Tyndall National Institute - Doctoral Theses
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- ItemThe design, synthesis and characterisation of selected chitosan-based thin films and studies of their use as materials for antimicrobial, heavy metal adsorption, and wound dressing applications(University College Cork, 2022-09) Pemble, Oliver James; Bardosova, Maria; Povey, IanChitosan is a naturally-derived polymer, sourced from the chitin present in crustacean shells and insect exoskeletons. It is a highly diverse molecule, with heavy metal adsorption, antibacterial and pH-based swelling properties. However, these properties may be hindered by the lack of strength of a singular polymer structure. Chitosan has the ability to cross-link with other polymers or reagents to create interpenetrating polymer networks (IPNs) and blends to improve the mechanical strength or application mechanisms. These composites can be cast into films which have superior properties for the applications listed above. The first half of this PhD thesis sets out to describe the process of synthesising thin films made from combining chitosan with cross-linking reagents and other polymer networks. These materials comprise two siloxane networks Tetraethyl-orthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES), glutaraldehyde (GA), and the polymer polyacrylamide (PAM). Aqueous acidic solutions of low molecular weight chitosan were made and combined with one of the four materials at different ratios to produce hydrogels that could then be cast into thin films. These chitosan-based films were characterised as to their molecular structures via FT-IR spectroscopy and their mechanical elasticity/plasticity via tensile strength tests. The method of casting the films was primarily drop-casting in a Petri dish and drying for 24 hours, but an alternative procedure that utilises a doctor blade slot-die head was also developed. This novel method was studied in-depth, and the findings were published. For this reason, the results of the slot-die casting studies are presented in their published form. Briefly, the slot-die casting technique produced high quality thin films of chitosan-based composites in under 2 hours. Further, there was no influence of the direction of travel of the films during deposition on their mechanical properties. This study served as a proof-of-concept that high volumes of chitosan-based films could be made quickly, cheaply, and reproducibly. The second half of this thesis explores the applications of the composite chitosan-based films, by use of their adsorption, antimicrobial, and swelling abilities. The adsorption of radioactive technetium pertechnetate 99mTcO4- ions via chelation from solution was evaluated and correlated based on the Langmuir and Freundlich isotherms. It was found that the chitosan-glutaraldehyde films showed the best ability to adsorb 99mTcO4- ions and that a Langmuir-type, monolayer-based adsorption process was most likely in operation. A preliminary study of the antimicrobial properties of the chitosan-based films was undertaken via Gram-negative and Gram-positive bacterial growth and attachment assays. The intent of the study was to test the antibacterial abilities of the films while also speculating as to the mechanism of said abilities. The chitosan-tetraethyl-orthosilicate films were found to be the most effective against both types of bacterial growth and attachment. However, the chitosan-glutaraldehyde films showed little-to-no antibacterial ability, suggesting the antibacterial mechanism may be affected by the cross-linking reagent. Finally, a prototype for a smart wound dressing device that incorporates a pH sensitive sensor for chronic wounds was designed and developed using the chitosan-based films. The device utilised chitosan’s natural swelling ability and colloidal photonic crystal technology to create an indicator that produced a visual colour change in response to fluctuating pH levels, which may occur in chronic wounds. The mechanism was based on the distortion of photonic crystal layers by the swelling of the chitosan-based films to give a distinct red to green colour change. This preliminary study shows the potential of chitosan /photonic crystal-based sensors for use in medical devices that do not require an external power source to operate.
- ItemLaser fabrication of porous, 3D graphene-like carbon from polyimide and sustainable bioplastics(University College Cork, 2022-06) Larrigy, Cathal; Quinn, Aidan J.; Iacopino, Daniela; Science Foundation IrelandLaser-induced graphitization (LIG) of materials provides a unique and advantageous method for fabrication of 3D, porous, conductive, carbon structures with high surface area. By using laser-irradiation of target substrates, conductive patterns such as electrochemical or chemiresistive sensing elements can be fabricated additively, thus reducing both the energy footprint and cost. However, typically LIG is fabricated on non-sustainable feedstock substrates, most commonly polyimide. Studies toward using alternative and more sustainable substrates have been researched, and in this thesis one such alternative is explored, chitosan-based laser-induced graphene. This thesis aims to show the possibilities of laser-induced graphene fabrication, in examining first the fabrication of LIG on polyimide using a low-cost hobbyist 405 nm laser engraving machine, as an alternative low energy intensive fabrication method. Following this the possibility of using a more sustainable substrate as a target precursor for laser-induced graphitization in the form of a chitosan-based LIG. Finally, a potential application using chitosan-based LIG was demonstrated in the form of chemi-resistive 2-terminal impedance devices for sensing humidity and volatile organic compounds.
- ItemMicro-transfer printing of micro-structured, ultra-thin light-emitting devices(University College Cork, 2023-03) Shaban, Zeinab; Corbett, Brian; Parbrook, Peter James; Science Foundation Ireland3D integration of optoelectronic devices is a crucial future technology, which can be applied in the areas of photonic integrated circuits, flexible displays, communication and more. Among the various technologies, micro-transfer printing has emerged as a precise and cost-effective way to assemble devices for 3D integration. To enable this technology, devices must be released from their native substrates, which open up a lot of possibilities. It can achieve integration with flexible or heat-conductive backplanes, as well as heterogeneous integration of multiple materials on a common platform, resulting in miniaturised chips. Also one can benefit from reclaiming and reusing the original substrates to reduce the production cost significantly. On the other hand, GaN devices exhibit unique optical properties in optoelectronics compared to other semiconductors, and GaN-based LEDs have established themselves in a variety of applications, due to their low power consumption, long lifetime, short response time, and high brightness. This thesis has focused on releasing high performance GaN LEDs and addressing their associated issue for micro-transfer printing. The first part of this work is focused on releasing and transfer-printing of GaN LEDs grown on Si substrate. There are several factors that limit the performance and manufacturing of GaN LEDs on Si. One issue is related to the deformation of the released coupons due to their high inbuilt strain, which could result in transfer-printing failures as well as challenges during the post-print integration process. To address this issue, COMSOL software was used to study the stress effect on the devices. Experimentally, the intrinsic deformation of the released LEDs was compensated by using compressed SiNx layers that resulted in flat devices after release. Another issue is related to the low light extraction for GaN LEDs on Si. To solve this problem, the underside of the released LEDs is roughened during the coupon preparation process prior to transfer printing. Furthermore, using the unique properties of transfer printing, the roughened LEDs are printed inside a fabricated reflective trench with 10 μm depth to direct the light to the surface normal. Results showed that roughening along with the reflective trench increased the collected power by a factor of ∼ 7 compared with LEDs on the original substrate. A second part of this study examines the release of GaN-based structures from substrates (i.e. sapphire or bulk GaN) by photoelectrochemical (PEC) etching when pure chemical etching is not possible. A sacrificial layer which can obtain smooth etch surfaces and uniform etching with high selectivity is needed. Also, from the perspective of transfer printing, thick rather than thin sacrificial layers are preferred to facilitate the releasing and picking process. In this work, 300 nm-thick releasing layers comprising of InGaN/AlInN stacks are proposed for PEC etching. The presence of two-dimensional hole gas at the interface of InGaN/AlInN due to the strong polarization field are indicated by modelling and capacitance-voltage measurement. This resulted in a smoother surface with a three times higher etch rate compared to the conventional InGaN/GaN superlattice structures used for PEC etching. Moreover, various electrolytes and post-PEC treatment were studied to improve the surface smoothness. Further work should be done to determine the impact of the adhesion layer in transfer printing on heat generation and device performance. Using the optimized sacrificial layer to release other structures like lasers should also be investigated.
- ItemDevelopment of electromagnetic vibration energy harvesters as powering solution for IoT based applications(University College Cork, 2022-09-20) Paul, Kankana; Roy, Saibal; Amann, Andreas; Kennedy, Peter; Science Foundation Ireland; Horizon 2020The drive towards building pervasive intelligence encompassing urban as well as rural environments has paved the way for the Internet of Things (IoT), which has reshaped our regular lifestyle alleviating the dependence on wired communication systems since its inception. The inexorable advancement in low to ultra-low power electronics have steered the rapid growth of the IoT platform expanding into several application fields. With the ongoing implementation of 5G (Fifth generation) and the emergence of 6G (Sixth generation) wireless technology on the horizon, the explosive growth of IoT connected devices reinforces the requirement of a robust and reliable power solution for the deployed wireless communication platforms. Utilizing distributed clean energy sources, especially the ubiquitous mechanical energy available in environment through dedicated transducers in the form of vibration energy harvesters (VEHs) to power the IoT-based wireless sensor platforms is a sought after alternatives to batteries in the forthcoming IoT applications. The potential of the resonant/linear VEHs have been limited owing to the narrow operable frequency bandwidth as well as due to the lack of intelligent device designs that aids to yield large electrical power from the provided mechanical energy. In this thesis, a concertina shaped linear VEH spring architecture has been exploited to instigate large amplitudes of oscillation, which aids to yield a high power density (455.6μW/cm3g2) at resonance from a relatively small device footprint. From the application perspective, this concertina-VEH has been utilized to power the electronics interface and enhance the performance of a NFC (Near Field Communication) based wireless sensor platform which offers the benefits of low power consumption and on call data acquisition through this short range NFC based communication protocol. Such a robust autonomous wireless sensing platform offers the potential to be used in a large number of IoT based applications. Despite of the large deliverable power obtained from the resonant VEH, the energy extraction drops dramatically as the excitation frequency deviates from the resonance condition, which is inevitable owing to the random nature of vibrations. A novel broadband VEH with tapered spring geometry has been developed as a part of this thesis to address this issue. Nonlinear restoring forces arising from the stretched springs enables the VEH to generate large power over a considerably wide bandwidth (45Hz of hysteresis width that is the difference of the jump down and jump up frequency with 1g excitation amplitude) of operable frequencies. Suitable power management strategies have been proposed to enhance the energy extraction capabilities. The nonlinear VEH has been successfully used to harness mechanical energy from the broadband vibrations of a car; the extracted energy is fed to a wireless sensor platform that reports on ambient temperature and humidity. This self-powered sensing system opens up the scope for exploiting this technology for monitoring food and medicinal quality during transportation while the VEH extracts mechanical energy from the transporting vehicle and perpetually powers the wireless sensor node. Multiple nonlinearities arising from the stretching of the VEH spring as well as from the interaction of repulsive magnets have been introduced into the energy harvester, which gives rise to coexisting multiple energy branches. Not all of these energy states are achieved through the typical excitation frequency routine, some of these energy states are rather hidden. Experimentally a route to achieve these hidden energy branches have been explored in this work. Suitable frequency routines have been designed to achieve and sustain these higher energy states. A useful graphical representation has been introduced in the form of ‘eye diagrams’ that essentially estimates the transaction of energy from mechanical to electrical domain, and provides deep insight of the dynamical features of each energy branches, based on time resolved measurements of acceleration and voltage. A mathematical model has been developed to investigate the intricate complexities of the nonlinear system, which supports the experimental findings. One of the major impediments in miniaturizing high-efficiency macroscale VEHs into MEMS (Micro-Electro-Mechanical-System) scale is the lack of matured technology for the CMOS (Complementary-Metal-Oxide-Semiconductor) compatible integration of magnets and the adverse effect of scaling on the permanent hard magnets. A part of the presented work investigates the effect of patterning continuous thin films of magnets into micromagnet array. With detailed analytical framework and exhaustive finite element analysis, the shape, size and distribution of these micromagnets have been optimized to maximize the stray magnetic field emanating from each edge of these magnets. Novel MEMS device topologies comprising of linear/nonlinear MEMS springs, micromagnet arrays and copper microcoil have been proposed which systematically maximizes the electromagnetic interaction between the micromagnets and the integrated coil that in turn translates into large deliverable power. In addition to the developed device prototypes and demonstrations, this thesis further provides a firm roadmap that highlights the potential routes for enhancing the energy harvesting capabilities through highly integrated MEMS scale VEHs as well as for improving system level integration to establish these VEHs as a reliable and sustainable alternative of batteries in IoT applications.
- ItemDevelopment and characterisation of macro-disc and micro-band electrodes for electrochemical sensing applications(University College Cork, 2022) Madden, Julia; Galvin, Paul; O'Riordan, Alan; Thompson, Michael; Science Foundation Ireland; Electronic Components and Systems for European LeadershipThe aim of this PhD thesis was to investigate potential next generation sensor platforms for electrochemical biosensor developments, specifically towards health monitoring applications. With increasing interest in the integration of miniaturised electrodes with minimally invasive and wearable devices, this thesis sought to explore electrodes fabricated using three different technologies for the construction of electrochemical biosensors: Silicon microfabrication, Laser scribing, and dispense printing. The first experimental section aimed to investigate the use of a single ultramicroband electrode fabricated on silicon for mediator-free glucose monitoring in bio-fluid environments. Six ultramicroband electrodes, a counter electrode and reference electrode were fabricated using standard microfabrication methods i.e. lithography and etching techniques. Glucose oxidase was selected as a model enzyme to attach onto a platinum modified gold microband electrode by electropolymerisation with an o-phenylenediamine/ß-cyclodextrin layer. The resulting microband biosensor demonstrated on-chip glucose detection in buffer based media. When applied to foetal bovine serum the sensor displayed a reduced sensitivity. The second experimental section explores the use of laser-scribed graphitic carbon for flexible sensing applications. A facile fabrication method was assessed involving electrodeposition of platinum followed by two casting steps to functionalise electrodes. This study examined the chronoamperometric response of the enzymatic lactate sensor whilst the flexible polyimide substrates were fixed at a curvature (K) of 0.14 mm-1. No noticeable change in signal response was observed in comparison to calibrations obtained with a flat substrate (K=0 mm-1), suggesting potential opportunities for sensor attachment or integration with oral-care products such as mouth swabs and mouth guards. Both laser scribed graphitic carbon and Ag/AgCl modified-laser scribed graphitic carbon were examined as reference electrodes for chronoamperometric lactate measurements. This device was applied for measuring lactate concentrations in artificial saliva and diluted sterile human serum. Finally, this study investigates the potential for a low cost additive printing tool to enable the fabrication of electrochemical sensor devices. To do this, electrodes were designed and printed onto polyimide substrates. Reproducibility between electrode dimensions was assessed using 3D microscopy. Standard electrochemical characterisation techniques were employed to study the reproducibility between electrode electrochemical response. Functionality was also assessed whilst electrodes were fixed were fixed at a curvature (K) of 0.14 mm-1. Finally, a simple casting approach was applied to the dispense printed working electrode to construct a lactate biosensor for a proof of concept electrochemical sensor demonstration.