Introduction to Nanotechnology

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i 9.2. PREPARATION OF QUANTUM NANOSTRUCTURES 229 The first step of the lithographic procedure is to place a radiation-sensitive resist on the surface of the sample substrate, as shown in Fig. 9.4a. The sample is then irradiated by an electron beam in the region where the nanostructure will be located, as shown in Fig. 9.4b. This can be done by using either a radiation mask that contains the nanostructure pattern, as shown, or a scanning electron beam that strikes the surface only in the desired region. The radiation chemically modifies the exposed area of the resist so that it becomes soluble in a developer. The third step in the process (Fig. 9.4~) is the application of the developer to remove the irradiated portions of the resist. The fourth step (Fig. 9.4d) is the insertion of an etching mask into the hole in the resist, and the fifth step (Fig. 9.4e) consists in lifting off the remaining parts of the resist. In the sixth step (Fig. 9.40 the areas of the quantum well not covered by the etching mask are chemically etched away to produce the quantum structure shown in Fig. 9.4f covered by the etching mask. Finally the etching mask is removed, if necessary, to provide the desired quantum structure (Fig. 9.4g), which might be the quantum wire or quantum dot shown in Fig. 9.3b. In Chapter 1 we mentioned the most common process called electron-beam lithography, which makes use of an electron beam for the radiation. Other types of lithography employ neutral atom beams (e.g., Li, Na, K, Rb, Cs), charged ion beams (e.g., Gaf), or electromagnetic radiation such as visible light, ultraviolet light, or X rays. When laser beams are utilized, frequency doublers and quadruplers can bring the wavelength into a range (e.g., A- 150nm) that is convenient for quantum-dot fabrication. Photochemical etching can be applied to a surface activated by laser light. The lithographic technique can be used to make more complex quantum structures than the quantum wire and quantum dot shown in Fig. 9.3b. For example one might start with a multiple quantum-well structure of the type illustrated in Fig. 9.5, place the resist on top of it, and make use of a mask film or template with six circles cut out of it, as portrayed at the top of Fig. 9.5. Following the lithographic procedure outlined in Fig. 9.4, one can produce the 24-quantum-dot array consisting of six columns, each containing four stacked quantum dots, that is sketched in Figure 9.5. Four-cycle multiple-quantum-well arrangement mounted on a substrate and covered by a resist. A radiation shielding template for lithography is shown at the top.
230 QUANTUM WELLS. WIRES, AND DOTS Figure 9.6. Quantum-dot array formed by lithography from the initial configuration of Fig. 9.5. This 24-fold quantum-dot array consists of six columns of four stacked quantum dots. Fig 9.6. As an example of the advantages of fabricating quantum dot arrays, it has been found experimentally that the arrays produce a greatly enhanced photo- luminescent output of light. Figure 9.7 shows a photoluminescence (PL) spectrum from a quantum-dot array that is much more than 100 times stronger than the spectrum obtained from the initial multiple quantum wells. The principles behind the photoluminescence technique are described in Section 8.3.1. The main peak of the spectrum of Fig. 9.7 was attributed to a localized exciton (LE), as explained in Section 9.4. This magnitude of enhancement shown in the figure has been obtained from initial samples containing, typically, a 15-period superlattice (SL) of alternating I LE^^ T=4K 0.70 0.75 0.80 0.85 0.90 E (ev) Figure 9.7. Photoluminescence spectrum of an array of 60-nm-diameter quantum dots formed by lithography, compared with the spectrum of the initial as-grown multiple quantum well. The intense peak at 0.7654eV is attributed to localized excitons (LE) in the superlattice (SL). The spectra were taken at temperature 4 K. [From T. P. Sidiki and C. M. S. Torres, in Nalwa (2000), Vol. 3, Chapter 5, p. 251 .]
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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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Page 204 and 205: FURTHER READING FURTHER READING 193
Page 206 and 207: 10- IR f IA -1 8.1. INTRODUCTION 19
Page 208 and 209: 8.2. INFRARED FREQUENCY RANGE 197 1
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Page 214 and 215: 8.2.3. Raman Spectroscopy 8.2. INFR
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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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Page 256 and 257: 9.5. SINGLE-ELECTRON TUNNELING 245
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Page 264 and 265: 9.7. SUPERCONDUCTIVITY 253 horizont
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Page 270 and 271: 10.1. SELF-ASSEMBLY 259 factor of 2
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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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Introduction to Nanotechnology

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