Effect of growth time on structural, morphological and electrical properties of tungsten oxide nanowire

In this work, tungsten oxide nanowires were grown directly on a tungsten substrate in 800 degrees C using thermal evaporation method in a horizontal tube furnace. The effect of growth time on structural, morphological, elemental composition and electrical properties of the tungsten oxide nanostructures was investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) technique and KIETHLEY 2361 system. Our experimental results show that tungsten oxide nanowires crystalline phase, electrical conductance and density on the substrate surface depend on the growth time. The XRD results showed that tungsten oxide nanowires are synthesized with a cubic WO3 structure. Moreover, the lattice strain, grain size and dislocation density were obtained in three different growth time. It is noteworthy that by increasing the growth time the crystallinity increases. The FESEM images at different growth times showed that the nanowires on grains begin to germinate when the growth time increases to 6 h. At this time, nanowire structures with 1 mu m in diameter and 40 mu m in length were formed and continued to grow which caused a change in the morphology. In addition, the XPS results showed that the sample that has grown at longer growth time exhibit two asymmetric W4d5/2 and W4d3/2 peak at 252 and 263 eV which can be assigned to W5+ and W4+ species, respectively. Moreover, the linear I-V curves are obtained and it is found that by increasing the growth time, the conductivity of the sample increases due to increasing number of wires on the sample surface. Finally, the conditions and mechanism of WO3 nanowire growth are discussed. The results can be used to guide a better understanding about the growth behavior of WO3 nanowires and can contribute towards the development of novel nanodevices.