• Korean Journal of Materials Research
• /
• v.23 no.3
• /
• pp.155-160
• /
• 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.

• Polymer(Korea)
• /
• v.25 no.4
• /
• pp.575-586
• /
• 2001

Stabilized polyacrylonitrile (PAN) fibers can be transformed into quasi-carbon fibers with different properties depending on heat-treatment processing parameters at lower temperatures than temperature for the fabrication of carbon fibers. It has been investigated from the preliminary work that appropriate quasi-carbonization processes at about 1100$^{\circ}C$ strongly influence various properties of quasi-carbon fiber/polymer composite as well as quasi-carbon fiber itself. The objective of the present work is to prepare quasi-carbon fibers from stabilized PAN fibers using various quasi-carbonization cycles and to examine their properties. Two temperature regions, up to 800$^{\circ}C$ and above 1000$^{\circ}C$, were used for quasi-carbonization processes. The chemical composition, physical properties, thermal stability, microstructure, mechanical properties and electrical resistivity of the quasi-carbon fibers prepared with different final heat-treatment temperatures, heating rates, holding times, heating steps, and purging gas purity were extensively examined. The results were also compared with those from stabilized PAN fiber and commercial PAN-based carbon fiber. The present study showed that a variety of properties of quasi-carbon fibers significantly depended on several quasi-carbonization process parameters.

• Proceedings of the Optical Society of Korea Conference
• /
• 2005.07a
• /
• pp.28-29
• /
• 2005

본 논문에서는 MEH-PPV와 DFPP의 폴리머 물질을 이용하여 photovoltaic device가 제작되었고, 그림 1에 두 물질의 분자 구조가 보여진다. Photovoltaic cell의 전기-광학적 특성은 활성층의 폴리머 물질에 의해 결정된다. 이러한 특성을 알아보기 위해서 홉수 스펙트럼이 측정되었다. DFPP는 chloroform, chlorobenzen, THF, acetone에 잘 녹았으며, 본 논문에서는 chloroform이 용매로 사용되었다. 제작 공정은 다음과 같다. 인듐 주석 산화물 (ITO)이 증착된 유리기판은 photolithography 공정을 거친 후, 왕수(HNO$_{3}$ + HCL)로 식각됨으로서 전극의 패턴이 제작되었다. 그리고 ITO 전극 패턴 된 유리기판 위에 PEDOT (CH8000, Baytron)이 코팅된 후 Ar이 주입되는 Convection Oven을 이용하여 120$^{\circ}$C에서 2시간 동안 열처리되어 수분이 제거되었다. 활성층에는 MEH-PPV와 DFPP가 9:1과 2.33:1로 혼합된 폴리머가 사용되었고, 이것은 0.3 %w.t.가 되도록 chloroform에 넣어 5시간 동안 스핀바를 돌려서 용해되었다. 이 용액은 ITO 전극 패턴이 형성된 글라스 위에 3000 rpm으로 45 초간 스핀코팅 되었다. 이 때 얻어진 유기물 박막층은 80$^{\circ}$C의 Ar이 주입되는 convection oven에서 3시간 동안 경화되었다. 경화된 단층 유기물 박막층 위에 Li-Al이 1000 ${\AA}$의 두께로 증착되어 전극이 형성되었고, 이후 질소가 채워진 globe box에서 소자는 encapsulation되어 산소와 수분에 대한 영향으로부터 차단되었다. 상기의 공정으로 제작된 소자의 박막구조는 그림 2에서 보여진다. 그림 3은 MEH-PPV와 DFPP를 혼합했을 때의 흡수 스펙트럼이다. 최대 흡수 파장은 511 nm였다. 그리고 photovoltaic cell의 V-I 특성 결과가 그림 4와 같이 측정되었다. 측정에서는 300${\sim}$700 nm의 파장대를 갖는 태양광 모사계가 사용되었고, 셀의 면적은 10 mm$^{2}$였다. 그림 5의 I-V 특성으로부터 MEH-PPV와 DFPP가 9:1 로 혼합했을 때보다 2.33:1 로 혼합했을 때, photovoltaic device의 효율이 향상됨을 확인할 수 있다. 빛이 75 mW/cm$^{2}$ 의 세기로 조사될 때 9:1과 2.33:1로 혼합된 소자의 open circuit voltage (V$_{oc}$)는 비슷하지만, short circuit current Density (J$_{sc}$)는 각각 -1.39 ${\mu}$A/cm$^{2}$ 와 -3.72${\mu}$A/cm$^{2}$ 로 약 2.7배 정도 증가되었음을 볼 수 있다. 이러한 결과를 통해 electron acceptor인 DFPP의 비율이 높아질수록 photovoltaic cell의 conversion efficiency가 더 크게 됨을 확인할 수 있다. 그러므로 효율이 최대가 되는 두 폴리머의 혼합 비율이 최적화되는 조건을 찾는 것은 매우 중요한 연구가 될 것이다.

• Korean Journal of Optics and Photonics
• /
• v.9 no.6
• /
• pp.428-432
• /
• 1998

We fabricated 1$\times$8 array of GaAs/AlGaAs quantum well infrared photodetectors for the long wavelength infrared detection which is based on the bound-continuum intersubband transition, and characterized its electrical and optical properties. The device was grown on SI-GaAs(100) by the molecular beam epitaxy and consisted of 25 period of 40 ${\AA} $ GaAs well and 500 ${\AA} $ $Al_{0.28} Ga_{0.72}$ As barrier. To reduce the possibility of interface states only the center 20 ${\AA} $ of the well was doped with Si ($N_D=2{\times}10^{18} cm^{-3}$). We etched the sample to make square mesas of 200$\times$200 $\mu\textrm{m}^2$ and made an ohmic contact on each pixel with Au/Ge. Current-voltage characteristics and photoresponse spectrum of each detector reveal that the array was highly uniform and stable. The spectral responsivity and the detectivity $D^＊$ were measured to be 180,260 V/W and $4.9{\times}10^9cm\sqrt{Hz}/W$ respectively at the peak wavelength of $\lambda$ =7.8 $\mu\textrm{m}$ and at T=10 K.

• Journal of the Society of Naval Architects of Korea
• /
• v.30 no.1
• /
• pp.125-133
• /
• 1993

Most studies on the vibration analysis of a beam-column with ends elastically restrained and various intermediate constraints have been based on the Euler beam theory, which is inadequate for beam-columns of low slenderness ratios. In this paper, analytical methods for vibration and dynamic sensitivity of a Timoshenko beam-column with ends elastically restrained and various intermediate constraints are presented. Firstly, an exact solution method is shown. Since the exact method requires considerable computational effort, a Rayleigh-Ritz analysis is also investigated. In the latter two kinds of trial functions are examined for comparisions : eigenfunctions of the base system(the system without intermediate constraints) and polynomials having properties corresponding to the eigenfunctions of the base system. The results of some numerical Investigations show that the Rayleigh-Ritz analysis using the characteristic polynomials is competitive with the exact solutions in accuracy, and that it is much more efficient in computations than using the eigenfunctions of the base system, especially in the dynamic sensitivity analysis. In addition, the prediction of the changes of natural frequencies due to the changes of design variables based on the first order sensitivity is in good agreements with that by the ordinary reanalysis as long as the changes of design variables are moderate.

• Proceedings of the Safety Management and Science Conference
• /
• 2013.11a
• /
• pp.483-497
• /
• 2013

현대사회가 발전 할수록 대량산업화와 도시화가 심화되어 건축물의 초고층화 및 대형화가 증가하고 있으며, 안전적인 건축물 보다는 건물 및 제조사업장의 시각적인 디자인에 치우쳐 화재하중이 높은 건축자재의 내 외장재 및 고급스러운 장식물을 사용함으로써 그 위험뿐 만 아니라 화재발생시 대규모 인명 및 재산상의 피해를 가져오게 된다. 그리고 제조사업장화재는 화재로 인한 직접적인 손실 즉 물적 손실은 물론 생산중단으로 인한 간접적인 손실은 실로 측정하기가 어렵다. 지금까지 발생한 제조사업장화재의 발화요인별 분석은 부주의, 전기적, 미상 순으로 인한 화재가 가장 많고 발화열원은 작동기기, 담뱃불(라이터), 마찰 전도 복사등이 주요 원인이 되고 있고 대형화제 취약시설로는 공장 및 창고로 나타나고 있다. 소방방재청의 통계자료를 살펴보면 2012년 화재 발생현황 중 발화요인에 대한 화재별 장소 건수를 검토 한 결과 비주거의 화재발생 16,009건 중 5,758건으로 (36%)부주의이고, 주거에도 화재발생 10,715건 중 5,560건으로 51.9%의 부주의로 가장 높은 것으로 나타났다. 그러므로 제조사업장의 사소한 부주의로 발생하는 화재를 예방하기 위해서는 소방안전관리자의 처우개선과 기업활동규제완화의 겸직 허용을 재검토 하여야 하며, 소방안전관라자의 실무능력 강화를 위한 소방안전관리 실무교육과정을 이론적 교육 보다는 현장 실습위주로 할 필요가 있다. 이를 위해서는 소방안전관리자에 대한 법정 실무교육 횟수를 확대하여 현행 2년에 1회 에서 1년에 1회로 하고, 실무교육에 있어서도 우수송방안전관리 업체를 선정하여 화재예방에 대한 구체적인 업무를 활성화 하고, 문제 발생요소들을 분석하여 실습을 통한 소방안전관리자의 실무교육을 실시해야 할 것이다. 이러한 전문 소방안전관리자로 소방대상물의 소방교육 및 훈련을 성실히 수행 해야 할 것 이다. 한순간의 부주의로 인하여 화재가 발생하면 돌이킬 수 없는 수백명의 생명을 앗아가고, 수백억원대의 재산피해를 줄이기 위해서는 소방안전관리자의 역량을 넓히고 화재예방 업무를 최우선적으로 수행해야 할 것이다. 화재예방을 위해 소방안전관리자의 업무개선 및 전문교육을 활성화 하여 업무능력을 향상 시켜 화재발생시 초기진압에 신속하고 정확하게 대처해야 한다는 것이 전문적인 화재예방 대책 일 것이다.

• The Journal of Natural Sciences
• /
• v.8 no.1
• /
• pp.61-69
• /
• 1995

It is hard to synthesize pure $BaTiO_3$ from $BaCO_3$ and $TiO_2$ in solid reaction for the activity of BaO and secondary phase. For this reason, the wet chemical techniques have been studied. Starting material which was used in these methods were expensive and the properties of powder which was synthesized in same defined. So, some process have been studying again to improve soild reaction method. This study which was one of those was to defin the forming mechanism of $Ba_2TiO_4$ and to control some condition of $Ba_2TiO_4$. The synthesis temperature of $BaTiO_3$ in solid reaction was near $1120^{\circ}C$. The quantity and forming temperature of $Ba_2TiO_4$ could be controlled by atmosphere heat treatment. $Ba_2TiO_4$ was related to expansion in Ba-rich region of $BaTiO_3$. $BaTiO_2O_5$ and $BaTiO_3O_7$ was reason to expand in Ti-rich region. The dielectrics of $CeAIO_3$ which was synthesized and sintered in reduction atmosphere and $BaTiO_3$ system were affected by $CeO_2$ which was formed for the decomposition of $CeAIO_3$ heat treatment in air.

• Journal of the Society of Cosmetic Scientists of Korea
• /
• v.36 no.4
• /
• pp.259-263
• /
• 2010

We measured and compared the partition coefficients and absorption levels of preservative phenoxyethanol (PE), antimicrobial ethylhexylglycerin (EG) and UV-filters widely used in cosmetic products and more specifically evaluated the relative absorption level of PE depending on various packaging materials. The resulting partition coefficients of 11 UV filters in relation to PE and EG displayed EG with a relatively higher partition coefficients. The partition coefficients of Tinsorb M and Solaveil CT434 were also high. Among the UV-filter ingredients with EG absorption levels exceeding 40 % were Gransil PSQ, UV Titan M 160 and Micro $TiO_2$ MT 100 TV, whereas Gransil PSQ and Scadder showed PE absorption levels above 40 %. In addition, we confirmed that PE had displayed an absorption level of 7 ~ 8 % as a result of 1 month-long exposure to packaging material polyoxymethylene. This extensive research illustrates the possibility of producing the most potent preservative contents based on studying the relative compatibility between UV-filters and preservatives and selecting the adequate preservatives to be used. Furthermore, preservative level can also decline with passage of time depending on the type of packaging material used.

• Geophysics and Geophysical Exploration
• /
• v.9 no.2
• /
• pp.163-170
• /
• 2006

The shortage of proven hydrocarbon reserves has resulted in exploration progressing from the offshore into progressively deeper water of the continental shelf. Despite the success of seismic acquisition at ever greater depths, there are marine geological terrenes in which the interpretation of seismic data is difficult, such regions dominated by scattering or high reflectivity that is characteristic of carbonate reefs, volcanic cover and submarine permafrost. A marine controlled-source electromagnetic (CSEM) method has recently been applied to the oil and gas exploration thanks to its high-resistivity characteristics of the hydrocarbon. In particular, this method produces better results in terms of sensitivity under the deep water environment rather than the shallow water. Only in the last five years has the relevance of CSEM been recognized by oil companies who now use it to help them make exploration drilling decisions. Initial results are most promising and several contractors now offer magnetotelluric and CSEM services.

• Geophysics and Geophysical Exploration
• /
• v.12 no.1
• /
• pp.69-76
• /
• 2009

We report an implementation of the Ground Penetrating Radar (GPR) survey at a site that corresponds to a ruined castle. The objective of the survey was to characterise buried archaeological structures such as walls and tiles in Van Khan Tooril's Ruin, Mongolia, by 2D and 3D GPR techniques. GPR datasets were acquired in an area 10mby 9 m, with 10 cm line spacing. Two datasets were collected, using GPR with 500MHz and 800MHz frequency antennas. In this paper, we report the use of instantaneous parameters to detect archaeological targets such as tile, brick, and masonry by polarimetric GPR. Radar polarimetry is an advanced technology for extraction of target scattering characteristics. It gives us much more information about the size, shape, orientation, and surface condition of radar targets. We focused our interpretation on the strongest reflections. The image is enhanced by the use of instantaneous parameters. Judging by the shape and the width of the reflections, it is clear that moderate to high intensity response in instantaneous amplitude corresponds to brick and tiles. The instantaneous phase map gave information about the location of the targets, which appeared as discontinuities in the signal. In order to increase our ability to interpret these archaeological targets, we compared the GPR datasets acquired in two orthogonal survey directions. A good correlation is observed for the alignments of reflections when we compare the two datasets. However, more reflections appear in the north-south survey direction than in the west-east direction. This is due to the electric field orientation, which is in the horizontal plane for north-south survey directions and the horizontally polarised component of the backscattered high energy is recorded.