• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2009년도 Korea Superconductivity Society Meeting 2009
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• pp.37-37
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• 2009

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2000년도 제1회 학술대회 논문집
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• pp.133-134
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• 2000

Effect of nitrogen doping on field emission characteristics of patterned Diamond-like Carbon (DLC) films was studied. The patterned DLC films were fabricated by the method reported previously[1]. Nitrogen doping in DLC film was carried out by introducing $N_2$ gas into the vacuum chamber during deposition. Higher emission current density of $0.3{\sim}0.4$ $mA/cm^2$ was observed for the films with 6 at % N than the undoped films but the emission current density decreased with further increase of N contents. Some changes in CN bonding characteristics with increasing N contents were observed. The CN bonding characteristics which seem to affect the electron emission properties of these films were studied by Raman spectroscopy, x-ray photoemission spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The electrical resistivity and the optical band gap measurements showed consistence with the above analyses.

• 한국전기전자재료학회논문지
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• 제26권6호
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• pp.451-456
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• 2013

To study emission properties of white phosphorescent organic light emitting devices (PHOLEDs), we fabricated white PHOLEDs of ITO(150 nm) / NPB(30 nm) / TcTa(10 nm) / mCP(7.5 nm) / light-emitting layer(25 nm) / UGH3(5 nm) / Bphen(50 nm) / LiF(0.5 nm) / Al(200 nm) structure. The total thickness of light-emitting layer with co-doping and blue-doping/co-doping using a host-dopant system was 25 nm and the dopant of blue and red was FIrpic and $Bt_2Ir$(acac) in UGH3 as host, respectively. The OLED characteristics were changed with position and thickness of blue doping layer and co-doping layer as light-emitting layer and the best performance seemed in structure of blue-doping(5 nm)/co-doping(20 nm) layer. The white PHOLEDs showed the maximum current density of $34.5mA/cm^2$, maximum brightness of $5,731cd/m^2$, maximum current efficiency of 34.8 cd/A, maximum power efficiency of 21.6 lm/W, maximum quantum efficiency of 15.6%, and a Commission International de L'Eclairage (CIE) coordinate of (0.367, 0.436) at $1,000cd/m^2$.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.226-226
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• 2016

PHOLED devices which have the structure of ITO/HAT-CN(5nm)/NPB(50nm)/EML(30nm)/TPBi(10nm)/Alq3(20nm)/LiF(0.8nm)/Al(100nm) are fabricated to investigate the green emission profile in EML by using a gasket doping method. CBP and Ir(ppy)3 (2% wt) are co-deposited homogeneously as a background material of EML for green PHOLED, then a 5nm thickness of additionally doped layer by Ir(btp)2 (8% wt) is formed as a profiler of the green emission. The total thickness of the EML is maintained at 30nm while the distance of the profiler from the HTL/EML interface side (x) is changed in 5nm steps from 0nm to 25nm. As shown in Fig. 1, the green (513nm) peak from Ir(ppy)3 is not observed when Ir(btp)2 is also doped homogeneously because Ir(ppy)3 works as an gasket dopant of the Ir(btp)2 :CBP system. Therefore, in this experment, Ir(btp)2 can be used as a profiler of the green emission in CBP:Ir(ppy)3 system. The emission spectra from the PHOLED devices with different x are shown in Fig. 2. In this gasket doping system, stronger red peak means more energy transfer from green to red dopant or higher exciton density by green dopant. To find the green emission profile, the external quantum efficiency (EQE) at 3mA/cm2 for red peaks are calculated. More green light emission at near EML/HBL interface than that of HTL/EML is observed (insert of Fig. 2). This means that the higher exciton density at near EML/HBL interface in homogeneously doped CBP with Ir(ppy)3. As shown in Fig. 3, excitons can be quenched easily to HTL(NPB) because the T1 level of HTL(2.5eV) is relatively lower than that of EML(2.6eV). On the other hand, the T1 level of HBL(2.7eV) is higher than that of EML.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.623-623
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• 2013

그래핀(graphene)의 라만 스펙트럼은 전하밀도(charge density)와 기계적 변형(strain)에 민감하여 수많은 연구에 활용되고 있다. 그러나 실제 시료에서 관찰되는 두 물질량의 복잡한 변이를 정량 분석하기 위해서는 기계적 변형뿐만 아니라 전하밀도의 영향에 대한 신뢰도 높은 검정곡선이 필요하다. 본 연구에서는 기계적 박리법으로 만들어진 그래핀에서 나타나는 기계적 변형과 황산 수용액이 미치는 p-형 화학도핑(chemical doping)의 영향을 라만 분광법을 이용하여 연구하였다. 농도 변화에 따른 G와 2D 피크의 진동수 변화는 정전기적 방법을 이용하여 보고된 결과보다 높은 재현성을 보여 검정곡선으로 활용되기에 적합함을 알 수 있었다. 본 연구에서는 514 nm 이외에도 널리 활용되는 몇 가지 파장에서 "전하밀도-변형" 검정곡선을 제시하고자한다.

• 한국초전도ㆍ저온공학회논문지
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• 제2권1호
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• pp.1-6
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• 2000

The effects of partial substitution of fluorine on physical properties were studied in Ag-sheathes tapes of $Tl_{0.8}Pb_{0.2}Sr_{1.8}Ba_{0.2} Ca_{2.2}Cu_3O_yF_x (0{\leq}x{\leq}1)$ nominal compositions. The tapes were prepared using the powder-in-tube method incorporating an in-situ reaction method. $CuF_2$ was used as a source of F. It was found that F-doping in Tl-1223 system resulted in a decrease in formation temperatire of Tl-1223 phase. and thus significantly deteriorated their superconducting properties. Such disadvantages seem to originate by the fromation of non-beneficial phases such as SrF2 in the early stage of the powder preparation process.

• Journal of the Optical Society of Korea
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• 제19권2호
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• pp.199-205
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• 2015

We investigated the effects of the thickness and doping concentration in p- and n-type poly-Si layers on the performance of a solar cell based on a carbon fiber in order to improve the energy conversion efficiency of the cell. The short-circuit current density and open-circuit voltage of the carbon fiber-based solar cell were significantly influenced by the thickness and doping concentration in the p- and n-type poly-Si layers. The solar cell efficiency was successfully enhanced to ~10.5%.

• 한국세라믹학회지
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• 제37권1호
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• pp.33-43
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• 2000

Up-conversion of rare-earth element added glass is promising area for short wavelength laser source by utilizing high power semiconductor infra-red laser if the efficiency can be increased by proper method. In this study, relatively low phonon energy fluoride glasses were prepared by co-doping rare-earth elements to realize the high efficiency up-convertor. The physical, chemical, andoptical properties of co-doped fluoride glasses were measured. 10 combinations of 5 different rare-earth fluoride elements doped samples were prepared and their transition temperatures, chemical durability, density, hardness, refractive index, absorption, fluorescence, and fluorescence lifetime were measured. 480nm wavelengths blue up-conversion was found in the Yb3+/Tm3+ co-doped glass sample with 800nm laser source and the optimum composition for the most efficient blue up-conversion was found from the glass sample with 0.3 mol% TmF3 and 1 mol% YbF3.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.436-439
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• 2000

Change of dielectric loss of use in high relative permitivity capacitor BaTiO$_3$ ceramic depends on Mn doping have been investigated. The powders used in this study were commercial BaTiO$_3$, TiO$_2$and, MnCO$_3$. Sample was fabricated by conventional ceramic process. The quantity of Mn was changed gradually from 0.lmol% to 10mo1%. The sintering densities were reduced with increasing amount of MnCO$_3$. This result is because of increase of low density second phase BaMnO$_3$. When the samples were doped by over 0.2mol% of MnCO$_3$, average grain sizes were enlarge to several tens ${\mu}{\textrm}{m}$. The dielectric losses were reduced by Mn doping to lmol% but, increased from lmol% to 10mo1% gradually.

• 한국세라믹학회지
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• 제53권4호
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• pp.400-405
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• 2016

Ferric oxide (${\alpha}-Fe_2O_3$, hematite) is an n-type semiconductor; due to its narrow band gap ($E_g=2.1eV$), it is a highly attractive and desirable material for use in solar hydrogenation by water oxidation. However, the actual conversion efficiency achieved with $Fe_2O_3$ is considerably lower than the theoretical values because the considerably short diffusion length (2-4 nm) of holes in $Fe_2O_3$ induces excessive charge recombination and low absorption. This is a significant hurdle that must be overcome in order to obtain high solar-to-hydrogen conversion efficiency. In consideration of this, it is thought that elemental doping, which may make it possible to enhance the charge transfer at the interface, will have a marked effect in terms of improving the photoactivities of ${\alpha}-Fe_2O_3$ photoanodes. Herein, we report on the synthesis by pulsed electrodeposition of ${\alpha}-Fe_2O_3$-based anodes; we also report on the resulting photoelectrochemical (PEC) properties. We attempted Ti-doping to enhance the PEC properties of ${\alpha}-Fe_2O_3$ anodes. It is revealed that the photocurrent density of a bare ${\alpha}-Fe_2O_3$ anode can be dramatically changed by controlling the condition of the electrodeposition and the concentration of $TiCl_3$. Under optimum conditions, a modified ${\alpha}-Fe_2O_3$ anode exhibits a maximum photocurrent density of $0.4mA/cm^2$ at 1.23 V vs. reversible hydrogen electrode (RHE) under 1.5 G simulated sunlight illumination; this photocurrent density value is about 3 times greater than that of unmodified ${\alpha}-Fe_2O_3$ anodes.