This thesis outlines the fundamental aspects of various coating fabrication methods
as well as the fundamentals of thin films and coatings that are typically studied and
utilised to achieve high laser induced damage threshold (LIDT) properties. An overview
of the two different novel high energy electron cyclotron resonance ion beam sputter deposition (ECR-IBSD) setups used to fabricate the coatings are described, along with
the fundamental theory and setups of all the characterisation methods used for the
films discussed. The materials of interest were hafnium oxide (HfO2), scandium oxide
(Sc2O3), and different mixture percentages of these two materials with silica (SiO2).
The effects of the reactive and sputtering oxygen partial pressures on the structure,
stoichiometry, and optical properties of the HfO2 and Sc2O3 thin films were systematically
investigated. The amorphous structures of both films were determined using X-ray Diffraction. Energy-dispersive X-ray Spectroscopy and Rutherford Backscattering
Spectrometry were carried out for the composition and stoichiometry analysis, which
suggested the formation of over-stoichiometric films. The transmission and reflectance
spectra of the films were measured using a spectrophotometer, where the spectra were
analysed by an optical fitting software SCOUT, which utilises the model modified by
O'Leary, Johnson and Lim, to extract the optical properties of the films. In addition to
this study, by utilising a novel 24-beam ECR-IBSD system, mixed films of HfO2:SiO2
and Sc2O3:SiO2 with different mixture percentages were investigated. The as-deposited
mixed films were also found to possess an amorphous structure. The optical constants
of the mixed films were extracted in the same manner as those of pure HfO2 and Sc2O3
films. In addition to studying the films at as-deposited, the effects of post-deposition
heat treatment on the structure and optical properties of all the films were also investigated.
From this work, it was established that the influence of oxygen incorporation in pure
materials from an optical and structural perspective shows that ECR-IBSD provides
over-stoichiometric HfO2 and Sc2O3 films. From the HfO2 study, it was found that
both the refractive index and extinction coefficient decreased with the increase of the
oxygen content, whereas the bandgap energy increased. For Sc2O3 films, there was no
real correlation with changing the oxygen content during deposition on the optical properties, except for the OJL bandgap energy, which increased as the oxygen percentage
increased. The effects of annealing are as follows: the HfO2 films remained amorphous
after annealing to 500°C and became crystalline with a monoclinic structure after annealing to 700°C, whereas Sc2O3 films remained amorphous even after annealing to 900°C.
For mixed materials, this study focused on the influence of different mixture percentages
on the optical, structural, and LIDT properties of the films. The mixture materials filled
the values for the refractive index between the two pure materials, indicating that the
refractive index can be tuned by changing the mixture percentage, which is the case for
both HfO2:SiO2 and Sc2O3:SiO2 mixed films. The same results were also found for both
the extinction coefficient values and OJL bandgap energies of the mixed films, leading
to the ability to easily fabricate films with tunable optical properties. The structure of
the films in this study is as follows: in both cases, the films remained amorphous when
heat treated up to 700°C. As the annealing temperature reached 900°C, the mixed films
with less than 10% SiO2 became more crystalline. In addition to the heat treatment
study, LIDT testing was also carried out for these films, which provided unexpected
results, where the main damage morphologies suggest that the main types of damage
observed were absorption induced damage and pits due to inclusions. Laser damage is
very sensitive to contamination within the nanosecond regime, and a large amount of
discharge occurs inside the chamber during deposition, which leads to contamination of
the films, which can lower the LIDT values. For future studies, working towards different methods to mitigate the discharges during deposition is important, as this will provide a better understanding of the causes laser induced damage of the films fabricated by ECR within the nanosecond regime. Further discussion of future work and experiment utilising ECR-IBSD have also been presented in details.
Date of Award | 20 Aug 2024 |
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Original language | English |
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Awarding Institution | - University Of Strathclyde
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Sponsors | University of Strathclyde |
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Supervisor | Stuart Reid (Supervisor) & Terry Gourlay (Supervisor) |
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