Optical properties of vanadium oxide nanostructures synthesized by laser pyrolysis
Date
2012-02-28
Authors
Shikwambana, Lerato David
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Abstract
In this work, the primary investigation has been on the development of the laser
pyrolysis setup and its optimization for the synthesis of nano-size VO2-x films.
More specifically the focus was on making VO2-x depositions using various laser
pyrolysis parameters and establish in this way (1) an optimum laser wavelength
threshold for the photon induced dissociation of the molecular precursors while
the thermal contribution was kept minimal by using low power density (laser
energy of 30 W) and (2) the lower threshold for pure thermal contributions by
working with wavelengths far from resonance in order to minimize pure photon
induced contributions. The interest in synthesizing nano-size VO2-x materials
stems from the low metal-insulator transition temperature at near room
temperature with opto-electronic and thermo-electronic properties that can be used
in specialised applications.
A large number of samples were synthesized under various conditions and
annealed under argon atmosphere for 17 hours. XRD analysis identified the
VO2 (B) and/or β-V2O5 vanadium oxide phases characteristic for certain samples
grown under optimum conditions. Raman spectroscopy also confirmed these
vanadium oxide phases with bands observed at 175, 228, 261, 303, 422 and 532
cm-1. SEM analysis revealed a plethora of different nanostructures of various size
and shapes. The particles have a range of sizes between 55 nm to 185 nm in
diameter. The particles showed morphologies which included nano-rods, nanospheres
and nano-slabs. An interesting phenomenon was observed on the samples
synthesized with high power density, which was observed and reported by Donev
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et al. EDS analysis on the particles was also used to probe the elemental
composition of the sample. Optical studies were performed on the samples which
showed transitions in the visible and infrared region in accordance with the ones
observed in the international literature using different nano-synthesis methods.
Description
M.Sc., Faculty of Science, University of the Witwatersrand, 2011
Keywords
Vanadium, Nanostructures, Nanostructured materials, Nanotechnology