Tuning Surface Wettability of InxGa(1–x)N Nanotip Arrays by Phosphonic Acid Modification and Photoillumination

Abstract

We report a facile route to reversibly tune surface wettability of In_xGa_(1–x)N (InGaN) nanotip arrays by octylphosphonic acid (OPA) modification and ultraviolet–visible (UV–vis) light illuminations. Well-aligned InGaN nanotip arrays were grown by chemical vapor deposition (CVD). OPA was covalently attached to the InGaN nanotip surface, which was initially oxidized in Piranha solution. Because of the high surface energy of polar groups, OPA-coated InGaN nanotip arrays demonstrated superhydrophobic properties (contact angle of 154°). Transitions between superhydrophobicity and hydrophilicity were obtained through OPA adsorption and UV–vis light illumination. The InGaN nanotip surface chemistry was further characterized by X-ray photoelectron spectroscopy (XPS), which suggested a scission mechanism at P–C and MO–P (M = In and Ga) bonds of bound OPA molecules. Meanwhile, no significant surface degradation was observed after the OPA modification and phototreatments.