Water contact angles of vertically aligned Si nanorod arrays

The equilibrium water contact angles of vertically aligned nanorod Si films were measured by the sessile drop method. For as-deposited hydrophilic films, there was a contact angle transition from a rough surface to a 'hemi-wicking' porous surface at normal film thickness d = 500 nm; while for the HF treated hydrophobic films, a transition from a partially composite to a composite surface was observed at the same film thickness. The observed results can be reasonably interpreted within the framework of the classical Young theory.