Introduction to Nanotechnology

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10- IR f IA -1 8.1. INTRODUCTION 195 Figure 8.1. Sketch of incident electromagnetic wave intensity Io being partially absorbed In, partially reflected IR and partially transmitted IT by a sample. result light is absorbed. In transmission spectroscopy the reflected signal is neglected, and the absorption is determined by a decrease in the transmitted intensity ZT as a function of the scanning frequency o (or A), while in reflection spectroscopy the transmission is neglected and the absorption is determined from the change Z, in the reflected light. The former is used for transparent samples and the latter, for opaque ones. Thus spectroscopic measurements can be made by gradually scanning E, o, or A of the incoming light beam and measuring its effect on ZT (or IR), whose amplitude is recorded during the scan. More modem equipment makes use of charge- coupled devices (CCDs) as light detectors. These are arrays of metal oxide semiconductors (MOS) that consist of a p-type silicon layer, a silicon dioxide layer, and a metal plate. Incident photons generate minority carriers, and the current is propor- tional to the intensity of the light, and the time of exposure. These devices make several rapid scans of the wavelength range, and in conjunction with computer pro- cessing, they enable the recording of the complete spectrum in a relatively short time. This chapter discusses investigations of nanomaterials using spectroscopic techniques in the infrared and Raman regions of the spectrum (frequencies from 10l2 to 4 x 1014Hz, wavelengths A from 300 to 1 pm), as well as visible and ultraviolet spectroscopy (frequencies from 4 x 1014 to 1.5 x A from 0.8 to 0.2 pm). Another type of spectroscopy is emission spectroscopy. An incident photon h oo raises an electron from its ground state Egnd to an excited energy level E,,,, the electron undergoes a radiationless transition to an intermediate energy state, and then it returns to its ground-state level, emitting in the process a photon h alum, that can be detected, as shown in Fig. 8.2. If the emission takes place immediately, it is called Jluorescence, and if it is delayed as a result of the finite lifetime of the intermediate metastable state Emet, it is calledphosphorescence. Both types of emission paths are referred to as luminescence, and the overall process of light absorption followed by emission is called photoemission. Emission spectroscopy can be studied by varying the frequency of the incident exciting light, by studying the frequency distribution of
196 OPTICAL AND VIBRATIONAL SPECTROSCOPY Incident photonhw, t i- Radiationless transition Luminescent emission hq,, Figure 8.2. Energy-level diagram showing an incident photon htuo raising an electron from its ground state Egnd to an excited state E,,,, and a subsequent radiationless transition to a longlived metastable state E,,,,, followed by luminescent emission of a photon ho,,,. the emitted light, or by combining both techniques. Luminescent spectra will be examined for all these variations. Light emission can also be induced by gradually heating a sample, and the resulting thermal luminescence manifests itself by the emission of light over a characteristic temperature range. This emission is called a glow peak. 8.2. INFRARED FREQUENCY RANGE 8.2.1. Spectroscopy of Semiconductors; Excitons These observations on spectroscopy that we have made are of a general nature, and apply to all types of ultraviolet, visible, Raman, and infrared spectroscopy. Semi- conductors are distinguished by the nature and the mechanisms of the processes that bring about the absorption or emission of light. Incident light with photon energies less than the bandgap energy E, passes through the sample without absorption, and higher-energy photons can raise electrons from the valence band to the conduction band, leaving behind holes in the valence band. Figure 8.3 presents a plot of the optical absorption coefficient for bulk GaAs, and we see that the onset of the absorption occurs at the bandgap edge where the photon energy A o equals Eg. The data tabulated in Table B.7 show that the temperature coefficient dE,/dT of the energy gap is negative for all 111-V and 11-VI semiconductors, which means that the onset of absorption undergoes what is called a blue shift to higher energies as the temperature is lowered, as shown on the figure. The magnitude of the absorption, measured by the value of the absorption coefficient, also becomes stronger at lower temperatures, as shown in Fig. 8.3. Another important contributor to the spectroscopy of semiconductors is the presence in the material of weakly bound excitons called Mott-Wannier excitons. This type of exciton is a bound state of an electron from the conduction band and a hole from the valence band attracted to each other by the Coulomb interaction e2/47d~,?, and having a hydrogen atom like system of energy levels called a Rydbergseries, as explained in Section 2.3.3. The masses me and mh, of the electron and the hole, respectively, in a zinc blende semiconductor are both much less than
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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 181 and 182: 170 NANOSTRUCTURED FERROMAGNETISM M
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Page 198 and 199: 7.7. FERROFLUIDS 187 Figure 7.22. M
Page 200 and 201: 7.7. FECIROFLUIDS 189 Figure 7.25.
Page 202 and 203: 7.7. FERRQFLUlOS 191 FerroRuids can
Page 204 and 205: FURTHER READING FURTHER READING 193
Page 208 and 209: 8.2. INFRARED FREQUENCY RANGE 197 1
Page 210 and 211: 8.2. INFRARED FREQUENCY RANGE 199 d
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 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
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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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