原子層沉積技術於鎳鈦形狀記憶合金表面改質之研究

鎳鈦記憶合金為最被廣泛應用之形狀記憶合金，由於其優越的形狀記憶效應、超彈性效應、生物相容性等優點，於生醫領域上被廣泛使用。但由於鎳鈦合金之鎳元素會於人體內微量釋出，對人體有造成危害之疑慮，而已有數種研究透過表面改質來隔絕鎳釋出，但所使用表面改質技術如陽極處理(anode treatment)、微弧氧化(Micro Arc Oxidation, MAO)等方法，其沉積膜層厚度都十分地厚，很厚的陶瓷膜層會侷限鎳鈦合金之形狀記憶效應與超彈性效應等優點。因此本研究透過原子層沉積技術(Atomic Layer Deposition, ALD)於鎳鈦合金上沉積氧化鋁膜層，來探討奈米尺度下之膜層於承受應變量與隔絕鎳溶出之能力。　　本研究以加熱式原子層沉積技術(Thermal mode ALD, T-ALD)沉積氧化鋁薄膜於鎳鈦合金上，比較表面沉積100, 200cycle氧化鋁薄膜之性質，評估方法為：化學組成、縱深分析、顯微組織觀察、彎曲測試、鎳溶出測試等，探討氧化鋁膜層應用於鎳鈦記憶合金之可能性。　　實驗結果顯示，施鍍於鎳鈦合金上的氧化鋁膜層具有良好均勻的化學組成，沒有殘留副產物與殘碳物，而鎳鈦合金上的薄膜成長速率與同製程下Si wafer相同，因此可以透過Si wafer來鑑定膜層厚度。膜層與底材的介面十分地貼合，證明膜層沉積十分均勻。而鎳鈦合金表面屬於親水性，施鍍膜層厚表面變得較為疏水，但角度仍小於90˚，其中接觸角不會隨cycle上升而有大幅改變。彎曲測試中顯示出膜層具有一定變形能力，而隨著cycle上升所能承受之變形量下降。而施鍍的膜層能夠增加表面之抗腐蝕性，膜層越厚、抗腐蝕性質越好。ALD的氧化鋁膜層能夠有效地隔絕鎳溶出，而膜層厚度增加對於隔絕鎳溶出不會有明顯改變，只要施鍍均勻薄膜層就能有效隔絕鎳溶出。

關鍵字

原子層沉積；鎳鈦形狀記憶合金；氧化鋁奈米鍍膜；鎳溶出

並列摘要

NiTi alloy is the most applicable shape memory alloy due to its wonderful properties of shape memory effect, pseudo-elasticity, biocompatibility, etc. It is usually used for biomedical applications. But NiTi alloy will slightly release Ni element which might hurt human body. Some documents point out that surface modification can reduce the amount of Ni release from NiTi alloy. The general methods in surface modification, like anode treatment or micro arc oxidation, will form a thick coating. This thick coating cannot bear large deformation strain. This problem seriously limits the shape memory effect and/or pseudo-elasticity of NiTi alloy. In this study, atomic layer deposition (ALD) was applied to deposit aluminum oxide (Al2O3) films on the surface of NiTi alloy. The ability of ALD-Al2O3 films to bear the deformation strain and the hindrance of Ni release from NiTi alloy were investigated. In this research, thermal mode ALD (T-ALD, TMA/H2O) was used to deposit Al2O3 film on the surface of NiTi alloy with 100 and 200 deposition cycles for comparison. Several experiments, including chemical composition, film’s thickness, microstructure, bending test, Ni release test, etc, were carried out to evaluate the performance of ALD-Al2O3 films and understand the possibility of ALD-Al2O3 films on NiTi alloy for biomedical applications. Experimental results show that chemical compositions of ALD-Al2O3 films are well homogeneous. There are no retained carbon-residue and byproduct. The ALD film’s growth rate per cycle coated on the NiTi alloys is similar to that on the Si wafer, so the coating thickness can be measured by the Si wafer of the same process. The interface between the ALD film and Ni-Ti substrate fits well. It indicates that the ALD films are very homogenous. The alloy’s surfaces coated with ALD-Al2O3 and -TiO2 films exhibit more hydrophobic, although the water contact angle of all is smaller than 90˚. Besides, the water contact angle does not change obviously with the increase of film’s thickness. Bending test shows that the ALD-Al2O3 and -TiO2 films exhibit a fair adhesion performance. These ALD films could tolerate a suitable deformation strain. But, the tolerable deformation strain is reduced if the film’s thickness increases. These ALD films exhibit excellent corrosion resistance, and corrosion resistance is better with increasing cycles. The ALD films can effectively reduce Ni release. The reduced Ni release does not change with cycles.

並列關鍵字

Atomic layer deposition ； NiTi shape memory alloy ； Al2O3 nano-film ； Ni release

參考文獻

21. 林世庭, Ti50Ni50及Ti49.3Ni50.7鈦鎳形狀記憶合金變態及機械性能之研究, in 材料科學與工程學研究所. 2010, 國立臺灣大學: 台北市. p. 115.

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原子層沉積技術於鎳鈦形狀記憶合金表面改質之研究

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