Immobilizing a drop of water: fabricating highly hydrophobic surfaces that pin water droplets

We describe the fabrication of a patterned, hydrophobic silicon substrate that can pin a water droplet despite its large contact angle. Arrays of nm tips in silicon were fabricated by reactive ion etching using polymer masks defined by photolithography. A droplet sitting on one class of these substrates did not fall even after the substrate was turned upside-down. The production allows the fabrication of large arrays of tips with a one-step simple etching process, along with silanization, to achieve a substrate with both very large contact and tilting angles.