• Korean Journal of Optics and Photonics
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• v.28 no.2
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• pp.53-58
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• 2017

This paper presents the design and fabrication of a planar nano-diffraction grating for an integrated miniature spectrometer module. The proposed planar nano-diffraction grating consists of nonuniform periods, to focus the reflected beams from the grating's surface, and an asymmetrical V-shaped groove profile, to provide uniform diffraction efficiency in the wavelength range from 400 to 650 nm. Also, to fabricate the nano-diffraction grating using low-cost UV-NIL technology, we analyzed the FT-IR spectrum of a uvcurable resin and optimized the conditions for the UV curing process. Then, we precisely fabricated the polymeric nano-diffraction grating within 5 nm in dimensional accuracy. The integrated spectrometer module using the fabricated polymeric planar nano-diffraction grating provides spectral resolution of 5 nm and spectral bandwidth of 250 nm. Our integrated spectrometer module using a polymeric planar nano-diffraction grating serves as a quick and easy solution for many spectrometric applications.

• Journal of the Korean Vacuum Society
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• v.12 no.S1
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• pp.95-99
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• 2003

We successfully grew InN/GaN single quantum well structures by metal-organic chemical vapor deposition and confirmed their formation by optical and structural measurements. We speculate that relatively high growth temperature ($730^{\circ}C$) of InN layer enhanced the formation of 2-dimensional quantum well structures, presumably due to high adatom mobility. As the growth interruption time increased, the PL emission efficiency from InN layer improved with peak position blue-shifted and the dislocation density decreased by one order of magnitude. The high resolution cross-sectional TEM images clearly showed that the InN layer thickness reduced from 2.5 nm (without GI) to about I urn (with 10 sec GI) and the InN/GaN interface became very flat with 10 sec GI. We suggest that decomposition and mass transport processes on InN during GI is responsible for these phenomena.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.49.1-49.1
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• 2010

The study of pores, small penumbraless sunspots, can give us a chance to understand how strong magnetic fields interact with convective motions in the photosphere. For a better understanding of this interaction, we investigate the temporal variation of several tiny pores smaller than 2". These pores were observed by the Solar Optical Telescope (SOT) onboard Hinode on 2006 December 29. We have analyzed the high resolution spectropolarimetric (SP) data and the G-band filtergrams taken during the observation. Magnetic flux density and Doppler velocities of the pores are estimated by applying the center of gravity (COG) method to the SP data. The horizontal motions in and around the pores are tracked by adopting the Nonlinear Affine Velocity Estimator (NAVE) method to the G-band filter images. As results, we found the followings. (1) Darkness of pores is positively correlated with magnetic flux density. (2) Downflows always exist inside and around the pores. (3) The speed of downflows inside the pores is negatively correlated with their darkness. (4) The pores are surrounded by strong downflows. (5) Brightness changes of the pores are correlated with the divergence of mass flow (correlation coefficient > 0.9). (6) The pores in the growing phase are associated with the converging flow pattern and the pores in the decay phase with the diverging flow pattern. Our results support the idea that a pore grows as magnetic flux density increases due to the convergence of ambient mass flow and it decays with the decrease of the flux density due to the diverging mass flow.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.39.4-40
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• 2017

According to the Korean government's Long-term Space Development Plan 2040, "Creative space science research" is included in a statement to investigate the origin and evolution of the universe by conducting a series of Korean space telescope missions: launch of space telescopes on a small satellite and an international collaboration explorer by 2020, a mid-size domestic space telescope by 2030, and a large size Korea leading international space telescope by 2040. We studied the feasibility of the future Korean Space Telescope (KST) for a mid-size domestic satellite platform. In order to pursue the uniqueness of the science program, we consider a wide range of observing wavelength (0.2um ~ 2.0um) with a spectral resolution of R~6 in the NUV and optical bands, and R~30 for NIR, utilizing an off-axis TMS(Three Mirror System) optics with a wide field of view ($2{\times}4$ degrees) which is optimized for ultra-low surface brightness sources. The main science goals of the mission include investigations of the galaxy formation, cosmic web, and the cosmic background radiation in the NUV-NIR regions. In this paper, we present the science cases and several technical challenges to be resolved along with the future milestones for the success of the KST mission.

• Journal of The Korean Astronomical Society
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• v.50 no.6
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• pp.157-165
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• 2017

$H_2O$ maser emission at 22 GHz in the circumstellar envelope is one of the good tracers of detailed physics and kinematics in the mass loss process of asymptotic giant branch stars. Long-term monitoring of an $H_2O$ maser spectrum with high time resolution enables us to clarify acceleration processes of the expanding shell in the stellar atmosphere. We monitored the $H_2O$ maser emission of the semi-regular variable R Crt with the Kagoshima 6-m telescope, and obtained a large data set of over 180 maser spectra over a period of 1.3 years with an observational span of a few days. Using an automatic peak detection method based on least-squares fitting, we exhaustively detected peaks as significant velocity components with the radial velocity on a $0.1kms^{-1}$ scale. This analysis result shows that the radial velocity of red-shifted and blue-shifted components exhibits a change between acceleration and deceleration on the time scale of a few hundred days. These velocity variations are likely to correlate with intensity variations, in particular during flaring state of $H_2O$ masers. It seems reasonable to consider that the velocity variation of the maser source is caused by shock propagation in the envelope due to stellar pulsation. However, it is difficult to explain the relationship between the velocity variation and the intensity variation only from shock propagation effects. We found that a time delay of the integrated maser intensity with respect to the optical light curve is about 150 days.

• Journal of Arbitration Studies
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• v.21 no.2
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• pp.47-64
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• 2011

The China International Economic and Trade Arbitration Commission(CIETAC) released online arbitration rules which apply the resolution of disputes over electronic commerce transactions, as well as other economic and trade disputes in which the parties agree to do. The evidence submitted by the parties may be electronic evidence created, sent, received or stored by electronic, optical or magnetic means. Electronic evidence with a reliable electronic signature shall carry the same effect and probative force as a document with a hand-written signature. Where a case is tried in a tribunal, the arbitration tribunal shall conduct an online trial hearing using internet video conference or other electronic or computer communication means. Unless the parties have another agreement, summary procedure shall apply to cases where the amount in dispute exceeds RMB 100,000 but no more than RMB 1 million, or where the amount in dispute exceeds RMB 1 million and a party submits a written application for summary procedure after obtaining the written consent of the other party. Unless the parties have agreed otherwise, fast-track procedure shall apply to cases where the amount in dispute does not exceed RMB 100,000 or where the amount in dispute exceeds RMB 100,000 and a party submits a written application for fast-track procedure after obtaining the written consent of the other party. Notable features of the Online Rules are as follows; first, there is not detailed consideration for online arbitration. Second, communications between the parties and the tribunal are allowed only through the Secretariat. Third, elaborate provisions regarding the electronic submission and transmission of documents is provided for. Forth, various factors must be considered by the tribunal in deciding the evidence's reliability. Fifth, reasonable endeavours is levied on CIETAC to keep data communications secure and encrypted. Sixth, the tribunal has the right to investigate and collect relevant evidence. And finally different procedures are provided for in consideration of the various types of E-commerce.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.361.2-361.2
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• 2014

Transition metal dichalcogenides (MoS2, WS2, WSe2, MoSe2, NbS2, NbSe2, etc.) are layered materials that can exhibit semiconducting, metallic and even superconducting behavior. In the bulk form, the semiconducting phases (MoS2, WS2, WSe2, MoSe2) have an indirect band gap. Recently, these layered systems have attracted a great deal of attention mainly due to their complementary electronic properties when compared to other two-dimensional materials, such as graphene (a semimetal) and boron nitride (an insulator). However, these bulk properties could be significantly modified when the system becomes mono-layered; the indirect band gap becomes direct. Such changes in the band structure when reducing the thickness of a WS2 film have important implications for the development of novel applications, such as valleytronics. In this work, we report for the controlled synthesis of large-area (~cm2) single-, bi-, and few-layer WS2 using a two-step process. WOx thin films were deposited onto a Si/SiO2 substrate, and these films were then sulfurized under vacuum in a second step occurring at high temperatures ($750^{\circ}C$). Furthermore, we have developed an efficient route to transfer these WS2 films onto different substrates, using concentrated HF. WS2 films of different thicknesses have been analyzed by optical microscopy, Raman spectroscopy, and high-resolution transmission electron microscopy.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.304.1-304.1
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• 2014

Flat-panel displays have been growing as an essential everyday product in the current information/communication ages in the unprecedented speed. The forward-coming applications require light-weightness, higher speed, higher resolution, and lower power consumption, along with the relevant cost. Such specifications demand for a new concept-based materials and applications, unlike Si-based technologies, such as amorphous Si and polycrystalline Si thin film transistors. Since the introduction of the first concept on the oxide-based thin film transistors by Hosono et al., amorphous oxide thin film transistors have been gaining academic/industrial interest, owing to the facile synthesis and reproducible processing despite of a couple of shortcomings. The current work places its main emphasis on the binary oxides composed of ZnO and SnO2. RF sputtering was applied to the fabrication of amorphous oxide thin film devices, in the form of bottom-gated structures involving highly-doped Si wafers as gate materials and thermal oxide (SiO2) as gate dielectrics. The physical/chemical features were characterized using atomic force microscopy for surface morphology, spectroscopic ellipsometry for optical parameters, X-ray diffraction for crystallinity, and X-ray photoelectron spectroscopy for identification of chemical states. The combined characterizations on Zn-Sn-O thin films are discussed in comparison with the device performance based on thin film transistors involving Zn-Sn-O thin films as channel materials, with the aim to optimizing high-performance thin film transistors.

• The Journal of the Korea Contents Association
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• v.8 no.11
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• pp.18-24
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• 2008

An organic light-emitting diode(OLED) has advantages of low power driving, self light-emitting, wide viewing angle, excellent high resolution, full color, high reproduction, fast response speed, simple manufacturing process, or the like. However, there are still a number of challenges to get over in order to put it to practical use as a high performance display. First of all, the most important thing is to improve the efficiency of the OLED element in order to commercialize it. To this end, its efficiency can be improved by lowering the driving voltage through the improvement of structure of the OLED element and the application of new organic substance. Therefore, in this study, we have manufactured a red OLED element by applying fluorescent dyes to the emitting layer of the element having the structure of ITO/TPD/ Znq2+DCJTB /Znq2/Al and the structure of ITO/CuPc/NPB/ Alq3+DCJTB/Alq3/Al, in order to light-emitting various colors or improve the brightness and the efficiency, and then we have evaluated its electrical and optical characteristics.

• Journal of Biomedical Engineering Research
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• v.31 no.4
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• pp.292-301
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• 2010

To restore visual sensation of blind patients, we have proposed a fully implantable retinal prosthesis comprising an three dimensionally (3D) stacked retinal chip for transforming optical signal to electrical signal, a flexible cable with stimulus electrode array for stimulating retina cells, and coupling coils for power transmission. The 3D stacked retinal chip is consisted of several LSI chips such as photodetector, signal processing circuit, and stimulus current generator. They are vertically stacked and electrically connected using 3D integration technology. Our retinal prosthesis has a small size and lightweight with high resolution, therefore it could increase the patients` quality of life (QOL). For realizing the fully implantable retinal prosthesis, we developed a retinal prosthesis module comprising a retinal prosthesis chip and a flexible cable with stimulus electrode array for generating optimal stimulus current. In this study, we used a 2D retinal chip as a prototype retinal prosthesis chip. We fabricated the polymide-based flexible cable of $20{\mu}m$ thickness where 16 channels Pt stimulus electrode array was formed in the cable. Pt electrode has an impedance of $9.9k{\Omega}$ at 400Hz frequency. The retinal prosthesis chip was mounted on the flexible cable by an epoxy and electrically connected by Au wire. The retinal prosthesis chip was cappted by a silicone to pretect from corrosive environments in an eyeball. Then, the fabricated retinal prosthesis module was implanted into an eyeball of a rabbit. We successfully recorded electrically evoked potential (EEP) elicited from the rabbit brain by the current stimulation supplied from the implanted retinal prosthesis module. EEP amplitude was increased linearly with illumination intensity and irradiation time of incident light. The retinal prosthesis chip was well functioned after implanting into the eyeball of the rabbit.