Preparation and comparison of standard and mesoporous $WO_3$ films

Abstract

In this study, standard and mesoporous sol-gel$ WO_3$ thin films were prepared by a spin coating technique from an ethanolic solution of tungsten hexachloride$ (WCl_6)$. Different types of polymers -were employed as d template to generate the mesoporous structure. These polymers: (BASFTM Pluronic $p_{123}$) $(p_1)$, poly(ethylene glycol) $(p_2)$, polyethylene glycol-ran-propylene glycol $(p_3)$ and polystyrene-co-allyl-alchl $(p_4)$. To avoid the varying degrees of crystallinity as a result of thermal treatment, a UV illumination method has been employed to remove the polymer surfactant. This room temperature approach uses ozone generated during UV illumination in air to oxidize the organic compounds. The electrochromic and optical properties of the mesoporous films are described and compared to standard sol-gel $WO_3$ films. Results are also presented on the samples prepared by thermal treatment. We demonstrate that the UV illumination treatment is a superior method to remove templates which enables us to more effectively investigate the effect of mesoporosity on the electrokinetics of ion insertion into $WO_3$ films. These mesoporous materials exhibit superior high rate ion-insertion performance when used as electrochromic layers, which is attributed to the high surface area of mesoporous$ WO_3$. The films were characterized by using transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), ellipsometre and cyclic voltammetry

Özet

Bu çalışmada, standart ve gözenekli $WO_3$ filmler, başlangıç malzemesi olarak tungsten hekzaklorit $(WCl_6)$ ve ethanol kullanılarak sol-gel yöntemlerinden olan döndürme tekniğiyle hazırlanmıştır. Gözenekli tungsten oksit filmler, tungsten oksit solune dört farklı tip polimer eklenerek kaplanmıştır. Söz konusu polimerler: (BASFTM Pluronic $p_{123}$) $(p_ ı)$, poly(ethylene glycol) $(p_2)$, polyethylene glycol-ran-propylene glycol$(p_3)$ ve polystyrene-co-allyl-alchl $(p_4)$ dır. Bu polimerler kullanılarak gözenekli$ WO_3$filmler hazırlanmış ve filmlerin optik, yapısal ve elektrokronik özellikleri standart $(s_1) WO_3$ filmler ile kıyaslanmıştır. Filmlerden UV aydınlatma yöntemi ile polimer kalıpların uzaklaştırılması başarılmıştır. Aynı zamanda UV aydınlatma işlemi uygulanmış tungsten oksit filmlerin renklenme etkinliği değerlerinde düzelme gözlenmiştir.