Tuning the Wettability of Indium Oxide Nanowires from Superhydrophobic to Nearly Superhydrophilic: Effect of Oxygen-Related Defects

Herein, the preparation of indium oxide nanowires (IO NWs) having superhydrophobic to nearly superhydrophilic water wetting capability without using any chemical coating is demonstrated. The oxygen-related defects strongly determine the giant variation in water wetting on IO NWs. It is found that the oxygen-rich IO NW surfaces are more favorable for wetting with water. The IO NWs were synthesized under three different ambient growth conditions, namely, oxidizing (IO_W), inert (IO_Ar), and reducing (IO_H-2), by using a chemical vapor deposition system. The deposition parameters were calibrated to obtain nanowire morphology. The observed static water contact angles were 8 degrees +/- 5 degrees, 134 degrees +/- 4 degrees, and 168 degrees +/- 2 degrees for the IO_W, IO_Ar, and IO_H2 samples, respectively. The effect of oxygen-related defects on the wettability of IO NW surfaces has been examined by photoluminescence, Fourier transform infrared spectroscopy, and electron paramagnetic resonance spectroscopy measurements. The results presented herein show that the oxygen-deficient IO NWs show superhydrophobic behavior, whereas stoichiometric IO NWs show nearly superhydrophilic nature. In addition, the ultraviolet light induced wetting transition from hydrophobic to hydrophilic is also studied.