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Piezoresistive effect (PRE) has been utilised as a dominant sensing principle in a wide range of applications. Since its discovery, piezoresistive effect has attracted considerable interest in developing sensors with higher sensitivity. However, a giant piezoresistive effect in intrinsic semiconductors with reliability is still facing great challenges such as the limited nature of piezoresistive materials and dynamic trapping of charge carriers at surfaces of nanostructures under mechanical strain. Therefore, finding a new strategy and approach to enhance the PRE not only improves the performance of piezoresistive sensors but also can open a new research direction. This research aims to discover and demonstrate the opto-electronically enhanced piezoresistive effect, which significantly improves the performance of the PRE. This research also analyses the key parameters contributing to this tuneable giant piezoresistive effect. In addition, a demonstration of the unprecedented enhancement of sensitivity, tunability, stability, and the expansion of detectable range in a pressure sensor by applying the opto-electronically enhanced piezoresistive effect is investigated. A new technology for harvesting light energy to selfpower and simultaneously sense mechanical acceleration in a monolithic structure, which is an expansion of application of the opto-electronically enhanced piezoresistive effect, are developed in this research. Finally, the feasibility of integrating light source into the sensors instead of using an external light source for the opto-electronically enhanced piezoresistive effect is demonstrated. The discovery of the opto-electronically enhanced piezoresistive effect and its demonstrated applications can pave the way for development of ultrasensitive sensor technology and a new technology for harvesting light energy and self-powering NEMS/MEMS sensors. The outstanding results of this research have been demonstrated by papers reviewed and published in high quality journals such as Nature Communications (IF=11.878), Journal of Materials Chemistry C (IF=7.059), and Nano Energy (IF=15.548). A part of these results is featured on the back cover of Journal of Materials Chemistry C. In addition, parts of the results from this research are under review second time at Materials Horizons (IF=13.870) and have been submitted to Small (IF=11.459).

Cua Dai Beach located adjacent to Cua Dai Inlet is a typical, seasonally varying tidal inlet. This famous beach has suffered extreme erosion since 1995 due to an apparent irregular-periodic process, a decrease of sediment supply from the river and its estuaries and increased squeeze by coastal developments. The main objective of this study is to unravel the physical processes that control the morphological development of Cua Dai Inlet while challenged by the fact that it is a data-limited environment. In order to identify and quantify the main processes governing the evolution of Cua Dai Beach and thereby aiming to explain the morphological changes and extreme erosion in recent years, a new approach was developed. Historical shoreline positions and sediment budget changes were derived from satellite images using empirical engineering assumptions. In addition, numerical models were used to investigate in detail sediment transports and morphodynamics under the influence of seasonal waves and rivers as well as the anthropogenically-driven impacts. Results of shoreline change rates indicate that Cua Dai Beach (located on the northern side of Cua Dai inlet) experienced an average erosion of 12m/y during the period from 2000 to 2010 and erosion continued further to the north while the southern coast of the inlet accreted with a mean rate of 11m/y. The overall system showed a significant sediment loss of about 243,000–310,000 m3/y. The annual cycle of two past morphological periods has been numerically simulated to evaluate the behavior of the system without and with human interventions. The first morphological simulation without the impact of the resorts successfully reproduced an overall erosion trend at the northern coast while the formation of an ebb tidal bar was also reproduced. The second morphological simulation reproduced the impact of the resorts that have been constructed along Cua Dai Beach. Simulations indicate that the presence of the resorts has enhanced the propagation of the existing erosion further to the north. The new approach of remote sensing combined with process-based modeling has been essential to investigate the main processes that govern the morphological changes and extreme erosion at Cua Dai inlet.