New Capabilities for Molecular Surface and in-Depth Analysis with Cluster Secondary Ion Mass Spectrometry A thesis submitted to the University of Manchester for the degree of Doctor of Philosophy in the Faculty of Science and Engineering 2018 Huriyyah Ahmed Alturaifi The University of Manchester Faculty of Science and Engineering School of Chemistry 1 Contents List of Figures 6 List of Tables 15 List of Equations 17 Abbreviations 18 Abstract 20 Declaration 21 Copyright Statements 21 Acknowledgements 22 1. Introduction 23 1.1. Secondary Ion Mass Spectrometry (SIMS) 23 1.2. Generation of Secondary Ions 25 1.2.1. The Sputtering Process 26 1.2.2. Ionisation 29 1.2.2.1. Nascent Ion Molecule Model 29 1.2.2.2. Deposition Ionisation Model 30 1.3. Models of Operations of SIMS 31 1.3.1. Dynamic SIMS 31 1.3.2. Static SIMS 32 1.3.3. Imaging SIMS 32 1.4. Cluster SIMS 33 1.5. Damage Cross-Section 36 1.6. Cross-linking 38 1.7. Molecular Depth Profiling 41 1.8. Molecular Dynamic Simulation 58 1.9. Aims of the Study 61 1.10. References 62 2. Instrumentation 70 2.1. ToF-SIMS Instrumentation 70 2.1.1. ToF Mass Analyser 70 2.1.2. ToF-SIMS Instrumentation Development 73 2 2.1.2.1. Sample Holder 76 2.1.2.1.1. Sample Holder insertion into the Instrumentation 77 2.1.2.1.2. Sample Handling Systems 78 2.1.2.2. Instrumentation Control 79 2.1.2.3. Electron Flood Gun 80 2.1.2.4. Polyatomic C60 Source 81 2.1.2.4.1. Mass Selection (Mass Filtration) 82 2.1.2.4.2. Spatial Resolution 83 2.1.2.5. Gas Cluster Ion Beams 84 2.1.2.5.1. Cluster Size Measurement 86 2.1.2.6. The J105 Secondary Ion Optics 86 2.1.2.7. Tandem Mass Spectrometry (MS/MS) 88 2.2. Film Deposition Techniques 88 2.2.1. Spin-Coating 88 2.2.2. Thermal Evaporation Films Deposition 90 2.3. Instrumentation for Measurements of Film Thickness 90 2.3.1. Stylus Profilometry 91 2.3.2. Atomic Force Microscopy (AFM) 91 2.3.2.1. How the Atomic Force Microscopy Work 91 2.3.2.1.1. The Atomic Force Microscopy Design 91 2.3.2.1.2. Principle of the Atomic Force Microscopy 92 2.3.2.1.3. Tapping Mode (Intermittent Mode) AFM Imaging Modes 93 2.4. References 94 3. Molecular Depth Profiles of PMMA with Time-of-Flight Secondary Ion Mass + Spectrometry (ToF-SIMS) Using Different Cluster Ion Beams (20 and 40 keV C60 + and 20 keV Arn ) at Different Temperatures 97 3.1. Introduction 97 3.2. Experimental Section 99 3.2.1. Sample Preparation 99 3.2.2. ToF-SIMS 100 3.3. Results and Discussion 101 3.3.1. PMM Sample Analysis ar Room Temperature 101 3.3.1.1. Secondary Ion Spectra of PMMA 101 3.3.1.2. Secondary Ion Yields at the Pseudo-Steady-State Region 107 3.3.1.3. Depth Profiling 108 3 + 3.3.1.3.1. Using 20 and 40 keV C60 Cluster Ion Beams 112 3.3.1.3.2. Using 20 keV Arn Cluster Ion Beams (n = 250-2000) - 114 3.3.2. Influence of Sample Cooling on the Depth Profiles of PMMA 122 + 3.3.2.1. Using 20 and 40 keV C60 Cluster Ion Beams 122 + + 3.3.2.2. Using 20 keV Ar500 and Ar2000 Cluster Ion Beams 128 3.4. Summary and Conclusions 135 3.5. References 137 4. Molecular Depth Profiling of Organic Semiconductors with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) Using Cluster Ion Beams (20 and + + 40 keV C60 and 20 keV Ar250-2000 ) at Different Temperatures 140 4.1. Introduction 140 4.2. Experimental Section 141 4.2.1. Sample preparation 141 4.2.1.1. PTAA 141 4.2.1.2. TIPS-penatcene 142 4.2.2. ToF-SIMS Analysis 142 4.3. Analysis of the PTAA Sample at Room Temperature 143 4.3.1. Results and Discussion 143 4.3.1.1. Secondary Ion Mass Spectra of PTAA 143 4.3.1.2. Depth Profiles of PTAA Sample at Room Temperature 148 + 4.3.1.2.1 Using 20 and 40 keV C60 Cluster Ion Beams 178 + 4.3.1.2.2 Using 20 keV Arn Cluster Ion Beams (n =250-2000) 150 4.4. Analysis of the TIPS-pentacene Sample at Room Temperature 155 4.4.1. Secondary Ion Spectra of TIPS-pentacene 155 4.4.2. Depth Profile of TIPS-pentacene Samples at Room Temperature 161 + 4.4.2.1 Using 20 and 40 keV C60 Cluster Ion Beams 161 + 4.4.2.2 Using 20 keV Arn Cluster Ion Beams (n = 250-2000) 163 4.4.3 Influence of Sample Cooling on Depth Profiles of PTAA samples 168 + 4.4.3.1 Using 20 keV C60 Cluster Ion Beams 168 4.4.4 Influence of Sample Cooling on Depth Profiles of TIPS-pentacene 170 + + 4.4.4.1 Using 20 keV Ar500 and Ar2000 Cluster Ion Beams 170 4.5. Summary and Conclusions 176 4.6. References 178 4 5. Investigation of the Interface between Bi-layered Organic Materials (Semiconductor and Insulating Materials), using Molecular Depth Profiling ToF- SIMS Cluster Ion Beams 180 5.1. Introduction 180 5.2. Experimental Section 181 5.2.1. Samples Preparation 181 5.2.2. ToF-SIMS Analysis 182 5.3. Results and Discussion 182 5.3.1. TIPS-Pentacene/PMMA/Si Bi-layer Films 182 5.3.2. PMMA/TIPS-pentacene/Si Bi-layer Films 189 5.3.3. PTAA/PMMS/Si Bi-layer Films 191 5.3.4. PMMA/PTAA/Si Bi-layer Films 193 5.4. Conclusions 196 5.5. References 197 6. Conclusions and Future Work 198 6.1. Conclusions 198 6.1.1. Sputtering Yields 198 6.1.2. Secondary Ion Yields at the Pseudo-Steady-State Region 201 6.1.3. Depth Resolution 203 6.2. Future work 205 6.3. References 208 7. Appendix 209 Word count: 41,272 5 List of Figures Figure 1.1: A schematic representation of the SIMS sputtering process. A primary ion beam strikes the sample surface causing a series of collision cascades. The ejected secondary particles are the majority of neutral (atoms or molecules (red)) and a small number of positively or negatively charged {cations (blue), anions (orange) and electrons (dark red)}. 28 Figure 1.2: Schematic presentation of the emission of the secondary ion by the nascent ion molecule model [10]. 30 Figure 1.3: Schematic of dynamic and static modes with SIMS. 31 Figure 1.4: Currents of normalized primary ions, for Aun and Bin clusters, as a function of + + cluster size and charge. Currents of Au1 and Bi1 are normalized to 100 % [31]. 34 Figure 1.5: Mechanism of PMMA degradation with irradiation. Adapted from [60]. 40 Figure 1.6: Different categories of molecular depth profiling of thin films (a-c) and bulk materials. (a) The ideal shape of the depth profile achieved under optimum conditions. (b and c) The depth profiles obtained under non-optimum conditions and result accumulation of damage, but a greater damage occurs in (c) as compared to (b). Three regions displayed during depth profiles are: (1) the signal intensity is decreased or increased in an initial surface transient region; (2) a steady state region (a) or pseudo steady state region (b), and (3) an interfacial region, in which molecular signal decreases and substrate signal increases. In bulk samples (d) after a certain critical fluence (4) signal intensity is lost. This critical fluence is affects by the choice of ion source and other parameters e.g. energy [50].- 41 Figure 1.7: Comparison of depth profiles, for a 180 nm thick sample. The sample is a vapor- + + deposited glutamate thin film, using SF5 and Ar primary ions, under dynamic SIMS conditions. + The required SF5 primary ion dose that could penetrate up to reach the silicon substrate was 2.4 × 1015 ions/cm2 [52]. 43 Figure 1.8: Positive secondary ion intensities of an ion fragment (m/z 69) plotted as a function of sputter depth, for ~ 160 nm of PMMA film, deposited on a Si substrate, in a + + dual beam mode: 10 keV Ar , for analysis and 5 keV SF5 , for sputtering. Depth profiles were acquired at three different temperatures, as displayed inside this Figure [57]. 45 + Figure 1.9: Positive depth profiles for bulk PMMA films, using 5 keV and 8 keV SF5 primary ions, at -100 °C. The PMMA (m/z 59) was plotted as a function of sputter depth [61]. 46 Figure 1.10: Positive ions ToF-SIMS depth profiles of a PS thin film, working with a 20 + keV C60 primary ion beam, at 48° and 76° incidence angles. The secondary ion intensity for m/z 91, of PS, was plotted as a function of sputter depth [64]. 48 + Figure 1.11: Depth profiles of (a) PVP/PMMA and (b) P4VP/PMMA, working with C60 , for sputtering and Ga+, for analysis [65]. 50 Figure 1.12: ToF-SIMS depth profiles of a) PMMA, b) PS and c) PC in positive secondary + ion spectra, obtained in a single beam mode, working with 5.5 keV Ar700 , for both sputtering and analysis purposes [67]. 52 6 Figure 1.13: Sputtering yield volume versus molecular weight for: a) PS and b) PMMA, obtained via three cluster sizes of Ar, which are 1500, 3000 and 5000 atoms/primary ion, with an incident energy of 10 keV [73].