Ms. Cheryl Suwen Law Profile

Cheryl Suwen Law

at Univ of Adelaide

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Publications (2)

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Proceedings Article | 2 January 2018 Paper

Fine tuning of transmission features in nanoporous anodic alumina distributed Bragg reflectors

Siew Yee Lim, Cheryl Suwen Law, Abel Santos

Proceedings Volume 10456, 1045659 (2018) https://doi.org/10.1117/12.2282250

KEYWORDS: Apodization, Photonics, Interferometry, Distributed Bragg reflectors, Refractive index, Aluminum, Optical filters

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This study introduces an innovative apodisation strategy to tune the filtering features of distributed Bragg reflectors based on nanoporous anodic alumina (NAA-DBRs). The effective medium of NAA-DBRs, which is modulated in a stepwise fashion by a pulse-like anodisation approach, is apodised following a logarithmic negative function to engineer the transmission features of NAA-DBRs. We investigate the effect of various apodisation parameters such as apodisation amplitude difference, anodisation period, current density offset and pore widening time, to tune and optimise the optical properties of NAA-DBRs in terms of central wavelength position, full width at half maximum and quality of photonic stop band. The transmission features of NAA-DBRs are shown to be fully controllable with precision across the spectral regions by means of the apodisation parameters. Our study demonstrates that an apodisation strategy can significantly narrow the width and enhance the quality of the characteristic photonic stop band of NAA-DBRs. This rationally designed anodisation approach based on the combination of apodisation and stepwise pulse anodisation enables the development of optical filters with tuneable filtering features to be integrated into optical technologies acting as essential photonic elements in devices such as optical sensors and biosensors.

Proceedings Article | 2 January 2018 Paper

Surface modification of nanoporous anodic alumina photonic crystals for photocatalytic applications

Siew Yee Lim, Cheryl Suwen Law, Abel Santos

Proceedings Volume 10456, 1045658 (2018) https://doi.org/10.1117/12.2282248

KEYWORDS: Photonic crystals, Sol-gels, Aluminum, Interferometry, Composites, Titanium dioxide

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Herein, we report on the development of a rationally designed composite photocatalyst material by combining nanoporous anodic alumina-rugate filters (NAA-RFs) with photo-active layers of titanium dioxide (TiO₂). NAA-RFs are synthesised by sinusoidal pulse anodisation and subsequently functionalised with TiO₂ by sol-gel method to provide the photonic structures with photocatalytic properties. We demonstrate that the characteristic photonic stopband (PSB) of the surface-modified NAA-RFs can be precisely tuned across the UV-visible-NIR spectrum to enhance the photon-toelectron conversion of TiO₂ by ‘slow photon effect’. We systematically investigate the effect of the anodisation parameters (i.e. anodisation period and pore widening time) on the position of the PSB of NAA-RFs as well as the photocatalytic performances displayed by these photonic crystal structures. When the edges of the PSB of surfacemodified NAA-RFs are positioned closely to the absorption peak of the model organic dye (i.e. methyl orange – MO), the photocatalytic performance of the system to degrade these molecules is enhanced under simulated solar light irradiation due to slow photon effect. Our investigation also reveals that the photocatalytic activity of surface-modified NAA-RFs is independent of slow photon effect and enhances with increasing period length (i.e. increasing anodisation period) of the photonic structures when there is no overlap between the PSB and the absorption peak of MO. This study therefore provides a rationale towards the photocatalytic enhancement of photonic crystals by a rational design of the PSB, creating new opportunities for the future development of high-performance photocatalysts.

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