• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.115-115
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• 1999

GaN는 직접천이형 wide band gap(3.4eV) 반도체로서 청색/자외선 발광소자 및 고출력 전자장비등에의 응용성 때문에 폭넓게 연구되고 있다. 이러한 넓은 분야의 응용을 위해서는 열 적으로 안정된 Ohmic contact을 반드시 실현되어야 한다. n-type GaN의 경우에는 GaN계면에서의 N vacancy가 n-type carrier로 작용하기 때문에 Ti, Al, 같은 금속을 접합하여 nitride를 형성함에 의해서 낮은 접촉저항을 갖는 Ohmic contact을 하기가 쉽다. 그러나 p-type의 경우에는 일 함수가 크고 n-type와 다르게 nitride가 형성되지 않는 금속이 Ohmic contact을 할 가능성이 많다. 시료는 HF(HF:H2O=1:1)에서 10분간 초음파 세척을 한 후 깨끗한 물에 충분히 헹구었다. 그런 후에 고순도 Ar 가스로 건조시켰다. Pd와 Ni은 열적 증착법(thermal evaporation)을 사용하여 p-GaN에 상온에서 증착하였다. 현 연구에서는 열처리에 의한 Pd의 clustering을 줄이기 위해서 wetting이 좋은 Ni을 Pd 증착 전과 후에 삽입하였으며, monchromatic XPS(x-ray photoelectron spectroscopy) 와 SAM(scanning Auger microscopy)을 사용하여 열처리 전과 40$0^{\circ}C$, 52$0^{\circ}C$ 그리고 695$0^{\circ}C$에서 3분간 열처리 후의 온도에 따른 morphology 변화, 계면반응(interfacial reaction) 및 벤드 휨(band bending)을 비교 연구하였다. Nls core level peak를 사용한 band bending에서 Schottky barrier height는 Pd/Ni bi-layer 접합시 2.1eV를, Ni/Pd bi-layer의 경우에 2.01eV를 얻었으며, 이는 Pd와 Ni의 이상적인 Schottky barrier height 값 2.38eV, 2.35eV와 비교해 볼 때 매우 유사한 값임을 알 수 있다. 시료를 후열처리함에 의해 52$0^{\circ}C$까지는 barrier height는 큰 변화가 없으나, $650^{\circ}C$에서 3분 열처리 후에 0.36eV, 0.28eV 만큼 band가 더 ？을 알 수 있었다. Pd/Ni 및 Ni/Pd 접합시 $650^{\circ}C$까지 후 열 처리 과정에서 계면에서 matallic Ga은 온도에 비례하여 많은 양이 형성되어 표면으로 편석(segregation)되어지나, In-situ SAM을 이용한 depth profile을 통해서 Ni/Pd, Pd/Ni는 증착시 uniform하게 성장함을 알 수 있었으며, 후열처리 함에 의해서 점차적으로 morphology 의 변화가 일어나기 시작함을 볼 수 있었다. 이는 $650^{\circ}C$에서 열처리 한후의 ex-situ AFM을 통해서 재확인 할 수 있었다. 이상의 결과로부터 GaN에 Pd를 접합 시 심한 clustering이 형성되어 Ohoic contact에 문제가 있으나 Pd/Ni 혹은 Ni/Pd bi-layer를 사용함에 의해서 clustering의 크기를 줄일 수 있었다. Clustering의 크기는 Ni/Pd bi-layer의 경우가 작았으며, $650^{\circ}C$ 열처리 후에 barrier height는 Pd/Ni bi-layer의 경우에도 Ni의 영향을 받음을 알 수 있었다.

• Journal of Applied Biological Chemistry
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• v.51 no.1
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• pp.17-19
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• 2008

Isoflavanone has been synthesized from the reduction of isoflavone in nearly quantitative yield. Isoflavone with seven equivalents of ammonium formate in the presence of Pd/C in ethanol under $N_2$ atmosphere exclusively produced the two-electron reduced product in two hours. It was characterized by various spectroscopic methods, including UV-VIS, EI-MS, $^1H$-NMR, $^{13}C$-NMR and $^1H$, $^1H$-COSY. The racemic mixture was separated by Sumi-Chiral column chromatography and the absolute configurations of the enantiomers were characterized by circular dichroism spectroscopy.

• Molecular & Cellular Toxicology
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• v.4 no.2
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• pp.106-112
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• 2008

Parkinson's disease (PD) progresses severely by a gradual loss of dopaminergic neurons in the substantia nigra (SN). Epidemiological studies showed that the incidences of PD were reduced by smoking of which the major component, nicotine might be neuroprotective. But the function of nicotine, which might suppress the incidences of PD, is still unknown. Fortunately, recently it was reported that a glial reaction and inflammatory processes might participate in a selective loss of dopaminergic neurons in the SN. The levels of tumour necrosis factor (TNF)-${\alpha}$ synthesised by astrocytes and microglia are elevated in striatum and cerebrospinal fluid (CSF) in PD. TNF-${\alpha}$ kills the cultured dopaminergic neurons through the apoptosis mechanism. TNF-${\alpha}$ release from glial cells may mediate progression of nigral degeneration in PD. Nicotine pretreatment considerably decreases microglial activation with significant reduction of TNF-${\alpha}$ mRNA expression and TNF-${\alpha}$ release induced by lipopholysaccharide (LPS) stimulation. Thus, this study was intended to explore the role of nicotine pretreatment to inhibit the expressions of TNF-${\alpha}$ mRNA in human fetal astrocytes (HFA) stimulated with IL-$1{\beta}$. The results are as follows: HFA were pretreated with 0.1, 1, and $10{\mu}g/mL$ of nicotine and then stimulated with IL-$1{\beta}$ (100 pg/mL) for 2h. The inhibitory effect of nicotine on expressions of TNF-${\alpha}$ mRNA in HFA with pretreated $0.1{\mu}g/mL$ of nicotine was first noted at 8hr, and the inhibitory effect was maximal at 12 h. The inhibitory effect at $1{\mu}g/mL$ of nicotine was inhibited maximal at 24 h. Cytotoxic effects of nicotine were noted above $10{\mu}g/mL$ of nicotine. Moreover, Nicotine at 0.1, 1 and $10{\mu}g/mL$concentrations significantly inhibited IL-$1{\beta}$-induced TF-${\kappa}B$ activation. Collectively, these results indicate that in activated HFA, nicotine may inhibit the expression of TNF-${\alpha}$ mRNA through the pathway which suppresses the NF-${\kappa}B$ activation. This study suggests that nicotine might be neuroprotective to dopaminergic neurons in the SN and reduce the incidences of PD.

• Advances in nano research
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• v.12 no.6
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• pp.639-652
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• 2022

The prolyl 3-hydroxylase family member 4 (P3H4), is associated with post-translational modification of fibrillar collagens and aberrantly activated in cancer leading to tumor progression. However, its role in clear cell renal cell carcinoma (ccRCC) is still unknown. Here we reported that P3H4 was highly expressed in renal cancer tissues and significantly positive correlated with poor prognosis. Knockdown of P3H4 inhibited the proliferation, migration and metastasis of renal cancer cells in vitro and in vivo, and also, overexpression of it enhanced the oncogenic process. Mechanistically, P3H4 depletion decreased the levels of GDF15-MMP9 axis and repressed its downstream signaling. Further functional studies revealed that inhibition of GDF15 suppressed renal cancer cell growth and GDF15 recombinant human protein (rhGDF15) supplementation effectively rescued the inhibitory effect induced by P3H4 knockdown. Moreover, decreased levels of MMP9 caused by inhibition of P3H4-GDF15 signaling constrained the expression of PD-L1 and suppression of P3H4 accordingly promoted anti-tumor immunity via stimulating the infiltration of CD4+ and CD8+ T cells in syngeneic mice model. Taken together, our findings firstly demonstrated that P3H4 promotes ccRCC progression by activating GDF15-MMP9-PD-L1 axis and targeting P3H4-GDF15-MMP9 signaling pathway can be a novel strategy of controlling ccRCC malignancy.

• Applied Chemistry for Engineering
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• v.10 no.8
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• pp.1210-1215
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• 1999

Optimum conditions of the hydrogenation of PNA to pure PPD were determined in a three-phase slurry reactor with suspended Pd/C catalyst particles. Minimization of mass transfer resistances at the interfaces of both gas-liquid and liquid-catalyst particles and control of overall reaction rate on catalyst surface leaded to decrease the hydrogen starvation on reaction active sites and to reduce the side reactions during hydrogenation. The optimum temperature, pressure, and catalysst concentration were confirmed to be in the range of $60^{\circ}C$, 60~70 psig, and 1~2 g-cat/L, respectively. Reaction rate was zero order with respect to the concentration of PNA and 1st order with respect to the pressure of hydrogen(P). Overall rate expression of the reaction was $R_A=6.44{\times}10^6{\cdot}H{\cdot}P{\cdot}m{\cdot}$exp(-4659/T) where H is constant, m is concentration of catalyst, and T is temperature.

• Journal of Radiation Protection and Research
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• v.36 no.3
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• pp.119-126
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• 2011

Mitochondrial DNA (mtDNA) deletion is a well-known marker for oxidative stress and aging, and contributes to harmful effects in cultured cells and animal tissues. mtDNA biogenesis genes (NRF-1, TFAM) are essential for the maintenance of mtDNA, as well as the transcription and replication of mitochondrial genomes. Considering that oxidative stress is known to affect mitochondrial biogenesis, we hypothesized that ionizing radiation (IR)-induced reactive oxygen species (ROS) causes mtDNA deletion by modulating the mitochondrial biogenesis, thereby leading to cellular senescence. Therefore, we examined the effects of IR on ROS levels, cellular senescence, mitochondrial biogenesis, and mtDNA deletion in IMR-90 human lung fibroblast cells. Young IMR-90 cells at population doubling (PD) 39 were irradiated at 4 or 8 Gy. Old cells at PD55, and H2O2-treated young cells at PD 39, were compared as a positive control. The IR increased the intracellular ROS level, senescence-associated ${\beta}$-galactosidase (SA-${\beta}$-gal) activity, and mtDNA common deletion (4977 bp), and it decreased the mRNA expression of NRF-1 and TFAM in IMR-90 cells. Similar results were also observed in old cells (PD 55) and $H_2O_2$-treated young cells. To confirm that a increase in ROS level is essential for mtDNA deletion and changes of mitochondrial biogenesis in irradiated cells, the effects of N-acetylcysteine (NAC) were examined. In irradiated and $H_2O_2$-treated cells, 5 mM NAC significantly attenuated the increases of ROS, mtDNA deletion, and SA-${\beta}$-gal activity, and recovered from decreased expressions of NRF-1 and TFAM mRNA. These results suggest that ROS is a key cause of IR-induced mtDNA deletion, and the suppression of the mitochondrial biogenesis gene may mediate this process.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.371-372
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• 2012

We have studied lead-based gapless semiconductors, $PbPdO_2$, which is very sensitive to external parameters such as temperature, pressure, electric field, etc[1]. We have fabricated pure $PbPdO_2$, Co- and Mn-doped $PbPdO_2$ thin films using the pulsed laser deposition. Because of the volatile element of Pb, it is very difficult to grow the films. Note that in case of $MgB_2$, Mg is also volatile element. So in order to enhance the quality of $MgB_2$, some experiments are carried out in annealing with Mg-rich atmosphere [2]. This annealing process with volatile element plays an important role in making smooth surface. Thus, we applied such process to our studies of $PbPdO_2$ thin films. As a result, we found the optimal condition of ex-situ annealing temperature ${\sim}650^{\circ}C$ and time ~12 hrs. The ex-situ annealing brought the extreme change of surface morphology of thin films. After ex-situ annealing with PbO-rich atmosphere, the grain size of thin film was almost 100 times enlarged for all the thin films and also the PbO impurity phase was smeared out. And from X-ray diffraction measurements, we determined highly crystallized phases after annealing. So, we measured electrical and magnetic properties. Because of reduced grain boundary, the resistivity of ex-situ annealed samples changed smaller than no ex-situ sample. And the carrier densities of thin films were decreased with ex-situ annealing time. In this case, oxygen vacancies were removed by ex-situ annealing. Furthermore, we will discuss the transport and magnetic properties in pure $PbPdO_2$, Co- and Mn-doped $PbPdO_2$ thin films in detail.

• Journal of the Korean Ceramic Society
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• v.22 no.4
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• pp.54-60
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• 1985

Gas sensing materials for detecting flammable gases such as $CH_4$, $C_3H_8$ and n-$C_4H_{10}$ were developed by util-izing $In_2O_3$ as the principal sensing material. The sensing materials were formulated by mixing $In_2O_3$ powder with one or two other chemicals such as $SnO_2$, $Y_2O_3$ and $Al_2O_3$ with a small addition of $PdCl_2$ as a catalyst. Sample of sensor were fabricated by coating each of the mixtures on a ceramic tube impregnating ethylsili-cate and firing at 75$0^{\circ}C$ Each material mixture was evaluated by measuring and comparing gas sensitivity(resistance in air/resistance with gas) to flammable gases such as $CH_4$, $C_3H-8$ and n-$C_4H_{10}$. It was found that among fifteen compositions tested three compositions as follows show the highest gas sensitivity and thus are very feasible for commercialization as the gas sensors ; o49.5 $In_2O_3$+50 Al2O3_0.5 PdCl2(wt%) o $20In_2O_3+29$ $SnO_2+50$ $Al_2O_3+1$ $PdCl_2$(wt%) o40 $In_2O_3$+9 $Y_2O_3+50$ $Al_2O_3+1$ $PdCl_2$(wt%)

• Applied Chemistry for Engineering
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• v.35 no.2
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• pp.134-139
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• 2024

In the steam reforming of methane reactions, the effect of adding noble metals Ru and Pd to a Ni-based catalyst as promoters was analyzed in terms of catalytic activity and hydrogen production. The synthesized catalysts were coated on the surface of a honeycomb-structured metal monolith to perform steam methane reforming reactions. The catalysts were characterized by XRD, TPR, and SEM, and after the reforming reaction, the gas composition was analyzed by GC to measure methane conversion, hydrogen yield, and CO selectivity. The addition of 0.5 wt% Ru improved the reduction properties of the Ni catalyst and exhibited enhanced catalytic activity with a methane conversion of 99.91%. In addition, reaction characteristics were analyzed according to various process conditions. Methane conversion of over 90% and hydrogen yield of more than 3.3 were achieved at a reaction temperature of 800 ℃, a gas hourly space velocity (GHSV) of less than 10000 h^-1, and a ratio of H₂O to CH₄ (S/C) higher than 3.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2369-2371
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• 2005

MEMS 기술을 이용하여 마이크로 $H_2$ 가스센서를 제작하고 마이크로 히터의 열적 특성과 $H_2$ 가스 농도 변화에 따를 마이크로 가스센서에 대한 감도를 분석하였다. 마이크로 가스센서의 전압 인가에 따른 히터의 온도는 1.0V에서 $250-280^{\circ}C$의 고온 특성을 보였으며, 동작온도 $250^{\circ}C$에서 $H_2$ 가스는 $SnO_2/V_2O_5/Pd$의 감응물질을 도포한 센서의 반응이 우수한 특성을 확인하였다. 동작 온도 $250^{\circ}C$ $H_2$ 농도 5000ppm의 조건에서 $SnO_2/V_2O_5/Pd$의 감응물질을 도포한 가스센서에서 $H_2$ 흡착 반응 시간은 3sec이 탈착 반응 시간은 8-10sec의 결과를 보였다.