Controlled fabrication and electrowetting properties of silicon nanostructures

Electrowetting on dielectric is of particular interest in various applications including digital microfluidics, optics, displays and in analysis of biological samples. In this paper, Ag-assisted etching of silicon has been used to prepare superhydrophobic surfaces that may add unique properties to such devices. The porosity is controlled by controlling the size of the Ag deposited on the surface. Etching is carried out in HF/H2O2 solution. From the SEM images, the small-sized Ag particles are found to produce a very porous irregular surface, while the larger Ag-sized particles deposited resulted in regular vertical nanostructures. The fabricated surface was chemically modified with fluoro alkyl silane to make it superhydrophobic. Wetting behaviour was studied by measuring the contact angle and contact angle hysteresis. The contact angle measured was greater than 150° and contact angle hysteresis was less than five. Electrowetting was studied by applying DC voltage between the droplet and silicon substrate.