• Journal of the Optical Society of Korea
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• v.18 no.5
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• pp.569-573
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• 2014

We demonstrate a low-cost, superbly efficient way of etching for the nano-, and micro-sized pyramid patterns on (100)-oriented Si wafer surfaces for use as a patterned master. We show a way of producing functional optical films for the viewing angle direction brightness-enhancement of Lambertian LED (light emitting diode)/OLED (organic light emitting diode) planar lighting applications. An optimally formulated KOH (Potassium hydroxide) wet etching process enabled random-positioned, and random size-distributed (within a certain size range) pyramid patterns to be developed over the entire (100) silicon wafer substrates up to 8" and a simple replication process of master patterns onto the PC (poly-carbonate) and PMMA (poly-methyl methacrylate) films were performed. Haze ratio values were measured for several film samples exhibiting excellent values over 90% suitable for LED/OLED lighting purposes. Brightness was also improved by 13~14% toward the viewing angle direction. Computational simulations using LightTools$^{TM}$ were also carried out and turned out to be in strong agreement with experimental data. Finally, we could check the feasibility of fabricating low-cost, large area, high performance optical films for commercialization.

• Analytical Science and Technology
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• v.36 no.4
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• pp.191-197
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• 2023

Radioactivity concentrations for natural radionuclides were determined from fine dust samples collected in Jeju, Korea according to atmospheric events (Asian dust, haze, fog-mist, and non-event), and radium equivalent activity was calculated. The mean atmospheric radioactivity concentrations for ²³⁸U, ²³²Th, and ⁴⁰K in 127 fine dust samples were 0.49, 0.24, and 7.23 µBq m^-3, respectively, and the radium equivalent activity was 33.25 Bq kg^-1. The mean concentrations of ²³⁸U and ²³²Th in the fine dust during the Asian dust period were 1.31 and 1.60 µBq m^-3, respectively, above the global average, while the values for the other three atmospheric events were lower. The ratio of ²³²Th/²³⁸U radioactivity during the Asian dust period was 1.22, higher than the ratio for the other three atmospheric events.

• Applied Chemistry for Engineering
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• v.34 no.4
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• pp.383-387
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• 2023

The quartz crystal microbalance (QCM), commonly used in high vacuum deposition, becomes difficult to use when a thick film is deposited on the quartz, affecting the crystal's inherent vibration. In this study, a non-destructive optical measurement method was developed to measure the film's deposition rate during the in-situ film deposition process. By measuring the scattered laser intensity caused by the dimer in the parylene gas passing through the gas flow path, it was successfully confirmed that the ratio of the dimer in the parylene gas increases as the pyrolysis temperature decreases. Additionally, it was noted that the film's thickness and haze increase as the pyrolysis temperature decreases by confirming the characteristics of the visible parylene films. Through the research results, we aim to utilize the stable in-situ film deposition rate measurement system to control the precise film deposition rate of parylene films.

• Journal of Korean Society for Atmospheric Environment
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• v.31 no.3
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• pp.209-222
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• 2015

Fine and coarse PM had been collected by LVCI (low volume cascade impactor) and HVAS (high volume air sampler) during January 1989 to April 2012 at Kyung Hee University, Global Campus located on the boarder of Yongin and Suwon. The database of PM mass concentration was constructed and then intensively and extensively investigated to understand monthly, seasonal, and annual patterns of each PM behavior. Especially the study separated all the PM data into the 5 Period Zones, which were classified on the basis of social, political, and environmental issues that might be influencing local ambient air quality during the monitoring period. The overall $PM_{10}$ level had been continuously decreased until 2005 and after then was staggering due to rapidly increasing $PM_{2.5}$ level in $PM_{10}$. The annual average of $PM_{2.5}$ concentration varied from $34.3{\mu}g/m^3$ to $59.0{\mu}g/m^3$, which were much higher than the 2015 ambient air quality standard. The $PM_{2.5}$ level was strongly associated with haze events, while both $PM_{10}$ and $PM_{2.5}$ levels were associated with Yellow storm events. Daily concentrations of $PM_{2.5}$ were ranged $13.1{\sim}212.9{\mu}g/m^3$ in haze days and $33.6{\sim}124.6{\mu}g/m^3$ in Asian dust days. The study also intensively investigated annual and seasonal patterns of $PM_{2.5}/PM_{10}$ ratios.

• Atmosphere
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• v.27 no.2
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• pp.225-233
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• 2017

Korea has recently suffered from severe hazes, largely being long-range transported from China but frequently mixed with domestic pollution. It is important to identify the origin of the frequently-occurring hazes, which is however hard to clearly determine in a quantitative term. In this regard, we suggest a possible classification procedure of various hazes into long-range transported haze (LH), Yellow Sand (YS), and urban haze (UH), based on mass loading of fine particles, time lag of PM mass concentrations between two sites aligned with dominant wind direction, backward trajectory of air mass, and the mass ratio of PM2.5 to PM10. The analysis sites are Seoul (SL) and Baengnyeongdo (BN), which are distant about 200 km from each other in the west to east direction. Aerosol concentrations at BN are overall lower than those of SL, indicative of BN being a background site for SL. We found distinct time lag of PM2.5 and PM10 concentrations between BN and SL in case of both LH and YS, but the intensity of YS being stronger than LH. Time scale (e-folding time scale) of LH appears to be longer and more variable than YS, which implies that LH covers much larger spatial scale. In addition, we found linear and significant correlations between ${\tau}_a$ obtained from sunphotometer and ${\tau}_{cal}$ calculated from surface aerosol scattering coefficient for LH episodes, relative to few correlation between those for YS, which might be associated with transported height of YS being much higher than LH. Therefore surface PM concentrations for the YS period are thought to be not representative for vertical integrated amount of aerosol loadings, probably by virtue of decoupled structure of aerosol vertical distribution. Improvement of various hazes classification based on the current result would provide the public as well as researchers with more accurate information of LH, UH, and YS, in terms of temporal scale, size, vertical distribution of aerosols, etc.

• Journal of the Korean Applied Science and Technology
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• v.26 no.1
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• pp.93-101
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• 2009

Antistatic acrylic resin is made from n-butyl methacrylate, methyl methacrylate, dimethyl amino ethyl methacrylate(DMAEMA), 2-ethyl hexyl methacrylate, hydroxy ethyl methacrylate, 2,2'-azobis iso-butyronitrile by synthesis. To achieve a lowest surface resistance of antistatic acrylic resin was applied to a variety of synthesis processes. The acrylic resin has been determined from the value of surface resistance and -then the antistatic acrylic resin including dimethyl amino ethyl methacrylate of the 10%, 20% and 30% is synthesized. Finally, dimethyl sulfate(DMS) on a variety of weight ratios is added to antistatic acrylic resin. When DMAEMA / DMS weight ratio is 1/1, antistatic acrylic resin isn't haze the lower the surface resistance. Compared to the traditional antistatic agent, all aspects of the physical properties is outstanding.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.345.2-345.2
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• 2016

Alumina (Al2O3) doped zinc oxide (ZnO) films (AZO) have been prepared from 2 wt.% Al2O3 doped ZnO target by DC magnetron sputtering at a 2 mTorr (0.27 Pa) chamber pressure in (15 sccm) argon ambient. We obtained films of various opto-electronic properties by variation of target angle from 32.5o to 72.5o. At lower target angle deposited films show higher values in optical gap, mobility of charge carrier, carrier concentration, crystallite grain size, transmission range of wavelength, which are favorable characteristics of AZO as a transparent conducting oxide (TCO). At higher target angle the sheet resistance, work function, surface roughness for the AZO films increases. Measured haze ratio of the films changed lower to higher and size of characteristic surface structure of as deposited film ranges from ~40 nm to ~300 nm. By a combination of low and high target angle we obtained a textured TCO film with high conductivity.

• Atmosphere
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• v.18 no.1
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• pp.1-14
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• 2008

The cloud amount, one of the basic parameter in atmospheric observation, have been observed by naked eyes of observers, which is affected by the subjective view. In order to ensure reliable and objective observation, a new algorithm to retrieve cloud amount was constructed using true color images composed of red, green and blue (RGB). The true color image is obtained by the Skyview, an all-sky imager taking pictures of sky, at the Science Building of Yonsei University, Seoul for a year in 2006. The principle of distinguishing clear sky from cloudy sky lies in the fact that the spectral characteristics of light scattering is different for air molecules and cloud. The result of Skyview's algorithm showed about 77% agreement between the observed cloud amount and the calculated, for the error range, the difference between calculated and observed cloudiness, within ${\pm}2$. Seasonally, the best accuracy of about 83% was obtained within ${\pm}2$ range in summer when the cloud amounts are higher, thus better signal-to-noise ratio. Furthermore, as the sky turbidity increased, the error also increased because of increased scattering which can explain the large error in spring. The algorithm still need to be improved in classifying sky condition more systematically with other complimentary instruments to discriminate thin cloud from haze to reduce errors in detecting clouds.

• Journal of Environmental Science International
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• v.29 no.7
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• pp.749-760
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• 2020

This study investigates the characteristics of diurnal, seasonal, and weekly roadside and residential concentrations of PM₁₀ and PM_2.5 in Busan, as well as relationship with meteorological phenomenon. Annual mean PM₁₀ and PM_2.5 concentrations in Busan were 44.2 ㎍/㎥ and 25.3 ㎍/㎥, respectively. The PM_2.5/PM₁₀ concentration ratio was 0.58. Diurnal variations of PM₁₀ and PM_2.5 concentrations in Busan were categorized into three types, depending on the number of peaks and times at which the peaks occurred. Roadside PM₁₀ concentration was highest on Saturday and lowest on Friday. Residential PM₁₀ concentration was highest on Monday and lowest on Friday. Residential PM_2.5 concentration was highest on Monday and Tuesday and lowest on Friday. PM₁₀ and PM_2.5 concentrations were highest on Asian dust and haze, respectively. The results indicate that understanding the spaciotemporal variation of fine particles could provide insights into establishing a strategy to control urban air quality.

• Korean Journal of Materials Research
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• v.19 no.5
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• pp.259-264
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• 2009

In this study we investigated the effect of the multi-step texturing process on the electrical and optical properties of hydrogenated Al-doped zinc oxide (HAZO) thin films deposited by rf magnetron sputtering. AZO films on glass were prepared by changing the $H_2/(Ar+H_2)$ ratio at a low temperature of $150^{\circ}C$. The prepared HAZO films showed lower resistivity and higher carrier concentration and mobility than those of non-hydrogenated AZO films. After deposition, the surface of the HAZO films was multi-step textured in diluted HCl (0.5%) for the investigation of the change in the optical properties and the surface morphology due to etching. As a result, the HAZO film fabricated under the type III condition showed excellent optical properties with a haze value of 52.3%.