Freeze Fracture Approachto Directly Visualize WettingTransitions on Nanopatterned Superhydrophobic Silicon Surfaces: Morethan a Proof of Principle.

Freeze fracturing is applied to make the wetting behaviorof artificiallynanopatterned Si surfaces directly visible. For this purpose, almosthexagonally arranged nanopillars of fixed areal density (127 μm–2) and diameters (35 nm) but varying heights (40–150nm) were fabricated on silicon. Measurement of contact angles (CAs)including hysteresis allowed to distinguish between the Wenzel (W)and the Cassie–Baxter (CB) states with droplets completelywetting the pillars or residing on top of them, respectively. Providingadditional depth contrast by evaporating the ice replica with thincarbon and (typically 3 nm) platinum layers under 45° allowedresolving 3D features of 5 nm within the ice replica. In this way,laterally sharp transitions from CB- to W-states could be revealed,indicating the formation of zero-curvature water surfaces even onthe nanoscale. [ABSTRACT FROM AUTHOR]