Rapid formation of tungsten oxide nanobundles with controllable morphology

Tungsten oxide (W18O49) nanobundles with controllable morphology were fabricated on Si substrates within 5 min by microwave plasma-enhanced chemical vapor deposition (MPECVD). The crystal structure and chemical composition of these nanobundles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). The results of these characterizations confirmed the formation of W18O49 nanobundles with [0 1 0] as the major growth direction. SEM images showed that the nanobundles were several micrometers long with diameters of 20–500 nm. The morphology of the nanobundles can be controlled by simply adjusting the reaction times to the desired level; nanowires (diameter: 15–30 nm), nanorods (diameter: 40–60 nm), and nanoslabs (thickness: 30 nm) were formed at 1.5, 3, and 4 min, respectively. With an increase in reaction times, the nanobundles steadily increased in dimensions to form nanoslabs. Thus, our results indicated that MPECVD is highly effective and suitable for fabrication of various tungsten oxide nanobundles.