The influence of filament temperature and oxygen concentration on tungsten oxide nanostructures by hot filament metal oxide deposition

Abstract

Tungsten oxide (WOx) nanostructures were prepared by a hot filament chemical vapour deposition system and the temperature of the hot tungsten filaments was changed by steps of degrees. The morphology and average growth rate were indicated by scanning electron microscopy which showed that the morphology was highly related to the filament temperature (Tf) and the distance between the filaments and the polished Si (1 0 0) substrates (df). The influence of Tf on the crystalline nature was studied by x-ray diffraction and Raman spectroscopy. The evolution of stoichiometry and types of defects was indicated by x-ray photoelectron spectroscopy and slow positron implantation spectroscopy. When Tf was up to 1750 °C, tungsten oxide nanostructure was synthesized. A turning point of Tf was found at which the nature of crystallinity and of stoichiometry was the best. As Tf increased to 2100 °C or df decreased, the film crystallinity decreased; correspondingly, the component ratio of stoichiometry WO3 decreased and lots of vacancy agglomerates were present. In order to develop the chemical phase from substoichiometry to stoichiometry, the oxygen gas concentration in the mixture gas during deposition should be raised to an appropriate level.

Study of the Thermal Annealing on Structural and Morphological Properties of High-Porosity A-WO3 Films Synthesized by HFCVD

“…Regarding the WO 3 synthesis films through HFCVD, a wide variety of morphologies have been obtained by controlling the surrounding gas [23], deposition time, O 2 partial pressure [24], filament temperature [25], and substrate temperature [26]. For instance, Feng et al deposited WO 3 nanorods at 1400 °C under methane, hydrogen, and oxygen environments [23]; A. Jafari et al synthesized monoclinic WO 3 nanowalls onto silicon substrates at different temperatures (600, 700, and 800 °C) in 50 s under a mixture of argon and oxygen gases [27]; and S. Pal et al obtained nanostructured WO 3 films under hexacarbonyl or hexafluoride atmospheres [26].…”

Tungsten Oxide Nanopowders and Nanorods Prepared by a Modified Plasma Arc Gas Condensation Technique

“…5) Hence, the relationship between the O 2 defects and properties of WO 3Àx nanomaterials has been extensively studied. [6][7][8] Many studies have focused on the preparation of nonstoichiometric WO 3Àx nanomaterials with various morphologies, such as nanopowders, 9) nanorods, 10) nanowires, 11) microtubes, 12) and nanorod bundles. 13) In these studies, controlling the O 2 contents during WO 3Àx nanomaterials synthesis is a major concern.…”