title: Freeze fracture approach to directly visualize wetting transitions on nanopatterned superhydrophobic silicon surfaces: more than a proof of principle.
abstract: Freeze fracturing is applied to make the wetting behavior of artificially nanopatterned Si surfaces directly visible. For this purpose, almost hexagonally arranged nanopillars of fixed areal density (127 μm(-2)) and diameters (35 nm) but varying heights (40-150 nm) 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 completely wetting the pillars or residing on top of them, respectively. Providing additional depth contrast by evaporating the ice replica with thin carbon and (typically 3 nm) platinum layers under 45° allowed resolving 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 on the nanoscale.
authors.affiliation: Institute of Solid State Physics, Ulm University, Ulm, Baden-Württemberg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Wiedemann
authors.forename: Alfred
authors.initials: A
authors.lastname: Plettl
authors.forename: Paul
authors.initials: P
authors.lastname: Walther
authors.forename: Paul
authors.initials: P
authors.lastname: Ziemann