Introduction to Nanoscience and Nanotechnology

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2 Introduction to Nanoscience and Nanotechnology K.K. CHATTOPADHYAY Thin Film and Nanoscience Laboratory Department of Physics Jadavpur University Kolkata A.N. BANERJEE Department Aerospace Engineering Sciences University of Colorado at Boulder Boulder New Delhi

3 INTRODUCTION TO NANOSCIENCE AND NANOTECHNOLOGY K.K. Chattopadhyay and A.N. Banerjee 2009 by PHI Learning Private Limited, New Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN The export rights of this book are vested solely with the publisher. Published by Asoke K. Ghosh, PHI Learning Private Limited, M-97, Connaught Circus, New Delhi and Printed by Rajkamal Electric Press, B-35/9, G.T. Karnal Road Industrial Area, Delhi

4 Contents Preface 1. INTRODUCTION Background of Nanoscience and Nanotechnology Definition of Nanoscience and Nanotechnology Possible Applications of Nanotechnology Organization of the Book 4 References 5 2. CRYSTAL BONDING, STRUCTURE, GROWTH AND SYMMETRIES Introduction Crystal Bonding Crystal Structure Crystal Growth Classification of Crystals by Symmetry Some Important Crystal Structures 22 Exercises 34 References BAND STRUCTURE AND DENSITY OF STATES AT NANOSCALE Introduction Energy Bands Density of States at Low-dimensional Structures 41 Exercises 46 References ELECTRICAL TRANSPORT IN NANOSTRUCTURE Electrical Conduction in Metals Classical Theory The Drude Model Quantum Theory The Free Electron Model 51 iii vii

5 iv Contents 4.2 Conduction in Insulators/Ionic Crystals Electron Transport in Semiconductors Various Conduction Mechanisms in 3D (Bulk), 2D (Thin Film) and Low-dimensional Systems Thermionic Emission Field-enhanced Thermionic Emission (Schottky Effect) Field-assisted Thermionic Emission from Traps (Poole Frenkel Effect) Arrhenius Type Thermally Activated Conduction Variable Range Hopping Conduction Polaron Conduction 67 Exercises 69 References INTRODUCTORY QUANTUM MECHANICS FOR NANOSCIENCE Introduction Size-effects in Smaller Systems: Pre-quantum Quantum Behaviour of Nanometric World Bohr s Model of Hydrogen Atom Wave-particle Duality: de Broglie Wavelength Wave Function Associated with an Electron Heisenberg Uncertainty Principle; Description of Matter Wave: Wave Packet Schrödinger Equation Applications of Schrödinger Equation 88 Exercises 105 References GROWTH TECHNIQUES OF NANOMATERIALS Introduction Top-down vs. Bottom-up Technique Lithographic Process and its Limitations Nonlithographic Techniques Plasma Arc Discharge Sputtering Evaporation Chemical Vapour Deposition Pulsed Laser Deposition Molecular Beam Epitaxy Sol Gel Technique Electrodeposition Other Processes 161 Exercises 171 References 172

6 Contents v 7. CHARACTERIZATION TOOLS OF NANOMATERIALS Scanning Probe Microscopy (SPM) Introduction Basic Principles of SPM Techniques The Details of STM Summary of STM General Concept and Defining Characteristics of AFM Scanned-Proximity Probe Microscopes Laser Beam Deflection AFM Cantilevers Piezoceramics Feedback Loop Alternative Imaging Modes AFM and Biology Electron Microscopy Introduction Resolution vs. Magnification Scanning Electron Microscope SEM Techniques Electron Gun Specimen Interactions Environmental SEM Transmission Electron Microscope High Resolution TEM Contrast Transfer Function 214 Exercises 215 References SOME SPECIAL TOPICS IN NANOTECHNOLOGY Introduction The Era of New Nanostructures of Carbon Buckminsterfullerene Carbon Nanotube Nanodiamond BN Nanotubes Nanoelectronics Single Electron Transistor Molecular Machine Nanobiometrics 251 Exercises 260 References 261 INDEX

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8 Preface The discipline of nanoscience and nanotechnology has recently become one of the most important areas of knowledge encompassing various scientific disciplines including physics, chemistry, biology and engineering. This tremendous interest is mainly due to two reasons. Firstly, nanoscale materials have many prospects in various technological applications because most of the time, they show novel functionalities. Secondly, there is tremendous scope of creating new knowledge in explaining the size dependencies of the evolution of various physical properties, and in explaining new and previously unnoticed features, etc. Nanostructured materials can be utilized in fabricating novel active devices with improved functionalities. For example, one-dimensional nanomaterials (tubes, wires, rods, etc.) are an important class of nanostructured materials with potential applications in electronics, composite fabrications or sensor developments. On the other hand, physical properties of the one-dimensional nanostructures will be different from their bulk behaviours. For example, electron transport processes will be different in the one-dimensional structures from their bulk counterpart. While physicists are more concerned with developing the requisite theories for describing the observed properties, technologists are interested in developing some useful devices or materials. Synthesis of nanomaterials is another key issue. Future prospects in developing nanoscale devices for various applications largely depend on the controlled growth of nanomaterials. General approaches in synthesizing nanomaterials involve vapour, liquid or solid state routes or their intelligent combinations. Substantial advancement has been achieved in terms of understanding the growth mechanism and also in creating exotic nanostructured materials in the last few decades. However, many other related issues are involved in developing new synthesis routes and also in fabricating useful devices. To achieve any new advancement in any of these related fields, it is of utmost importance to have a thorough understanding of the fundamental issues of low-dimensional systems. Moreover, acquiring an understanding of the physical phenomena in nanostructured materials is now a common scientific issue. In recent times, graduate and postgraduate courses have begun to be offered in nanoscience and nanotechnology in many universities and institutes. The students come from various backgrounds including different branches of the basic sciences and also from various engineering disciplines. Our vii

9 viii Preface experience during the last several years of teaching M.Tech students in nanoscience and nanotechnology has made us realize that some common minimum platform of knowledge is essential for the students to understand and assimilate the key issues of this emerging subject matter. This book has originated from this specific need. The knowledge base of the nanoscience and nanotechnology has already reached a tremendous volume to which new ideas are being added everyday. A large number of review articles by many leading scientists from various parts of the world and numerous research papers are being published regularly. Several international journals are specifically dedicated to publishing papers on nanoscience and nanotechnology. It is difficult even for a specialist to remain up-to-date with the latest information. The field of nanoscience and nanotechnology has become too vast, too interdisciplinary and also too dynamic to be covered exhaustively in a book of this size. On the other hand, there are many new starters in this field in universities, institutes and also in industries. In this book, we have tried to cover some basic issues of the nanoscience and nanotechnology. We believe that this book will not only serve as a textbook for the undergraduate and postgraduate students in nanoscience and nanotechnology, but also be used as a reference book by the researchers in the field. We have tried to discuss the basic scientific issues for imparting a thorough understanding of the fundamental aspects of nanoscience and nanotechnology rather than merely describing some general informations. There are many scientists, students and teachers to whom the authors are grateful for helping them in different ways in preparing the manuscript of this book. Particularly, the authors wish to acknowledge the scholars of the Thin Film and Nanoscience Laboratory of Jadavpur University for many suggestions and useful discussions. The authors are extremely grateful to Prof. M.K. Mitra, Prof. G.C. Das, Prof. S. Mukherjee of Jadavpur University, Prof. T. Endo of Mie University, Japan, and Prof. I. An of Hanyang University, Korea, for their useful suggestions and discussions. We also wish to thank our wives for the support which they provided during the writing of the manuscript. In spite of our best efforts, there may be some unintentional mistakes. Comments and suggestions to improve the book are always welcome and we will try to incorporate those in the future editions. Finally, we fervently hope that this book will be useful to a large spectrum of students and researchers who wish to enter this field. K.K. Chattopadhyay A.N. Banerjee

10 1 Introduction 1.1 BACKGROUND OF NANOSCIENCE AND NANOTECHNOLOGY Today s widespread activities in nanoscience and technology are actually rooted in the ideas of some leading scientists of the last century. Among them, the foremost name was Richard P. Feynman. He delivered a legendary talk entitled there is plenty of room at the bottom in the Annual general body meeting of the American Physical society on December 29, 1959 [1] at California Institute of Technology. In that talk he discussed about the ideas of manipulating and controlling things at the atomic scale. In this famous lecture the great scientist uttered also these famous words the principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom. He also envisioned building circuits having sizes few nanometers that can be used as elements in more powerful computers. In that time these ideas were regarded too speculative. But nearly twenty years later from this prophetic talk, many inventions and discoveries began to appear justifying Feynman s timeahead ideas. Soon the technology advisors and predictors realized the importance of these discoveries and declared that a new revolution is imminent namely nanotechnology, just as in the past we experienced industrial revolution and information revolution. Drexler expanded Feynman s ideas and definition in a stimulating and lateral thinking way in his book, Engines of Creation, the Coming Age of Nanotechnology [2]. We can quote Drexler to have some ideas about nanotechnology: Nanotechnology is the principle of manipulation atom by atom, through control of the structure of matter at the molecular level. It entails the ability to build molecular systems with atom-by-atom precision, yielding a variety of nanomachines. In recognition with this reality National Science and Technology Council (NSTC) of USA created an integrating working group on nanoscience, engineering and technology in Then in the year 2001 they announced the National Nanotechnology Initiative (NNI) programme with a large amount of fund in the budgetary provisions [3]. The major objective of this initiative was to create a common platform for the academia, industries and also private sector for working on this new technology. Following this example, most of the advanced countries in the world and many developing countries including China and India invested heavily on research and development in this new field of science and technology. 1

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