Hyoung-Do Kim

Formation of 2–5 nm size pre-precipitates of cF96 phase in a Hf–Co–Al glassy alloy

Abstract The devitrification behaviour of Hf 55 Co 25 Al 20 glassy alloy was studied by X-ray diffractometry, transmission electron microscopy, differential scanning and isothermal calorimetry. Formation of a nanoscale structure with a pre-precipitate of the cF96 Ti 2 Ni-type phase embedded in the residual glassy matrix was observed upon annealing. We obtained an Avrami exponent value of 2.6, indicating that the primary pre-precipitates are formed by steady state nucleation and diffusion-controlled growth of nuclei.

Effects of Fluorine Doping on the Electrical Performance of ZnON Thin-Film Transistors

In this work, the effects of fluorine incorporation in high mobility zinc oxynitride (ZnON) semiconductor are studied by both theoretical calculations and experimental evaluation of thin film transistors (TFTs). From density functional theory (DFT) calculations, fluorine acts as a carrier suppressor in the ZnON matrix when it substitutes a nitrogen vacant site (VN). Thin films of ZnON and ZnON:F were grown by reactively cosputtering Zn metal and ZnF2 targets, and their electrical, physical, and chemical characteristics were studied. X-ray photoelectron spectroscopy (XPS) analyses of the nitrogen 1s peaks in ZnON and ZnON:F suggest that as the fluorine incorporation increases, the relative fraction of Zn-N bonds from stoichiometric Zn3N2 increases. On the other hand, the Zn-N bond characteristics arising from nonstoichiometric ZnxNy and N-N bonds decrease, implying that indeed fluorine anions have an effect of passivating the N-related defects. The corresponding TFTs exhibit optimum transfer characteristics and switching ability when approximately 3.5 atomic percent of fluorine is present in the 40 nm thick ZnON:F active layer.

Characteristics of Indium Tin Zinc Oxide Thin Film Transistors with Plastic Substrates

We examined the characteristics of indium tin zinc oxide (ITZO) thin film transistors (TFTs) on polyimide (PI) substrates for next-generation flexible display application. In this study, the ITZO TFT was fabricated and analyzed with a SiOx/SiNx gate insulator deposited using plasma enhanced chemical...

Highly Stable Thin-Film Transistors Based on Indium Oxynitride Semiconductor

In this study, the properties of indium oxynitride (InON) semiconductor films grown by reactive radio frequency sputtering were examined both experimentally and theoretically. Also, thin-film transistors (TFTs) incorporating InON as the active layer were evaluated for the first time. It is found that InON films exhibit high stability upon prolonged exposure to air and the corresponding TFTs are more stable when subjected to negative bias illumination stress, compared to devices based on indium oxide (In2O3) or zinc oxynitride (ZnON) semiconductors. X-ray photoelectron spectroscopy analyses of the oxygen 1s peaks suggest that as nitrogen is incorporated into In2O3 to form InON, the relative fraction of oxygen-deficient regions decreases significantly, which is most likely to occur by having the valence band maximum shifted up. Density functional theory calculations indicate that the formation energy of InN is much lower than Zn3N2, thus accounting for the higher stability of InON compared to ZnON in air.

Preliminary Analysis of SGTR Accident for an Integral Effect Test Facility, SMART-ITL

SMART-ITL (system-integrated modular advanced reactor-integral test loop) has been built at Korea Atomic Energy Research Institute (KAERI) in order to validate the safety and performance of SMART. It is an integral effect test facility and its scale is 1/1 in height and 1/49 in volume with respect to SMART plant. The objectives of SMART-ITL are to investigate and understand the integral performance of reactor systems and components and the thermal-hydraulic phenomena occurred in the system during normal, abnormal and emergency conditions, and to verify the system safety during various design basis events of SMART. The integral-effect test data will also be used to validate the related thermal-hydraulic models of the safety analysis code such as TASS/SMR-S, which is used for performance and accident analysis of SMART design.SMART with a rated thermal power of 330 MWt has been developed at KAERI. SMART is an integral type pressurized water reactor with a mixture of the proven technologies and advanced design features. The enhancement of safety is realized by incorporating inherent safety features and passive safety systems. The licensing has been approved by the Korean nuclear regulatory authority in 2012. TASS/SMR-S code can analyze thermal hydraulic phenomena of SMART in a full range of reactor operating and accident conditions. A steam generator tube rupture (SGTR) accident is one of the safety related design basis events and should be analyzed with thermal hydraulic and radiological viewpoint. A preliminary analysis of an SGTR accident for SMART-ITL was performed using TASS/SMR-S code to setup test procedure.The thermal-hydraulic analysis for SMART-ITL SGTR accident with the geometrical, thermal-hydraulic parameters and modeling information was performed. The major concern of this analysis was to find the thermal-hydraulic phenomena and maximum leakage amount from a primary to a secondary side caused by an SGTR accident. The result was also compared with the result of SMART SGTR accident analysis. In spite of the different assumptions and scaling, the compared results are reasonable. The characteristics of SMART SGTR accident are well reflected on SMART-ITL. The analysis result of preliminary SMART-ITL SGTR accident estimates the major effects of SMART SGTR accident successfully.© 2013 ASME