INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 40 (2007) 192–197 doi:10.1088/0022-3727/40/1/014 Fabrication and characterization of ultra-water-repellent alumina–silica composite films Takahiro Ishizaki 1 , Nagahiro Saito 2 , Yasushi Inoue 1 , Makoto Bekke 3 and Osamu Takai 1 1 EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan 2 Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan 3 Department of Materials Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan E-mail: ishizaki@eco-t.esi.nagoya-u.ac.jp Received 5 July 2006, in final form 7 November 2006 Published 15 December 2006 Online at stacks.iop.org/JPhysD/40/192 Abstract Ultra-water-repellent (UWR) films were prepared by microwave plasma-enhanced chemical vapour deposition using trimethylmethoxysilane and aluminium (III) diisopropoxide ethylacetoacetate (ADE) as raw materials. The film was mainly composed of silica and alumina and was apparently transparent. The film thickness was approximately 500 nm. The sample surface was treated with an organosilane in order to introduce hydrophobic groups. The hydrophobic modification led to a water contact angle of more than 150 ◦ , whose value corresponds to the UWR surface. The hardness of film with an optimized Al content was significantly improved compared with that without Al. The maximum hardness was 1.71 GPa. In consequence, we successfully prepared an UWR film in the silica–alumina system. 1. Introduction Ultra-water-repellent (UWR) film has a water contact angle of more than 150 ◦ . The water drops on such a surface roll over and over. The characteristic is expected to be applied in various engineering productions such as eyeglasses, lenses and automobile windows [1]. The UWR property is governed by the chemical composition and geometrical structure of surface [2, 3]. A surface becomes more hydrophobic with a lowering of surface energy. As the simplest example, the surface covered with CH 3 - or CF 3 -groups has low surface energy and water repellent property [4]. However, the surface energy is insufficient to produce UWR films. A suitable roughness or surface texture is required for the UWR films [5–7]. Thus, methods to provide roughness to solid surfaces have been developed [8–17]. Many fabrication methods had been employed to fabricate the UWR surfaces [18–37]. In order to realize the above-mentioned applications, it is necessary for the UWR film to have good mechanical properties. We have successfully fabricated thin films with ultra-water repellency and high transparency by controlling pressures of organosilane and CO 2 gases in microwave plasma-enhanced chemical vapour deposition (MPECVD) [38]. However, in the previous study, water contact angles of the films were lowered with an increase in the hardness, and the ultra-water repellency was changed into water repellency. This was due to the decrease in surface roughness. We aim to fabricate an UWR thin film with high hardness and high transparency. In order to achieve this aim, we examined a composite material in the silica–alumina system. The alumina component would harden the UWR film without losing the ultra-water repellency and transparency [39–41]. In this research, we report on an UWR film with high hardness and transparency through MPECVD using trimethylmethoxysilane (TMMOS, (CH 3 ) 3 Si(OCH 3 )) and (ADE) (C 12 H 23 AlO 5 ) as raw materials. The water repellency and hardness of the films were discussed from the viewpoint of surface nanotextures, sliding angles and alumina content. 0022-3727/07/010192+06$30.00 © 2007 IOP Publishing Ltd Printed in the UK 192