Self-Assembled Monolayers of Thiolates on Metals as a Form of Nanotechnology J. Christopher Love, † Lara A. Estroff, † Jennah K. Kriebel, † Ralph G. Nuzzo,* ,‡ and George M. Whitesides* ,† Department of Chemistry and the Fredrick Seitz Materials Research Laboratory, University of Illinois-Urbana-Champaign, Urbana, Illinois 61801 and Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138 Received July 19, 2004 Contents 1. Introduction 1104 1.1. What Is Nanoscience? 1104 1.2. Surfaces and Interfaces in Nanoscience 1106 1.3. SAMs and Organic Surfaces 1106 1.4. SAMs as Components of Nanoscience and Nanotechnology 1106 1.5. Scope and Organization of the Review 1106 2. Preparation of SAMs 1108 2.1. Types of Substrates 1108 2.1.1. Preparation of Thin Metal Films as Substrates for SAMs 1108 2.1.2. Other Substrates for SAMs 1110 2.1.3. Why Is Gold the Standard? 1111 2.2. Protocols for Preparing SAMs from Organosulfur Precursors 1111 2.2.1. Adsorption of Alkanethiols from Solution 1111 2.2.2. Adsorption of Disulfides and Sulfides from Solution 1113 2.2.3. “Mixed” SAMs 1113 2.2.4. Adsorption from Gas Phase 1114 3. Characterization of SAMs: Structure, Assembly, and Defects 1114 3.1. Nature of the Metal-SAM Interface 1114 3.1.1. Thermodynamic Analysis of Gold-Thiolate Bonds 1115 3.1.2. Surface Structure of Thiolates on Gold 1115 3.1.3. Surface Structure of Thiolates on Palladium 1116 3.1.4. Surface Structure of Thiolates on Silver 1116 3.1.5. Surface Structure of Thiolates on Copper 1117 3.2. Organization of the Organic Layer 1117 3.2.1. Single-Chain Model for Describing the Average Organization of the Organic Layer in SAMs 1117 3.2.2. “Odd-Even” Effect for SAMs on Gold 1118 3.2.3. Multichain Unit Cells 1119 3.2.4. Effect of the Organic Component on the Stability of the SAM 1119 3.3. Mechanisms of Assembly 1119 3.3.1. Assembly of SAMs from the Gas Phase 1119 3.3.2. Assembly of SAMs from Solution 1121 3.4. Defects in SAMs 1121 3.4.1. Defects Caused by Variations in the Surface of the Substrate 1121 3.4.2. Reconstruction of the Surface during Assembly 1121 3.4.3. Composition of SAMs 1121 3.4.4. Structural Dynamics of SAMs Induce Defects 1121 4. Removing SAMs from Surfaces 1122 4.1. Electrochemical Desorption of SAMs 1122 4.2. Displacement of SAMs by Exchange 1122 4.3. Photooxidation of SAMs. 1123 5. Tailoring the Composition and Structure of SAMs 1123 5.1. Why Modify SAMs after Formation? 1123 5.2. Strategies for Covalent Coupling on SAMs 1124 5.2.1. Direct Reactions with Exposed Functional Groups 1124 5.2.2. Activation of Surfaces for Reactions 1125 5.2.3. Reactions that Break Covalent Bonds 1126 5.2.4. Surface-Initiated Polymerizations 1126 5.2.5. How Does the Structure of the SAM Influence Reactivity on Surfaces? 1126 5.3. Noncovalent Modifications 1127 5.3.1. Nonspecific Adsorption of Molecules from Solution onto SAMs 1127 5.3.2. Fusion of Vesicles on SAMs 1127 5.3.3. Selective Deposition onto SAMs 1128 5.3.4. Modifications via Molecular Recognition 1128 6. SAMs as Surface Layers on Nanoparticles 1128 6.1. Formation of Monolayer-Protected Clusters (MPCs) 1128 6.1.1. Thiols Are a Special Subclass of Surfactants 1129 6.1.2. Thiols Can Influence the Size and Shape of Nanoparticles 1129 6.2. Strategies for Functionalizing Nanoparticles with Ligands 1130 6.2.1. Formation of Nanoparticles in the Presence of Thiols 1130 6.2.2. Ligand-Exchange Methods 1130 6.2.3. Covalent Modification 1131 6.3. Structure of SAMs on Highly Curved Surfaces 1131 6.3.1. Spectroscopic Evidence for SAM Structure on Nanoparticles 1132 6.3.2. Evidence for the Structure of SAMs on Nanoparticles based on Chemical Reactivity 1132 6.4. SAMs and the Packing of Nanocrystals into Superlattices 1132 * To whom correspondence should be addressed. R.G.N.: phone, 217-244-0809; fax, 217-244-2278; e-mail: r-nuzzo@uiuc.edu. G.M.W.: phone, (617) 495-9430; fax, (617) 495-9857; e-mail: gwhitesides@gmwgroup.harvard.edu. † Harvard University. ‡ University of IllinoissUrbana-Champaign. 1103 Chem. Rev. 2005, 105, 1103-1169 10.1021/cr0300789 CCC: $53.50 © 2005 American Chemical Society Published on Web 03/25/2005