Flexible carbon capture and storage (CCS) has the potential to play a significant part in the decarbonisation of electricity generation portfolios which have significant penetration from intermittent renewable sources. Post-combustion capture (PCC) with amine solvents is a mature technology and is currently the state-of-the-art for CO2 emissions reduction from power stations. However, knowledge of the dynamic capture process is currently limited due to a dearth of dynamic datasets which reflect real plant operation, lack of a robust in-situ solvent analysis method for plant control and uncertainty about how changing plant design affects the response to dynamic operations. In addition, the nature of interfacial gas-liquid dynamics inside the absorber column are not well known and rely on correlations for effective mass transfer area and liquid holdup which may have uncertainties of up to +/- 13%. This could result in absorption columns being improperly sized for CCS operations. Two pilot-scale test campaigns are implemented in order to gain an understanding of how the capture plant responds to dynamic operations, the first on natural gas combined cycle (NGCC)-equivalent flue gas, the second on pulverised coal (PC)-equivalent. Changes in flue gas flow rates and steam supply which are designed to be representative of PCC operation on real NGCC and PC plant are implemented, using 30%wt monoethanolamine (MEA) as absorbent in both cases. Dynamic datasets are obtained for 5 scenarios with NGCC and 8 with PC flue gas. The test campaigns are carried out using two separate pilot-scale facilities and highlight the effect of plant design on hydrodynamics and hence, the response of the capture plant to dynamic operations. Finally, a novel solvent sensor is used to demonstrate, for the first time, control of the capture facility using in-situ measurements of solvent composition, combined with knowledge of test facility hydrodynamics and response times. Results from the pilot-scale test campaign are then used along with a mathematical NGCC capture plant scale up to investigate the potential effects of dynamic operations on total yearly CO2 emissions and the associated environmental penalties, depending on CO2 price. Manufacturers of column internals for CCS often rely on computational fluid dynamic (CFD) software tools for design, but existing commercial codes are unable to handle complex two-phase flows such as those encountered in the absorber column of a CO2 capture plant. An open-source direct numerical simulation (DNS) tool which will be capable of rigorously modelling two-phase flow with turbulence and mass transfer has been developed and could eventually replace the empirical methods currently used in packing design. The DNS code requires validation by experiment. For the purpose of validation a dual-purpose wetted-wall column is constructed, which in addition to mass transfer measurements can be used to determine liquid film thickness using an optical method. Measurements of average film thickness, wave amplitude, frequency, velocity and growth rate are provided for three liquid flow rates of fresh 30%wt MEA solution. Wave measurements are made with quiescent, laminar and turbulent gas flow, with and without mass transfer. These measurements can be used to validate the DNS code at its existing level of complexity, and in the future when turbulence and mass transfer are added.

Nanocrystalline silicon (nc-Si:H) is an attractive material for fabrication of low temperature, large area electronic devices due to superior properties versus the traditional amorphous silicon (a-Si:H) and polycrystalline silicon (polySi). Nanocrystalline silicon possess higher carrier mobility and better stability than a-Si:H and better device uniformity and lower fabrication cost than polySi. This thesis looks at the application of nc-Si:H material in fabricating two different diodes used for rectification and light generation. Optimization of n-type nc-Si:H deposited via plasma enhanced vapor chemical deposition (PECVD) was achieved through adjusting the concentration ratio of phosphine (PH3) dopant source gas versus silane (SiH4). Optimizing for dark conductivity, n+ nc-Si:H material with dark conductivity of 25.3 S/cm was deposited using a [PH3]/[SiH4] ratio of 2%. Using the optimized n+ nc-Si:H film, a p-n junction diode utilizing an undoped and an n+ nc-Si:H layers was fabricated designed for rectification use. The diode achieved a current density of 1 A/cm2, an ON/OFF current ratio of 106 and a non-ideality factor of 1.9. When the 200*200µm2 nc-Si:H diodes were employed in a full-wave bridge rectifier, a 2.6 V direct current voltage could be generated from an input sine wave signal with amplitude 2 VRMS and frequency of 13.56 MHz, thus demonstrating the feasibility of using nc-Si:H to fabricate diodes for using on radio frequency identification (RFID) tags. Nanocrystalline silicon was also applied in fabrication of a light emitting diode (LED), by utilizing the nanocrystals embedded inside nc-Si:H, inside which recombination of carriers could result in radiative recombination. By limiting the deposition time of the nc-Si:H, 10 – 20 nm thick films of nc-Si:H were used to fabrication a p-i-n structure LED with average crystallite size between 7.5 nm to 13.7 nm corresponding to an theoretical emission wavelengths in the near infrared region of 875 nm to 963 nm. Unfortunately, light emission from the nc-Si:H LED were not detected using two different methods. Undetectable emission could have been due to a combination of low recombination efficiency due to carriers recombining in defects in the a-Si:H matrix and majority of current travelling completely through the nc-Si:H films without recombining. A study of the thin intrinsic nc-Si:H films used in the LED was carried out. The thin films were found to be highly defected, with large variation in current-voltage relationship measured and hysteresis observed in the IV characteristic. Annealing the nc-Si:H films were found to cause a drop in conductivity explained through hydrogen effusion from the nc-Si:H film during annealing. Passivation of defects was achieved through the use of hydrogen plasma which resulted in a lowering of activation energy measured in the film. Oxygen plasma was also trialed for passivating the nc-Si:H film but the effect was only a temporary increase in current conduction attributed to oxygen ions chemisorbing temporarily at the film surface.

Nanocrystalline silicon (nc-Si:H) is an attractive material for fabrication of low temperature, large area electronic devices due to superior properties versus the traditional amorphous silicon (a-Si:H) and polycrystalline silicon (polySi). Nanocrystalline silicon possess higher carrier mobility and better stability than a-Si:H and better device uniformity and lower fabrication cost than polySi. This thesis looks at the application of nc-Si:H material in fabricating two different diodes used for rectification and light generation. Optimization of n-type nc-Si:H deposited via plasma enhanced vapor chemical deposition (PECVD) was achieved through adjusting the concentration ratio of phosphine (PH3) dopant source gas versus silane (SiH4). Optimizing for dark conductivity, n+ nc-Si:H material with dark conductivity of 25.3 S/cm was deposited using a [PH3]/[SiH4] ratio of 2%. Using the optimized n+ nc-Si:H film, a p-n junction diode utilizing an undoped and an n+ nc-Si:H layers was fabricated designed for rectification use. The diode achieved a current density of 1 A/cm2, an ON/OFF current ratio of 106 and a non-ideality factor of 1.9. When the 200*200µm2 nc-Si:H diodes were employed in a full-wave bridge rectifier, a 2.6 V direct current voltage could be generated from an input sine wave signal with amplitude 2 VRMS and frequency of 13.56 MHz, thus demonstrating the feasibility of using nc-Si:H to fabricate diodes for using on radio frequency identification (RFID) tags. Nanocrystalline silicon was also applied in fabrication of a light emitting diode (LED), by utilizing the nanocrystals embedded inside nc-Si:H, inside which recombination of carriers could result in radiative recombination. By limiting the deposition time of the nc-Si:H, 10 – 20 nm thick films of nc-Si:H were used to fabrication a p-i-n structure LED with average crystallite size between 7.5 nm to 13.7 nm corresponding to an theoretical emission wavelengths in the near infrared region of 875 nm to 963 nm. Unfortunately, light emission from the nc-Si:H LED were not detected using two different methods. Undetectable emission could have been due to a combination of low recombination efficiency due to carriers recombining in defects in the a-Si:H matrix and majority of current travelling completely through the nc-Si:H films without recombining. A study of the thin intrinsic nc-Si:H films used in the LED was carried out. The thin films were found to be highly defected, with large variation in current-voltage relationship measured and hysteresis observed in the IV characteristic. Annealing the nc-Si:H films were found to cause a drop in conductivity explained through hydrogen effusion from the nc-Si:H film during annealing. Passivation of defects was achieved through the use of hydrogen plasma which resulted in a lowering of activation energy measured in the film. Oxygen plasma was also trialed for passivating the nc-Si:H film but the effect was only a temporary increase in current conduction attributed to oxygen ions chemisorbing temporarily at the film surface.

The semiconductor industry was benefited by the advances in technology in the last decades. This fact has an impact on the sensors field, where the simple transducer was evolved into smart miniaturized multi-functional microsystems. However, commercially available gas and biological sensors are mostly bulky, expensive, and power-hungry, which act as obstacles to mass use. The aim of this work is gas and biological sensing using capacitive structures. Capacitive sensors were selected due to its design simplicity, low fabrication cost, and no DC power consumption. In the first part, the dominant structure among interdigitated electrodes (IDEs), fractal curves (Peano and Hilbert) and Archimedean spiral was investigated from capacitance density perspective. The investigation consists of geometrical formula calculations, COMSOL Multiphysics simulations and cleanroom fabrication of the capacitors on a silicon substrate. Moreover, low-cost fabrication on flexible plastic PET substrate was conducted outside cleanroom with rapid prototyping using a maskless laser etching. The second part contains the humidity, Volatile Organic compounds (VOCs) and Ammonia sensing of polymers, Polyimide and Nafion, and metal-organic framework (MOF), Cu(bdc)2.xH2O using IDEs and tested in an automated gas setup for experiment control and data extraction. The last part includes the biological sensing of C - reactive protein (CRP) quantification, which is considered as a biomarker of being prone to cardiac diseases and Bovine serum albumin (BSA) protein quantification, which is used as a reference for quantifying unknown proteins.