• Carbon letters
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• v.12 no.1
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• pp.16-20
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• 2011

Commercial PAN fibers were thermally stabilized at 220 or $240^{\circ}C$ for 30 min. Those fibers were further stabilized using radio-frequency (RF) capacitive plasma discharge during 5 or 15 min. From Fourier transform infrared spectroscopy results, it was observed that an additional plasma treatment led to further stabilization of PAN fibers. After stabilization, carbonization was performed to investigate the final tensile properties of the fabricated carbon fibers (CFs). The results revealed that a combination of thermal and plasma treatment is a possible stabilization process for manufacturing CFs. Morphology of CFs was investigated using scanning electron microscopy. The morphology shows that the plasma stabilization performed by the RF large gap plasma discharge may damage the surface of the CF, so it is necessary to select a proper process condition to minimize the damage.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.100-101
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• 2012

The plasma damage free and room temperature processedthin film deposition technology is essential for realization of various next generation organic microelectronic devices such as flexible AMOLED display, flexible OLED lighting, and organic photovoltaic cells because characteristics of fragile organic materials in the plasma process and low glass transition temperatures (Tg) of polymer substrate. In case of directly deposition of metal oxide thin films (including transparent conductive oxide (TCO) and amorphous oxide semiconductor (AOS)) on the organic layers, plasma damages against to the organic materials is fatal. This damage is believed to be originated mainly from high energy energetic particles during the sputtering process such as negative oxygen ions, reflected neutrals by reflection of plasma background gas at the target surface, sputtered atoms, bulk plasma ions, and secondary electrons. To solve this problem, we developed the NBAS (Neutral Beam Assisted Sputtering) process as a plasma damage free and room temperature processed sputtering technology. As a result, electro-optical properties of NBAS processed ITO thin film showed resistivity of $4.0{\times}10^{-4}{\Omega}{\cdot}m$ and high transmittance (>90% at 550 nm) with nano- crystalline structure at room temperature process. Furthermore, in the experiment result of directly deposition of TCO top anode on the inverted structure OLED cell, it is verified that NBAS TCO deposition process does not damages to the underlying organic layers. In case of deposition of transparent conductive oxide (TCO) thin film on the plastic polymer substrate, the room temperature processed sputtering coating of high quality TCO thin film is required. During the sputtering process with higher density plasma, the energetic particles contribute self supplying of activation & crystallization energy without any additional heating and post-annealing and forminga high quality TCO thin film. However, negative oxygen ions which generated from sputteringtarget surface by electron attachment are accelerated to high energy by induced cathode self-bias. Thus the high energy negative oxygen ions can lead to critical physical bombardment damages to forming oxide thin film and this effect does not recover in room temperature process without post thermal annealing. To salve the inherent limitation of plasma sputtering, we have been developed the Magnetic Field Shielded Sputtering (MFSS) process as the high quality oxide thin film deposition process at room temperature. The MFSS process is effectively eliminate or suppress the negative oxygen ions bombardment damage by the plasma limiter which composed permanent magnet array. As a result, electro-optical properties of MFSS processed ITO thin film (resistivity $3.9{\times}10^{-4}{\Omega}{\cdot}cm$, transmittance 95% at 550 nm) have approachedthose of a high temperature DC magnetron sputtering (DMS) ITO thin film were. Also, AOS (a-IGZO) TFTs fabricated by MFSS process without higher temperature post annealing showed very comparable electrical performance with those by DMS process with $400^{\circ}C$ post annealing. They are important to note that the bombardment of a negative oxygen ion which is accelerated by dc self-bias during rf sputtering could degrade the electrical performance of ITO electrodes and a-IGZO TFTs. Finally, we found that reduction of damage from the high energy negative oxygen ions bombardment drives improvement of crystalline structure in the ITO thin film and suppression of the sub-gab states in a-IGZO semiconductor thin film. For realization of organic flexible electronic devices based on plastic substrates, gas barrier coatings are required to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency flexible AMOLEDs needs an extremely low water vapor transition rate (WVTR) of $1{\times}10^{-6}gm^{-2}day^{-1}$. The key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required (under ${\sim}10^{-6}gm^{-2}day^{-1}$) is the suppression of nano-sized defect sites and gas diffusion pathways among the grain boundaries. For formation of high quality single inorganic gas barrier layer, we developed high density nano-structured Al2O3 single gas barrier layer usinga NBAS process. The NBAS process can continuously change crystalline structures from an amorphous phase to a nano- crystalline phase with various grain sizes in a single inorganic thin film. As a result, the water vapor transmission rates (WVTR) of the NBAS processed $Al_2O_3$ gas barrier film have improved order of magnitude compared with that of conventional $Al_2O_3$ layers made by the RF magnetron sputteringprocess under the same sputtering conditions; the WVTR of the NBAS processed $Al_2O_3$ gas barrier film was about $5{\times}10^{-6}g/m^2/day$ by just single layer.

• The Korean Journal of Nuclear Medicine
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• v.3 no.2
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• pp.1-16
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• 1969

The double tracer study on erythrokinetics was carried out experimentally with radioactive iron ($^{59}Fe$) and chromium ($^{51}Cr$) in rabbits. The 0.1% canthalidin solution and 1% pot. perchlomate solution was given subcutaneously to 20 rabbits respectively. 3 and 6 days after injection, the blood chemistry, urine examination, ferrokinetics and apparent half survival time of RBC were ($^{51}Cr\;T\frac{1}{2}$)determined. Following were the results: 1) Red blood cell hematocrit and hemoglobin values were moderately reduced and B.U.N. and serum creatinine values were slight]y inercased in the canthalidin group, while B.U.N. and serum creatinine values were within normal limits in the pot. perchlomate group. Reticulocyte values were slight]y increased in the canthalidin group, while was normal range in the pot. perchlomate group. 2) Blood chemistry finding was not significant statistically in both experimental groups, but serum iron value was moderately reduced in both group. 3) Plasma volume was unchanged in both group, but red cell volume and whole blood volume were slightly reduced in both groups. 4) Results of ferrokinetics were as follows: i) The plasma iron disappearance rate was delayed in both groups. Plasma iron turnover rate, red cell iron utilization and red cell iron turnover rate were decreased in both groups, and then red cell iron turnover rate was more decreased than plasma iron turnover rate in both groups. Circulating red cell iron was slight]y increased in canthalidin group and red cell iron concentration was within normal range in both groups. ii) P.I.T.R.-R.C.I.T. value was moderately increased in the canthalidin group and slightly increased in the pot. perchlomate group. Reticulocyte index, red cell iron turnover index, plasma iron turnover index and effective erythropoiesis index were whole]y reduced in both groups. iii) The red cell life span was slightly shortened in the canthalidin group while was within normal range in pot. perchlomate group. The pathologic finding of renal biopsy of the canthalidin group shows a selective damage in glomerulus, while shows almost normal range or slight damage in tubules. And that of the pot. perchlomate group shows a selective damage in tubules with slight damage of glomerulus.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.4
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• pp.319-324
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• 2002

In this study, the reduce of plasma etching damage in PZT thin film with addictive gas and re-annealing after etching have been investigated. The PZT thin films were etched as a function of $Cl_2/CF_4$ with addition of Ar and $O_2$ with inductively coupled plasma. The etch rates of PZT thin films were 1450 ${\AA}/min$ at 30% additive Ar and 1100 ${\AA}/min$ at 10% auditive $O_2$ into $Cl_2/CF_4$ gas mixing ratio of 8/2. In order to reduce plasma damage of PZT thin films after etching, the etched PZT thin films were re-annealed at various temperatures at $O_2$ atmosphere. From the hysteresis curries, the ferroelectric properties are improved by $O_2$ re-annealing process. The improvement of ferroelectric behavior at annealed PZT films is consistent wish the increase of the (100) and (200) PZT peaks revealed by x-ray diffraction (XRD). From x ray photoelectron spectroscopy (XPS) analysis, the intensity of Pb-O, Zr-O and Ti-O peak are increased and the chemical residue peak is reduced by $O_2$ re-annealing. The ferroelectric behavior consistent with the dielectric nature of $Ti_xO_y$ is recovered by $O_2$ recombination during rapid thermal annealing process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.178-181
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• 2003

In this work, we etched PZT films with various additive gases ($O_2$ and Ar) in $Cl_2/CF_4$ plasmas, while mixing ratio was fixed at 8/2. After the etching, the plasma induced damages are characterized in terms of hysteresis curves, leakage current, retention properties, and switching polarization. When the electrical properties of PZT etched in $O_2$ or Ar added $Cl_2/CF_4$ were compared, the value of remanent polarization in $O_2$ added $Cl_2/CF_4$ plasma is higher than that in Ar. added plasma. The maximum etch rate of the PZT thin films was 145 nm/min for 30% Ar added $Cl_2/CF_4$ gas having mixing ratio of 8/2 and 110 nm/min for 10% $O_2$ added to that same gas mixture. In order to recover the ferroelectic properties of the PZT thin films after etching, we annealed the etched PZT thin films at $550^{\circ}C$ in an $O_2$ atmosphere for 10 min. From the hysteresis curves, leakage current, retention property and switching polarization, the reduction of the etching damage and the recovery via the annealing was turned out to be more effective when $O_2$ was added to $Cl_2/CF_4$ than Ar. X-ray diffraction (XRD) showed that the structural damage was lower when $O_2$ was added to $Cl_2/CF_4$. And the improvement in the ferroelectric properties of the annealed samples was consistent with the increased intensities of the (100) and the (200) PZT peaks.

• Journal of the Semiconductor & Display Technology
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• v.18 no.4
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• pp.35-39
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• 2019

Effect of Ge₂Sb₂Te₅ (GST) chalcogen composition on plasma induced damage was investigated by using Ar ions and F radicals. Experiments were carried out with three different modes; the physical etching, the chemical etching, and the ion-enhanced chemical etching mode. For the physical etching by Ar ions, the sputtering yield was obtained according to ion bombarding energy and there was no change in GST composition ratio. In the plasma mode, the lowest etch rate was measured at the same applied power and there was also no plasma induced damage. In the ion-enhanced chemical etching conditions irradiated with high energy ions and F halogen radicals, the GST composition ratio was changed according to the density of F radicals, resulting in higher roughness of the etched surface. The change of GST composition ratio in halogen plasma is caused by the volatility difference of GST-halogen compounds with high energy ions over than the activation energy of surface reactions.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.523-523
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• 2012

As the wafer geometric requirements continuously complicated and minutes in tens of nanometers, the expectation of real-time add-on sensors for in-situ plasma process monitoring is rapidly increasing. Various industry applications, utilizing plasma impedance monitor (PIM) and optical emission spectroscopy (OES), on etch end point detection, etch chemistry investigation, health monitoring, fault detection and classification, and advanced process control are good examples. However, process monitoring in semiconductor manufacturing industry requires non-invasiveness. The hypothesis behind the optical monitoring of plasma induced ion current is for the monitoring of plasma induced charging damage in non-invasive optical way. In plasma dielectric via etching, the bombardment of reactive ions on exposed conductor patterns may induce electrical current. Induced electrical charge can further flow down to device level, and accumulated charges in the consecutive plasma processes during back-end metallization can create plasma induced charging damage to shift the threshold voltage of device. As a preliminary research for the hypothesis, we performed two phases experiment to measure the plasma induced current in etch environmental condition. We fabricated electrical test circuits to convert induced current to flickering frequency of LED output, and the flickering frequency was measured by high speed optical plasma monitoring system (OPMS) in 10 kHz. Current-frequency calibration was done in offline by applying stepwise current increase while LED flickering was measured. Once the performance of the test circuits was evaluated, a metal pad for collecting ion bombardment during plasma etch condition was placed inside etch chamber, and the LED output frequency was measured in real-time. It was successful to acquire high speed optical emission data acquisition in 10 kHz. Offline measurement with the test circuitry was satisfactory, and we are continuously investigating the potential of real-time in-situ plasma induce current measurement via OPMS.

• Journal of Information Display
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• v.8 no.3
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• pp.5-10
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• 2007

Twin target sputtering (TTS) system with a configuration of vertically parallel facing Al targets and a substrate holder perpendicular to the Al target plane has been designed to realize a direct Al cathode sputtering on organic light emitting diodes (OLEDs). The TTS system has a linear twin target gun with ladder type magnet array for effective and uniform confinement of high density plasma. It is shown that OLEDs with Al cathode deposited by the TTS show a relatvely lower leakage current density $({\sim}1{\times}10^{-5}mA/cm^2)$ at reverse bias of -6V, compared to that ($1{\times}10^{-2}{\sim}10^{-3}$ $mA/cm^2$ at -6V) of OLEDs with Al cathodes grown by conventional DC magnetron sputtering. In addition, it was found that Al cathode films prepared by TTS were amorphous structure with nanocrystallines due to low substrate temperature. This demonstrates that there is no plasma damage caused by the bombardment of energetic particles. This indicates that the TTS system with ladder type magnet array could be useful plasma damage free deposition technique for direct Al cathode sputtering on OLEDs or flexible OLEDs.

• Journal of Nutrition and Health
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• v.55 no.4
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• pp.450-461
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• 2022

Purpose: DNA damage and repair responses are induced by metabolic diseases and environmental stress. The balance of DNA repair response and the antioxidant system play a role in modulating the entire body's health. This study uses a high-fat and high-calorie (HFC) drink to examine the new roles of a plant-based multivitamin/mineral supplement with phytonutrients (PMP) for regulating the antioxidant system and cellular DNA repair signaling in the body resulting from metabolic stress. Methods: In a double-blind, randomized, parallel-arm, and placebo-controlled trial, healthy adults received a capsule containing either a PMP supplement (n = 12) or a placebo control (n = 12) for 8 weeks. Fasting blood samples were collected at 0, 1, and 3 hours after consuming a HFC drink (900 kcal). The blood samples were analyzed for the following oxidative stress makers: areas under the curve reactive oxygen species (ROS) levels, plasma malondialdehyde (MDA), erythrocytes MDA, urinary MDA, oxidized low-density lipoprotein, and the glutathione:oxidized glutathione ratio at the time points. We further examined the related protein levels of DNA repair signaling (pCHK1 (Serine 345), p-P53 (Serine 15), and 𝛄H2AX expression) in the plasma of subjects to evaluate the time-dependent effects of a HFC drink. Results: In a previous study, we showed that PMP supplementation for eight weeks reduces the ROS and endogenous DNA damage in human blood plasma. Results of the current study further show that PMP supplementation is significantly correlated with antioxidant defense. Compared to the placebo samples, the blood plasma obtained after PMP supplementation showed enhanced DNA damage response genes such as pCHK1(Serine 345) (a transducer of DNA response) and 𝛄H2AX (a hallmark of DNA damage) during the 8 weeks trial on metabolic challenges. Conclusion: Our results indicate that PMP supplementation for 8 weeks enhances the antioxidant system against oxidative stress and prevents DNA damage signaling in humans.

• Nutrition Research and Practice
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• v.11 no.3
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• pp.214-222
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• 2017

BACKGROUND/OBJECTIVES: Glutathione S-transferase (GST) forms a multigene family of phase II detoxification enzymes which are involved in the detoxification of xenobiotics by conjugating substances with glutathione. The aim of this study is to assess the antioxidative status and the degree of DNA damage in the subclinical hypertensive patients in Korea using glutathione S-transferase polymorphisms. SUBJECTS/METHODS: We examined whether DNA damage and antioxidative status show a difference between GSTM1 or GSTT1 genotype in 227 newly diagnosed, untreated (systolic blood pressure $(BP){\geq}130mmHg$ or diastolic $BP{\geq}85mmHg$) subclinical hypertensive patients and 130 normotensive subjects (systolic BP < 120 mmHg and diastolic BP < 80 mmHg). From the blood of the subjects, the degree of the DNA damage in lymphocyte, the activities of erythrocyte superoxide dismutase, the catalase, and the glutathione peroxidase, the level of glutathione, plasma total radical-trapping antioxidant potential (TRAP), anti-oxidative vitamins, as well as plasma lipid profiles and conjugated diene (CD) were analyzed. RESULTS: Of the 227 subjects studied, 68.3% were GSTM1 null genotype and 66.5% were GSTT1 null genotype. GSTM1 null genotype had an increased risk of hypertension (OR: 2.104, CI: 1.38-3.35), but no significant association in GSTT1 null genotype (OR 0.982, CI: 0.62-1.55). No difference in erythrocyte activities of superoxide dismutase, catalase, or glutathione peroxidase, and plasma TRAP, CD, lipid profiles, and GSH levels were observed between GSTM1 or GSTT1 genotype. Plasma levels of ${\alpha}-tocopherol$ increased significantly in GSTT1 wild genotype (P < 0.05); however, plasma level of ${\beta}-carotene$ increased significantly in GSTT1 null genotype (P < 0.01). DNA damage assessed by the Comet assay was significantly higher in GSTM1 null genotype than wild genotype (P < 0.05). CONCLUSIONS: These results confirm the association between GSTM1 null genotype and risk of hypertension as they suggest that GSTM1 null genotype leads to an increased oxidative stress compared with wild genotype.