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Synthesis and Characterization of Nbox Thin Film Synthesis and Characterization of NbOx Thin Film A Thesis Submitted to the College of Graduate and Postdoctoral Studies In Partial Fulfillment of the Requirements For the Degree of Master of Science In the Department of Mechanical Engineering University of Saskatchewan Saskatoon Canada By Nazmul Hossain © Copyright Nazmul Hossain, April, 2019. All rights reserved. Permission to Use In presenting this thesis in partial fulfillment of the requirements for a postgraduate degree from the University of Saskatchewan, I agree that the Libraries of this University may make it freely available for inspection. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor who supervised my thesis work or, in their absence, by the College of Graduate and Postdoctoral Studies (CGPS), Head of the Department or the Dean of the College in which my thesis work was done. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in my thesis. Requests for permission to copy or to make other use of material in this thesis in whole or part should be addressed to: Head of the Department of Mechanical Engineering 57 Campus Drive, University of Saskatchewan Saskatoon, Saskatchewan, S7N 5A9 Canada OR Dean College of Graduate and Postdoctoral Studies University of Saskatchewan 116 Thorvaldson Building, 110 Science Place Saskatoon, Saskatchewan, S7N 5C9 Canada i Abstract Niobium Oxides (NbOx) thin films have been deposited on silicon (100) and quartz substrates by magnetron sputtering using metallic Nb target in an optimized argon-oxygen atmosphere. To date, suitable deposition conditions for crystalline NbOx thin films by reactive sputtering techniques have not been established. Therefore, this work investigates the dependence of structure-property relations on the key deposition parameters towards establishing optimum deposition conditions for the growth of NbOx crystalline films. It is found that a substrate temperature of 720 °C, low gas pressures of 8 mtorr and a target to substrate distance of 45 mm gives NbOx thin films with good homogeneity and a high degree of crystallinity. X-Ray Diffraction (XRD) and Raman spectroscopy confirmed the tetragonal phase of NbO2 and orthorhombic phase of Nb2O5 for similar deposition temperatures. Scanning Electron Microscopy (SEM) observations indicate that NbO2 has a unique nanoslice structure while Nb2O5 has a flake-like structure. Effect of post deposition annealing on the structural properties are also investigated in this dissertation. It is found that structural changes in NbO2 samples are prominent after annealing in air or Ar atmosphere. In contrast, well crystalline Nb2O5 samples do not show significant changes after annealing in air atmosphere. However, amorphous Nb2O5 can be transformed to tetragonal NbO2 after annealing in Ar atmosphere (reduction). The electrical conductivity and optical transmittance of the films have been investigated and found to be dependent on the oxygen gas content; the conductivity increases, and the optical transmittance decreases with increasing O2 gas content. Optical constants of the films were calculated by fitting model calculations to experimental transmittance data using the modified Swanepoel technique. The nanohardness and stress in the films were measured by nanoindentation and an optical profilometer, respectively. Nano hardness and stress in the film show no large dependence on the oxygen gas content except at high oxygen gas content. V being one of the prominent transition metals, is doped with NbO2 to evaluate the structural variations and the optical transmittance. It is found that higher sputtering power of V is required to be doped with NbO2 and V contents have less effect on optical transmittance of NbO2. ii Acknowledgments I would like to express my sincere gratitude to my supervisors, Professor Qiaoqin Yang and Professor Safa Kasap for their continuous instructions and encouragements. I will always be thankful to my supervisors for their immense support, patience and kind advice throughout my master’s research. I would like to appreciate my committee members Professor W.J. (Chris) Zhang and Professor Duncan Cree for their valuable advice. I am very thankful to the members of this project Dr. Cyril Koughia, Dr. Zhang Chunzi, Ozan Günes and my group colleagues Dr. Yuanshi Li, Masoud Mohammadtaheri, Jesus Corona Gomez and Irtaza Khan for their insight discussion and advice of my research. I would like to thank Mr. Zhao Nan Fang, Mr. Robert Peace and Dr. George Belev for their assistance, training and technical support during my experimental studies. I am thankful with Dr. Jason Maley for Raman spectroscopy training, Dr. Jianfeng Zhu for Grazing XRD training and Dr. Danielle Covelli for XPS measurements at the Saskatchewan Structural Science Center and Dr. Eiko Kawamura for SEM imaging at WCV Image Centre. I highly appreciate the financial support throughout this project by the Cisco, Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI), and the University of Saskatchewan. Finally, I would like to thank my parents and entire family members for their love and support all during my life and my aunt Dr. Jebunnaher and my cousin Dr. Jahangir for giving inspiration and motivations from my childhood. To my beloved parents Amir Hossain and Nurunnaher Begum, my brother Fahim Hossain and my family members… iii Table of Contents Permission to Use…………………………………………………………………………………. i Abstract………………………………………………………………………………………….... ii Acknowledgments………………………………………………………………………….......…iii Table of Contents…………………………………………….……………………………………….....iv List of Tables……...…………………………………………………………………...............................viii List of Figures……...…………………………………………………………………................................ix Acronyms……………………………………………………………………………...............................xii 1 - Introduction .............................................................................................................................. 1 1.1 Motivation…………………………………………………………………………….1 1.2 Objectives……………………………………………………………………………..3 1.3 Methodology………………………………………………………………….……….3 1.4 Organization of Dissertation…………………………………………………………..3 2- Literature Review ..................................................................................................................... 5 2.1 Niobium and Its Oxides……………………………………………………………….5 2.1.1 Niobium (Nb) ........................................................................... …………………..5 2.1.2 Niobium Oxidation .............................................................................................. ..7 2.1.2.1 Niobium Mono-Oxide (NbO) .................................................................. 8 2.1.2.2 Niobium Di-Oxide (NbO2) ..................................................................... 9 2.1.2.3 Niobium Penta-Oxide (Nb2O5) .............................................................. 11 2.1.2.4 Metastable Niobium Oxide s ................................................................. 13 2.1.3 Doping Niobium Oxide s ..................................................................................... 15 2.2 Deposition Techniques………………………………………………………………16 2.2.1 Fundamentals of Sputtering Deposition .............................................................. 17 2.3 Structural Characterization…………………………………………………………..22 2.3.1 Raman Spectroscopy ........................................................................................... 22 iv 2.3.2 X-ray Diffraction (XRD) ..................................................................................... 24 2.3.3 X-ray Photoelectron Spectroscopy (XPS) ........................................................... 26 2.4 Surface Morphology…………………………………………………………………27 2.4.1 Scanning Electron Microscopy (SEM) ................................................................ 27 2.4.2 Optical Profilometer ............................................................................................ 29 2.5 Mechanical Characterizations……………………………………………………….31 2.5.1 Nano Indentation ................................................................................................. 31 2.6 Optical Characterization……………………………………………………………..33 2.6.1 Optical Spectrophotometer .................................................................................. 33 2.7 Electrical Characterizations………………………………………………………….35 2.7.1 Four Point Probe .................................................................................................. 35 3- Experimental Methods ........................................................................................................... 38 3.1 Thin Film Deposition……………………..…………………………………………38 3.1.1 DC/RF Sputtering ................................................................................................ 38 3.2 Experimental Design………………………………………………………………...39 3.3 Effect of Annealing………………………………………………………………….42 3.3.1 Post Deposition Annealing .................................................................................. 43 3.4 Characterization Techniques………………………………………………………...43 3.4.1 X-Ray Diffraction (XRD) ...................................................................................
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