底材及電極結構對原子層沉積二氧化鈦薄膜光觸媒效率之影響

Abstract

本研究使用ALD沉積系統於不同基板(glass、SnO2/glass、Ni/Ti/glass、SnO2/Ni/Ti /glass)上沉積二氧化鈦薄膜，探討製程溫度、異質接面、部分裸露底材導電層以及外加偏壓對光觸媒效率的影響。 實驗以原子力顯微鏡(AFM)觀察二氧化鈦薄膜表面型貌，並透過X光繞射分析儀(XRD)觀察晶體結構，最後採用光學吸收光譜儀(UV-VIS)量測亞甲基藍分解前後的穿透率，將其換算成吸收度後，求出衰減係數k藉以探討不同薄膜間的光觸媒效率。 在鎳膜底材上於250℃沉積二氧化鈦之薄膜其光觸媒效率受厚度影響，在原子層沉積系統製程循環次數為300次以下時之結晶性不佳且觸媒能力差，但隨著製程循環次數提升至600次以上，二氧化鈦薄膜開始結晶且觸媒效率亦提升，此時效率與底材鎳膜厚度有正相關。 對三種底材異質接面(SnO2/glass、Ni/Ti/glass、SnO2/Ni/Ti/glass)而言，三者皆有效提升二氧化鈦光觸媒效率，但是底材鍍膜會使得TiO2薄膜結晶相較易從Anatase轉變為觸媒能力較差的Rutile，而沉積在空白玻璃之二氧化鈦薄膜，則在550℃成長時仍具有Anatase結晶相，且因高製程溫度造成的高表面粗糙度，其觸媒效率亦佳。 將底材導電層部分裸露之試片進行光觸媒反應，發現僅少數樣品的觸媒效率有提升，原因應是底材導電層裸露能有效提升光觸媒效率，但無法彌補二氧化鈦薄膜面積減少所造成的損失。於底材裸露層接上正偏壓發現其能有效萃取電子提升光觸媒效率。

In this study, TiO2 films were deposited on different substrates (glass, SnO2/glass, Ni/Ti/glass, SnO2/Ni/Ti/glass) by ALD. We attempt to find out the effect of deposition temperature, heterojunction, underlying conductive layer and external bias potential on the photocatalytic efficiency of TiO2 films. The morphology of the TiO2 film was determined by AFM. The crystal structure was observed by XRD , and the transmittance of methylene blue during experiment was measured by optical absorption spectrometer. After converting transmittance into absorbance, the exponential decay coefficient k was found out, and we can quantify the photocatalytic efficiency of different films. First, we found that TiO2 films deposited on nickel film with ALD cycles of 150/300 at deposition temperature of 250℃have poor crystallinity, but when the process cycles increase up to 600cycles, the TiO2 film begins to crystallize and result in an increase of photocatalytic efficiency. And the photocatalytic efficiency of TiO2 film is positively correlated with the thickness of nickel film. . Second, all of the underlying layer of substrates SnO2, Ni/Ti and SnO2/Ni/Ti can effectively improve the photocatalystic efficiency of TiO2 fims, but the underlying coating makes the film structure easily converting from anatase to rutile .In contrast, TiO2 film deposited on the glass still remains the phase of anatase at 550°C,and its catalystic efficiency is good because of high surface roughness and crystalline anatase phase. After measuring the photocatalytic efficiency of samples in which the conductive layer was partially exposed. We found that only a few samples were enhanced in photocatalytic efficiency. The main reason is that exposure of the conductive layer can effectively improve the photocatalystic efficiency, but it can not make up the loss caused by the reduction of the reaction area of TiO2 film. We then applied a positive bias potential to the exposed layer and found that the photocatalystic efficiency was effectively enhance.