Thermal-Oxidative Growth of Substoichiometric WO3–x Nanowires at Mild Conditions

Abstract

Herein, the growth of substoichiometric tungsten oxide (WO3–x) nanowires (NWs) via thermal oxidation of W films (a few 10 to a few 100 nm thick) deposited by Ar-plasma sputtering on fluorine-doped tin oxide (FTO) substrates is reported. A thermal treatment at relatively low temperature (525–550 °C) in Ar at atmospheric pressure leads to the conversion of the W films into W suboxide (WO3–x) NW arrays. Such NWs have a length of ≈500 nm and their diameter ranges from 10 to 40 nm depending on the duration of the annealing process. These growth conditions for the formation of WO3–x NWs are significantly milder and more straightforward than those reported in previous literature. This avoids high temperatures (e.g., above 600 °C), vacuum conditions, or the addition of catalysts. A thermal-oxidative approach of these sputtered films is suitable to directly form WO3–x NWs on various surfaces, including conductive substrates to fabricate photoelectrodes or large-scale supports, e.g., for smart windows.