Spectroscopy for Materials Characterization

Simonpietro Agnello received his Ph.D. in Physics at the Department of Physics and Chemistry, University of Palermo, Italy, where he currently works as Associate Professor. His research in experimental physics focuses on spectroscopic characterization of materials, matter-radiation interaction processes, and thermal modification of materials. Prof. Agnello is an expert of spectroscopic techniques, namely electron paramagnetic resonance, optical absorption spectroscopy, Raman spectroscopy and time-resolved optical spectroscopy. He actively studies advanced materials, nanostructured silica materials, carbon-based materials, and 2D materials. He has published about 300 research articles in peer-reviewed journals and has achieved an h-index of 28.

Preface xv

List of Contributors xvii

1 Radiation–Matter Interaction Principles: Optical Absorption and Emission in the Visible-Ultraviolet Region 1
Simonpietro Agnello

1.1 Empirical Aspects of Radiation–Matter Interaction 1

1.1.1 Optical Absorption: The Lambert–Beer Law 1

1.1.2 Emission: Fluorescence and Phosphorescence 5

1.2 Microscopic Point of View 7

1.2.1 Einstein Coefficients 7

1.2.2 Oscillator Strength, Lifetime, Quantum Yield 11

1.2.3 Vibronic States: Homogeneous and Inhomogeneous Lineshape 14

1.2.4 Jablonski Energy Level Diagram: Permitted and Forbidden Transitions 20

1.2.5 Excited States Rate Equations 22

1.3 Instrumental Setups 23

1.3.1 Typical Block Diagram of Spectrometers 23

1.3.2 Light Sources 24

1.3.3 Dispersion Elements: Gratings and Resolution Power 25

1.3.4 Detectors: Photodiode, Photomultiplier, Charge Coupled Device 27

1.4 Case Studies 29

1.4.1 Optical Absorption in Visible-Ultraviolet Range 29

1.4.1.1 Scanning Device (Bandwidth and Scanning Speed Effects) 29

1.4.1.2 CCD Fiber Optic Device 31

1.4.2 Photoluminescence 31

1.4.2.1 Emission and Excitation Spectra: Energy Levels Reconstruction 32

References 33

2 Time-Resolved Photoluminescence 35
Marco Cannas and Lavinia Vaccaro

2.1 Introduction to Photoluminescence Spectroscopy 35

2.1.1 Photoluminescence Properties Related to Points Defects: Electron–Phonon Coupling 35

2.1.2 Optical Transitions: The Franck–Condon Principle 38

2.1.3 Zero-Phonon Line 40

2.1.4 Phonon Line Structure 43

2.1.5 Vibrational Structure 45

2.1.6 Inhomogeneous Effects 48

2.2 Experimental Methods and Analysis 48

2.2.1 Time-Resolved Luminescence 48

2.2.2 Site-Selective Luminescence 50

2.2.3 Basic Design of Experimental Setup: Pulsed Laser Sources; Monochromators; Detectors 51

2.2.3.1 Tunable Laser 52

2.2.3.2 Time-Resolved Detection System: Spectrograph and Intensified CCD Camera 52

2.3 Case Studies: Luminescent Point Defects in Amorphous SiO2 54

2.3.1 Emission Spectra and Lifetime Measurements 55

2.3.2 Zero-Phonon Line Probed by Site-Selective Luminescence 58

References 63

3 Ultrafast Optical Spectroscopies 65
Alice Sciortino and Fabrizio Messina

3.1 Femtosecond Spectroscopy: An Overview 65

3.2 Ultrafast Optical Pulses 67

3.2.1 General Properties 67

3.2.1.1 Dispersion Effect: Group Velocity Dispersion 67

3.2.2 Nonlinear Optics: Basis and Applications 69

3.2.2.1 Second Harmonic Generation and Sum Frequency Generation 69

3.2.2.2 Noncollinear Optical Parametric Amplifier 70

3.2.2.3 Supercontinuum Generation 72

3.3 Transient Absorption Spectroscopy 73

3.3.1 The Experimental Method 74

3.3.2 Typical Experimental Setups 76

3.3.3 Data Analysis and Interpretation 78

3.4 Ultrafast Fluorescence Spectroscopies 79

3.4.1 FLUC: The Experimental Method 80

3.4.2 FLUC: Typical Experimental Setups 80

3.4.3 FLUC: Data Analysis and Interpretation 82

3.4.4 Kerr-Based Femtosecond Fluorescence Spectroscopy 82

3.5 Femtosecond Stimulated Raman Spectroscopy 83

3.5.1 The Experimental Method 83

3.5.2 Typical Experimental Setups 84

3.5.3 Data Analysis and Interpretation 87

3.6 Case Studies 88

3.6.1 Ultrafast Relaxation Dynamics of Molecules in Solution Phase 88

3.6.2 Relaxation of Excited Charge Carriers and Excitons in Semiconductor Nanoparticles 89

3.6.3 Ultrafast Relaxation Dynamics of Carbon-based Nanomaterials 91

References 92

4 Confocal and Two-Photon Spectroscopy 97
Giuseppe Sancataldo and Valeria Vetri

4.1 Introduction and Historical Perspectives 97

4.1.1 Point Spread Function and Optical Resolution 98

4.1.2 Optical Sectioning and Imaging of 3D Samples 101

4.2 Fluorescence Imaging 102

4.2.1 Laser Scanning Confocal Fluorescence Microscope 103

4.2.2 Two-Photon Microscope 105

4.2.3 The Importance of Sample Preparation from Solid State to Dynamic Specimens 108

4.2.4 Setting Up a Measurement 109

4.3 Spectroscopy Using a Microscope 110

4.3.1 Observables in Fluorescence Microscopy 111

4.3.2 Measuring Dynamics: Gaining Information Below Resolution 113

4.4 Case Studies 117

4.4.1 Understanding Microstructures and Mechanistic Aspects in Materials 117

4.4.2 Fluctuation Methods for the Analysis of Nanosystems 121

References 124

5 Infrared Absorption Spectroscopy 129
Tiziana Fiore and Claudia Pellerito

5.1 Fundamentals 129

5.1.1 Introduction 130

5.1.2 Basic Principles 130

5.1.3 Infrared Spectra 135

5.1.4 Fourier Transform Infrared Spectrometers (Interferometers) 137

5.2 Sources and Detectors 140

5.3 Techniques and Sampling Methods 144

5.3.1 Transmission Methods 144

5.3.1.1 Solid Samples 144

5.3.1.2 Liquid and Solution Samples 147

5.3.1.3 Gas Samples 148

5.3.2 Attenuated Total Reflectance (ATR) Method 148

5.3.3 FTIR Microspectroscopy 150

5.3.4 AFM-IR Spectroscopy 150

5.3.5 Hyphenated Techniques 150

5.4 Applications and Case Studies 151

5.4.1 Chemical Characterization and Kinetics 151

5.4.2 Surfaces 152

5.4.3 Medical and Life Science (Pharmaceutical, Medical, Biological, Biotechnological) 153

5.4.4 Cultural Heritage and Forensic 156

5.4.5 Environmental and Geological 157

5.4.6 Food Industry 158

References 158

6 Raman and Micro-Raman Spectroscopy 169
Giuliana Faggio, Rossella Grillo, and Giacomo Messina

6.1 Basic Theory 169

6.1.1 Introduction 169

6.1.2 Spectroscopic Units 169

6.1.3 Molecular Vibrations 170

6.1.4 Classical Theory of the Raman Scattering 171

6.1.5 Simplified Quantum Approach to Raman Scattering 174

6.1.6 Raman and IR Activities 178

6.1.7 Crystal Vibrations 180

6.1.8 Raman Scattering in Crystals 183

6.1.9 Surface-Enhanced Raman Scattering (SERS) 185

6.2 Instrumentation 187

6.2.1 Laser Sources and Optical Filters 187

6.2.2 Monochromators 188

6.2.3 Detectors 189

6.2.4 Raman Microscopy and Raman Mapping 189

6.3 Case Studies 191

6.3.1 Raman Indicators 191

6.3.2 Identification of Materials and Crystalline Quality 191

6.3.3 Graphene and Graphite Raman Spectra 193

6.3.4 Doping Detection 196

6.3.5 Basic Examples of SERS 196

References 198

7 Thermally Stimulated Luminescence 201
Federico Moretti

7.1 Theory of Thermally Stimulated Luminescence 202

7.1.1 Simple Model 205

7.1.1.1 First-Order Kinetics 207

7.1.1.2 Second-Order Kinetics 211

7.1.1.3 General-Order Kinetics 211

7.1.2 Localized Transitions 213

7.1.3 Beyond the Ideal Behavior 214

7.1.3.1 Luminescence Quenching 215

7.1.3.2 Trap Energy Distributions 216

7.2 Data Analysis Methods 216

7.2.1 Initial Rise 217

7.2.2 Peak Shape 218

7.2.3 Heating Rate Method 220

7.2.4 Glow Curve Fit 221

7.3 Instrumentation and Considerations on Samples 221

7.4 Case Studies 222

7.4.1 Lanthanide Energy Level Position in the Bandgap 223

7.4.2 Bandgap Engineering 224

7.4.3 Correlation of TSL Data with EPR Results 225

Note 225

References 226

8 Spectroscopic Studies of Radiation Effects on Optical Materials 229
Sylvain Girard, Vincenzo De Michele, and Adriana Morana

8.1 Introduction 229

8.1.1 Radiation Environments 229

8.1.2 Applications for Optical Materials 230

8.2 Radiation-Induced Effects on Optical Materials and Optical Fibers 231

8.2.1 Radiation-Induced Attenuation – RIA 231

8.2.2 Radiation-Induced Emission – RIE 233

8.2.3 Radiation-Induced Compaction – RIC and Refractive Index Change – RIRIC 234

8.2.4 Origins of Radiation-Induced Optical Changes 234

8.3 Radiation-Induced Attenuation Measurements 235

8.3.1 Postirradiation RIA Measurements 235

8.3.1.1 Bulk Glasses 235

8.3.1.2 Optical Fibers 235

8.3.2 In Situ RIA Measurements 236

8.3.2.1 Bulk Glasses 236

8.3.2.2 Optical Fibers 237

8.3.3 Exploitation of RIA Spectra: Point Defect Identification 241

8.3.3.1 Spectral Decomposition 241

8.3.3.2 Point Defect Kinetics 243

8.4 Radiation-Induced Luminescence (RIL) 243

8.4.1 Architectures of Fiber-Based Sensors: Extrinsic and Intrinsic 243

8.4.2 Calibration of the RIL Versus Proton Flux 245

8.4.3 Bragg Peak Measurements for Proton-Therapy Applications 245

8.5 Case Studies 246

8.5.1 Characterization of Bulk Glasses for Space Optical Systems 246

8.5.2 Fiber-Based Dosimetry with Phosphorus-Doped Optical Fibers 247

8.5.3 Proton Flux Measurements Through the RIL of Optical Fibers 249

References 249

9 Electron Paramagnetic Resonance Spectroscopy (EPR) 253
Antonino Alessi and Franco Gelardi

9.1 Introduction 253

9.2 Basic Principle of EPR 253

9.3 Anisotropy of g and Spectral Lineshape 255

9.4 The EPR Lineshape in Powder or in Amorphous 257

9.5 Hyperfine Interactions 258

9.6 Paramagnetic Center with S = 1 261

9.7 Basics of Continuous Wave EPR Setup 263

9.8 Parameters for EPR Signal Acquisition 266

9.9 Cw EPR Case Studies 268

9.10 Time-Resolved EPR Spectroscopy 270

9.10.1 Saturation Transients 270

9.10.2 Spin Nutations 272

9.10.3 Free Induction Decay 274

9.10.4 Spin Echo 276

References 277

10 Nuclear Magnetic Resonance Spectroscopy 281
Alberto Spinella and Pellegrino Conte

10.1 Introduction 281

10.2 NMR General Concepts 281

10.2.1 Nuclear Spin and Magnetic Moment 281

10.2.2 Spin Precession and Larmor Frequency 283

10.2.3 Longitudinal Magnetization 283

10.2.4 Transverse Magnetization and NMR Signal 284

10.2.5 Spin Interactions 285

10.2.6 Fourier Transform NMR 287

10.3 Liquid-State NMR 288

10.3.1 The NMR Spectrometer 288

10.3.2 Sample Preparation 288

10.3.3 How to Set an Experiment 289

10.3.4 Longitudinal Relaxation Time Measurement 289

10.3.5 Transverse Relaxation Time Measurement 290

10.3.6 2D-Liquid-State NMR Techniques 291

10.3.7 Considerations on the Molecular Dynamics by NMR Spectroscopy 292

10.4 Solid-State NMR 293

10.4.1 Powdered Samples 293

10.4.2 Cross-Polarization and Heteronuclear Decoupling 294

10.4.3 Magic-Angle Spinning 296

10.4.4 Homonuclear Dipolar Decoupling 299

10.4.5 2D-Solid State NMR Techniques 299

10.4.6 Recoupling Techniques 300

10.4.7 Molecular Dynamics by Solid-State NMR Spectroscopy 301

10.5 Nonconventional NMR Techniques 301

10.5.1 Time Domain NMR 302

10.5.2 Fast Field Cycling NMR Relaxometry 302

10.5.3 Earth’s Magnetic Field NMR 309

10.6 Case Studies 309

10.6.1 Polymers and Polymer-Based Composites 309

10.6.2 Mesoporous Materials 310

10.6.3 Cultural Heritage 311

10.6.4 Food 313

10.6.5 Environmental NMR: Rocks, Soils, Waters, Air 313

10.6.6 NMR of “Exotic” Nuclei 314

References 315

11 X-Ray Absorption Spectroscopy and X-Ray Raman Scattering Spectroscopy for Energy Applications 319
Alessandro Longo, Francesco Giannici, and Christoph J. Sahle

11.1 Introduction 319

11.2 The X-Ray Absorption Coefficient and the EXAFS Technique 320

11.2.1 The EXAFS Equation and the Key Approximations 322

11.2.1.1 Many-Body Effects 323

11.2.1.2 Inelastic Effects 324

11.2.2 Multiple Scattering Theory: Basic Information 325

11.2.3 XANES or Near-Edge X-Ray Absorption Fine Structure and Pre-Edge Region 328

11.3 EXAFS: Data Analysis Overview 331

11.4 Experimental Setups 333

11.4.1 Transmission Geometry 333

11.4.2 Fluorescence Geometry 334

11.5 X-Ray Raman Scattering Spectroscopy 335

11.5.1 Theoretical Background 335

11.5.2 Experimental Setup 338

11.5.2.1 Instrumentation 338

11.5.2.2 Data Processing 338

11.6 Case Studies: Application of XAFS and XRS for Energy Materials 339

11.6.1 CO Oxidation Reaction: The Au/CeO2 Catalyst 339

11.6.2 Materials for Solid Oxide Fuel Cells 340

11.6.3 Oxide-Ion Conductors: Dopants and Vacancies 342

11.6.4 Proton-Conducting Oxides 343

11.6.5 The Role of Oxygen in Fuel Cell Cathodes 344

References 346

12 X-Ray Photoelectron Spectroscopy 351
Michelangelo Scopelliti

12.1 General Principles 351

12.2 Instrumental Setup 352

12.2.1 Vacuum and Ultrahigh Vacuum, UHV 353

12.2.1.1 Roughing Pumps 354

12.2.1.2 Turbomolecular Pumps 355

12.2.1.3 Ion Pumps 355

12.2.1.4 Titanium Sublimation Pumps 356

12.2.2 Magnetic Shielding 356

12.2.3 Sources 356

12.2.4 Sample Manipulators 358

12.2.5 Charge Neutralization Systems 359

12.2.5.1 Electron Guns 360

12.2.5.2 Ion Guns 360

12.2.6 Analyzers and Detectors 361

12.3 Applications 362

12.3.1 Quantitative Analysis 364

12.3.2 Qualitative Analysis 365

12.3.3 Surface Maps 365

12.3.4 Profiles 367

12.3.4.1 Depth Profiles 367

12.3.4.2 Angle-Resolved Profiles 368

12.4 Data Analysis 368

12.4.1 Shift Corrections 370

12.4.2 Background 371

12.4.3 Line Shapes 372

12.4.4 Nonlinear Fitting 375

12.5 Case Studies 376

12.5.1 Hydrocarbon Contamination 376

12.5.2 Energy Loss 376

12.5.3 Depth Profiles/1 378

12.5.4 Depth Profiles/2 379

References 380

13 Ultraviolet Photoelectron Spectroscopy – Materials Science Technique 383
Dmitry A. Zatsepin and Anatoly F. Zatsepin

13.1 UPS History and Capabilities 383

13.2 Theory and Experimental Methodology of UPS 384

13.2.1 Physical Principles of UPS 384

13.2.2 Angle-Resolved UPS 389

13.3 UPS Experiment and Factors of Influence 391

13.3.1 Vacuum System and Pumping 391

13.3.2 Sample and External Spectral Standard Preparation 392

13.3.3 Ultraviolet Source 395

13.3.4 Charge Neutralizer 397

13.3.5 Staff Requirements 400

References 401

14 Transmission Electron Spectroscopy 405
Raffaele Giuseppe Agostino and Vincenzo Formoso

14.1 Empirical Aspects of Electron–Matter Interaction 405

14.1.1 Fast Electrons Interaction with a Solid 405

14.1.2 Electron Energy Loss Spectroscopy (EELS) 406

14.1.2.1 Inner Shell Excitations 408

14.1.2.2 Low-Loss Excitations 411

14.1.2.3 Energy-Filtered Images 413

14.2 Instrumental Setups 415

14.2.1 TEM in a Nutshell 415

References 422

15 Atomic Force Microscopy and Spectroscopy 425
Gianpiero Buscarino

15.1 Introduction 425

15.2 The AFM Microscope 426

15.2.1 The Probe 426

15.2.2 Harmonic Excitation of the Cantilever 427

15.2.3 Scanning System 428

15.2.4 Measurement of the Cantilever’s Deflection 430

15.2.5 Feedback System 432

15.3 Tip–Surface Interaction Forces 432

15.3.1 Van der Waals 433

15.3.2 Short-Range Repulsive 434

15.3.3 Adhesion 435

15.3.4 Capillary 438

15.3.5 Other Forces 439

15.4 AFM Acquisition Modes 440

15.4.1 Contact Mode 440

15.4.2 Tapping Mode 442

15.5 AFM Spectroscopy 451

15.6 Case Studies 454

15.6.1 Roughness of a Flat Surface 454

15.6.2 Size Distribution of Nanoparticles 456

References 458

Index 461