• 한국재료학회지
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• 제20권5호
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• pp.262-266
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• 2010

ZnO nanostructures were grown on an Au seed layer by a hydrothermal method. The Au seed layer was deposited by ion sputter on a Si (100) substrate, and then the ZnO nanostructures were grown with different precursor concentrations ranging from 0.01 M to 0.3M at $150^{\circ}C$ and different growth temperatures ranging from $100^{\circ}C$ to $250^{\circ}C$ with 0.3 M of precursor concentration. FE-SEM (field-emission scanning electron microscopy), XRD (X-ray diffraction), and PL (photoluminescence) were carried out to investigate the structural and optical properties of the ZnO nanostructures. The different morphologies are shown with different growth conditions by FE-SEM images. The density of the ZnO nanostructures changed significantly as the growth conditions changed. The density increased as the precursor concentration increased. The ZnO nanostructures are barely grown at $100^{\circ}C$ and the ZnO nanostructure grown at $150^{\circ}C$ has the highest density. The XRD pattern shows the ZnO (100), ZnO (002), ZnO (101) peaks, which indicated the ZnO structure has a wurtzite structure. The higher intensity and lower FWHM (full width at half maximum) of the ZnO peaks were observed at a growth temperature of $150^{\circ}C$, which indicated higher crystal quality. A near band edge emission (NBE) and a deep level emission (DLE) were observed at the PL spectra and the intensity of the DLE increased as the density of the ZnO nanostructures increased.

• 한국진공학회지
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• 제16권6호
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• pp.463-467
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• 2007

[ $Al_2O_3$ ]기판을 산소 plasma 또는 수소 plasma로 표면 처리한 후 그 위에 plasma-assisted molecular beam epitaxy 방법으로 성장된 ZnO 박막의 구조적 특성과 광학적 발광 특성을 체계적으로 조사하였다. 제작된 ZnO 박막은 high resolution X-ray diffraction 측정과 atomic force microscope를 사용하여 구조적 특성과 표면 특성을 관찰하였으며, photoluminescence (PL) 측정을 통하여 엑시톤과 관련된 광학적 전이특성을 온도에 따라 조사하였다. free exciton, bound exciton, 그리고 이들의 phonon replica들의 특성을 온도에 따라 분석하였으며, 산소 plasma로 표면 처리한 시료의 PL 세기가 수소 plasma 표면 처리한 시료의 PL 세기보다 상당히 커짐을 관찰하였다. 산소 plasma로 처리된 기판 위에 성장된 ZnO 시료가 수소 plasma로 처리된 경우보다 우수한 구조적 특성과 광학적 특성을 보였는데, 이는 산소 plasma로 표면 처리함으로써 산소 공공(oxygen vacancy)과 같은 결함 구조가 적게 생성되고 좋은 격자 상수 일치를 보여주므로 구조적 특징과 발광 특징이 향상되는 것으로 해석되었다.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.26.4-27
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• 2010

The main payload of STSAT-3 (Science and Technology Satellite 3), MIRIS (Multipurpose InfraRed Imaging System) is the first Korean infrared space mission to explore the near-infrared sky with a small astronomical instrument, which is being developed by KASI. The 8-cm passively cooled telescope with a wide field of view (3.67 deg. $\times$ 3.67 deg.) will be operated in the wavelength range from 0.9 to $2{\mu}m$. It will carry out wide field imaging and the emission line survey. The main purposes of MIRIS are to perform the Cosmic Infrared Background (CIB) observation at two wide spectral bands (I and H band) and to survey the Galactic plane at $1.88{\mu}m$ wavelength, the Paschen-$\alpha$ emission line. CIB observation enables us to reveal the nature of degreescale CIB fluctuation detected by the IRTS (Infrared Telescope in Space) mission and to measure the absolute CIB level. The Pashen-$\alpha$ emission line survey of Galactic plane helps us to understand the origin of Warm Ionized Medium (WIM) and to find the physical properties of interstellar turbulence related to star formation. Here, we also discuss the observation plan with MIRIS.

• 천문학논총
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• 제32권1호
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• pp.11-15
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• 2017

We present the AKARI far-infrared (FIR) all-sky maps and describe its characteristics, calibration accuracy and scientific capabilities. The AKARI FIR survey has covered 97% of the whole sky in four photometric bands, which cover continuously 50-180 micron with band central wavelengths of 65, 90, 140, and 160 microns. The data have been publicly released in 2014 (Doi et al., 2015) with improved data quality that have been achieved since the last internal data release (Doi et al., 2012). The accuracy of the absolute intensity is ${\leq}10%$ for the brighter regions. Quantitative analysis of the relative intensity accuracy and its dependence upon spatial scan numbers has been carried out. The data for the first time reveal the whole sky distribution of interstellar matter with arcminute-scale spatial resolutions at the peak of dust continuum emission, enabling us to investigate large-scale distribution of interstellar medium in great detail. The filamentary structure covering the whole sky is well traced by the all-sky maps. We describe advantages of the AKARI FIR all-sky maps for the study of interstellar matter comparing to other observational data.

• 천문학회보
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• 제39권2호
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• pp.95-95
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• 2014

The mass measurement of neutron stars or black holes is of fundamental importance in our understanding of the evolution of massive stars and core-collapse supernova explosions as well as some exotic physics of the extreme conditions. Despite the importance, however, it's very difficult to measure mass of these objects directly. One way to do this, if they are in binary systems, to measure their binary motions (i.e., Doppler shifts) which can give us direct information on their mass. Recently many new highly-obscured massive X-ray binaries have been discovered by new hard X-ray satellites such as INTEGRAL and NuSTAR. The new highly-obscured massive X-ray binaries are faint in the optical, but bright in the infrared with many emission lines. Based on the near-infrared spectroscopy, one can first understand the nature of stellar companions to the compact objects, determining its spectral types and luminosity classes as well as mass losses and conditions of (potential) circumstellar material. Next, spectroscopic monitoring of these objects can be used to estimate the mass of compact objects via measuring the Doppler shifts of the lines. For the former, broad-band spectroscopy is essential; for the latter, high-resolution spectroscopy is critical. Therefore, IGRINS appears to be an ideal instrument to study them. An IGRINS survey of these new highly-obscured massive X-ray binaries can give us a rare opportunity to carry out population analyses for understanding the evolution of massive binary systems and formation of compact objects and their mass ranges. In this talk, we will present a sample near-infrared high resolution spectra of HMXB, IGR J19140+0951 and discuss about its spectral feature. These spectra are obtained on 13th July, 2014 from IGRINS commissioning run at McDonald 2.7m telescope. And at final, we will introduce the upgrade plan of IGRINS Operation Software (IGOS), to gather the input from IGRINS observer.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.174-174
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• 2010

Gallium Nitride(GaN) attracts great attention due to their wide band gap energy (3.4eV), high thermal stability to the solid state lighting devices like LED, Laser diode, UV photo detector, spintronic devices, solar cells, sensors etc. Recently, researchers are interested in synthesis of polycrystalline and amorphous GaN which has also attracted towards optoelectronic device applications significantly. One of the alternatives to deposit GaN at low temperature is to use Single Source Molecular Percursor (SSP) which provides preformed Ga-N bonding. Moreover, our group succeeds in hybridization of SSP synthesized GaN with Single wall carbon nanotube which could be applicable in field emitting devices, hybrid LEDs and sensors. In this work, the GaN thin films were deposited on c-axis oriented sapphire substrate by MBE (Molecular Beam Epitaxy) using novel single source precursor of dimethyl gallium azido-tert-butylamine($Me_2Ga(N_3)NH_2C(CH_3)_3$) with additional source of ammonia. The surface morphology, structural and optical properties of GaN thin films were analyzed for the deposition in the temperature range of $600^{\circ}C$ to $750^{\circ}C$. Electrical properties of deposited thin films were carried out by four point probe technique and home made Hall effect measurement. The effect of ammonia on the crystallinity, microstructure and optical properties of as-deposited thin films are discussed briefly. The crystalline quality of GaN thin film was improved with substrate temperature as indicated by XRD rocking curve measurement. Photoluminescence measurement shows broad emission around 350nm-650nm which could be related to impurities or defects.

• 한국전기전자재료학회논문지
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• 제15권1호
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• pp.67-74
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• 2002

A phosphor for Plasma Display Panel, BaMgAl$_{10}$ O$_{17}$ :Eu$^{2+}$, showing a blue emission band at about 450nm was prepared by a solid-state reaction using BaCO$_3$, $Al_2$O$_3$, MgO, Eu$_2$O$_3$ as starting materials wish flux AlF$_3$. The study of the behaviour of Eu in BAM phosphor was carried out by the photoluminescence spectra and the Rietveld method with X-ray and neutron powder diffraction data to refine the structural parameters such as lattice constants, the valence state of Eu, the preferential site of Mg atom and the site fraction of each atom. The phenomenon of the concentration quenching was abound 2.25~2.3wt% of Eu due to a decrease in the critical distance for energy transfer of inter-atomic Eu. Through the combined Rietveld refinement, R-factor, R$_{wp}$, was 8.11%, and the occupancy of Eu and Mg was 0.0882 and 0.526 at critical concentration. The critical distance of Eu$^{2+}$ in BAM was 18.8$\AA$ at 2.25% Eu of the concentration quenching. Furthermore, c/a ratio was decreased to 3.0wt% and no more change was observed over that concentration. The maximum entropy electron density was found that the modeling of $\beta$-alumina structure in BaMgAl$_{10}$ O$_{17}$ :Eu$^{2+}$correct coincided showing Ba, Eu, O atoms of z= 1/4 mirror plane.e.ane.e.

• 천문학회보
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• 제36권2호
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• pp.112.2-112.2
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• 2011

We carry out a systematic study of HI shells and supershells in the first Galactic quadrant (l = $32^{\circ}$ to $77^{\circ}$, b = $-10^{\circ}$ to $10^{\circ}$) using the "Inner-Galaxy Arecibo L-band Feed Array (I-GALFA)" HI 21-cm survey data. The high-resolution (3.'4) and high sensitivity (0.2 K) of the survey provide us an opportunity to exploit the true nature of the sources detected in previous low-resolution studies and also to detect faint and/or small shells that were not detectable before. Our work is composed of three parts: (1) confirm the objects in the low-resolution (about 30') catalog of Heiles (1979), (2) search for fast-expanding HI shells associated with Galactic supernova remnants (SNRs), and (3) search for new shell structures. Among the 21 Heiles' supershells in the I-GALFA survey area, we confirm fourteen. The high resolution data reveal their complex morphology, and provide direct evidence for expansion in some sources. Among the 39 Galactic SNRs in the survey area, we find five with associated fast expanding HI shells, which is consistent with previous results. A remarkable result from the SNR study is the detection of HI gas at very high negative velocities in the SNR W44 that should be from the approaching part of the HI expanding shell. This is the first time to detect both the approaching and receding sides of an expanding shell in HI 21-cm emission line in SNRs. We have found 33 new shell candidates of angular sizes ranging from 0.5 to 6.5 degrees, half of which appear to be expanding. We summarize these results and discuss some individual interesting objects in detail.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.105-105
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• 2011

ZnO is a promising material since it could be applied to many fields such as solar cells, laser diodes, thin films transistors and gas sensors. ZnO has a wide and direct band gap for about 3.37 eV at room temperature and a high exciton binding energy of 60 meV. In particular, ZnO features high sensitivity to toxic and combustible gas such as CO, NOX, so on. The development of gas sensors to monitor the toxic and combustible gases is imperative due to the concerns for enviromental pollution and the safety requirements for the industry. In this study, we investigated the effect of substrate temperature and post-annealing on structural and electrical properties of ZnO thin films. ZnO thin films were deposited by pulsed laser deposition (PLD) at various temperatures at from room temperature to $600^{\circ}C$. After that, post-annealing were performed at $600^{\circ}C$. To inspect the structural properties of the deposited ZnO thin films, X-ray diffraction (XRD) was carried out. For gas sensors, the morphology of the films is dominant factor since it is deeply related with the film surface area. Therefore, the atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) were used to observe the surface of the ZnO thin films. Furthermore, we analyzed the electrical properties by using a Hall measurement system.

• 천문학회보
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• 제39권2호
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• pp.78.2-78.2
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• 2014

MIRIS (Multi-purpose Infrared Imaging System) is the primary payload on the Korean science and technology satellite, STSAT-3, which was launched on 2013 November 21. It is designed to observe the near-infrared sky with a $3.67^{\circ}{\times}3.67^{\circ}$ field of view and a $51.6^{{\prime}{\prime}}{\times}51.6^{{\prime}{\prime}}$ pixel resolution. Using two narrow-band filters at $1.88{\mu}m$ (Pa ${\alpha}$ line) and $1.84+1.92{\mu}m$ (Pa ${\alpha}$ dual continuum), the Paschen ${\alpha}$ Galactic plane survey has been carrying out, and the area for the Galactic longitude from $+280^{\circ}$ to $+100^{\circ}$ (with the width of $-3^{\circ}$ < b < $+3^{\circ}$) has been covered by 2014 August 31. In this contribution, we present the preliminary results of the MIRIS Paschen ${\alpha}$ emission maps and compare them with other wavelength maps such as $H{\alpha}$ and dust maps. Many of the Paschen ${\alpha}$ features have been detected along the plane, and some of them are weak or invisible in the $H{\alpha}$ map and coincide well with dense cloud regions.