Synthesis of Nanostructured Tungsten Oxide Thin Films: A Simple, Controllable, Inexpensive, Aqueous Sol−Gel Method

Abstract

Among the available metal oxide nanostructures, tungsten oxide has remained, at times, troublesome to fabricate, with many synthetic methods often requiring exotic equipment and or reagents. In this work, we present a systematic investigation demonstrating a new method for the deposition of anhydrous and hydrated nanostructured tungsten oxide thin films via spin coating. The attributes of these materials include the following: high surface area, controllable deposition, and compatibility with existing semiconductor fabrication infrastructure making this method a suitable candidate for application in the manufacture of gas sensors and dye sensitized solar cells. We will show that it is possible to form micrometer thick highly crystalline nanostructured thin films and, using Raman, SEM, XRD, XPS, and TEM analysis, will prove that these nanostructures can be rendered into anhydrous or partially or fully hydrated tungsten oxides. We further demonstrate the application of these materials in the fabrication of an inexpensive NO2 gas sensor, capable of sensing sub-ppm levels of NO2 concentrations at a modest operating temperature of 175 °C.

High electrochemical activity from hybrid materials of electrospun tungsten oxide nanofibers and carbon black

“…Figure 2b shows the typical Raman spectrum of the WO 3 nanofibers, where all the arisen peaks well matches those of the monoclinic and triclinic phases [44]. According to the literatures [45,46], the peaks below 200 cm -1 can be ascribed to the lattice modes related to the collective motions of the WO 6 octahedrons and that in 200-500 cm -1 and above 500 cm -1 originate from O-W-O bending modes of the bridging oxygens and W-O stretching modes in the WO 6 octahedral units, respectively. The characteristic peaks for the monoclinic and triclinic phases appear at 32 and 42 cm -1 [34,44], respectively, while their high frequency modes ([200 cm -1 ) are almost identical [44].…”

Electrical and optical properties of mixed phase tungsten trioxide films grown by laser pyrolysis

“…Our XRD diffractogram was also compared against the ICCD database and was found to match best with sodium tungstate compound (PDF number 01-080-2471). The sodium tungstate phase was confirmed by the weak Raman shift at 915 cm -1 [26] for spot 2 in Figure 2.…”

“…2.1 Vibrational and structural analysis Raman and XRD analysis of tungsten trioxide have been reported numerous times [22][23][24][25][26], and despite the simple stoichiometry, the structure is very complex [27][28][29]. Raman spectroscopy was done on two areas of the sample as denoted by spot 1 and spot 2 of the Raman image shown in the inset of Figure 2.…”

“…The XRD diffractogram in Figure 3 was compared to [26,[37][38][39] and indicates peaks of hydrated, hexagonal phase WO 3 , tetragonal phase WO 3 and sodium tungstate. It is noted here that to get an idea of the crystallite size in our sample to correlate with SEM micrographs, Scherrer's formula [40][41] was applied to the peaks in our diffractogram.…”

Facile synthesis of WO₃·H₂O square nanoplates via a mild aging of ion-exchanged precursor

“…Then, the intermediates condense to form a [WO 5 (OH 2 )] octahedral layer through oxolation reaction along to the equivalent a-and c-directions, i.e., along to {010} plane. 15), 19) The [WO 5 (OH 2 )] octahedral layers are bonded to each other by hydrogen bonds between the terminal oxygen and coordinated water molecules in neighboring layers, leading to the formation of a layered and platelet WO 3 ·H 2 O structure. From the above consideration, the present aging temperature definitely promotes the two-dimensional oxolation reaction, i.e., extending [WO 5 (OH 2 )] octahedral layer which cause the formation nanoplatelets.…”