The Synthesis of Transition Metal Silicide and Germanide Nanostructures within the Solution- based Solvent Vapour Growth System Department of Chemical Sciences and Bernal Institute, University of Limerick Martin Sheehan Supervisor: Prof. Kevin M. Ryan Submitted to the University of Limerick for the Degree of Doctor of Philosophy June 2017 Table of Contents Acknowledgements .................................................................................................... i Declaration ................................................................................................................ ii Abstract ....................................................................................................................iii List of Publications ................................................................................................... v Chapter 1: Introduction ........................................................................ 1 1.1 Background ......................................................................................................... 1 1.2 Formation of Silicon and Germanium based Nanowires (NWs) ................... 2 1.2.1 Elemental Silicon and Germanium NWs ...................................................... 2 1.2.1.1 NW Growth Mechanisms ........................................................................ 2 1.2.1.2 Approaches to Silicon and Germanium NW Growth .............................. 8 1.2.1.2.1 Chemical Vapour Deposition ................................................... 8 1.2.1.2.2 Supercritical Fluid-based Synthesis ......................................... 9 1.2.1.2.3 Solvent Vapour Growth System ............................................. 10 1.2.2 Formation of Transition Metal Silicide and Germanide NWs ................. 12 1.2.2.1 Silicidation/Germanidation of preformed NWs .................................... 12 1.2.2.2 Silicon/Germanium delivery to metal film growth substrates............... 16 1.2.2.2.1 Synthesis of Nickel Silicide NWs ........................................... 16 1.2.2.2.2 Synthesis of Nickel Germanide NWs ...................................... 23 1.2.2.2.3 Synthesis of Copper Silicide NWs .......................................... 24 1.2.2.3 Transition metal delivery to Silicon/Germanium growth substrates ..... 28 1.2.2.4 Simultaneous metal and Silicon/Germanium delivery to growth substrates ............................................................................................... 31 1.3 Potential Applications of Transition Metal Silicides and Germanides ....... 38 1.3.1 Nanoelectronics .............................................................................................. 38 1.3.2 Nanoscale Field Emitters ................................................................................ 39 1.3.3 Lithium-ion Batteries ...................................................................................... 40 1.4 References ......................................................................................................... 42 Chapter 2: Experimental Procedures and Characterisation Techniques ............................................................................................ 60 2.1 General Synthetic Strategy .............................................................................. 60 2.2 Characterisation Techniques .......................................................................... 62 2.2.1 Scanning Electron Microscopy (SEM) ........................................................... 62 2.2.2 Transmission Electron Microscopy (TEM)..................................................... 65 2.2.2.1 Electron Diffraction .............................................................................. 67 2.2.2.2 Scanning Transmission Electron Microscopy (STEM) ........................ 68 2.2.3 Energy Dispersive X-ray Spectroscopy (EDS) ............................................... 70 2.2.4 X-ray Diffraction (XRD) ................................................................................. 71 2.2.5 Electrochemical Characterisation .................................................................... 73 2.2.5.1 Galvanostatic Charge and Discharge Cycling ....................................... 73 2.2.5.2 Calculation of C-rate ............................................................................. 75 2.3 References ......................................................................................................... 76 Chapter 3: The Selective Synthesis of Nickel Germanide Nanowires and Nickel Germanide Seeded Germanium Nanowires within a Solvent Vapour Growth System .......................................... 79 3.1 Abstract .............................................................................................................. 79 3.2 Introduction ........................................................................................................ 79 3.3 Experimental Section ......................................................................................... 82 3.4 Results and Discussion ....................................................................................... 84 3.5 Conclusion ........................................................................................................ 102 3.6 References ........................................................................................................ 103 Chapter 4: The Effect of Enhanced Precursor Decomposition on the Synthesis of Copper Silicide Nanostructures within a Solvent Vapour Growth System .................................................................... 110 4.1 Abstract ............................................................................................................ 110 4.2 Introduction ...................................................................................................... 110 4.3 Experimental Section ....................................................................................... 112 4.4 Results and Discussion ..................................................................................... 114 4.5 Conclusion ........................................................................................................ 133 4.6 References ........................................................................................................ 134 Chapter 5: Synthesis of Nickel Silicide Nanowires and Axial Heterostructure NixSi/Si Nanowires within a Solution-based System ................................................................................................. 138 5.1 Abstract ............................................................................................................ 138 5.2 Introduction ...................................................................................................... 138 5.3 Experimental Section ....................................................................................... 141 5.4 Results and Discussion ..................................................................................... 143 5.5 Conclusion ........................................................................................................ 156 5.6 References ........................................................................................................ 157 Chapter 6: Amorphous Silicon coated Copper Silicide Nanowire Arrays for Lithium-ion Battery Anodes .......................................... 163 6.1 Abstract ............................................................................................................ 163 6.2 Introduction ...................................................................................................... 163 6.3 Experimental Section ....................................................................................... 166 6.4 Results and Discussion ..................................................................................... 168 6.5 Conclusion ........................................................................................................ 182 6.6 References ........................................................................................................ 183 Chapter 7: Conclusions and Recommendations for Future Work ................................................................................................... 188 7.1 Conclusions ...................................................................................................... 188 7.2 Recommendations for Future Work ................................................................. 191 7.2.1 FIB sectioning to study NW Formation ........................................................ 191 7.2.2 Alternative Si/Ge Precursors ......................................................................... 192 Appendix A: XRD Reference Patterns ............................................ 193 Acknowledgements I would first like to acknowledge my supervisor, Prof. Kevin M. Ryan, for his guidance and support over the last number of years. I am eternally grateful for this opportunity he has given to me. It has been a genuine pleasure to have worked in his research group. I would also like to acknowledge my fellow group members, both past and present. I am very lucky to have made such truly great friends over the last number of years. Claudia and Grace: Thank you both so much for all the help and the laughs and the brownies…. OH GOD, THE BROWNIES… You have no idea how grateful I am to have made such great friends… Hugh and Tadhg: Thank you both for all the