Synthesis of tungsten oxide nanostructures by laser pyrolysis

Abstract

Since the proposal to synthesise materials by laser assisted pyrolysis in the 1970s, and its practical realisation in 1982, a number of researchers have used this method in obtaining nano-powders from liquid droplets. This study revisits this technique by introducing a new aspect in that it considers obtaining thin films rather than powders. A full experimental arrangement, including laser optimisation, optical layout and materials processing procedures is described. Synthesis of WO 3 nanostructures by this method is reported for the first time, with the mean diameter and length determined to be 51 nm and 6.8 µm, respectively. A possible mechanism for production of such nano structures is proposed owing to the selective dissociation of the O-C bonds in the tungsten ethoxide precursor liquid which resonate with the 10.6 µm emission wavelength of the CO 2 laser employed.

Progress in Ultrasonic Spray Pyrolysis for Condensed Matter Sciences Developed From Ultrasonic Nebulization Theories Since Michael Faraday

“…The Ostwald's ripening observed here should be distinguished from the opposite effect which was observed recently and reported in Mwakikunga et al [55,[243][244][245][246][247]333,511].…”

“…One-dimensional growth from spheres of WO 3 which transform themselves into W x O y nanowires after thermal annealing at 500 o C in argon for 17 hours [Ref. [243][244][245][246][247]333,511] has been observed. Recently dense one-dimensional nano-ribbons of VO 2 grown by USP at 700 o C in argon carrier gas without the need for thermal annealing [ Fig.…”

Flame temperature trends in reacting vanadium and tungsten ethoxide fluid sprays during CO2-laser pyrolysis

“…The final "equilibrium" temperature of molecules that are entrained into a CO 2 laser beam found either by letting t → ∞ as can be seen in (6). In a typical experiment, the equilibrium is reached in a fraction of a second after the laser beam is switched-on as will be shown in the experimental sections that follow.…”

“…The first laser pyrolysis experiments (named differently then) with the CO 2 laser tuned at its 10P 20 line of wavelength 10.59 µm are known to have been first performed by Bachmann [5] between 1974 and 1975. Laser pyrolysis of vanadium and tungsten compounds, in our group, has led to very interesting nanostructures-nanowires of WO 3 and nanobelts of VO 2 [6][7][8][9]. These nanostructures were obtained without the knowledge of the temperature of processing as has been the case with many reports on laser pyrolysis.…”

“…These cooling rates are the radiation and convection heat loss rates given in the previous sections. 6 form after a few weeks when left at room temperature. When the CO 2 laser photons of frequency ω emits light they exert forces on a group of electrons as illustrated in Figs.…”