陽極處理鎢所產生的幾何圖形

有許多的研究指出利用化學陽極處理在鋁上可產生自組成(self-organization)且規則排列的多孔狀氧化層結構；而在適當的條件下，外加不同的電壓可在鋁的表面上產生不同的幾何圖形。近年來，在鈦、鉭、鈮、鎢等過渡金屬中也陸續被發現透過陽極處理的方式，在中性或酸性環境底下可產生多孔狀氧化層結構。一般若將鎢置於鹼性溶液中做陽極處理，由於鎢的氧化物在鹼性環境下會自發性地迅速溶解而難以觀察到其氧化層的結構，同時表面會進行電解拋光(electro-polishing)而形成平坦表面。然而在本實驗中，我們發現鎢的表面在氫氧化鈉溶液中同樣有隨電壓變化的幾何圖形生成，並透過在陽極處理進行的過程中局部地降低在表面附近溶液的pH值，不僅抑止氧化層在氫氧化鈉溶液中的溶解，並觀察到鎢的氧化層也有相對應電壓的不同結構產生。我們並首度發現在特定的條件下，氧化鎢會有自組成且緊密排列的奈米孔洞陣列，其週期約在50奈米。在我們的實驗中，整個陽極處理是控制在低溫環境下進行，配製不同濃度的氫氧化鈉水溶液作為電解液，而電壓控制的範圍在10V到110V之間。我們發現，不同幾何圖形的轉換條件只與陽極表面上的外加電壓有關。而在對應特定電壓所產生的多孔狀氧化層結構，會隨著溶液濃度的改變影響表面孔洞的排列。在本篇論文中，我們主要展示在鹼性環境下經由陽極處理及改變不同實驗參數時所得到的表面幾何圖形，並探討其因外加電壓而產生不同幾何圖形的可能機制。

關鍵字

鎢；陽極處理；電化學

並列摘要

In recent years, the growth of porous oxide structures has been largely observed on metals by using anodization. Particularly, in the case of anodic aluminum oxide discovered by Masuda and Fukuda, highly ordered self-organized porous structure can be formed under optimized anodizing conditions. On the other hand, Yuzhakov et al. found that the electropolishing of aluminum results in various patterns by applying different anodic voltage and proposed a model to explain its instability mechanisms. In our experiment, we observed the formation of pattern driven by applied voltage as well on tungsten and W-oxides surface. The tungsten films were anodized in NaOH electrolytes under various conditions. Due to the high dissolution rate of W-oxides in strong basic solutions, we need to locally suppress the concentration of electrolytes above the anode to block the chemical oxidation and dissolution reactions so that the morphology of W-oxides could be retained. Amazingly, under specific conditions, it was the first time that the highly ordered nanohole array was observed on W-oxides, with period about 50nm. In the end of this thesis, we will modify the model proposed by Yuzhakov et al. to elucidate the possible instability mechanisms in our system.

並列關鍵字

tungsten ； anodization ； formation of pattern

參考文獻

1. Masuda, H. and K. Fukuda, ORDERED METAL NANOHOLE ARRAYS MADE BY A 2-STEP REPLICATION OF HONEYCOMB STRUCTURES OF ANODIC ALUMINA. Science, 1995. 268(5216): p. 1466-1468.

2. Beranek, R., H. Hildebrand, and P. Schmuki, Self-organized porous titanium oxide prepared in H2SO4/HF electrolytes. Electrochemical and Solid State Letters, 2003. 6(3): p. B12-B14.

3. Sieber, I.V. and P. Schmuki, Porous tantalum oxide prepared by electrochemical anodic oxidation. Journal of the Electrochemical Society, 2005. 152(9): p. C639-C644.

4. Tsuchiya, H., et al., Self-organized porous WO3 formed in NaF electrolytes. Electrochemistry Communications, 2005. 7(3): p. 295-298.

5. Tsuchiya, H. and P. Schmuki, Thick self-organized porous zirconium oxide formed in H2SO4/NH4F electrolytes. Electrochemistry Communications, 2004. 6(11): p. 1131-1134.

國際替代計量

陽極處理鎢所產生的幾何圖形

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