Face-Selective Crystal Growth of Hydrothermal Tungsten Oxide Nanowires for Sensing Volatile Molecules

Here, we demonstrate the impact of tungsten precursor concentration on anisotropic crystal growth of hydrothermal tungsten oxide (WO3) nanowires. When varying the tungsten precursor concentration, we found two different critical concentrations for crystal growth on the (001) top plane and (100) sidewall plane of WO3 nanowires. A (001) plane-selective crystal growth is achieved by precisely controlling the tungsten precursor concentration in between these critical concentrations, while a crystal growth on the (100) plane tends to simultaneously occur above such a concentration range. Furthermore, the crystal growth rate on the (001) plane tends to be suppressed when the number density of nanowires increases due to competitive material supply between nanowires. The observed concentration dependence on nanowire growth can be interpreted in terms of a competition between the nucleation in solution and the crystal growth on the nanowire surface. The suggested mechanism offers a rational way to precisely control the nanowire structure and the number yield of nanowires. Using a single nanowire device composed of a structurally controlled WO3 nanowire, we demonstrate highly sensitive electrical molecular sensing of nonanal at 27 ppb.