Introduction to Nanotechnology

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WE) Quantum Dot Number of Electrons N(E) L E 9.3. SIZE AND DIMENSIONALITY EFFECTS 243 Density I of states, D(E) E Quantum Wire ,n E E Quantum we,: n E E NE) Bulk Conductor E E Figure 9.15. Number of electrons N(E) (left side) and density of states D(€J (right side) plotted against the energy for four quantum structures in the square welKermi gas approximations.
244 QUANTUM WELLS, WIRES, AND DOTS electronic density of states D(E) at the Fermi level, and its lack of dependence on the temperature. When a good conductor such as aluminum is bombarded by fast electrons with just enough energy to remove an electron from a particular A1 inner-core energy level, the vacant level left behind constitutes a hole in the inner-core band. An electron from the conduction band of the aluminum can fall into the vacant inner-core level to occupy it, with the simultaneous emission of an X ray in the process. The intensity of the emitted X radiation is proportional to the density of states of the conduction electrons because the number of electrons with each particular energy that jumps down to fill the hole is proportional to D(E). Therefore a plot of the emitted X-ray intensity versus the X-ray energy E has a shape very similar to a plot of D(E) versus E. These emitted X rays for aluminum are in the energy range from 56 to 77 e\! Some other properties and experiments that depend on the density of states and can provide information on it are photoemission spectroscopy, Seebeck effect (thermopower) measurements, the concentrations of electrons and holes in semiconductors, optical absorption determinations of the dielectric constant, the Fermi contact term in nuclear magnetic resonance (NMR), the de Haas-van Alphen effect, the superconducting energy gap, and Josephson junction tunneling in superconduc- tors. It would take us too far afield to discuss any of these topics. Experimental measurements of these various properties permit us to determine the form of the density of states D(E), both at the Fermi level EF and over a broad range of temperature. 9.4. EXCITONS Excitons, which were introduced in Section 2.3.3, are a common occurrence in semiconductors. When an atom at a lattice site loses an electron, the atom acquires a positive charge that is called a hole. If the hole remains localized at the lattice site, and the detached negative electron remains in its neighborhood, it will be attracted to the positively charged hole through the Coulomb interaction, and can become bound to form a hydrogen-type atom. Technically speaking, this is called a Mott-Wunnier type of exciton. The Coulomb force of attraction between two charges Q, = -e and Qh = +e separated by a distance r is given by F = -k2/&?, where e is the electronic charge, k is a universal constant, and E is the dielectric constant of the medium. The exciton has a Rydberg series of energies E sketched in Fig. 2.20 and a radius given by Eq. (2.19): ueff = 0.0529(~/~,)/(m*/m,), where &/EO is the ratio of the dielectric constant of the medium to that of free space, and m*/mo is the ratio of the effective mass of the exciton to that of a free electron. Using the dielectric constant and electron effective mass values from Tables B. 11 and B.8, respectively, we obtain for GaAs E = 5.2meV ueff = 10.4nm (9.10)
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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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(c) 5.4. CARBON NANOTUBES 115 Figur
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5.4. CARBON NANOTUBES 1 17 The mech
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5.4. CARBON NANOTUBES 11 9 investig
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5.4. CARBON NANOTUBES 121 energy gr
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5.4. CARBON NANOTUBES 123 stretch c
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5.5. APPLICATIONS OF CARBON NANOTUB
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- v) 450 : 400 3 350 1 300 : 5 250
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BULK NANOSTRUCTURED MATERIALS In th
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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
Page 204 and 205: FURTHER READING FURTHER READING 193
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Page 208 and 209: 8.2. INFRARED FREQUENCY RANGE 197 1
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Page 212 and 213: s C CTI e 8 9 4( 8.2. INFRARED FREQ
Page 214 and 215: 8.2.3. Raman Spectroscopy 8.2. INFR
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Page 218 and 219: - r I 520 51 8 v 6 516 a" 51 4 51 2
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Page 222 and 223: v) - C 3 8 600 400 100 0 e e 10 20
Page 224 and 225: i E (cm-’ ) 20 c I 1 ID 0 4x107 8
Page 226 and 227: - ? m v .- - z In C a, c C - .. . .
Page 228 and 229: Excitatior I [eV]: 2.175 2.214 2.25
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Page 236 and 237: FURTHER READING 225 P. Milani and C
Page 238 and 239: 9.2. PREPARATION OF QUANTUM NANOSTR
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Page 264 and 265: 9.7. SUPERCONDUCTIVITY 253 horizont
Page 266 and 267: 9.7. SUPERCONDUCTIVITY 255 applied
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Page 270 and 271: 10.1. SELF-ASSEMBLY 259 factor of 2
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Page 292 and 293: I1 ORGANIC COMPOUNDS AND POLYMERS 1
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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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