• Journal of Soil and Groundwater Environment
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• v.29 no.4
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• pp.12-20
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• 2024

Diffusive gradients in thin films (DGT) are passive sampling devices used to determine the time-weighted average concentrations (TWAC) of contaminants. To ensure accurate performance in groundwater, it is crucial to identify environmental characteristics and maintain optimal operational conditions. This study examined the deployment time required to reach effective capacity, the thickness of the diffusive boundary layer (DBL) under stagnant water conditions, and biofilm formation on the DGT surface using groundwater samples. When using DGT with Chelex gel (A=3.14 cm²), the effective capacity was 0.7 ㎍ for Cd and 250 ㎍ for Zn, with a deployment time of 24 h. Lower Cd accumulation was due to the competition effect of coexisting ions. The DBL thickness under stagnant conditions was 0.074 cm, 93% of the diffusion gel's thickness (0.08 cm). Neglecting DBL thickness in TWAC calculations led to a 79% decrease in the determined concentration. No biofouling was observed during the 28-d DGT deployment in groundwater. In conclusion, it is essential to consider the appropriate deployment time, DBL thickness, and biofilm formation to ensure accurate DGT performance in determining contaminant levels in groundwater.

• Journal of Information Display
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• v.9 no.3
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• pp.16-22
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• 2008

A novel class of conjugated dendritic molecules bearing N-hexyl-substituted carbazoles as peripheral groups and various conjugative aromatic cores was synthesized through Heck coupling and the Horner-Emmons reaction. A multilayered structure of ITO/PEDOT:PSS (30 nm)/emitting material (50 nm)/BCP (10 nm)/$Alq_3$ (10 nm)/LiF (1 nm)/Al (100 nm) was employed to evaluate the synthesized dendritic materials. The electroluminescence spectrum of the multilayered device made of 3Cz predominantly exhibited blue emissions. Similar emissions were observed in the PL spectra of it's the device's thin film. The multilayered devices made of 3Cz, 3BCz, and 4BCz showed luminance values of 6,250 cd $m^{-2}$ at 24 V, 3,000 cd $m^{-2}$ at 25 V, and 1,970 cd $m^{-2}$ at 36 V, respectively. The smallest molecule, 3Cz, which bore three carbazole peripheral groups, exhibited a blue-like emission with CIE 1931 chromaticity coordinates of x = 0.17 and y = 0.21.

• Journal of Sensor Science and Technology
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• v.2 no.1
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• pp.81-86
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• 1993

Polycrystalline CdSe thin films were grown on ceramic substrate using a chemical bath deposition (CBD) method. They were annealed at various temperature and X-ray diffraction patterns were measured by X-ray diffractometer in order to study CdSe polycrystal structure. Using extrapolation method of X-ray diffraction patterns for the CdSe samples annealed in $N_{2}$ gas at $450^{\circ}C$ it was found hexagonal structure whose lattice parameters $a_{o}$ and $c_{o}$ were $4.302{\AA}$ and $7.014{\AA}$, respectively. Its grain size was about $0.3{\mu}m$. Hall effect on this sample was measured by Van der Pauw method and studied on carrier density and mobility depending on temperature. From Hall data, the mobility was likely to be decreased by piezo electric scattering at temperature range of 33 K and 200 K, and by polar optical scattering at temperature range of 200 K and 293 K. We measured also spectral response, sensitivity (${\gamma}$), maximum allowable power dissipation and response time on these samples.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.14 no.2
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• pp.122-127
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• 2021

This paper produces CdS thin film using ITO glass as substrates. The MDS (Multiplex Deposition Sputter System) was used to produce devices by changing RF power and deposition time. The manufactured specimen was analyzed for its optical properties. The purpose of this paper is to find the fabrication conditions that can be applied to the photo-absorbing layer of solar cells. When RF power was 50W and deposition time was 10 minutes, the thickness was measured at 64Å. At 100W, the thickness was measured at 406Å and at 150 W, the thickness was measured at 889Å. Thin films were found to increase in thickness as RF power increased. As a result of the light transmittance measurement, 550-850nm was observed to have a transmittance of approximately 70% or more when the RF power was 50W, 100W, and 150W. Increasing RF power increased thickness and increased particle size, resulting in increased thin film density, resulting in reduced light transmittance. When RF power was 100W and deposition time was 15 minutes, the band gap was calculated at 3.998eV. When deposition time is 20 minutes, it is 3.987eV, 150W is 3.965eV at 15 minutes, and 3.831eV at 20 minutes. It was measured that the band gap decreased as the RF power increased. At XRD analysis, diffraction peaks at 2Θ=26.44 could be observed regardless of changes in RF power and deposition time. The FWHM was shown to decrease with increasing deposition time. And it was measured that the particle size increased as RF power was constant and deposition time was increased.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.1
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• pp.36-43
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• 2000

The sulfur pressure and TRA(rapid thermal annealing) conditions of the fabricated SrS:CuCl TFEL devices were optimized to improve blue color luminance. The thickness of the phosphor layer of SrS:CuCl TFEL devices fabricated by electron beam deposition system was 6000 ~ 8000 ${\AA}$. The fabricated TFEL devices were annealed at 800 $^{\circ}C$ for 3 min. It was shown that the crystallinity of SrS:CuCl phosphor was improved by an increase in RTA temperature and RTA time. Blue color was emitted from the TFEL device with emission peak wavelength of 468 nm and 500 nm. The CIE color coordinates were x = 0.21, y = 0.33. The luminance($L_{40}$) of TFEL device strongly depended on the sulfur pressure of deposition chamber and increased from 262 cd/$m^2$ to 728 cd/m2 as the sulfur pressure increased from $8{\times}10^{-6}$ torr to $2{\times}10^{-5}$ torr.

• Journal of Sensor Science and Technology
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• v.2 no.1
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• pp.3-10
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• 1993

Polycrystalline CdS thin films were grown on ceramic substrate using a chemical bath deposition method. They were annealed at various temperature and X-ray diffraction patterns were measured by X-ray diffractometer in order to study CdS polycrystal structure. Using extrapolation method of X-ray diffraction patterns for the CdS samples annealed in $N_{2}$ gas at $550^{\circ}C$ it was found hexagonal structure whose lattice constants $a_{o}$ and $c_{o}$ were $4.1364{\AA}$ and $6.7129{\AA}$, respectively. Its grain size was about $0.35{\mu}m$. Hall effect on this sample was measured by Van der Pauw method and studied on carrier density and mobility defending on temperature. From Hall data, the mobility was likely to be decreased by piezo electric scattering at temperature range of 33K and 150k and by polar optical scattering at temperature range of 150K and 293K. We measured also spectral response, sensitivity (${\gamma}$), maximum allowable power dissipation and response time on these samples.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.10
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• pp.625-630
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• 2017

ZnS was chemically deposited as a buffer layer alternative to CdS, for use as a Cd-free buffer layer in $Cu(In_{1-x}Ga_x)Se_2$ (CIGS) solar cells. The deposition of a thin film of ZnS was carried out by chemical bath deposition, following which the structural and optical properties of the ZnS layer were studied. For the experiments, zinc sulfate hepta-hydrate ($ZnSO_4{\cdot}7H_2O$), thiourea ($SC(NH_2)_2$), and ammonia ($NH_4OH$) were used as the reacting agents. The mole concentrations of $ZnSO_4$ and $SC(NH_2)_2$ were fixed at 0.03 M and 0.8 M, respectively, while that of ammonia, which acts as a complexing agent, was varied from 0.3 M to 3.5 M. By varying the mole concentration of ammonia, optimal values for parameters like optical transmission, deposition rate, and surface morphology were determined. For the fixed mole concentrations of $0.03M\;ZnSO_4{\cdot}7H_2O$ and $0.8M\;SC(NH_2)_2$, it was established that 3.0 M of ammonia could provide optimal values of the deposition rate (5.5 nm/min), average optical transmittance (81%), and energy band gap (3.81 eV), rendering the chemically deposited ZnS suitable for use as a Cd-free buffer layer in CIGS solar cells.

• Korean Journal of Materials Research
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• v.31 no.11
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• pp.619-625
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• 2021

Cu₂ZnSn(S,Se)₄ (CZTSSe) based thin-film solar cells have attracted growing attention because of their earth-abundant and non-toxic elements. However, because of their large open-circuit voltage (V_oc)-deficit, CZTSSe solar cells exhibit poor device performance compared to well-established Cu(In,Ga)(S,Se)₂ (CIGS) and CdTe based solar cells. One of the main causes of this large V_oc-deficit is poor absorber properties for example, high band tailing properties, defects, secondary phases, carrier recombination, etc. In particular, the fabrication of absorbers using physical methods results in poor surface morphology, such as pin-holes and voids. To overcome this problem and form large and homogeneous CZTSSe grains, CZTSSe based absorber layers are prepared by a sputtering technique with different RTA conditions. The temperature is varied from 510 ℃ to 540 ℃ during the rapid thermal annealing (RTA) process. Further, CZTSSe thin films are examined with X-ray diffraction, X-ray fluorescence, Raman spectroscopy, IPCE, Energy dispersive spectroscopy and Scanning electron microscopy techniques. The present work shows that Cu-based secondary phase formation can be suppressed in the CZTSSe absorber layer at an optimum RTA condition.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.164-164
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• 2003

UV 발광소자 재료로서 유망한 ZnO film을 ALE법으로 증착하고 photoluminescence특성을 조사하였다. Zn소스로서 DEZn(Diethylzinc)를, 산소 소스로서 DI water를 사용하였고 $N_2$ gas로서 챔버내에 주입된 소스물질을 purge하였다. ALE 공정온도 범위인 17$0^{\circ}C$와 CVD 반응온도 범위인 40$0^{\circ}C$로 ZnO 박막을 증착하고 이 시편을 산소 분위기에서 600-100$0^{\circ}C$의 온도로 1시간 동안 열처리하였다. 그리고 He-Cd laser를 사용하여 photoluminescence를 측정하였다. 17$0^{\circ}C$와 40$0^{\circ}C$ 에서 증착된 시편 모두 as-grown 상태에서는 거의 발광특성을 나타내지 못하였으나 후열처리를 거치면서 발광특성을 나타내었고 열처리 온도가 높을수록 발광강도가 증가하였다. 40$0^{\circ}C$에서의 증착된 시편의 경우는CVD반응이 발생하여 Zn-Zn결합이 많이 생성되어 열처리 온도가 증가하여도 발광강도가 약하였고 가시광 영역의 발광 또한 크게 증가하였으며 17$0^{\circ}C$에서 증착된 시편의 경우는 열처리 온도가 증가할수록 UV영역의 발광강도만이 크게 증가하였으며 가시광 영역의 발광은 거의 증가하지 않았다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.124-125
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• 2007

Single crystal $CdGa_2Se_4$ layers were grown on a thoroughly etched semi-insulating GaAs(100) substrate at $420^{\circ}C$ with the hot wall epitaxy (HWE) system by evaporating the polycrystal source of $CdGa_2Se_4$ at $630^{\circ}C$ prepared from horizontal electric furnace. The photocurrent and the absorption spectra of $CdGa_2Se_4$/SI(Semi-Insulated) GaAs(100) are measured ranging from 293K to 10K. The temperature dependence of the energy band gap of the $CdGa_2Se_4$, obtained from the absorption spectra was well described by the Varshni's relation, $E_g$(T) = 2.6400 eV - $(7.721{\times}10^{-4}\;eV/K)T^2$/(T + 399 K). Using the photocurrent spectra and the Hopfield quasicubic model, the crystal field energy$({\Delta}cr)$ and the spin-orbit splitting energy$({\Delta}so)$ for the valence band of the $CdGa_2Se_4$ have been estimated to be 106.5 meV and 418.9 meV at 10 K, respectively. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1^-},\;B_{1^-},\;and\;C_{11^-}$ exciton peaks.