Introduction to Nanotechnology

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7.1. BASICS OF FERROMAGNETISM 7 NANOSTRUCTU RED FERROMAGNETISM In this chapter we discuss the effect of nanostructure on the properties of ferromagnets, and how the size of nanograins that make up bulk magnet materials affects ferromagnetic properties. We will examine how control of nanoparticle size can be used to design magnetic materials for various applications. In order to understand the role of nanostructure on ferromagnetism, we will present a brief overview of the properties of ferromagnets. In Chapter 4 we saw that certain atoms whose energy levels are not totally filled have a net magnetic moment, and in effect behave like small bar magnets. The value of the magnetic moment of a body is a measure of the strength of the magnetism that is present. Atoms in the various transition series of the periodic table have unfilled inner energy levels in which the spins of the electrons are unpaired, giving the atom a net magnetic moment. The iron atom has 26 electrons circulating about the nucleus. Eighteen of these electrons are in filled energy levels that constitute the argon atom inner core of the electron configuration. The d level of the N = 3 orbit contains only 6 of the possible 10 electrons that would Introduction to Nanotechnology, by Charles P. Poole Jr. and Frank J. Owens. ISBN 0-471-07935-9. Copyright 0 2003 John Wiley & Sons, Inc. 165
166 NANOSTRUCTURED FERROMAGNETISM fill it, so it is incomplete to the extent of four electrons. This incompletely filled electron d shell causes the iron atom to have a strong magnetic moment. When crystals such as bulk iron are formed from atoms having a net magnetic moment a number of different situations can occur relating to how the magnetic moments of the individual atoms are aligned with respect to each other. Figure 7.1 illustrates some of the possible arrangements that can occur in two dimensions. The point of the arrow is the north pole of the tiny bar magnet associated with the atom. If the magnetic moments are randomly arranged with respect to each other, as shown in Fig. 7.la, then the crystal has a zero net magnetic moment, and this is referred to as theparamagnetic state. The application of a DC magnetic field aligns some of the moments, giving the crystal a small net moment. In a ferromagnetic crystal these moments all point in the same direction, as shown in Fig. 7.lb, even when no DC magnetic field is applied, so the whole crystal has a magnetic moment and behaves like a bar magnet producing a magnetic field outside of it. If a crystal is made of two types of atoms, each having a magnetic moment of a different strength (indicated in Fig. 7.lc by the length of the arrow) the arrangement shown in Fig. 7.lc can occur, and it is calledferrimagnetic. Such a crystal will also have a net magnetic moment, and behave like a bar magnet. In an antiferromagnet the moments are arranged in (a) PARAMAGNETIC +++ +++ +++ (b) FERROMAGNETIC (c) FERRIMAGNETIC + - ++ -- f-- -f-- + ++ (d) ANTIFERROMAGNETIC Figure 7.1. Illustration of various arrangements of individual atomic magnetic moments that constitute paramagnetic (a), ferromagnetic (b), ferrimagnetic (c), and antiferromagnetic (d) materials.
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INTRODUCTION TO NANOTECHNOLOGY Char
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CONTENTS Preface xi 1 Introduction
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5.2 Carbon Molecules 103 5.2.1 Natu
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9.4 Excitons 244 9.5 Single-Electro
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PREFACE In recent years nanotechnol
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INTRODUCTION The prefix nano in the
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INTRODUCTION 3 he recognized the ex
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1000 (I) a 900 4 800 a 900 I 6 700
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INTRODUCTION 7 developed before the
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2.1. STRUCTURE 9 mechanics, the res
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X T 2.1. STRUCTURE 11 Figure 2.4. C
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2.1. STRUCTURE 13 Figure 2.6. Thirt
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Sodium Nanoparticle Na, Magic Numbe
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2.1. STRUCTURE 17 of the large anio
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2.1. STRUCTURE 19 other, and high-f
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2.2. ENERGY BANDS 21 Conduction Ban
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2.2. ENERGY BANDS 23 Figure 2.13. S
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2.2. ENERGYBANDS 25 band at point T
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A X ' Wavevector A Si c z 2.2. ENER
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2.2. ENERGY BANDS 29 bands of Figs.
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2.3. LOCALIZED PARTICLES 31 add ele
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1 meV 10 meV 100 meV FJ E W 1 eV 10
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3 METHODS OF MEASURING PROPERTIES 3
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3.2. STRUCTURE 37 Table 3.1. Crysta
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3.2. STRUCTURE 39 Figure 3.2. Two-d
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3.2. STRUCTURE 41 The widths of the
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44 METHODS OF MEASURING PROPERTIES
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3.3. MICROSCOPY 51 types of transit
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3.3. MICROSCOPY 53 Actual diverging
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Tunneling current Tunneling current
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3.3. MrCAOSCOPY 57 and the latter m
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3.4. SPECTROSCOPY 59 From Eq. (3.8)
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1 Average Panicle FWHM Size (nm) in
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CdSe colloidal NCs a = 1.2 nrn 3.4.
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El X-RAY TUBE 8000 - A 6000 - 4000
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2 N I w 3.0 2.5 2.0 1.5 1 .o 0.5 3.
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i 3.4. SPECTROSCOPY 69 NMR involves
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T=220K - 2G H FURTHER READING 71 Fi
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NUMBER OF ATOMS RADIUS (nm) 1 10 1
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I L 7 3 5 7 9 11 13 15 17 NUMBER OF
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JELLIUM MODEL OF CLUSTERS ATOMS CLU
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1.02 { 1.01 - 1 - 0.99 - 4.2. METAL
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4.2. METAL NANOCLUSTERS 81 Figure 4
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4.2. METAL NANOCLUSTERS 83 Figure 4
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-0 100 200 300 400 500 600 MASSICHA
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a 42. METAL NANOCLUSTERS 87 Figure
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. . . .. . - . D 111111111111111111
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3 4 2.5 0 cn g 2 0 z d 1.5 t a 9 1
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4.3. SEMICONDUCTING NANOPARTICLES 9
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4.4. RARE GAS AND MOLECULAR CLUSTER
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4.5. METHODS OF SYNTHESIS 97 d Figu
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4.5. METHODS OF SYNTHESIS 99 isopro
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PULSED LASER BEAM 1 1 1 1 1 I ROTAT
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5.1. INTRODUCTION CARBON NANOSTRUCT
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5.2. CARBON MOLECULES 105 methane d
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5.3. CARBON CLUSTERS 107 -0 20 40 6
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PHOTON ENERGY (electron volts) 5.3.
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Figure 5.6. Structure of the CEO fu
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1 30 0 14.1 14.2 14.3 14.4 14.5 LAT
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- ? m v .- - z In C a, c C - .. . .
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Excitatior I [eV]: 2.175 2.214 2.25
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6 100 200 300 Time (ns) 8.3. LUMINE
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400 nm Laser / Free excitons Trappe
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8.4. NANOSTRUCTURES IN ZEOLITE CAGE
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FURTHER READING 225 P. Milani and C
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9.2. PREPARATION OF QUANTUM NANOSTR
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i 9.2. PREPARATION OF QUANTUM NANOS
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9.3. SIZE AND DIMENSIONALITY EFFECT
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w n 3 2 1 9.3. SIZE AND DIMENSIONAL
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WE) Quantum Dot Number of Electrons
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9.5. SINGLE-ELECTRON TUNNELING 245
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9.5. SINGLE-ELECTRON TUNNELING 247
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1 pair section ;- COT. .; . . I. .
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o.6 LWIR: T = 77 K 45" incidence AD
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9.7. SUPERCONDUCTIVITY 253 horizont
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9.7. SUPERCONDUCTIVITY 255 applied
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10.1. SELF-ASSEMBLY 10 SELF-ASSEMBL
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10.1. SELF-ASSEMBLY 259 factor of 2
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(a) (LI (dl 10.1. SELF-ASSEMBLY 261
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10.1. SELF-ASSEMBLY 263 atoms, as n
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- c v) ._ C 3 2 9 40 c - .- e m v w
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10.2. CATALYSIS 267 where the lengt
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10.2. CATALYSIS 269 are also other
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1600 2 1200 t p - Bi2M020, 10.2. CA
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7 - I 2,330 m .- c r 0 2 2,300 - u)
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10.2. CATALYSIS 275 with a top and
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10.2. CATALYSIS 277 based on the pr
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10.2. CATALYSIS 279 CnHlnfl, which
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I1 ORGANIC COMPOUNDS AND POLYMERS 1
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11.2. FORMING AND CHARACTERIZING PO
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1 1.3. NANOCRYSTALS 285 This expres
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-1 5 0) C a, -1 1 000 300 100 30 10
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11.3. NANOCRYSTALS 289 Table 11.1.
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11.3. NANOCRYSTALS 291 R’ groups
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11.4. POLYMERS 293 Figure 11.9. Ske
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11.5. SUPRAMOLECULAR STRUCTURES 295
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M Et3P OTf M=Pd M=Pt M=Pd, 41 % M=P
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11.5. SVPRAMOLECUUAR STRUCTURES 2s
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11 5. SUPRAMOLECULAR STRUCTURES 303
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BiodegradaWe surface 4 Functional g
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FURTHER READING 309 F. J. Owens and
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12.2. BIOLOGICAL BUILDING BLOCKS 31
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314 BIOLOGICAL MATERIALS which we w
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316 BIOLOGICAL MATERIALS Table 12.2
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318 BIOLOGICAL MATERtALS i J / Flgu
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320 BIOLOGICAL MATERIALS Pyrimidine
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322 BlOLMjlCAL MATERiALS (a) DNA do
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324 BIOLOGICAL MATERIALS so each wo
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326 BIOLOGICAL MATERIALS 12.4.2. Mi
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328 BIOLOGICAL MATERIALS tions they
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330 BIOLOGICAL MATERIALS hardened f
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13 NANOMACHINES AND NANODEVICES In
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334 NANOMACHINES AND NANODEVICES CA
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336 NANOMACHINES AND NANODEVICES Op
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338 NANOMACHINES AND NANODEVICES ti
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340 NANOMACHINES AN0 NANODEVICES PO
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342 NANOMACHINES AND NANODEVICES X
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344 NANOMACHINES AND NANODEVICES na
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346 NANOMACHINES AND NANODEVICES 31
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348 NANOMACHINES AND NANODEVICES -
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350 NANOMACHINES AND NANODEVICES re
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352 NANOMACHINES AND NANODEVICES 1
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354 NANOMACHINES AND NANODEVICES -1
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A.l. INTRODUCTION APPENDIX A FORMUL
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A.3. PARTIAL CONFINEMENT 359 limiti
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APPENDIX B TABULATIONS OF SEMICONDU
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TABULATIONS OF SEMICONDUCTING MATER
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Table B.8. Effective masses m+ rela
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372 INDEX amoeba, 3 16 amphiphilic,
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374 INDEX CdS, 9, 130, 213, 216, 36
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376 INDEX dispersion, 277 disulfide
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378 INDEX Ga (gallium) (continued)
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380 INDEX length (continued) critic
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382 INDEX multiple ionization, 93 r
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384 INDEX pi-conjugation, 282, 292
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silica, 269 silica-alumina, 269, 27
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388 INDEX wavefimction (continued)
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