Metallic Nanoparticles

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• Publisher: Elsevier Science
• Year: 2008
• Print ISBN: 9780444512406
• eBook ISBN: 9780080559698
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Metallic nanoparticles display fascinating properties that are quite different from those of individual atoms, surfaces or bulk rmaterials. They are a focus of interest for fundamental science and, because of their huge potential in nanotechnology, they are the subject of intense research effort in a range of disciplines. Applications, or potential applications, are diverse and interdisciplinary. They include, for example, use in biochemistry, in catalysis and as chemical and biological sensors, as systems for nanoelectronics and nanostructured magnetism (e.g. data storage devices), where the drive for further miniaturization provides tremendous technological challenges and, in medicine, there is interest in their potential as agents for drug delivery.The book describes the structure of metallic nanoparticles, the experimental and theoretical techniques by which this is determined, and the models employed to facilitate understanding. The various methods for the production of nanoparticles are outlined. It surveys the properties of clusters and the methods of characterisation, such as photoionization, optical spectroscopy, chemical reactivity and magnetic behaviour, and discusses element-specific information that can be extracted by synchrotron-based techniques such as EXAFS, XMCD and XMLD. The properties of clusters can vary depending on whether they are free, deposited on a surface or embedded in a matrix of another material; these issues are explored. Clusters on a surface can be formed by the diffusion and aggregation of atoms; ways of modelling these processes are described. Finally we look at nanotechnology and examine the science behind the potential of metallic nanoparticles in chemical synthesis, catalysis, the magnetic separation of biomolecules, the detection of DNA, the controlled release of molecules and their relevance to data storage.The book addresses a wide audience. There was a huge development of the subject beginning in the mid-1980s where researchers began to study the properties of free nanoparticle and models were developed to describe the observations. The newcomer is introduced to the established models and techniques of the field without the need to refer to other sources to make the material accessible. It then takes the reader through to the latest research and provides a comprehensive list of references for those who wish to pursue particular aspects in more detail. It will also be an invaluable handbook for the expert in a particular aspect of nanoscale research who wishes to acquire knowledge of other areas.The authors are specialists in different aspects of the subject with expertise in physics and chemistry, experimental techniques and computational modelling, and in interdisciplinary research. They have collaborated in research. They have also collaborated in writing this book, with the aim from the outset of making it is a coherent whole rather than a series of independent loosely connected articles.* Appeals to a wide audience* Provides an introduction to established models and techniques in the field* Comprehensive list of references

Chapter 1 Introduction

J.A. Blackman^1,2, C. Binns²

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¹ Department of Physics, University of Reading, Whiteknights, Reading RG6 6AF, UK

² Department of Physics and Astronomy, University Road, University of Leicester, Leicester LE1 7RH, UK

Abstract

This chapter outlines the scope of the book. It begins with a discussion of origins of the concepts of ‘nanoscience’, ‘nanotechnology’ and the ‘nano’ prefix. The context is set with a note of the size and the surface/volume ratio of nanoparticles. The idea of geometric and electronic structures are introduced. The four basic methods of production are summarised, together with a note of some key properties such as the optical and magnetic behaviour. Suggestions for further reading are given.

keywords

Nanoscience • Nanotechnology • Nano

1.1 Nanoscience and nanotechnology

Since the 1980s, there has been a rapid expansion in the field now known as nanoscience [1]. The research area encompasses physics, chemistry, biology, engineering, medicine and materials science, and impacts on other disciplines as well. Nanoscience addresses a large number of important issues, with many of these having the potential for novel technical applications. When the focus moves from the basic science towards the applications, the term nanotechnology is more commonly used.

Nanoscience is generally defined as the study of phenomena on the scale of 1–100 nm, although it is often convenient to extend the range a little at either end. Nanotechnology is the ability to create, control and manipulate objects on this scale with the aim of producing novel materials that have specific properties (functionalised materials).

As defined above, nanoscience is nothing new. Faraday [2] studied colloidal gold particles and lectured on his investigations in 1857. The motivation for his study was the red colour of the gold particles, a striking contrast to the familiar yellow appearance of gold in its bulk form. By a similar argument, the use of small metal particles (smaller than 100 nm) to produce decorative effects in stained glass for church windows or in pottery glazes would date nanotechnology back to mediaeval times or even earlier [3,4].

However, it is the recent invention of a variety of tools for studying systems at the atomic level, coupled with the development of techniques for producing nanoparticles, that has led to the emergence of nanoscience as a new field of study. Of primary importance are the scanning probe microscopes, that make it possible not just to “see” individual atoms and molecules on the surfaces of materials but to move them on the nanoscale as well. The scanning tunnelling microscope (STM), the first scanning probe microscope, appeared in 1982 [5,6] and, in 1986, Gerd Binnig and Heinrich Rohrer were awarded the Nobel Prize in physics for its design. Important also is the ability to study the properties of isolated nanoclusters. Even if the technological interest is in clusters on a surface or embedded in a material, an investigation in their isolated state unencumbered by the background material is an essential first step for understanding their properties. New sources to produce clusters in the gas phase were developed during the 1960s and 1970s [7], but it was in the 1980s that Knight's group [8] first produced clusters of alkali metals with up to about 100 atoms and systematically studied their properties.

Nano-objects have a size that is intermediate between atoms (or molecules) and bulk matter. Even for clusters of 1000 atoms, more than one-quarter of the atoms lie on the surface, resulting in properties that are very different from those of atoms or bulk. The properties vary strongly with the size, shape and composition of the nanoparticle. This has been exploited, certainly since the 1960s, in heterogeneous catalysis [9]. Catalysts comprise metallic nanoparticles dispersed on a porous material, with optimisation for the best reaction rate and selectivity largely by trial and error. However, the catalysts can now be fully characterised using the available nanoscience techniques.

More recently, there have been developments towards biological and medical uses of nanoparticles. The entrapment of anticancer drugs in nanoparticles, and the decoration of the particles with molecular ligands for the targeting of cancerous cells, offers the prospect of more effective cancer therapy with reduced side-effects [10]. An alternative strategy for the use of nanoparticles in cancer treatment is photothermal tumour ablation [11]. Nanoparticles absorb laser light at a characteristic frequency and the associated heating can be used to destroy solid tumours. The aim would be to tune the particle to a frequency for which the absorption by tissue is low.

The binding of biological molecules (DNA) to metallic nanoparticles provides the basis for a number of possible applications. DNA is highly programmable and this characteristic can, in principle, be exploited to self-assemble functionalised nanoparticles into structures with more complex architecture [12]. One possible use is as sensors of biological or chemical molecules.

There is considerable potential for exploiting the magnetic properties of nanoscale structures in spintronics (also known as magnetoelectronics) [13]. High-density data storage is one of the goals, and possible systems for quantum information devices [14] are being explored that are based on the quantum tunnelling of the magnetisation of a cluster through a magnetic anisotropy barrier. The most successful spintronics device to date is the spin valve. This is based on two magnetic layers, one hard and one soft magnetically. An external magnetic field can switch the direction of the magnetisation of the soft layer while leaving that of the other layer unchanged. The switch is accompanied by a sharp increase in the electrical resistance due to spin-dependent scattering of the electrons.

1.2 A note on etymology, neologisms and terminology

The prefix nano- is variously said to derive from the Greek word ν

νος or the Latin word nannus, both meaning dwarf. It was adopted as an official SI prefix, meaning 10⁻⁹ of an SI base unit, at the 11th Conférence Générale des Poids et Mesures (CGPM) in 1960 (Comptes Rendus de la CGPM, 87, Rés. 12) [15,16], although it had informal status before that.

The Oxford English Dictionary (OED) [17] credits Taniguchi [18] with the first use of the word “nanotechnology” in 1974, followed sometime after by Drexler [19] in a book entitled Engines of Creation. Interestingly, the OED does not see fit to include “nanoscience” in its compilation of nano- words, although the term was certainly in use by the early 1990s [20,21].

Taniguchi, a precision engineer, had in mind technologies operating to tolerances of less than 100 nm, whereas Drexler's idea of nanotechnology concerned the manipulation and assembly of structures at the molecular scale, a concept already discussed in 1959 by Feynman in a lecture entitled There's Plenty of Room at the Bottom[22]. One of the legacies of Drexler's imaginative work is the term “grey goo”, which describes a nightmare scenario where nanorobots run out of control and destroy everything while replicating themselves. Unfortunately the term can be (and has been) used to spice up articles about nanoscience in the sensational press and give it a negative slant, inhibiting sensible discussion.

Although nanoscience and nanotechnology are generally the preferred words used to describe national research programmes [23], the terms are so broad that the umbrella covers many topics that have little in common. As a consequence, the prefix is increasingly appearing in front of traditional disciplines as in nanophysics, nanomaterials or nanomedicine. Doubtless the use of the word nano in product names [24], such as the iPod and the car from Tata Motors, provides further confusion for those who are not part of the scientific community.

We shall be concerned in this book with metallic nanoparticles. The scope of material covered is summarised in the rest of this chapter. A brief note on terminology concludes this section. Two main approaches are used in creating nanostructures: “bottom-up” and “top-down”. The top-down method involves starting with a larger piece of material and forming a nanostructure from it by removing material through etching or machining. The various lithography techniques (e.g. electron beam and focused ion beam (FIB) lithograp...

Table of contents

• Cover image
• Title page
• Table of Contents
• Handbook of Metal Physics
• Copyright page
• Dedication
• Preface
• Volume Preface
• Chapter 1 Introduction
• Chapter 2 Shell Models of Isolated Clusters
• Chapter 3 Production of Nanoparticles on Supports Using Gas-Phase Deposition and MBE
• Chapter 4 Theory of Cluster Growth on Surfaces
• Chapter 5 Chemical Methods for Preparation of Nanoparticles in Solution
• Chapter 6 Structure of Isolated Clusters
• Chapter 7 Photoexcitation and Optical Absorption
• Chapter 8 Magnetism in Isolated Clusters
• Chapter 9 Magnetism in Supported and Embedded Clusters
• Chapter 10 Some Applications of Nanoparticles
• Index