Introduction to Nanotechnology

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8.2. INFRARED FREQUENCY RANGE 199 dioxide on the surface. Note that the OH absorption signal is in the negative (downward) direction. This means that the initial activated titania surface, whose spectrum had been subtracted, had many more OH groups on it than the same surface after CO adsorption. Apparently OH groups originally present on the surface have been replaced by C02 groups. Also the spectrum exhibits structure in the range from 2100 to 2400 cm-' due to the vibrational-rotational modes of the CO and C02. In addition, the gradually increasing absorption for decreasing wavenumber shown at the right side of the figure corresponds to a broad spectral band that arises from electron transfer between the valence and conduction bands of the n-type titania semiconductor. To learn more about an infrared spectrum, the technique of isotopic substitution can be employed. We know from elementary physics that the frequency of a simple harmonic oscillator o of mass m and spring constant C is proportional to (C/m)''2, which means that the frequency o, and the energy E given by E= Fim, both decrease with an increase in the mass m. As a result, isotopic substitution, which involves nuclei of different masses, changes the IR absorption frequencies of chemical groups. Thus the replacements of ordinary hydrogen 'H by the heavier isotope deuterium 2D (0.015% abundant), ordinary carbon I2C by 13C (1.1 1% abundant), ordinary 14N by 15N (0.37% abundant), or ordinary I6O by "0 (0.047% abundant) all increase the mass, and hence decrease the infrared absorption frequency. The decrease is especially pronounced when deuterium is substituted for ordinary hydrogen since the mass ratio mD/mH = 2, so the absorption frequency is expected to decrease by the factor fi 1.414. The FTIR spectrum of boron nitride (BN) nanopowder after deuteration (H/D exchange), presented in Fig. 8.5, exhibits this fi shift. The figure shows the initial spectrum (tracing a) of the BN nanopowder after activation at 875 K, (tracing b) of the nanopowder after subsequent deuteration, and (tracing c) after subtraction of the two spectra. It is clear that the deuteration converted the initial B-OH, B-NH2, and B2-NH groups on the surface to B-OD, B-ND2, and B2-ND, respectively, and that in each case the shift in wavenumber (Le., frequency) is close to the expected a. The overtone bands that vanish in the subtraction of the spectra are due to harmonics of the fundamental BN lattice vibrations, which are not affected by the H/D exchange at the surface. Boron nitride powder is used commercially for lubrication. Its hexagonal lattice, with planar B3N3 hexagons, resembles that of graphite. A close comparison of the FTIR spectra from gallium nitride GaN nanoparticles illustrated in Fig. 8.6 with the boron nitride nanoparticle spectra of Fig. 8.5 show how the various chemical groups -OH, -NH2, and -NH and their deuterated analogues have similar vibrational frequencies, but these frequencies are not pre- cisely the same. For example, the frequency of the B-ND2 spectral line of Fig. 8.5 is somewhat lower than that of the Ga-ND2 line of Fig. 8.6, a small shift that results from their somewhat different chemical environments. The H/D exchange results of Fig. 8.6 show that all of the Ga-OH and Ga-NH2 are on the surface, while only some of the NH groups were exchanged. Notice that the strong GaH absorption band near 21,000 cm-' was not appreciably disturbed by the H/D exchange, suggesting that it arises from hydrogen atoms bound to gallium inside the bulk.
200 OPTICAL AND VIBRATIONAL SPECTROSCOPY Figure 8.5. FTIR spectra of boron nitride nanopowder surfaces after activation at 875 K (tracing a), after subsequent deuteration (tracing b), and (c) difference spectrum of a subtracted from b (tracing c). [From M.4. Baraton and L. Merhari, P. Quintard, V. Lorezenvilli, Langrnuir, 9, 1486 (1 993).] An example that demonstrates the power of infrared spectroscopy to elucidate surface features of nanomaterials is the study of y-alumina (A1203), a catalytic material that can have a large surface area, up to 20&300m2/g, due to its highly porous morphology. It has a defect spinel structure, and its large oxygen atoms form a tetragonally distorted face-centered cubic lattice (see Section 2.1.2). There are one octahedral (VI) and two tetrahedral (IV) sites per oxygen atom in the lattice, and aluminum ions located at these sites are designated by the notations vIA13+ and IvA13+, respectively, in Fig. 8.7. There are a total of five configurations assumed by adsorbed hydroxyl groups that bond to aluminum ions at the surface, and these are sketched in the figure. The first two, types Ia and Ib, involve the simple cases of OH bonded to tetrahedrally and octahedrally coordinated aluminum ions, respectively. The remaining three cases involve the hydroxyl radical bound simultaneously to two or three adjacent trivalent aluminum ions. The frequency shifts assigned to these five surface species, which are listed in the figure (v(OH)), are easily distinguished by infrared spectroscopy. The FTIR spectra from y-alumina nanopowder before and after deuteration presented in Fig. 8.8 display broad absorption bands with structure arising from
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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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Page 228 and 229: Excitatior I [eV]: 2.175 2.214 2.25
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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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