Direct synthesis of W18O49 nanorods from W2N film by thermal annealing

Abstract

Tungsten oxide nanorods were prepared from W2N film by a simple annealing method. W2N film was deposited on a Si( 100) substrate by chemical vapour deposition (CVD) at 450 degrees C, and then heating of the film at 600 - 700 degrees C produces a high density of tungsten oxide nanorods. The morphology, structure, composition and chemical binding states of the prepared nanorods were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), energy dispersive x-ray analysis (EDX) and transmission electron microscopy (TEM) measurements. XRD and TEM analysis showed that the grown nanorods were single-crystalline W18O49. According to XPS analysis, the W18O49 nanorods contained similar to 62% of W6+, similar to 28% of W5+, and similar to 10% of W4+. Field-emission measurements showed a low turn-on field of 9.5 V mu m(-1) for the W18O49 nanorods, indicating that they can be used as potential field emitters. Also, a synthesis reaction mechanism based on thermodynamics is proposed for the growth of tungsten oxide nanorods from W2N.