• Transactions on Electrical and Electronic Materials
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• 제12권5호
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• pp.193-196
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• 2011

Lead zirconate titanate (PZT)/ bismuth ferrite (BFO) multilayer thin films have been fabricated by the spin-coating method on Pt(200 nm)/Ti(10 nm)/$SiO_2$(100 nm)/p-Si(100) substrates using $BiFeO_3$ and $Pb(Zr_{0.52}Ti_{0.48})O_3$ metal alkoxide solutions. The PZT/BFO multilayer thin films show a uniform and void-free grain structure, and the grain size is smaller than that of PZT single films. The reason for this is assumed to be that the lower BFO layers play an important role as a nucleation site or seed layer for the formation of homogeneous and uniform upper PZT layers. The dielectric constant and dielectric losses decreased with increasing number of coatings, and the six-layer PZT/BFO thin film has good properties of 162 (dielectric constant) and 0.017 (dielectric losses) at 1 kHz. The remnant polarization and coercive field of three-layer PZT/BFO thin films were 13.86 ${\mu}C/cm^2$ and 37 kV/cm respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.533-538
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• 2001

The ZnSe sample grown by chemical bath deposition (CBD) method were annealed in Ar gas at 450$^{\circ}C$ Using extrapolation method of X-ray diffraction pattern, it was found to have zinc blend structure whose lattice parameter a$\_$o/ was 5.6687 ${\AA}$. From Hall effect, the mobility was likely to be decreased by impurity scattering at temperature range from 10 K to 150 K and by lattice scattering at temperature range from 150 K to 29 3K. The band gap given by the transmission edge changed from 2.7005 eV at 293 K to 2.8739 eV at 10 K. Comparing photocurrent peak position with transmission edge, we could find that photocurrent peaks due to excition electrons from valence band, $\Gamma$$\_$8/ and $\Gamma$$\_$7/ to conduction band $\Gamma$$\_$6/ were observed at photocurrent spectrum. From the photocurrent spectra by illumination of polarized light on the ZnSe thin film, we have found that values of spin orbit coupling splitting Δso is 0.0981 eV. From the PL spectra at 10 K, the peaks corresponding to free bound excitons and D-A pair and a broad emission band due to SA is identified. The binding energy of the free excitons are determined to be 0.0612 eV and the dissipation energy of the donor -bound exciton and acceptor-bound exciton to be 0.0172 eV, 0.0310 eV, respectively.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.81-81
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• 2011

Sol-gel spin-coating법을 이용하여 ZnO 박막을 증착하였다. Sol 전구체 용액을 Si(100) 기판에 증착하고 전열처리(pre-heat treatment)하여 gel 상태의 ZnO 박막을 형성시킨 후 다른 속도로 냉각시켰다. Atomic force microscopy (AFM), X-ray diffraction (XRD), Raman, photoluminescence (PL)을 이용하여 냉각속도가 ZnO 박막의 구조적 및 광학적 특성에 미치는 영향을 분석하였다. 느린 속도($5^{\circ}C$/min)로 냉각시킨 ZnO 박막은 나노섬유질구조(nano-fibrous structure)를 나타내었고, 상온에서 바로 냉각시킨 ZnO 박막은 매우 매끄러운 표면(mirror-like surface)을 나타내었다. ZnO (100), ZnO (002), ZnO (101) 방향을 나타내는 회절피크가 관찰되었고, 냉각속도에 따른 ZnO 박막의 배향성을 알아보기 위하여 texture coefficient (TC)를 계산해 보았다. 상온에서 바로 냉각시킨 ZnO 박막(TC(002)=76.3%)이 느린 속도로 냉각시킨 박막(TC(002)=45.2%)보다 (002) 방향으로의 배향성이 우세하게 나타났으며, 잔류응력도 작았다. 뿐만 아니라 PL을 이용한 광학적 특성평가에서도 상온에서 바로 냉각시킨 ZnO 박막에서 더 강한 강도와 좁은 반치폭(full-width at halt-maximum)을 갖는 near-band-edge emission (NBE) 피크가 관찰되었다. 후열처리에 따른 구조적 및 광학적 특성 변화 또한 연구하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.377-377
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• 2011

Organic solar cells (OSCs) with low cost have been studied to apply on flexible substrate by solution process in low temperature [1]. In previous researches, conventional organic solar cell was composed of metal oxide anode, buffer layer such as PEDOT:PSS, photoactive layer, and metal cathode with low work function. In this structure, indium tin oxide (ITO) and Al was generally used as metal oxide anode and metal cathode, respectively. However, they showed poor reliability, because PEDOT:PSS was sensitive to moisture and air, and the low work function metal cathode was easily oxidized to air, resulting in decreased efficiency in half per day [2]. Inverted organic solar cells (IOSCs) using high work function metal and buffer layer replacing the PEDOT:PSS have focused as a solution in conventional organic solar cell. On the contrary to conventional OSCs, ZnO and TiO2 are required to be used as a buffer layer, since the ITO in IOSC is used as cathode to collect electrons and block holes. The ZnO is expected to be excellent electron transport layer (ETL), because the ZnO has the advantages of high electron mobility, stability in air, easy fabrication at room temperature, and UV absorption. In this study, the IOSCs based on poly [N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT) : [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) were fabricated with the ZnO electron-transport layer and MoO3 hole-transport layer. Thickness of the ZnO for electron-transport layer was controlled by rotation speed in spin-coating. The PCDTBT and PC70BM were mixed with a ratio of 1:2 as an active layer. As a result, the highest efficiency of 2.53% was achieved.

• 전기학회논문지
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• 제63권5호
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• pp.676-682
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• 2014

In this paper, precipitation echo(PRE) and non-precipitaion echo(N-PRE)(including ground echo and clear echo) through weather radar data are identified with the aid of neuro-fuzzy algorithm. The accuracy of the radar information is lowered because meteorological radar data is mixed with the PRE and N-PRE. So this problem is resolved by using RBFNN and judgement module. Structure expression of weather radar data are analyzed in order to classify PRE and N-PRE. Input variables such as Standard deviation of reflectivity(SDZ), Vertical gradient of reflectivity(VGZ), Spin change(SPN), Frequency(FR), cumulation reflectivity during 1 hour(1hDZ), and cumulation reflectivity during 2 hour(2hDZ) are made by using weather radar data and then each characteristic of input variable is analyzed. Input data is built up from the selected input variables among these input variables, which have a critical effect on the classification between PRE and N-PRE. Echo judgment module is developed to do echo classification between PRE and N-PRE by using testing dataset. Polynomial-based radial basis function neural networks(RBFNNs) are used as neuro-fuzzy algorithm, and the proposed neuro-fuzzy echo pattern classifier is designed by combining RBFNN with echo judgement module. Finally, the results of the proposed classifier are compared with both CZ and DZ, as well as QC data, and analyzed from the view point of output performance.

• 한국재료학회지
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• 제12권7호
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• pp.587-590
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• 2002

A silver indium sulfide ($AgInS_2$) epilayer was grown by the hot wall epitaxy method, which has not been reported in the literature. The grown $AgInS_2$ epilayer has found to be a chalcopyrite structure and evaluated to be high quality crystal. From the photocurrent measurement in the temperature range from 30 K to 300 K, the two peaks of A and B were only observed, whereas the three peaks of A, B, and C were seen in the PC spectrum of 10 K. These peaks are ascribed to the band-to-band transition. The valence band splitting of $AgInS_2$ was investigated by means of the photocurrent measurement. The crystal field splitting, $\Delta_{cr}$ , and the spin orbit splitting, $\Delta_{so}$ , have been obtained to be 0.150 eV and 0.009 eV at 10 K, respectively. And, the energy band gap at room temperature has been determined to be 1.868 eV. Also, the temperature dependence of the energy band gap, $E_{g}$(T), was determined.d.

• 한국재료학회지
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• 제29권2호
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• pp.87-91
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• 2019

We report on stretchable electrochromic films of poly(3-hexylthiophene) (P3HT) fabricated on silver nanowire (AgNW) electrodes. AgNWs electrodes are prepared on polydimethylsiloxane (PDMS) substrates using a spray coater for stretchable electrochromic applications. On top of the AgNW electrode, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is introduced to ensure a stable resistance over the electrode under broad strain range by effectively suppressing the protrusion of AgNWs from PDMS. This bilayer electrode exhibits a high performance as a stretchable substrate in terms of sheet resistance increment by a factor of 1.6, tensile strain change to 40 %, and stretching cycles to 100 cycles. Furthermore, P3HT film spin-coated on the bilayer electrode shows a stable electrochromic coloration within an applied voltage, with a color contrast of 28.6 %, response time of 4-5 sec, and a coloration efficiency of $91.0cm^2/C$. These findings indicate that AgNWs/PEDOT:PSS bilayer on PDMS substrate electrode is highly suitable for transparent and stretchable electrochromic devices.

• 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.

• 한국자기학회지
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• 제13권3호
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• pp.97-102
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• 2003

고집적 TMR소자의 프리층에 적용될 수 있는 인위적페리층(synthetic ferrimagnetic layer : SyFL)인 NiFe/Ru/NiFe박막을 만들고, 결정에너지, 지만에너지, 교환에너지를 고려한 총에너지로부터 평형상태에서의 관계식에서 Ru두께에 따른 보자력( $H_{c}$)변화와, 스핀플로핑자계( $H_{sf}$ ), 포화자계( $H_{s}$)에 대해 알아보았다. Ta(50$\AA$)/NiFe(50$\AA$)Ru(4~20$\AA$)/NiFe(30$\AA$)/Ta(50$\AA$) 구조를 ICP (inductively coupled plasma)형 헬리콘스퍼터로 제작하고, 주어진 Ru두께에서의 시편을 SQUID로 $\pm$15kOe까지 분석하여 M-H루프를 측정하였다. 에너지를 고려한 평형상태 예측은 실험과 잘 일치하였으며, 이방성에너지 $K_{u}$= 1000erg/㎤, 교환에너지 $J_{ex}$= 0.7erg/$\textrm{cm}^2$까지 조절이 가능하였다. 상온에서 $H_{c}$를 10 Oe이하로 만드는 것이 가능하였고, 공업적으로 의미있는 $H_{s}$, $H_{sf}$ 의 범위를 Ru두께 4~10 $\AA$에서 선택이 가능하였다. 또한 50 $\AA$이하의 얇은 NiFe박막에서 자기탄성계수는 0이 아닌 (+)로 작용할 수 있다는 점과 NiFe/Ru 계면 조도를 간접적으로 예상하는 것이 가능하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.175-178
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• 2004

The stochiometric mixture of evaporating materials for the $ZnIn_2S_4$ single crystal thin film was prepared from horizontal furnace. To obtain the $ZnIn_2S_4$ single crystal thin film, $ZnIn_2S_4$ mixed crystal was deposited on throughly etched semi-insulating GaAs(100) in the Hot Wall Epitaxy(HWE) system. The source and substrate temperature were $610^{\circ}C$ and $450^{\circ}C$, respectively and the growth rate of the $ZnIn_2S_4$ sing1e crystal thin film was about $0.5\;{\mu}m/hr$. The crystalline structure of $ZnIn_2S_4$ single crystal thin film was investigated by photoluminescence and double crystal X-ray diffraction(DCXD) measurement. The carrier density and mobility of $ZnIn_2S_4$ single crystal thin film measured from Hall effect by van der Pauw method are $8.51{\times}10^{17}\;cm^{-3}$, $291\;cm^2/V{\cdot}s$ at $293_{\circ}\;K$, respectively. From the photocurrent spectrum by illumination of perpendicular light on the c - axis of the $ZnIn_2S_4$ single crystal thin film, we have found that the values of spin orbit splitting ${\Delta}S_O$ and the crystal field splitting ${\Delta}Cr$ were 0.0148 eV and 0.1678 eV at $10_{\circ}\; K$, respectively. From the photoluminescence measurement of $ZnIn_2S_4$ single crystal thin film, we observed free excition $(E_X)$ typically observed only in high quality crystal and neutral donor bound exciton $(D^{o},X)$ having very strong peak intensity The full width at half maximum and binding energy of neutral donor bound excition were 9 meV and 26 meV, respectively, The activation energy of impurity measured by Haynes rule was 130 meV.