Designing Nanomaterials For Electronic And Optoelectronic Devices Through Charge Carrier Control

Colloidal semiconductor nanocrystals (NCs) have been shown to be promising materials for electronic and optoelectronic device applications because of their unique size-dependent properties and low-cost solution processability. However, the integration of these materials into devices has been challenging due to a lack of available methods to: 1) accurately control charge carrier statistics, such as majority carrier type and concentration, and carrier mobilities, and 2) efficiently passivate surface defects inherent in NC materials arising from their high surface-volume ratio. In this thesis, we study the fundamental physics of charge carriers paramount for device application. Then, we introduce several measurement techniques to characterize the type, concentration, and mobility of charge carriers and the density and energy of surface states. Lastly, we propose a novel, systematic, and rational method to engineer those properties, in order to design high performance electronic and optoelectronic nanostructured devices. We develop stoichiometry control method through thermal evaporation or solution based atomic layer deposition to precisely control the electronic and optoelectronic properties of nanocrystals. We demonstrate that remote doping in nanostructured device is effective and a promising route to realizing high mobility and reducing scattering, in contrast to commonly pursued substitutional doping methods. Thermal diffusion doping process to passivate the trap states and the use of small ligands to enhance the electronic coupling are introduced. In addition, we emphasize the important role of the metal-semiconductor interface and semiconductor-gate dielectric layer, to enhance charge injection and prevent charge trapping, respectively. Through the careful engineering of the interface and junction, as well as the precise charge carrier statistics and trap states controls, we design and fabricate low cost, high performance nanocrystal thin film field-effect transistors, photodetectors, and solar cells. Finally, we introduce novel techniques, correlated scanning photocurrent microscopy and scanning confocal photoluminescence measurement system, that can explore the photoelectric and photophysical properties of semiconductor structures and devices

Experimental Assessment on the Flexural Bonding Performance of Concrete Beam with GFRP Reinforcing Bar under Repeated Loading

This study intends to investigate the flexural bond performance of glass fiber-reinforced polymer (GFRP) reinforcing bar under repeated loading. The flexural bond tests reinforced with GFRP reinforcing bars were carried out according to the BS EN 12269-1 (2000) specification. The bond test consisted of three loading schemes: static, monotonic, and variable-amplitude loading to simulate ambient loading conditions. The empirical bond length based on the static test was 225 mm, whereas it was 317 mm according to ACI 440 1R-03. Each bond stress on the rib is released and bonding force is enhanced as the bond length is increased. Appropriate level of bond length may be recommended with this energy-based analysis. For the monotonic loading test, the bond strengths at pullout failure after 2,000,000 cycles were 10.4 MPa and 6.5 MPa, respectively: 63–70% of the values from the static loading test. The variable loading test indicated that the linear cumulative damage theory on GFRP bonding may not be appropriate for estimating the fatigue limit when subjected to variable-amplitude loading

Prediction of long-term creep deflection of seismic isolation bearings

Isolation structures use high damping rubber bearings (HDRBs), lead rubber bearings (LRBs), and natural rubber bearings (NRBs) in order to significantly reduce the seismic forces transmitted from a substructure to a superstructure. The laminated rubber bearing is the most important structural member of a seismic isolation system. We present an analysis of a 1000 hr ongoing creep test conducted at 7.5 and 8.37 MPa in our laboratory. The long term behavior of bridge bearings (e.g., laminated rubber bearings) is determined through compression creep tests subjected to actual environmental conditions. These tests indicate that the maximum creep deformation is about 0.3 to 1.92 % of the total rubber thickness