• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.174-175
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• 2012

(In, Ga) N-based III-nitride semiconductor materials have been viewed as the most promising materials for the applications of blue and green light emitting devices such as light-emitting diodes (LEDs) and laser diodes. Although the InGaN alloy can have wide range of visible wavelength by changing the In composition, it is very hard to grow high quality epilayers of In-rich InGaN because of the thermal instability as well as the large lattice and thermal mismatches. In order to avoid phase separation of InGaN, various kinds of structures of InGaN have been studied. If high-quality In-rich InGaN/GaN multiple quantum well (MQW) structures are available, it is expected to achieve highly efficient phosphor-free white LEDs. In this study, we proposed a novel InGaN double hetero-structure grown on GaN nano-pyramids to generate broad-band red-color emission with high quantum efficiency. In this work, we systematically studied the optical properties of the InGaN pyramid structures. The nano-sized hexagonal pyramid structures were grown on the n-type GaN template by metalorganic chemical vapor deposition. SiNx mask was formed on the n-type GaN template with uniformly patterned circle pattern by laser holography. GaN pyramid structures were selectively grown on the opening area of mask by lateral over-growth followed by growth of InGaN/GaN double hetero-structure. The bird's eye-view scanning electron microscope (SEM) image shows that uniform hexagonal pyramid structures are well arranged. We showed that the pyramid structures have high crystal quality and the thickness of InGaN is varied along the height of pyramids via transmission electron microscope. Because the InGaN/GaN double hetero-structure was grown on the nano-pyramid GaN and on the planar GaN, simultaneously, we investigated the comparative study of the optical properties. Photoluminescence (PL) spectra of nano-pyramid sample and planar sample measured at 10 K. Although the growth condition were exactly the same for two samples, the nano-pyramid sample have much lower energy emission centered at 615 nm, compared to 438 nm for planar sample. Moreover, nano-pyramid sample shows broad-band spectrum, which is originate from structural properties of nano-pyramid structure. To study thermal activation energy and potential fluctuation, we measured PL with changing temperature from 10 K to 300 K. We also measured PL with changing the excitation power from 48 ${\mu}W$ to 48 mW. We can discriminate the origin of the broad-band spectra from the defect-related yellow luminescence of GaN by carrying out PL excitation experiments. The nano-pyramid structure provided highly efficient broad-band red-color emission for the future applications of phosphor-free white LEDs.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.222-222
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• 2012

Metal oxide gas sensors based on semiconductor type have attracted a great deal of attention due to their low cost, flexible production and simple usability. However, most works have been focused on n-type oxides, while the characteristics of p-type oxide gas sensors have been barely studied. An investigation on p-type oxides is very important in that the use of them makes possible the novel sensors such as p-n diode and tandem devices. Monoclinic cupric oxide (CuO) is p-type semiconductor with narrow band gap (~1.2 eV). This is composed of abundant, nontoxic elements on earth, and thus low-cost, environment-friendly devices can be realized. However, gas sensing properties of neat CuO were rarely explored and the mechanism still remains unclear. In this work, the neat CuO layers with highly ordered mesoporous structures were prepared by a template-free, one-pot solution-based method using novel ink solutions, formulated with copper formate tetrahydrate, hexylamine and ethyl cellulose. The shear viscosity of the formulated solutions was 5.79 Pa s at a shear rate of 1 s-1. The solutions were coated on SiO2/Si substrates by spin-coating (ink) and calcined for 1 h at the temperature of $200{\sim}600^{\circ}C$ in air. The surface and cross-sectional morphologies of the formed CuO layers were observed by a focused ion beam scanning electron microscopy (FIB-SEM) and porosity was determined by image analysis using simple computer-programming. XRD analysis showed phase evolutions of the layers, depending on the calcination temperature, and thermal decompositions of the neat precursor and the formulated ink were investigated by TGA and DSC. As a result, the formation of the porous structures was attributed to the vaporization of ethyl cellulose contained in the solutions. Mesoporous CuO, formed with the ink solution, consisted of grains and pores with nano-meter size. All of them were strongly dependent on calcination temperature. Sensing properties toward H2 and C2H5OH gases were examined as a function of operating temperature. High and fast responses toward H2 and C2H5OH gases were discussed in terms of crystallinity, nonstoichiometry and morphological factors such as porosity, grain size and surface-to-volume ratio. To our knowledge, the responses toward H2 and C2H5OH gases of these CuO gas sensors are comparable to previously reported values.

• 한국지리정보학회지
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• 제15권2호
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• pp.113-125
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• 2012

다목적실용위성 3A호에 탑재되는 고해상도의 중적외선 영상자료에 대한 지표면 식별 특성을 파악하기 위하여, 고해상도 중적외선 영상 획득이 가능한 AHS(Airborne Hyperspectral Scanner) 자료를 사용하여 중적외선 영상 자료의 지표면 온도 산출 가능성과 토지피복도 분류 정확도를 평가하였다. 먼저 AHS 열적외선 자료로 작성한 지표면 온도 영상과 AHS 중적외선 각 밴드의 화소값을 비교한 결과 주간과 야간 모두 밴드 68(중심파장 $4.64{\mu}m$)의 결정계수가 0.74이상으로 가장 높았다. 다음으로 AHS 중적외선 밴드를 이용하여 토지피복도를 작성한 결과 주간의 경우 지붕, 도로, 초지, 식생, 수역 등이 구분 가능했지만 야간의 경우 초지와 식생, 도로와 수역, 지붕과 도로 등 일부 클래스들이 서로 중복되어 나타났다. AHS 중적외선 밴드의 지표면 식별 능력의 향상 가능성을 파악하기 위하여 주간과 야간자료의 편차 영상을 구하여 토지피복도를 작성한 결과 Zone 1과 Zone 2의 소지역별 분류정확도가 각각 67.5%, 64.3%로서, 주간 또는 야간 중적외선 밴드로 작성된 토지피복도에 비해 10% 이상 향상된 것으로 나타났다. 결과적으로 고해상도 중적외선 밴드 영상자료는 지표면온도 산출시 지표 피복 특성을 고려한 알고리즘 개발이 요구되며, 지표면 식별 능력은 주간에 비해 야간이 낮으므로 주간과 야간의 편차 영상을 이용할 경우 지표면 식별 능력을 향상시킬 수 있을 것으로 판단된다.

• 한국지리정보학회지
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• 제20권3호
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• pp.90-103
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• 2017

본 연구는 도심온도 저감을 위한 녹지의 기능을 규명하기 위하여 여름철 고온 시간대에 도심녹지에서 나타나는 표면온도 특성을 분석하였다. 도시 내 고립된 녹지인 익산 소라산 자연마당을 대상으로 고해상도 UAV 영상을 활용하여 정밀한 표면온도 자료를 취득하였고, 피복유형, 식생유형, 수종유형, 수종별 녹지용적과 표면온도와의 관계를 분석하였다. 연구결과 피복유형 중 습지와 산림은 저온역, 포장지는 표면온도가 월등히 높은 고온역으로 확인되었다. 식생유형에서는 산림 내 침엽수보다 활엽수의 표면온도가 낮았고, 조경수식재지 내에선 활엽수보다 침엽수의 표면온도가 낮은 반대의 결과가 확인되었다. 장초지보다 단초지의 표면온도가 높아 초지의 용적에 따른 온도차이가 확인되었다. 산림수종유형별 표면온도는 침엽수인 소나무림보다 활엽수인 아까시나무림과 활엽수혼효림의 표면온도가 낮았고, 활엽수혼효림과 아까시나무림간의 미세한 표면온도 차이가 확인되었다. 산림수종유형별 녹지용적과 표면온도 분석결과 소나무림과 활엽수혼효림에서는 기존 연구 결과와 유사하게 녹지용적 증가에 따라 표면온도가 감소하는 음의상관관계가 확인되었다. 그러나 아까시나무림은 용적의 증가에 따라 미세하게 표면온도가 상승하는 약한 양의상관관계가 확인되어 수종에 따라서는 용적과 온도의 일관된 상관성에 예외가 있을 수 있음을 확인하였다. 향후 침엽수와 활엽수간 차이, 용적과 온도의 관계, 수종별 차이 등 녹지의 세부적 속성과 온도의 관계에 관하여 정밀한 공간자료를 활용한 다각적인 연구가 계속되어야 할 것으로 판단된다.

• 대한의용생체공학회:의공학회지
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• 제28권2호
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• pp.306-309
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• 2007

PXLM(Phosphor based x-ray light modulator) has a combined structure by phosphor, photoconductor, and liquid crystal and it can realize x-ray image of high resolution in clinical diagnosis area. In this study, we fabricated a photoconductor and investigated electrical and optical properties to confirm application possibility of radiator detector of PXLM structure. As photoconductor, amorphous selenium(a-Se), which is used most in DR(Digital radiography) of direct conversion method, was used and for formation of thin film, it was formed as $20{\mu}m-thick$ by using thermal vacuum evaporation system. For a produced a-Se film, through XRD(X-ray diffraction) and SEM(Scanning electron microscope), we investigated that amorphous structure was uniformly established and through optical measurement, for visible light of 40 $0\sim630nm$, it had absorption efficiency of 95 % and more. After fabricated a-Se film on the top of ITP substrate, hybrid structure was manufactured through forming $Gd_2O_3:Eu$ phosphor of $270{\mu}m-thick$ on the bottom of the substrate. As the result to confirm electrical property of the manufactured hybrid structure, in the case of appling $10V/{\mu}m$, leakage current of $2.5nA/cm^2$ and x-ray sensitivity of $7.31nC/cm^2/mR$ were investigated. Finally, we manufactured PXLM structure combined with hybrid structure and liquid crystal cell of TN(Twisted nematic) mode and then, investigated T-V(Transmission vs. voltage) curve of external light source for induced x-ray energy. PXLM structure showed a similar optical response with T-V curve that common TN mode liquid crystal cell showed according to electric field increase and in appling $50\sim100V$, it showed linear transmission efficiency of $12\sim18%$. This result suggested an application possibility of PXLM structure as radiation detector.

• Restorative Dentistry and Endodontics
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• 제21권1호
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• pp.321-338
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• 1996

The purpose of this study was to evaluate the effect of moistening and air-drying of acid conditioned dentin and enamel on the marginal microleakage. In this study, Class V cavity were prepared on both buccal and lingual surface of sixty extracted human premolars with cementum margin. These specimens were randomly devided into three groups and three dentin adhesives(Scotchbond Multi-Purpose, All bond 2, Prisma Universal Bond 3) were applied to each group. The specimens in each group were subdevided into four groups (Wet/primed, Dry/primed, Wet/not primed, Dry/not primed) and the etched dentin and enamel surface were treated these four surface treatments prior to the placement of a bonding agent or adhesive. Wet/primed group was simply blot-dried with a damp facial tissue before primer placement ; Dry/primed group was air dried for 30 seconds before the placement of a primer ; Wet/not primed group and Dry/not primed group were not primed after blot dried and air dried for 30 seconds each group. The bonding agent and composite resin were applied for each group. All specimens were exposed to 500 cycle of thermal stress. Specimens were placed in a silver nitrate solution and then sectioned buccolingually through the center of the restoration. The dye penetrations of the specimens were observed with a stereo microscope. The statistical test were applied to the results using a one way analysis variance (ANOVA) and Duncan's multiple range test. The aspects of silver ion penetration into the resin/dentin interface were examined under scanning electron microscopy. The results were as follows. 1. In all groups, the enamel margin showed significantly lower leakage value than the cementum margin (p<0.05). 2. Regardless of various surface treatment and dentin adhesives, there was no significant difference at the enamel margins (p>0.05). 3. At the dentin margins, the leakage values of Dry/not primed group showed significantly higher than that of the other groups (p<0.05). The leakage values of Wet/primed group showed significantly lower than that of the other groups, but, there was no significant difference between Wet group and Dry group. 4. There was no significantly difference between the dentin adhesives regarding the surface treatments in all groups(p>0.05). 5. On the backscatterd scanning electron microscopy observation, the penetration of the silver ion occured at the bonding resin/dentin interface. In the Wet/primed group, resindentin hybrid zone and resin penetration into the dentin was observed. The resin tags were compactively formed to a thickness of $3\sim4{\mu}m$ at the upper part of dentinal tubules. In the Dry/primed group, the thickness of the hybrid zone and the diameter, depth of the resin tags diminished. In the Non-primed groups, the hybrid zone was not identified and few resin tag was observed. There was the gap formation in the resin/dentin interface.

• 전기학회논문지
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• 제60권6호
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• pp.1274-1279
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• 2011

The purpose of this paper is to present the manufacturing defect and damage pattern of a 3 phase 22.9/3.3kV oil immersed transformer, as well as to present an objective basis for the prevention of a similar accident and to secure data for the settlement of PL related disputes. It was found that in order to prevent the occurrence of accidents to transformers, insulating oil analysis, thermal image measurement, and corona discharge diagnosis, etc., were performed by establishing relevant regulation. The result of analysis performed on the external appearance of a transformer to which an accident occurred, the internal insulation resistance and protection system, etc., showed that most of the analysis items were judged to be acceptable. However, it was found that the insulation characteristics between the primary winding and the enclosure, those between the ground and the secondary winding, and those between the primary and secondary windings were inappropriate due to an insulating oil leak caused by damage to the pressure relief valve. From the analysis of the acidity values measured over the past 5 years, it is thought that an increase in carbon dioxide (CO2) caused an increase in the temperature inside the transformer and the increase in the ethylene gas increased the possibility of ignition. Even though 17 years have passed since the transformer was installed, it was found that the system's design, manufacture, maintenance and management have been performed well and the insulating paper was in good condition, and that there was no trace of public access or vandalism. However, in the case of transformers to which accidents have occurred, a melted area between the upper and the intermediate bobbins of the W-phase secondary winding as well as between its intermediate and lower bobbins. It can be seen that a V-pattern was formed at the carbonized area of the transformer and that the depth of the carbonization is deeper at the upper side than the lower side. In addition, it was found that physical bending and deformation occurred inside the secondary winding due to non-uniform pressure while performing transformer winding work. Therefore, since it is obvious that the accident occurred due to a manufacturing defect (winding work defect), it is thought that the manufacturer of the transformer is responsible for the accident and that it is lawful for the manufacture to investigate and prove the concrete cause of the accident according to the Product Liability Law (PLL).

• Journal of Electrical Engineering and Technology
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• 제6권4호
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• pp.543-550
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• 2011

Conductive SiC-$ZrB_2$ composites were produced by subjecting a 40:60 (vol%) mixture of zirconium diboride (ZrB2) powder and ${\beta}$-silicon carbide (SiC) matrix to spark plasma sintering (SPS). Sintering was carried out for 5 min in an argon atmosphere at a uniaxial pressure and temperature of 50 MPa and $1500^{\circ}C$, respectively. The composite sintered at a heating speed of $25^{\circ}C$/min and an on/off pulse sequence of 12:2 was denoted as SZ12L. Composites SZ12H, SZ48H, and SZ10H were obtained by sintering at a heating speed of $100^{\circ}C$/min and at on/off pulse sequences of 12:2, 48:8, and 10:9, respectively. The physical, electrical, and mechanical properties of the SiC-$ZrB_2$ composites were examined and thermal image analysis of the composites was performed. The apparent porosities of SZ12L, SZ12H, SZ48H, and SZ10H were 13.35%, 0.60%, 12.28%, and 9.75%, respectively. At room temperature, SZ12L had the lowest flexural strength (286.90 MPa), whereas SZ12H had the highest flexural strength (1011.34 MPa). Between room temperature and $500^{\circ}C$, the SiC-$ZrB_2$ composites had a positive temperature coefficient of resistance (PTCR) and linear V-I characteristics. SZ12H had the lowest PTCR and highest electrical resistivity among all the composites. The optimum SPS conditions for the production of energy-friendly SiC-$ZrB_2$ composites are as follows: 1) an argon atmosphere, 2) a constant pressure of 50 MPa throughout the sintering process, 3) an on/off pulse sequence of 12:2 (pulse duration: 2.78 ms), and 4) a final sintering temperature of $1500^{\circ}C$ at a speed of $100^{\circ}C$/min and sintering for 5 min at $1500^{\circ}C$.

• 한국산학기술학회논문지
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• 제13권9호
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• pp.3815-3821
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• 2012

LCD 프레임은 중 대형 TFT-LCD BLU의 기본형상을 유지시켜주는 중요한 부분이다. 중 대형 LCD 프레임을 효율적으로 생산하기 위해 1 캐비티에서 2 캐비티 사출 공정으로의 개선이 필요하다. 2 캐비티 금형 구조는 콤팩트하게 되었고 핫 런너 존이 증가되었기 때문에 사출온도를 조절하기 어렵게 되었다. 본 연구에서는 2 캐비티 사출성형공정으로 생산된 프레임에 대한 품질을 평가하기 위해서 유한요소해석 프로그램을 사용하여 사출해석을 수행하였다. 1 캐비티와 2 캐비티 공정에서 계산된 사출압력과 최대 변형량은 각각 41.13 MPa과 1.62 mm, 40.49 MPa과 1.66 mm이다. 1 캐비티 프레임의 측정된 최대 굽힘 하중, 표면거칠기가 140 N, 0.13 ${\mu}m$, 인데 비하여 2 캐비티 중 좌, 우 프레임의 측정값들은 209 N, 0.08 ${\mu}m$와 193 N, 0.10 ${\mu}m$이다. 열화상은 2 캐비티 금형 중 좌 우 금형 온도의 최대 표준 편차값은 $1.23^{\circ}C$임을 나타내고 있다. 시뮬레이션과 측정은 전체적으로 2 캐비티 사출공정의 프레임 품질이 1 캐비티 품질보다 나쁘지 않다는 것을 보여주고 있다. 그러나 2 캐비티 공정에서 프레임의 최대 굽힘 하중값은 1 캐비티 공정의 하중값보다 매우 증가되었다.

• 자원환경지질
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• 제45권4호
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• pp.397-406
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• 2012

2010년 2차 울릉분지 가스 하이드레이트 시추 (UBGH2)를 통하여 총 10개 정점에서 가스 하이드레이트 함유 퇴적물 코아를 채취하였다. 이 연구에서는 열화상 분석과 입도분석 결과에 따라 퇴적물 입도분포, 온도 이상(${\Delta}T$), 가스 하이드레이트 포화도, 가스 하이드레이트 산출형태간의 상관관계를 연구하였다. 가스 하이드레이트는 유형 I(니질층의 단열을 충진하는 형태), 유형 II(니질층의 산재하는 형태), 그리고 유형 III(사질층의 공극을 충진하는 형태)로 분류하였다. 입도분석 결과, 유형 I과 II는 가스 하이드레이트 함유 및 미함유 구간 모두 입도가 유사한 니질층으로 이루어진 반면, 유형 III는 입도가 뚜렷이 구별되는 사질층과 니질층으로 이루어져 있다. 유형 III에서는 모래 함량이 증가할 수록 가스 하이드레이트 포화도가 증가함을 확인하였다. 열화상에서 분석된 ${\Delta}T$는 가스 하이드레이트 산출형태와 상관없이 가스 하이드레이트 포화도와 비례하는 경향을 보인다. 시추지점의 암상과 탄성파 단면의 특징에서 보면, 탄성파 단면에서 침니 구조가 나타나는 지점은 유형 I이, 사질층이 거의 없는 분지사면에서는 유형 II가, 저탁류 사질층이 자주 협재하는 지점에서는 유형 III가 우세하게 나타난다. 이와 같은 특징으로 보아 가스 하이드레이트 산출형태는 가스 하이드레이트 함유 지층의 지질학적 특징과 관련 있으며, 특히 퇴적물의 입도분포에 큰 영향을 받음을 보여준다.