Preface ........................................................ xi
Authors ........................................................ xv
1 Introduction ................................................. 1
References ................................................... 5
2 Historical Perspective ....................................... 7
References .................................................. 15
3 Growth Techniques ........................................... 17
3.1 Introduction ........................................... 17
3.2 Liquid-Phase Techniques ................................ 17
3.2.1 Template-Based Methods .......................... 18
3.2.1.1 Template Preparation ................... 18
3.2.1.2 Deposition Methods ..................... 23
3.2.2 Template-Free Methods ........................... 32
3.2.2.1 Hydrothermal Method .................... 32
3.2.2.2 Sonochemical Method .................... 34
3.2.2.3 Surfactant-Assisted Growth: Soft
Directing Agents ....................... 35
3.2.2.4 Catalyst-Assisted Solution-Based
Approaches ............................. 36
3.3 Vapor-Phase Techniques ................................. 37
3.3.1 One-Dimensional Growth Concepts ................. 38
3.3.1.1 Vapor-Liquid-Solid Schemes Using
Foreign Metal Clusters ................. 38
3.3.1.2 Vapor-Liquid-Solid Schemes Using
Low-Melting Metal Clusters ............. 39
3.3.1.3 Vapor-Liquid-Solid Schemes Using
Large Size, Molten Metal Clusters ...... 40
3.3.1.4 Vapor-Solid-Solid Scheme ............... 40
3.3.1.5 Oxygen-Assisted Growth (OAG) Scheme .... 40
3.3.2 Source Generation and Reactors for Vapor-Phase
Synthesis of Nanowires .......................... 40
3.3.2.1 Thermal Evaporation .................... 41
3.3.2.2 Laser Ablation ......................... 42
3.3.2.3 Metal Organic Chemical Vapor
Deposition ............................. 44
3.3.2.4 Chemical and Molecular Beam Epitaxy .... 47
3.3.2.5 Plasma Arc Discharge-Based
Techniques ............................. 49
3.4 Bulk Production Methods ................................ 50
3.4.1 Hot Filament CVD Method ......................... 50
3.4.2 Supercritical Fluid Approach .................... 52
3.4.3 Direct Oxidation Schemes Using Plasma ........... 52
3.4.4 Direct Gas-Phase Reactions Using Plasma
Discharges ...................................... 53
3.5 Future Developments .................................... 55
References .................................................. 57
4 Thermodynamic and Kinetic Aspects of Nanowire Growth ........ 61
4.1 Introduction ........................................... 61
4.2 Thermodynamic Considerations for Vapor-Liquid-Solid
Growth ................................................. 63
4.2.1 Thermodynamic Considerations of Nucleation
from Molten Metal Droplets ...................... 63
4.2.1.1 Gibbs-Thompson Relationship ............ 63
4.2.1.2 Nucleation from Molten Metal Alloy
Droplet ................................ 65
4.2.1.3 Nucleation from Various Molten Metal
Droplets ............................... 66
4.2.1.4 Thermodynamic Estimation of
Supersaturation for Spontaneity of
Nucleation ............................. 70
4.2.1.5 Rational Choice of Metal for Tip-Led
Growth of Nanowires (Avoiding
Nucleation) ............................ 73
4.2.1.6 Experimental Conditions for Promoting
Tip-Led Growth Using Any Molten
Metal .................................. 76
4.2.2 Interfacial Energy and Tip-Led Growth ........... 77
4.2.2.1 Role of Interfacial Energy in the
Nanowire Growth Stability .............. 77
4.2.2.2 Role of Interfacial Energy in
Nanowire Faceting ...................... 81
4.2.2.3 Role of Interfacial Energy on the
Nanowire Growth Direction .............. 85
4.3 Kinetic Considerations of Nanowire Growth under VLS
Growth ................................................. 87
4.3.1 Kinetics of Vapor-Liquid-Solid Equilibrium ...... 87
4.3.2 Role of Direct Impingement in Growth Kinetics ... 89
4.3.3 Role of Surface Diffusion in Growth Kinetics .... 91
4.3.4 Direct Impingement and Diffusion ................ 94
4.3.5 Role of Surface Diffusion on the Metal
Droplet ......................................... 95
4.3.6 Role of Interwire Spacing ....................... 97
References .................................................. 98
5 Modeling of Nanowire Growth ................................ 101
5.1 Introduction .......................................... 101
5.2 Energetics of Stable Surface Faceting: Silicon
Nanowire Example ...................................... 102
5.3 Simulation of Individual Nanowire Growth .............. 104
5.3.1 Simulation Methodology ......................... 105
5.3.2 Kinetic Monte Carlo Simulation Results ......... 108
5.3.3 Experimental Results on Growth Direction
and Surface Faceting ........................... 112
5.4 Modeling of Multiple Nucleation and Growth of
One-Dimensional Structures ............................ 115
5.5 Modeling Nanowire Array Growth ........................ 117
References ................................................. 121
6 Semiconducting Nanowires ................................... 123
6.1 Introduction .......................................... 123
6.2 Silicon Nanowires ..................................... 123
6.2.1 SiCl4/H2 System ................................. 124
6.2.2 Silane Feedstock in VLS Growth ................. 134
6.2.3 Other Sources .................................. 135
6.2.4 Oxide-Assisted Growth .......................... 136
6.2.5 Template-Assisted Synthesis .................... 137
6.2.6 Plasma Enhancement ............................. 138
6.2.7 Doping of SiNWs ................................ 139
6.2.8 Properties of SiNWs ............................ 140
6.3 Germanium Nanowires ................................... 142
6.3.1 Synthesis Using Germanium Powder ............... 143
6.3.2 Germane and Related Sources .................... 146
6.4 Catalyst Choice ....................................... 147
6.5 III-V Nanowires ....................................... 148
6.5.1 GaAs Nanowires ................................. 149
6.5.2 InAs Nanowires ................................. 152
6.5.3 InP Nanowires .................................. 152
6.5.4 GaP Nanowires .................................. 154
References ................................................. 155
7 Phase Change Materials ..................................... 161
7.1 Introduction .......................................... 161
7.2 Phase Change Nanowire Growth .......................... 162
7.3 Properties Relevant to PRAM ........................... 167
References ................................................. 169
8 Metallic Nanowires ......................................... 171
8.1 Bismuth Nanowires ..................................... 171
8.2 Silver Nanowires ...................................... 173
8.3 Copper Nanowires ...................................... 174
8.4 Nickel Nanowires ...................................... 176
8.5 Zinc Nanowires ........................................ 178
References ................................................. 180
9 Oxide Nanowires ............................................ 183
9.1 Introduction .......................................... 183
9.2 Synthesis Methodologies ............................... 184
9.2.1 Catalyst-Assisted Synthesis .................... 184
9.2.2 Direct Oxidation Schemes Using Low-Melting
Metals ......................................... 190
9.2.2.1 Direct Oxidation of Molten Metal
Clusters .............................. 190
9.2.2.2 Direct Chemical/Reactive Vapor
Deposition of Low-Melting Metal
Oxides ................................ 193
9.2.3 Chemical Vapor Transport or Deposition of
High-Melting Metal Oxides ...................... 196
9.2.4 Plasma and Thermal Oxidation of Foils .......... 202
9.3 Directed Growth and Morphological Control ............. 206
9.3.1 Branched Nanowire Structures ................... 206
9.3.2 Networking of Nanowires ........................ 208
9.3.3 Nanobelts ...................................... 209
9.3.4 Tubular Nanostructures ......................... 212
9.3.4.1 High-Melting Metal Oxides ............. 212
9.3.4.2 Low-Melting Metal Oxides .............. 213
9.4 Oxygen Vacancies, Doping, and Phase Transformation .... 214
9.4.1 Oxygen Vacancies ............................... 214
9.4.2 Doping and Alloying ............................ 216
9.4.3 Phase Transformation of Metal Oxide
Nanowires ...................................... 217
References ................................................. 220
10 Nitride Nanowires .......................................... 225
10.1 Introduction .......................................... 225
10.2 Synthesis of Group III-Nitride Nanowires .............. 225
10.2.1 Catalyst-Assisted Synthesis .................... 226
10.2.1.1 Choice of Precursors .................. 229
10.2.1.2 Substrates for Epitaxial Array
Growth ................................ 230
10.2.1.3 Choice of Catalysts and Process
Variables ............................. 231
10.2.1.4 Control of Nanowire Growth
Direction ............................. 232
10.2.2 Direct Reaction and Self-Catalysis Schemes ..... 233
10.2.2.1 Control of Growth Direction .......... 239
10.2.3 Synthesis of Nanotubes ......................... 240
10.2.4 Micro/Nanomorphologies ......................... 243
10.2.4.1 III-Nitride Nanobelts ................. 243
10.2.4.2 Tapered Morphologies .................. 245
10.3 Branching of Nanowires ................................ 247
10.3.1 Homobranching or "Tree-Like" Structures ........ 247
10.3.2 Heterobranching ................................ 248
10.4 Diameter Reduction of III-Nitride Nanowires ........... 249
10.5 Direction-Dependent Properties ........................ 252
References ................................................. 254
11 Other Nanowires ............................................ 257
11.1 Antimonides ........................................... 257
11.2 Selenides ............................................. 260
11.2.1 Zinc Selenide .................................. 260
11.2.2 Other Selenides ................................ 263
11.3 Tellurides ............................................ 264
11.3.1 Bismuth Telluride .............................. 264
11.3.2 Cadmium Telluride .............................. 265
11.3.3 Other Tellurides ............................... 265
11.4 Sulfides .............................................. 266
11.4.1 Zinc Sulfide ................................... 266
11.4.2 Other Sulfides ................................. 267
11.5 Silicides ............................................. 269
References ................................................. 269
12 Applications in Electronics ................................ 275
12.1 Introduction .......................................... 275
12.2 Silicon Nanowire Transistors .......................... 278
12.3 Vertical Transistors .................................. 280
12.4 Germanium Nanowire Transistors ........................ 284
12.5 Zinc Oxide and Other Nanowires in Electronics ......... 286
12.6 III-V Transistors ..................................... 289
12.7 Memory Devices ........................................ 290
12.7.1 Phase-Change Random Access Memory ............. 292
References ................................................. 296
13 Applications in Optoelectronics ............................ 299
13.1 Introduction .......................................... 299
13.2 Photodetectors ........................................ 299
13.3 Light-Emitting Diodes ................................. 303
13.4 Nanoscale Lasers ...................................... 306
References ................................................. 310
14 Applications in Sensors .................................... 313
14.1 Introduction .......................................... 313
14.2 Chemical Sensors ...................................... 314
14.2.1 Sensor Requirements and the Role
of Nanomaterials ............................... 314
14.2.2 Nanowires in Sensor Fabrication ................ 317
14.2.3 Sensing Mechanisms ............................. 327
14.2.4 Selectivity and Electronic Nose ................ 331
14.3 Biosensors ............................................ 337
14.3.1 Nanoelectrode Arrays .......................... 340
References ................................................. 344
15 Applications in the Energy Sector .......................... 349
15.1 Introduction .......................................... 349
15.2 Solar Cells ........................................... 350
15.2.1 Dye-Sensitized Solar Cells ..................... 350
15.2.1.1 Titania Nanowire-Based DSSCs .......... 353
15.2.1.2 ZnO Nanowire-Based DSSCs .............. 357
15.2.1.3 SnO2 NW-Based DSSCs ................... 358
15.2.1.4 Inorganic Nanotubes, Polymers, and
Nb2O5 Nanowires for DSSCs ............. 358
15.2.1.5 Quantum Dot Sensitizers for
Nanowire-Based Solar Cells ............ 360
15.2.1.6 Hybrid/Composite Structures ........... 360
15.2.1.7 Transport and Recombination ........... 363
15.2.2 Direct Absorption PEC Cells .................... 366
15.2.3 p-n Junction Solar Cells ....................... 366
15.2.4 PEC Cells for Chemical Conversion .............. 368
15.3 Electrochromic Devices ................................ 373
15.4 Li-Ion Batteries ...................................... 377
15.4.1 Challenges with Anode Materials ................ 378
15.4.2 Challenges Facing Cathode Materials ............ 379
15.4.3 One-Dimensional Materials for Anodes ........... 380
15.4.3.1 Carbon Nanotubes (CNTs) ............... 380
15.4.3.2 Metal/Metal Oxide Nanowires ........... 381
15.4.3.3 Nanowires of Silicon and Related
Materials ............................. 386
15.4.4 Rational Concepts for Nanowire-Based
Architectures .................................. 387
15.4.4.1 A Concept of Nanometal Cluster-
Decorated Metal Oxide Nanowires ....... 387
15.4.4.2 Nanowire Arrays on Conducting
Substrates ............................ 389
15.4.4.3 Miscellaneous Concepts of 3-D
Geometries ............................ 390
15.4.5 Nanowire-Based Materials for Cathodes .......... 391
References ................................................. 393
16 Other Applications ......................................... 399
16.1 Field Emission Devices ................................ 399
16.1.1 Background ..................................... 399
16.1.2 Work Function (Ф) .............................. 400
16.1.3 Field Emission Testing ......................... 401
16.1.4 Field Emission Characteristics of
Nanowire-Based Materials ....................... 404
16.2 Thermoelectric Devices ................................ 414
References ................................................. 416
Index ......................................................... 421
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