• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.10
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• pp.883-890
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• 2005

In this paper, the established model of NBTI (Negative Bias Temperature Instability) mechanism was reviewed. Based on this mechanism, then, the influence of nitrogen was discussed among other processes. A constant concentration of nitrogen exists inside $SiO_2$ in order to prevent boron from diffusing and to increase dielectric constant. It was shown that NBTI improvement was achieved by controlling nitrogen profile. It was supposed that the existence of low activation energy of Si-N bonds at $Si-SiO_2$ interface attributes the improvement by making hydrogen prevent interface traps. It was also shown that improvement of NBTI can be achieved by more effective control of nitrogen profile. It was supposed that the maximum control of nitrogen profile can be achieved by DPN (Decoupled Plasma Nitridation) process.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.807-809
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• 2001

Permanent-magnet generators have been used for wind turbines for many years. This paper deals with the AFPM(Axial - Flux Permanent Magnet) Generator with a high power-to-weight ratio, dedicated for small wind turbines. The designed and constructed generator as a prototype in this study is a slotless type AFPM Generator with Neodymium-Iron-Boron magnet rotor. Based on that construction, a magnetic circuit analysis of the generator is carried out. Some important equations covering its characteristics and construction are derived and its magnetic and electrical characteristics are investigated.

• Transactions of Materials Processing
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• v.18 no.4
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• pp.304-309
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• 2009

Quenchable boron steel is a new type of high strength steel to reduce the weight of automobiles and maintain the safety conditions. Quenchable blanks can be hot-stamped and hardened in a water-cooled tool to achieve high strength. In this paper, new alloy for hot stamping is designed based on requirement of mechanical properties and two types of surface coating are investigated in viewpoints of oxidization and exfoliation. An automotive part of center pillar is manufactured by hot-stamping using Al-Si coated sheet. The performance of developed part is compared by static compression test and side impact crash test.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.937-942
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• 1995

Great interest has prompted Boron Neutron Capture Therapy (BNCT) as a new treatment for brain tumors. The use of $^{252}$Cf as a neutron source for BNn makes the in-hospital treatments of tumors to be possible. Newly proposed subcritical multiplying assemblies (SMA) are explored to improve relatively tow neutron fluxes of the source and construct the feasibilities of $^{252}$Cf as a neutron source. The MCNP code has been used to evaluate the effective multiplication factor of the entire system and the intensities and percentages of epithermal neutron flux at the patient-end surface of the system. The neutron beam using SMA shows the epithermal neutron flux enhancement of about 13 times as large as the beam without using SMA. It is expected that the neutron beam proposed in this research will be more effective for treatment of tumors due to the increased therapeutic neutron fluxes.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.11a
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• pp.155-156
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• 2017

Borosilicate glass was incorporated to improve the neutron shielding capability of concrete. Boron is a typical neutron shielding material, and it is contained in borosilicate glass. However, borosilicate glass causes alkali-silica reaction, which damages the concrete. Therefore, studied to reduce the expansion due to alkali-silica reaction and to improve the neuton shielding capability. The measurement of the expansion due to the alkali-silica reaction was based on ASTM C 1260. Experimental results show that the expansion due to alkali-silica reaction is reduced when borosilicate glass powder incorporated. In addition, the neutron shielding capability was significantly improved when the fine aggregate replaced with borosilicate glass.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.6
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• pp.586-591
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• 2004

We studied the dependence of hot-tarrier-induced degradation characteristics on nitrogen concentration in NO(Nitrided-Oxide) gate of nMOS, under ac and dc stresses. The $\Delta$V$_{t}$ and $\Delta$G$_{m}$ dependence of nitrogen concentration were observed, We observed that device degradation was suppressed significantly when the nitrogen concentration in the gate was increased. Compared to $N_2$O oxynitride, NO oxynitride gate devices show a smaller sensitivity to ac stress frequency. Results suggest that the improved at-hot carrier immunity of the device with NO gate may be due to the significantly suppressed interface state generation and neutral trap generation during stress.ess.

• Nuclear Engineering and Technology
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• v.8 no.1
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• pp.29-40
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• 1976

An investigation on the effect of electrostatic drift field which can bring an additional aid to the photogenerated carrier collection in one side of the silicon solar cell has been carried out. The drift field was produced by the gradient of boron concentration in the p-type side in virtue of the strain compensation due to the tin dopant. A new method of ion implantation which is based on the principle of chiefly radiation-enhanced diffusion is adopted for forming the p-n junction in the solar cell. The open circuit voltage and the conversion efficiency of the ion-implanted silicon solar cell sample can be figured out to be 0.44 V and 5%, respectively.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3448-3451
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• 2022

Biochar is a novel carbon based material derived from waste that shows promising properties for several applications. In this paper we investigate its potential use as a low cost, greener alternative to commonly used aggregates employed to enhance the neutron shielding performance of concrete. Monte Carlo simulations are performed with the PHITS code to estimate the neutron attenuation of blank and biochar-reinforced concrete exposed to high energy neutrons. We find that the shielding performance of concrete with 15% biochar is comparable with commonly used materials such as Boron Carbide at 20% and exceeds that of Basalt fibers with the same concentration, making these composites an interesting greener alternative to current solutions. A combination of biochar and heavier fillers also show extremely promising performance.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1642-1651
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• 2021

In this study, isophtalic neopentyl glycol polyester (NPG-PES) based composites with different loading ratios of pure tungsten metal (W), tungsten (VI) oxide (WO₃), tungsten boron (WB) and tungsten carbide (WC) composites were prepared as alternative shielding materials for ionizing electromagnetic radiation (IEMR) shielding. Structural characterizations of the composites were done. Gamma spectrometric analysis of composites for 80-2000 keV energy range was performed and their usability as IEMR shielding was discussed. As a result, the produced composites showed a shielding performance of 60-100% of the lead (the most widely used IEMR shielding material) depending on the reinforcement material, reinforcement loading rate and experimental conditions. Thus, it was reported that produced composites could be an alternative to lead shieldings that have several disadvantages as toxic properties, difficulty of processing and inelasticity.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.100-100
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• 2016

Among various two-dimensional (2D) materials, 2D semiconductors and insulators have attracted a great deal of interest from nanoscience community beyond graphene, due to their attractive and unique properties. Such excellent characteristics have triggered highly active researches on 2D materials, such as hexagonal boron nitride (hBN), molybdenum disulfide (MoS2), and tungsten diselenide (WSe2). New physics observed in 2D semiconductors allow for development of new-concept devices. Especially, these emerging 2D materials are promising candidates for flexible and transparent electronics. Recently, van der Waals heterostructures (vdWH) have been achieved by putting these 2D materials onto another, in the similar way to build Lego blocks. This enables us to investigate intrinsic physical properties of atomically-sharp heterostructure interfaces and fabricate high performance optoelectronic devices for advanced applications. In this talk, fundamental properties of various 2D materials will be introduced, including growth technique and influence of defects on properties of 2D materials. We also fabricate high performance electronic/optoelectronic devices of vdWH, such as transistors, memories, and solar cells. The device platform based on van der Waals heterostructures show huge improvement of devices performance, high stability and transparency/flexibility due to unique properties of 2D materials and ultra-sharp heterointerfaces. Our work paves a new way toward future advanced electronics based on 2D materials.