臺灣博碩士論文加值系統

We have successfully fabricated long-range (~2.5 mm) ordered gold nanocube (~40 nm) and octahedra (~40 nm) assembled structures on the substrates at room temperature in moist condition. Gold nanocube (~40 nm) and rhombic dodecahedral nanocrystals (~40 nm) at high CTAC and particle concentrations can form respectively cubic or octahedral supercrystals on a wafer at 90 ºC in an environment with high humdity. Rhombic dodecahedral (~40 nm) and octahedral (~40 nm) nanocrystals at high CTAC and particle concentrations can assemble into platelike and rhombic dodecahedral supercrystal at room temperature under this humid condition. It may not form supercrystals using larger nanocubes (~75 nm), octahedral (~65 nm) and rhombic dodecahedral (~55 nm) nanocrystals. The key conditions for fabricating supercrystals are size–dependent, high surfactant and particle concentrations, and a sufficient long time for nanocrystal assembly.
We have found two types of gold nanocube assembly. At room temperature, each cube in the second layer sits right in the center of four cubes underneath, while nanocubes contact each other by face-to-face fashion at high temperature. There are three types of octahedral gold nanocrystal assembled structures. One packing structure is through faces contacting the substrate. Another assembled structure is with their edges contacting the underlying substrate. The third assembled structure is unstable in which the octahedra contact each other exactly face to face and five octahedra organize into a unit. No strong force exists between layer 1 and layer 2.
Rhombic dodecahedra (~40 nm) and ordered nanocube (~40 nm) assembly may form “hot spots” and have been shown to exhibit good SERS enhancement, while disordered nanocube and fused octahedral (~40 nm) structures do not. UV－vis spectra of gold nanocube assembly show absorption bands in the near-infrared region .

Abstract of the Thesis ……………………………………………… i
Acknowledgement ……………………………………………… iv
Table of contents ……………………………………………… vi
List of Figures ……………………………………………… viii
List of Schemes ……………………………………………… xii

CHAPTER 1 Methods for the Fabrication of Ordered Nanostructure Assembly and Their Applications

1.1 Introduction 1
1.1.2 Methods for Fabricating Assembly of Nanocrystals 3
1.2.1 Langmuir−Blodgett (LB) Technique 3
1.2.2 Evaporation-Based Technique 6
1.2.3 Electrostatic Interaction 12
1.2.4 Solvophobic Interaction 14
1.3 Properties and Applications 16
1.4 References 22

CHAPTER 2 Fabrication of Long-Range Ordered Nanocrystal Assembly and Supercrystals on Substrates Using Gold Nanocubes, Octahedra and Rhombic Dodecahedra as Building Blocks
2.1 Introduction 25
2.2 Experimental Section 27
2.2.1 Chemicals 27
2.2.2 Synthesis of Gold Seeds 27
2.2.3 Synthesis of Cubic Nanocrystals (40 nm) 27
2.2.4 Synthesis of Rhombic Dodecahedral Gold Nanocrystals (40 nm) 28
2.2.5 Synthesis of Larger Cubic and Rhombic Dodecahedral Gold Nanocrystals 28
2.2.6 Synthesis of Octhedral Gold Nanocrystals 29
2.2.7 Long-Range Ordered Self-Assembly of Gold Nanocubes 30
2.2.8 Instrumentation 33
2.3 Results and Discussion 34
2.4 Conclusion 68
2.5 References 69

LIST OF FIGURES
CHAPTER 1 Methods for the Fabrication of Ordered Nanostructure Assembly and Their Applications
Figure 1.1 The setup of LB technique and SEM images of superlattices composed of truncated cubes, cuboctahedra and octahedra of silver nanocrystals. 5
Figure 1.2 The mechanism of Au nanocrystal self-assembly during the drying process. 8
Figure 1.3 Schematic illustration of a Au nanorod and SEM images of ordered Au nanorod superstructures. 9
Figure 1.4 SEM images of the ordered assembly formed from polyhedra, nanocubes, and bipyramids. 10
Figure 1.5 FE-SEM images of four different alkyl chain length thiolate- stabilized Au nanoparticle superlattices and their diffraction patterns. 11
Figure 1.6 Scheme of AuMUA and AgTMA nanoparticles and SEM images of AuMUA-AgTMA crystals. 13
Figure 1.7 The crystallization progress and SEM images of octahedral MnO nanocrystals formed cubic supercrystals. 15
Figure 1.8 Snapshots of cuboctahedral nanocrystals superlattice and corresponding SEM images at surface pressures of = 0 , 1.0 and 14 mN m–1. 19
Figure 1.9 Reflectance spectra of cubes, cuboctahedra, and octahedra superlattice, and Dark-field scattering spectra for the cuboctahedra monolayer. 20
Figure 1.10 Extinction spectra of four different chain length thiolate- stabilized Au nanoparticle superlattices and isolated Au nanoparticles. 21
Figure 1.11 I-V curves of silver nanoparticle deposited on Au(111) substrate. 21








CHAPTER 2 Fabrication of Long-Range Ordered Nanocrystal Assembly and Supercrystals on Substrates Using Gold Nanocubes, Octahedra and Rhombic Dodecahedra as Building Blocks
Figure 2.1 The setup for assembling nanocrystals and OM image of the ordered gold nanocube assembly on a substrate. 32
Figure 2.2 Optical microscopy images for gold nanocube assembly after drying. 35
Figure 2.3 SEM images of assembled structures from gold nanocubes with different surfactant concentrations or drying times. 39
Figure 2.4 SEM image of gold cubic supercrystals at 90 °C. 42
Figure 2.5 SEM images and schematic drawings of two types of gold nanocube assembly. 43
Figure 2.6 SEM images of long-range ordered assembled structures from octahedral gold nanocrystals. 49
Figure 2.7 SEM images and schematic drawings of the three types of self-assembled structures of the octahedral gold nanocrystals. 50
Figure 2.8 SEM images and schematic drawings of octahedral gold supercrystals. 53
Figure 2.9 SEM images and schematic drawings of platelike gold supercrystals. 54
Figure 2.10 SEM images of rhombic dodecahedral gold supercrystals. 55
Figure 2.11 SEM images of rhombic dodecahedral and octahedral gold assembled structures at room temperature in a drying oven. 57
Figure 2.12 SEM images of assembled structures from larger gold nanocubes nanocrystals. 60
Figure 2.13 SEM images of assembled structures from larger rhombic dodecahedral gold nanocrystals. 61
Figure 2.14 SEM images of 2D monolayer assembly from larger octahedral gold nanocrystals. 62
Figure 2.15 SERS spectra of four different assembled structures and corresponding SEM images. 65
Figure 2.16 UV-vis spectra of ordered gold nanocube assembly and corresponding SEM images. 67




LIST OF SCHEMES
CHAPTER 2 Fabrication of Long-Range Ordered Nanocrystal Assembly and Supercrystals on Substrates Using Gold Nanocubes, Octahedra and Rhombic Dodecahedra as Building Blocks
Scheme 2.1 Schematic illustration of the synthesis procedure for preparing Au nanocrystals with different sizes and shapes. 30
Scheme 2.2 Schematic illustration of the procedure for preparing Au colloidal solution containing different CTAC concentrations. 32
Scheme 2.3 The mechanism of gold nanocrystal self-assembly during the slow drying process at high surfactant concentration. 36
Scheme 2.4 Schematic illustration of ordered gold nanoparticle assembly by entropy-driven formation. 42

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