• 한국전기전자재료학회논문지
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• 제21권3호
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• pp.227-231
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• 2008

In this study, in order to improve the electrical properties of low temperature sintering piezoelectric ceramics, $[0.05Pb(Zn_{1/2}W_{1/2})-0.07Pb(Mn_{1/3}Nb_{2/3})-0.088Pb(Zr_{0.48}Ti_{0.52})]O_3$(abbreviated as PZW-PMN-PZT) ceramic systems were fabricated using $Bi_2O_3$, CuO and $Li_2CO_3$ as sintering aids and then their piezoelectric and dielectric properties were investigated according to the amount of $Li_2CO_3$ and post-annealing process. Post-annealing process enhanced all physical properties except for mechanical quality factor (Qm). 0.2 wt% $Li_2CO_3$ added and post-annealed specimen showed the excellent values suitable for low loss piezoelectric actuator application as follow: the density = 7.86 $g/cm^3$ electromechanical coupling factor (kp) = 0.575, piezoelectric constant $d_{33}$ = 370 pC/N, dielectric constant ($\varepsilon_r$) = 1546, and mechanical quality factor (Qm) = 1161, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.191-191
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• 2009

$Bi_4Ti_3O_{12}$ (BiT) thin films were well developed on the Pt/Ti/$SiO_2/Si$ substrate by a metal organic decomposition (MOD) method. Oxygen was effective on the crystallization of the BiT thin films during a rapid thermal annealing process. The electrical properties of the BiT films dependant on the oxygen partial pressure were investigated. No crystalline phase was observed for the BiT film annealed at $700^{\circ}C$ under oxygen free atmosphere. However, its crystallinity was significantly evolutionned with increasing oxygen partial pressure. In addition, its dielectric and piezoelectric properties were enhanced with increasing oxygen partial pressure to 10 torr. Especially, the BiT film, annealed at $700^{\circ}C$ and 10 torr oxygen pressure, showed good dielectric properties: dielectric constant of 51 and dielectric loss of 0.2 % at 100 kHz. Its leakage current and piezoelectric constant ($d_{33}$) was also considerably improved, being as 0.62 nA/$cm^2$ at 1 V and approximately 51 pm/V, respectively.

• 한국전기전자재료학회논문지
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• 제22권4호
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• pp.290-296
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• 2009

$Bi_{4}Ti_{3}O_{12}$ (BiT) thin films were grown on the Pt/Ti/$SiO_2$/si substrate using a metal organic decomposition (MOD) method. Effects of oxygen annealing on the structural properties and dielectric properties of the BiT thin films were investigated. The BiT films were well developed when rapid thermal annealed at $>500^{\circ}C$ in oxygen ambient. For the film annealed at $700^{\circ}C$, no crystalline phase was observed under oxygen free annealing atmosphere while its crystallinity was significantly enhanced as the oxygen pressure increased. The BiT film also exhibited a smooth surface with defect free grains. A high dielectric constant and a low dielectric loss were achieved satisfactory in the frequency range from 75 kHz to 1 MHz. Especially, the BiT film, annealed at $700^{\circ}C$ and 10 torr oxygen pressure, showed good dielectric properties: dielectric constant of 51 and dielectric loss of 0.2 % at 100 kHz. Its leakage current was also considerably improved, being as $0.62\;nA/cm^2$ at 1 V. Therefore, it is considered that the oxygen annealing has effects on an enhancement of crystallinity and dielectric properties of the BiT films.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.211-212
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• 2010

GaN 기반의 상부발광형 LED는 동작되는 동안 생기는 전기적 단락, 그리고 칩 위의 p-형 전극과 n-형 전극 사이에 생기는 누설전류 및 신뢰성 확보를 위하여 칩 표면에 passivation 층을 형성하게 된다. SiO2, Si3N4와 같은 passivation layers는 일반적으로 PECVD (Plasma Enhanced Chemical Vapor Deposition)공정을 이용한다, 하지만 이는 공정 특성상 plasma로 인한 damage가 유발되기 때문에 표면 누설 전류가 증가 한다. 이로 인해 forward voltage와 reverse leakage current의 특성이 저하된다. 본 실험에서는 원자층 단위의 박막 증착으로 인해 PECVD보다 단차 피복성이 매우 우수한 PEALD(Plasma Enhanced Atomic Layer Deposition)공정을 이용하여 Al2O3 passivation layer를 증착한 후, 표면 누설전류와 빛의 출력 특성에 대해서 조사해 보았다. PSS (patterned sapphire substrate) 위에 성장된 LED 에피구조를 사용하였고, TCP(Trancformer Copled Plasma)장비를 사용하여 에칭 공정을 진행하였다. 이때 투명전극을 증착하기 위해 e-beam evaporator를 사용하여 Ni/Au를 각각 $50\;{\AA}$씩 증착한 후 오믹 특성을 향상시키기 위하여 $500^{\circ}C$에서 열처리를 해주었다. 그리고 Ti/Au($300/4000{\AA}$) 메탈을 사용하여 p-전극과 n-전극을 형성하였다. Passivation을 하지 않은 경우에는 reverse leakage current가 -5V 에서 $-1.9{\times}10-8$ A 로 측정되었고, SiO2와 Si3N4을 passivation으로 이용한 경우에는 각각 $8.7{\times}10-9$과 $-2.2{\times}10-9$로 측정되었다. Fig. 1 에서 보면 알 수 있듯이 5 nm의 Al2O3 film을 passivation layer로 이용할 경우 passivation을 하지 않은 경우를 제외한 다른 passivation 경우보다 reverse leakage current가 약 2 order ($-3.46{\times}10-11$ A) 정도 낮게 측정되었다. 그 이유는 CVD 공정보다 짧은 ALD의 공정시간과 더 낮은 RF Power로 인해 plasma damage를 덜 입게 되어 나타난 것으로 생각된다. Fig. 2 에서는 Al2O3로 passivation을 한 소자의 forward voltage가 SiO2와 Si3N4로 passivation을 한 소자보다 각각 0.07 V와 0.25 V씩 낮아지는 것을 확인할 수 있었다. 또한 Fig. 3 에서는 Al2O3로 passivation을 한 소자의 output power가 SiO2와 Si3N4로 passivation을 한 소자보다 각각 2.7%와 24.6%씩 증가한 것을 볼 수 있다. Output power가 증가된 원인으로는 향상된 forward voltage 및 reverse에서의 leakage 특성과 공기보다 높은 Al2O3의 굴절률이 광출력 효율을 증가시켰기 때문인 것으로 판단된다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.88.2-88.2
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• 2010

Dye-sensitized solar cells (DSSCs) have attracted considerable attention on account of their high solar energy-to-conversion efficiencies and low cost processes compared to conventional p-n junction solar cells. The mechanism of DSSC is based on the injection of electrons from the photo excited dyes into the conduction band of the semiconductor electrode. The oxidized dye is reduced by the hole injection into either the hole conductor or the electrolyte. Thus, the light harvesting effect of dye plays an important role in capturing the photons and generating the electron/hole pair, as well as transferring them to the interface of the semiconductor and the electrolyte, respectively. We used the organic fluorescence materials which can absorb short wavelength light and emit longer wavelength region where dye sensitize effectively. In this work, the DSSCs were fabricated with fluorescence materials added $TiO_2$ photo-electrode which were sensitized with metal-free organic dyes. The photovoltaic performances of fluorescence aided DSSCs were compared, and the recombination dark current curves and the incident photon-to-current (IPCE) efficiencies were measured in order to characterize the effects of the additional light harvesting effect in DSSC. Electro-optical measurements were also used to optimize the fluorescence material contents on TiO2 photo-electrode surface for higher conversion efficiency (${\eta}$), fill factor (FF), open-circuit voltage (VOC) and short-circuit current (ISC). The enhanced light harvesting effect by the judicious choice/design of the fluorescence materials and sensitizing dyes permits the enhancement of photovoltaic performance of DSSC.

• 대한치과교정학회지
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• 제44권5호
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• pp.246-253
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• 2014

Objective: To evaluate the bioactivity, and the biomechanical and bone-regenerative properties of Ti6Al4V miniscrews subjected to anodization, cyclic precalcification, and heat treatment (APH treatment) and their potential clinical use. Methods: The surfaces of Ti6Al4V alloys were modified by APH treatment. Bioactivity was assessed after immersion in simulated body fluid for 3 days. The hydrophilicity and the roughness of APH-treated surfaces were compared with those of untreated (UT) and anodized and heat-treated (AH) samples. For in vivo tests, 32 miniscrews (16 UT and 16 APH) were inserted into 16 Wistar rats, one UT and one APH-treated miniscrew in either tibia. The miniscrews were extracted after 3 and 6 weeks and their osseointegration (n = 8 for each time point and group) was investigated by surface and histological analyses and removal torque measurements. Results: APH treatment formed a dense surface array of nanotubular TiO2 layer covered with a compact apatite-like film. APH-treated samples showed better bioactivity and biocompatibility compared with UT and AH samples. In vivo, APH-treated miniscrews showed higher removal torque and bone-to-implant contact than did UT miniscrews, after both 3 and 6 weeks (p < 0.05). Also, early deposition of densely mineralized bone around APH-treated miniscrews was observed, implying good bonding to the treated surface. Conclusions: APH treatment enhanced the bioactivity, and the biomechanical and bone regenerative properties of the Ti6Al4V alloy miniscrews. The enhanced initial stability afforded should be valuable in orthodontic applications.

• ETRI Journal
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• 제24권3호
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• pp.211-220
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• 2002

This study characterizes an oxide etching process in a magnetically enhanced reactive ion etching (MERIE) reactor with a $CHF_3/CF_4$ gas chemistry. We use a statistical $2^{4-1}$ experimental design plus one center point to characterize the relationships between the process factors and etch responses. The factors that we varied in the design include RF power, pressure, and gas composition, and the modeled etch responses were the etch rate, etch selectivity to TiN, and uniformity. The developed models produced 3D response plots. Etching of $SiO_2$ mainly depends on F density and ion bombardment. $SiO_2$ etch selectivity to TiN sensitively depends on the F density in the plasma and the effects of ion bombardment. The process conditions for a high etch selectivity are a 0.3 to 0.5 $CF_4$ flow ratio and a -600 V to -650 V DC bias voltage according to the process pressure in our experiment. Etching uniformity was improved with an increase in the $CF_4$ flow ratio in the gas mixture, an increase in the source power, and a higher pressure. Our characterization of via etching in a $CHF_3/CF_4$ MERIE using neural networks was successful, economical, and effective. The results provide highly valuable information about etching mechanisms and optimum etching conditions.

• 한국결정성장학회지
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• 제22권5호
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• pp.227-232
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• 2012

차세대 원자력발전용 고온 열교환기 소재로 이용될 가능성이 높은 Ni-Cr계 고온합금인 Inconel 617과 Hastelloy X의 표면처리에 따른 FLiNaK(LiF-NaF-KF) 용융염 하에서의 고온물성에 대한 연구를 수행하였다. Inconel 617과 Hastelloy X기판 상에 각각 PVD인 arc discharge 및 sputtering법에 의해 TiAlN 및 $Al_2O_3$ 박막을 코팅 하였다. 이러한 표면처리가 이들 합금의 FLiNaK 용융염 하 고온 안정성에 미치는 영향에 대해 연구하였다. 용융염 하 Ni-Cr계 고온합금의 부식 원리를 이해하기 위해, 용융염 수송 loop에 사용 중 파단된 Inconel 파이프에 대한 미세구조 분석을 수행하였다. 표면처리 된 합금들을 $600^{\circ}C$ 용융염 내에서 열처리 하였으며, 열처리 전후 시편들에 대해 상형성, 미세구조 등 고온 물성 변화를 측정하였다. 연구결과 코팅되지 않은 경우 보다 TiAlN 및 $Al_2O_3$ 박막이 코팅된 소재에서 보다 우수한 고온 안정성을 보여주었다.

• Natural Product Sciences
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• 제26권3호
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• pp.207-213
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• 2020

Characterization and in vitro inhibition studies of protease inhibitor from the mushroom Pleurotus floridanus (PfTI) towards the pest Papilio demoleus is studied. The addition of 1 mM Mn²⁺, Na²⁺, Ba²⁺ and Ni ²⁺ enhanced the PfTI activity. The ICP-atomic emission spectrum showed the presence of Ca²⁺, Mg²⁺ and Zn²⁺ in the PfTI. Surfactants SDS and CTAB at a concentration of 1% reduced the PfTI activity whereas, the nonionic detergents Triton X and Tween 80 increased the activity. The inhibitory activity gradually decreased with increase in concentration of DMSO and H₂O₂. The activity was increased by dithiothreitol up to a concentration of 80 μM and inactivated at 140 μM. The activity of PMSF modified PfTI was drastically reduced to 0.234 U/mL at 4 mM concentration and similar results were obtained for modification of cysteine by N-Ethylmaleimide at slightly higher concentrations. The complex of trypsin and PfTI showed complete loss in fluorescence intensity at 343 nm compared with control. In vitro inhibition studies of PfTI with midgut proteases isolated from citrus pest P. demoleus with protease activity of 1.236 U was decreased to 0.613 U by 50 μL (0.1 mg/mL) of the inhibitor. Inhibitor was stable up to 0.04 M concentration of HCl.

• 한국재료학회지
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• 제28권9호
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• pp.489-494
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• 2018

Lead free $(1-x)(0.675BiFeO_3-0.325BaTiO_3)-xLiTaO_3$ (BFBTLT, x = 0, 0.01, 0.02, and 0.03, with 0.6 mol% $MnO_2$ and 0.4 mol% CuO) were prepared by a solid state reaction method, followed by air quenching and their crystalline phase, morphology, dielectric, ferroelectric and piezoelectric properties were explored. An X-ray diffraction study indicates that lithium (Li) and tantalum (Ta) were fully incorporated in the BFBT materials with the absence of any secondary phases. Dense ceramic samples (> 92 %) with a wide range of grain sizes from $3.70{\mu}m$ to $1.82{\mu}m$ were obtained in the selected compositions ($0{\leq}x{\leq}0.03$) of BFBTLT system. The maximum temperatures ($T_{max}$) were mostly higher than $420^{\circ}C$ in the studied composition range. The maximum values of maximum polarization ($P_{max}{\approx}31.01{\mu}C/cm^2$), remnant polarization ($P_{rem}{\approx}22.82{\mu}C/cm^2$) and static piezoelectric constant ($d_{33}{\approx}145pC/N$) were obtained at BFBT-0.01LT composition with 0.6 mol% $MnO_2$ and 0.4 mol% CuO. This study demonstrates that the high $T_{max}$ and $d_{33}$ for BFBTLT ceramics are favorable for industrial applications.