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Xray Generation by Field Emission XRAY GENERATION BY FIELD EMISSION Richard Parmee Pembroke College Electrical Engineering Division Department of Engineering University of Cambridge This dissertation is submitted for the degree of Doctor of Philosophy April 2018 2 Richard Parmee – April 2018 DECLARATION This dissertation is submitted to the University of Cambridge for the degree of Doctor of Philosophy. The work described was carried out between October 2010 and March 2018 at the Department of Engineering, University of Cambridge. This dissertation is my own work, although some work was done in collaboration with others as specified in the Acknowledgements. It has not been previously submitted, in part or whole, to any university of institution for any degree, diploma, or other qualification. In accordance with the Department of Engineering guidelines, this thesis is does not exceed 65,000 words, and it contains less than 150 figures. Signed:_______________________________________________________ Date:_________________________________________________________ Richard Parmee MA Cambridge Richard Parmee – April 2018 i ii Richard Parmee – April 2018 ABSTRACT Since the discovery of X-rays over a century ago the techniques applied to the engineering of X-ray sources have remained relatively unchanged. From the inception of thermionic electron sources, which, due to simplicity of fabrication, remain central to almost all X-ray applications at this time, there have been few fundamental technological advances. The emergence of new materials and manufacturing techniques has created an opportunity to replace the traditional thermionic devices with those that incorporate Field Emission electron sources. One of the most important attributes of Field Emission X-ray sources is their controllability, and in particular the fast response time, which opens the door to applying techniques which have formerly been the preserve of optical systems. The work in this thesis attempts to bridge the gap between the fabrication and optimisation of the vacuum electronic devices and image processing aspects of a new approach to high speed radiographic imaging, particularly with a view to addressing practical real-world problems. Off the back of a specific targeted application, the project has involved the design of a viable field emission X-ray source, together with the development of an understanding of the failure modes in such devices, both by analysis and by simulation. This thesis reviews the capabilities and the requirements of X-ray sources, the methods by which nano-materials may be applied to the design of those devices and the improvements and attributes that can be foreseen. I study the image processing methods that can exploit these attributes, and investigate the performance of X-ray sources based upon electron emitters using carbon nanotubes. Modelling of the field emission and electron trajectories of the cathode assemblies has led me to the design of equipment to evaluate and optimise the parameters of an X-ray tube, which I have used to understand the performance that is achievable. Finally, I draw conclusions from this work and outline the next steps to provide the basis for a commercial solution. Richard Parmee – April 2018 iii Xray Generation by Field Emission iv Richard Parmee – April 2018 ACKNOWLEDGEMENTS I would like to express my sincere thanks to all involved, directly and indirectly, with my work over the last seven years. Both those inside the department who shared their expertise and those outside who helped make this time so enjoyable, without your friendship this thesis would not have been possible. I am most grateful for the help and guidance from my supervisor, Professor Bill Milne. His patience and support was invaluable. Special thanks go to Dr. Matthew Cole and Dr. David Hasko, whose energy, advice and knowledge in guiding me through the academic and practical aspects of my work were outstanding and this work would not have been possible without them. I am grateful for the help of and Professor Ravi Silva, who provided CNT samples, and Dr. Xuesong Yuan, who, as a visiting scholar to our group, assisted with electron trajectory modelling. I would like to thank all the members of the Electronic Devices and Materials Group, and more generally the wider group of academics in the Electrical Division, Engineering Department, past and present. Their support has made my period of work a pleasure and they were always available to answer my questions, listen to my ideas and encourage me. Special thanks are reserved for all my friends at Pembroke College and throughout the University over the last 7 years. Their interest in my activities has been much appreciated, and they have been a wonderful source of encouragement and entertainment and I value all our memories. I must also mention the Disability Resource Centre, for their assistance, and my clinical teams in Addenbrookes Hospital, who have variously, over the last years, cured me of cancer, fixed my broken leg and regularly helped to keep me upright and walking. Last but not least I would like to thank my long term shield and defender, Barbara. Her support and assistance for the last 37 years have helped me to achieve all that I have. This thesis would not have been possible without her friendship and it is dedicated to her. Richard Parmee – April 2018 v Xray Generation by Field Emission vi Richard Parmee – April 2018 PUBLICATIONS Journal Articles M. T. Cole, M. Doherty, R. Parmee, P. Dawson, & W. I. Milne, “Ultra-broadband polarisers based on metastable free-standing aligned carbon nanotube membranes”, Adv. Opt. Mater., 2, 10, 929-937, 2014 Parmee R, Collins C, Milne W and Cole M “X-ray generation using carbon nanotubes” Nano Convergence 2, 1, 2015 Ding S, Cole M, Li C, Zhou Y, Collins C M, Kang M H, Parmee R J, Lei W, Zhang X, Dai Q, Milne B and Wang b “Towards Graphane Field Emitters” RSC Advances 5 (127) 105111-105118 2015 C. M. Collins, R. J. Parmee, W. I. Milne, & M. T. Cole “High Performance Field Emitters” Adv. Sci., 2, 3, 2016 M. T. Cole, R. J. Parmee, & W. I. Milne “Nanomaterial-based X-ray Sources” Nanotech., 27, 8, 2016 M. T. Cole, R. J. Parmee, A. Kumar, C. M. Collins, M. H. Kang, J. Xiao, C. Cepek, X. Yuan, & W. I. Milne “Conjugated Polyelectrolyte Nano Field Emission Adlayers” Nanoscale Horiz. 1, (4), 304-312 2016 M. T. Cole, S. Coskun, R. J. Parmee, P. Hiralal, C. Cepek, A. W. Robertson, C. Li, Q. Dai, J. H. Warner, W. I. Milne, & H. Unalan “Suppressed Hysteretic Field Emission from Polymer Encapsulated Silver Nanowires” IEEE Nano. Exp., 99, 2016 X. Yuan, Y. Zhang, M. T. Cole, Y. Yan, X. Li, R. Parmee, J. Wu, N. Xu, W. I. Milne & S. Deng “A Truncated-Cone Carbon Nanotube Cold-Cathode Electron Gun” Carbon 2017 Richard Parmee – April 2018 vii Xray Generation by Field Emission Nagaraja Rao, Brian Ament, Richard Parmee, Jonathan Cameron, Martin Mayo “Rapid, non-destructive inspection and classification of inhalation blisters using low-energy x-ray imaging”, J.Pharm.Innovation, 1-13. May 2018 Book Chapters M. T. Cole, C. Collins, R. Parmee, & W. I. Milne, “NanoCarbon Electron Emitters: Advances & Applications”, Chemical Functionalisation of Carbon Nanomaterials: Chemistry & Applications - Structure & Synthesis , (Taylor & Francis), 2014 viii Richard Parmee – April 2018 CONTENTS 1 RESEARCH PROBLEM STATEMENT ........................................................... 21 1.1 BACKGROUND .................................................................................................. 22 1.2 SPECIFIC APPLICATION FIELD ........................................................................... 22 1.3 PRIOR WORK .................................................................................................... 23 1.4 SCOPE OF THE PROJECT .................................................................................... 23 1.5 COMMERCIAL BACKGROUND ........................................................................... 25 1.6 CONTENTS OF THIS THESIS ............................................................................... 25 1.7 REFERENCES .................................................................................................... 26 2 BACKGROUND ................................................................................................... 27 2.1 HISTORICAL PERSPECTIVE ............................................................................... 27 2.2 IMPORTANCE OF X-RAY TECHNOLOGY ............................................................. 30 2.3 APPLICATIONS IN MANUFACTURING ................................................................ 31 2.4 CONSTRUCTION OF THE XRAY SOURCE ............................................................ 32 2.5 FIELD EMISSION SOURCES AND THE PRINCIPLES OF FIELD EMISSION .............. 36 2.6 CARBON NANOTUBES IN A FIELD EMISSION DEVICE........................................ 38 2.7 CONCLUSIONS .................................................................................................. 38 2.8 REFERENCES .................................................................................................... 38 3 INTRODUCTION TO NANO ENGINEERED ELECTRON SOURCES ...... 43 3.1 ELECTRON EMISSION ........................................................................................ 43 3.2 FIELD EMISSION APPLICATION OF CNTS .......................................................... 47 3.3 CATHODE FABRICATION ................................................................................... 49 3.3.1 Drop, Spray and Cast ...................................................................................
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