Study, investigate and fabricate optical nanostructures and devices using advanced techniques and novel materials

Rashid, Ijaz ORCID: 0000-0001-5502-1392 (2020). Study, investigate and fabricate optical nanostructures and devices using advanced techniques and novel materials. University of Birmingham. Ph.D.

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This thesis covers studies on nano-photonic bandgap structures and devices inspired from nature, with the potentials to be used as filters and smart sensors such as hydrogel based photonic bandgap sensors for detection in various industries including medical applications, food and cosmetics. Research was conducted on two samples of feathers that exist in nature namely Nicobar pigeon and Monal pheasant bird species in order to study the structural colouration originating from the internal barbule nanostructures. The structural colouration of these species have not been studied or reported anywhere else before. Optical microscopy and spectroscopy measurements were performed showing a variety of colours observed with change in illumination and viewing angle. The variation in colour observed is reflected by red, green and blue photonic bandgap structures present in the internal structure of the feathers. Hydrophilic and Hydrophobic properties of the optical material were also investigated. Contact angle measurements were performed resulting in ~ 156° in the case of Nicobar pigeons demonstrating it to be super hydrophobic whereas a contact angle of ~ 120° was recorded in case of Monal pheasant. Feathers were also immersed in different liquids and the spectral shifts were recorded and analysed which were correlated with the refractive indices of these liquids. The structural colouration in Nicobar pigeon and Monal pheasants can be mimicked for applications such as colour filters, non-reflecting coating, bio sensors, photonic bandgap hydrogel sensors and sensors based on refractive indices used in food, medical, health monitoring and cosmetic industries.
To support the theory, a simple silica thin film grating structure was designed using silicon and silicon dioxide having different refractive indices. The structure was simulated with variation of various parameters in order to get the best colour change. Two samples were successfully fabricated for testing and confirmation purposes. Both concepts of thin film and diffraction grating were in combination and the mechanism was studied in detail. Titanium nanostructures were also fabricated with varied dimensions in size using laser interference ablation method in order to study the interaction of a liquid droplet with nanostructures. The change in hydrophobicity with respect to change in nanostructure size was captured, analysed and studied in detail. A surface profile with large spacing and size in nanostructures prevents the absorption on the surface with availability of wider channels for the liquid’s excessive flow allowing very low contact angles whereas very narrow and smaller size of nanostructures allow no wettability with ability of nanostructures to hold the liquid drop resulting higher contact angles.
The main focus was to explore more on photonic bandgap structures that exist in nature and have not been investigated and suggest their possible use in applications such as integration in hydrogel based photonic bandgap sensors to enhance fast and facile fabrication with simple detection methods using change in physiological conditions of the photonic bandgap structure integrated in the hydrogel.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Engineering
Funders: Wellcome Trust
Subjects: Q Science > Q Science (General)
Q Science > QC Physics


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