1 Plasmonic Model 45914.2.2 Mie Theory for a Single Spherical Nanoparticle 46014.2.3 Effective Medium Approaches for the Dielectric Function

and for the Thermal Conductivity of a Nanoparticle Cluster 46214.2.4 Optically Generated Temperature 46214.2.5 Mie Theory for Nanoparticles and Clusters 46314.2.5.1 Small Spherical Nanoparticles and Clusters 46314.2.5.2 Large Clusters 46414.3 Physical Examples and Applications 46714.3.1 Melting of the Matrix 46714.3.2 Heating from a Collection of Nanoparticles: Heat

Accumulation Effect 46814.4 Application to Biological Cells: Control of Voltage Cellular

Dynamics with Photothermal Actuation 47114.5 Summary 474

References 474

Contents XV

15 Metal Nanoparticles in Biomedical Applications 477Jun Hui Soh and Zhiqiang Gao

15.1 Introduction 47715.2 Biosensing and Diagnostics 47815.2.1 Localized Surface Plasmon Resonance Detection 47915.2.2 Colorimetric Detection 48215.2.3 Surface-Enhanced Raman Scattering Detection 48715.2.4 Electrochemical and Electrical Detection 49115.2.5 Magnetic Resonance-Based Detection 49515.3 Therapeutic Applications 49815.3.1 Applications in Tissue Engineering 49915.3.2 Application in Drug Delivery 50115.3.3 Cancer Therapy 50415.4 Bioimaging 50815.5 Conclusions and Outlook 513

References 515

16 Anisotropic Nanoparticles for Efficient Thermoelectric Devices 521Nguyen T. Mai, Derrick Mott, and Shinya Maenosono

16.1 Introduction 52116.2 Chemical Synthesis Methods of Complex-Shaped TE NPs 52316.2.1 Thermal Decomposition Method 52316.2.2 Hydrothermal Method 52316.2.3 Solvent-Based Reduction Method 52316.2.4 Important Factors in the Synthesis Toward Complex-Shaped

TE NPs 52416.3 One-Dimensional TE NPs 52516.3.1 Pb(Te, Se) System 52516.3.2 (Bi, Sb)(Te, Se) System 52816.4 Two-Dimensional TE NPs 53116.4.1 Pb(Te, Se) System 53116.4.2 (Bi, Sb)(Te, Se) System 53116.5 Other Complex-Shaped TE NPs 53516.6 Properties of Complex-Shaped TE NPs 53816.7 Conclusions and Future Outlook 540

References 541

Index 545

XVI Contents

Preface

Metallic materials have been one of the most ancient themes of study. Metals thataccount for 24% of the mass of the planet and about two-thirds of the elementsoccupy a unique place in the progress of human civilization. Properties such asstrength, toughness, thermal and electrical conductivities, ductility, high meltingpoint, etc. make the metals useful for applications ranging from household items tospace ship. Traditional applications aremainly based on the bulkmetallic properties.New applications exploit the novel properties of nanomaterials of metals. Nano-materials exhibit fascinating size-, shape-, and crystal form-dependent properties.Like the bulk metals, nanomaterials of metals are also going to bring profoundchanges in many spheres of our life, science, technology, and industry.

Though metal nanoparticles have a long history of preparation and applications,the field has undergone explosive growth in recent years. Metal nanoparticles withplethora of morphologies have been prepared, such as polyhedrons, plates, prisms,rods, wires, nanoboxes, nanocages, dumbbells, nanoshuttles, stars, branched rodsand wires, dendrites, nanorings, nanotubes, and so on. We have witnessed emer-gence of many novel approaches to synthesis and synthetic design, control ofcomposition, size, morphology, and assembly structure and impressive advancesin the characterization and manipulation techniques of metallic nanoparticles. Anumber of applications have been realized and multitudes of new applications havebeen envisaged.We feel that there is a need to have a single podiumwhere one couldfind the various techniques of preparation and characterization of metal nanopar-ticles of different morphologies and architectures, the details of the basic principlesinvolved in such techniques and why, how, and where these novel nanomaterials arebeing used. We also notice that there is often no scope for the discussion onfoundations of the scientific concepts in most of the research articles. This is whywe have introduced this book. This book compiles selected tutorial reviews on metalnanoparticles of different morphologies and architectures. The chapters provide asound review of existing knowledge from the basics to the recent developments inthe field of theory andmodeling, synthesis, characterization, properties, and variousaspects of applications of metal nanoparticles, emphasizing the underlying conceptsand principles in detail. The contributors are experienced research scientists from all

XVII

over the world. It is our hope that this book will not only prove suitable for self-studyand teaching purposes but will also inspire further discovery in many fields, thussetting the standard in the field of metal nanoparticles of complex morphologies foryears to come.

Hyderabad and Hong Kong Tapan K. Sau andNovember 2011 Andrey L. Rogach

XVIII Preface

List of Contributors

XIX

Amanda S. BarnardCSIRO Materials Science andEngineeringGate 5, Normanby RoadClayton, Victoria 3168Australia

Nadja C. BigallPhilipps-University of MarburgDepartment of PhysicsBiophotonics GroupAm Renthof 635032 MarburgGermany

Chun-Hua CuiUniversity of Science and Technologyof ChinaDepartment of ChemistryHefei National Laboratory for PhysicalSciences at MicroscaleDivision of Nanomaterials andChemistryHefei 230026China

Arnaud DemortiereArgonne National Laboratory9700 South Cass Avenue, Building 440Argonne, IL 60439USA

Alexander EychmllerTU DresdenPhysical ChemistryBergstrasse 66b01062 DresdenGermany

Zhiyuan FanOhio UniversityDepartment of Physics and Astronomy,and Department of Chemistry andBiochemistryAthens, OH 45701USA

Jochen FeldmannLudwig-Maximilians-UniversittMnchenDepartment of Physics and Center forNanoSciencePhotonics and Optoelectronics GroupAmalienstr. 5480799 MnchenGermany

Zhiqiang GaoNational University of SingaporeDepartment of Chemistry3 Science Drive 3Singapore 117543Singapore

Ana L. GonzlezUniversidad Nacional Autnoma deMxicoInstituto de FsicaMexico, D.F. 01000Mexico

Alexander O. GovorovOhio UniversityDepartment of Physics and Astronomy,and Department of Chemistry andBiochemistryAthens, OH 45701USA

Anne-Kristin HerrmannTU DresdenPhysical ChemistryBergstrasse 66b01062 DresdenGermany

Frank JckelLudwig-Maximilians-UniversittMnchenDepartment of Physics and Center forNanoSciencePhotonics and Optoelectronics GroupAmalienstr. 5480799 MnchenGermany

Thomas A. KlarJohannes-Kepler-Universitt LinzInstitute of Applied PhysicsAltenberger Str. 694040 LinzAustria

and

Center for NanoScience (CeNS)Schellingstr. 480799 MunichGermany

Wen-Yin KoNational Chung-Hsing UniversityDepartment of ChemistryTaichung 402Taiwan

Kuan-Jiuh LinNational Chung-Hsing UniversityDepartment of ChemistryTaichung 402Taiwan

Lehui LuChinese Academy of SciencesChangchun Institute for AppliedChemistryRenmin Street 5625Changchun 130022China

Shinya MaenosonoJapan Advanced Institute of Science andTechnologySchool of Materials Science1-1 AsahidaiNomi, Ishikawa 923-1292Japan

Nguyen T. MaiJapan Advanced Institute of Science andTechnologySchool of Materials Science1-1 AsahidaiNomi, Ishikawa 923-1292Japan

XX List of Contributors

Derrick MottJapan Advanced Institute of Science andTechnologySchool of Materials Science1-1 AsahidaiNomi, Ishikawa 923-1292Japan

Pritish MukherjeeUniversity of South FloridaDepartment of Physics4202 East Fowler AvenueTampa, FL 33620USA

Alexander B. NeimanOhio UniversityDepartment of Physics and Astronomy,and Department of Chemistry andBiochemistryAthens, OH 45701USA

Cecilia NoguezUniversidad Nacional Autnoma deMxicoInstituto de FsicaMexico, D.F. 01000Mexico

Christophe PetitUniversit Pierre et Marie CurieUMR CNRS 7070Laboratoire des MatriauxMsoscopiques et Nanomtriques(LM2N)4 place Jussieu75251 Paris Cedex 05France

Manh-Huong PhanUniversity of South FloridaDepartment of Physics4202 East Fowler AvenueTampa, FL 33620USA

Vladimir PrivmanClarkson UniversityDepartment of PhysicsCenter for Advanced MaterialsProcessing8 Clarkson AvenuePotsdam, NY 13699USA

Tulio C.R. RochaFritz-Haber-Institut der Max-Planck-GesellschaftDepartment of Inorganic ChemistryFaradayweg 4-6Berlin 14195Germany

Andrey L. RogachCity University of Hong KongDepartment of Physics and MaterialsScienceCenter for Functional PhotonicsTat Chee Avenue 83KowloonHong Kong

Caroline SalzemannUniversit Pierre et Marie CurieUMR CNRS 7070Laboratoire des MatriauxMsoscopiques et Nanomtriques(LM2N)4 place Jussieu75251 Paris Cedex 05France

Tapan K. SauInternational Institute of InformationTechnology, HyderabadCentre for Computational NaturalSciences & BioinformaticsGachibowliHyderabad, AP 500032India

List of Contributors XXI

Jun Hui SohInstitute of Bioengineering andNanotechnologyBiosensors and Biodevices31 Biopolis WaySingapore 138669Singapore

Hariharan SrikanthUniversity of South FloridaDepartment of Physics4202 East Fowler AvenueTampa, FL 33620USA

Kristen StojakUniversity of South FloridaDepartment of Physics4202 East Fowler AvenueTampa, FL 33620USA

Shi-Gang SunXiamen UniversityCollege of Chemistry and ChemicalEngineeringState Key Laboratory of PhysicalChemistry of Solid SurfacesDepartment of Chemistry422 Si-Ming-Nan-LuXiamen, Fujian 361005China

Nguyen T. K. ThanhUniversity College LondonDepartment of Physics & AstronomyGower StreetLondon WC1E 6BTUK

and

The Royal Institution of Great BritainThe Davy-Faraday Research Laboratory21 Albemarle StreetLondon W1S 4BSUK

Na TianXiamen UniversityCollege of Chemistry and ChemicalEngineeringState Key Laboratory of PhysicalChemistry of Solid SurfacesDepartment of Chemistry422 Si-Ming-Nan-LuXiamen, Fujian 361005China

Yu-Hua WenXiamen UniversityDepartment of Physics and Institute ofTheoretical Physics and Astrophysics422 Si-Ming-Nan-LuXiamen, Fujian 361005China

Herbert WinnischoferFederal University of Paran UFPRDepartment of ChemistryCentro PolitecnicoJardim das AmricasCuritiba, PR 81531-990Brazil

Shu-Hong YuUniversity of Science and Technology ofChinaDepartment of ChemistryHefei National Laboratory for PhysicalSciences at MicroscaleDivision of Nanomaterials andChemistryHefei 230026China

XXII List of Contributors

Daniela ZanchetState University of CampinasInstitute of ChemistryC.P. 6154Campinas, SP 13083-970Brazil

Zhi-You ZhouXiamen UniversityCollege of Chemistry and ChemicalEngineeringState Key Laboratory of PhysicalChemistry of Solid SurfacesDepartment of Chemistry422 Si-Ming-Nan-LuXiamen, Fujian 361005China

List of Contributors XXIII

Metal Nanoparticles of Complex Morphologies:A General Introduction

Metal nanoparticles constitute a very active area of research and development in thefield of nanoscience and nanotechnology. Humankind has been crafting themetallicmaterials intonumeroususeful shapes and formssince the copperandbronzeages.Currently, one can manipulate metallic materials at nanometer length scales gener-ating so-called nanoparticles and nanostructures of different sizes, shapes, andstructures.Nanoparticles andnanostructureshave sizes, inat least onedimension, onthe nanometer scale, typically in the range of about 109107 m (i.e., about1100 nm) [1]. The size of these nanoobjects is generally larger than smallmolecules,but much smaller than that of bulk material. The sharpest tip of a quilting needle isapproximately 500 000 nm in diameter. In the size range of 12 nm, the number ofmetal atoms per particle of AunLm (where L is a ligand, typically thiolate), n, is roughlywithin the range of about 10250 atoms [1]. In this size regime, electronic, physical,and chemical properties of themetallicmaterials often differ substantially from theirconstituent atoms or bulk counterparts. The fundamental properties of the nanopar-ticlesandnanostructuresarefunctionsofnotonly thesizebutalsonanomorphology,as described by the shape (dimensional anisotropy), structure, crystallinity, andphaseof the nanomaterial. This gives an opportunity to generate new properties and tunethesepropertiesbyvarying themorphologyof thenanomaterials.Dramaticchanges inthe properties of metallic nanomaterials may result from small changes in theirmorphologies. The complexmorphologies of themetallic nanomaterials, particularlycolloidal nanoparticles, are the theme of the present book.

Chemists are familiar with the relationships among valence, stoichiometry,molecular geometry (i.e., the way the atoms or molecules arrange themselves), andreactivity of molecules and solids. The molecular morphology has been observed toaffect the properties of polymeric materials. Similarly, in nanomaterials where a fewtens to hundreds of atoms (ormolecules) are put together as a single entity, it is logicalto expect that the particle morphology will be an important factor in determining theproperties of the nanomaterials. However, in nanoparticles, the surface energybecomes a major player in determining the particle geometry unlike the valenceshell electron pair repulsion and bond energy in the molecules (and small clusters),because of the larger size of the nanoparticles compared to the molecules (andclusters). The size domain of nanoparticles matches with the de Broglie wavelengths

Complex-shaped Metal Nanoparticles: Bottom-Up Syntheses and Applications, First Edition.Edited by Tapan K. Sau and Andrey L. Rogach. 2012 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2012 by Wiley-VCH Verlag GmbH & Co. KGaA.

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of the electrons, phonons, and excitons propagating in them. This leads to the spatialconfinement of the electrons, phonons, and electric fields in and around theseparticles and the quantum effects begin to dominate. For example, the electronconfinement effect in a nanoparticle modifies its spectral properties via shifting ofquantum levels and change in transition probabilities [2]. Nanoparticles have verylarge surface area-to-volume ratio because of their small sizes. The large ratio ofsurface area to volume affects their individual as well as interaction properties.Surface atoms have coordinatively unsaturated dangling bonds. Furthermore, nano-particles bear a high fraction of edge- and cornerlike curved regions [3]. Edges andcorners have more coordinatively unsaturated atoms (dangling bonds) than the flatsurfaces. Large fractions of undercoordinated surface, corner, and edge atoms in ananoparticle increase the surface energy and affect its surface bonding properties andchemical reactivity. The surface of a nanoparticle can be unstable due to the highsurface energy and large surface curvature. Thismay cause deviations from the usualbulk atomic arrangements. Large surface area and changed electronic properties arevery important in the context of catalysis, active sites, adsorption, and electrodeactivities. Properties such as particleparticle or particleenvironment interactionsare affected by the large surface area-to-volume ratio as well as spatial confinementphenomena. Nanoparticles of complex morphologies are essentially in kineticallyfrozen states with metastable structures [4] and offer characteristic orientationalconfinements and further modifications in the internal structures and surfacecharacteristics.

Strict control of the nanoparticle morphology is therefore required in order toobtainmaterials of desired properties. In otherwords, one can generate particleswithnew properties from the same materials and can fine-tune the properties of thenanoparticles by simply tuning the nanoparticle morphology. Researchers haveexplored many ways to prepare nanoparticles of controlled morphologies.The present quest for shape-controlled colloidal particles can be traced back to thework of Matijevic [5]. In recent years, there has been spectacular progress in the fieldof preparation and characterization ofmetal nanoparticles of differentmorphologies.These morphologies include but are not limited to the coreshell, rod, wire, hollow/porous, heterodimer, andbranchedmultipods.Chapters 15 give a detailed picture ofthe principles underlying the preparation of colloidal nanoparticles, particularlymetal nanoparticles, and the recent advances in the synthesis and characterizationfronts of differentmetals with emphasis on nanomorphology control. State-of-the-artmethods of syntheses such as chemical, electrochemical, template-directed, biosyn-thesis, solvothermal, etc. and have been discussed. How various ways of variation ofthe growth conditions can yield particles of different compositions andmorphologiesof coinage, noble, precious, and magnetic metals have been discussed in thesechapters. Various factors affecting the morphology and the mechanisms of mor-phology development of the metal nanoparticles have also been discussed in detail.Studies of the growthmechanism leading to nanoparticle anisotropy are important inthe elucidation of crystal growth mechanism. Furthermore, an ability to engineermaterials on the nanometer length scale enables investigation into the fundamentalsize- and shape-dependent properties of matter.

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As a substantial advancement in the experimental front of nanomorphologycontrol has occurred, the theoretical and computer simulation descriptions of thecolloidal synthesis of nanoparticles are catching up, providing valuable informationregarding the exact mechanisms of nanomorphology development in the particles.Chapters 68 discuss the theoretical aspects of the size- and morphology-controlledsynthesis of metal nanoparticles. We know that a number of metals like Ag, Au, andPt have a face-centered cubic (fcc) structure and, therefore, require a symmetrybreakingmechanism for the formation of highly anisotropic particles. Three primarymechanisms have been proposed for symmetry breaking in metals: the presence ofstructural defects, oriented attachment, and layer-by-layer growth. Chapter 6describes the structural aspects of anisotropic growth inmetal nanoparticles. Chapter7 discusses about themodeling of the nucleation and growth of polycrystalline colloidparticles, nanocrystals, and surface nanostructures of uniform sizes and shapes insolution. The chapter particularly considers dynamic selection of geometrical fea-tures andmorphology inprocesses ranging fromnucleation to growthby aggregationand kinetics involving diffusional transport ofmatter in solution and restructuring ofthe growing particle surfaces, yielding well-defined structures and particles.We havementioned earlier that the crystallization of a nanomaterial into a particular structureis usually kinetically driven. However, the choice of which structure occurs in aspecific size range or under specific chemical conditions often depends on thethermodynamic factors of the system. It has been well established that manymaterials exist in a variety of different polymorphs, depending upon their thermo-dynamic environment. Chapter 8 gives a detailed account of a method calledthermodynamic cartography, which describes a mapping of the thermodynamicallypreferred structure (size, phase, polymorph, polymotif, and shape) in a space definedby a range of parameters such as temperature, pressure, different measures of thechemical environment, and so on.

Nanoparticleshave several inherent features that change their chemistry comparedto their bulk counterparts or constituent atoms or molecules, since adsorption andreactivityarehighlystructure-sensitiveproperties [6].Dueto thefinelydividedstatesofnanoscale systems, one canobtain large surface areas for agivenquantity ofmaterials.Particles with complex morphologies offer ample corners, steps, edges, and defects,several crystal surfaces, and different surface roughness. Each crystallographic planeprovides different atomic arrangements and surface terminations. The surface of ananoparticle may be structurally and compositionally different from that of the bulkdue to the surface relaxation and reconstruction, and the presence of adsorbedlayers of reaction by-products and stabilizing molecules [6]. Exposure of differentcrystallographic facets, together with the increased number of edges, corners, andfaces, is of critical importance in controlling the catalytic activity aswell as the productselectivity. Nanoparticles of complex morphologies are therefore highly desirable ascatalysts in fuel cells, waste reduction, bioprocessing, and chemical industry. Theeffects of nanoparticle morphology on catalysis, particularly on electrocatalysis, havebeen discussed in Chapter 3. Use of metals in thermoelectric materials has beenhistorically an interesting topic of research because of their potential applicationsin saving energy otherwise lost through heat. Chapter 16 discusses on how

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low-dimensional, quantum-confined 1D and 2D nanoparticles have been intenselyinvestigated as a promising candidate for highly efficient thermoelectric materials.Magnetic nanoparticles constitute an important class of nanoparticles due to theirapplications in biomedicine and data storage. Shape anisotropy has a significantimpact on themagneticpropertiesof thenanoparticles.Therefore,Chapter5hasbeendevoted to the synthesis, size- and shape-dependentmagnetic properties, andapplica-tions of the magnetic metal and metal oxide nanoparticles.

Chapters 9 and 10 deal with various ordered and nonordered superstructures ofmetal nanoparticles. Future devices require nanoparticles to be assembled into one-,two-, or three-dimensional functional structures. The bottom-up approach offerscost-effective, mesoscale-controlled directed or self-organization of the buildingblocks to form hierarchical nanostructures. Though researchers have been usingsimple isotropic and homogeneous nanoparticles to study the fundamental phe-nomena involving self-assembly structures, building structures with desired dimen-sions and symmetries, increased hierarchy, and complexity will be necessary torealize the goal of future nanoscale devices. A number of factors control theorganization or assembly process of the nanoparticles. One such important factorfor the directed or self-assembly of nanoparticles of a specific shape is the particleanisotropy. Therefore, not only the individual but also the useful collective propertiesof the nanoparticles can be obtained by tuning the morphology of the nanoparticles.The morphology influences the interaction between nanoparticles and their packingarrangement into the assembled structures. Ordered and nonordered superstruc-tures have attractedmuch attention for both fundamental studies and applications invarious areas like nanophotonics, catalysis, surface-enhanced Raman scattering(SERS) (discussed in detail in Chapter 13), membranes and separation techniques,electrodes, sensors, actuators, and advanced electronic devices.

One of the main motivations of the studies of metal nanoparticles is their uniqueoptical properties, especially of metals like copper, silver, and gold. Metal nanopar-ticles strongly couple with incident light through excitation of their surface plasmonresonances, which are collective oscillations of the free conduction electrons near theinterface between the metal nanoparticle (a conductor) and ambient (an insulator).This coupling leads to unique optical properties, called localized surface plasmonresonance (LSPR), particularly in silver and gold nanoparticles. LSPR is associatedwith novel phenomena like localization and consequent enhancement of theelectromagnetic field at the nanometer scale surrounding the metal nanoparticles,which is addressed in detail in Chapter 11. The optical properties of the nanoparticlesand their arrays have been exploited for a number of applications such as controllingthe growth of nanoparticles via enhanced optical forces, enhancement in thesensitivity of sensors and spectroscopies, improving efficiency of photovoltaicdevices via increased light absorption, photothermal destruction of cancer cells andpathogenic bacteria, energy transport and storage, and so on [6]. Basic principles tothe state-of-the-art experimental and theoretical results on how the optical propertiesof metallic nanoparticles vary with varying particle morphologies and local dielectricenvironments and their major areas of applications with a particular focus onbiomedical ones are covered in Chapters 1215.

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