Yusof Abdullah

Effects of Neutron and Electron Irradiation on 4H-SiC Diodes

4H-SiC Schottky barrier diodes (SBDs) were irradiated to neutron fluence of 3.55 x1016 cm-2 and 6.6 x 1015 cm-2 (15,000 kGy) electrons respectively. In general, characterization of the irradiated samples show that the current characteristics of the diodes decreased. The performance of Schottky gate contact is less for electron irradiated sample compared to neutron irradiated sample. The d-spacing, crystallite sizes and lattice strains were calculated from X-ray diffraction (XRD) measurements. SiC Schottky interface damage and radiation defects, as observed in atomic force microscopy (AFM) topography and scanning electron microscope (SEM) morphology images is possibly the main reason for this reduction in performance.

The Effects of Electron Beam Irradiation on Structural and Optical Properties of TiO2 Particles

The effect of electron irradiation on structural and optical properties of TiO2 particles has been studied. The crystallinity change was observed at low dose irradiation (4-20 kGy) while phase transformation from pure anatase to mixture of anatase-rutile was inevitable after 100 kGy without significant change in crystallinity. The highest fraction of rutile:anatase ratio was 20:80 obtained at 700 kGy. Morphology study demonstrated that TiO2 particles were spherical, nano-sized and heavily agglomerated with no obvious microstructural changes were observed after irradiation. The direct and indirect band gap (Eg) showed a decrement at low dose but re-increased after irradiation at >100 kGy. The highest Eg was at 700 kGy which can be explained by the changes of TiO2 atomic structure in the presence of mixture anatase:rutile. Therefore, the electron beam irradiation does affect both structural and optical properties of TiO2 nanoparticles. This is expected to affect the photocatalytic activity of TiO2.

Radiation Damage Study of Electrical Properties in GaN LEDs Diode after Electron Irradiation

Nitride-based light emitting diodes (LEDs) is an attractive material due to its high temperature tolerance and suitable to be used in extreme environment. The irradiation process of Gallium Nitride (GaN) diode was carried out by electron irradiation with 1000 kGy and 1500 kGy doses with a conveyor speed of 50 kGy per pass. Capacitance-voltage (C-V) and current-voltage (I-V) characterization for both pre and post irradiation samples was done. Both current and capacitance show decreasing while reverse leakage current increased after irradiation. The reverse leakage current revealed that the current were start leakage at 1.0 x10 -7 A and 1.0 x10-9 A for 1000 kGy and 1500 kGy irradiations respectively. The current-voltage graph indicated that the effect of electron irradiation on diode produced weak spots as defect cause leakage current. The traps and bulk defect is believed to contributed to the leakage current increased.

The Effects of Substrate Orientation on Galvanic Growth of ZnO Structures

Electrochemical route has been a favorite technique for the fabrication of ZnO as it is relatively cheap and capable of producing abundance amount of materials. In this paper, we investigate the morphologies of hydrothermally synthesized ZnO structures assisted by galvanic process on conducting Au-coated silicon substrate. To induce the galvanic process, the substrate was in contact with aluminum so that the difference in the reduction potentials between the two materials provided the driving force for the formation of the ZnO structures. The galvanic process was found to promote compact and anisotropy growth of ZnO nanorods along the (001) plane. It was also found that substrate orientations in the electrolyte solution had an important bearing on the morphologies of ZnO. Well aligned periodic hexagonal arrays of ZnO nanorods of homogeneous diameters were obtained on gold-coated Si substrate with face-down orientation in the electrolyte solution.

Preliminary study of neutron absorption by concrete with boron carbide addition

Concrete has become a conventional material in construction of nuclear reactor due to its properties like safety and low cost. Boron carbide was added as additives in the concrete construction as it has a good neutron absorption property. The sample preparation for concrete was produced with different weight percent of boron carbide powder content. The neutron absorption rate of these samples was determined by using a fast neutron source of Americium-241/Be (Am-Be 241) and detection with a portable backscattering neutron detector. Concrete with 20 wt % of boron carbide shows the lowest count of neutron transmitted and this indicates the most neutrons have been absorbed by the concrete. Higher boron carbide content may affect the concrete strength and other properties.

Study of the Effect of Boron Carbide Content in Concrete as Radiation Shielding Application

Keywords: Boron carbide, concrete, shielding, neutron, attenuation. Abstract. Boron carbide (B4C) is a ceramic material which is effectively absorb thermal neutron due to wide neutron absorption cross section. In this work, B4C is added into concrete as fine aggregates to test the attenuation properties by getting the attenuation coefficient of the concrete/ B4C. The samples of concrete/ B4C were exposing to the thermal neutron radiation source (241-Americium-Berylium) at the dose rate of 29.08 mR/h. The result show that the attenuation coefficient of the sample with 20wt% B4C is 0.299 cm-1 and the sample without B4C is 0.238 cm-1 and hence, concrete/ B4C is suitable as a shielded for thermal neutron radiation.

Effect of Neutron Irradiation on Electrical Properties of Bi2Sr2CaCu2 (Bi-2212) Phase Superconductor

The effect of neutron irradiation on superconducting properties of Bi2Sr2CaCu2 (Bi-2212) phase superconductor was studied. TRIGA MARK II research reactor with neutron flux of 2.00 × 1011 /cm2s was used as the neutron source. Results between non-irradiated and irradiated samples have been analyzed from the aspects of microstructure and electrical properties. In this work, the bulk samples were prepared using the conventional solid-state reaction method. Molar ratio of Bi2O3, Sr2CO3, CaCO3 and CuO were mixed according to its ratio into composition of Bi:Sr:Ca:Cu = 2:2:1:2. The samples were sintered at 840°C during the sample preparation process. Some of the fully synthesized samples were irradiated with neutron irradiation. Neutron irradiation has been proved to promote better flux pinning properties by introducing larger defects in various superconductor ceramics. Enhanced flux pinning centers in the superconductor is responsible in enhancing the critical current, Ic and critical current density, Jc of the irradiated samples. The samples were characterized through X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The transition temperature, Tc and the Jc were measured by using a cryogenic four-point probe system. The XRD patterns for the non-irradiated and irradiated samples show well-defined peaks of which could be indexed on the basis of the Bi-2212 phase structure. XRD patterns also indicate that irradiation did not affect the Bi-2212 superconducting phase. However, the enhancement of Jc was observed in the neutron irradiated sample and this indicates the effectiveness of .neutron irradiation in creating defects that acted as effective flux pinning centers for vortices.

Gamma (γ) irradiated and non-irradiated poly (L-lactide) carboxymethyl starch composite film

A film of poly (L-lactide)(PLLA) and carboxymethyl starch (CMS) is prepared by casting evaporation method. The use of CMS blended with PLLA induces the porous film that is potentially used in tissue engineering applications. PLLA is blended with CMS in solution form and rolled on glass to produce a film. The film is then irradiated with gamma-ray (γ) at 10 and 80 kGy. FTIR analysis indicates weak interaction between PLLA and CMS at 10 kGy. Degradation and crosslinking are predicted to have occurred simultaneously at 10 kGy and massive degradation at 80 kGy as indicated in differential scanning calorimetry (DSC) curves. Mechanical analysis shows a higher strength at 10 kGy indicating that crosslinking has occured whereas degradation takes place at higher doses as shown in the reduction of mechanical strength for both PLLA and PLLA/CMS.

The effects of electron irradiation and thermal dependence measurements on 4H-SiC Schottky diode

In this paper the effects of high energy (3.0 MeV) electrons irradiation over a dose ranges from 6 to 15 MGy at elevated temperatures 298 to 448 K on the current-voltage characteristics of 4H-SiC Schottky diodes were investigated. The experiment results show that after irradiation with 3.0 MeV forward bias current of the tested diodes decreased, while reverse bias current increased. The degradation of ideality factor, n, saturation current, Is, and barrier height, Φb, were not noticeable after the irradiation. However, the series resistance, Rs, has increased significantly with increasing radiation dose. In addition, temperature dependence current-voltage measurements, were conducted for temperature in the range of 298 to 448 K. The Schottky barrier height, saturation current, and series resistance, are found to be temperature dependent, while ideality factor remained constant.

Structural and Surface Morphology of ZnO

The raw material of the extraction process is dust from the electric arc furnace dust (EAFD). EAFD is a byproduct of steel mills which comprises mainly of iron (33-35%) and zinc (22-27%). In this study, ZnO was extracted and purified from EAFD using solvent extraction technique to remove other impurities. Solvent extraction process can easily be adapted into small and large capacities. Characterization of the samples has been done and the results show the production of purity of ZnO samples was quite high. The sample was characterized using equipment such as X-ray fluorescence, XRF, X-ray diffraction, XRD and field emission scanning electron microscope (FESEM).