| Description |
An in-depth analysis of the 4-step sol-gel deposition process for thin films consisting of 1) dip-coating 2) rapid solvent evaporation 3) brief thermal treatment and 4) shock-cooling was performed. Bragg stacks consisting of alternating silica and titania layers were prepared and the versatility of the process was exhibited by preparing samples of varying layer thickness with reflection bands spanning the entire visible range. Post-synthetic thermal annealing was found to increase the crystallinity of the titania films while resulting in a blue-shift of the main reflection peak due to titania layer shrinkage. The photo-stability of these Bragg stacks was investigated by laser-induced damage threshold studies. Results obtained by optical microscopy, reflectance spectroscopy, and SEM imaging showed that Bragg stacks annealed at higher temperatures exhibit a decrease in damage threshold as a result of increased interlayer stress, suggesting that interfacial properties rather than the quality of individual layers are more important for determining stability of Bragg stacks under intense laser irradiation. This is an important result, as it shows that it is beneficial to forego the final thermal annealing step often employed when fabricating Bragg stacks, leading to a decrease in overall energy cost and an increase in throughput for the synthesis of Bragg-type optical components. A new “additive-free†sol-gel technique featuring simple reactants and reactant conditions was developed to deposit various iron-based oxide films on silicon and quartz substrates. The reactant concentrations were carefully tuned to control the hydrolysis and condensation rates of iron salts to synthesize a homogeneous iron oxide sol. Single-phase films including α-Fe2O3, YIG, CoFe2O4, and NiFe2O4 were obtained after thermal annealing and exhibited a high level of crystallinity by XRD analysis. The magnetic properties were investigated by VSM and showed very good magnetic ordering. The thickness of the deposited films was tuned by adjusting the precursor and reactant concentrations as well as repeating the deposition cycle using the same solution. Composition analysis was performed by XPS and confirmed the oxidation states and ratios of ions present in the films were in excellent agreement with the expected results. |
