Complex-shaped Metal Nanoparticles E-Book

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 1123

Veröffentlichungsjahr: 2012

Beschreibung

The past few years have witnessed the development of non-spherical metal nanoparticles with complex morphologies, which offer tremendous 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 field, 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 nanoparticles, inspiring further research in this field.

Leseprobe

Contents

Cover

Related Titles

Title Page

Copyright

Dedication

Foreword

Preface

List of Contributors

Metal Nanoparticles of Complex Morphologies: A General Introduction

References

Chapter 1: Colloidal Synthesis of Noble Metal Nanoparticles of Complex Morphologies

1.1 Introduction

1.2 Classification of Noble Metal Nanoparticles

1.3 Synthesis Methodologies

1.4 Characterization

1.5 Thermodynamic–Kinetic Factors and Particle Morphology

1.6 Mechanisms of Morphology Evolution

1.7 Conclusions and Outlook

1.8 Acknowledgments

References

Chapter 2: Controlling Morphology in Noble Metal Nanoparticles via Templating Approach

2.1 Introduction

2.2 Galvanic Replacement Method

2.3 Hard Template-Directed Method

2.4 Soft Template-Directed Method

2.5 Conclusions and Outlook

Acknowledgments

References

Chapter 3: Shape-Controlled Synthesis of Metal Nanoparticles of High Surface Energy and Their Applications in Electrocatalysis

3.1 Introduction

3.2 Fundamentals and Background

3.3 Progress in Shape-Controlled Synthesis of Metal Nanoparticles of High Surface Energy and Their Applications

3.4 Theoretical Simulations of Structural Transformation and Stability of Metal Nanoparticles with High Surface Energy

3.5 Conclusions

Acknowledgments

References

Chapter 4: Shape-Controlled Synthesis of Copper Nanoparticles

4.1 Introduction

4.2 Metallic Copper

4.3 Electrodeposition Method for Growth of Cu Nanoparticles of Different Shapes

4.4 Conclusions

Acknowledgment

References

Chapter 5: Size- and Shape-Variant Magnetic Metal and Metal Oxide Nanoparticles: Synthesis and Properties

5.1 Introduction

5.2 Synthesis of Size- and Shape-Variant Ferrite Nanoparticles

5.3 Other Magnetic Nanoparticles: Synthesis, Size Variance, and Shape Variance

5.4 Magnetism in Ferrite Nanoparticles

5.5 Magnetic Nanoparticles for Biomedical Applications

5.6 Concluding Remarks and Future Directions

Acknowledgments

References

Chapter 6: Structural Aspects of Anisotropic Metal Nanoparticle Growth: Experiment and Theory

6.1 Introduction

6.2 Atomic Packing on Metal NPs

6.3 Structural Aspects in the Anisotropic Growth: The Silver Halide Model

6.4 Experimental Requisites to Produce Anisotropic NPs

6.5 Concluding Remarks

Acknowledgments

References

Chapter 7: Colloids, Nanocrystals, and Surface Nanostructures of Uniform Size and Shape: Modeling of Nucleation and Growth in Solution Synthesis

7.1 Introduction

7.2 Burst Nucleation Model for Nanoparticle Growth

7.3 Colloid Synthesis by Fast Growth

7.4 Improved Models for Two-Stage Colloid Growth

7.5 Particle Shape Selection in Solution Synthesis

7.6 Applications for Control of Morphology in Surface Structure Formation

7.7 Summary

Acknowledgments

References

Chapter 8: Modeling Nanomorphology in Noble Metal Particles: Thermodynamic Cartography

8.1 Introduction

8.2 Ab Initio Simulation of Small Gold Nanoclusters

8.3 Ab Initio Simulation of Gold Nanoparticles

8.4 Thermodynamic Cartography

8.5 Gold Nanorods and Dimensional Anisotropy

8.6 Comparison with Platinum and Inclusion of Surface Defects

8.7 Conclusions

Acknowledgments

References

Chapter 9: Platinum and Palladium Nanocrystals: Soft Chemistry Approach to Shape Control from Individual Particles to Their Self-Assembled Superlattices

9.1 Introduction

9.2 Influence of the Chemical Environment on the NC Shape

9.3 Synthesis of Platinum Nanocubes

9.4 Supercrystals Self-Assembled from Nonspherical NCs

9.5 Conclusions

Acknowledgments

References

Chapter 10: Ordered and Nonordered Porous Superstructures from Metal Nanoparticles

10.1 Introduction

10.2 Metallic Porous Superstructures

10.3 Summary and Outlook

References

Chapter 11: Localized Surface Plasmons of Multifaceted Metal Nanoparticles

11.1 Introduction

11.2 Light Absorption and Scattering by Metal NPs

11.3 Spectral Representation Formalism

11.4 Spherical and Spheroidal NPs

11.5 Discrete Dipole Approximation

11.6 SPRs in Multifaceted Morphologies

11.7 Summary

Acknowledgments

References

Chapter 12: Fluorophore–Metal Nanoparticle Interactions and Their Applications in Biosensing

12.1 Introduction

12.2 Fluorescence Decay Rates in the Vicinity of Metal Nanostructures

12.3 Shaping of Fluorescence Spectra by Metallic Nanostructures

12.4 Shaping of Extinction Spectra by Strong Coupling

12.5 Specific Issues on the Interaction of Fluorophores with Complex-Shaped Metallic Nanoparticles

Acknowledgments

References

Chapter 13: Surface-Enhanced Raman Scattering Using Complex-Shaped Metal Nanostructures

13.1 Introduction

13.2 Basics

13.3 Modeling

13.4 SERS Substrate Preparation

13.5 Fundamental Studies

13.6 Applications

13.7 Conclusions and Outlook

Acknowledgments

References

Chapter 14: Photothermal Effect of Plasmonic Nanoparticles and Related Bioapplications

14.1 Introduction

14.2 Theory of the Photothermal Effect for Single Nanoparticles and for Nanoparticle Clusters

14.3 Physical Examples and Applications

14.4 Application to Biological Cells: Control of Voltage Cellular Dynamics with Photothermal Actuation

14.5 Summary

Acknowledgments

References

Chapter 15: Metal Nanoparticles in Biomedical Applications

15.1 Introduction

15.2 Biosensing and Diagnostics

15.3 Therapeutic Applications

15.4 Bioimaging

15.5 Conclusions and Outlook

References

Chapter 16: Anisotropic Nanoparticles for Efficient Thermoelectric Devices

16.1 Introduction

16.2 Chemical Synthesis Methods of Complex-Shaped TE NPs

16.3 One-Dimensional TE NPs

16.4 Two-Dimensional TE NPs

16.5 Other Complex-Shaped TE NPs

16.6 Properties of Complex-Shaped TE NPs

16.7 Conclusions and Future Outlook

References

Index

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

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. The science of the past has allowed us to understand how the optical properties of such metal 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 shaped metal nanoparticles has become a science in its own right. The reader of this book will happily observe that at its best, science can become art – in the form of the beautiful structures, spectra, and calculational maps that are abundant throughout its pages.

I am very happy to see the breadth of coverage in this book, which is edited by two outstanding scholars in the field and contains contributions from over a dozen luminaries. Theory and experiment are well balanced. The fundamentals of crystal growth and assembly are also well balanced by the application space of these materials, which encompasses chemical sensing, photothermal therapy, and thermoelectrics. The readers of this book will, I hope, be inspired to contribute to the science of the future in the area of complex-shaped metal nanoparticles.

Enjoy!

University of Illinois at Urbana-Champaign

Urbana, IL

Catherine J. Murphy

Preface

Metallic materials have been one of the most ancient themes of study. Metals that account for ~24% of the mass of the planet and about two-thirds of the elements occupy a unique place in the progress of human civilization. Properties such as strength, toughness, thermal and electrical conductivities, ductility, high melting point, etc. make the metals useful for applications ranging from household items to space ship. Traditional applications are mainly based on the bulk metallic properties. New applications exploit the novel properties of nanomaterials of metals. Nanomaterials exhibit fascinating size-, shape-, and crystal form-dependent properties. Like the bulk metals, nanomaterials of metals are also going to bring profound changes 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 with plethora of morphologies have been prepared, such as polyhedrons, plates, prisms, rods, wires, nanoboxes, nanocages, dumbbells, nanoshuttles, stars, branched rods and wires, dendrites, nanorings, nanotubes, and so on. We have witnessed emergence of many novel approaches to synthesis and synthetic design, control of composition, size, morphology, and assembly structure and impressive advances in the characterization and manipulation techniques of metallic nanoparticles. A number of applications have been realized and multitudes of new applications have been envisaged. We feel that there is a need to have a single podium where one could find the various techniques of preparation and characterization of metal nanoparticles of different morphologies and architectures, the details of the basic principles involved in such techniques and why, how, and where these novel nanomaterials are being used. We also notice that there is often no scope for the discussion on foundations of the scientific concepts in most of the research articles. This is why we have introduced this book. This book compiles selected tutorial reviews on metal nanoparticles of different morphologies and architectures. The chapters provide a sound review of existing knowledge from the basics to the recent developments in the field of theory and modeling, synthesis, characterization, properties, and various aspects of applications of metal nanoparticles, emphasizing the underlying concepts and principles in detail. The contributors are experienced research scientists from all over the world. It is our hope that this book will not only prove suitable for self-study and teaching purposes but will also inspire further discovery in many fields, thus setting the standard in the field of metal nanoparticles of complex morphologies for years to come.

Hyderabad and Hong Kong

November 2011

Tapan K. Sau and

Andrey L. Rogach

List of Contributors

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 and ChemistryHefei 230026China

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

Alexander EychmüllerTU DresdenPhysical ChemistryBergstrasse 66b01062 DresdenGermany

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

Jochen FeldmannLudwig-Maximilians-Universität MünchenDepartment of Physics and Center for NanoSciencePhotonics and Optoelectronics GroupAmalienstr. 5480799 MünchenGermany

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

Ana L. GonzálezUniversidad Nacional Autónoma de MéxicoInstituto de FísicaMexico, 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 JäckelLudwig-Maximilians-UniversitätMünchenDepartment of Physics and Center forNanoSciencePhotonics and Optoelectronics GroupAmalienstr. 5480799 MünchenGermany

Thomas A. KlarJohannes-Kepler-Universität LinzInstitute of Applied PhysicsAltenberger Str. 69 4040 LinzAustriaandCenter for NanoScience (CeNS)Schellingstr. 4 80799 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 Applied ChemistryRenmin 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

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 Autónoma de MéxicoInstituto de FísicaMexico, D.F. 01000Mexico

Christophe PetitUniversité Pierre et Marie CurieUMR CNRS 7070Laboratoire des MatériauxMésoscopiques et Nanométriques(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 Materials Processing8 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 Materials ScienceCenter for Functional PhotonicsTat Chee Avenue 83KowloonHong Kong

Caroline SalzemannUniversité Pierre et Marie CurieUMR CNRS 7070Laboratoire des MatériauxMésoscopiques et Nanométriques(LM2N)4 place Jussieu75251 Paris Cedex 05France

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

Jun Hui SohInstitute of Bioengineering and NanotechnologyBiosensors and Biodevices 31 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 Paraná – UFPRDepartment of ChemistryCentro PolitecnicoJardim das AméricasCuritiba, PR 81531-990Brazil

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

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

Metal Nanoparticles of Complex Morphologies: A General Introduction

Metal nanoparticles constitute a very active area of research and development in the field of nanoscience and nanotechnology. Humankind has been crafting the metallic materials into numerous useful shapes and forms since the “copper and bronze ages.” Currently, one can manipulate metallic materials at nanometer length scales generating so-called “nanoparticles” and “nanostructures” of different sizes, shapes, and structures. Nanoparticles and nanostructures have sizes, in at least one dimension, on the nanometer scale, typically in the range of about 10−9–10−7 m (i.e., about 1–100 nm) [1]. The size of these nanoobjects is generally larger than small molecules, but much smaller than that of bulk material. The sharpest tip of a quilting needle is approximately 500 000 nm in diameter. In the size range of 1–2 nm, the number of metal atoms per particle of AunLm (where L is a ligand, typically thiolate), n, is roughly within the range of about 10–250 atoms [1]. In this size regime, electronic, physical, and chemical properties of the metallic materials often differ substantially from their constituent atoms or bulk counterparts. The fundamental properties of the nanoparticles and nanostructures are functions of not only the size but also “nanomorphology,” as described by the shape (dimensional anisotropy), structure, crystallinity, and phase of the nanomaterial. This gives an opportunity to generate new properties and tune these properties by varying the morphology of the nanomaterials. Dramatic changes in the properties of metallic nanomaterials may result from small changes in their morphologies. The complex morphologies of the metallic nanomaterials, particularly colloidal 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), and reactivity of molecules and solids. The molecular morphology has been observed to affect the properties of polymeric materials. Similarly, in nanomaterials where a few tens to hundreds of atoms (or molecules) are put together as a single entity, it is logical to expect that the particle morphology will be an important factor in determining the properties of the nanomaterials. However, in nanoparticles, the surface energy becomes a major player in determining the particle geometry unlike the valence shell electron pair repulsion and bond energy in the molecules (and small clusters), because of the larger size of the nanoparticles compared to the molecules (and clusters). The size domain of nanoparticles matches with the de Broglie wavelengths of the electrons, phonons, and excitons propagating in them. This leads to the spatial confinement of the electrons, phonons, and electric fields in and around these particles and the quantum effects begin to dominate. For example, the electron confinement effect in a nanoparticle modifies its spectral properties via shifting of quantum levels and change in transition probabilities [2]. Nanoparticles have very large surface area-to-volume ratio because of their small sizes. The large ratio of surface area to volume affects their individual as well as interaction properties. Surface atoms have coordinatively unsaturated dangling bonds. Furthermore, nanoparticles bear a high fraction of edge- and cornerlike curved regions [3]. Edges and corners have more coordinatively unsaturated atoms (dangling bonds) than the flat surfaces. Large fractions of undercoordinated surface, corner, and edge atoms in a nanoparticle increase the surface energy and affect its surface bonding properties and chemical reactivity. The surface of a nanoparticle can be unstable due to the high surface energy and large surface curvature. This may cause deviations from the usual bulk atomic arrangements. Large surface area and changed electronic properties are very important in the context of catalysis, active sites, adsorption, and electrode activities. Properties such as particle–particle or particle–environment interactions are affected by the large surface area-to-volume ratio as well as spatial confinement phenomena. Nanoparticles of complex morphologies are essentially in kinetically frozen states with metastable structures [4] and offer characteristic orientational confinements and further modifications in the internal structures and surface characteristics.

Strict control of the nanoparticle morphology is therefore required in order to obtain materials of desired properties. In other words, one can generate particles with new properties from the same materials and can fine-tune the properties of the nanoparticles by simply tuning the nanoparticle morphology. Researchers have explored many ways to prepare nanoparticles of controlled morphologies. The present quest for shape-controlled colloidal particles can be traced back to the work of Matijevic [5]. In recent years, there has been spectacular progress in the field of preparation and characterization of metal nanoparticles of different morphologies. These morphologies include but are not limited to the core–shell, rod, wire, hollow/porous, heterodimer, and branched multipods. Chapters 1, 2, 3, 4, 5 give a detailed picture of the principles underlying the preparation of colloidal nanoparticles, particularly metal nanoparticles, and the recent advances in the synthesis and characterization fronts of different metals with emphasis on nanomorphology control. State-of-the-art methods of syntheses such as chemical, electrochemical, template-directed, biosynthesis, solvothermal, etc. and have been discussed. How various ways of variation of the growth conditions can yield particles of different compositions and morphologies of coinage, noble, precious, and magnetic metals have been discussed in these chapters. Various factors affecting the morphology and the mechanisms of morphology development of the metal nanoparticles have also been discussed in detail. Studies of the growth mechanism leading to nanoparticle anisotropy are important in the elucidation of crystal growth mechanism. Furthermore, an ability to engineer materials on the nanometer length scale enables investigation into the fundamental size- and shape-dependent properties of matter.

As a substantial advancement in the experimental front of nanomorphology control has occurred, the theoretical and computer simulation descriptions of the colloidal synthesis of nanoparticles are catching up, providing valuable information regarding the exact mechanisms of nanomorphology development in the particles. Chapters 6, 7, 8 discuss the theoretical aspects of the size- and morphology-controlled synthesis of metal nanoparticles. We know that a number of metals like Ag, Au, and Pt have a face-centered cubic (fcc) structure and, therefore, require a symmetry breaking mechanism for the formation of highly anisotropic particles. Three primary mechanisms have been proposed for symmetry breaking in metals: the presence of structural defects, oriented attachment, and layer-by-layer growth. Chapter 6 describes the structural aspects of anisotropic growth in metal nanoparticles. Chapter 7 discusses about the modeling of the nucleation and growth of polycrystalline colloid particles, nanocrystals, and surface nanostructures of uniform sizes and shapes in solution. The chapter particularly considers dynamic selection of geometrical features and morphology in processes ranging from nucleation to growth by aggregation and kinetics involving diffusional transport of matter in solution and restructuring of the growing particle surfaces, yielding well-defined structures and particles. We have mentioned earlier that the crystallization of a nanomaterial into a particular structure is usually kinetically driven. However, the choice of which structure occurs in a specific size range or under specific chemical conditions often depends on the thermodynamic factors of the system. It has been well established that many materials exist in a variety of different polymorphs, depending upon their thermodynamic environment. Chapter 8 gives a detailed account of a method called thermodynamic cartography, which describes a mapping of the thermodynamically preferred structure (size, phase, polymorph, polymotif, and shape) in a space defined by a range of parameters such as temperature, pressure, different measures of the chemical environment, and so on.

Nanoparticles have several inherent features that change their chemistry compared to their bulk counterparts or constituent atoms or molecules, since adsorption and reactivity are highly structure-sensitive properties [6]. Due to the finely divided states of nanoscale systems, one can obtain large surface areas for a given quantity of materials. Particles with complex morphologies offer ample corners, steps, edges, and defects, several crystal surfaces, and different surface roughness. Each crystallographic plane provides different atomic arrangements and surface terminations. The surface of a nanoparticle may be structurally and compositionally different from that of the bulk due to the surface relaxation and reconstruction, and the presence of adsorbed layers of reaction by-products and stabilizing molecules [6]. Exposure of different crystallographic facets, together with the increased number of edges, corners, and faces, is of critical importance in controlling the catalytic activity as well as the product selectivity. Nanoparticles of complex morphologies are therefore highly desirable as catalysts in fuel cells, waste reduction, bioprocessing, and chemical industry. The effects of nanoparticle morphology on catalysis, particularly on electrocatalysis, have been discussed in Chapter 3. Use of metals in thermoelectric materials has been historically an interesting topic of research because of their potential applications in saving energy otherwise lost through heat. Chapter 16 discusses on how low-dimensional, quantum-confined 1D and 2D nanoparticles have been intensely investigated as a promising candidate for highly efficient thermoelectric materials. Magnetic nanoparticles constitute an important class of nanoparticles due to their applications in biomedicine and data storage. Shape anisotropy has a significant impact on the magnetic properties of the nanoparticles. Therefore, Chapter 5 has been devoted to the synthesis, size- and shape-dependent magnetic properties, and applications of the magnetic metal and metal oxide nanoparticles.

Chapters 9 and 10 deal with various ordered and nonordered superstructures of metal nanoparticles. Future devices require nanoparticles to be assembled into one-, two-, or three-dimensional functional structures. The “bottom-up” approach offers cost-effective, mesoscale-controlled directed or self-organization of the building blocks to form hierarchical nanostructures. Though researchers have been using simple isotropic and homogeneous nanoparticles to study the fundamental phenomena involving self-assembly structures, building structures with desired dimensions and symmetries, increased hierarchy, and complexity will be necessary to realize the goal of future nanoscale devices. A number of factors control the organization or assembly process of the nanoparticles. One such important factor for the directed or self-assembly of nanoparticles of a specific shape is the particle anisotropy. Therefore, not only the individual but also the useful collective properties of the nanoparticles can be obtained by tuning the morphology of the nanoparticles. The morphology influences the interaction between nanoparticles and their packing arrangement into the assembled structures. Ordered and nonordered superstructures have attracted much attention for both fundamental studies and applications in various 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 unique optical properties, especially of metals like copper, silver, and gold. Metal nanoparticles strongly couple with incident light through excitation of their surface plasmon resonances, which are collective oscillations of the free conduction electrons near the interface between the metal nanoparticle (a conductor) and ambient (an insulator). This coupling leads to unique optical properties, called localized surface plasmon resonance (LSPR), particularly in silver and gold nanoparticles. LSPR is associated with novel phenomena like localization and consequent enhancement of the electromagnetic field at the nanometer scale surrounding the metal nanoparticles, which is addressed in detail in Chapter 11. The optical properties of the nanoparticles and their arrays have been exploited for a number of applications such as controlling the growth of nanoparticles via enhanced optical forces, enhancement in the sensitivity of sensors and spectroscopies, improving efficiency of photovoltaic devices via increased light absorption, photothermal destruction of cancer cells and pathogenic bacteria, energy transport and storage, and so on [6]. Basic principles to the state-of-the-art experimental and theoretical results on how the optical properties of metallic nanoparticles vary with varying particle morphologies and local dielectric environments and their major areas of applications with a particular focus on biomedical ones are covered in Chapters 12, 13, 14, 15.

In summary, metal nanoparticles differ from their bulk counterparts or constituent atoms because of the large surface area-to-volume ratio and quantum size effects. The properties of the metal nanoparticles are sensitive to their composition, size, and morphology (described by the shape, dimensional anisotropy, structure, and crystallinity of the nanoparticles). Intensive research activities are going on for the understanding of physicochemical basis of morphology-controlled synthesis of metal nanoparticles and spectacular progress has been made in this field. Control of morphology in metal nanoparticles offers features and functionalities that are often difficult to obtain otherwise such as by simple size tuning in spherical nanoparticles. These properties of the metal nanoparticles and their arrays have opened doors to numerous new scientific studies and technological applications in the field of catalysis, photonics, optoelectronics, biological labeling and imaging, sensing, magnetic devices, information storage, and so on. We have witnessed progress on both the experimental and theoretical fronts, though at different levels. The book provides an up-to-date, detailed coverage of such experimental and theoretical investigations of the syntheses and properties along with applications of metal nanoparticles of different morphologies and their assemblies.

References

1. Jin, R., Qian, H., Wu, Z., Zhu, Y., Zhu, M., Mohanty, A., and Garg, N. (2010) J. Phys. Chem. Lett., 1, 2903.

2. Daniel, M.-C. and Astruc, D. (2004) Chem. Rev., 104, 293.

3. Herron, N. and Thorn, D.L. (1998) Adv. Mater., 10, 1173.

4. Yacaman, M.J., Perez-Tijerina, E., and Mejia-Rosales, S. (2007) J. Mater. Chem., 17, 1035.

5. Matijevic, E. (1981) Acc. Chem. Res., 14, 22.

6. Sau, T.K., Rogach, A.L., Jäckel, F., Klar, T.A., and Feldmann, J. (2010) Adv. Mater., 22, 1805.

Chapter 1

Colloidal Synthesis of Noble Metal Nanoparticles of Complex Morphologies

Tapan K. Sau and Andrey L. Rogach

1.1 Introduction

Interesting properties and small volume of nanoparticles (NPs) have made them desirable for numerous studies and applications in many frontier scientific and technological fields. Synthesis plays crucial roles in tuning the volume as well as the properties of NPs. Many properties, which are known to be constant for bulk materials, vary with the size, shape, and surface structure of the nanomaterials. Therefore, one needs to develop the synthesis methodologies that can produce NPs of precisely controlled size, shape, crystal structure, surface chemistry, and chemical composition. This has prompted the researchers to produce an impressive range of NPs through various physical and (bio)chemical methods of synthesis. With the progress in synthesis, many exciting new nanomaterials with unique properties have been generated, which in turn has initiated numerous new scientific studies and technological applications.

NPs can be produced in the solid, liquid, solution, or gaseous state, following two broad, basic approaches, classified as “top-down” and “bottom-up” in the literature. In the top-down approach, one achieves structure sizes in the medium to lower nanometer range starting from large materials entity by using the physical and lithographic principles of micro- and nanotechnology. In the bottom-up approach, ionic, atomic, and molecular units assemble through various processes to form structures of nanometer length scale. The bottom-up approach in essence is the chemical synthesis method. In this approach, chemical synthesis principles are primarily employed starting from the generation of the constituents to their growth into nanoentity. The bottom-up approach allows, in principle, designing and producing NPs of any size and morphology via unit-by-unit deposition of the constituents. This approach offers an opportunity to understand the atomic/molecular-level aspects of the morphology development and the structure–property relationship in a particle. The bottom-up solution-phase synthesis methods are often denoted as “chemical colloidal” (or “colloid chemical”) methods, because they involve precipitation of nanometer-sized particles within a continuous solvent matrix forming colloidal sols. These methods of syntheses are inexpensive, versatile, and technologically simple to implement. Chemical colloidal methods and the materials thus produced are suitable for further processing, which is essential for integrating NPs in complex systems and devices. Therefore, chemical colloidal methods have been preferred methods for producing a wide-ranging NPs and nanocomposites of a variety of materials (e.g., metals, alloys, intermetallics, semiconductors, and ceramics).

Chemical colloidal synthesis routes have been extensively employed to prepare metal NPs, especially noble metal nanoparticles (NMNPs). NMNPs preparation via the chemical colloidal synthesis routes basically involves the (bio)chemical reduction of metal salts, photochemical and electrochemical pathways, or sonochemical/thermal decomposition of metallic compounds in aqueous or organic solvents in the presence of a variety of additives, such as surfactants, ligands, polymers, etc. In this chapter, we provide an overview of the chemical, photochemical, biochemical, and electrochemical synthesis routes that have been used to prepare NMNPs of “complex morphologies” (of mainly Ag, Au, Pd, and Pt metals). In our complex morphology terminology, we exclude single-component spherical NPs. Readers are referred to other chapters of this book as well as to a few excellent review articles for further reading [1–6]. Particle synthesis by sonochemical and thermal decomposition or hydrothermal methods is not considered here. Interested readers are referred to Refs [7, 8].