Introduction to Nanotechnology

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. . . .. . - . D 11111111111111111111111111111111111111IIIIIIL 4.2. METAL NANOCLUSTERS 89 = 0 2 :::I 1 1 0.4 . 2 ~ OL 0 NUMBER OF ATOMS Figure4.17. Plot of the magnetic moment per atom of rhenium nanoparticles versus the number of atoms in the particle. [Adapted from A. J. Cox et al., Phys. Rev. 849, 12295 (1994).] Clusters of gold have been found to have the same melting point of bulk gold only when they contain 1000 atoms or more. Figure 4.18 is a plot of the melting temperature of gold nanoparticles versus the diameter of the particle. The average separation of copper atoms in a copper cluster approaches the value of the bulk material when the clusters have 100 atoms or more. In general, it appears that different physical properties of clusters reach the characteristic values of the solid at different cluster sizes. The size of the cluster where the transition to bulk behavior occurs appears to depend on the property being measured. .--- 1300-1 I I 4 I I I I I I I I I I I I I I I I I I A:~TI - - '- - - LI 1250 > - / / 1200 F - 1150 Y g 1100 + / / I I I I I ; - - - 3 k 1050 - 1000; ; - 3 - 5 950 I- 900 F ; - I 850 I - : I 800~1"""1""""""'1"'-
90 PROPERTIES OF INDIVIDUAL NANOPARTICLES 4.3. SEMICONDUCTING NANOPARTICLES 4.3.1. Optical Properties Because of their role in quantum dots, nanoparticles made of the elements, which are normal constituents of semiconductors, have been the subject of much study, with particular emphasis on their electronic properties. The title of this section, “semiconducting nanoparticles,” is somewhat misleading. Nanoparticles made of cad- mium, germanium, or silicon are not themselves semiconductors. A nanoparticle of Si,, can be made by laser evaporation of a Si substrate in the region of a helium gas pulse. The beam of neutral clusters is photolyzed by a UV laser producing ionized clusters whose mass to charge ratio is then measured in a mass spectrometer. The most striking property of nanoparticles made of semiconducting elements is the pronounced changes in their optical properties compared to those of the bulk material. There is a significant shift in the optical absorption spectra toward the blue (shorter wavelength) as the particle size is reduced. In a bulk semiconductor a bound electron-hole pair, called an exciton, can be produced by a photon having an energy greater than that of the band gap of the material. The band gap is the energy separation between the top filled energy level of the valence band and the nearest unfilled level in the conduction band above it. The photon excites an electron from the filled band to the unfilled band above. The result is a hole in the otherwise filled valence band, which corresponds to an electron with an effective positive charge. Because of the Coulomb attraction between the positive hole and the negative electron, a bound pair, called an exciton, is formed that can move through the lattice. The separation between the hole and the electron is many lattice parameters. The existence of the exciton has a strong influence on the electronic properties of the semiconductor and its optical absorption. The exciton can be modeled as a hydrogen-like atom and has energy levels with relative spacings analogous to the energy levels of the hydrogen atom but with lower actual energies, as explained in Section 2.3.3. Light-induced transitions between these hydrogen- like energy levels produce a series of optical absorptions that can be labeled by the principal quantum numbers of the hydrogen energy levels. Figure 4.19 presents the optical absorption spectra of cuprous oxide (Cu20), showing the absorption spectra due to the exciton. We are particularly interested in what happens when the sue of the nanoparticle becomes smaller than or comparable to the radius of the orbit of the electron-hole pair. There are two situations, called the weak-conjinement and the strong-conjnement regimes. In the weak regime the particle radius is larger than the radius of the electron-hole pair, but the range of motion of the exciton is limited, which causes a blue shift of the absorption spectrum. When the radius of the particle is smaller than the orbital radius of the electron-hole pair, the motion of the electron and the hole become independent, and the exciton does not exist. The hole and the electron have their own set of energy levels. Here there is also a blue shift, and the emergence of a new set of absorption lines. Figure 4.20 shows the optical absorption spectra of a CdSe nanoparticle at two different sizes measured at 10 K. One can see that the lowest energy absorption region, referred to as the absorption edge, is
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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
Page 50 and 51: 3.2. STRUCTURE 39 Figure 3.2. Two-d
Page 52 and 53: 3.2. STRUCTURE 41 The widths of the
Page 55 and 56: 44 METHODS OF MEASURING PROPERTIES
Page 62 and 63: 3.3. MICROSCOPY 51 types of transit
Page 64 and 65: 3.3. MICROSCOPY 53 Actual diverging
Page 66 and 67: Tunneling current Tunneling current
Page 68 and 69: 3.3. MrCAOSCOPY 57 and the latter m
Page 70 and 71: 3.4. SPECTROSCOPY 59 From Eq. (3.8)
Page 72 and 73: 1 Average Panicle FWHM Size (nm) in
Page 74 and 75: CdSe colloidal NCs a = 1.2 nrn 3.4.
Page 76 and 77: El X-RAY TUBE 8000 - A 6000 - 4000
Page 78 and 79: 2 N I w 3.0 2.5 2.0 1.5 1 .o 0.5 3.
Page 80 and 81: i 3.4. SPECTROSCOPY 69 NMR involves
Page 82 and 83: T=220K - 2G H FURTHER READING 71 Fi
Page 84 and 85: NUMBER OF ATOMS RADIUS (nm) 1 10 1
Page 86 and 87: I L 7 3 5 7 9 11 13 15 17 NUMBER OF
Page 88 and 89: JELLIUM MODEL OF CLUSTERS ATOMS CLU
Page 90 and 91: 1.02 { 1.01 - 1 - 0.99 - 4.2. METAL
Page 92 and 93: 4.2. METAL NANOCLUSTERS 81 Figure 4
Page 94 and 95: 4.2. METAL NANOCLUSTERS 83 Figure 4
Page 96 and 97: -0 100 200 300 400 500 600 MASSICHA
Page 98 and 99: a 42. METAL NANOCLUSTERS 87 Figure
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Page 104 and 105: 4.3. SEMICONDUCTING NANOPARTICLES 9
Page 106 and 107: 4.4. RARE GAS AND MOLECULAR CLUSTER
Page 108 and 109: 4.5. METHODS OF SYNTHESIS 97 d Figu
Page 110 and 111: 4.5. METHODS OF SYNTHESIS 99 isopro
Page 112 and 113: PULSED LASER BEAM 1 1 1 1 1 I ROTAT
Page 114 and 115: 5.1. INTRODUCTION CARBON NANOSTRUCT
Page 116 and 117: 5.2. CARBON MOLECULES 105 methane d
Page 118 and 119: 5.3. CARBON CLUSTERS 107 -0 20 40 6
Page 120 and 121: PHOTON ENERGY (electron volts) 5.3.
Page 122 and 123: Figure 5.6. Structure of the CEO fu
Page 124 and 125: 1 30 0 14.1 14.2 14.3 14.4 14.5 LAT
Page 126 and 127: (c) 5.4. CARBON NANOTUBES 115 Figur
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Page 130 and 131: 5.4. CARBON NANOTUBES 11 9 investig
Page 132 and 133: 5.4. CARBON NANOTUBES 121 energy gr
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Page 144 and 145: BULK NANOSTRUCTURED MATERIALS In th
Page 146 and 147: h 8 0 6.1. SOLID DISORDERED NANOSTR
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6.1. SOLID DISORDERED NANOSTRUCTURE
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6.2. NANOSTRUCTURED CRYSTALS 153 qu
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6.2. NANOSTRUCTURED CRYSTALS 155 Fi
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158 BULK NANOSTRUCTURED MATERIALS 6
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160 BULK NANOSTRUCTURED MATERIALS w
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162 BULK NANOSTRUCTURED MATERIALS 0
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164 BULK NANOSTRUCTURED MATERIALS n
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166 NANOSTRUCTURED FERROMAGNETISM f
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168 NANOSTRUCTURED FERROMAGNETISM i
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170 NANOSTRUCTURED FERROMAGNETISM M
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172 NANOSTRUCTURED FERROMAGNETISM h
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174 NANOSTRUCTURED FERROMAGNETISM d
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176 NANOSTRUCTURED FERROMAGNETISM o
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4 h $ 3 7.5. NANOCARBON FERROMAGNET
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7.6. GIANT AND COLOSSAL MAGNETORESI
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1.4 N 1 1.2 z " 1 0 v 5 h 0.8 0 0.6
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7.6. GIANT AND COLOSSAL MAGNETORESI
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7.7. FERROFLUIDS 187 Figure 7.22. M
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7.7. FECIROFLUIDS 189 Figure 7.25.
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7.7. FERRQFLUlOS 191 FerroRuids can
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FURTHER READING FURTHER READING 193
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10- IR f IA -1 8.1. INTRODUCTION 19
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8.2. INFRARED FREQUENCY RANGE 197 1
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8.2. INFRARED FREQUENCY RANGE 199 d
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s C CTI e 8 9 4( 8.2. INFRARED FREQ
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8.2.3. Raman Spectroscopy 8.2. INFR
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8.2. INFRARED FREQUENCY RANGE 205 a
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- r I 520 51 8 v 6 516 a" 51 4 51 2
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8.2. INFRARED FREQUENCY RANGE 209 i
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v) - C 3 8 600 400 100 0 e e 10 20
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i E (cm-’ ) 20 c I 1 ID 0 4x107 8
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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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