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|Issue Date: ||2009-12-30 13:44:50 (UTC+8)|
|Abstract: ||本計畫成功地利用反應性DC/RF電漿共濺鍍法與化學水浴法成長含S系列之可見光光觸媒薄膜，探討製備參數對光觸媒薄膜基本特性及其功能性之影響。第1年研究成果為利用反應性DC/RF磁控共濺鍍法(Reactive DC/RF co-sputtering)，在氬氣與反應性氣體硫化氫的氣氛下共濺鍍銀銦鋅靶，沈積AgIn5S8-ZnS之可見光光觸媒薄膜於載玻片、ITO玻璃之基材上。沈積結果分別由PL-螢光光譜儀、XRD、電性量測儀等對於沈積之薄膜進行表面結構、物性、功能性的測試，經由結果分析各沈積參數與薄膜性質之關係，以歸納出最佳的製程操作參數。藉著濺鍍功率DC/RF＝50/50、基板溫度300 ℃和氣體流量Φ＝0.4之最佳操作參數，可以製備出Eg（Energy band gap）在2.3~2.4 eV之間的光觸媒薄膜，薄膜之結構由XRD可以得AgIn5S8、ZnS之結晶相。並且在施加1伏特之偏壓，300 W之氙燈照射下，可以產生最大光電流為12.96 mA。第2年研究成果為採用經濟、可成長大面積薄膜、操作簡單之化學水浴沉積法(Chemical Bath Deposition, CBD)，於酸性條件下成長Ag-In-S三系列之半導體光觸媒薄膜在導電玻璃上，改變操作參數(鍍膜次數、藥劑濃度等)，以獲得有效提昇AgIn5S8半導體薄膜光電流效率之操作條件。第3年研究成果為於鹼性條件下成長Ni-doped ZnS在導電玻璃上，改變操作參數(Ni藥劑濃度)，探討Ni-doped ZnS薄膜的成長機制。歸納以上結果可以得知，利用反應性共濺鍍法或化學水浴法，可以製備出高品質、大面積和均勻性佳之薄膜，非常適合於光觸媒薄膜製備之應用。
Ag and In-doped ZnS thin films were prepared by direct current and radio frequency reactive co-sputtering of a zinc target and an indium target covered by Ag wires in gas mixtures of argon and hydrogen sulfide. The influences of the various deposition parameters on the structural, optical and electrical performances of thin films as visible-light-active photoelectrodes have been investigated. The X-ray diffraction data revealed that the polycrystalline (Ag, In, Zn)S thin films contain mixed structures of AgIn5S8 and ZnS. The images from an atomic force microscopy showed that the surface roughness was significantly increased with incremental increases of plasma power, resulting in increases of the refractive index and the reduction in photocurrent. The film deposited in the optimal deposition parameters, DC and RF powers at 50 W using a hydrogen sulfide ratio of 0.40 with a substrate temperature of 300 °C, exhibits the smallest refractive index, highest donor density, and the highest photocurrent density under illumination with a solar simulator (AM 1.5) at +1.00 V vs. Ag/AgCl. The band-gap energies of as-prepared films are found to be in the range of 2.28 to 2.39 eV and flat-band potentials determined by application of the Mott–Schottky equation vary from −0.55 to −0.68 V versus normal hydrogen electrode.
The AgIn5S8 polycrystalline films were grown on indium–tin-oxide-coated glass substrates by using chemical bath deposition. New procedures for the growth of AgIn5S8 films are presented. The solutions containing silver nitrate, indium nitrate, triethanolamine, ammonium nitrate and thioacetamide in acidic solution were used for the growth of AgIn5S8 film electrodes. The influences of various deposition parameters on structural, optical, and electrical performances of films have been investigated. The X-ray diffraction patterns of the samples demonstrate the presence of polycrystalline structures of AgIn5S8 phase in these films and show AgIn5S8 phase is the major crystal structure. With different substrates, the different crystal structures were obtained. The thickness, band gaps and carrier densities of these samples determined from transmittance spectra and electrochemical analysis are in the range of 647–1123 nm, 1.70–1.73 eV and 4.02×l014–6.36×l014 cm−3, respectively. The flat band potentials of these samples are located between−0.293 and−0.403V versus normal hydrogen electrode with the Mott-Schottky measurements. The conduction bands and valance bands of films determined from flat band potentials are in the range of −0.517 to −0.618 V, and +1.213 to +1.082 V versus normal hydrogen electrode. The maximum photocurrent density of samples prepared in this study with external potential kept at 3.5V was found to be 6.0 mA/cm2 under the illumination with white light intensity kept at 100 mW/cm2.
Undoped and Ni-doped ZnS photoelectrodes, (x = 0-0.01), were prepared by using the process of chemical bath deposition. X-ray diffraction patterns of hexagonal wurtzite structure with preferential orientation along the (008) plane appeared on undoped ZnS films. An increase in the molar ratios of Ni in the starting solution resulted in a decrease in the intensity of the (008) and the formation of nickel chalcogenide (NiS). Images from a scanning electron microscope revealed a drastic change of the surface morphology of the Ni-doped ZnS film due to ion-by-ion deposition. The absorption spectra of films showed a red shift as the value of x increased, and the energy band gaps of the Ni doped ZnS films shifted to lower energy levels between 3.34-3.01 eV. Moreover, increasing the Ni ratio lead to a shift in the flat-band potential of the film towards a more positive value compared to that of ZnS. It was shown that the Ni-doped ZnS films experienced a type conversion from the n-type to the p-type when the molar ratios of Ni changed from 0.003 to 0.005. The photocurrent densities of Ni-doped ZnS film (x = 0.003) reached 3.74 mA/cm2 at an external potential of 1.5 V versus a Pt electrode and exhibit a three-fold enhancement of photocurrent density compared to naked ZnS. A cathodic photocurrent of 0.82 mA/cm2 at an external potential of -1.5 V was obtained for the Ni concentration at x = 0.005.
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