• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.189-189
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• 2012

Lead sulfide (PbS) nanocrystal quantum dots (NQDs) are promising materials for various optoelectronic devices, especially solar cells, because of their tunability of the optical band-gap controlled by adjusting the diameter of NQDs. PbS is a IV-VI semiconductor enabling infrared-absorption and it can be synthesized using solution process methods. A wide choice of the diameter of PbS NQDs is also a benefit to achieve the quantum confinement regime due to its large Bohr exciton radius (20 nm). To exploit these desirable properties, many research groups have intensively studied to apply for the photovoltaic devices. There are several essential requirements to fabricate the efficient NQDs-based solar cell. First of all, highly confined PbS QDs should be synthesized resulting in a narrow peak with a small full width-half maximum value at the first exciton transition observed in UV-Vis absorbance and photoluminescence spectra. In other words, the size-uniformity of NQDs ought to secure under 5%. Second, PbS NQDs should be assembled carefully in order to enhance the electronic coupling between adjacent NQDs by controlling the inter-QDs distance. Finally, appropriate structure for the photovoltaic device is the key issue to extract the photo-generated carriers from light-absorbing layer in solar cell. In this step, workfunction and Fermi energy difference could be precisely considered for Schottky and hetero junction device, respectively. In this presentation, we introduce the strategy to obtain high performance solar cell fabricated using PbS NQDs below the size of the Bohr radius. The PbS NQDs with various diameters were synthesized using methods established by Hines with a few modifications. PbS NQDs solids were assembled using layer-by-layer spin-coating method. Subsequent ligand-exchange was carried out using 1,2-ethanedithiol (EDT) to reduce inter-NQDs distance. Finally, Schottky junction solar cells were fabricated on ITO-coated glass and 150 nm-thick Al was deposited on the top of PbS NQDs solids as a top electrode using thermal evaporation technique. To evaluate the solar cell performance, current-voltage (I-V) measurement were performed under AM 1.5G solar spectrum at 1 sun intensity. As a result, we could achieve the power conversion efficiency of 3.33% at Schottky junction solar cell. This result indicates that high performance solar cell is successfully fabricated by optimizing the all steps as mentioned above in this work.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.279.2-279.2
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• 2016

InGaN/GaN multiple quantum wells (MQWs) have been attracted much attention as light-emitting diodes (LEDs) in the visible and UV regions. Particularly, quantum efficiency of green LEDs is decreased dramatically as approaching to the green wavelength (~500 nm). This low efficiency has been explained by quantum confined Stark effect (QCSE) induced by piezoelectric field caused from a large lattice mismatch between InGaN and GaN. To improve the quantum efficiency of green LED, several ways including epitaxial lateral overgrowth that reduces differences of lattice constant between GaN and sapphire substrates, and non-polar method that uses non- or semi-polar substrates to reduce QCSE were proposed. In this study, graded short-period InGaN/GaN superlattice (GSL) was grown below the 5-period InGaN/GaN MQWs. InGaN/GaN MQWs were grown on the patterned sapphire substrates by vertical-metal-organic chemical-vapor deposition system. Five-period InGaN/GaN MQWs without GSL structure (C-LED) were also grown to compare with an InGaN/GaN GSL sample. The luminescence properties of green InGaN/GaN LEDs have been investigated by using photoluminescence (PL) and time-resolved PL (TRPL) measurements. The PL intensities of the GSL sample measured at 10 and 300 K increase about 1.2 and 2 times, respectively, compared to those of the C-LED sample. Furthermore, the PL decay of the GSL sample measured at 10 and 300 K becomes faster and slower than that of the C-LED sample, respectively. By inserting the GSL structures, the difference of lattice constant between GaN and sapphire substrates is reduced, resulting that the overlap between electron and hole wave functions is increased due to the reduced piezoelectric field and the reduction in dislocation density. As a results, the GSL sample exhibits the increased PL intensity and faster PL decay compared with those for the C-LED sample. These PL and TRPL results indicate that the green emission of InGaN/GaN LEDs can be improved by inserting the GSL structures.

• 대한화학회지
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• 제45권6호
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• pp.570-576
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• 2001

YOB에 $Eu^{3+}$를 첨가하여 고상 반응으로 합성하였다. YOBr: $Eu^{3+}$ 형광체는 621nm에서 강한 적색 발광을 보이며, $Eu^{3+}$이온 농도가 0.05mol일 때 외대 발광 휘도를 나타냈다. 이때, 적색 발광을 유발하는 전이는 $^5D_0{\to} ^7F_2$ 이며, $Eu^{3+}$이온의 농도에 따른 발광 스펙트럼과 잔광시간 곡선을 통해 YOBr: $Eu^{3+}$형광체의 PL거동을 규명하였다. Inokuti-Hirayama식으로 잔광시간 곡선을 fitting 한 결과, YOBr내의 $Eu^{3+}$간 다중 극자 상호작용 유형(multipolar interaction)은 쌍극자-쌍극자 상효작용(dipole-dipole interaction)으로 밝혀졌다. 또한 본 연구에서는 임계거리를 구하기 위해 임계농도에 의한 계산 외에도 Inokuti-Hirayama식으로부터 fitting한 C/$C_0$값으로 구하는 방법과 $Eu^{3+}$의 여기 및 발광 스펙트럼으로 spectral overlap하여 임계거리를 구하고자 시도 하였다. 각각의 방법으로 구한 임계거리는 17.30, 10.51 및 7.18$\AA$으로 약간의 편차를 보이지만 대략적인 크기를 갖고 있어, 이는 계산이나 측정상의 오차를 감안하면 모두 임계거리를 구하는 유용한 방법으로 판단된다.

• 한국의학물리학회지:의학물리
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• 제5권2호
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• pp.13-20
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• 1994

본 연구에서는 감마선 조사, 전자선 조사방법에 의한 전자만의 주업 및 이온 주업 후 전자선조사 방법으로 전자들이 주입된 $\alpha$-$Al_2O_3$의 열자극 발광(Thermoluminescence : TL)에 관련된 결함 형태를 조사하였다. 감마선 조사된 $\alpha$-$Al_2O_3$의 열자극 발광 곡선은 380K, 415K, 440K, 460K 및 475K에서 TL peak가 나타났다. 광흡수 스펙트럼과 자외선 photobleaching 결과로부터 감마선 조사된 $\alpha$-$Al_2O_3$의 380K와 475K TL peak는 F center에, 415K TL peak는 $F^{+}$ center에 기인함을 알았다. 전자선 조사방법에 의하여 전자 주입된 $\alpha$-$Al_2O_3$의 열자극 발광 곡선은 380K, 415K, 440K 및 460K TL peak를 가졌고, $Li^{+}$ 이온 주입 후 전자선 조사방법으로 전자들이 주입된 $\alpha$-$Al_2O_3$는 440K에서 TL peak가 나타났다. 전자선 조사방법에 의한 전자만의 주입과 $Li^{+}$ 이온 주입 후 전자선 조사방법으로 전자들이 주입된 $\alpha$-$Al_2O_3$의 열자극 발광 특성은 380K TL peak는 F center에, 440K TL peak는 $F^{+}$ center에 기인함을 보였다.

• 한국진공학회지
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• 제22권3호
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• pp.119-125
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• 2013

In-line magnetron sputtering system을 사용하여 대면적($60{\times}60cm^2$) 소다라임 유리기판위에 투명전도성 ZnO(Al)와 ZnO(AlGa) 박막을 500 nm에서 1,450 nm까지 두께별로 증착하여 전기적, 광학적 특성을 연구하였다. XRD를 통해 c-축 방향성(002)을 가지고 성장된 것을 확인 하였다. Hall 특성 분석을 통해 이동도 및 캐리어 농도의 특성을 확인 하였으며, 그에 따른 ZnO(AlGa)의 비저항이 $9.03{\times}10^{-4}{\Omega}{\cdot}cm$에서 $7.83{\times}10^{-4}{\Omega}{\cdot}cm$으로 ZnO(Al) 보다 높게 나타났으며, 가시광선 영역에서 투과율은 87.6%에서 84.3%으로 나타났다. 따라서 ZnO(AlGa)는 전기적 특성이 우수하고 높은 투과율로 대면적용 투명전도성 재료로의 활용에 적합한 특성을 지닌 것을 확인 할 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.264-264
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• 2010

Single-walled carbon nanotubes (SWCNTs) were grown on a Si wafer by using thermal chemical vapor deposition (t-CVD). We investigated the effect of the catalyst deposition rate on the types of CNTs grown on the substrate. In general, smaller islands of catalyst occur by agglomeration of a catalyst layer upon annealing as the catalyst layer becomes thinner, which results in the growth of CNTs with smaller diameters. For the same thickness of catalyst, a slower deposition rate will cause a more uniformly thin catalyst layer, which will be agglomerated during annealing, producing smaller catalyst islands. Thus, we can expect that the smaller-diameter CNTs will grow on the catalyst deposited with a lower rate even for the same thickness of catalyst. The 0.5-nm-thick Fe served as a catalyst, underneath which Al was coated as a catalyst support as well as a diffusion barrier on the Si substrate. The catalyst layers were. coated by using thermal evaporation. The deposition rates of the Al and Fe layers varied to be 90, 180 sec/nm and 70, 140 sec/nm, respectively. We prepared the four different combinations of the deposition rates of the AI and Fe layers. CNTs were synthesized for 10 min by flowing 60 sccm of Ar and 60 sccm of $H_2$ as a carrier gas and 20 sccm of $C_2H_2$ as a feedstock at 95 torr and $810^{\circ}C$. The substrates were subject to annealing for 20 sec for every case to form small catalyst islands prior to CNT growth. As-grown CNTs were characterized by using field emission scanning electron microscopy, high resolution transmission electron microscopy, Raman spectroscopy, UV-Vis NIR spectroscopy, and atomic force microscopy. The fast deposition of both the Al and Fe layers gave rise to the growth of thin multiwalled CNTs with the height of ${\sim}680\;{\mu}m$ for 10 min while the slow deposition caused the growth of ${\sim}800\;{\mu}m$ high SWCNTs. Several radial breathing mode (RBM) peaks in the Raman spectra were observed at the Raman shifts of $113.3{\sim}281.3\;cm^{-1}$, implying the presence of SWCNTs (or double-walled CNTs) with the tube diameters 2.07~0.83 nm. The Raman spectra of the as-grown SWCNTs showed very low G/D peak intensity ratios, indicating their low defect concentrations.

• 한국식품영양과학회지
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• 제42권6호
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• pp.911-916
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• 2013

열처리에 따른 수경재배인삼과 잎줄기의 화학성분과 효소활성 변화를 살펴보기 위하여 90, 110, 130 및 $150^{\circ}C$에서 2시간 열처리한 후 갈변도, 5-HMF, 유리당, 유기산 함량, 효소활성을 살펴보았다. Tyrosinase와 ACE 저해활성 등 효소활성은 높은 저해활성을 나타내지는 않았지만 온도가 증가함에 따라 유의적으로 그 활성이 증가하였다. Maillard 반응의 중간 및 최종 단계의 생성물인 5-HMF, 유리당, 유기산의 함량은 열처리 온도가 증가함에 따라 유의적으로 증가하였다. 5-HMF 함량은 수경재배인삼과 잎줄기 모두 대조구에서는 검출되지 않았지만 열처리 온도가 증가함에 따라 증가하였다. 유리당은 수경재배인삼에서는 fructose, glucose 및 sucrose 3종류의 당이 검출되었다. Sucrose는 열처리 온도가 증가함에 따라 감소하였으며, fructose 및 glucose 함량은 증가하였다. 열처리 온도가 증가함에 따라 이당류가 단당류로 분해되고 지속적인 열분해로 인하여 HMF, furfural 및 5-methyl furfural 등과 유기산으로 분해되기 때문에 유기산 함량 또한 증가하였다. 본 연구결과를 바탕으로 기능성 식품 소재로의 이용을 위하여 다양한 열처리 조건을 검토해야 할 것으로 판단된다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.29-29
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• 2009

On this research, laser welding technology for manufacturing automobile body is studied. Laser welding technology is one of the important technologies used in the manufacturing of lighter, safer automotive bodies at a high level of productivity; the leading automotive manufacturers have replaced spot welding with laser welding in the process of car body assembly. Korean auto manufacturers are developing and applying the laser welding technology using a high output power Nd:YAG laser and a 6-axes industrial robot. On the other hand, the robot-based remote laser welding system was equipped with a long focal laser scanner system in robotic end effect. Laser system, robot system, and scanner system are used for realizing the high speed laser welding system. The remote laser welding system and industrial robotic system are used to consist of robot-based remote laser welding system. The robot-based remote laser welding system is flexible and able to improve laser welding speed compared with traditional welding as spot welding and laser welding. The robot-based remote laser systems used in this study were Trumpf's 4kW Nd:YAG laser (HL4006D) and IPG's 1.6kW Fiber laser (YLR-1600), while the robot systems were of ABB's IRB6400R (payload:120kg) and Hyundai Heavy Industry's HX130-02 (payload:130kg). In addition, a study of quality evaluation and monitoring technology for the remote laser welding was conducted. The welding joints of steel plate and steel plate coated with zinc were butt and lapped joints. The quality testing of the laser welding was conducted by observing the shape of the beads on the plate and the cross-section of the welded parts, analyzing the results of mechanical tension test, and monitoring the plasma intensity and temperature by using UV and IR detectors. Over the past years, Trumf's 4kW Nd:YAG laser and ABB's IRB6400R robot system was used. Nowadays, the new laser source, robot and laser scanner system are used to increase the processing speed and to improve the efficiency of processes. This paper proposes the robot-based remote laser welding system as a means of resolving the limited welding speed and accuracy of conventional laser welding systems.

• 한국재료학회지
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• 제23권3호
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• pp.155-160
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• 2013

ZnO thin films co-doped with Mg and Ga (MxGyZzO, x + y + z = 1, x = 0.05, y = 0.02 and z = 0.93) were prepared on glass substrates by RF magnetron sputtering with different sputtering powers ranging from 100W to 200W at a substrate temperature of $350^{\circ}C$. The effects of the sputtering power on the structural, morphological, electrical, and optical properties of MGZO thin films were investigated. The X-ray diffraction patterns showed that all the MGZO thin films were grown as a hexagonal wurtzite phase with the preferred orientation on the c-axis without secondary phases such as MgO, $Ga_2O_3$, or $ZnGa_2O_4$. The intensity of the diffraction peak from the (0002) plane of the MGZO thin films was enhanced as the sputtering power increased. The (0002) peak positions of the MGZO thin films was shifted toward, a high diffraction angle as the sputtering power increased. Cross-sectional field emission scanning electron microscopy images of the MGZO thin films showed that all of these films had a columnar structure and their thickness increased with an increase in the sputtering power. MGZO thin film deposited at the sputtering power of 200W showed the best electrical characteristics in terms of the carrier concentration ($4.71{\times}10^{20}cm^{-3}$), charge carrier mobility ($10.2cm^2V^{-1}s^{-1}$) and a minimum resistivity ($1.3{\times}10^{-3}{\Omega}cm$). A UV-visible spectroscopy assessment showed that the MGZO thin films had high transmittance of more than 80 % in the visible region and that the absorption edges of MGZO thin films were very sharp and shifted toward the higher wavelength side, from 270 nm to 340 nm, with an increase in the sputtering power. The band-gap energy of MGZO thin films was widened from 3.74 eV to 3.92 eV with the change in the sputtering power.

• 한국재료학회지
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• 제19권3호
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• pp.163-168
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• 2009

$Eu^{3+}$-doped $Y_2O_3$ red phosphor was synthesized in a flux method using the chemicals $Y_2O_3,\;Eu_2O_3,\;H_3BO_3$ and $BaCl_2{\cdot}2H_2O$. The effect of a flux addition on the preparation of $Y_2O_3:Eu_{3+}$ red phosphor used as a cold cathode fluorescence lamp was investigated. $H_3BO_3$ and $BaCl_2{\cdot}2H_2O$ fluxes were used due to their different melting points. The crystallinity, thermal properties, morphology, and emission characteristics were measured using XRD, TG-DTA, SEM, and a photo-excited spectrometer. Under UV excitation of 254 nm, $Eu_2O_3$ 3.7 mol% doped $Y_2O_3$ exhibited a strong narrow-band red emission, peaking at 612 nm. From this result, the phosphor synthesized by firing $Y_2O_3$ with 3.7 mol% of $Eu_2O_3$, 0.25 mol% of $H_3BO_3$ and 0.5 mol% of $BaCl_2{\cdot}2H_2O$ fluxes at $1400^{\circ}C$ for 2 hours had a larger particle size of $4{\mu}m$ on average compared to the phosphor of the $H_3BO_3$ flux alone. In addition, a phosphor synthesized by the two fluxes together had a rounder corner shape, which led to the maximum emission intensity.