Fabrication of transparent superhydrophobic surfaces via self-catalytic InOx nanoshells: a lithography-free approach

Abstract

Recently, transparent superhydrophobic surfaces have attracted significant attention for their potential applications in various optical fields. However, superhydrophobicity is typically associated with surface roughness, which is in contrast to transparency. To achieve both properties simultaneously, a specific surface structure is required, often necessitating patterning processes such as photolithography. In this study, we developed a transparent superhydrophobic surface with a water contact angle greater than 153.7° 1.6°, without the need for conventional lithographic patterning processes. The superhydrophobicity was achieved via a two-step process involving nanostructure formation and subsequent surface energy reduction through a self-assembled monolayer coating. We used indium, a low-melting metal that forms island-like deposits, and induced the self-catalytic growth of indium oxide through annealing in a controlled oxygen atmosphere. This approach, which involves the use of low-temperature heat treatment and the omission of patterning steps, has resulted in a straightforward and cost-effective method for fabricating transparent superhydrophobic surfaces. While vacuum deposition and plasma treatment are included, these steps rely on standardized large-area processing systems commonly used in display and photovoltaic industries. The omission of lithography significantly reduces process complexity and capital cost compared to conventional nanoscale structuring methods. The graded-index mechanism induced by the unique InOx nanoshell structure plays a crucial role in simultaneously enhancing both the optical transparency and the superhydrophobic properties. This results from the gradual variation in refractive index, which aids in preserving transparency while promoting superhydrophobicity. The fabricated transparent superhydrophobic surfaces have promising applicants in self-cleaning, anti-icing, anti-fogging and chemical shielding. Furthermore, our approach results in a visible light transmittance of 93.3% 0.1%, nearly identical to that of bare glass, showcasing the excellent transparency of the nanostructured surface.