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Özgün Başlık
Titanyum Dioksit ve Çinko Oksitten Yansıtmayıcı Filtre Üretimi

Yazarlar
Durşen Saygın Hınczewskı, Fatma Z. Tepehan

Dergi Adı
İTÜ Dergisi C : Fen Bilimleri

Cilt
Kasım 2009, Cilt 7, Sayı 1, ss. 3-8

Anahtar Kelimeler
ZnO ; TiO2 ; sol-jel ; döndürerek kaplama ; yansıtmayıcı filtre

Özet
Sol-jel döndürerek kaplama yöntemiyle hazırlanmış TiO2 (titanyum dioksit) ve ZnO (çinko oksit) ince filmleri kullanılarak görünür bölgenin belli bir dalgaboyu aralığı için çok katmanlı yansıtmayıcı filtre elde edilmiştir. Filtre tasarımı ZnO / TiO2 / taşıyıcı / TiO2 / ZnO olarak gerçekleştirilmiş ve taşıyıcı olarak Corning 2947 camı kullanılmıştır. Filtredeki filmlerin optik özellikleri belirlenerek tek-katman film sonuçlarıyla kıyaslanmışlardır. Başka bir karşılaştırma, tek-katman filmler ile filtrenin yüzey pürüzlülükleri arasında yapılmıştır. Tek-katman ZnO filmi ve filtre içindeki ZnO filminin optik band aralığı değeri neredeyse aynı iken, TiO2 filminin optik band aralığı filtrede tekkatman TiO2 filmine göre oldukça yüksek çıkmıştır. Filtre içinde hem ZnO hem de TiO2 filmlerinin kalınlıkları tek-katman filmlere göre daha ince bulunmuştur. Ayrıca ZnO'te TiO2'e göre daha fazla incelme gözlemlenmiştir. Kırma indisi değerleri 550 nm dalgaboyunda TiO2 için tek-katmanda ve filtrede neredeyse aynı bulunmuştur, aynı durum ZnO için de geçerlidir. Tek-katman TiO2 ve ZnO filmlerinin yüzeyleri oldukça pürüzsüzken filtrenin yüzeyinin daha pürüzlü olduğu ortaya çıkarılmıştır ; yani ZnO filmi cam yerine TiO2 üstüne kaplandığında yüzeyi daha pürüzlü olmaktadır. Elde edilen filtrede, yansıtmanın minimumu 650 nm dalgaboyunda %0.808 değeri ile meydana gelmekte, ayrıca yansıtma, 635-665 nm dalgaboyu aralığı için %1'den, 585-720 nm için %4'den az çıkmaktadır. Sonuçta, sol-jel yöntemi kullanılarak elde edilen ZnO filminin, TiO2 filmiyle beraber yansıtmayıcı filtrelerde kullanılabileceği gösterilmiştir.

Başlık (Yabancı Dil)
The Production of an Antireflective Filter From Titanium Dioxide and Zinc Oxide

Anahtar Kelimeler (Yabancı Dil)
ZnO ; TiO2 ; sol-gel ; spin coating ; antireflective fitler

Özet (Yabancı Dil)
Antireflective filters are mostly used to increase the efficiency of solar cells. They vary from each other in their method of coating, the filter design, the materials that are used, and where their minimum occurs. In the present work, we coated TiO2 (titanium dioxide) and ZnO (zinc oxide) thin films through the sol-gel spin coating method to obtain an antireflective filter. First, single films were coated, producing a substrate / film system. The transmittance and reflectance of this system were obtained in the UV-visible region. The thicknesses, refractive indices and extinction coefficients of the films were determined. By choosing the appropriate film thicknesses and refractive indices needed for an antireflective filter in the desired wavelength region, the single films were combined to build filters with a ZnO / TiO2 / substrate / TiO2 / ZnO structure. Then the optical properties of the individual films in the multilayer stack were extracted and were compared to the single film results. The surface roughness of the single films was also compared to the filter's surface rouhgness. The experimental procedure involves sol preparation, coating of the films, and characterization methods. The sol-gel coating method was chosen for a variety of reasons : it is cheap to fabricate, there is minimal loss of material during coating, it is suitable for mass production, homogenous films can be obtained, and by changing the amount of the chemical components and coating parameters, one can get a desired film thickness. For the TiO2 sol, ethyl alcohol, titanium (IV) butoxide and acetic acid were used. 2-propanol, Zinc acetate dehydrate, diethanolamine and distilled water were used to prepare the ZnO sol. Both the single layer films and the filter were coated on Corning 2947 as a substrate. The films in the filter were coated at different rotation speeds and number of layers. All the sub layers were preheated at the same temperature with the same duration time, which was 1 min at 250oC. Finally the stack firing method was applied to the filter for 15 min at 450oC. As for characterization methods, the transmittance and reflectance of the single films and the filter were obtained through a UV-visible spectrophotometer. The thicknesses, refractive indices and extinction coefficients were determined by fitting to a modified Tauc-Lorentz model for the ZnO films and a Tauc-Lorentz model for the TiO2 films. The surface roughness of the single films and the filter was determined by atomic force microscopy. The characterization of the films and filter lead to the following results. The optical bandgap value of the TiO2 film was found to be 3.37 eV in the single layer and 3.53 eV in the stack. ZnO had a bandgap value of 3.25 eV in the single layer which shifted to 3.29 eV in the stack. Thus, the bandgap value of ZnO stays almost the same while the one of TiO2 increases by a substantial amount. The thickness value of TiO2 in the single layer was 168 nm and dropped to 157 nm in the stack. The ZnO film had a thickness of 111 nm for the single layer but 81 nm for the one in the stack. As a percentage of the single layer thickness, the reduction in size was larger for ZnO than TiO2. The refractive index of TiO2 at λ=550 nm in the single layer was 2.04 and 2.02 in the stack. The ZnO layer had a refractive index of 1.40 in the single layer and 1.38 in the stack. This shows that for both of the films, the indices in the stack and single layers stay almost the same, which allows the single layer properties to be useful in predicting the behavior of the stack. The root mean square roughness values for the single layer TiO2 and ZnO films are 0.5 and 5.2 nm, respectively. When the ZnO film is fabricated in the filter, its roughness value increased to 9.2 nm, which means that if the ZnO film is coated onto TiO2 instead of glass, its surface becomes slightly rougher. The filter had a minimum at λ=650 nm with 0.808% reflection. The reflection for the wavelength range 635-665 nm was less than 1% and for 585-720 nm it was less than 4%. To summarize, it is shown here that sol-gel-made ZnO films can be used in an antireflective filter incorporating a TiO2 layer.