• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.99-105
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• 2008

Core-shell structured $BaTiO_3$ powders were produced via nano-coating of $Cr_2O_3$ and $Mn_2O_3$ to barium titanate powder system for MLCCs. From preliminary experiments, the optimal solution reaction condition employing using $KMnO_4$, $K_2Cr_2O_4$ and sulfur was established. Not only powders of $Cr_2O_3$ and $Mn_2O_3$ were synthesized but also their coating on $BaTiO_3$ powders were peformed under the same reaction condition. The coating was carried out in two ways, one-step and two-step, and its results were characterized for comparison. Conclusively speaking, two oxide additives were coated onto the $BaTiO_3$ powder surface with high quality and excellent reaction yield even under mild condition, which indicates that the contents as well as the properties of additive shell layer can be precisely controlled with rather ease.

• Polymer(Korea)
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• v.38 no.6
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• pp.702-707
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• 2014

Corneal endothelium is mono-inner cell layer of cornea and lay on Descmet's membrane which comprised of various proteins called extracellular matrix such as fibronectin, collagen, laminin, and proteoglycan, etc. In this study, we fabricated transparent poly(lactic-co-glycolic acid) (PLGA) film because PLGA is widely used for tissue engineering based on their properties. We investigated the behaviors of rabbit corneal endothelial cells (rCEnCs) on PLGA film surfaces coated with various cell-adhesive molecules like fibronectin, laminin, collagen type I and IV and FNC coating mix. The morphologic images, proliferation and adhesion assay, immunofluorescence for ZO-1 and $Na^+/K^+-ATPase$ and RT-PCR for expression of specific markers were conducted. These results showed that PLGA film plays a role as CEnC carriers in vitro and the cell-adhesive molecules give positive effects on the behaviors of rCEnC.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.851-856
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• 2002

Tribological behavior of plasma-sprayed $Cr_2O_3$-based coatings containing $MoO_3$ at 450$^{\circ}C$ was investigated to understand the influence of $MoO_3$. A reciprocal disc-on-plate type tribo-tester was employed to examine fricition and wear behavior of the specimens. The microstructure and phase composition of the coating was characterized with Transmission Electron Microscopy(TEM). The TEM analysis indicated that $MoO_3$ was dispersed into the grain boundary, resulting in the increase of the hardness and density of the coating. Worn surfaces were investigated by scanning electron microscopy and chemistry of the worn surfaces was analyzed using a X-ray Photoelectron Spectrometer(XPS). The results showed that the friction coefficient of the $MoO_3$-added coatings was lower than that without $MoO_3$ addition. The larger protecting layers were observed at the worn surface of plasma spray coated specimens with $MoO_3$ composition in the protecting layer appears to be more favorable in reducing the friction.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.229-229
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• 2007

나노결정 합금재료를 전력선 통신 커플러용 자심재료로 응용하기 위해서는 고주파 대역에서의 손실 특성이 제어되어야 한다. 즉 고속 전력선 통신을 위한 자심재료의 투자율 및 완화 주파수 등의 전자기적 특성은 30MHz까지 우수하고 안정적으로 유지되어야 하며, 높은 투자율 및 자속밀도, 공진주파수뿐만 아니라 낮은 전력손실 값을 가져야 한다. 따라서 본 연구에서는 나노결점 합금 리본 표면에 딥 코팅, 졸-겔법, 진공함침 등의 방법을 이용하여 PZT, $TiO_2$ 및 $SiO_2$ 등의 산화물 고저항층을 형성시켜 자기적 성질을 유지하면서 고주파 대역의 와전류 손실을 감소시켜 통신용 자심재료로의 응용성을 향상시키고자 하였다. PZT 슬러리의 제타전위 조절을 통해 최적의 분산조건을 얻을 수 있었고, 평균 150nm인 PZT 입자의 초미립자와 가소제, 분산제, 결합제의 첨가조건을 확립할 수 있었다. 딥-코팅은 슬러리 내 유지시간 10초, 인상속도 5mm/min로 30회 반복되었을 때 가정 우수한 특성을 나타내었으며, 고주파 대역에서의 손실 감소효과를 나타내었다. 그리고 졸-겔법에 의해 제조된 슬러리를 이용한 $TiO_2$와 $SiO_2$ 산화물 저항층 코팅을 통해 금속 알콕사이드의 혼합조건 및 저항층 형성용 슬러리의 제조조건을 확립하였고, 합금 리본표면에 균일하고 우수한 점착력을 가지는 저항층을 형성시킬 수 있었으며, 이에 따른 코어손실의 감소효과를 나타낼 수 있었다. 또한 진공 함침법을 통한 저항층 형성에서, $TiO_2$ 나노분말을 표면 저항층으로 코팅했을 때, 가장 높은 코어손실 감소효과를 나타내었다. 한편, 표면 저항층이 형성된 나노결정 합금으로 제조한 자심재료를 이용하여 전력선 통신용 비접촉식 커플러에의 적용과 시험을 통해 고주파 손실 감소효과에 의한 신호전송 특성과 전류특성을 향상시킬 수 있었다.

• Membrane Journal
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• v.13 no.3
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• pp.162-173
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• 2003

The pseudo n-type polyaniline was prepared by doping of camphorsulfonic acid(CSA) and dodecylbenzenesulfonic acid(DBSA) as the dopants in solvent of N-methyl-2-pyrrolidinone(NMP). The dopants in polymer structure was qualitatively analyzed using FT-IR. The influence on electrochemical properties with dopant concentration of PANI film were investigated. The electrochemical characteristics of the n-type PANI electrode that coated on ITO were evaluated by cyclic voltammetry(CV) and AC impedance method. The prepared PANI were confirmed as n-type PANI from FT-IR and CV. The charge transfer resistance of film on PANI/CSA electrode were measured as 1.14{\sim}1.09k{\mu}$by AC impedance. The charge transfer resistance of PANI/DBSA electrode decreased with increasing the mole ratio of DBSA as 27.73{\sim}8.37 k{\mu}$. The double layer capacitance of PANI/CSA electrode was showed almost constant value as $13.47{\sim}14.59 {\mu}F$ and that of PANI/DBSA electrode increased with increasing mole ratio of DBSA from 0.49 to $1.20 {\mu}F$.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.289-289
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• 2013

While there are plenty of studies on synthesizing semiconducting germanium nanowires (Ge NWs) by vapor-liquid-solid (VLS) process, it is difficult to inject dopants into them with uniform dopants distribution due to vapor-solid (VS) deposition. In particular, as precursors and dopants such as germane ($GeH_4$), phosphine ($PH_3$) or diborane ($B_2H_6$) incorporate through sidewall of nanowire, it is hard to obtain the structural and electrical uniformity of Ge NWs. Moreover, the drastic tapered structure of Ge NWs is observed when it is synthesized at high temperature over $400^{\circ}C$ because of excessive VS deposition. In 2006, Emanuel Tutuc et al. demonstrated Ge NW pn junction using p-type shell as depleted layer. However, it could not be prevented from undesirable VS deposition and it still kept the tapered structures of Ge NWs as a result. Herein, we adopt $C_2H_2$ gas in order to passivate Ge NWs with carbon sheath, which makes the entire Ge NWs uniform at even higher temperature over $450^{\circ}C$. We can also synthesize non-tapered and uniformly doped Ge NWs, restricting incorporation of excess germanium on the surface. The Ge NWs with carbon sheath are grown via VLS process on a $Si/SiO_2$ substrate coated 2 nm Au film. Thin Au film is thermally evaporated on a $Si/SiO_2$ substrate. The NW is grown flowing $GeH_4$, HCl, $C_2H_2$ and PH3 for n-type, $B_2H_6$ for p-type at a total pressure of 15 Torr and temperatures of $480{\sim}500^{\circ}C$. Scanning electron microscopy (SEM) reveals clear surface of the Ge NWs synthesized at $500^{\circ}C$. Raman spectroscopy peaked at about ~300 $cm^{-1}$ indicates it is comprised of single crystalline germanium in the core of Ge NWs and it is proved to be covered by thin amorphous carbon by two peaks of 1330 $cm^{-1}$ (D-band) and 1590 $cm^{-1}$ (G-band). Furthermore, the electrical performances of Ge NWs doped with boron and phosphorus are measured by field effect transistor (FET) and they shows typical curves of p-type and n-type FET. It is expected to have general potentials for development of logic devices and solar cells using p-type and n-type Ge NWs with carbon sheath.

• Polymer(Korea)
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• v.36 no.1
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• pp.22-28
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• 2012

Functionalized graphene/epoxy composites were prepared to miprove thermal conductivities of epoxy composites and to maintain electrical insulating property. Graphene oxide (GO) was prepared using Hummers method, and then GO was reacted with aluminum isopropoxide to functionalize $Al(OH)_3$ layer onto GO surface by a simple sol-gel method (Al-GO). GO and Al-GO were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. The analyses confirm that GO was coated with a large and dense coverage of $Al(OH)_3$. GO and Al-GO (1 and 3 wt%) were embedded in bisphenol A (DGEBA) to investigate the effects of electrical insulating property. Electrical resistivity showed that Al-GO had better insulating property than GO. Further, the thermal conductivity of GO and Al-GO/epoxy composites was higher than that of neat epoxy resins. In particular, the thermal conductivity of Al-GO/bisphenol F (DGEBF) improved by 23.3% and Al-GO/DGEBA enhanced by 21.8% compared with pure epoxy resins.

• Journal of the Korea Convergence Society
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• v.10 no.2
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• pp.21-28
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• 2019

The study was to expand the choice of electric toothbrush by number of operations of the plaque removal effect on the tooth surface. Three different toothbrushes were selected for oscillations and pulsations type of electric toothbrush. A is Oral-B D12 (7,600 pulsations), B is Oral-B D16 (20,000 oscillations and a 7,600 pulsations), C is Oral-B D20 (40,000 oscillations and an 8,800 pulsations). In each trial, each tooth was brushed for 2 seconds. For the 10 trials. And each tooth was coated with 1layer, 2layers and 3layers. After the experiment, the plaque removal effect was calculated and analzed using the Image J program(p<0.05). According to the study, C toothbrush had the highest rate of plaque removal effect. Based on this results of the study, dental worker will need to evaluate oral hygiene and recommend appropriate toothbrushes according to oral conditions.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.111-117
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• 2019

This study proposed the fabrication and deposition of high purity crystalline $core-TiO_2/shell-Al_2O_3$ nanoparticles. Morphological properties of $core-TiO_2$ and coated $shell-Al_2O_3$ were confirmed by transmission electron microscope (TEM) and transmission electron microscope - energy dispersive spectroscopy (TEM-EDS). The electrical properties of the prepared $core-TiO_2/shell-Al_2O_3$ nanoparticles were evaluated by applying them to a working electrode of a Dye-Sensitized Solar Cell (DSSC). The particle size, growth rate and the main crystal structure of $core-TiO_2$ were analyzed through dynamic light scattering system (DLS), scanning electron microscope (SEM) and X-ray diffraction (XRD). The $core-TiO_2$, which has a particle size of 17.1 nm, a thin film thickness of $20.1{\mu}m$ and a main crystal structure of anatase, shows higher electrical efficiency than the conventional paste-based dye-sensitized solar cell (DSSC). In addition, the energy conversion efficiency (6.28%) of the dye-sensitized solar cell (DSSC) using the $core-TiO_2/shell-Al_2O_3$ nanoparticles selectively controlled to the working electrode is 26.1% higher than the energy conversion efficiency (4.99%) of the dye-sensitized solar cell (DSSC) using the conventional paste method.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.412-421
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• 2023

Ultrasound brain stimulation is spot-lighted by its capability of inducing brain cell activation in a localized deep brain region and ultimately treating impaired brain function while the efficiency and directivity of neural modulation are highly dependent on types of stimulus waveforms. Therefore, to optimize the types of stimulation parameters, we propose a cell-cultivable ultrasonic transducer having a series stack of a spin-coated polymer piezoelectric element (Poly-vinylidene fluoride-trifluorethylene, PVDF-TrFE) and a parylene insulating layer enhancing output acoustic pressure on a glass-coverslip which is commonly used in culturing cells. Due to the uniformity and high accuracy of stimulus waveform, tens of neuronal cell responses located on the transducer surface can be recorded simultaneously with fluorescence microscopy. By averaging the cell response traces from tens of cells, small changes to the low intensity ultrasound stimulations can be identified. In addition, the reduction of stimulus distortions made by standing wave generated from reflections between the transducers and other strong reflectors can be achieved by placing acoustic absorbers. Through the proposed ultrasound transducer, we could successfully observe the calcium responses induced by low-intensity ultrasound stimulation of 6 MHz, 0.2 MPa in astrocytes cultured on the transducer surface.