Nanoscale details of liquid drops on 1D patterned surfaces revealed by etching

Abstract

This paper reports the wetting properties and spatially dependent etch rate variation on the interaction of a dilute potassium hydroxide (KOH):water droplet with a nanopatterned one-dimensional, 500-nm period, grooved photoresist surface. The KOH liquid drop showed a hydrophilic contact angle both along and perpendicular to the grooves and a more significant elongation distortion as compared to a deionized water drop. From the etching of the photoresist lines by the KOH solution, monitored by SEM after the drop was removed, the droplet was in a Cassie–Baxter state with the liquid excluded from the grooves and was pinned at the edge of the grating lines. The etch rate varied with the evaporation rate of the droplet and showed a dependence on the local contact angle with faster etching for smaller contact angles.