• Applied Chemistry for Engineering
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• v.28 no.5
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• pp.587-592
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• 2017

Uniform and optimum sized silver nanoplates were synthesized through the liquid phase reduction method by using silver nitrate solution as a starting chemical, dimethylformmide (DMF) as a reducing solvent, and polyvinylpyrrolidone (PVP) as reducing and surfactant agents. Synthesized and also film samples were characterized by using SEM, TEM, UV-Vis-NIR spectroscopy, particle size analyzer (PSA), and XRD. Triangle nanoplates with the size of 100~200 nm were found from the sample synthesized at $70^{\circ}C$ for 72 h using silver nitrate, DMF and 26 wt% PVP. The sample could reflect near-infrared light because it showed the maximum absorbing peak at about 1,000 nm. When the content or particle size of silver nanoplates increased in coating solutions, the transmittance decreased and the reflectance increased in film samples.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.4
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• pp.483-489
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• 2007

We have investigated quantitative measurement techniques of the degree of dispersion of single-walled carbon nanotubes (SWNTs). SWNTs were suspended in aqueous media using a sodium dodecyl sulfate (SDS) surfactant. SWNTs with different dispersion states were prepared by controlling the intensity and time of sonication and centrifugation. The laser spectroscopic techniques were employed to characterize the dispersion state; i.e., raman fluorescence and absorption spectroscopic techniques. Raman spectroscopy has been used to probe the dispersion and aggregation state of SWNTs in solution. Individually suspended SWNTs show increased fluorescence peaks and decreased roping peaks at a raman shift 267 $cm^{-1}$ compared with the samples containing bundles of SWNTs. The ultraviolet-visible-near infrared (UV-vis-NIR) absorption spectrum of decanted supernatant samples show sharp van Hove singularity peaks

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.1
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• pp.101-112
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• 2015

II~VI compound semiconductors, $Zn_xCd_{1-x}S$ thin films have been synthesized onto indium-tin-oxide(ITO) coated glass substrates using thermal evaporation technique. The composition ratio x($0{\leq}x{\leq}1$) was varied to fabricate different kinds of $Zn_xCd_{1-x}S$ thin films including CdS(x=0) and ZnS(x=1) thin films. Then, the deposited thin films were thermally annealed at $400^{\circ}C$ to enhance their crystallinity. The chemical composition and electronic structure of films were investigated by using X-ray photoelectron spectroscopy(XPS). The optical energy gaps of the samples were determined by ultra violet-visible-near infrared(UV-Vis-NIR) spectroscopy and were found to vary in the range of 2.44 to 3.98 eV when x changes from 0 to 1. Finally, we measured the THz characteristics of the $Zn_xCd_{1-x}S$ thin films using THz-TDS(time domain spectroscopy) system to identify the capability for electronic and optical devices in THz region.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.53.1-53.1
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• 2009

실리콘 다층박막 태양전지를 위한 초고효율 실리콘 양자점 박막을 연구하기 위해 Silicon target과 Carbon target을 동시에 스퍼터하여 Silicon Carbide 박막을 증착하였다. Silicon Carbide 박막의 조성비는 target에 인가되는 RF Power를 조절하여 Auger Electro Spectroscopy를 사용하여 Si, C, O, N원소의 양을 정량화하여 측정하였다. Si Power를 200W에 고정하고, C Power를 0W에서 400W까지 변화시킬 때, $Si_{1-x}$ $C_x$ 박막에서 조성비 x는 0 ~ 0.43 범위였다. 이 박막을 증착 한 후에 질소 분위기에서 600 ~ $1000^{\circ}C$ 온도로 열처리를 진행하였다. High resolution TEM과 Raman 분석을 통해, 박막의 열처리 후 $Si_{1-x}$ $C_x$ 박막 내에 실리콘 양자점이 형성되었음을 관찰할 수 있었고, 2 ~ 10 nm 의 크기를 가지는 것으로 확인할 수 있었다. 이 실리콘 양자점을 포함한 $Si_{1-x}$ $C_x$ 박막을 적층하여 UV-VIS-NIR spectroscopy, FTIR및 PL와 같은 측정을 통해 광학적 에너지 밴드갭의 변화와 그에 따른 특성을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.207-207
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• 2013

기존의 그래핀 성장에 관한 연구는 열화학기상증착법(Chemical vapor deposition; CVD)을 이용한다. 그래핀 성장 제어 요소로는 촉매 기판인 전이 금속[Ru, Ir, Co, Re, Pt, Pd, Ni, Cu], 기판 전처리 과정, 수소/메탄 가스 혼합비, 작업 진공 상태, 기판온도[$800{\sim}1,000^{\circ}C$, 냉각 속도 등으로 보고 되고 있다. 그래핀 성장 원리는 Cu 촉매 기판에 메탄 가스를 $1,000^{\circ}C$ 온도에서 분해해서 탄소를 고용 시킨 후 급랭하는 도중에 석출되는 탄소에 의해 그래핀 시트가 형성되는 것으로 알려져 있다. 기존의 CVD를 열원을 이용할 경우 내부 챔버에 생기는 잠열에 의해 cooling profile의 제어가 용이하지 않다. 본 연구에서는 근적외선(Near Infrared; NIR) 열원을 이용한 CVD로 챔버 내부 잠열을 최소화하고, 냉각 공정을 Natural, Linear, Convex cooling type으로 디자인해서 cooling profile 제어가 그래핀 성장에 미치는 영향을 연구 하였다. 이렇게 성장된 그래핀을 임의의 기판(SiO2, Glass, PET film) 위에 습식방법으로 전이 시킨 후, 전기적 구조적 및 광학적 특성을 면저항(four-point probe), 전계방사 주사전자현미경(Field Emission Scanning Electron Microscope; FE-SEM), 마이크로 라만 분광법(Micro Raman spectroscopy) 및 광학현미경(optical microscope), 투과도(UV/Vis spectrometer)의 측정으로 잠열이 최소화된 NIR-CVD에서 cooling profile에 따른 그래핀 성장을 평가하였다.

• Applied Chemistry for Engineering
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• v.26 no.4
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• pp.427-431
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• 2015

In this study, vanadium dioxide ($VO_2$) powder well known as a thermochromic material was prepared from $V_2O_5$ powder and oxalic acid dihydrate by hydrothermal and calcination process at various conditions. The chemical bonding and crystal structures in addition to thermal property of samples were determined using FE-SEM, XRD, XPS, and DSC. Also, spectroscopic and thermochromic properties of film samples were analyzed by UV-Vis-NIR spectroscopy after the thin film was prepared from the sol dispersed with the size of below 50 nm by the ball-milling of powder sample. With increasing the calcination temperature, the phase transition temperature of samples increased from $40^{\circ}C$ to $70^{\circ}C$ due to the increase of particle size.

• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.681-685
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• 2015

In this study, pure $BiVO_4$ powder and metal-doped $M-BiVO_4$ (M = Mg, Cu) powder, well known as thermochromic materials, were prepared from a mixed aqueous solution of bismuth nitrate ($Bi(NO_3)_3$) and ammonium vanadate ($NH_4VO_3$) in autoclave by hydrothermal method. The crystal structure, microstructure, and thermochromic property of samples were analyzed using FE-SEM, FT-IR, XRD, DSC, UV-Vis-NIR spectroscopy and colorimeter. When heating samples above phase transition temperature, the color of $M-BiVO_4$ (M = Mg, Cu) sample was thermally changed more clearly than that of using only pure $BiVO_4$ sample.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.34 no.2
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• pp.41-47
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• 2024

In this study, the resistance characteristics of semi-insulating SiC single crystals grown using the PVT method were investigated, considering the purity level of SiC source powders used in PVT growth and the cooling procedure after crystal growth. Two β-SiC powders with different purities were employed, and the cooling rate after growth was adjusted to achieve various resistance values. 4-inch HPSI-SiC ingots were grown using the PVT method, utilizing SiC powders with low nitrogen concentration and relatively high nitrogen concentration. These ingots were then subjected to different cooling procedures to modify the cooling rate. Transmission/absorption spectra and crystal quality of the grown crystals were analyzed through UV/VIs/NIR spectroscopy and X-ray rocking curve analysis, respectively. Additionally, electrical properties were investigated through non-contact resistivity analysis to identify the dominant factors influencing resistivity properties.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.32.1-32.1
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• 2011

Ultra thin tantalum nitride (TaNx) films with various thicknesses (10 nm to 40 nm) have been deposited by rf magnetron sputtering technique on glass substrates. The as deposited films were systematically characterized by several analytical techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, atomic force microscopy, UV-Vis-NIR double beam spectrophotometer and four point probe method. From the XRD results, the as deposited films are in amorphous nature, irrespective of the film thicknesses. The films composition was changed greatly with increasing the film thickness. SEM micrographs exhibited the densely pack microstructure, and homogeneous surface covered by small size grains at lower thickness deposited films. The surface roughness of the films was linearly increases with increasing the films thickness, consequently the transmittance decreased. The absorption edge was shifted towards higher wavelength as the film thickness increases.

• Journal of the Korean Ceramic Society
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• v.29 no.1
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• pp.48-52
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• 1992

Indium tin oxide (ITO) layers are of considerable interest on account of the combination of properties they provide high electrical conductivity, high infrared reflection with high solar energy transmission, high transmission in the visible range. We are concerned about the variation of the spectral transmittances and sheet resistances as the thickness of SiO2-ZrO2 barrier layer and ITO layers and heat treating conditions are changed. Transmittances and reflectivities were studied by measuring UV-VIS-NIR-, FT-IR spectroscopy. ITO films are crack free, homogeneous and of polycrystalline cubic structure. The microstructure of good ITO films shows a narrow grain size distribution and mean value of 100 nm. The selectivity of absorbing properties is improved by increasing the thickness of ITO films. The increase of sheet resistance of ITO films are due to the increase in the reaction between films and glass substrate.