Superhydrophobic sputtered Al2O3 coating films with high transparency

Summary form only given. Antireflection, self-cleaning coatings are widely used in various applications such as display panels, solar cells and optical lenses [1]. Many surfaces in nature are highly hydrophobic, making the deposition of a water drop almost impossible. Examples include the wings of butterflies and the leaves of plants. The best known illustration of a self-cleaning surface is indubitably that of the leaves of the lotus plant (Nelumbo nucifera) [2]. The key feature of the lotus leaf is a microscopically rough surface consisting of randomly distributed arrays of micropapillae with length-scale ranging from 5 to 200 microns. In order to obtain this biomimetic surface, several approaches have been proposed mostly based on sol-gel method [3,4].We have prepared superhydrophobic and highly oleophobic Al2O3 coating on fused silica substrates by the sputtering method. Deposition conditions, thickness and density of the film play critical roles in establishing the omniphobic behaviour of the substrates. By choosing the right process parameters, it is possible to form a nanoflower like structure (Fig. 1 left) of 20nm to 50nm with enough porosity to affect the surface free energy. The size of the microstructure is too small to scatter visible light leaving the material to have high transparency, 96% (Fig. 1 right), while maintaining low haze <; 2%. With the addition of a fluoropolymer coating, the water repellency became superhydrophobic with a contact angle greater than 165°. The oleophobicity of the coatings was greater than typical fluoropolymer coatings on flat surface with a contact angle equal to 130°.The capability of having high transparency, low haze and a high degree of water and oil repellency creates a great potential for an anti-reflection coating on glass. More details about the preparation method, surface structure, optical transparency, mechanical tests and contact angle for water and hexadecane of superhydrophobic Al2O3 thin film microstructures on fused SiO2 substrates, will be presented at the Conference.