UNIVERSITY OF CALIFORNIA RIVERSIDE Electrochemical Synthesis of Tellurium & Lead Telluride from Alkaline Baths and Their Thermoelectric Properties A Dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemical and Environmental Engineering by Tingjun Wu June 2016 Dissertation Committee: Dr. Nosang V. Myung, Chairperson Dr. Juchen Guo Dr. David Jassby Copyright by Tingjun Wu 2016 The Dissertation of Tingjun Wu is approved: Committee Chairperson University of California, Riverside Acknowledgements In this long journey, there are a number of people whom I would like to acknowledge. Foremost, I would like to thank my advisor, Professor Nosang V. Myung, for his support, help, and the lessons he gave me both on my personal life and research. His enthusiasm and curiosity about science have always motivated me to move my project forward and I learned how to logically think under his valuable guidance. I would like to express my gratitude to my committee, Professor Juchen Guo and Professor David Jassby, for the review of my dissertation as well as their insightful comments. I would like to acknowledge my previous and current group members: Miluo Zhang, Wayne Bosze, Hengchia Su, Jiwon Kim, Michael Nalbandian, Nicha Chartuprayoon, Hyunsung Jung, Saba Seyedmahmoudbaraghani, Navaneet Ramabadran and Sooyoun Yu; and those who gave me the possibility to complete this dissertation. Finally, I would like to thank my family for their love, encouragement, and endless support during this journey. iv ABSTRACT OF THE DISSERTATION Electrochemical Synthesis of Tellurium & Lead Telluride from Alkaline Baths and Their Thermoelectric Properties by Tingjun Wu Doctor of Philosophy, Graduate Program in Chemical and Environmental Engineering University of California, Riverside, June 2016 Dr. Nosang V. Myung, Chairperson Heat is the natural by-product of energy conversion processes. Of the 4.25 × 1020 J of energy the United States consumes every year, more than 60% is wasted in the form of heat. Therefore, waste heat recovery is a crucial step to improve the energy generation and utilization efficiency. Thermoelectric (TE) materials, which can directly convert rejected or waste heat into usable electric power, has been extensively developed for this issue. Thick-film-based devices have advantages over conventional TE module because of its compact size. By shrinking the size of thermoelectric devices, it not only allows the device to operate under smaller temperature gradients, but by so doing it expands its capability to handle a wider range of thermal and power management microelectronic systems. The combination of electrochemical deposition of compound semiconductors (metal tellurides) with standard integrated circuit technique makes fabrication of thermoelectric microdevices possible. v The overall objective of this work is to develop new baths to achieve high-rate electrodeposition of Te and PbTe thick films. The electrodeposition mechanisms of Te and PbTe were examined by electrochemical analysis method. Furthermore, the thermoelectric property of thick PbTe films were optimized by introducing energy barriers from crystal grain boundary and tellurium nanoinclusion, which was achieved by tailoring composition and crystal structures of the thick PbTe films. Additionally, control over the composition and crystal structures was realized by tuning the electrodeposition conditions, as well as post-annealing process. vi TABLE OF CONTENTS 1 Introduction: Electrochemical Synthesis Methods and Thermoelectrics .............................................................................. 1 1.1 World Energy Challenges ................................................................................................ 1 1.2 Thermoelectrics................................................................................................................ 2 1.2.1 An Overview of Thermoelectrics ............................................................................. 2 1.2.2 Thermoelectric figure of merit and efficiency ......................................................... 3 1.2.3 Thermoelectric materials.......................................................................................... 6 1.2.4 Micro- -printing ......... 6 1.3 Electrochemical synthesis ................................................................................................ 8 1.3.1 Electrochemistry of Te ............................................................................................. 9 1.3.2 Electrochemical synthesis of tellurium .................................................................. 15 1.3.3 Electrochemistry of lead telluride (PbTe) .............................................................. 26 1.4 References ...................................................................................................................... 30 2 Synthesis of Tellurium Hetero-structures by Galvanic Displacement Reaction using Zinc as A Sacrificial Material .. 49 2.1 Abstract .......................................................................................................................... 49 2.2 Introduction .................................................................................................................... 50 vii 2.3 Experimental .................................................................................................................. 52 2.4 Results and discussion ................................................................................................... 54 2.5 Conclusions .................................................................................................................... 62 2.6 References ...................................................................................................................... 63 3 Size Controlled Synthesis of Tellurium Nanorices by Galvanic Displacement Reaction of Aluminum ........................ 79 3.1 Abstract .......................................................................................................................... 79 3.2 Introduction .................................................................................................................... 79 3.3 Experimental .................................................................................................................. 82 3.4 Results and discussion ................................................................................................... 83 3.4.1 Synthesis and material characterization of Te “rice-like” nanostructures ............. 83 3.4.2 Electrochemical behavior of GDR ......................................................................... 88 3.5 Conclusions .................................................................................................................... 95 3.6 References ...................................................................................................................... 96 4 Electrodeposition of Tellurium Thick Films from Alkaline Baths ............................................................................................ 115 4.1 Abstract ........................................................................................................................ 115 4.2 Introduction .................................................................................................................. 115 4.3 Experimental ................................................................................................................ 117 viii 4.4 Results and discussion ................................................................................................. 118 4.5 Conclusion ................................................................................................................... 129 4.6 Reference ..................................................................................................................... 129 5 Reaction Kinetics of Reduction Reactions of Te(IV) to Te(0) to Te(-I) in Alkaline Solution .................................................... 156 5.1 Abstract ........................................................................................................................ 156 5.2 Introduction .................................................................................................................. 156 5.3 Experimental ................................................................................................................ 158 5.4 Results and discussion ................................................................................................. 159 5.5 Conclusion ................................................................................................................... 167 5.6 Reference ..................................................................................................................... 168 6 Electrodeposition of Dense Thick PbTe Film in Alkaline Solution ........................................................................................ 192 6.1 Abstract ........................................................................................................................ 192 6.2 Introduction .................................................................................................................. 192 6.3 Experimental ................................................................................................................ 195 6.4 Results and discussion ................................................................................................