Study of Radiative Defects Using Current-Voltage Characteristics in ZnO Rods Catalytically Grown on 4H-p-SiC

High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate. The current transport mechanisms of the diodes at room temperature (RT) have been explained in term of the space-charge-limited current model based on the energy band diagram of ZnO rods/4H-p-SiC heterostructure. The tunneling mechanism via deep-level states was found to be the main conduction process at low-applied voltage but at trap-filled limit voltage V TFL all traps are filled and the space-chargelimited current conduction dominated the current transport. From the RT current voltage measurements, the energy of the deep level trap and the trap concentration were obtained as ∼ 0.24 ± 0.02 eV and 4.4 × 10 18 cm -3 , respectively. The deep level states observed correspond to zinc interstitial (Zn i ), responsible for the violet emission

The phenomenon of vehicle park brake rollaway

When a vehicle is parked on a slope with hot brakes, what appears to be a sufficient parking brake action can sometimes become insufficient. When the brakes cool down, the braking force reduces due to relaxation of the entire parking brake system, and the vehicle may start to move, leading to obvious catastrophic consequences. This phenomenon is known as vehicle rollaway. This thesis describes the problem in detail and postulates a mechanism that accounts for the occurrence of the rollaway event on vehicles using integrated rear callipers. Different testing methods are presented that are used to investigate the propensity of a vehicle's parking brake system to rollaway. These include on-vehicle evaluations and laboratory based measurements. A description is given of a novel dynamometer facility that was developed for this research that is capable of testing vehicle parking brake systems for rollaway. Two mathematical modelling techniques are presented that demonstrate how the parking brake system parameters influence the likelihood of rollaway occurring. A finite element model was used to simulate the change in contact pressure at the frictional interface during a rollaway event. A numerical model was also used to predict the change in torque developed by a parking brake system cooling from an initial elevated temperature. The change in clamp load at the frictional interface was modelled using an essentially I-D quasi-static system that showed how the stiffness and the thermal properties of the system qualitatively affect the phenomenon. The research found that rollaway does not always start with a uniform motion, but with a stick/slip motion. The likelihood of rollaway occurring was found to be directly linked to the temperature of the brake when the vehicle is parked. Rollaway can be reduced by lowering the initial temperature of the brake prior to parking. Rollaway can also be reduced by increasing the input load to the system when applying the parking brake. The research identifies the key design parameters of the brake system components whose values require close control within the real system if rollaway is to be avoided.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A new challenge for meteorological measurements: The meteoMet project-Metrology for meteorology

Climate change and its consequences require immediate actions in order to safeguard the environment and economy in Europe and in the rest of world. Aiming to enhance data reliability and reduce uncertainties in climate observations, a joint research project called MeteoMet-Metrology for Meteorology started in October 2011 coordinated by the Italian Istituto Nazionale di Ricerca Metrologica (INRiM). The project is focused on the traceability of measurements involved in climate change: surface and upper air measurements of temperature, pressure, humidity, wind speed and direction, solar irradiance and reciprocal influences between measurands. This project will provide the first definition at the European level of validated climate parameters with associated uncertainty budgets and novel criteria for interpretation of historical data series. The big challenge is the propagation of a metrological measurement perspective to meteorological observations. When such an approach will be adopted the requirement of reliable data and robust datasets over wide scales and long terms could be better met. © 2013 AIP Publishing LLC

Influence of helium-ion bombardment on the optical properties of ZnO nanorods/p-GaN light-emitting diodes

Light-emitting diodes (LEDs) based on zinc oxide (ZnO) nanorods grown by vapor-liquid-solid catalytic growth method were irradiated with 2-MeV helium (He+) ions. The fabricated LEDs were irradiated with fluencies of approximately 2 × 1013 ions/cm2 and approximately 4 × 1013 ions/cm2. Scanning electron microscopy images showed that the morphology of the irradiated samples is not changed. The as-grown and He+-irradiated LEDs showed rectifying behavior with the same I-V characteristics. Photoluminescence (PL) measurements showed that there is a blue shift of approximately 0.0347 and 0.082 eV in the near-band emission (free exciton) and green emission of the irradiated ZnO nanorods, respectively. It was also observed that the PL intensity of the near-band emission was decreased after irradiation of the samples. The electroluminescence (EL) measurements of the fabricated LEDs showed that there is a blue shift of 0.125 eV in the broad green emission after irradiation and the EL intensity of violet emission approximately centered at 398 nm nearly disappeared after irradiations. The color-rendering properties show a small decrease in the color-rendering indices of 3% after 2 MeV He+ ions irradiation

Broadband luminescence in defect-engineered electrochemically produced porous Si/ZnO nanostructures

The fabrication, by an all electrochemical process, of porous Si/ZnO nanostructures with engineered structural defects, leading to strong and broadband deep level emission from ZnO, is presented. Such nanostructures are fabricated by a combination of metal-assisted chemical etching of Si and direct current electrodeposition of ZnO. It makes the whole fabrication process low-cost, compatible with Complementary Metal-Oxide Semiconductor technology, scalable and easily industrialised. The photoluminescence spectra of the porous Si/ZnO nanostructures reveal a correlation between the lineshape, as well as the strength of the emission, with the morphology of the underlying porous Si, that control the induced defects in the ZnO. Appropriate fabrication conditions of the porous Si lead to exceptionally bright Gaussian-type emission that covers almost the entire visible spectrum, indicating that porous Si/ZnO nanostructures could be a cornerstone material towards white-light-emitting devices