Cluster Secondary Ion Mass Spectrometry
Principles and Applications
Wiley Series on Mass Spectrometry Series

Explores the impact of the latest breakthroughs in cluster SIMS technology

Cluster secondary ion mass spectrometry (SIMS) is a high spatial resolution imaging mass spectrometry technique, which can be used to characterize the three-dimensional chemical structure in complex organic and molecular systems. It works by using a cluster ion source to sputter desorb material from a solid sample surface. Prior to the advent of the cluster source, SIMS was severely limited in its ability to characterize soft samples as a result of damage from the atomic source. Molecular samples were essentially destroyed during analysis, limiting the method's sensitivity and precluding compositional depth profiling. The use of new and emerging cluster ion beam technologies has all but eliminated these limitations, enabling researchers to enter into new fields once considered unattainable by the SIMS method.

With contributions from leading mass spectrometry researchers around the world, Cluster Secondary Ion Mass Spectrometry: Principles and Applications describes the latest breakthroughs in instrumentation, and addresses best practices in cluster SIMS analysis. It serves as a compendium of knowledge on organic and polymeric surface and in-depth characterization using cluster ion beams. It covers topics ranging from the fundamentals and theory of cluster SIMS, to the important chemistries behind the success of the technique, as well as the wide-ranging applications of the technology. Examples of subjects covered include:

• Cluster SIMS theory and modeling
• Cluster ion source types and performance expectations
• Cluster ion beams for surface analysis experiments
• Molecular depth profiling and 3-D analysis with cluster ion beams
• Specialty applications ranging from biological samples analysis to semiconductors/metals analysis
• Future challenges and prospects for cluster SIMS

This book is intended to benefit any scientist, ranging from beginning to advanced in level, with plenty of figures to help better understand complex concepts and processes. In addition, each chapter ends with a detailed reference set to the primary literature, facilitating further research into individual topics where desired. Cluster Secondary Ion Mass Spectrometry: Principles and Applications is a must-have read for any researcher in the surface analysis and/or imaging mass spectrometry fields.

Contributors xi

About the Editor xiii

1 AN INTRODUCTION TO CLUSTER SECONDARY ION MASS SPECTROMETRY (CLUSTER SIMS) 1
Christine M. Mahoney and Greg Gillen

1.1 Secondary Ion Mass Spectrometry in a Nutshell 2

1.1.1 SIMS Imaging 4

1.1.2 SIMS Depth Profiling 4

1.2 Basic Cluster SIMS Theory 5

1.3 Cluster SIMS: An Early History 6

1.3.1 Nonlinear Sputter Yield Enhancements 6

1.3.2 Molecular Depth Profiling 7

1.4 Recent Developments 8

1.5 About this Book 9

Acknowledgment 11

References 11

2 CLUSTER SIMS OF ORGANIC MATERIALS: THEORETICAL INSIGHTS 13
Arnaud Delcorte, Oscar A. Restrepo, and Bartlomiej Czerwinski

2.1 Introduction 13

2.2 Molecular Dynamics Simulations of Sputtering with Clusters 15

2.2.1 The Cluster Effect 15

2.2.2 Computer Simulations and the Molecular Dynamics “Experiment” 18

2.2.3 Light and Heavy Element Clusters, and the Importance of Mass Matching 20

2.2.4 Structural Effects in Organic Materials 21

2.2.4.1 Amorphous Molecular Solids and Polymers 21

2.2.4.2 Organic Crystals 26

2.2.4.3 Thin Organic Layers on Metal Substrates 28

2.2.4.4 Hybrid Metal–Organic Samples 32

2.2.5 Induced Chemistry 34

2.2.6 Multiple Hits and Depth Profiling 36

2.2.7 From Small Polyatomic Projectiles to Massive Clusters 38

2.2.7.1 Light-Element Clusters 38

2.2.7.2 Large Argon Clusters 41

2.2.7.3 Massive Gold Clusters 45

2.3 Other Models 46

2.3.1 Analytical Models: From Linear Collision Cascades to Fluid Dynamics 46

2.3.2 Recent Developments and Hybrid Approaches 47

2.4 Conclusions 50

Acknowledgments 51

References 51

3 ION SOURCES USED FOR SECONDARY ION MASS SPECTROMETRY 57
Albert J. Fahey

3.1 Introduction 57

3.2 Research Needs that have Influenced the Development of Primary Ion Sources for Sputtering 58

3.3 Functional Aspects of Various Ion Sources 59

3.3.1 Energy Spread in the Beam 59

3.3.2 Point-Source Ionization 60

3.3.3 Stable Emission 60

3.3.4 Ion Reactivity 60

3.3.5 Source Lifetime 60

3.3.6 Penetration Depth and Surface Energy Spread of the Projectile 61

3.4 Atomic Ion Sources 61

3.4.1 Field Emission 61

3.4.2 Radio Frequency (RF) Ionization 62

3.4.3 Electron Impact 63

3.4.4 Thermal Ionization 64

3.4.5 DC-Glow Discharge 65

3.4.6 Sputtering 66

3.5 Molecular Ion Sources 66

3.5.1 Field Emission 66

3.5.2 Radio Frequency Discharge 67

3.5.3 Electron Impact 68

3.5.4 DC-Glow Discharge 69

3.5.5 Sputtering 69

3.6 Cluster Ion Sources 70

3.6.1 Jets and Electron Impact (Massive Gas Clusters) 71

3.6.2 Field Emission 72

3.7 Summary 73

References 74

4 SURFACE ANALYSIS OF ORGANIC MATERIALS WITH POLYATOMIC PRIMARY ION SOURCES 77
Christine M. Mahoney

4.1 Introduction 77

4.2 Cluster Sources in Static SIMS 78

4.2.1 A Brief Introduction to Static SIMS 78

4.2.2 Analysis beyond the Static Limit 79

4.2.3 Increased Ion Yields 80

4.2.4 Decreased Charging 81

4.2.5 Surface Cleaning 82

4.3 Experimental Considerations 83

4.3.1 When to Employ Cluster Sources as Opposed to Atomic Sources 83

4.3.2 Type of Cluster Source Used 84

4.3.2.1 Liquid Metal Ion Gun (LMIG) 84

4.3.2.2 C + 60 for Mass Spectral Analysis and Imaging Applications 85

4.3.2.3 The Gas Cluster Ion Beam (GCIB) 86

4.3.2.4 Au 4+ 400 86

4.3.2.5 Other Sources 88

4.3.3 Cluster Size Considerations 88

4.3.4 Beam Energy 90

4.3.5 Sample Temperature 92

4.3.6 Matrix-Enhanced and Metal-Assisted Cluster SIMS 92

4.3.7 Matrix Effects 95

4.3.8 Other Important Factors 96

4.4 Data Analysis Methods 96

4.4.1 Principal Components Analysis 96

4.4.1.1 Basic Principles of PCA 97

4.4.1.2 Examples of PCA in the Literature 98

4.4.2 Gentle SIMS (G-SIMS) 101

4.5 Other Relevant Surface Mass-Spectrometry-Based Methods 101

4.5.1 Desorption Electrospray Ionization (DESI) 103

4.5.2 Plasma Desorption Ionization Methods 105

4.5.3 Electrospray Droplet Impact Source for SIMS 107

4.6 Advanced Mass Spectrometers for SIMS 108

4.7 Conclusions 109

Appendix A: Useful Lateral Resolution 110

References 110

5 MOLECULAR DEPTH PROFILING WITH CLUSTER ION BEAMS 117
Christine M. Mahoney and Andreas Wucher

5.1 Introduction 117

5.2 Historical Perspectives 120

5.3 Depth Profiling in Heterogeneous Systems 123

5.3.1 Introduction 123

5.3.2 Quantitative Depth Profiling 125

5.3.3 Reconstruction of 3D Images 127

5.3.4 Matrix Effects in Heterogeneous Systems 128

5.4 Erosion Dynamics Model of Molecular Sputter Depth Profiling 130

5.4.1 Parent Molecule Dynamics 131

5.4.2 Constant Erosion Rate 134

5.4.3 Fluence-Dependent Erosion Rate 136

5.4.4 Using Mass Spectrometric Signal Decay to Measure Damage Parameters 138

5.4.5 Surface Transients 141

5.4.6 Fragment Dynamics 141

5.4.7 Conclusions 145

5.5 The Chemistry of Atomic Ion Beam Irradiation in Organic Materials 146

5.5.1 Introduction 146

5.5.2 Understanding the Basics of Ion Irradiation Effects in Molecular Solids 146

5.5.3 Ion Beam Irradiation and the Gel Point 147

5.5.4 The Chemistry of Cluster Ion Beams 150

5.5.5 Chemical Structure Changes and Corresponding Changes in Depth Profile Shapes 152

5.6 Optimization of Experimental Parameters for Organic Depth Profiling 156

5.6.1 Introduction 156

5.6.2 Organic Delta Layers for Optimization of Experimental Parameters 157

5.6.3 Sample Temperature 159

5.6.4 Understanding the Role of Beam Energy During Organic Depth Profiling 167

5.6.5 Optimization of Incidence Angle 171

5.6.6 Effect of Sample Rotation 174

5.6.7 Ion Source Selection 178

5.6.7.1 SF + 5 and Other Small Cluster Ions 178

5.6.7.2 C n+ 60 and Similar Carbon Cluster Sources 179

5.6.7.3 The Gas Cluster Ion Beam (GCIB) 180

5.6.7.4 Low Energy Reactive Ion Beams 188

5.6.7.5 Electrospray Droplet Impact (EDI) Source for SIMS 189

5.6.7.6 Liquid Metal Ion Gun Clusters (Bi + 3 and Au + 3 ) 193

5.6.8 C + 60 /Ar+ Co-sputtering 195

5.6.9 Chamber Backfilling with a Free Radical Inhibitor Gas 197

5.6.10 Other Considerations for Organic Depth Profiling Experiments 197

5.6.11 Molecular Depth Profiling: Novel Approaches and Methods 198

5.7 Conclusions 198

References 200

6 THREE-DIMENSIONAL IMAGING WITH CLUSTER ION BEAMS 207
Andreas Wucher, Gregory L. Fisher, and Christine M. Mahoney

6.1 Introduction 207

6.2 General Strategies 210

6.2.1 Three-Dimensional Sputter Depth Profiling 210

6.2.2 Wedge Beveling 216

6.2.3 Physical Cross Sectioning 217

6.2.4 FIB-ToF Tomography 219

6.3 Important Considerations for Accurate 3D Representation of Data 225

6.3.1 Beam Rastering Techniques 225

6.3.2 Geometry Effects 226

6.3.3 Depth Scale Calibration 228

6.4 Three-Dimensional Image Reconstruction 233

6.5 Damage and Altered Layer Depth 238

6.6 Biological Samples 242

6.7 Conclusions 243

References 244

7 CLUSTER SECONDARY ION MASS SPECTROMETRY (SIMS) FOR SEMICONDUCTOR AND METALS DEPTH PROFILING 247
Greg Gillen and Joe Bennett

7.1 Introduction 247

7.2 Primary Particle–Substrate Interactions 248

7.2.1 Collisional Mixing and Depth Resolution 248

7.2.2 Transient Effects 249

7.2.3 Sputter-Induced Roughening 251

7.3 Possible Improvements in SIMS Depth Profiling—The Use of Cluster Primary Ion Beams 253

7.4 Development of Cluster SIMS for Depth Profiling Analysis 255

7.4.1 CF + 3 Primary Ion Beams 255

7.4.2 NO + 2 and O + 3 Primary Ion Beams 256

7.4.3 SF + 5 Polyatomic Primary Ion Beams 257

7.4.4 CSC − 6 and C − 8 Depth Profiling 258

7.4.5 Os3(CO)12 and Ir4(CO)12 Primary Ion Beams 262

7.4.6 C + 60 Primary Ion Beams 263

7.4.7 Massive Gaseous Cluster Ion Beams 265

7.5 Conclusions and Future Prospects 266

References 266

8 CLUSTER TOF-SIMS IMAGING AND THE CHARACTERIZATION OF BIOLOGICAL MATERIALS 269
John Vickerman and Nick Winograd

8.1 Introduction 269

8.2 The Capabilities of TOF-SIMS for Biological Analysis 270

8.3 New Hybrid TOF-SIMS Instruments 270

8.3.1 Introduction 270

8.3.2 Benefits of New DC Beam Technologies 271

8.4 Challenges in the Use of TOF-SIMS for Biological Analysis 273

8.4.1 Sample Handling of Biological Samples for Analysis in Vacuum 273

8.4.2 Analysis is Limited to Small to Medium Size Molecules 274

8.4.3 Ion Yields Limit Useful Spatial Resolution for Molecular Analysis to not Much Better than 1 μm 275

8.4.4 Matrix Effects Inhibit Application in Discovery Mode and Greatly Complicates Quantification 275

8.4.5 The Complexity of Biological Systems can Result in Data Sets that Need Multivariate Analysis (MVA) to Unravel 276

8.5 Examples of Biological Studies Using Cluster-TOF-SIMS 276

8.5.1 Analysis of Tissue 277

8.5.2 Drug Location in Tissue 285

8.5.3 Microbial Mat—Surface and Subsurface Analysis in Streptomyces 289

8.5.4 Cells 291

8.5.5 Depth Scale Measurement 302

8.5.6 High Throughput Biomaterials Characterization 306

8.6 Final Thoughts and Future Directions 310

Acknowledgments 310

References 310

9 FUTURE CHALLENGES AND PROSPECTS OF CLUSTER SIMS 313
Peter Williams and Christine M. Mahoney

9.1 Introduction 313

9.2 The Cluster Niche 314

9.3 Cluster Types 314

9.4 The Challenge of Massive Molecular Ion Ejection 315

9.4.1 Comparing with MALDI: The Gold Standard 316

9.4.2 Particle Impact Techniques 317

9.5 Ionization 318

9.5.1 “Preformed” Ions 319

9.5.2 Radical Ions and Ion Fragments 319

9.5.3 Ionization Processes for Massive Clusters 320

9.6 Matrix Effects and Challenges in Quantitative Analysis 321

9.7 SIMS Instrumentation 322

9.7.1 Massive Cluster Ion Source Technology 323

9.8 Prospects for Biological Imaging 324

9.9 Conclusions 325

References 326

Index 329

Christine M. Mahoney, PhD, is a recognized expert and leader in the field of Secondary Ion Mass Spectrometry (SIMS). Throughout her career, she has focused primarily on the application of SIMS to molecular targets, and has played a significant role in the development of cluster SIMS for polymer depth profiling applications. She received her PhD in analytical chemistry from SUNY Buffalo in 1993. She spent the following eight years at the National Institute of Standards and Technology (NIST), where much of her molecular depth profiling work was performed. Christine is currently employed as a senior research scientist at the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory (PNNL), where she continues to lead research in the field of SIMS.