Molecular-Scale Electronics Concept, Fabrication and Applications

Xuefeng Guo, PhD, is a Professor at Peking University, China. His current research is focused on functional nanometer/molecular devices. Professor Guo has authored over 170 scientific publications and has received numerous scientific awards.

Dong Xiang, PhD, is a Professor in the College of Electronic Information and Optical Engineering, Nankai University. His current research interests focus on single molecule studies and optoelectronic molecular devices.

Yu Li, PhD, is a research scientist in the College of Chemistry and Molecular Engineering at Peking University, China. Her research interest includes single-molecule device physics and biophysics.

1 Introduction 1

References 4

2 Metal Electrodes for Molecular Electronics 7

2.1 Single-Molecule Junctions 7

2.1.1 Scanning Probe Microscopy Break Junctions 7

2.1.1.1 Beyond Traditional SPM Break Junctions 13

2.1.1.2 Applications of SPM Beyond Electron Transport 16

2.1.2 Mechanically Controllable Break Junctions 19

2.1.2.1 Work Principle and Advantages 19

2.1.2.2 MCBJ Chip Fabrication 23

2.1.2.3 MCBJ Applications 25

2.1.3 Electromigration Breakdown Junctions 32

2.1.3.1 Device Fabrication 33

2.1.3.2 Gap Size Control 34

2.1.3.3 Electromigration Applications 37

2.1.4 Electrochemical Deposition Junctions 40

2.1.5 Surface-Diffusion-Mediated Deposition Junctions 43

2.2 Ensemble Molecular Junctions 45

2.2.1 Lift-and-Float Approach 45

2.2.2 Liquid Metal Contact 47

2.2.3 Nanopore and Nanowell 50

2.2.4 On-Wire Lithography 52

2.2.5 Transfer Printing Techniques 54

2.2.6 Self-Aligned Lithography 60

2.2.7 Buffer Interlayer-Based Junction 62

2.2.8 On-Edge Molecular Junction 65

2.2.9 Suspended-Wire Molecular Junctions 68

References 71

3 Carbon Electrodes for Molecular Electronics 93

3.1 Carbon Nanotube-Based Electrodes 93

3.1.1 Electrical Breakdown 94

3.1.2 Lithography-Defined Oxidative Cutting 98

3.2 Graphene-Based Electrodes 102

3.2.1 Electroburning 103

3.2.2 Dash-Line Lithography 103

3.3 Other Carbon-Based Electrodes 107

References 109

4 Other Electrodes for Molecular Electronics 113

4.1 Silicon-Based Electrodes 113

4.2 Polymer-Based Electrodes 116

References 117

5 Novel Phenomena in Single-Molecule Junctions 119

5.1 Quantum Interference 119

5.1.1 Prediction of QI Effects 119

5.1.2 Signature of Quantum Interference 120

5.1.3 Different Transport Pathways 123

5.1.4 Chemical Design to Tune Quantum Interference 124

5.2 Coulomb Blockade and Kondo Resonance 125

5.3 Thermoelectricity 128

5.4 Electronic–Plasmonic Conversion 130

References 132

6 Supramolecular Interactions in Single-Molecule Junctions 137

6.1 Hydrogen Bonds 137

6.2 π–π Stacking Interactions 140

6.3 Host–Guest Interactions 144

6.4 Charge-Transfer Interactions 149

References 152

7 Characterization Techniques for Molecular Electronics 157

7.1 Inelastic Electron Tunneling Spectroscopy 157

7.1.1 History and Background 158

7.1.2 IETS Measurement 160

7.1.3 IETS Applications 163

7.2 Temperature–Length–Variable Transport Measurement 166

7.3 Noise Spectroscopy 170

7.3.1 Thermal Noise and Shot Noise 171

7.3.2 Generation–Recombination and Flicker Noise 172

7.3.3 Noise Spectroscopy Measurements 173

7.3.4 Application of Noise Spectroscopy 174

7.4 Optical and Optoelectronic Spectroscopy 180

7.4.1 Raman Spectroscopy 180

7.4.2 Ultraviolet–Visible Spectroscopy 182

7.4.3 X-ray Photoelectron Spectroscopy 183

7.4.4 Ultraviolet Photoelectron Spectroscopy 184

7.5 Data Characterization Approaches 185

7.5.1 Transition Voltage Spectroscopy 185

7.5.1.1 TVS Models 185

7.5.1.2 Applications of TVS 188

7.5.2 One Dimensional (1D), Two Dimensional (2D) Histogram and QuB 191

References 195

8 Theoretical Aspects for Electron Transport Through Molecular Junctions 209

8.1 Theoretical Description of the Tunneling Process 209

8.2 Electron Transport Mechanism 212

8.2.1 Coherent Electron Transport Through Molecular Junctions 212

8.2.2 Electron–Phonon Interaction Effects on Transport Mechanism 214

8.3 First-Principles Modeling 215

8.3.1 Introduction to Density Functional Theory 215

8.3.2 Current–Voltage Characteristics Calculations 217

References 221

9 Integrating Molecular Functionalities into Electrical Circuits 225

9.1 Wiring Toward Nanocircuits 225

9.1.1 Backbones as Charge Transport Pathways 226

9.1.1.1 Hydrocarbon Chains 227

9.1.1.2 Metal Containing Compounds 234

9.1.1.3 Porphyrin Arrays 237

9.1.1.4 Carbon Nanotubes 239

9.1.1.5 Biological Wires 241

9.1.2 Conductance of Single Molecules 244

9.1.2.1 Interfacial Coupling 245

9.1.2.2 Energy Level Alignment 250

9.1.2.3 Photon-Assisted Conductance Enhancement 252

9.1.2.4 Molecular Conductance Measurements 256

9.2 Rectification Toward Diodes 258

9.2.1 General Mechanisms for Molecular Rectification 259

9.2.1.1 Aviram–Ratner Model 259

9.2.1.2 Kornilovitch–Bratkovsky–Williams Model 261

9.2.1.3 Datta–Paulsson Model 262

9.2.2 Rectification Stemming from Molecules 262

9.2.2.1 D–σ–A and D–π–A System 262

9.2.2.2 D–A Diblock Molecular System 263

9.2.3 Rectification Stemming from Different Interfacial Coupling 267

9.2.3.1 Different Electrodes 267

9.2.3.2 Anchoring Groups 268

9.2.3.3 Contact Geometry 269

9.2.3.4 Interfacial Distance 269

9.2.4 Other Molecular Rectifiers 270

9.3 Negative Differential Conductance Toward Oscillators 272

9.3.1 Mechanisms for Negative Differential Conductance 272

9.3.2 Measurement of NDC 274

9.3.3 Application of NDC 276

9.4 Gating Toward Molecular Transistors 277

9.4.1 Back Gating for Novel Physical Phenomenon Investigation 277

9.4.2 Side Gating for Electron Transport Control 282

9.4.3 Electrochemical Gating for Efficient Gate Coupling 283

9.5 Switching Toward Memory Devices 284

9.5.1 Switch Stem from Conformation Change 285

9.5.1.1 Electrical Field Induced Switch 285

9.5.1.2 Tunneling Electron (Charge) Triggered Switch 286

9.5.1.3 Mechanical Force Induced Switch 289

9.5.1.4 Chemical Stimuli Triggered Switch (Redox and pH) 290

9.5.1.5 Light-Triggered Switch 293

9.5.2 Electrochemically Gated Switch 297

9.5.3 Spintronics-Based Switch 301

9.5.4 Other Memory Devices 305

9.6 Molecular Computing 306

9.6.1 DNA-Based Computing 306

9.6.2 Molecular Logic Gates 308

9.7 Transduction Toward Molecular Sensors 313

9.7.1 Sensing Based on Chemical Reactions 314

9.7.2 Sensing Based on Biological Interactions 319

9.7.2.1 Nanocarbon-Based Molecular Electronics 321

9.7.2.2 Silicon-Based Devices 327

9.7.3 Sensing Based on Thermoelectrical Conversion 331

9.8 High-Frequency Molecular Devices 333

9.9 Molecular Machines 337

9.9.1 Molecular Motors 337

9.9.2 Molecular Elevators 338

9.9.3 Molecular Scissors 341

9.9.4 Other Multicomponent Mechanical Machines 344

References 347

10 Summary and Perspectives 375

10.1 Primary Challenges 377

10.1.1 In Situ Measurement 377

10.1.2 Device Fabrication Yield 378

10.1.3 Device-to-Device Variation and Instability 378

10.1.4 Integration Capability 379

10.1.5 Energy Consumption 380

10.1.6 Addressability 380

10.1.7 General Strategies to Meet Challenges 381

10.2 Open Questions 382

10.3 Outlook 384

References 385

Index 389

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