• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.464-464
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• 2013

그래핀 옥사이드(Graphene Oxide)는 그래핀과 마찬가지로 많은 분야로의 응용 가능성을 보이는 소자중 하나로 각광받고 있다. 그래핀 옥사이드가 가지는 유전체 특징은 전하 트랩층(charge trap layer)으로 사용을 가능하게 하고 또한 물에 녹는 수용성 특징은 스핀코터(spin coator)를 이용한 간단한 도포과정을 통하여 저비용으로 간단하게 소자를 제작 가능하게 한다. 이 연구에서 우리는 금속-절연체-반도체 구조를 가지는 메모리 소자를 제작하여 0.4 mg/ml의 농도로 DI에 용해된 그래핀 옥사이드가 플로팅게이트(floating gate)로써 사용되었을 때의 특성을 알아보기 위해 Boonton 720를 사용하여 C-V (hysteresis) 커브와 C-T(Capacitance-Time)를 측정하여 그래핀 옥사이드의 유무에 따른 메모리 윈도우 폭의 증가 및 저장된 정보가 손실되지 않고 얼마나 길게 유지 되는지를 살펴봄으로 플로팅게이트로써 그래핀 옥사이드의 특성을 살펴보았다. 먼저 터널링층으로 쓰이는 SiO2가 5 nm 증착된 P타입 Si기판위에 플로팅게이트로 쓰이는 그래핀 옥사이드층을 쉽게 쌓기 위하여 APTES 자기조립 단분자막 코팅을 한 후 그래핀 옥사이드를 3,000 rpm으로 40초간 스핀코팅을 하였다. 그 후 블로킹층으로 쓰이는 400 nm 두께의 폴리비닐페놀(PVP)를 3,000 rpm으로 40초간 스핀코팅을 하고 $130^{\circ}C$에서 열처리를 하였으며 $10^{-5}$ Torr의 압력에서 진공 열증착으로 알루미늄 게이트 전극을 증착했다.

• 한국전기전자재료학회논문지
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• 제26권11호
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• pp.801-805
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• 2013

In this study, electrocaloric effects of Pb-free $(Ba_{0.85}Ca_{0.15})(Ti_{0.92}Zr_{0.08})O_3$ ferroelectric ceramics were investigated and discussed using the characteristics of P-E hysteresis loops at wide temperature range from room temperature to $140^{\circ}C$. The remnant polarization $P_r$ and coercive field $E_c$ were decreased with increasing temperature. The temperature change ${\Delta}T$ by the electrcaloric effect was calculated by Maxwell's relations, and reached the maximum of ~0.15 at $120^{\circ}C$ under applied electric field of 30 kV/cm.

• 한국전기전자재료학회논문지
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• 제30권4호
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• pp.223-228
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• 2017

In this study, in order to develop composition ceramics for refrigeration device application at a temperature of less than $90^{\circ}C$, a $Ba(Ti_{1-x}Zr_x)O_3$ composition was fabricated using a conventional solid-state method. Electrocaloric properties of these ceramics were investigated using the characteristics of P-E hysteresis loops in a wide temperature range from room temperature to $150^{\circ}C$. The Curie temperature of $Ba(Ti_{1-x}Zr_x)O_3$ ceramics decreased with the increase of x. The maximum value of ${\Delta}T=0.07^{\circ}C$ in an ambient temperature of $85^{\circ}C$ under 30 kV/cm appeared when x = 0.125. It was concluded that the composition (x = 0.125) ceramics can be used for refrigeration device applications.

• 한국전기전자재료학회논문지
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• 제21권2호
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• pp.156-161
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• 2008

The fabrication of vanadium oxide films directly on Si(100) substrates by plasma atomic layer deposition(ALD) with vanadium oxytriisopropoxide(VOIP) and oxygen as the reactants have been performed at temperature ranging from 250 to $450^{\circ}C$. Growth rate of vanadium oxide was $2.8{\AA}$/cycle at $300{\sim}400^{\circ}C$ defined as ALD acceptable temperature window, Vanadium oxide has been shown the different phases at $250^{\circ}C$ and more than $300^{\circ}C$. It has been confirmed that the phase of the films deposited at $250^{\circ}C\;was\;V_2O_5$ type and that of the films above $300^{\circ}C\;was\;VO_2(T)$ type measured at room temperature, respectively. A large change in resistance and small temperature hysteresis corresponding to a temperature has been observed in the vanadium oxide film deposited at temperature $350^{\circ}C$.

• Journal of Magnetics
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• 제16권1호
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• pp.15-18
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• 2011

We have studied the $TiO_2$ doping effects on the flux pinning behavior of an $MgB_2$ superconductor synthesized by the in-situ solid-state reaction. From the field-cooled and zero-field-cooled temperature dependences of magnetization, the reversible-irreversible transition of $TiO_2$-doped $MgB_2$ was determined in the H-T diagram (the temperature dependence of upper critical magnetic field and irreversibility line). For comparison, the similar measurements are also obtained from SiC-doped $MgB_2$. The critical current density was estimated from the width of hysteresis loops in the framework of Bean's model at different temperatures. The obtained results manifest that nano-scale $TiO_2$ inclusions served as effective pinning centers and lead to the enhanced upper critical field and critical current density. It was concluded that the grain boundary pinning mechanism was realized in a $TiO_2$-doped $MgB_2$ superconductor.

• 한국결정성장학회지
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• 제7권3호
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• pp.359-365
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• 1997

$K_2CoCl_4$ 단결정을 Ar분위기에서 Czochralski법으로 육성하였다. 육성된 결정의 물리적 성질의 조사로서 먼저 유전적 특성을 조사하여 commensurate-incommensurate(C-INC) 상전이에서 유전율의 thermal hysteresis가 $5^{\circ}C$ 이하의 값을 가짐을 보였고, incommensurate(INC) 상에서 $K^+$ 이온에 의한 ionic hopping mechanism으로 전도도를 해석하였으며 이때 activation energy는 0.62 eV 이었다. 각각의 결정축으로 열팽창을 조사하여 c축으로 가장 큰 열팽창을 보였으며 열팽창계수를 계산하였다. 광학적 특성의 조사로서 200 nm~ 3000 nm 영역에서 흡수 스펙트럼을 측정하여 나타나는 흡수 peak을 결정장내의 에너지 준위의 분리에 따른 전이 에너지로 해석하였으며, 800 nm~ 1200 nm 영역의 투과특성으로 optical band filter로서의 가능성을 제시하였다.

• Archives of Pharmacal Research
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• 제27권7호
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• pp.806-810
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• 2004

Metformin is a biguanide antihyperglycemic agent often used for the treatment of non-insulin dependent diabetics (NIDDM). In this study, the pharmacokinetics and pharmacodynamics of metformin were investigated in Korean healthy volunteers during a fasting state for over 10 h. In order to evaluate the amount of glucose-lowering effect of metformin, the plasma concentrations of glucose were measured for a period of 10 h followed by the administration of metformin (oral 500 mg) or placebo. In addition, the concentration of metformin in blood samples was determined by HPLC assay for the drug. All volunteers were consumed with 12 g of white sugar 10 minutes after drug intake to maintain initial plasma glucose concentration. The time courses of the plasma concentration of metformin and the glucose-lowering effect were analyzed by nonlinear regression analysis. The estimated $C_{max}$, $T_{max}$, $CL_{t}$/F (apparent clearance), V/F(apparent volume of distribution), and half-life of metformin were 1.42$\{pm}$0.07 $\mu\textrm{g}$/mL, 2.59$\{pm}$0.18h, 66.12$\{pm}$4.6 L/h, 26.63 L, and 1.54 h respectively. Since a significant counterclock-wise hysteresis was found for the metformin concentration in the plasma-effect relationship, indirect response model was used to evaluate pharmacodynamic parameters for metformin. The mean concentration at half-maximum inhibition $IC_{50}$, $k_{in}$, $k_{out}$ were 2.26 $\mu\textrm{g}$/mL, 83.26 $H^{-1}$, and 0.68 $H^{-1}$, respectively. Therefore, the pharmacokinetic-pharmacodynamic model may be useful in the description for the relationship between plasma concentration of metformin and its glucose-lowering effect.

• 대한화학회지
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• 제63권6호
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• pp.453-458
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• 2019

Synthesis of ZnCo₂O₃ oxide is performed by sol-gel method via nitrate-citrate route. Powder X-ray diffraction (XRD) study shows monoclinic unit cell having lattice parameters: a = 5.721(1) Å, b = 8.073(2) Å, c = 5.670(1) Å, β = 93.221(8)°, space group P_2/m and Z = 4. Average crystallite sizes determined by Scherrer equation are the range ~14-32 nm, whereas SEM micrographs show nano-micro meter size particles formed in ZnCo₂O₃. Endothermic peak at ~798 K in the Differential scanning calorimetric (DSC) trace without weight loss could be due to structural transformation and the endothermic peak ~1143 K with weight loss is due to reversible loss of O₂ in air atmosphere. Energy Dispersive X-ray (EDX) analysis profile shows the presence of elements Zn, Co and O which indicates the purity of the sample. Magnetic measurements in the range of +12 kOe to -12 kOe at 10 K, 77 K, 120 K and at 300 K by PPMS-II Physical Property Measurement System (PPMS) shows hysteresis loops having very low values of the coercivity and retentivity which indicates the weakly ferromagnetic nature of the oxide. Observed X-band EPR isotropic lineshapes at 300 K and 77 K show positive g-shift at g_iso ~2.230 and g_iso ~2.217, respectively which is in agreement with the presence of paramagnetic site Co²⁺(3d⁷) in the oxide. DC conductivity value of 2.875 ×10^-8 S/cm indicates very weakly semiconducting nature of ZnCo₂O₃ at 300 K. DRS absorption bands ~357 nm, ~572 nm, ~619 nm and ~654 nm are due to the d-d transitions ⁴T_1g(⁴F)→²E_g(²G), ⁴T_1g(⁴F)→⁴T_1g(⁴P), ⁴T_1g(⁴F)→⁴A_2g(⁴F), ⁴T_1g(⁴F)→⁴T_2g(⁴F), respectively in octahedral ligand field around Co²⁺ ions. Direct band gap energy, E_g~ 1.5 eV in the oxide is obtained by extrapolating the linear part of the Tauc plot to the energy axis indicates fairly strong semiconducting nature of ZnCo₂O₃.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.73.1-73.1
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• 2010

For the successful cold starting of a fuel cell engine, either internal of external heat supply must be made to overcome the formation of ice from water below the freezing point of water. In the present study, switchable vanadium oxide compounds as variable temperature-electrical resistance materials onto the surface of flat metallic bipolar plates have been prepared by a dip-coating technique via an aqueous sol-gel method. Subsequently, the chemical composition and micro-structure of the polycrystalline solid thin films were analyzed by X-ray diffraction, X-ray fluorescence spectroscopy, and field emission scanning electron microscopy. In addition, it was carefully measured electrical resistance hysteresis loop over a temperature range from $-20^{\circ}C$ to $80^{\circ}C$ using the four-point probe method. The experimental results revealed that the thin films was mainly composed of Karelianite $V_2O_3$ which acts as negative temperature coefficient materials. Also, it was found that thermal dissipation rate of the vanadium oxide thin films partially satisfy about 50% saving of the substantial amount of energy required for ice melting at $-20^{\circ}C$. Moreover, electrical resistances of the vanadium-based materials converge on an extremely small value similar to that of pure flat metallic bipolar plates at higher temperature, i.e. $T{\geq}40^{\circ}C$. As a consequence, experimental studies proved that it is possible to apply the variable temperature-electrical resistance material based on vanadium oxides for the cold starting enhancement of a fuel cell vehicle and minimize parasitic power loss and eliminate any necessity for external equipment for heat supply in freezing conditions.

• 한국자기학회지
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• 제12권5호
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• pp.184-188
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• 2002

수직자기이방성을 가지는 Cu/Ni/Cu(002)/Si(100) 자성박막을 전자빔 증발법을 이용하여 초고진공에서 증착 하였다. 증착 시 RHEED로 측정 한 결과 실리콘 기판 위에 자성박막이 적층성장되었음을 확인하였다. 이러한 Cu/Ni/Cu(001)/Si(100) 자성박막에 1 MeV C 이온을 이온선량 2$\times$$10^{16}$ ions/$\textrm{cm}^2$로 조사한 후 MOKE로 자기이력곡선을 측정한 결과 이온 조사에 의해 자화용이축이 수직에서 수평방향으로 변화되었음을 확인하였다 포항 방사광가속기를 이용하여 X-선 반사도와 Grazing Incident X-ray diffraction(GE) 분석을 수행한 결과 첫 번째 Cu층과 Ni층 사이의 계면은 이온 조사 후 거칠기는 증가하였으나, Cu와 Ni의 전자밀도의 대비는 더욱 명확해졌다. 그리고, 증착 후 Cu와 Ni원자의 격자 상수 차이에 의해 Ni층이 가지고 있었던 strain은 이온 조사 후 완화되었음을 알 수 있었다. 끝으로, 이온조사 시 자성특성 변화와 직접적인 관계가 있는 strain 완화, 계면 혼합층(혹은 새로운 상)등이 생성되는 기구를 탄성충돌 및 비탄성충돌에 의한 열화학적 구동력으로 규명하였다.