• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.19 no.2
• /
• pp.90-94
• /
• 2009

Mong Hsu rubies from Myanmar were heat treated in oxidizing(oxygen) atmosphere at $1650^{\circ}C$ for 1 hour. The investigations of the micro-structural defects in the samples before and after heat treatment have been carried out by the variety of analysis techniques of FTIR, UV-VIS-NIR and SEM-EDS. It was found that after heat treatment the dark blue cores region were disappeared and turned to orange red color with the presence of the dense cloudy brownish colored tiny particles in and near former blue zoning. As-received ruby samples only revealed the presence of FTIR absorption peaks of diaspore, boehmite and O-H stretching, at 1986, 2115 and $3078/3319\;cm^{-1}$ respectively. The UV-VIS-NIR absorption of as-received and heat treated ruby samples similarly showed peaks at 405, 554 and 693 nm associated with $Cr^{3+}$, but for the same samples, the absorption peak of heat-treated ruby samples at 693 nm was somewhat stronger than that of the untreated ruby samples. Especially the presence of $Cr^{3+}$ peaks at 659 and 675 nm was found obviously in as-received ruby samples only. The SEM-EDS investigation disclosed the micro-porous defect structures commonly related to the core regions of the untreated ruby samples, which after heat treatment in an oxidizing environment those defect features have been dissolved into the host phase resulting in the lightening or disappearance of the dark coloration of ruby core.

• Applied Chemistry for Engineering
• /
• v.26 no.6
• /
• pp.681-685
• /
• 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 Vacuum Society
• /
• v.6 no.2
• /
• pp.114-121
• /
• 1997

The transparent conductiong thin films of tin oxides were prepared on pyrex glass substrates by the pulse laser deposition. In the atmospheres of vacuum, O2, and $Sn(CH_3)_4$ a polycrystalline $SnO_2$ target was ablated by Nd-YAG laser beam to deposit thin films on the substrates at room temperature, and as-deposited films were subsequently heat-treated in the air for 2 h at 230, 420 and $610^{\circ}C$, respectively. The characteristics of the thin films were examined by UV-VIS-NIR spectrometry and X-ray diffractometry, and the electrical properties were measured by four-point probe method along with film thickness monitored by the stylus method. It was observed that in the presence of $Sn(CH_3)_4$, $SnO_2$ phases were grown even at room temperature. This suggests that the microplasma producted during the laser ablation plays an important role in the dissociaation of precursor molecules.

• Korean Journal of Materials Research
• /
• v.18 no.10
• /
• pp.515-520
• /
• 2008

We fabricated 10 nm-$TiO_2$ thin films for DSSC (dye sensitized solar cell) electrode application using ALD (atomic layer deposition) method at the low temperatures of $150^{\circ}\;and\;250^{\circ}$. We characterized the crosssectional microstructure, phase, chemical binding energy, and absorption of the $TiO_2$ using TEM, HRXRD, XPS, and UV-VIS-NIR, respectively. TEM analysis showed a 10 nm-thick flat and uniform $TiO_2$ thin film regardless of the deposition temperatures. Through XPS analysis, it was found that the stoichiometric $TiO_2$ phase was formed and confirmed by measuring main characteristic peaks of Ti $2p^1$, Ti $2p^3$, and O 1s indicating the binding energy status. Through UV-VIS-NIR analysis, ALD-$TiO_2$ thin films were found to have a band gap of 3.4 eV resulting in the absorption edges at 360 nm, while the conventional $TiO_2$ films had a band gap of 3.0 eV (rutile)${\sim}$3.2 eV (anatase) with the absorption edges at 380 nm and 410 nm. Our results implied that the newly proposed nano-thick $TiO_2$ film using an ALD process at $150^{\circ}$ had almost the same properties as thsose of film at $250^{\circ}$. Therefore, we confirmed that the ALD-processed $TiO_2$ thin film with nano-thickness formed at low temperatures might be suitable for the electrode process of flexible devices.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.34 no.2
• /
• pp.41-47
• /
• 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 Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.207-207
• /
• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.28 no.2
• /
• pp.99-103
• /
• 2015

One-dimensional photonic crystals (1D PCs) were fabricated by RF sputtering technique on p-Si (100), and fused quartz substrates. The 1D PCs structures consisted of $TeO_x$ (x=1.42), and $SiO_2$ with the difference refractive index. In order to estimate the effect on a defect level within 1D PCs structures, samples were prepared with both normal, and defect mode. The structural and optical properties were confirmed by Scanning electron microscope (SEM), and Ultraviolet visible near-infrared spectrophotometer (UV-VIS-NIR) respectively. In the case of a 1D PC normal mode without defect layer, it had a photonic band gap (PBG) in the near infrared (NIR) region. In the case of a 1D PC defect mode with defect layer, it had a sharp transmission band owing to a defect level, and moved towards the longer wavelength after exposing He-Cd laser with a wavelength of 325 nm.

• Proceedings of the KOSOMBE Conference
• /
• v.1996 no.05
• /
• pp.52-55
• /
• 1996

The spectra of whole blood EDTA samples from two people were generated using a CARY 5E (UV-VIS-NIR) spectrophotometer from 400 to 1000nm which contain visible and NIR region. Only the data between 400 and 800nm were used to analyze the components of blood. Using the same spectrophotometer, the spectra of Water, normal saline, plasma were generated These spectra were subtracted from each blood sample, and then the first derivative of each of the subtracted data was taken to minimize baseline variations and indicated the wavelength-shift of peak and valley. Normalization and division between two blood samples were used to correlate the quantity ratio of specific components with feature of spectra. Samples were controlled at $30^{\circ}C,\;37^{\circ}C$, ambient temperature.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.351-352
• /
• 2012

UV LED에서 p-GaN층의 높은 일함수와 자체 면저항이 크기 때문에 current spreading layer인 ITO (indium tin oxide) 투명전극이 사용되고 있다. 따라서 높은 UV 파장대 투과율과 낮은 면 저항이 매우 중요하다. 본 연구에서, RF magnetron sputter를 사용하여 ITO 투명전극을 glass(boro33)에 120 nm 두께로 증착하였다. 그 후 RTA (rapid thermal annealing)을 이용해 120초 동안 $600^{\circ}C$에서 Air, $N_2$ (15 sccm), vacuum 환경에서 열처리를 하여 UV-Vis-NIR spectrophotometer를 사용해 ITO 박막의 투과율을 측정하고, Hall measurement system을 이용하여 전기적 특성을 측정하였다. Fig. 1과 같이 열처리 환경에 따라 ITO 박막의 투과율이 변하고 또한 Table 1과 같이 전기적 특성도 변함을 알 수 있었다. Air 환경에서의 열처리는 reference 샘플과 비교 했을 때 400 nm 이하의 파장에서 투과율이 증가하였지만 400 nm 이상의 파장에서는 투과율이 낮아짐을 볼 수 있고, 면 저항 (Ohm/sq)은 오히려 reference (as deposited) 샘플과 비교하여 24 Ohm/sq 증가하는 것을 알 수 있었다. 반면에 $N_2$, vacuum 환경에서 열처리는 reference (as deposited) 샘플 보다 380 nm 파장대에서 16% 정도 높은 투과율을 보였고, 면저항 역시 2배 이상 낮아졌다. 둘 다 비슷한 투과율과 면저항을 나타내었지만 vacuum 환경이 좀 더 우수한 광학적 특성을 나타내었고 반면에 $N_2$ 환경은 좀 더 낮은 면저항을 나타내었다. ITO 박막을 증착한 후 vacuum 환경에서 열처리를 통하여 제작된 UV-LED (중심 파장 380 nm)가 Fig. 2와 같이 입력 전류 450 mA에서 광출력이 46% 정도 향상 되었고 안정된 I-V 특성 보였다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.111-111
• /
• 2012

In this talk, we represent a novel approach to investigating intra-nanorod surface plasmon coupling with control over block compositions. The multi-component rod-like nanostructures, which consist of optically active components (Au and Ag) and optically less active component (for example, Ni) in UV-vis-NIR spectral window, showed interesting optical response depending on each block length and the total length of the structure. By controlling the composition and relative lengths of the blocks that comprise these structures, we can tailor the overall optical properties. Depending on the relative fraction of Au and Ag blocks, the intensity of the transverse modes varied without noticeable peak shifts. However, the strong intraparticle surface plasmon coupling resulted in the collective appearance of longitudinal LSP modes, including higher-order modes. The experimental observations were confirmed by theoretical calculation, using a discrete dipole approximation method. In addition, we will briefly discuss how single nanorod solar cells can be synthesized by using by using electrochemical deposition and AAO hard templates.