• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.234-234
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• 2011

Electron-neutral collision frequency is one of the important parameters in the plasma physics and in industrial plasma engineering. We can understand the momentum, energy, and charge transport properties of the plasma using electron-neutral collision frequency.[1] The wave-cutoff method is a diagnostic method for the electron density measurement, but the cutoff peak value depends on gas pressure. The wave-cutoff signal becomes unclear as increasing gas pressure. The reason of pressure dependence is that the electron-neutral collision disturbs electron motion so that microwave can propagate through plasma at plasma frequency.[2] Using the pressure dependence of wave-cutoff method we can find the electron-neutral collision frequency. At first we tried to confirm this method using well known gas such as Ar. The cutoff signal decrease as increasing gas pressure (the simulation result). The wave-cutoff signal is unclear at a gas pressure of 500 mTorr. (electron density $1.0{\times}10^{10}/cm^3$, electron temperature 1.7 eV, electron -neutral collision frequency~1 GHz). In this condition, the electron-neutral collision frequency is closed to the wave-cutoff frequency.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.87.2-87.2
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• 2012

The HI absorption against bright continuum source provides a unique opportunity to measure spin temperature of the neutral hydrogen gas. We find three cases among the sample of the VIVA (VLA Imaging of Virgo galaxies in Atomic gas) study with self absorption of strong central continuum by galactic HI gas. Using the HI flux ratio of emission and absorption, we constrain the spin temperature of the neutral hydrogen gas on their disk. The HI absorption is marginally resolved in these galaxies, which also allows us to probe the kinematics of the absorbing gas. All three galaxies are severely stripped in HI due to the intra cluster medium (ICM). We discuss the influence of environmental processes on the temperature and kinematics of HI in these galaxies.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.251-252
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• 2012

Recently, the growing interest in organic microelectronic devices including OLEDs has led to an increasing amount of research into their many potential applications in the area of flexible electronic devices based on plastic substrates. However, these organic devices require a gas barrier coating to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency OLEDs require an extremely low Water Vapor Transition Rate (WVTR) of $1{\times}10^{-6}g/m^2$/day. The Key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required ($1{\times}10^{-6}g/m^2$/day) is the suppression of defect sites and gas diffusion pathways between grain boundaries. In this study, we developed an $Al_2O_3$ nano-crystal structure single gas barrier layer using a Neutral Beam Assisted Sputtering (NBAS) process. The NBAS system is based on the conventional RF magnetron sputtering and neutral beam source. The neutral beam source consists of an electron cyclotron Resonance (ECR) plasma source and metal reflector. The Ar+ ions in the ECR plasma are accelerated in the plasma sheath between the plasma and reflector, which are then neutralized by Auger neutralization. The neutral beam energies were possible to estimate indirectly through previous experiments and binary collision model. The accelerating potential is the sum of the plasma potential and reflector bias. In previous experiments, while adjusting the reflector bias, changes in the plasma density and the plasma potential were not observed. The neutral beam energy is controlled by the metal reflector bias. The NBAS process can continuously change crystalline structures from an amorphous phase to nano-crystal phase of various grain sizes within a single inorganic thin film. These NBAS process effects can lead to the formation of a nano-crystal structure barrier layer which effectively limits gas diffusion through the pathways between grain boundaries. Our results verify the nano-crystal structure of the NBAS processed $Al_2O_3$ single gas barrier layer through dielectric constant measurement, break down field measurement, and TEM analysis. Finally, the WVTR of $Al_2O_3$ nano-crystal structure single gas barrier layer was measured to be under $5{\times}10^{-6}g/m^2$/day therefore we can confirm that NBAS processed $Al_2O_3$ nano-crystal structure single gas barrier layer is suitable for OLED application.

• Journal of the Korean Vacuum Society
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• v.19 no.2
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• pp.121-127
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• 2010

Neutral gas in a Hall-effect thruster in a small satellite is simulated using a molecular dynamics code. Investigated are neutral density, pressure, axial average velocity, and temperature for the variation of diffusive reflection ratio, initial gas temperature, and channel length. Expected through this research are improving of discharge simulation through the neutral simulation and understanding of real system.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.178-178
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• 2012

Neutral atom temperature was measured by Laser Rayleigh scattering method using neutral depletion by neutral heating with ideal gas law in Inductively coupled plasma. We observed sudden pressure change when plasma is turned on and off. We analyzed mechanism of neutral heating by employing zero-dimensional neutral and ion energy balance model simultaneously. The results showed that neutral atom temperature increase with ion density. The mechanism of neutral atom heating and cooling is mainly dominated by ion-neutral collision including elastic and charge-exchange collision and by wall cooling respectively.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.43.1-43.1
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• 2017

A three-dimensional (3D) $Ly{\alpha}$ radiative transfer code is developed to study the Wouthuysen-Field effect, which couples the 21 cm spin temperature of neutral hydrogen and the $Ly{\alpha}$ radiation field, and the escape fraction of $Ly{\alpha}$ from galaxies. The Monte Carlo code is capable of treating arbitrary 3D distributions of $Ly{\alpha}$ source, neutral hydrogen and dust densities, gas temperature, and velocity field. It is demonstrated that the resonance-line profile at the center approaches to the Boltzmann distribution with the gas temperature. A plane-parallel ISM model, which is appropriate for the neutral ISM of our Galaxy, is used to calculate the $Ly{\alpha}$ radiation field strength as a function of height above the galactic plane. We also use a two-phase, clumpy medium model which is composed of the cold and warm neutral media (WNM). It is found that the $Ly{\alpha}$ radiation field is strong enough to thermalize the 21 cm spin temperature in the WNM to the gas kinetic temperature. The escape fraction of $Ly{\alpha}$ is found to be a few percent, which is consistent with the $Ly{\alpha}$ observations of our Galaxy and external galaxies.

• Journal of the Korean Society of Safety
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• v.39 no.1
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• pp.27-32
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• 2024

This study analyzed cases of hydrogen (H₂) and natural gas (CH₄) leakage from a hydrogen-blended natural gas pipeline to determine a range of leakage characteristics, including leakage type, pipe material, pipe diameter, pressure, and damage size. Based on the results of this analysis, five hydrogen-blended natural gas leakage scenarios were selected. The national vision for a carbon-neutral society by 2050 is a very important strategic objective and promotes environmentally sustainable economic development in the age of the climate crisis. Accordingly, zero-carbon and low-carbon policies are being promoted in various fields, including energy production, consumption, and industrial processes. Hydrogen-blended natural gas is eco-friendly and is considered an important step towards carbon neutrality, with various countries including the United States and several European countries conducting empirical research to further investigate its potential. In Korea, a national research project commenced in April 2023 to verify and demonstrate the life cycle safety of blending hydrogen into the natural gas network. The results of this study will provide important data for the analysis of the damage impacts caused by the leakage of hydrogen-blended natural gas, such as the diffusion of gas clouds, fires, and gas explosions.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.41.1-41.1
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• 2021

Neutral (HI) gas clouds associated with galaxies are responsible for fuelling the star-formation in the universe. In literature, the extremely strong damped Lyman-alpha absorbers (or ESDLAs) have been known to be sensitive to the effects of HI-H2 transition and star-formation in galaxies. Yet, ESDLAs are rare to probe due to the smaller cross section they subtend on the sky (similar to galaxies). In my talk, I will focus primarily on my study of the nature of ESDLAs that are observed as absorption signature along the line-of-sight (LOS) of a quasar (QSO). I will further look at the HI-H2 transition and interesting results relevant to diffuse molecular gas and the multi-phase medium (gas in different ionization states) that are associated with ESDLAs. Furthermore, I will also discuss how the ESDLA environments differ from the high star-forming and molecular environments detected in blind optical and radio surveys consecutively.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2011.05a
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• pp.135-136
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• 2011

본 연구에서는 실리콘 기판위의 형성된 AAO (Anodic Aluminum Oxide)의 barrier layer를 $Cl_2/BCl_3$ gas mixture에서 Neutral Beam Etching (NBE)과 Ion Beam Etching (IBE)로 각각 식각한 후 그 결과를 비교하였다. 이온빔의 경우 나노사이즈의 AAO pore의 charging에 의해 pore 아래쪽의 위치한 barrier layer를 어떤 식각조건에서도 제거하지 못하였다. 하지만, charging effect가 없고, 높은 중성화율을 나타내는 low angle forward reflected 방식의 neutral beam etching (NBE)에서는 $BCl_3$-rich $Cl_2/BCl_3$ gas mixture인 식각조건에서 AAO pore에 휘발성 $BO_xCl_y$를 형성하면서 barrier layer를 제거할 수 있었다.

• Journal of the Korean Institute of Gas
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• v.27 no.1
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• pp.70-77
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• 2023

Air environment regulations have been strengthened due to increasing air pollutant emissions, the target of reducing emissions has increased and interest in gas measurement methods is also increasing. The sampling method is mainly used, but due to the spatial and temporal measurement limitations, the laser absorption spectroscopy which is a real-time and in-situ method is in the spotlight. In this study, we studied the wavelength modulation spectroscopy and described the calibration-free algorithm. The developed algorithm was modified to reflect 46 multi-absorption lines and was applied to light absorption signal analysis in visible and mid-infrared regions. In addition, the difference between the modulation parameters of laser was analyzed. As a result of reviewing the performance through O₂ and NO gas measurement experiments of various concentration conditions, the linearity was R²_O2=0.99999 and R²_NO=0.99967.