Length and Diameter Control of Ultrathin Nanowires of Substoichiometric Tungsten Oxide with Insights into the Growth Mechanism

Tungsten oxide ultrathin nanowires have potential applications in electrochromic devices, dye sensitized solar cells, gas sensors, and as photocatalysts. Herein, we report a synthesis for solution phase ultrathin nanowires with independent control over the length and diameter. W(CO)6 is used as the tungsten source, and the solvents octadecanol and octadecene are used. Morphological control is obtained by varying the ratios between these three components as well as reaction conditions such as time and temperature. Such precise synthetic tuning will enable future investigations on the role of the aspect ratio and diameter for the above-mentioned applications. We can infer from experimental data a plausible nucleation pathway that involves the formation of tungsten alkoxide clusters. Raman spectroscopy, X-ray photoelectron spectroscopy, electron microscopy, and X-ray and electron diffraction are used to characterize the nanowires, and the results indicate the phase to be a crystallographic sheer structure, such as W20O58.