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All-Dielectric Colloids and Hybrid Nanostructure for Nanophotonics from High to Low Index Materials

  • YongDeok Cho (조용덕, KU-KIST융합대학원 NBIT융합전공)

초록/요약

In the rapidly evolving field of nanophotonics, the advancements in light-matter interactions at the nanoscale have been significantly driven by the development of nanoantennas. Optically resonant nanostructures, especially those made from noble metals like gold and silver, have played a pivotal role due to their ability to enhance various optical responses. However, these plasmonic nanostructures have intrinsic limitations, such as inevitable Joule heating under resonant excitations, which lead to challenges like the degradation of fluorescent dyes and bleaching issues. This constrains their broader applicability and efficiency as nanoantennas at optical frequencies. To overcome these challenges, the focus has shifted towards all-dielectric nanoparticles, particularly those with high (> 3.0) or moderate (1.7-3.0) refractive indices. These all-dielectric nanoparticles, serving as a cornerstone for meta-optics, offer low-loss, low-heating, and quenching-free Mie resonances. Over the last decade, all-dielectric materials have gained significant attention in nanophotonic systems for applications in directional scattering, Fano resonance, Purcell effect, metasurfaces, and highly integrated photonic chip devices. However, developing all-dielectric nanospheres through scalable and versatile synthetic routes, while ensuring uniformity, roundness, and robustness, remains a challenging goal. In this dissertation, we pioneered a transition from the innovation of selenium colloids to the exploration of hybrid nanostructures, aiming at the potential for self-assembled motifs. The dissertation began with the synthesis of selenium colloids, overcoming the inherent instability of these colloids and stabilizing them. This marked a significant milestone, setting the foundation for further advancements in nanophotonics. Building upon this, we focused on the precise measurement and characterization of these novel materials. We introduced a new substrate, an ultra-thin polymer film, to mitigate the substrate effect and enhance the accuracy of optical observations. This was crucial in accurately interpreting the unique properties of the selenium colloids and understanding their interaction with light. The research then progressed to the synthesis of metal-dielectric hybrid nanostructures. Here, the challenge was to synergize the different properties of metals and dielectrics into a harmonious hybrid structure. These hybrid nanostructures combined the electromagnetic energy confinement near metallic regions with the minimal losses and high Q-factor of dielectric parts. This innovative approach opened new avenues in nanophotonics, providing ideal components for advanced colloidal systems. Then, we developed our research for exploring the potential for these materials to self-assemble into unique motifs. In this part of the dissertation, we studied how the delicate interplay between the gold and silica components, driven by van der Waals forces, facilitates the self-assembly of colloids into designed patterns and structures. This investigation is crucial for understanding the emergent properties of these nanostructures and their potential applications in nanophotonic systems. This dissertation does not only cover various aspects of nanophotonics but also a demonstration of how innovative synthesis, precise measurement, and creative material design can come together to advance our understanding and manipulation of light at the nanoscale.

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목차

ABSTRACT ........................................................................................................................... i
국문 초록 ............................................................................................................................. iii
PREFACE............................................................................................................................. vi
TABLE OF CONTENTS .................................................................................................... vii
LIST OF FIGURES .............................................................................................................. ix
CHAPTER 1. INTRODUCTION .......................................................................................... 1
1.1 Introduction of Nanoantenna ................................................................................. 1
1.2 The Material library for nanoantenna .................................................................... 2
1.3 Scope of thesis ....................................................................................................... 4
CHAPTER 2. Selenium colloids as Mie resonator ................................................................ 6
2.1 Introduction............................................................................................................ 6
2.2 Theoretical background ......................................................................................... 7
2.3 The progress and limitation in conventional materials .......................................... 8
2.4 The advent of selenium colloids as alternative .................................................... 10
2.5 The New Synthetic method for Se colloids ......................................................... 12
2.6 The various platforms with selenium colloids ..................................................... 16
2.6.1 The Kerker-type directional scattering of colloidal suspension .............. 16
2.6.2 Field confinement through self-assembled cluster motif ........................ 22
2.6.3 Photonic bandgap manipulation via self-assembled colloidal crystal ..... 27
CHAPTER 3. Ultra Low-loss substrate in Nanophotonics ................................................. 30
3.1 Introduction.......................................................................................................... 30
3.2 Conventional method of measuring scattering of nanomaterials ......................... 31
3.3 Formvar substrate for plasmonics ........................................................................ 35
3.4 The cluster motif AuNSs heptamer analysis with Formvar film ......................... 38
3.4 All-dielectric colloidal analysis via Formvar membrane ..................................... 42
CHAPTER 4. Hybrid Nanostructure for Nano-optics ......................................................... 47
4.1 Introduction.......................................................................................................... 47
4.2 The Synthetic pathway of hybrid Nanostructure ................................................. 48
4.2.1 Kinetically and thermodynamically controlled synthetic pathway ......... 51
4.2.2 Geometically controlled synthetic way ................................................... 62
4.3 Colorant of colloids via sub-radiant properties .................................................... 66
CHAPTER 5. Metallodielectric colloidal behavior ............................................................. 72
5.1 Introduction.......................................................................................................... 72
5.2 Van der Waals colloids ........................................................................................ 74
5.2.1 The quantification of van der Waals interaction ..................................... 78
5.2.2 The electrostatic repulsion force. ............................................................ 80
5.2.3 Net DLVO potential energy .................................................................... 81
5.3.1 Phase diagram of colloidal behavior in crystallization ........................... 81
5.3.2 Bandwidth tunability of bandgap via manipulating the effective index of colloids ............................................................................................................. 85
5.3.3 Bandgap tuning through core size ........................................................... 87
Chapter 6. Conclusion ......................................................................................................... 91
REFERENCES .................................................................................................................... 93

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