Thạc Sĩ 3D photonic bandgap materials fabricated self-assembled colloidal microspheres as the template

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Table of Contents
Summary . . . vii
Nomenclature .ix
Glossary . . xii
List of Tables . .xiii
List of Figures . .xiv
CHAPTER 1. INTRODUCTION . . 1
1.1 Photonics and all-optical devices . 2
1.2 Photonic bandgap (PBG) and PBG materials . . 4
1.3 Fabrication methods of 3D PBG materials . 6
1.3.1. The “top-down” methods 6
1.3.2. The “bottom-up” methods 7
1.4 The self-assembly method for fabrication of 3D PBG materials . 8
1.4.1. Colloidal crystal template 9
1.4.2. Morphology control . 9
1.4.3. Fabrication of heterogeneous structure 10
1.5 Objectives of the project 11
1.6 Structure of thesis . 12
CHAPTER 2. LITERATURE REVIEW . .13
2.1 Theory of photonic bandgap (PBG) materials 13
2.2 Modeling and simulation .18
2.3 Fabrication of PBG materials . 20
2.3.1. The “top-down” approaches to 3D photonic crystals 21
2.3.2. The “bottom-up” approaches to 3D photonic crystals 27 Table of Contents
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2.4 Defect engineering in photonic crystals 53
2.4.1. The importance of defects 53
2.4.2. Defecting engineering using lithography method .54
2.4.3. Defecting engineering using self-assembly method .55
2.5 Applications of 3D photonic crystals 57
2.6 Motivation of this thesis project 60
CHAPTER 3. EXPERIMENTAL SECTION 61
3.1 Chemicals .61
3.2 synthesis of colloidal microspheres .62
3.2.1. Synthesis of polystyrene microspheres 62
3.2.2. Synthesis of silica microspheres 65
3.3 Fabrication of colloidal crystals .67
3.3.1. Vertical deposition (VD) method 67
3.3.2. Follow-controlled vertical deposition (FCVD) method 67
3.3.3. Centrifugation method 68
3.3.4. Annealing 68
3.4 Fabrication of 3D PBG materials .68
3.4.1. Fabrication of silica inverse opal 68
3.4.2. Fabrication of organosilica inverse opal .69
3.4.3. Fabrication of carbon inverse opal .69
3.4.4. Fabrication of TiO 2 inverse opal 69
3.5 Fabrication of 3D heterostructural PBG materials 70
3.5.1. Multilayer colloidal crystal heterostructures 70
3.5.2. Fabrication of defects in photonic crystals . 71
3.5.3. Fabrication of surface coated heterostructures 74 Table of Contents
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3.6 Fabrication of surface pattern 76
3.6.1. Fabrication carbon pattern on glass substrate .77
3.6.2. Fabrication silica pattern on glass and silicon substrate .77
3.6.3. Fabrication nanopits on silicon substrate 77
3.7 Characterization .77
CHAPTER 4. SYNTHESIS OF MONODISPERSE COLLOIDAL
MICROSPHERES 84
4.1 Synthesis of polystyrene (PS) microspheres .85
4.1.1 Emulsion polymerization .85
4.1.2 Seed polymerization .92
4.2 Synthesis of SiO 2 microspheres .94
4.3 Summary 100
CHAPTER 5. FABRICATION OF 3D PHOTONIC BANDGAP
MATERIALS 101
5.1 Fabrication of colloidal crystals with a FCVD method 102
5.2 Fabrication of inverse opals .119
5.2.1 Silica inverse opals .119
5.2.2 Organosilica inverse opals .131
5.2.3 Carbon inverse opals 140
5.2.4 TiO 2 inverse opals 145
5.3 Summary .146
CHAPTER 6. FABRICATION OF PHOTONIC CRYSTAL
HETEROSTRUCTURES .148
6.1 Multilayer colloidal crystal heterostructures 149 Table of Contents
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6.1.1 Size heterostructures .149
6.1.2 Composition heterostructures .152
6.2 Defect engineering 171
6.2.1 Plane defects embedded in 3D photonic crystals 171
6.2.2 Line defects embedded in photonic crystals .173
6.3 Surface coating 179
6.3.1 Carbon-coated silica heterostructures .180
6.3.2 Carbon macroporous structures 188
6.3.3 Fabrication of magnetic carbon capsules .198
6.4 Summary .203
CHAPTER 7. NANOSPHERE LITHOGRAPHY FOR SURFACE
PATTERNING 205
7.1 Carbon pattern on glass substrate 206
7.2 Silica pattern on glass substrate 210
7.3 Silica pattern on silicon substrate .221
7.4 Summary .229
CHAPTER 8. CONCLUSIONS AND RECOMMENDATIONS .230
8.1 Conclusions .230
8.2 Recommendations 233
REFERENCES 234
APPENDIX 259Summary
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Summary
We have witnessed that research on semiconductors has led to a revolution in
the electronic industry over the later half of the 20
th
century. However, the
semiconductors have reached their limitations in terms of bandwidth and speed of
information processing. It has been widely believed that photonics, an analogy of
electronics, will push the electronics out of the marketplace. The word of “photonics"
comes from "photon" which is the smallest unit of light, just as the electron is the
smallest unit of electronics. Central to photonics technology are photonic bandgap
(PBG) materials, also know as photonic crystals (PCs), which are the analogy of
semiconductors. Thus, similar to the bandgap in a semiconductor, which is able to
control electrons, the presence of a PBG in a PC allows one to control the flow of light.
Over the past decade, breakthroughs have been made in the fabrication of 1D
and 2D PBG materials because they are relatively easy to fabricate using the
conventional “top-down” lithography techniques. However, when it comes to 3D PCs,
conventional lithography approaches have trouble. Thus, it has been a great challenge
to fabricate 3D periodic PC structures in a controllable way, in copious quantities, and
at an acceptable cost.
The self-assembly method, on the other hand, has been recently extensively
explored and demonstrated as a simple and inexpensive route to fabricating 3D PCs.
Briefly speaking, colloidal microspheres can be spontaneously assembled into
colloidal crystal. Then the voids among the spheres of colloidal crystal are infiltrated
with a material of high refractive index. Removal of the spheres produces a porous
structure with air holes, of which the size is determined by the diameter of the
microspheres. Summary
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Although the self-assembly method has been demonstrated to afford 3D PCs
with a full PBG, it is still far away from practical applications because of the main two
issues associated with self-assembled 3D PBG materials. One is the domain size of a
self-assembled colloidal crystal (template) is not large and uniform enough to realize
photonic devices. The other one is that it lacks a generalized method for fabrication of
artificial defects embedded into a self-assembled PC (the presence of defects in 3D
PCs is as important as that in semiconductors). Thus, these two issues became the
research focus of this thesis project.
To solve the first problem, a flow-controlled vertical deposition (FCVD)
method for self-assembly of colloidal spheres was introduced in this thesis work.
Colloidal crystals fabricated using the FCVD method are uniform in thickness and
have a domain size of several hundred micrometers. Colloidal spheres as large as 1.5
àm can be assembled into colloidal crystals using the FCVD method, which is
important to fabricate PCs using in telecommunications. In addition, the FCVD
method was also observed to work well for infiltration of the colloidal crystals to
create different surface morphologies. To solve the second problem, a totally novel
fabrication strategy was developed — by combining self-assembly with
photolithography, various defects including planar and point defects have been
precisely inserted into a 3D PC to create PC heterostructures.
Along with the main stream of the thesis work, various surface patterning was
attempted to generate on silicon and glass substrates, which were further used to create
ordered nanoarrays, nanorings, and nanopits. In addition, by using a layer-by-layer
growth mechanism, size and composite colloidal-crystal heterostructures were also
fabricated.