Nanogap Electrodes

Tao Li is Associate Professor in the Department of Chemistry at Shanghai Jiao Tong University. His research interests are molecular electronics, molecular-scale devices, sythesis and application of organic functional materials and molecular solar thermal batteries.

• Preface xi1 Nanogap Electrodes and Molecular Electronic Devices 1Tao Li1.1 Introduction 11.2 Overview of Molecular Electronics 21.2.1 Why Molecular Electronics 31.2.1.1 History of Computing 31.2.1.2 Moore’s Law 61.2.1.3 Molecular Electronics: A Beyond-CMOS Option 81.2.2 Molecular Materials for Organic Electronics 101.2.2.1 OLEDs 111.2.2.2 OFETs 111.2.2.3 OPVs 121.2.3 Molecules for Molecular-Scale Electronics 131.3 Introduction to Nanogap Electrodes 161.4 Summary and Outlook 19References 192 Electron Transport in Single Molecular Devices 25Lei-Lei Nian, Liang Ma, and Jing-Tao Lü2.1 Introduction 252.2 General Methods 262.2.1 Transport Mechanisms 262.2.2 Nonequilibrium Green’s Function Method 262.2.3 Master Equation Method 292.3 Single Electron Transport Through Single Molecular Junction 312.3.1 Coherent Transport 312.3.2 Hopping Transport 322.4 Effect of Many-Body Interactions 352.4.1 Electron-Vibration Interaction 352.4.1.1 Weak Coupling Regime 372.4.1.2 Strong-Coupling Regime 402.4.2 Electron–Electron Interaction 432.4.2.1 Coulomb Blockade 432.4.2.2 Kondo Effect 452.5 Thermoelectric Transport 482.6 First-Principles Simulations of Transport in Molecular Devices 512.7 Conclusions 52References 523 Fabricating Methods and Materials for Nanogap Electrodes 57Xianhui Huang, Weiqiang Zhang, Dong Xiang, and Tao Li3.1 Introduction 573.2 Mechanical Controllable Break Junctions 593.3 Electrochemical and Chemical Deposition Method 683.3.1 Electroplating and Feedback System 683.3.2 Chemical Deposition 743.4 Oblique Angle Shadow Evaporation 753.5 Electromigration and Electrical Breakdown Method 783.5.1 Device Fabrication 793.5.2 Gap Size Control 823.5.3 Electromigration Applications 843.6 Molecular Scale Template 893.6.1 Molecular Rulers 893.6.2 Inorganic Films as Templates 943.6.3 On-Wire Lithography 963.6.4 Nanowire Mask 1003.7 Focused Ion Beam 1023.8 Scanning Probe Lithography and Conducting Probe-Atomic Force Microscopy 1083.8.1 DestructiveWay 1083.8.2 ConstructiveWay 1113.8.3 Conducting Probe-Atomic Force Microscopy 1123.9 Nanogap Electrodes Prepared with Nonmetallic Materials 1133.9.1 Introduction 1133.9.2 Nanogap Electrodes Made from Carbon Materials 1143.9.2.1 Advantages of Carbon Materials 1143.9.2.2 Carbon Nanotubes for Nanogap Electrodes 1153.9.2.3 Graphene 1303.9.2.4 Silicon Nanogap Electrodes 1533.9.2.5 Other Materials 1713.10 Summary and Outlook 174References 1754 Characterization Methods and Analytical Techniques for Nanogap Junction 189Baili Li, Ziyan Wang, Bin Han, and Xi Yu4.1 Current–Voltage Analysis 1894.1.1 Coherent Tunneling Transport 1904.1.2 Transition Voltage Spectroscopy 1954.1.3 Incoherent Transport 1984.2 Inelastic Tunneling Spectroscopy (IETS) 2064.2.1 Principle and Measurement of IETS 2064.2.2 Selection Rule and Charge Transport Pathway 2094.2.3 Line Shape of the IETS 2144.2.4 Application of the IETS 2184.2.5 Mapping the Charge Transport Pathway in Protein Junction by IETS 2194.2.6 STM Imaging by IETS 2224.3 Optical and Optoelectronic Spectroscopy 2264.4 Concluding Remarks 232Appendix 233References 2345 Single-Molecule Electronic Devices 239Shengxiong Xiao5.1 Introduction 2395.2 Wiring Molecules into “Gaps”: Anchoring Groups and Assembly Methods 2405.2.1 Anchor Groups 2405.2.2 Effect of Anchor–Bridge Orbital Overlaps on Conductance 2455.2.3 In Situ Chemical Reactions to Produce Covalent Contacts 2505.3 Electrical Rectifier 2525.3.1 Rectification Toward Diodes 2555.3.2 General Mechanisms for Molecular Rectification 2565.3.2.1 Aviram–Ratner Model 2565.3.2.2 Kornilovitch–Bratkovsky–Williams Model 2575.3.2.3 Datta–Paulsson Model 2585.3.3 Rectification Originated from Molecules 2595.3.3.1 D–σ–A and D–π–A Systems 2595.3.3.2 D–A Diblock Molecular System 2605.3.4 Rectification Stemming from Different Interfacial Coupling 2645.3.4.1 Different Electrodes 2645.3.4.2 Anchoring Groups 2655.3.4.3 Contact Geometry 2655.3.4.4 Interfacial Distance 2665.3.5 Additional Molecular Rectifiers 2675.4 Conductance Switches 2695.4.1 Voltage Pulse Induced Switches 2705.4.2 Light-Induced Switching 2715.4.3 Switching Triggered by Chemical Process (Redox and pH) 2755.4.4 Spintronics-Based Switch 2785.5 Gating the Transport: Transistor-Like Single-Molecule Devices 2825.5.1 Electrostatic Gate Control 2825.5.2 Side Gating 2875.5.3 Electrochemical Gate Control 2885.5.4 Molecular Quantum Dots 2905.6 Challenges and Outlooks 291References 2926 Molecular Electronic Junctions Based on Self-Assembled Monolayers 301Yuqing Liu and Zhongming Wei6.1 Introduction 3016.2 Molecular Monolayers for Molecular Electronics Devices 3026.2.1 Monolayers Covalently Bonded to Noble Metals 3036.2.2 Monolayers Attached to Non-metal Substrates 3096.2.3 Langmuir–Blodgett Method 3126.3 Top Electrodes 3146.3.1 Deposited Metal 3146.3.1.1 Direct Evaporation 3156.3.1.2 Indirect Evaporation 3166.3.2 Make Top Contact by Soft Methods 3196.3.2.1 Lift-and-Float Approach 3196.3.2.2 Crosswire Junction 3206.3.2.3 Transfer Printing 3226.3.2.4 Graphene as Top Electrode 3236.3.2.5 Liquid Metal Contact 3266.4 Experimental Progress with Ensemble Molecular Junctions 3296.5 Outlook 334References 3357 Toward Devices and Applications 345Ajuan Cui and Kasper Nørgaard7.1 Introduction 3457.2 Major Issues: Reliability and Robustness 3467.2.1 Single Molecular Device 3477.2.1.1 Top-Contact Junctions 3477.2.1.2 Planar Metallic Nanogap Electrodes 3477.2.1.3 Planar Nanogap Electrodes Based on SingleWalled Carbon Nanotubes (SWCNTs) or Graphene 3497.2.1.4 The Absorption of Molecule on the Surface of SWCNTs or Graphene 3507.2.2 Molecular Device Based on Molecule Monolayer 3517.2.2.1 Bottom Electrodes 3537.2.2.2 Insulating Layer with Holes to Define the Size of the Bottom Electrodes 3537.2.2.3 Molecule Monolayer Formation 3547.2.2.4 Top Electrodes 3547.3 Potential Integration Solutions 3587.3.1 Carbon Nanotube or Graphene Interconnects 3597.3.2 Self-Assembled Monolayers for Integrated Molecular Junctions 3647.3.3 Cross Bar Architecture 3687.4 Beyond Simple Charge Transport 3717.4.1 Mechanics 3717.4.2 Thermoelectronics 3757.4.3 Quantum Interference 3817.4.4 Spintronics 3867.4.4.1 SAM-Based Magnetic Tunnel Junctions 3867.4.4.2 Molecule Based Spin-Valves or Magnetic Tunnel Junctions 3877.4.4.3 Single Molecular Spin Transistor 3897.4.4.4 Single Molecular Nuclear Spin Transistor 3917.4.4.5 Molecule Based Hybrid Spintronic Devices 3937.5 Electrochemistry with Nanogap Electrodes 395References 400Index 411