Papers by Keyword: Ultraviolet Irradiation

Abstract: We propose the new practical and effective method, called Selective E-V-C (Expansion-Visualization-Contraction) technique, to screen out the basal plane dislocations (BPDs) which might cause the forward voltage degradation of SiC devices. Since the method can be adopted at the epi wafer receiving inspection process in early stage of production line, it may replace the very time-consuming so-called "burn-in" operation currently utilized in some device manufacturers.

Abstract: This study aims to optimize the production conditions for forming graphene directly on a quartz substrate, using a carbon 60 (C₆₀) thin film as a solid carbon source. In this experiment, we focused on the relationships between the thickness of the C₆₀ film and the nickel (Ni) catalyst film and the heat treatment conditions. As the thicknesses of the C₆₀ and Ni catalyst films increased, high-crystallinity multi-layered graphene was formed, however the optical transparency of the graphene film decreased. Scanning Electron Microscopy (SEM) observations and Raman scattering spectroscopy showed that after changing the atmosphere of the heat-treatment from an argon (Ar) gas to an Ar+ hydrogen (H₂) gas, the optical transparency of the graphene film was remarkably improved, due to the migration and vaporization of the Ni film, and due to etching of the multi-layered graphene.

Abstract: Photodegradation of bis (4-hydroxyphenyl) methane (BPE) was investigated under ultraviolet light (λ=254nm) based on the inclusion of two kinds cyclodextrin (α-CD, β-CD) in aqueous solution. The inclusion interaction of α-and β-cyclodextrin with BPE was characterized by fluorescence spectrophotometer. The addition of cyclodextrin could promote photodegradation efficiency of BPE, which the β-CD promoted the most. The kinetics of BPE photodegradation with different initial concentrations was investigated by first-order reaction model. Experiment results demonstrate that β-cyclodextrin inclusion complexation can accelerate BPE photodegradation in aqueous solution under ultraviolet irradiation.

Abstract: In this study, we investigated the possibility of removing and smoothing a single-crystal silicon carbide (SiC) surface under ultraviolet (UV) irradiation in hydrogen peroxide (H₂O₂) solution. In this method, a SiC substrate was excited by UV irradiation that transmitted synthetic quartz, and then an oxide layer on the SiC substrate was formed by photochemical reaction. Simultaneously, hydroxyl radical (OH*) was generated by the decomposition of H₂O₂ solution by UV irradiation. OH* plays an important role of oxidation of SiC surface. With these chemical reactions, oxide layer was effectively formed on the SiC surface. Finally, the oxide layer generated on a SiC substrate was chemically and/or mechanically removed by synthetic quartz and solutions. The polishing characteristics of this method were investigated by controlling the process parameters. Additionally, surface quality and removal depth were measured and evaluated by a phase-shift interference microscopy. Obtained results show that the surface morphology and the removal rate are strongly dependent on the existence of the UV irradiation. Moreover, it is shown that the removal characteristics of the SiC substrate depend on the process parameters such as the process time, reciprocating speed, and contact load. The processed surface has revealed that many scratches on the preprocessed surface was completely removed. The microroughness of the processed surface was improved to 0.15 nm (Rms) and 1.62 nm (p-v), respectively. These results provide useful information for obtaining an atomically smooth SiC surface.

Abstract: Titanium dioxide photocatalyst films were prepared by dip-coating method using titanium dioxide sol solution in order to research the H₂O addition effect on the photocatalytic activities. The sol solution was prepared with titanium tetra-isopropoxide, urea and 2-methoxyethanol, then irradiated ultraviolet light and added distilled H₂O. The substrates for the dip-coating were fused silica plates and as-prepared films were dried at 100 °C then annealed at 650 °C. The films prepared by these methods showed visible light absorption in wavelengths longer than 380 nm and accelerated photodegradation of methylene blue by visible light irradiation. Furthermore, the photocatalytic activities of these films were depending on the H₂O additions to the sol solution.

Abstract: Titanium dioxide sol solution was prepared using titanium tetra-isopropoxide, urea, 2-methoxyethanol. After that, ultraviolet light was irradiated to the sol solution, then, H2O was added to the solution. The prepared sol solution was dip-coated onto fused silica plates. The as-prepared films were dried at 100 °C and then annealed at 650 °C. The annealed films were anatase type titanium dioxides. Visible light absorption by the films was observed in wavelengths longer than 380 nm. Also, photodegradation of methylene blue by visible light irradiation was accelerated in the presence of the films prepared by these methods.

Abstract: The performance of UV/TiO2 (100 mg/L TiO2) process for Orange II degrdation was emphatically compared at pH 2.3, 6.9 and 11.5 by means of UV-Visible spectra, ionic chromatography, TOC, and HPLC analyses. The results revealed that the reaction intermediates were produced in different contents with the increasing reaction time due to the different pH conditions. The dye was oxidized more completely at pH 2.3 while the highest color removal percentage was achieved at pH 11.5. It was proved that active electrons, which is photo-generated along with positive holes on TiO2, not only contribute to the discoloration and mineralization of the dye due to the producing of oxidative species such as O2•- and •OOH, but also contribute to the discoloration of Orange II as reductive species. The most possible mechanism was put forward to explain the key roles of active electrons in dye degradation by UV/TiO2 process at pH 2.3 and 11.5.

Abstract: The ultraviolet irradiation-assisted ultra precision polishing was performed on single crystal diamond substrates. This polishing method has been newly developed in our laboratory. The change of polishing performances was investigated by the presence of the UV irradiation. The polished surfaces were evaluated by the observation with WYKO. The experimental results are as follows; Surface roughness of diamond substrates polished under UV irradiation has become clearly smoother than that without UV irradiation. The surface roughness by this polishing method was reached to be 0.19 nm Ra on (100) surface of single crystal diamond. The equivalent surface was obtained on (110) surface by the UV-polishing.