Introduction to Nanotechnology

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10.2. CATALYSIS 277 based on the proposed zirconium ion Zr,804(0H)36(S04),4, the trivalent titanium ion [Ti(CH3COO)6,(OH)o~4~~l,~]~~ . 1 lH,O, hexavalent chromium octahedra forming the ions [Cr4(OH),(H20), ,I6+ and [Cr40(OH)6(H20),o]5+, an alumina-silica A1203-SiO, combination, and silica Si02 supplemented by some titania Ti02. The availability of these nonaluminum pillars, which differ in their dimensions, can provide catalysts with a wide range of pore sizes. These catalysts have been studied for their capability in carrying out various chemical reactions, such as cracking, in which hydrocarbons or other molecules are broken up and their fragments are recombined into desirable product molecules. An example is crude oil and gas cracking to produce gasoline. One of the liabilities of these pillared catalysts is their tendency toward coke formation whereby the surface becomes coated with carbon, and acid sites become deactivated or unable to function. 10.2.5. Colloids Nanosized particles of metals are ordinarily insoluble in inorganic or organic solvents, but if they can be prepared in colloidal form, they can function more readily as catalysts. A colloid is a suspension of particles in the range from 1 nm to 1 pm @e., 1000 nm) in size, larger than most ordinary molecules, but still too small to be seen by the naked eye. Many colloidal particles can, however, be detected by the way they scatter light, such as dust particles in air. These particles are in a state of constant random movement called Brownian motion arising from collisions with solvent molecules, which themselves are in motion. Particles are kept in suspension by repulsive electrostatic forces between them. The addition of salt to a colloid can weaken these forces and cause the suspended particles to gather into aggregates, and eventually they collect as a sediment at the bottom of the solvent. This process of the settling out of a colloid is calledflocculution. Some of the colloidal systems to be discussed are colloidal dispersions of insoluble materials (e.g., nanoparticles) in organic liquids, and these are called orgunosols. Analogous colloidal dispersions in water are called hydrosols. In Section 2.1.3 we discussed the formation of face-centered cubic nanoparticles such as Au,, with structural magic numbers of atoms, in this case 55. This nanoparticle has been ligand-stabilized in the form Au,,(PPh3),,C1, to make it less reactive, and hence more stable. This sturdiness is brought about by adding atomic or organic groups between the atoms of the cluster, or on their surfaces. These FCC metallic nanoparticles can be stabilized as colloids by the use of surfactants, which can operate, for example, by lowering the surface tension. The ring compounds tetrahydrofuran (THF) and tetrahydrothiophene, with structures sketched in Fig. 10.20, have been used to stabilize metallic nanoparticles as colloids. Figure 10.21 shows a Til3 nanocluster coordinated with the oxygen atoms of six THF molecules in an octahedral configuration. In this cluster the Ti-Ti distance (0.2804 nm) is slightly less than that (0.289 nm) in the bulk metal. A way to obtain colloidal dispersions in organic liquids is to stabilize a metallic core using a lipophilic surfactant tetraalkylammonium halide NhX, where X is a halogen such as chlorine (Cl) or bromine (Br), and R represents the alkyl group
278 SELF-ASSEMBLY AND CATALYSIS /O\ H- C II C- H II H 0 H- C C- H I I H- C- C- H I I \ H H \/bH H /"-" H Furan Tetrahydro Furan (THF) / s\ H- C C- H II II S H \/\/H H- C C- H I I H- C- C- H \ H /"-" H I H I H Thiophene Tetrahydro Thiophene (THT) Figure 10.20. Sketches of the structures of the heterocyclic ring compound furan, its hydrated analogue tetrahydrofuran (THF), and the corresponding sulfur compounds thiophene and tetrahydrothiophene (THT). Figure 10.21. Titanium neutral metal cluster Til3 bonded to the oxygen atoms of octahedrally coordinated tetrahydrofuran (C4H80) molecules. Only the oxygen atoms of the THF are shown. [From H. Bonnemann and W. Brijoux, in Moser (1996), Chapter 7, p. 169.1
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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
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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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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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