一、水相中以一鍋合成法製備銀奈米立方體及其形貌變化

本文於50 ºC利用一鍋合成方式在水相中進行銀奈米立方體的合成。以氯化十六烷基三甲基銨鹽作為保護劑並將其與硝酸銀水溶液混合形成氯化銀，利用維生素C作為還原劑且加入氫氧化鈉提升還原力反應六小時將氯化銀還原成銀奈米立方體。藉由增加硝酸銀劑量得到62─80奈米的銀奈米立方體。氫氧化鈉的用量會影響銀奈米粒子的形貌。增加氫氧化鈉用量時會增加反應的速率，因此會促進{111}晶面的生成使銀奈米粒子會由立方體轉變成截角立方體及截半立方體。此外，使用去除大量氯離子的氯化十六烷基三甲基銨鹽作為保護劑時也會提升反應速率得到銀截半立方體。繼續增加反應溫度會使銀截半立方體轉變成截角八面體。


二、不同形狀及不同厚度金鈀核殼異質結構的製備及其電漿性質的探討

本實驗對於不同大小的金鈀核殼立方體，截半立方體，截角八面體及八面體進行光學性質的探討。利用金八面體作為板模並使用植晶法在水相中進行金鈀核殼異質結構的合成。在50 ºC下以溴化十六烷基三甲基銨鹽作為保護劑，將其與金八面體，四氯合鈀酸及維生素C水溶液混合並於兩小時內完成反應。這些形狀均一且具有不同殼厚度的金鈀核殼異質結構使我們能對其局部表面電漿共振性質進行研究及探討。當殼厚度在薄的情況下，光譜中出現金鈀核殼異質結構中金的局部表面電漿共振吸收，而相較於金八面體的吸收其具有藍位移的現象。由於殼厚度會影響在一顆奈米粒子中鈀與金之間的比例及鈀對金的影響，因此當金鈀核殼異質結構由立方體轉變成八面體時金的局部表面電漿共振吸收會逐漸的紅位移並變得越來越明顯。相較於過去的文獻，這是第一次對於不同形狀及不同大小的雙金屬核殼異質結構進行其光學性質的探討。此外，金鈀核殼八面體有明顯的金的局部表面電漿共振吸收，因此未來可嘗試應用於光學感測上，如氫氣感測。

CHAPTER 1
One−Pot Synthesis of Silver Nanocubes and Their Morphological Transformation

We have used one-pot reaction to synthesize cubic silver nanoparticles with average sizes of 62 to 80 nm in aqueous solution at 50 ºC for 6 hours. The reagents used here are AgNO3, cetyltrimethylammonium chloride (CTAC), ascorbic acid, and NaOH. In this method, silver nanoparticles are obtained by using ascorbic acid as reducing agent to reduce AgCl(s) in the presence of CTAC. NaOH is added to increase the reducing ability of ascorbic acid. Silver nanocubes with sizes varying from 62 to 80 nm are obtained by increasing the amount of AgNO3. Different amounts of NaOH also influence the morphology of silver nanoparticles. By increasing the amount of NaOH, the formation of {111} facets is enhanced and the shapes of silver nanoparticles change from cubes to truncated cubes and cuboctahedra due to the increased reaction rate. In addition, reaction rate is also increased when CTA+NO3─ serve as the surfactant. Furthermore, silver cuboctahedra are obtained and evolve into truncated octahedra by increasing the reaction temperature.


CHAPTER 2
Synthesis and Plasmonic Properties of Au−Pd Core−Shell Heterostructures with Variable Shapes and Shell Thickness

In this work, we report the investigation of plasmonic properties of Au−Pd core−shell heterostructures with different shapes, including cubes, cuboctahedra, truncated octahedra, and octahedra. Here, we have used a seed-mediated growth method to synthesize Au−Pd core−shell heterostructures with 35, 45, and 74 nm gold octahedra as cores. Au−Pd core−shell heterostructures with various shapes and sizes are prepared by mixing cetyltrimethylammonium bromide (CTAB), octahedral gold cores, H2PdCl4, and ascorbic acid at 50 ºC in less than 2 hours. The uniform shape of these nanocrystals and the ability to tune the shell thickness allow us to investigate their localized surface plasmon resonance (LSPR) properties. When the shell thickness become thin enough, blue shift of Au LSPR absorption band of Au−Pd core−shell heterostructures is observed. The Au LSPR absorption band red-shifts and become more obvious when the shape of core−shell nanostructures transforms from cubes to octahedra due to the shell thickness variation induced by change in the mole ratios of Pd : Au in a nanoparticle. Comparing to previous studies, this is the first time the plasmonic properties of bimetallic core−shell heterostructures with various shapes and tunable sizes is investigated. For Au−Pd core−shell octahedra, their Au LSPR absorption band is more pronounced and they may have the potential to be applied for plasmonic sensing such as hydrogen sensing.

ABSTRACT OF THE THESIS i
ACKNOWLEDGEMENTS vi
TABLE OF CONTENTS vii
LIST OF FIGURES x
LIST OF TABLES xv
LIST OF SCHEMES xvii


1.1 Introduction 1
1.1.1 Methods for the Synthesis of Silver Nanocrystals 3
1.1.2 Seed-Mediated Growth Method 3
1.1.3 Hydrothermal Process 6
1.1.4 Polyol Synthesis of Silver Nanocubes 7
1.1.5 Synthesis of Silver Nanoparticles with Shape Evolution
10
1.1.6 Introduction of the Thesis Study 14
1.2 Experimental Section 16
1.2.1 Chemicals 16
1.2.2 Preparation of Cubic Silver Nanocrystals with Size
Control 16
1.2.3 Preparation of Silver Nanocrystals by Varying the
Amount of NaOH 17
1.2.4 Preparation of Silver Nanocrystals with Different
Surfactants 17
1.2.5 Instrumentation 18
1.3 Results and discussion 19
1.4 Conclusion 38
1.5 References 39


2.1 Introduction 41
2.1.1 Studies of Palladium Nanocrystals 42
2.1.2 Studies of Gold Nanocrystals 44
2.1.3 Studies of Bimetallic and Metal−Semiconductor Core
−Shell Heterostructures 44
2.1.4 Introduction of the Thesis Study 56
2.2 Experimental Section 57
2.2.1 Chemicals 57
2.2.2 The Synthesis of Au Octahedra with Sizes of 35, 45,
and 74 nm 57
2.2.3 Synthesis of Polyhedral Au−Pd Core−Shell Nanocrystals
59
2.2.4 Instrumentation 63
2.3 Results and Discussion 64
2.4 Conclusion 93
2.5 References 94

CHAPTER 1 One−Pot Synthesis of Silver Nanocubes and Their Morphological Transformation

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