Cluster Secondary Ion Mass Spectrometry

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.

• Contributors xiAbout the Editor xiii1 AN INTRODUCTION TO CLUSTER SECONDARY ION MASS SPECTROMETRY (CLUSTER SIMS) 1Christine M. Mahoney and Greg Gillen1.1 Secondary Ion Mass Spectrometry in a Nutshell 21.1.1 SIMS Imaging 41.1.2 SIMS Depth Profiling 41.2 Basic Cluster SIMS Theory 51.3 Cluster SIMS: An Early History 61.3.1 Nonlinear Sputter Yield Enhancements 61.3.2 Molecular Depth Profiling 71.4 Recent Developments 81.5 About this Book 9Acknowledgment 11References 112 CLUSTER SIMS OF ORGANIC MATERIALS: THEORETICAL INSIGHTS 13Arnaud Delcorte, Oscar A. Restrepo, and Bartlomiej Czerwinski2.1 Introduction 132.2 Molecular Dynamics Simulations of Sputtering with Clusters 152.2.1 The Cluster Effect 152.2.2 Computer Simulations and the Molecular Dynamics “Experiment” 182.2.3 Light and Heavy Element Clusters, and the Importance of Mass Matching 202.2.4 Structural Effects in Organic Materials 212.2.4.1 Amorphous Molecular Solids and Polymers 212.2.4.2 Organic Crystals 262.2.4.3 Thin Organic Layers on Metal Substrates 282.2.4.4 Hybrid Metal–Organic Samples 322.2.5 Induced Chemistry 342.2.6 Multiple Hits and Depth Profiling 362.2.7 From Small Polyatomic Projectiles to Massive Clusters 382.2.7.1 Light-Element Clusters 382.2.7.2 Large Argon Clusters 412.2.7.3 Massive Gold Clusters 452.3 Other Models 462.3.1 Analytical Models: From Linear Collision Cascades to Fluid Dynamics 462.3.2 Recent Developments and Hybrid Approaches 472.4 Conclusions 50Acknowledgments 51References 513 ION SOURCES USED FOR SECONDARY ION MASS SPECTROMETRY 57Albert J. Fahey3.1 Introduction 573.2 Research Needs that have Influenced the Development of Primary Ion Sources for Sputtering 583.3 Functional Aspects of Various Ion Sources 593.3.1 Energy Spread in the Beam 593.3.2 Point-Source Ionization 603.3.3 Stable Emission 603.3.4 Ion Reactivity 603.3.5 Source Lifetime 603.3.6 Penetration Depth and Surface Energy Spread of the Projectile 613.4 Atomic Ion Sources 613.4.1 Field Emission 613.4.2 Radio Frequency (RF) Ionization 623.4.3 Electron Impact 633.4.4 Thermal Ionization 643.4.5 DC-Glow Discharge 653.4.6 Sputtering 663.5 Molecular Ion Sources 663.5.1 Field Emission 663.5.2 Radio Frequency Discharge 673.5.3 Electron Impact 683.5.4 DC-Glow Discharge 693.5.5 Sputtering 693.6 Cluster Ion Sources 703.6.1 Jets and Electron Impact (Massive Gas Clusters) 713.6.2 Field Emission 723.7 Summary 73References 744 SURFACE ANALYSIS OF ORGANIC MATERIALS WITH POLYATOMIC PRIMARY ION SOURCES 77Christine M. Mahoney4.1 Introduction 774.2 Cluster Sources in Static SIMS 784.2.1 A Brief Introduction to Static SIMS 784.2.2 Analysis beyond the Static Limit 794.2.3 Increased Ion Yields 804.2.4 Decreased Charging 814.2.5 Surface Cleaning 824.3 Experimental Considerations 834.3.1 When to Employ Cluster Sources as Opposed to Atomic Sources 834.3.2 Type of Cluster Source Used 844.3.2.1 Liquid Metal Ion Gun (LMIG) 844.3.2.2 C + 60 for Mass Spectral Analysis and Imaging Applications 854.3.2.3 The Gas Cluster Ion Beam (GCIB) 864.3.2.4 Au 4+ 400 864.3.2.5 Other Sources 884.3.3 Cluster Size Considerations 884.3.4 Beam Energy 904.3.5 Sample Temperature 924.3.6 Matrix-Enhanced and Metal-Assisted Cluster SIMS 924.3.7 Matrix Effects 954.3.8 Other Important Factors 964.4 Data Analysis Methods 964.4.1 Principal Components Analysis 964.4.1.1 Basic Principles of PCA 974.4.1.2 Examples of PCA in the Literature 984.4.2 Gentle SIMS (G-SIMS) 1014.5 Other Relevant Surface Mass-Spectrometry-Based Methods 1014.5.1 Desorption Electrospray Ionization (DESI) 1034.5.2 Plasma Desorption Ionization Methods 1054.5.3 Electrospray Droplet Impact Source for SIMS 1074.6 Advanced Mass Spectrometers for SIMS 1084.7 Conclusions 109Appendix A: Useful Lateral Resolution 110References 1105 MOLECULAR DEPTH PROFILING WITH CLUSTER ION BEAMS 117Christine M. Mahoney and Andreas Wucher5.1 Introduction 1175.2 Historical Perspectives 1205.3 Depth Profiling in Heterogeneous Systems 1235.3.1 Introduction 1235.3.2 Quantitative Depth Profiling 1255.3.3 Reconstruction of 3D Images 1275.3.4 Matrix Effects in Heterogeneous Systems 1285.4 Erosion Dynamics Model of Molecular Sputter Depth Profiling 1305.4.1 Parent Molecule Dynamics 1315.4.2 Constant Erosion Rate 1345.4.3 Fluence-Dependent Erosion Rate 1365.4.4 Using Mass Spectrometric Signal Decay to Measure Damage Parameters 1385.4.5 Surface Transients 1415.4.6 Fragment Dynamics 1415.4.7 Conclusions 1455.5 The Chemistry of Atomic Ion Beam Irradiation in Organic Materials 1465.5.1 Introduction 1465.5.2 Understanding the Basics of Ion Irradiation Effects in Molecular Solids 1465.5.3 Ion Beam Irradiation and the Gel Point 1475.5.4 The Chemistry of Cluster Ion Beams 1505.5.5 Chemical Structure Changes and Corresponding Changes in Depth Profile Shapes 1525.6 Optimization of Experimental Parameters for Organic Depth Profiling 1565.6.1 Introduction 1565.6.2 Organic Delta Layers for Optimization of Experimental Parameters 1575.6.3 Sample Temperature 1595.6.4 Understanding the Role of Beam Energy During Organic Depth Profiling 1675.6.5 Optimization of Incidence Angle 1715.6.6 Effect of Sample Rotation 1745.6.7 Ion Source Selection 1785.6.7.1 SF + 5 and Other Small Cluster Ions 1785.6.7.2 C n+ 60 and Similar Carbon Cluster Sources 1795.6.7.3 The Gas Cluster Ion Beam (GCIB) 1805.6.7.4 Low Energy Reactive Ion Beams 1885.6.7.5 Electrospray Droplet Impact (EDI) Source for SIMS 1895.6.7.6 Liquid Metal Ion Gun Clusters (Bi + 3 and Au + 3 ) 1935.6.8 C + 60 /Ar+ Co-sputtering 1955.6.9 Chamber Backfilling with a Free Radical Inhibitor Gas 1975.6.10 Other Considerations for Organic Depth Profiling Experiments 1975.6.11 Molecular Depth Profiling: Novel Approaches and Methods 1985.7 Conclusions 198References 2006 THREE-DIMENSIONAL IMAGING WITH CLUSTER ION BEAMS 207Andreas Wucher, Gregory L. Fisher, and Christine M. Mahoney6.1 Introduction 2076.2 General Strategies 2106.2.1 Three-Dimensional Sputter Depth Profiling 2106.2.2 Wedge Beveling 2166.2.3 Physical Cross Sectioning 2176.2.4 FIB-ToF Tomography 2196.3 Important Considerations for Accurate 3D Representation of Data 2256.3.1 Beam Rastering Techniques 2256.3.2 Geometry Effects 2266.3.3 Depth Scale Calibration 2286.4 Three-Dimensional Image Reconstruction 2336.5 Damage and Altered Layer Depth 2386.6 Biological Samples 2426.7 Conclusions 243References 2447 CLUSTER SECONDARY ION MASS SPECTROMETRY (SIMS) FOR SEMICONDUCTOR AND METALS DEPTH PROFILING 247Greg Gillen and Joe Bennett7.1 Introduction 2477.2 Primary Particle–Substrate Interactions 2487.2.1 Collisional Mixing and Depth Resolution 2487.2.2 Transient Effects 2497.2.3 Sputter-Induced Roughening 2517.3 Possible Improvements in SIMS Depth Profiling—The Use of Cluster Primary Ion Beams 2537.4 Development of Cluster SIMS for Depth Profiling Analysis 2557.4.1 CF + 3 Primary Ion Beams 2557.4.2 NO + 2 and O + 3 Primary Ion Beams 2567.4.3 SF + 5 Polyatomic Primary Ion Beams 2577.4.4 CSC − 6 and C − 8 Depth Profiling 2587.4.5 Os3(CO)12 and Ir4(CO)12 Primary Ion Beams 2627.4.6 C + 60 Primary Ion Beams 2637.4.7 Massive Gaseous Cluster Ion Beams 2657.5 Conclusions and Future Prospects 266References 2668 CLUSTER TOF-SIMS IMAGING AND THE CHARACTERIZATION OF BIOLOGICAL MATERIALS 269John Vickerman and Nick Winograd8.1 Introduction 2698.2 The Capabilities of TOF-SIMS for Biological Analysis 2708.3 New Hybrid TOF-SIMS Instruments 2708.3.1 Introduction 2708.3.2 Benefits of New DC Beam Technologies 2718.4 Challenges in the Use of TOF-SIMS for Biological Analysis 2738.4.1 Sample Handling of Biological Samples for Analysis in Vacuum 2738.4.2 Analysis is Limited to Small to Medium Size Molecules 2748.4.3 Ion Yields Limit Useful Spatial Resolution for Molecular Analysis to not Much Better than 1 μm 2758.4.4 Matrix Effects Inhibit Application in Discovery Mode and Greatly Complicates Quantification 2758.4.5 The Complexity of Biological Systems can Result in Data Sets that Need Multivariate Analysis (MVA) to Unravel 2768.5 Examples of Biological Studies Using Cluster-TOF-SIMS 2768.5.1 Analysis of Tissue 2778.5.2 Drug Location in Tissue 2858.5.3 Microbial Mat—Surface and Subsurface Analysis in Streptomyces 2898.5.4 Cells 2918.5.5 Depth Scale Measurement 3028.5.6 High Throughput Biomaterials Characterization 3068.6 Final Thoughts and Future Directions 310Acknowledgments 310References 3109 FUTURE CHALLENGES AND PROSPECTS OF CLUSTER SIMS 313Peter Williams and Christine M. Mahoney9.1 Introduction 3139.2 The Cluster Niche 3149.3 Cluster Types 3149.4 The Challenge of Massive Molecular Ion Ejection 3159.4.1 Comparing with MALDI: The Gold Standard 3169.4.2 Particle Impact Techniques 3179.5 Ionization 3189.5.1 “Preformed” Ions 3199.5.2 Radical Ions and Ion Fragments 3199.5.3 Ionization Processes for Massive Clusters 3209.6 Matrix Effects and Challenges in Quantitative Analysis 3219.7 SIMS Instrumentation 3229.7.1 Massive Cluster Ion Source Technology 3239.8 Prospects for Biological Imaging 3249.9 Conclusions 325References 326Index 329