• Ceramist
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• v.22 no.3
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• pp.316-327
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• 2019

Carbon nitride has drawn broad interdisciplinary attention in diverse fields such as catalyst, energy storage, gas adsorption, biomedical sensing and even imaging. Intensive studies on carbon dioxide (CO₂) capture using carbon nitride materials with various nanostructures have been reported since it is needed to actively remove CO₂ from the atmosphere against climate change. This is mainly due to its tunable structural features, excellent physicochemical properties, and basic surface functionalities based on the presence of a large number of -NH or -NH₂ groups so that the nanostructured carbon nitrides are considered as suitable materials for CO₂ capture for future utilization as well. In this review, we summarize and highlight the recent progress in synthesis strategies of carbon nitride nanomaterials. Their superior CO₂ adsorption capabilities are also discussed with the structural and textural features. An outlook on possible further advances in carbon nitride is also included.

• Journal of Electrochemical Science and Technology
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• v.11 no.3
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• pp.220-237
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• 2020

Modern electrochemical energy devices involve generation and reduction of fuel gases through electrochemical reactions of water splitting, alcohol oxidation, oxygen reduction, etc. Initially, these processes were executed in the presence of noble metal-based catalyst that showed low overpotential and high current density. However, its high cost, unavailability, corrosion and related toxicity limited its application. The search for alternative with high stability, durability, and efficiency led scientists towards carbon nanoparticles supported catalysts which has high surface area, good electrical conductivity, tunable morphology, low cost, ease of synthesis and stability. Carbon nanoparticles are classified into two groups based on morphology, one and zero dimensional particles. Carbon nanoparticles at zero dimension, denoted as carbon dots, are less used carbon support compared to other forms. However, recently carbon dots with improved electronic properties have become popular as catalyst as well as catalyst support. This review focused on the recent advances in electrocatalytic activities of carbon dots. The mechanisms of common electrocatalytic reactions and the role of the catalysts are also discussed. The review also proposed future developments and other research directions to overcome current limitations.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.6 no.2
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• pp.35-44
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• 1995

In this paper, the single E-plane structure which is inserted in the slot of waveguide tube for good yield has been proposed and analyzed by the variational method. A CAD program for designing of the narrow-band waveguide bandpass filters has been developed by the passband correction method with filter synthesis theory. Using the developed CAD program, 0.02dB equi-ripple Chebyshev type 5-section bandpass filter is designed at the center frequency of 3.82GHz, fabricated with tunable structure. The experimental results show good agreements with the theoretical results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.616-619
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• 2003

This work presents the design, fabrication and microwave performance of distributed analog phase shifter (DAPS) fabricated on $(Ba,\;Sr)TiO_3$ (BST) thin films for X-band applications. Ferroelectric BST thin films were deposited on MgO substrates by pulsed laser deposition. The DAPS consists of high impedance coplanar waveguide (CPW) and periodically loaded tunable BST interdigitated capacitors (IDC). In order to reduce the insertion loss of DAPS and to remove the alteration of unloaded CPW properties according to an applied dc bias voltage, BST layer under transmission lines were removed by photolithography and RF-ion milling. The measured results are in good agreement with the simulated results at the frequencies of interest. The measured differential phase shift based on BST thin films was $24^{\circ}$ and the insertion loss decreased from 1.1 dB to 0.7 dB with increasing the bias voltage from 0 to 40V at 10 GHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.776-779
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• 2004

The dielectric and electrical characteristics of Ce doped (Ba0.6Sr0.4)TiO3 (BST) thin films were investigated as a function of Ce content. Both atomic force microscopy (AFM) and x-ray diffraction (XRD) analysis showed that increasing the Ce doping ratio causes the decrease in grain size while the surface remains smooth and crack-free. The dielectric properties of the Ce doped BST films were found to be strongly dependent on the Ce contents. The dielectric constant and dielectric loss of the BST films decreased with increasing Ce content. However, it was also found that, compared with undoped films, the increase of Cecontent improves the leakage-current characteristics. The improvement of the electrical properties of Ce-doped BST films may be related to the decrease in the concentration of oxygen vacancies. The figure of merit (FOM) reached the maximum value of 48.9 at the 1 mol % of Cedoping. The dielectric constant, loss factor, and tunability of the 1 mol% Ce doped Ba0.6Sr0.4TiO3 thin films were 320, 0.011, and 46.3%, respectively.

• Journal of IKEEE
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• v.15 no.3
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• pp.205-210
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• 2011

A novel hysteresis tunable monolithic comparator circuit based on a 0.35 ${\mu}m$ CMOS process is suggested in this paper. To tune the threshold voltage of the hysteresis in the comparator circuit, two external digital bits are used with supply voltage of 3.3V. The threshold voltage of the suggested comparator circuit is controlled by 234mV by change of 4 digital control bits in the simulation, which is a close agreement to the analytic calculation.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.203-207
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• 1999

In this paper we report new integration technology developed for three-dimensional metallic microstructures in an arbitrary shape. We have developed the two fabrication methods: Multi-Exposure and Single-Development (MESD) and Sacrificial Metallic Mold(SMM) techniques. Three-dimensional photoresist mold can be formed by the MESD method while unlimited number of structural levels can be realized by the SMM technique. Using these two techniques we have fabricated solenoid inductors and levitated spiral inductors for RF applications. We have achieved peak Q- factors over 40 in the 2-10㎓ range, the highest number among the inductors reported to date. Finally, we propose "On-Chip Passives" as a post IC process for monolithic integration of inductors, tunable capacitors, microwave switches, transmission lines, and mixers and filters toward future single-chip transceiver integration.

• Current Optics and Photonics
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• v.3 no.6
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• pp.577-582
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• 2019

We report on a continuous-wave (cw) optical parametric oscillator (OPO) optimized for mid-infrared emission above 5.0 ㎛. The OPO is based on a magnesium-oxide-doped periodically poled LiNbO₃(MgO:PPLN) crystal with a fan-out grating design. A linear two-mirror cavity resonating both at the pump and signal wavelengths is stabilized to the pump laser by using the modified Pound-Drever-Hall (PDH) method. The idler wavelength is continuously tunable from 4.7 ㎛ up to 5.3 ㎛ by varying the poling period of the fan-out grating crystal. Pumped by a diode-pumped solid state (DPSS) laser with a power of 1.1 W at 1064 nm, the maximum idler output power is measured to be 5.3 mW at 4.8 ㎛. The output power above 5.0 ㎛ is reduced to the hundreds of ㎼ level due to increased absorption in the crystal, but is stable and strong enough to be measured with a conventional detector.

• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.84-89
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• 1994

A tunable pulsed dye laser was operated in a single longitudinal mode by injection locking with a cw ring dye laser. A doubled Nd:YAG laser was used as the pumping source. Phase sensitive detection technique was applied to maintain the required match between the master laser frequency and the slave resonator cavity length. The fluctuation of the center frequency of the pulsed laser was < 10 MHz, and the pulse duration (FWHM) was 6 ns. The linewidth measured by scanning confocal interferometer was 130 MHz. When pumped by 50 mJ of the doubled Nd:YAG laser, the output energy of the pulsed dye laser was 2 mJ and the peak power was 330 kW. 30 kW.

• Korean Journal of Optics and Photonics
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• v.8 no.5
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• pp.366-371
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• 1997

We performed the velocity selective optical pumping(VSOP) spectroscopy using the rubidium atomic vapor in the room temperature. This spectroscopic technique removes the Doppler broadening by both optical pumping effect and the selection of atoms with a particular velocity. In this experiment, we used two independent lasers; one was a locked laser whose frequency was fixed and the other was a sweep laser whose frequency was tunable. The two beams were passing through the sample in the same direction unlike the conventional VSOP spectroscopy using two counter-propagating beams. We could make the velocity selective range of atoms much wider with this method than the old one.