The Physics and Chemistry of Nanosolids

Preface xv

1. Physics of Bulk Solids 1

1.1 Structure 1

1.1.1 Size Dependence of Properties 1

1.1.2 Crystal Structures 2

1.1.3 Face-Centered Cubic Nanoparticles 7

1.1.4 Large Face-Centered Cubic Nanoparticles 9

1.1.5 Tetrahedrally Bonded Semiconductor Structures 10

1.1.6 Lattice Vibrations 14

1.2 Surfaces of Crystals 16

1.2.1 Surface Characteristics 16

1.2.2 Surface Energy 17

1.2.3 Face-Centered Cubic Surface Layers 18

1.2.4 Surfaces of Zinc Blende and Diamond Structures 21

1.2.5 Adsorption of Gases 23

1.2.6 Electronic Structure of a Surface 25

1.2.7 Surface Quantum Well 26

1.3 Energy Bands 26

1.3.1 Insulators, Semiconductors, and Conductors 26

1.3.2 Reciprocal Space 27

1.3.3 Energy Bands and Gaps of Semiconductors 28

1.3.4 Effective Mass 34

1.3.5 Fermi Surfaces 35

1.4 Localized Particles 36

1.4.1 Donors, Acceptors, and Deep Traps 36

1.4.2 Mobility 37

1.4.3 Excitons 38

Problems 40

References 41

2. Methods of Measuring Properties of Nanostructures 43

2.1 Introduction 43

2.2 Structure 44

2.2.1 Atomic Structures 44

2.2.2 Crystallography 45

2.2.3 Particle Size Determination 50

2.2.4 Surface Structure 54

2.3 Microscopy 54

2.3.1 Transmission Electron Microscopy 54

2.3.2 Field Ion Microscopy 59

2.3.3 Scanning Microscopy 59

2.4 Spectroscopy 66

2.4.1 Infrared and Raman Spectroscopy 66

2.4.2 Photoemission, X-Ray, and Auger Spectroscopy 72

2.4.3 Magnetic Resonance 78

2.5 Various Bulk Properties 81

2.5.1 Mechanical Properties 81

2.5.2 Electrical Properties 81

2.5.3 Magnetic Properties 82

2.5.4 Other Properties 82

Problems 82

References 83

3. Properties of Individual Nanoparticles 85

3.1 Introduction 85

3.2 Metal Nanoclusters 86

3.2.1 Magic Numbers 86

3.2.2 Theoretical Modeling of Nanoparticles 88

3.2.3 Geometric Structure 91

3.2.4 Electronic Structure 94

3.2.5 Reactivity 97

3.2.6 Fluctuations 100

3.2.7 Magnetic Clusters 100

3.2.8 Bulk-to-Nano Transition 103

3.3 Semiconducting Nanoparticles 104

3.3.1 Optical Properties 104

3.3.2 Photofragmentation 106

3.3.3 Coulomb Explosion 107

3.4 Rare-Gas and Molecular Clusters 107

3.4.1 Inert-Gas Clusters 107

3.4.2 Superfluid Clusters 108

3.4.3 Molecular Clusters 109

3.4.4 Nanosized Organic Crystals 111

3.5 Methods of Synthesis 111

3.5.1 RF Plasma 111

3.5.2 Chemical Methods 111

3.5.3 Thermolysis 112

3.5.4 Pulsed-Laser Methods 114

3.5.5 Synthesis of Nanosized Organic Crystals 114

3.6 Summary 118

Problems 118

4. The Chemistry of Nanostructures 121

4.1 Chemical Synthesis of Nanostructures 121

4.1.1 Solution Synthesis 121

4.1.2 Capped Nanoclusters 122

4.1.3 Solgel Processing 124

4.1.4 Electrochemical Synthesis of Nanostructures 125

4.2 Reactivity of Nanostructures 125

4.3 Catalysis 127

4.3.1 Nature of Catalysis 127

4.3.2 Surface Area of Nanoparticles 127

4.3.3 Porous Materials 131

4.4 Self-Assembly 135

4.4.1 The Self-Assembly Process 135

4.4.2 Semiconductor Islands 136

4.4.3 Monolayers 139

Problems 141

5. Polymer and Biological Nanostructures 143

5.1 Polymers 143

5.1.1 Polymer Structure 143

5.1.2 Sizes of Polymers 146

5.1.3 Nanocrystals of Polymers 148

5.1.4 Conductive Polymers 151

5.1.5 Block Copolymers 152

5.2 Biological Nanostructures 154

5.2.1 Sizes of Biological Nanostructures 154

5.2.2 Polypeptide Nanowire and Protein Nanoparticles 160

5.2.3 Nucleic Acids 162

5.2.3.1 DNA Double Nanowire 162

5.2.3.2 Genetic Code and Protein Synthesis 166

5.2.3.3 Proteins 167

5.2.3.4 Micelles and Vesicles 169

5.2.3.5 Multilayer Films 172

Problems 174

References 174

6. Cohesive Energy 177

6.1 Ionic Solids 177

6.2 Defects in Ionic Solids 183

6.3 Covalently Bonded Solids 185

6.4 Organic Crystals 186

6.5 Inert-Gas Solids 190

6.6 Metals 191

6.7 Conclusion 193

Problems 193

7. Vibrational Properties 195

7.1 The Finite One-Dimensional Monatomic Lattice 195

7.2 Ionic Solids 197

7.3 Experimental Observations 199

7.3.1 Optical and Acoustical Modes 199

7.3.2 Vibrational Spectroscopy of Surface Layers of Nanoparticles 201

7.3.2.1 Raman Spectroscopy of Surface Layers 201

7.3.2.2 Infrared Spectroscopy of Surface Layers 201

7.4 Phonon Confinement 207

7.5 Effect of Dimension on Lattice Vibrations 209

7.6 Effect of Dimension on Vibrational Density of States 211

7.7 Effect of Size on Debye Frequency 215

7.8 Melting Temperature 216

7.9 Specific Heat 218

7.10 Plasmons 220

7.11 Surface-Enhanced Raman Spectroscopy 222

7.12 Phase Transitions 223

Problems 226

References 227

8. Electronic Properties 229

8.1 Ionic Solids 229

8.2 Covalently Bonded Solids 232

8.3 Metals 234

8.3.1 Effect of Lattice Parameter on Electronic Structure 235

8.3.2 Free-Electron Model 235

8.3.3 The Tight-Binding Model 239

8.4 Measurements of Electronic Structure of Nanoparticles 242

8.4.1 Semiconducting Nanoparticles 242

8.4.2 Organic Solids 248

8.4.3 Metals 250

Problems 251

9. Quantum Wells, Wires, and Dots 253

9.1 Introduction 253

9.2 Fabricating Quantum Nanostructures 253

9.2.1 Solution Fabrication 254

9.2.2 Lithography 257

9.3 Size and Dimensionality Effects 261

9.3.1 Size Effects 261

9.3.2 Size Effects on Conduction Electrons 263

9.3.3 Conduction Electrons and Dimensionality 264

9.3.4 Fermi Gas and Density of States 265

9.3.5 Potential Wells 268

9.3.6 Partial Confinement 272

9.3.7 Properties Dependent on Density of States 273

9.4 Excitons 275

9.5 Single-Electron Tunneling 276

9.6 Applications 280

9.6.1 Infrared Detectors 280

9.6.2 Quantum Dot Lasers 280

Problems 285

References 285

10. Carbon Nanostructures 287

10.1 Introduction 287

10.2 Carbon Molecules 287

10.2.1 Nature of the Carbon Bond 287

10.2.2 New Carbon Structures 289

10.3 Carbon Clusters 289

10.3.1 Small Carbon Clusters 289

10.3.2 Buckyball 292

10.3.3 The Structure of Molecular C₆₀ 293

10.3.4 Crystalline C₆₀ 296

10.3.5 Larger and Smaller Buckyballs 300

10.3.6 Buckyballs of Other Atoms 300

10.4 Carbon Nanotubes 301

10.4.1 Fabrication 301

10.4.2 Structure 304

10.4.3 Electronic Properties 306

10.4.4 Vibrational Properties 312

10.4.5 Functionalization 314

10.4.6 Doped Carbon Nanotubes 322

10.4.7 Mechanical Properties 325

10.5 Nanotube Composites 327

10.5.1 Polymer–Carbon Nanotube Composites 327

10.5.2 Metal–Carbon Nanotube Composites 329

10.6 Graphene Nanostructures 330

Problems 335

11. Bulk Nanostructured Materials 337

11.1 Solid Methods for Preparation of Disordered Nanostructures 337

11.1.1 Methods of Synthesis 337

11.1.2 Metal Nanocluster Composite Glasses 340

11.1.3 Porous Silicon 343

11.2 Nanocomposites 347

11.2.1 Layered Nanocomposites 347

11.2.2 Nanowire Composites 349

11.2.3 Composites of Nanoparticles 350

11.3 Nanostructured Crystals 351

11.3.1 Natural Nanocrystals 351

11.3.2 Crystals of Metal Nanoparticles 352

11.3.3 Arrays of Nanoparticles in Zeolites 355

11.3.4 Nanoparticle Lattices in Colloidal Suspensions 357

11.3.5 Computational Prediction of Cluster Lattices 358

11.4 Electrical Conduction in Bulk Nanostructured Materials 359

11.4.1 Bulk Materials Consisting of Nanosized Grains 359

11.4.2 Nanometer-Thick Amorphous Films 364

11.5 Other Properties 364

Problems 365

12. Mechanical Properties of Nanostructured Materials 367

12.1 Stress–Strain Behavior of Materials 367

12.2 Failure Mechanisms of Conventional Grain-Sized Materials 370

12.3 Mechanical Properties of Consolidated Nano-Grained Materials 371

12.4 Nanostructured Multilayers 374

12.5 Mechanical and Dynamical Properties of Nanosized Devices 376

12.5.1 General Considerations 376

12.5.2 Nanopendulum 378

12.5.3 Vibrations of a Nanometer String 380

12.5.4 The Nanospring 381

12.5.5 The Clamped Beam 382

12.5.6 The Challenges and Possibilities of Nanomechanical Sensors 385

12.5.7 Methods of Fabrication of Nanosized Devices 387

Problems 390

13. Magnetism in Nanostructures 393

13.1 Basics of Ferromagnetism 393

13.2 Behavior of Powders of Ferromagnetic Nanoparticles 398

13.2.1 Properties of a Single Ferromagnetic Nanoparticle 398

13.2.2 Dynamics of Individual Magnetic Nanoparticles 400

13.2.3 Measurements of Superparamagnetism and the Blocking Temperature 402

13.2.4 Nanopore Containment of Magnetic Particles 405

13.3 Ferrofluids 406

13.4 Bulk Nanostructured Magnetic Materials 413

13.4.1 Effect of Nanosized Grain Structure on Magnetic Properties 413

13.4.2 Magnetoresistive Materials 416

13.4.3 Carbon Nanostructured Ferromagnets 424

13.5 Antiferromagnetic Nanoparticles 429

Problems 430

14. Nanoelectronics, Spintronics, Molecular Electronics, and Photonics 433

14.1 Nanoelectronics 433

14.1.1 N and P Doping and PN Junctions 433

14.1.2 MOSFET 435

14.1.3 Scaling of MOSFETs 436

14.2 Spintronics 440

14.2.1 Definition and Examples of Spintronic Devices 440

14.2.2 Magnetic Storage and Spin Valves 440

14.2.3 Dilute Magnetic Semiconductors 445

14.3 Molecular Switches and Electronics 449

14.3.1 Molecular Switches 449

14.3.2 Molecular Electronics 453

14.3.3 Mechanism of Conduction through a Molecule 458

14.4 Photonic Crystals 459

Problems 465

Reference 466

15. Superconductivity in Nanomaterials 467

15.1 Introduction 467

15.2 Zero Resistance 467

15.2.1 The Superconducting Gap 469

15.2.2 Cooper Pairs 470

15.3 The Meissner Effect 472

15.3.1 Magnetic Field Exclusion 472

15.3.2 Type I and Type II Superconductors 474

15.4 Properties of Flux 478

15.4.1 Quantization of Flux 478

15.4.2 Vortex Configurations 479

15.4.3 Flux Creep and Flux Flow 480

15.4.4 Vortex Pinning 484

15.5 Dependence of Superconducting Properties on Size Effects 484

15.6 Resistivity and Sheet Resistance 484

15.7 Proximity Effect 488

15.8 Superconductors as Nanomaterials 490

15.9 Tunneling and Josephson Junctions 491

15.9.1 Tunneling 491

15.9.2 Weak Links 491

15.9.3 Josephson Effect 493

15.9.4 Josephson Junctions 494

15.9.5 Ultrasmall Josephson Junctions 494

15.10 Superconducting Quantum Interference Device (Squid) 495

15.11 Buckministerfullerenes 496

15.11.1 The Structure of C₆₀ and Its Crystal 496

15.11.2 Alkali-Doped C₆₀ 496

15.11.3 Superconductivity in C₆₀ 497

Problems 498

References 499

Appendix A Formulas for Dimensionality 501

A.1 Introduction 501

A.2 Delocalization 501

A.3 Square and Parabolic Wells 502

A.4 Partial Confinement 503

Appendix B Tabulations of Semiconducting Material Properties 507

Appendix C Face-Centered Cubic and Hexagonal Close-Packed Nanoparticles 515

C.1 Introduction 515

C.2 Face-Centered Cubic Nanoparticles 515

C.3 Hexagonal Close-Packed Nanoparticles 519

Index 521