Langmuir -Blodgett Films

Edited by

GARETH ROBERTS Thorn EMI pic

Hayes, Middlesex, United Kingdom and University of Oxford Oxford, United Kingdom

Plenum Press • New York and London

Contents

Chapter 1 Historical Introduction

С. H. Giles, S. D. Forrester, and G. G. Roberts

1.1. Introduction 1 1.2. Early Contributors to the Field of Monolayer Science 2

1.2.1. Franklin (1706-1790) 3 1.2.2. Shields (1822-1890) 4 1.2.3. Aitken (1839-1919) 5 1.2.4. Rayleigh (1842-1919) 6 1.2.5. Pockels (1862-1935) 8 1.2.6. Langmuir (1881-1957) 9 1.2.7. Blodgett (1898-1979) 11

1.3. Conclusion 13 References 14

Chapter 2 Molecular Structure and Monolayer Properties

R. A. Hann

2.1. Introduction 17 2.2. Formation and Stability of Monolayers 18

2.2.1. Surface Pressure/Area Isotherms 19 2.2.2. Modeling Molecular Structure 24 2.2.3. Other Properties of Langmuir Films 25 2.2.4. Mixed Monolayers 26

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2.3. Langmuir-Blodgett Deposition 27 2.4. Types of Molecules Known to Form Monolayers and Langmuir-

Blodgett Films 32 2.4.1. Fatty Acids and Their Derivatives 32

2.4.1.1. Chemical Structure of Fatty Acids 32 2.4.1.2. Incorporation of Metal Ions 33 2.4.1.3. Fatty Acids with Modified Hydrophobic Tailgroups . . 35 2.4.1.4. Modifications to the Hydrophilic Headgroup 41

2.4.2. Molecules Containing Five- or Six-Membered Rings 45 2.4.2.1. Derivatives of Benzene 45 2.4.2.2. Derivatives of Polycyclic Aromatic Hydrocarbons . . . 46 2.4.2.3. Heterocyclic Compounds and Dyes 53

2.4.3. Porphyrins and Phthalocyanines 59 2.4.4. Mixed Monolayers of Unsubstituted Hydrophobic Materials . . . 67

2.5. Polymers and Polymerizable Materials 68 2.5.1. Preformed Polymers 68 2.5.2. Polymers Formed in situ by Addition of Carbon-Carbon

Double Bonds 73 2.5.3. Diacetylenes 76 2.5.4. Oxirans 78 2.5.5. Condensation Polymers 78 2.5.6. Opportunities for New Materials 78

2.6. Exceptions 79 2.6.1. Non-Langmuir-Blodgett Multilayers 79 2.6.2. Nonaqueous Subphases 81

2.7. Prospects 82 2.8. Postscript 83 References 83

Chapter 3 Film Deposition

M. С Petty and W. A. Barlow

3.1. Deposition Principles 93 3.2. Subphase and Containment 98 3.3. Compression Mechanisms 100

3.3.1. Single Movable Barrier 100 3.3.2. Circular Trough 101 3.3.3. Constant Perimeter Barrier 102

3.4. Ancillary Equipment 105 3.4.1. Surface Pressure Measurement 105 3.4.2. Surface Area Measurement 108 3.4.3. Deposition Equipment 109

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3.4.4. Control Systems 110 3.5. Trough Environment 112 3.6. Experimental Techniques ИЗ

3.6.1. Surface Cleaning 113 3.6.2. Monolayer Spreading 114 3.6.3. Substrate Preparation 115 3.6.4. Monolayer Transfer 118

3.7. Other Systems 120 3.7.1. Continuous Fabrication 120 3.7.2. Alternate-Layer Troughs 122

References 123

Chapter 4 Characterization and Properties

M. С Petty 4.1. Introduction 133 4.2. Evaluation of Film Thickness 134

4.2.1. Interference Techniques 134 4.2.2. Ellipsometry 136 4.2.3. X-Ray Diffraction 137 4.2.4. Neutron Diffraction and Reflection 140 4.2.5. Alternative Methods 141

4.3. Film Structure 141 4.3.1. Electron Microscopy 142 4.3.2. Optical Microscopy 148 4.3.3. IR and Visible Spectroscopy 149 4.3.4. Raman Scattering 154 4.3.5. Surface Analytical Techniques 157 4.3.6. Other Characterization Methods 160

4.4. Optical Properties 162 4.4.1. Refractive Index 162 4.4.2. Nonlinear Effects 165

4.5. Electrical Characterization 167 4.5.1. Specimen Preparation 167 4.5.2. Quantum Mechanical Tunneling 169 4.5.3. Direct Current Conduction through Multilayers 175 4.5.4. Conductance 181 4.5.5. Permittivity 187 4.5.6. Permanent Polarization 190 4.5.7. Dielectric Breakdown 192

4.6. Other Phenomena 193 4.6.1. Mechanical Properties 193

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4.6.2. Permeability Studies 195 References 196

Chapter 5

Spectroscopy of Complex Monolayers

D. Möbius

5.1. Introduction 223 5.2. Transmission, Absorption, and Reflection of Light 224

5.2.1. Transmission 225 5.2.2. Reflection 234 5.2.3. Infrared Spectroscopy 249

5.3. Emission 251 5.3.1. Steady State Fluorescence 252 5.3.2. Fluorescence Decay 259 5.3.3. Phosphorescence 263

5.4. Indirect Optical Methods 263 5.4.1. Holographic Techniques 264 5.4.2. Photoacoustic Spectroscopy 265 5.4.3. Coupling to Surface Plasmons 266

References 267

Chapter 6

Monolayers and Multilayers of Biomolecules

R. M. Swart

6.1. Introduction 273 6.2. Langmuir Monolayers of Biological Molecules 276

6.2.1. Phospholipids and Sterols 277 6.2.2. Proteins 282 6.2.3. Pigments 284 6.2.4. Fatty Acids and Polymerizable Phospholipids 285

6.3. Preparation of Supported Multilayers 287 6.3.1. Dipping Phospholipids onto a Vertical Support 288 6.3.2. Dipping Phospholipids onto a Horizontal Support 289 6.3.3. Dipping Phospholipids: General Considerations 290 6.3.4. Dipping Polymerizable Derivatives of Phospholipids 291 6.3.5. Oriented Multilayers by Other Methods 292 6.3.6. Proteins and Pigments 293

6.4. Studies Employing Supported Molecular Layers 295 6.4.1. Spectroscopic Studies 295 6.4.2. Membrane Properties 297 6.4.3. Proteins 299

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6.4.4. Pigments and Photosynthesis 301 6.4.5. Electrical Properties 301 6.4.6. Polymerie Surfaces 302

6.5. Concluding Remarks 303 6.6. Appendix 304 References 307

Chapter 7

Potential Applications of Langmuir-Blodgett Films

G. G. Roberts

7.1. Introduction 317 7.1.1. Molecular Electronics 317 7.1.2. Supermolecular Electronics 318 7.1.3. Possible Niches for Langmuir-Blodgett Films 320

7.2. Patents Filed by Langmuir and Blodgett 321 7.2.1. Image Reproduction 321 7.2.2. Optical Devices 322 7.2.3. Step Gauge 323 7.2.4. Mechanical Filters 324 7.2.5. Sensors 324 7.2.6. Summary 324

7.3. Model Systems in Basic Research 325 7.3.1. Energy Transfer in Complex Monolayers 325 7.3.2. Magnetic Monolayers 326 7.3.3. Determination of Electron Energy Ranges 328 7.3.4. Biological and Permeable Membranes 329

7.4. Passive Thin-Film Applications 332 7.4.1. Electron Beam Microlithography 332 7.4.2. Lubrication 334 7.4.3. Enhanced Device Processing 336

7.4.3.1. Surface Acoustic Waves 336 7.4.3.2. Liquid Crystal Alignment 337

7.5. Piezoelectric and Pyroelectric Organic Films 339 7.5.1. Piezoelectric Properties 342 7.5.2. Pyroelectric Properties 344

7.5.2.1. Theoretical Consideration in a Thermal Imager . . . . 345 7.5.2.2. Pyroelectric Langmuir-Blodgett Films 347

7.6. Applied Optics Using Langmuir-Blodgett Films 351 7.6.1. Waveguiding in Langmuir-Blodgett Films 352 7.6.2. Nonlinear Optics: Relevant Theory 353

7.6.2.1. Second-Order Effects 354 7.6.2.2. Third-Order Effects 356

7.6.3. Optoelectronic Applications of Organic Films 357

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7.6.4. Nonlinear Optics: Langmuir-Blodgett Films 358 7.6.4.1. Second-Order Effects 358 7.6.4.2. Electrooptic Effects 362 7.6.4.3. Third-Harmonic Effects 362 7.6.4.4. Summary 365

7.6.5. Optical Information Storage 365 7.7. Electrical Properties of Monolayers and Multilayers 368

7.7.1. Electrical Conductivity in Langmuir-Blodgett Films 368 7.7.2. Langmuir-Blodgett Films as Insulators 370 7.7.3. Photoelectronic Behavior of Langmuir-Blodgett Films

on Metals 371 7.7.4. Molecular Rectification and Cooperation 373

7.7.4.1. Molecular Pumping 373 7.7.4.2. Superconductivity 374 7.7.4.3. Organic Rectification 374

7.8. Langmuir-Blodgett Films on Semiconductors 375 7.8.1. Metal-Insulator-Semiconductor Diodes 376 7.8.2. Schottky Barrier Modification 380

7.8.2.1. Photovoltaic Cells 380 7.8.2.2. Electroluminescent Diodes 384

7.8.3. Field-Effect Transistors 384 7.8.3.1. Group III-V Semiconductors 386 7.8.3.2. Silicon 388

7.9. Chemical/Biological Sensors and Transducers 389 7.9.1. Conductivity Devices 390 7.9.2. Field-Effect Devices 390 7.9.3. Optical Sensors 392 7.9.4. Acoustoelectric Sensors 394

7.9.4.1. Quartz Oscillator 394 7.9.4.2. Surface Acoustic Wave Oscillator 395

7.9.5. Biosensors 397 7.10. Summary 400 References 401

Index 413