Multifunctional Thin Films of Vanadium Oxides for Enhanced Energy Applications
Citation:
Ainabayev, Ardak, Multifunctional Thin Films of Vanadium Oxides for Enhanced Energy Applications, Trinity College Dublin, School of Physics, Physics, 2024Download Item:
Abstract:
This thesis deals with the growth, characterisation, and application of VO2
and V2O3 thin films. Various methods were employed to prepare and analyze
the VO2 and V2O3 films, aiming to explore the suitability of their properties
for potential applications.
A high-quality epitaxial ultrathin film M1-VO2 on c-plane Al2O3 was prepared
by pulsed laser deposition. The low deposition temperature and tuning
of the oxygen partial pressure during the growth process enable control over
the grain size and oxygen vacancy concentration. This facilitated controlling
the metal-insulator transition (MIT) parameters of the samples. It is demonstrated
that the high density of grain boundaries associated with nanosized
grains suppresses the thermal hysteresis of MIT. Simultaneous control over
the density of oxygen vacancies and the size of grains enables the adjustment
of the temperature coefficient of resistance, room temperature resistivity,
MIT temperature, sharpness, and thermal hysteresis toward suitable values
for the fabrication of efficient VO2-based uncooled bolometers. Compared
with other VO2 fabrication methods, this approach can be viewed as a simpler
alternative for VO2 fabrication with favorable properties for practical
bolometer applications.
It is demonstrated that simple, versatile, and easily scalable spray pyrolysis
(SP) is capable of producing M1-VO2 and V2O3 thin films of various
properties which is important considering the multifunctionality and wide
commercial applicability of M1-VO2 and V2O3 oxides. Epitaxial M1-VO2
thin film on c-Al2O3 was deposited by SP method via direct single-step
growth of M1-VO2 and via growth of V2O3 with the subsequent topotactical
transformation into M1-VO2 via post-annealing. The obtained M1-VO2
films exhibit MIT properties comparable to those obtained using other more
complicated growth methods such as molecular beam epitaxy (MBE), pulsed
laser deposition (PLD), or magnetron sputtering. The M1-VO2 samples obtained
by post-annealing V2O3 demonstrate improved surface roughness in
comparison to the direct growth approach. It was found that post-annealing
is better for tuning the oxygen content of M1-VO2, which can be useful for the
fabrication of M1-VO2 with various MIT behaviour. It appears that oxygen
concentration variation during growth changes the morphology of the deposited
samples. It is proposed that directly grown M1-VO2 samples? MIT,
electrical and thermoelectrical properties are influenced by the morphology
rather than oxygen concentration variation. This offers the potential applicability
of the M1-VO2 as near room temperature thermoelectric material
due to enhanced power factor values.
Further study revealed that SP-grown epitaxial V2O3 possesses p-type
conductivity. The deposited p-type V2O3 has measurable mobility and high
carrier concentration exhibiting excellent electrical performance for films deposited
by inexpensive chemical synthesis methods. The optical transparency
is on the lower side at higher thicknesses but improves at lower thicknesses.
The calculated transparent conductive oxide (TCO) related figure of merit
(FoM) of the p-type V2O3 thin films are highly competitive in comparison
to some other PVD deposited p-type TCOs. It is proposed that the electric
and optical performance of the V2O3 can be improved further by better
control over growth orientation and morphology. The ability of the SP to
produce high-quality epitaxial V2O3 with excellent electric and moderate optical
properties can be suitable for the fabrication of an active element made
of V2O3 facilitating the transport of photogenerated holes in solar cells.
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https://tcdlocalportal.tcd.ie/pls/EnterApex/f?p=800:71:0::::P71_USERNAME:AINABAYADescription:
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Author: Ainabayev, Ardak
Advisor:
Chvets, IgorPublisher:
Trinity College Dublin. School of Physics. Discipline of PhysicsType of material:
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