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    CMOS-compatible nanostructured colour filters for visible and near-infrared regions : a thesis presented in total fulfillment for the degree of Doctor of Philosophy in the Department of Mechanical and Electrical Engineering, Massey University
    (Massey University, 2022) Shaukat, Ayesha
    The human eye is sensitive to electromagnetic radiations with a wavelength range from 380 to 700 nm, and the mechanism of the eye’s colour filtering is emulated in colour image sensing devices. Today, image sensing devices can detect colour with distinct hue, brightness, and saturation characteristics. In contrast, spectral imaging filters are developed to perceive electromagnetic radiations, which the human eye cannot perceive. A spectral filter should ideally have narrow bandwidth, high transmission, and independence from incident and polarization angles of incident light. Most importantly, it should be compatible with current power saving CMOS technology for high throughput and cost-effectiveness. Unfortunately, such filters do not exist, and the replacement of pigment-based colour filters is still not realized. Therefore, new designs and materials need to be explored to address the current limitations. This thesis presents an all-dielectric cascaded multilayered thin film filter for near-infrared (NIR) filtration, which is helpful for spectral imaging applications. With preference to the CMOS compatibility, the material investigation is done through rigorous numerical simulations. Furthermore, the behaviour of the device is observed by varying thicknesses of layered films. This helped in finalizing a design comprised of only eight layers, consisting of amorphous silicon (A-Si) and silicon nitride (Si3N4), deposited successively on a glass substrate. Simulation results demonstrate a distinct peak in the NIR region with a transmission efficiency of up to 70 % and full width at half maximum (FWHM) is 77 nm. The results are angle insensitive up to 60◦ and show polarization insensitivity in Transverse Magnetic (TM) and Transverse Electric (TE) modes. The design is fabricated and tested at Australian National Fabrication Facility (ANFF). The physical and optical characterization including polarization insensitivity and angle invariance of the thin films are obtained through Spectroscopic Ellipsometry (SE), which shows practical relevance to the theoretical results with angle invariance up to 50◦. However, the thicknesses obtained through Scanning Electron Microscopy (SEM) are not helpful, and show discrepancies in the simulated and experimental results. The discrepancy is accredited to the same average atomic mass of the utilized materials. In addition, rigorous study of CMOS compatible materials led to the usage of tungsten (W) for the design of a three-layered subtractive colour filter based on asymmetric Fabry-P´erot (FP) nanocavity, where titanium oxide (TiO2) nanocavity is sandwiched between thin tungsten (W) and optically thick aluminium (Al) film. The filter outputs vivid colours with 41.3 % of standard red, green, and blue (sRGB) coverage on the CIE 1931 map. The results show incident angle insensitivity up to 40o. The device is fabricated, but the physical characterization of the sample with the help of an SEM image is not helpful to obtain the thicknesses of the deposited films. However, the thicknesses obtained with the help of spectroscopic ellipsometry agree with the results obtained from optical characterization.
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    Optical Micromachines for Biological Studies
    (MDPI (Basel, Switzerland), 13/02/2020) Andrew P-K; Williams MAK; Avci E
    Optical tweezers have been used for biological studies since shortly after their inception. However, over the years research has suggested that the intense laser light used to create optical traps may damage the specimens being studied. This review aims to provide a brief overview of optical tweezers and the possible mechanisms for damage, and more importantly examines the role of optical micromachines as tools for biological studies. This review covers the achievements to date in the field of optical micromachines: improvements in the ability to produce micromachines, including multi-body microrobots; and design considerations for both optical microrobots and the optical trapping set-up used for controlling them are all discussed. The review focuses especially on the role of micromachines in biological research, and explores some of the potential that the technology has in this area.
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    Study of microchannels fabricated using desktop fused deposition modeling systems
    (MDPI AG, 25/12/2020) Rehmani MAA; Jaywant SA; Arif KM
    Microfluidic devices are used to transfer small quantities of liquid through micro-scale channels. Conventionally, these devices are fabricated using techniques such as soft-lithography, paper microfluidics, micromachining, injection moulding, etc. The advancement in modern additive manufacturing methods is making three dimensional printing (3DP) a promising platform for the fabrication of microfluidic devices. Particularly, the availability of low-cost desktop 3D printers can produce inexpensive microfluidic devices in fast turnaround times. In this paper, we explore fused deposition modelling (FDM) to print non-transparent and closed internal micro features of in-plane microchannels (i.e., linear, curved and spiral channel profiles) and varying cross-section microchannels in the build direction (i.e., helical microchannel). The study provides a comparison of the minimum possible diameter size, the maximum possible fluid flow-rate without leakage, and absorption through the straight, curved, spiral and helical microchannels along with the printing accuracy of the FDM process for two low-cost desktop printers. Moreover, we highlight the geometry dependent printing issues of microchannels, pressure developed in the microchannels for complex geometry and establish that the profiles in which flowrate generates 4000 Pa are susceptible to leakages when no pre or post processing in the FDM printed parts is employed.
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    All-Dielectric Transreflective Angle-Insensitive Near-Infrared (NIR) Filter
    (MDPI (Basel, Switzerland), 2022-08) Shaukat A; Umer R; Noble F; Arif K
    This paper presents an all-dielectric, cascaded, multilayered, thin-film filter, allowing near-infrared filtration for spectral imaging applications. The proposed design is comprised of only eight layers of amorphous silicon (A-Si) and silicon nitride (Si₃N₄), successively deposited on a glass substrate. The finite difference time domain (FDTD) simulation results demonstrate a distinct peak in the near-infrared (NIR) region with transmission efficiency up to 70% and a full-width-at-half-maximum (FWHM) of 77 nm. The theoretical results are angle-insensitive up to 60⁰ and show polarization insensitivity in the transverse magnetic (TM) and transverse electric (TE) modes. The theoretical response, obtained with the help of spectroscopic ellipsometry (SE), is in good agreement with the experimental result. Likewise, the experimental results for polarization insensitivity and angle invariance of the thin films are in unison with the theoretical results, having an angle invariance up to 50⁰.
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    Acoustic Multi-Detection of Gliadin Using QCM Crystals Patterned with Controlled Sectors of TEM Grid and Annealed Nanoislands on Gold Electrode
    (MDPI (Basel, Switzerland), 20/04/2020) Casari Bariani G; Zhou L; Poggesi S; Mittapalli R; Manzano M; Ionescu RE
    Celiac diseases are a group of gluten ingestion-correlated pathologies that are widespread and, in some cases, very dangerous for human health. The only effective treatment is the elimination of gluten from the diet throughout life. Nowadays, the food industries are very interested in cheap, easy-to-handle methods for detecting gluten in food, in order to provide their consumers with safe and high-quality food. Here, for the first time, the manufacture of controlled micropatterns of annealed gold nanoislands (AuNIs) on a single QCM crystal (QCM-color) and their biofunctionalization for the specific detection of traces of gliadin is reported. In addition, the modified quartz crystal with a TEM grid and 30 nm Au (Q-TEM grid crystal) is proposed as an acoustic sensitive biosensing platform for the rapid screening of the gliadin content in real food products.