Chemistry and Properties of Nanocrystals of Different Shapes Clemens Burda,* ,²,‡ Xiaobo Chen, ² Radha Narayanan, § and Mostafa A. El-Sayed* ,§ Center for Chemical Dynamics and Nanomaterials Research, Department of Chemistry, Case Western Reserve UniversitysMillis 2258, Cleveland, Ohio 44106, and Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 Received July 22, 2004 Contents 1. General Introduction and Comments 1025 2. Preparation of Nanostructures of Different Shapes 1027 2.1. Introduction: Nucleation and Particle Growth 1027 2.2. Preparation Methods 1028 2.2.1. Sol Process 1028 2.2.2. Micelles 1031 2.2.3. Sol-Gel Process 1034 2.2.4. Chemical Precipitation 1034 2.2.5. Hydrothermal Synthesis 1036 2.2.6. Pyrolysis 1036 2.2.7. Vapor Deposition 1038 2.3. Growth Mechanism of Nanostructures of Different Shapes 1040 2.3.1. Effect of Monomer Concentration on the Shape of the Semiconductor QDs 1040 2.3.2. Vapor-Liquid-Solid Growth for Nanowire by CVD and PVD Methods 1041 2.3.3. Light-Induced Shape Change Mechanism of Metal Nanorods 1042 3. Surface Chemical Modification of Nanoparticles 1042 4. Assembly of Nanoparticles 1042 5. Optical, Thermal, and Electrical Properties of Particles of Different Sizes and Shapes 1047 5.1. Semiconductor Nanoparticles 1047 5.1.1. Discrete Electronic Structure 1047 5.1.2. Optical Transitions in Nanostructures of Different Shapes 1048 5.2. Metallic Nanoparticles 1057 5.3. High Surface-to-Volume Ratio 1059 5.4. Melting Point 1060 5.5. Conductivity and Coulomb Blockade 1061 6. Nonradiative Relaxation of Nanoparticles of Different Shapes 1063 6.1. Nonradiative Relaxation in Metal Nanostructured Systems 1063 6.1.1. Background 1063 6.1.2. Theoretical Modeling of the Transient Optical Response 1063 6.1.3. Electron-Electron Thermalization in Gold Nanoparticles 1063 6.1.4. Electron-Phonon Relaxation in Gold Nanoparticles 1064 6.1.5. Shape and Size Dependence on the Electron-Phonon Relaxation Rate 1065 6.1.6. Pump Power Dependence of the Electron-Phonon Relaxation Rate 1066 6.2. Nonradiative Relaxation in Semiconductor Nanostructured Systems 1066 6.2.1. II-VI Semiconductor Systems 1067 6.2.2. I-VII Semiconductor Systems 1074 6.2.3. III-V Semiconductor Systems 1074 6.2.4. Group IV Semiconductor Systems 1074 6.2.5. Metal Oxides Systems 1075 6.2.6. Other Systems 1075 6.3. Hot Electrons and Lattice Temperatures in Nanoparticles 1076 6.4. Phonon Bottleneck 1078 6.5. Quantized Auger Rates 1079 6.6. Trapping Dynamics 1079 7. Nanocatalysis 1081 7.1. Introduction 1081 7.2. Homogeneous Catalysis 1081 7.2.1. Chemical Reactions Catalyzed Using Colloidal Transition Metal Nanocatalysts 1083 7.3. Heterogeneous Catalysis on Support 1086 7.3.1. Lithographically Fabricated Supported Transition Metal Nanocatalysts 1087 7.3.2. Chemical Reactions Catalyzed Using Supported Transition Metal Nanocatalysts 1087 8. Summary 1090 8.1. Reviews 1090 8.1.1. Synthesis 1090 8.1.2. Properties 1090 8.1.3. General 1091 8.2. Books 1091 8.2.1. Metal Nanoparticles 1091 8.2.2. Semiconductor Nanoparticles 1091 8.2.3. Carbon Nanotubes and Nanoparticles 1091 8.2.4. Nanoparticles in General 1092 9. Acknowledgment 1092 10. References 1092 1. General Introduction and Comments The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-894- 0292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025-1102 10.1021/cr030063a CCC: $53.50 © 2005 American Chemical Society Published on Web 03/18/2005