• Journal of the Semiconductor & Display Technology
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• v.20 no.4
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• pp.72-77
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• 2021

The radial distribution of etch rate was analyzed using the ion energy flux model in VHF-CCP. In order to exclude the effects of polymer passivation and F radical depletion on the etching. The experiment was performed in Ar/SF6 plasma with an SF6 molar ratio of 80% of operating pressure 10 and 20 mTorr. The radial distribution of Ar/SF6 plasma was diagnosed with RF compensated Langmuir Probe(cLP) and Retarding Field Energy Analyzer(RFEA). The radial distribution of ion energy flux was calculated with Bohm current times the sheath voltage which is determined by the potential difference between the plasma space potential (measured by cLP) and the surface floating potential (by RFEA). To analyze the etch rate uniformity, Si coupon samples were etched under the same condition. The ion energy flux and the etch rate show a close correlation of more than 0.94 of R² value. It means that the etch rate distribution is explained by the ion energy flux.

• Journal of Technologic Dentistry
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• v.30 no.1
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• pp.25-31
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• 2008

Cp-Ti and Ti-6Al-4V alloys commonly used dental implant materials, particularly for orthopaedic and osteosynthesis because of its suitable mechanical properties and excellent biocompatibility. This alloys have excellent corrosion behavior in the clinical environment. The first factor to decide the success of dental implantation is sufficient osseointegration and high corrosion resistance between on implant fixture and its surrounding bone tissue. In this study, in order to increase corrosion resistance and biocompatibility of Cp-Ti and Ti-6Al-4V alloy that surface of manufactured alloy was coated with TiN by RF-magnetron sputtering method. The electrochemical behavior of TiN coated Cp-Ti and Ti-6Al-4V alloy were investigated using potentiodynamic (EG&G Co, PARSTAT 2273. USA) and potentiostatic test (250mV) in 0.9% NaCl solution at 36.5 $\pm$ 1$^{\circ}C$. These results are as follows : 1. From the microstructure analysis, Cp-Ti showed the acicular structure of $\alpha$-phase and Ti-6Al-4V showed the micro-acicular structure of ${\alpha}+{\beta}$ phase. 2. From the potentiodynamic test, Ecorr value of Cp-Ti and Ti-6Al-4V alloys showed -702.48mV and -319.87mV, respectively. Ti-6Al-4V alloy value was higher than Cp-Ti alloy. 3. From the analysis of TiN and coated layer, TIN coated surface showed columnar structure with 800 nm thickness. 4. The corrosion resistance of TiN coated Cp-Ti and Ti-6Al-4V alloys were higher than those of the non-coated Ti alloys in 0.9% NaCl solution from potentiodynamic test, indicating better protective effect. 5. The passivation current density of TiN coated Cp-Ti and Ti-6Al-4V alloys were smaller than that of the noncoated implant fixture in 0.9% NaCl solution, indicating the good protective effect resulting from more compact and homogeneous layer formation.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.230-237
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• 2017

In this study, electrochemical methods were used to determine the optimum protection potential of S355ML steel for the cathodic protection of offshore wind-turbine-tower substructures. The results of potentiodynamic polarization experiments indicated that the anodic polarization curve did not represent a passivation behavior, while under the cathodic polarization concentration, polarization was observed due to the reduction of dissolved oxygen, followed by activation polarization by hydrogen evolution as the potential shifted towards the active direction. The concentration polarization region was found to be located between approximately -0.72 V and -1.0 V, and this potential range is considered to be the potential range for cathodic protection using the impressed current cathodic protection method. The results of the potentiostatic experiments at various potentials revealed that varying current density tended to become stable with time. Surface characterization after the potentiostatic experiment for 1200 s, by using a scanning electron microscope and a 3D analysis microscope confirmed that corrosion damage occurred as a result of anodic dissolution under an anodic polarization potential range of 0 to -0.50 V, which corresponds to anodic polarization. Under potentials corresponding to cathodic polarization, however, a relatively intact surface was observed with the formation of calcareous deposits. As a result, the potential range between -0.8 V and -1.0 V, which corresponds to the concentration polarization region, was determined to be the optimum potential region for impressed current cathodic protection of S355ML steel.

• Journal of the Korean Electrochemical Society
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• v.6 no.4
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• pp.250-254
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• 2003

In this study, the IR drop theory was adopted to explain the initiation of crevice corrosion in the framework of IR drop in crevice electrolyte. Furthermore, the electrochemical polarization was measured to study the mechanism of crevice corrosion for type STS430 stainless steel. lest method adopts under condition that the size of specimen is $10\times20\times5mm,\;in\;1N\;H_2SO_4+0.1N\;NaCl$ solution, and the artificial crevice gap sizes are three kinds, the Micro capillary tube size is inner diameter 0.04 mm, outer diameter 0.08 mm. Crevice corrosion is measured under the applied voltage of passivation potential -200mV/SCE, resulted from anodic potentio-dynamic polarization to the external surface along the crevice. The potential difference was measured by depth profile by Micro capillary tube which inserted in the crevice. The obtained results of this study showed that 1) As artificial crevice gap size became narrow, the current density was increased, whereas no crevice corrosion was found in the crevice gap size $3\times0.5\times16mm\;in\;1N\;H_2SO_4+0.1N\;NaCl\;solution\;at\;20^{\circ}C$ 2) potential of the crevice was about from -220 to -358mV which is lower than that of external surface potential of -200mV The results so far confirmes that the potential drop(so-called IR drop) in the crevice is one of the major mechanisms the process of crevice corrosion for 430 stainless steel.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.11
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• pp.3260-3268
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• 2009

A test apparatus has been fabricated to simulate chemical effect on head loss through a strainer in a pressurized water reactor (PWR) containment water pool after a loss of coolant accident (LOCA). Tests were conducted under condition of same ratio of strainer surface area to water volume between the test appratus and the containment sump. A series of tests have been performed to investigate the effects of spray, existence of calcium-silicate with tri-sodium phosphate (TSP), and composition of materials. The results showed that head loss across the chemical bed with even a small amount of calcium-silicate insulation instantaneously increased as soon as TSP was added to the test solution. Also, the head loss across the test screen is strongly affected by spray duration and is increased rapidly at the early stage, because of high dissolution and precipitation of aluminum and zinc. After passivation of aluminum and zinc by corrosion, the head loss increase is much slowed down and is mainly induced by materials such as calcium, silicon, and magnesium leached from NUKONTM and concrete. Furthermore, it is newly found that the spay buffer agent, tri-sodium phosphate, to form protective coating on the aluminum surface and reduce aluminum leaching is not effective for a large amount of aluminum and a long spray.

• The Journal of Korean Academy of Prosthodontics
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• v.31 no.3
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• pp.423-446
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• 1993

Titanium and its alloys are finding increasing use in medical devices and dental implants. The strong selling point of titanium is its resistance to the highly corrosive body fluids in which an implant must survive. This corrosion resistance is due to a tenacious passive oxide or film which exists on the metal's surface and renders it passive. Potentiodynamic polarization measurement is one of the most commonly used electro-chemical methods that have been applied to measure corrosion rates. And the potentiodynamic polarization test supplies detailed information such as open circuit, rupture, and passivation potential. Furthermore, it indicates the passive range and sensitivity to pitting corrosion. This study was designed to compare the corrosion resistance of the commonly used dental implant materials such as CP Ti, Ti-6A1-4V, Co-Cr-Mo alloy, and 316L stainless steel. And the effects of galvanic couples between titanium and the dental alloys were assessed for their useful-ness-as. materials for superstructure. The working electrode is the specimen , the reference electrode is a saturated calomel electrode (SCE), and the counter electrode is made of carbon. In $N_2-saturated$ 0.9% NaCl solutions, the potential scanning was performed starting from -800mV (SCE) and the scan rate was 1 mV/sec. At least three different polarization measurements were carried out for each material on separate specimen. The galvanic corrosion measurements were conducted in the zero-shunt ammeter with an implant supraconstruction surface ratio of 1:1. The contact current density was recorded over a 24-hour period. The results were as follows : 1. In potential-time curve, all specimens became increasingly more noble after immersion in the test solution and reached between -70mV and 50mV (SCE) respectively after 12 hours. 2. The Ti and Ti alloy in the saline solution were most resistant to corrosion. They showed the typical passive behavior which was exhibited over the entire experimental range. Therefore no breakdown potentials were observed. 3. Comparing the rupture potentials, Ti and Ti alloy had the high(:st value (because their break-down potentials were not observed in this study potential range ) followed by Co-Cr-Mo alloy and stainless steel (316L). So , the corrosion resistance of titanium was cecellent, Co-Cr-Mo alloy slightly inferior and stainless steel (316L) much less. 4. The contact current density sinks faster than any other galvanic couple in the case of Ti/gold alloy. 5. Ag-Pd alloy coupled with Ti yielded high current density in the early stage. Furthermore, Ti became anodic. 6. Ti/Ni-Cr alloy showed a relatively high galvanic current and a tendency to increase.

• Journal of the Korean Chemical Society
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• v.60 no.6
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• pp.402-409
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• 2016

Thin films of lead sulfide colloidal quantum dots (CQDs) of 2.8 nm in diameter are fabricated and their surfaces are passivated by 3-mercaptopropionic acid (MPA) ligand or hybrid type ($MPA+CdCl_2$) ligand, respectively. The changes in valence band electronic structure and atomic composition of each PbS CQD film upon post-treatment such as air, N2 annealing or UV/Ozone have been studied by photoelectron spectroscopy. The air annealing makes the CQD fermi level to move toward the valence band leading to "p-type doping" regardless of ligand type. The UV/Ozone post-treatment generates $Pb(OH)_2$, $PbSO_x$ and PbO on both CQD surfaces. But the amount of the PbO has been reduced in hybrid type ligand case, especially. That is probably because the extra Pb cations in (111) surface are additionally passivated by $Cl_2$ ligand, which limits the reaction between the Pb cation and ozone.

• Journal of Adhesion and Interface
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• v.21 no.3
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• pp.107-112
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• 2020

Recently, the atomically thin transition-metal dichalcogenide (TMD) semiconductors have attracted much attention owing to their remarkable properties such as tunable bandgap with high carrier mobility, flexibility, transparency, etc. However, because these TMD materials have a significant drawback that they are easily degraded in an ambient environment, various attempts have been made to improve chemical stability. In this research article, I report a method to improve the air stability of WSe₂ one of the TMD materials via surface passivation with an h-BN insulator, and its application to field-effect transistors (FETs). With a modified hot pick-up transfer technique, a vertical heterostructure of h-BN/WSe₂ was successfully made, and then the structure was used to fabricate the top-gate bottom-contact FETs. The fabricated WSe₂-based FET exhibited not only excellent air stability, but also high hole mobility of 150 ㎠/Vs at room temperature, on/off current ratios up to 3×10⁶, and 192 mV/decade of subthreshold swing.

• Journal of Periodontal and Implant Science
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• v.30 no.4
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• pp.707-727
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• 2000

매식된 인공치아의 성공을 위해서는 적절한 교합과 수동적 적합성을 갖는 보철물의 제작과 구강내 노출 직후부터의 세균성 치태조절이 요구된다. 본 연구는 전처리(passivation과 tridodecyl - methyl - ammonium chloride(TDMAC) 처리)가 다른 타이타늄 표 면에 chlorhexidine varnish와 테트라사이클린 을 도포시 약제의 방출역학을 알아보고 구강내 치태형성의 억제정도를 평가하기 위하여 시행 되었다. 이를 위해 방출용액으로 인산완충액 성분의 인조타액을 1일${\sim}$1개월간 매일 교환하여 약제농도를 측정하고 타이타늄 박막에 잔류한 약제 활성을 측정하였으며 항균제 도포한 타이타늄 원판을 부착한 장치를 구강내 위치시킨 1일${\sim}$3주 후 원판을 제거하여 주사전자현미경으로 세균 부착상을 관찰하였다. 테트라사이클린은 TDMAC 처리된 표면에서 $10{\sim}18$일까지 유효농도로 방출되었고 표면의 유효 항균 활성은 $3{\sim}4$주간 유지되었으며, chlorhexidine varnish 도포 시에는 TDMAC 전처리시 초기에 $3{\sim}7$일 간 증가한 유효 항균 활성을 방출하여 매식지대치 등에 이러한 항균제도포 시 매식치 주위환경에 항균활성 공급원으로 작용할 수 있음을 보였다. 주사현미경적 관찰시 모든 타이타늄 표면에서 구강내 위치 30분 후에는 세균이 부착되어 있지 않고 타액 단백질 성분에서 유래한 것으로 보이는 피막물질이 표면을 부분 또는 전면에 걸쳐 덮고 있었다. 구강내 노출 2시간 후 항균제 미도포 표본들에는 약간의 구균이 단층으로, $1{\sim}3$일 후에는 부분적으로 두꺼운 세균층을 형성하였고 7일 후에는 표면전체에 걸쳐 세균층이 덮여있었으며 주로 구균과 약간의 간균이 주종을 이루었다. 항균제 도포시 구강내 노출 1주일 이전까지는 미도포군에 비해 치태형성이 지연되는 경향을 보였지만 2주 이후에는 세균 수나 치태형성 양상이 유사하였다. 이 연구로부터 항균제 도포시 1주일 이전의 초기 치태형성을 감소시킬 수 있음을 알 수 있었으며 이러한 연구결과는 타이타늄 임프란트 지대치 표면에 항균제의 도포가 임상적으로 유용할 수 있음을 시사하였다.

• Journal of the Semiconductor & Display Technology
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• v.13 no.4
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• pp.21-25
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• 2014

The silicon nitride ($SiN_x$) film for surface passivation and anti-reflection coating of crystalline silicon solar cell is very important and it is generally deposited by plasma enhanced chemical vapor deposition (PECVD). PECVD can be divided into low and high frequency method. In this paper, the $SiN_x$ film deposited by low and high frequency PECVD method was studied. First, to optimize the $SiN_x$ film deposited by low frequency PECVD method, the refractive index was measured by varying the process conditions like $SiH_4$, $NH_3$, $N_2$ gas rate, and RF power. When $SiH_4$ gas rate was increased and $NH_3$ gas rate was decreased, the refractive index was increased. The refractive index was also increased with RF power decline. Second, to compare the characteristics of the low and high frequency PECVD $SiN_x$ film, the refractive index was measured by varying $NH_3/SiH_4$ gas ratio and RF power and the minority carrier lifetime of before and after high temperature treatment process was also measured. The refractive index of both low and high frequency PECVD $SiN_x$ film was decreased with increase in $NH_3/SiH_4$ gas ratio and RF power. After high temperature treatment process, the minority carrier lifetime of both low and high frequency PECVD $SiN_x$ film was increased and increased degree was similar. The minority carrier lifetime of low frequency PECVD $SiN_x$ was increased from $11.03{\mu}m$ to $28.24{\mu}m$ and that of high frequency PECVD $SiN_x$ was increased from $11.60{\mu}m$ to $27.10{\mu}m$.