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  • 學位論文

以植晶法製備長度可調之超長金奈米棒和奈米線

Seed-Mediated Growth of Ultralong Gold Nanorods and Nanowires with a Wide Range of Length Tunability

指導教授 : 黃暄益
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摘要


本篇論文利用三步驟植晶法合成長度為200到4450 nm的金奈米棒和金奈米線,在奈米棒頂部具有five-fold twinned的結構。在第一個合成序列,我們藉由改變金奈米棒成長溶液之酸鹼值從3.0到9.1,得到長度為200到400 nm的金奈米棒,直徑約20 nm。隨著成長溶液的酸鹼值持續增加,金奈米棒的長度會變得越來越短,而金奈米棒的產率也會隨著酸鹼值的提高而增加。我們並藉由測量金奈米棒的紫外―可見光吸收來觀察金奈米棒的純度,在紫外―可見光吸收圖譜中,金奈米片狀的吸收大概在800到900 nm,藉由比較片狀吸收和金奈米棒短軸吸收的相對強度,發現隨著酸鹼值的提升其吸收有著下降的趨勢,這也符合我們在掃描式電子顯微鏡中觀察到的結果。在第二序列,因為在較低的酸鹼值下合成超長金奈米棒,產物往往會伴隨許多的奈米片狀,所以我們藉由降低四氯金酸濃度以及酸只加入第三杯成長溶液的改良方法,可以取得高產率及片狀較少的金奈米棒,並將奈米棒的長度從600 nm 增長到2850 nm,直徑約30 nm。第三序列則將第二序列做些微變動,將第二杯成長溶液轉移到第三杯成長溶液的量從2 mL減少至2 µL,我們可以將奈米棒的長度從700 nm 再增長到4450 nm,最長還可以得到6 m的超長金奈米線,但這序列的直徑相對地變大(50 nm)。另外我們發現成長溶液在鹼性溶液下合成出來的金奈米棒長度較短但產率高,可由溶液顏色變色時間來看,從粉紅色到紫色最後到深紫色,其變色時間不到五分鐘。當成長溶液在酸環境下製備,其變色時間長達一個半小時,可將金奈米棒延伸長至金奈米線。我們並利用穿透式電子顯微鏡來鑑定金奈米線在酸性環境下的成長過程,其長度會隨著反應時間而增加。另外我們也發現成長溶液不管在鹽酸或硝酸下,皆可以合成出相似的長度,證明硝酸根離子的加入並不會影響金奈米棒的形成。我們的合成方法能很方便地調控金奈米棒和奈米線的長度,因此可以針對不同需求的應用來選擇製備適當長度的金奈米棒和奈米線。

關鍵字

奈米結構 植晶法 奈米線 奈米棒

並列摘要


In this study, we have used a simple seed-mediated synthesis method for the preparation of penta-twinned gold nanorods with average lengths from 200 to 4.5 µm. In series I, the gold nanorods can be synthesized from 200 to 400 nm with ~20 nm diameter by tuning the pH of growth solution from 3.0 to 9.1. As the solution pH increases, the length of nanorods becomes shorter but with nanorod yield was much higher. The percentage of nanoplate byproducts decrease substantially as the solution pH increases by comparing the absorbance values of the absorption band of nanoplates to that of the transverse SPR band of nanorods. In Series II, we have systematically extended the lengths of gold nanorods and nanowires from 580 nm to 2850 nm by mainly decreasing the concentrations of tetrachloroauric acid used and raising the amount of nitric acid added to the last growth solution. However, when the pH of the growth solution is very low, the products usually accompanies with lots of nanoplates. In Series III, by lowering the transfer volume of the second growth solution to the third growth solution from 2 mL to 0.2 mL and progressively increasing the amount of nitric acid added only to the third growth solution, ultralong gold nanorods and nanowires with tunable average lengths varying from 700 nm to 4450 nm can be synthesized. The longest nanowires can reach lengths of more than 6 µm. The high uniformity and relatively short lengths of the nanorods synthesized is primarily due to the rapid particle growth rate in a basic solution condition, as evidenced by the fast solution color changes from pink to light purple and then dark purple in less than five minutes. In an acidic condition, the particle growth rate is much slower and the growth progress takes much longer time, allowing the nanorods to grow and extend their lengths. The slow growth rate has been confirmed by examining the intermediate nanorods formed during the particle growth process. HCl was found to be as effective as HNO3 in producing long gold nanorods with similar lengths, showing that the presence nitrate ions is not important to the growth of long gold nanords. These ultralong gold nanorods and nanowires are highly useful materials for a wide range of applications. Their tunable length means that selection of nanorods and nanowires most suitable for a particular situation is possible.

參考文獻


(16) Huang, J.-S.; Callegari, V.; Geisler, P.; Brüning, C.; Kern, J.; Prangsma, J. C.; Wu, X.; Feichtner, T.; Ziegler, J.; Weinmann, P.; Kamp, M.; Forchel, A.; Biagioni, P.; Sennhauser, U.; Hecht, B. Nature Commun. 2010, 1, 150.
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Chapter 1
(1) Huang, X.; Neretina, S.; El-Sayed, M. A. Adv. Mater. 2009, 21, 4880-4910.

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