在本篇研究中，利用啞鈴型金奈米棒作為模板，來合成啞鈴型金銀核殼型奈米棒。銀殼的形態調控已知經由微調溫度和pH值會受到很大的影響，因此我們在這針對改變溫度和pH值來探討。室溫下，硝酸銀的銀離子(Ag+)與CTAB的溴離子(Br-)形成溴化銀，這使得維生素C還原能力不足將銀離子還原至啞鈴型金奈米棒上；因此我們利用氫氧化鈉來增加pH值，使得銀離子快速還原至啞鈴型金奈米棒上，最後銀殼形狀偏向圓形以及不規則形狀。當反應溫度較高將導致雙三角錐產生缺角。此外，也發現在AuDBs中，銀先沉積在兩側將可能形成長方形；在AuDBs中，銀先沉積在某一側將可能形成雙三角錐。如果在室溫下先包覆薄薄的銀殼，當380 nm左右的特徵吸收峰強度明顯的變強，這也使得無法形成長方形與三角形。此外AuDBs先利用胺基酸分子半胱胺酸進行表面修飾，實驗觀察出也會有相同結果。實驗結果顯示，銀殼在AuDBs表面初期的成長可能扮演著決定核殼最後構形的關鍵步驟。 Gold Nanodumbbells (AuDBs) are prepared from gold nanorods by chemical reduction and used as the templates to synthesize Au-Ag core-shell nanoparticles. The rate of silver shell growth could be controlled by temperature and pH, and the final morphology of those core-shell nanoparticles will be discussed. Silver ion reacts with bromide at room temperature, and results in the formation AgBr complexes which prevent the reduction of silver ions by ascorbic acid. But, the rapid epitaxial growth of Ag on AuDBs takes place with the addition of NaOH. The final core-shell nanoparticles displayed either sphere-like or irregular faceted morphologies. On the other hand, the special structures such as bar and triangular bipyramids with truncated corners were obtained at higher temperature. The Ag shell is preferentially grew on the one side of AuDBs in the latter, but the shape of the Ag shell in the former is a rectangular in which the reduction of Ag atoms is deposited on the both sides of AuDBs. If AuDBs were wrapped with thin silver shells at room temperature and the intensity of the 380nm peak increases, then anisotropic Ag coating occurs and prevents the formation of the two structures. At the same time, the similar results were also observed when the ends of AuDBs are modified by cysteine molecules. The experimental results show that the initial growth of the silver shell on the surface of AuDBs could play the important step to determine the final morphology of the core-shell nanoparticles.
