LIQUID METAL-BASED TERAHERTZ ... - University of Utah

LIQUID METAL-BASED TERAHERTZ METAMATERIALS

by Jinqi Wang

A dissertation submitted to the faculty of The University of Utah

in partial fulfillment of the requirements for the degree of

Doctor of Philosophy

Department of Electrical and Computing Engineering The University of Utah August 2015

Copyright ? Jinqi Wang 2015 All Rights Reserved

The University of Utah Graduate School

STATEMENT OF DISSERTATION APPROVAL

The dissertation of

Jinqi Wang

has been approved by the following supervisory committee members:

Ajay Nahata Steven Blair Hanseup Kim Michael Bartl Sivaraman Guruswamy

Chair Member Member Member Member

05/12/2015

Date Approved

05/12/2015

Date Approved

05/12/2015

Date Approved

05/12/2015

Date Approved

05/12/2015

Date Approved

and by

_________________Gianluca Lazzi_________________ , Chair/Dean of

the Department/College/School o f ______ Electrical and Com puter Engineering

and by David B. Kieda, Dean of The Graduate School.

ABSTRACT

Metamaterials have gained significant attention over the last decade because they can exhibit electromagnetic properties that are not readily available in naturally occurring materials. This dissertation describes our work on design, fabrication and characterization of liquid metal-based metamaterials with focus on their applications in the terahertz (THz) frequency range. In contrast to the more conventional approaches to fabricating these structures, which rely on vacuum deposited solid metal films, we used metals that are liquid at room temperature. This family of materials is especially attractive for such applications, since it enables large-scale reconfigurability in the overall geometry of the device. We demonstrate a number of unique plasmonic and metamaterial devices. Within the topic of plasmonics, we demonstrate a device that allows for mechanical stretching that is reversibly deformable. In an analogous structure, we can change the geometry dramatically by injecting or withdrawing liquid metals from specific area of the pattern. We also developed a liquid metal-based reconfigurable THz metamaterial device that is not only pressure driven, but also exhibits pressure memory. As an alternate approach to demonstrate reconfigurability, we developed a technique for creating dramatic configuration changes in a device via selective erasure and refilling of metamaterial unit cells that utilizes hydrochloric acid. While the approach is successful in changing the geometry, it does not allow for fine spatial control of the pattern. Thus, we have refined the approach by developing an electrolytic process to change the geometry of a liquid

metal-based structured device in a more localized and controlled manner. Since liquid metals can be solidified under certain conditions, we have demonstrated a novel technique for fabrication of free-standing two-dimensional and three-dimensional terahertz metamaterial devices using injection molding of gallium. Finally, we developed a technique of printing three-dimensional solid metal structures by pulling liquid gallium out of a reservoir via solid/liquid interface. Based on these results, we are currently extending our work towards development of metamaterials that can be used in real-world applications. Based on the significant progress made the THz field over the last two decades, the likelihood of THz systems level applications is much brighter.

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TABLE OF CONTENTS

ABSTRACT............................................................................................................................ iii

ACKNOWLEDGEMENTS.................................................................................................viii

CHAPTERS

1. INTRODUCTION............................................................................................................ 1

1.1 Terahertz Technology .......................................................................................... 1 1.2 Metamaterials and Plasmonics.............................................................................3 1.3 Gallium-Based Liquid Metals..............................................................................6 1.4 Outlines..................................................................................................................8 1.5 References........................................................................................................... 12

2. DEVICE FABRICATION AND MEASUREMENT.................................................. 20

2.1 Device Fabrication of Liquid Metal Structures............................................... 20 2.2 3D Printing Technique....................................................................................... 22 2.3 Terahertz Time-Domain Spectroscopy.............................................................23 2.4 References........................................................................................................... 25

3. LIQUID METAL-BASED PLASMONICS................................................................. 27

3.1 Introduction......................................................................................................... 28 3.2 Experimental Details.......................................................................................... 29 3.3 Experimental Results and Discussion............................................................... 33 3.4 Conclusion.......................................................................................................... 40 3.5 References........................................................................................................... 40

4. RECONFIGURABLE PLASMONIC DEVICES USING LIQUID M ETALS........ 43

4.1 Introduction......................................................................................................... 44 4.2 Experimental D etail........................................................................................... 46 4.3 Experimental Results and Discussion............................................................... 49 4.4 Conclusion.......................................................................................................... 55 4.5 References........................................................................................................... 56

5. RECONFIGURABLE LIQUID METAL-BASED TERAHERTZ METAMATERIALS VIA SELECTIVE ERASURE AND REFILLING TO THE UNIT CELL LEVEL...................................................................................................... 59

5.1 Introduction......................................................................................................... 60 5.2 Results and Discussion...................................................................................... 61 5.3 Conclusion.......................................................................................................... 71 5.4 References........................................................................................................... 72

6. ELECTROLYTIC REDUCTION OF LIQUID METAL OXIDES AND ITS APPLICATION TO RECONFIGURABLE STRUCTURED DEVICES..................74

6.1 Introduction......................................................................................................... 75 6.2 Results and Discussion...................................................................................... 77 6.3 Conclusion.......................................................................................................... 90 6.4 Methods............................................................................................................... 90 6.5 References........................................................................................................... 91

7. RECONFIGURABLE TERAHERTZ METAMATERIAL DEVICE WITH PRESSURE MEMORY..................................................................................................94

7.1 Introduction......................................................................................................... 95 7.2 Experimental Details.......................................................................................... 97 7.3 Results and Discussion.................................................................................... 100 7.4 Conclusion........................................................................................................ 111 7.5 References......................................................................................................... 111

8. INJECTION MOLDING OF FREE-STANDING THREE-DIMENSIONAL ALL METAL TERAHERTZ METAMATERIALS...........................................................114

8.1 Introduction....................................................................................................... 115 8.2 Results and Discussion.................................................................................... 117 8.3 Conclusion........................................................................................................ 129 8.4 Experimental Section....................................................................................... 130 8.5 References......................................................................................................... 132

9. 3D PRINTING OF RECYCLABLE SOLID METAL STRUCTURES..................135

9.1 Introduction....................................................................................................... 135 9.2 Results and Discussion.................................................................................... 136 9.3 Conclusion........................................................................................................ 146 9.4 References......................................................................................................... 147

10. FUTURE WORK AND CONCLUSION................................................................... 149

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10.1 Future W ork....................................................................................................149 10.2 Conclusion...................................................................................................... 152

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