Wettability and "petal effect" of GaAs native oxides

TL;DR

This paper investigates the reversible transitions between hydrophilic and hydrophobic states of GaAs native oxide surfaces under ambient conditions, revealing effects of surface treatment and storage on wettability.

Contribution

It uncovers unreported reversible wettability transitions of GaAs surfaces and links surface oxide chemistry with hydrophobic and hydrophilic behaviors.

Findings

Superhydrophilicity observed after oxygen plasma treatment

Reversible hydrophobicity achieved with HCl etching

Surface oxide state influences wettability transitions

Abstract

We discuss unreported transitions of oxidized GaAs surfaces between (super)hydrophilic and hydrophobic states when stored in ambient conditions. Contact angles higher than 90deg and high adhesive force were observed for several air-aged epitaxial samples grown under different conditions as well as on epi-ready wafers. Regardless of the morphologies of the surface, superhydrophilicity of oxygen-plasma treated samples was observed, an effect disappearing with storage time. Reproducible hydrophobicity was likewise observed, as expected, after standard HCl surface etching. The relation between surface oxides and hydrophobic/hydrophilic behavior is discussed.