UNIVERSITY OF CALIFORNIA RIVERSIDE Investigation of Photoelectric Effect in Transition Metal Dichalcogenides Field Effect Transistors A Thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in Materials Science and Engineering by I-Hsi Daniel Lu September 2017 Thesis Committee: Dr. Ludwig Bartels, Chairperson Dr. Richard Wilson Dr. Sinisa Coh Copyright by I-Hsi Daniel Lu 2017 The Thesis of I-Hsi Daniel Lu is approved: Committee Chairperson University of California, Riverside Acknowledgements I would like to thank my principal investigator and advisor, Professor Ludwig Bartels, for his guidance over these past two years. I especially want to thank him for giving me many opportunities to learn and explore the semiconductor field. Over the last two years, I have had a chance to lead and support many projects from the group, collaborators, and national labs. I would like to thank Professor Bartels for sending me to different collaborators and conferences where I excel in developing new skills and presenting my work to the representatives from industries. I would like to thank Professor Richard Wilson and Professor Sinisa Coh for serving on my master thesis committees. I thank you for your time and support for my thesis defense in such short notice. I would like to thank all my published co-authorship works in ACS Nano, 2D Materials, Nano Letters, Nature Communications, ACS photonics, and Applied Physics Letters. I would like to thank the following professors for the publications: John Mann, Joshua C. H. Lui, Volker J. Sorger, Hubert J. Krenner, Velveth Klee, and Evan J. Reed. I would like to thank my family for always being supportive. I would also like to thank my colleagues in Bartels’ group, and in Sorger’s group. Thank you for making my graduate career fun and engaging. Lastly, I want to thank Cindy Merida for always being supportive and helpful during my career. iv Table of Contents Chapter 1: Introduction ................................................................ 1 Overview ..................................................................................................................................... 1 Introduction to TMDs................................................................................................................ 1 Instrumentation ......................................................................................................................... 1 Raman Spectroscopy ............................................................................................................. 2 Photoluminescence Spectroscopy ......................................................................................... 2 Chapter 2: Materials and Methods .............................................. 4 Chemical Vapor Deposition ...................................................................................................... 4 Chapter 3: Electrical contacts and Measurements on TMDs .... 7 Electron Beam Lithography ...................................................................................................... 7 MOSFET ..................................................................................................................................... 9 Electrical Probe Station ............................................................................................................. 9 Scanning Photocurrent Microscopy ....................................................................................... 10 Chapter 4: Composition-dependent photocurrent in CVD- grown Monolayer MoS2(1-x)Se2x Alloy Devices ........................... 14 Introduction .............................................................................................................................. 14 Methods ..................................................................................................................................... 15 Results and Discussion ............................................................................................................. 17 Conclusion ................................................................................................................................ 29 Chapter 5: Ferroelectric Control of 2D MoS2 ........................... 31 Introduction .............................................................................................................................. 31 Methods ..................................................................................................................................... 32 Results and Discussion ............................................................................................................. 33 Conclusion ................................................................................................................................ 43 Chapter 6: Hybrid Field-Effect and Acousto-Electric Devices 45 Introduction .............................................................................................................................. 45 Methods ..................................................................................................................................... 46 Results and Discussion ............................................................................................................. 48 v Conclusion ................................................................................................................................ 56 Figures ....................................................................................................................................... 58 Chapter 7: WS2 Band Structure ................................................. 62 Introduction .............................................................................................................................. 62 Methods ..................................................................................................................................... 63 Results and Discussion ............................................................................................................. 64 Figures ....................................................................................................................................... 69 Chapter 8: Tunable Properties of CVD Growth of Few-Layer MoTe2 ............................................................................................. 73 Introduction .............................................................................................................................. 73 Methods ..................................................................................................................................... 74 Results and Discussion ............................................................................................................. 74 Conclusion ................................................................................................................................ 78 Figures ....................................................................................................................................... 79 Chapter 9: Interlayer Breathing and Shear Modes in NbSe2 atomic layers ................................................................................. 82 Introduction .............................................................................................................................. 82 Methods ..................................................................................................................................... 83 Results and Discussion ............................................................................................................. 84 Conclusion ................................................................................................................................ 87 Figures ....................................................................................................................................... 89 Chapter 10: Efficacy of Light Emission Enhancement in Nanoscale Antenna ....................................................................... 92 Introduction .............................................................................................................................. 93 Methods ..................................................................................................................................... 93 Results and Discussion ............................................................................................................. 95 Conclusion ................................................................................................................................ 96 Figures ....................................................................................................................................... 98 References ................................................................................... 102 vi List of Figures Figure 1 ........................................................................................................................................... 4 Figure 2 ........................................................................................................................................... 5 Figure 3 ........................................................................................................................................... 8 Figure 4 ........................................................................................................................................