以直流磁控及高功率脈衝磁控濺鍍之TiO2光觸媒薄膜的特性分析比較

Abstract

本研究以TiO2半導體材料為靶材，分別使用直流(direct current, DC)磁控濺鍍及高功率脈衝磁控濺鍍(high-power impulse magnetron sputtering, HiPIMS)沉積TiO2光觸媒薄膜，於無鹼玻璃(non-alkali glass)及可撓性塑膠(Polyethylene terephthalate, PET)基材。以田口實驗設計(Taguchi methods)，L9直交表(Orthogonal arrays)配合變異數分析，探討TiO2光觸媒沉積參數(直流功率、濺鍍壓力、基板溫度、沉積時間)對薄膜的沉積速率、亞甲基藍(Methylene Blue, MB)降解程度、水滴接觸角(親水性)、抗菌效果等特性。使用AFM、SEM、及XRD探討TiO2薄膜的表面型態、微結構及結晶性質。 為防止氧化物靶材(oxide targets) 於濺鍍時產生靶中毒，因此皆以射頻為薄膜沉積的電源。但是氧化物靶材只要有合理的導電性，就可以使用DC磁控濺鍍，TiO2陶瓷靶為半導體材料(導電率約0.3 Ω cm)，對於DC電源有足夠的導電性，不會產生靶中毒現象。TiO2陶瓷靶使用DC磁控濺鍍，優點為沉積層容易控制，可有效提昇薄膜沉積速率，且薄膜有良好的附着性及均勻性。此外TiO2光觸媒薄膜需在高溫或高能量製程，才可獲得銳鈦礦(anatase)與金紅石(rutile)結構。因此，若將TiO2光觸媒薄膜，以直流(DC)磁控濺鍍沉積於PET塑膠基板，因塑膠無法耐高溫，TiO2薄膜無法獲得足夠能量成長，所以其光催化效果不顯著。本研究使用高功率脈衝磁控濺鍍(HiPIMS)，屬於低溫電漿製程，基板不需加熱，就能使薄膜獲得足夠能量。高功率脈衝磁控濺鍍(HiPIMS)藉由調整脈衝中斷時間，將能量累積於電容，瞬間釋放出來，使靶材原子獲得更強大的能量濺射到基板，增加薄膜的緻密性、附著力與晶體結構，解決傳統磁控濺鍍於耐熱性低的基材，不易製作TiO2光觸媒薄膜的問題，研究顯示使用HiPIMS可以有效提昇TiO2光觸媒薄膜沉積於PET塑膠的光催化效果。

In this study, TiO2 photocatalytic thin films were deposited on non-alkali glass and polyethylene terephthalate (PET) substrates, by means direct current (DC) sputtering of and high-power impulse magnetron sputtering (HiPIMS), using a ceramic TiO2 target in an argon gas environment. The Taguchi method with orthogonal array, signal-to-noise ratio and analysis of variance were employed to study the performance characteristics. The experimental studies were conducted under different powers, sputtering pressures, substrate temperatures, and deposition time. Effects of coating parameters on the structural, surface morphology, and photocatalytic activities of the TiO2 thin films were investigated. We performed the photoinduced decomposition of methylene blue (MB), photoinduced hydrophilicity and antibacterial under UV light illumination. The films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV-vis-NIR spectroscopy. Oxide targets can be used in DC operated magnetrons, provided they are reasonably electrically conducting. The TiO2 ceramic target was a semiconductor having a sufficient conductivity of approximately 0.3 Ωcm as a target for DC sputtering. The DC magnetron sputtering from TiO2 ceramic targets can be readily controlled and the deposited layers show good adhesion as well as good coating uniformity. Crystallite films can grow through substrate heating. High substrate temperature results in good crystalline structure, whereas low substrate temperature leads to amorphous TiO2 structure. The HiPIMS is a recently developed sputtering technique, where very short and intense pulses are used. The plasma density near the target increases enough to ionize a significant proportion of the sputtered metal ions, to improve thin film adhesion, density or texture. The experimental results show that using the HiPIMS improved the photocatalytic characteristics of the TiO2 films deposited on PET substrates.