• Korean Journal of Materials Research
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• v.30 no.10
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• pp.558-565
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• 2020

AZO thin films are grown on a p-Si(111) substrate by RF magnetron sputtering. The characteristics of various thicknesses and heat treatment conditions are investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Hall effect and room-temperature photoluminescence (PL) measurements. The substrate temperature and the RF power during growth are kept constant at 400 ℃ and 200 W, respectively. AZO films are grown with a preferred orientation along the c-axis. As the thickness and the heat treatment temperature increases, the length of the c-axis decreases as Al³⁺ ions of relatively small ion radius are substituted for Zn²⁺ ions. At room temperature, the PL spectrum is separated into an NBE emission peak around 3.2 eV and a violet regions peak around 2.95 eV with increasing thickness, and the PL emission peak of 300 nm is red-shifted with increasing annealing temperature. In the XPS measurement, the peak intensity of Al_2p and O_ll increases with increasing annealing temperature. The AZO thin film of 100 nm thickness shows values of 6.5 × 10¹⁹ cm^-3 of carrier concentration, 8.4 cm^-2/V·s of mobility and 1.2 × 10^-2 Ω·cm electrical resistivity. As the thickness of the thin film increases, the carrier concentration and the mobility increase, resulting in the decrease of resistivity. With the carrier concentration, mobility decreases when the heat treatment temperature increases more than 500 ℃.

• Korean Journal of Materials Research
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• v.12 no.3
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• pp.215-219
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• 2002

For the purpose of annihilating tumor in body, hematoporphyrin as a photosensitizer was coated onto magnetic particles of $Fe_3O_4$ prepared by coprecipitation which could be concentrated around the tumor by magnetic field. The photosensitizer was applied differently before, during and after adsorbing the 1st surfactant on the particles. Its added amount was $5{\times}10^{-4}/mol$, and the coating reaction proceeded at temperatures of 60, 70 and 8$0^{\circ}C$. The amounts of photosensitizer coated on the magnetic particles were obtained by calculating an optical density with the maximum UV spectrum. As a result of the UV analysis, the coating amount of photosensitizer increased with higher reaction temperatures. When applied at 8$0^{\circ}C$ after adsorbing the 1st surfactant, the photosensitizer was coated with a maximum value of $3.8{\times}10^{-3}/mo1/$\ell$$. The TGA analysis revealed that the ferrofluids included the particles of 30.115 g/$\ell$. It was suggested that the magnetite particles was coated with photosensitizer of $1.26{\times}10^{-4}/mo1/g$. A small-sized device for magnetic field and light emission was designed, in which LED sheets coverts the permanent magnet of Nd-Fe-B. The LED sheet was connected in series circuit and also protected with a silicon tube. The power was supplied with rechargable battery of 9V and 100-120mA.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.7 no.1
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• pp.20-25
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• 2014

There are several severe problems for LED device, the next generation's economy green lighting: as the temperature increases, the lamp efficiency decreases; if the temperature is over $80^{\circ}C$, the lifetime of lighting decreases; Red Shift phenomenon that wavelength of spectrum line moves toward long wavelength occurs; and optical power decreases as $T_j$ increases. Thus, Heat sink design that can minimize the heat of LED device is currently in progress. While the thermal resistance of COB Type LED was reduced by direct coupling of LED chip to the board, residential 13.5W requires Heat sink in order resolve heat issue. This study designed Heat Sink suitable for residential 13.5W COB LED down-light and selected the optimum Fin thickness through flow simulation that packaged the designed Heat Sink and 13.5W COB. And finally it analyzed and evaluated the thermal modes using contacting thermometer.

• Korean Journal of Optics and Photonics
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• v.3 no.2
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• pp.77-85
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• 1992

The design of a flat-field XUV spectrograph is optimized for a high throughput, aberration-corrected spectral image in the wavelength region of 50-300 $\AA$ The varied-line spacing (VLS) concave grating theory for an XUV spectrograph with a toroidal mirror in front of an entrance slit is derived. Since the derived theory includes the arbitrary shaped source, it is able to correct the limit of the simple optimization theory which considers only a point source at the center of the entrance slit. The reflection matrix at the toroidal mirror and the diffraction matrix at VLS grating are derived and compared with those of a holographic grating. The absolute energy efficiency of a flat-field spectrograph is calculated by considering the reflectivities of the toroidal mirror and the Au coated concave grating and the grating efficiency. The alignment sensitivity of the toroidal mirror and the concave grating is investigated, and the method to achieve the best imaging of XUV spectrum is discussed. The calculated resolving power of the flat-field XUV spectrograph is more than 4000 in the aberration-corrected wavelength range. The focused spot size at the dispersion plane is less than $20\mu \textrm m\times \mu \textrm m$at the wavelength 100$\AA$ It is shown that a high throughput characteristic can also be achieved through a careful adjustment of alignment parameters.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.49.1-49.1
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• 2021

We carried out simultaneous monitoring observations of five maser lines, H₂O (22 GHz), SiO 𝝊 =1, 2, J =1-0 (43.1, 42.8 GHz), and SiO 𝝊 =1, J=2-1, J =3-2 (86.2, 129.3 GHz), toward the Mira variable star WX Serpentis with the 21-m antennas of the Korean VLBI Network (KVN) in 2009-2021 (~12 years). Most spectra of the H₂O maser are well separated into two parts of two blue- and one redshifted features within ± 10 km s-1 of the stellar velocity. All detected SiO masers are generally concentrated within ± 5 km s-1 of the stellar velocity, and sometimes appear split into two components. Overall, the profiles of SiO and H₂O masers detected in WX Serpentis illustrate typical characteristics of the Mira variable. In addition, flux variations of both SiO and H₂O masers are well correlated with the optical light curve of the central star, showing a phase lag of ~ 0.1 for SiO masers and ~ 0.2 for H₂O maser. This phenomenon is considered to be the direct effect of propagating shock waves generated by the stellar pulsation, because SiO and H₂O masers are sequentially distributed at different positions with respect to the central star. In addition, we analyzed long-term trends and characteristics of maser velocities, maser ratio, and the velocity extents (the full width at zero power; FWZP). We also investigated a spectral energy distribution (SED) ranging from 1.2 to 240 ㎛ obtained using several infrared data: 2MASS, WISE, IRAS, ISO, COBE DIBRE, RAFGL, and AKARI (IRC and FIS). From the IRAS LRS and ISO SWS spectra of this star, we identified 9.7 and 12 ㎛ silicate emission features consistent with the SE6 spectrum model, corresponding to the typical AGB phase.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.68-72
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• 2008

Fiber-optic strain sensors based on Bragg reflection gratings produce the change of reflection spectrum when an external stress is applied on the sensor. To measure the Bragg reflection wavelength in high speed, an arrayed waveguide grating device is incorporated in this work. By monitoring the output power from each channel of the AWG, the peak wavelength corresponding to the applied strain could be obtained. To enhance the accuracy of the AWG wavelength interrogation system, a chirped fiber Bragg grating with a 3-dB bandwith of 5.4 nm is utilized. The high-speed response of the proposed system is demonstrated by measuring a fast varying strain produced by the damped oscillation of a cantilever. An oscillation frequency of 17.8 Hz and a damping time constant of 0.96 second are obtained in this measurement.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.7
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• pp.6-13
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• 2006

Tin doped indium oxide(ITO) and Al doped zinc oxide(ZnO:Al) films, which are widely used as a transparent conductor in optoelectronic devices, were prepared by using the capacitively coupled DC magnetron sputtering method. ITO and ZnO:Al films with the optimum growth conditions showed each resistivity of $1.67{\times}10^{-3}[{\Omega}-cm],\;2.2{\times}10^{-3}[{\Omega}-cm]$ and transmittance of 89.61[%], 90.88[%] in the wavelength range of the visible spectrum. The two types of 5 inch-PDP cells with ZnO:Al and ITO transparent electrodes were made under the same manufacturing conditions. The PDP cell with ZnO:Al film was optimally operated in the mixing gas rate of Ne(base)-Xe(8[%]), and at gas pressure of 400[Torr]. It also shows the average measured brightness of $836[cd/m^2]$ at voltage range of $200{\sim}300$[V]. Luminous efficiency, one of the key parameter for high brightness and low power consumption, ranges from 1.2 to 1.6[lm/W] with increasing frequency of ac power supplier from 10 to 50[Khz]. The brightness and luminous efficiency are lower than those with ITO electrode by about 10[%]. However, these values are considered to be enough for the normal operation of PDP TV.

• Korean Journal of Applied Biomechanics
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• v.26 no.2
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• pp.167-174
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• 2016

Objective: The purpose of this study was to determine the interrelationship between ranges of motion of the knee and ankle joints on the sagittal plane and the attenuation magnitude of impact shock at high frequency (9~20 Hz) in the support phase during downhill running. Method: Fifteen male heel-toe runners with no history of lower extremity injuries were recruited for this study (age, $25.07{\pm}5.35years$; height, $175.4{\pm}4.6cm$; mass, $75.8{\pm}.70kg$). Two uniaxial accelerometers were mounted to the tuberosity of tibia and sacrum, respectively, to measure acceleration signals. The participants were asked to run at their preferred running speed on a treadmill set at $0^{\circ}$, $7^{\circ}$, and $15^{\circ}$ downhill. Six optical cameras were placed around the treadmill to capture the coordinates of the joints of the lower extremities. The power spectrum densities of the two acceleration signals were analyzed and used in the transfer function describing the gain and attenuation of impact shock between the tibia and the sacrum. Angles of the knee and ankle joints on the sagittal plane and their angle ranges were calculated. The Pearson correlation coefficient was used to test the relationship between two variables, the magnitude of impact shock, and the range of joint angle under three downhill conditions. The alpha level was set at .05. Results: Close correlations were observed between the knee joint range of motion and the attenuation magnitude of impact shock regardless of running slopes (p<.05), and positive correlations were found between the ranges of motion of the knee and ankle joints and the attenuation magnitude of impact shock in $15^{\circ}$ downhill running (p<.05). Conclusion: In conclusion, increased knee flexion might be required to attenuate impact shock during downhill and level running through change in stride or cadence while maintaining stability, and strong and flexible ankle joints are also needed in steeper downhill running.

• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.629-635
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• 2012

Two novel conjugated copolymers utilizing 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DTBT) coupled with cyano (-CN) substituted vinylene, as the electron deficient moeity, have been synthesized and evaluated in bulk heterojunction solar cell. The electron deficient moeity was coupled with carbazole and fluorene unit by Knoevenagel condition to provide poly(bis-2,7-((Z)-1-cyano-2-(5-(7-(2-thienyl)-2,1,3-benzothiadiazol-4-yl)-2-thienyl)ethenyl)-alt-9-(1-octylnonyl)-9H-carbazol-2-yl-2-butenenitrile) (PCVCNDTBT) and poly(bis-2,7-((Z)-1-cyano-2-(5-(7-(2-thienyl)-2,1,3-benzothiadiazol-4-yl)-2-thienyl)ethenyl)-alt-9,9-dihexyl-9H-fluoren-2-yl) (PFVCNDTBT). The optical band gaps of PCVCNDTBT (1.74 eV) and PFVCNDTBT (1.80 eV) are lower than those of PCDTBT (1.88 eV) and PFVDTBT (2.13 eV), which is advantageous to provide better coverage of the solar spectrum in the longer wavelength region. The high $V_{oc}$ value of the PSC of PCVCNDTBT (~0.91 V) is attributed to its lower HOMO energy level ( 5.6 eV) as compared to PCDTBT ( 5.5 eV). Bulk heterojunction solar cells based on the blends of the polymers with [6,6]phenyl-$C_{61}$-butyric acid methyl ester ($PC_{61}BM$) gave power conversion efficiencies of 0.76% for PCVCNDTBT under AM 1.5, 100 mW/$cm^2$.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.189-189
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• 2012

Lead sulfide (PbS) nanocrystal quantum dots (NQDs) are promising materials for various optoelectronic devices, especially solar cells, because of their tunability of the optical band-gap controlled by adjusting the diameter of NQDs. PbS is a IV-VI semiconductor enabling infrared-absorption and it can be synthesized using solution process methods. A wide choice of the diameter of PbS NQDs is also a benefit to achieve the quantum confinement regime due to its large Bohr exciton radius (20 nm). To exploit these desirable properties, many research groups have intensively studied to apply for the photovoltaic devices. There are several essential requirements to fabricate the efficient NQDs-based solar cell. First of all, highly confined PbS QDs should be synthesized resulting in a narrow peak with a small full width-half maximum value at the first exciton transition observed in UV-Vis absorbance and photoluminescence spectra. In other words, the size-uniformity of NQDs ought to secure under 5%. Second, PbS NQDs should be assembled carefully in order to enhance the electronic coupling between adjacent NQDs by controlling the inter-QDs distance. Finally, appropriate structure for the photovoltaic device is the key issue to extract the photo-generated carriers from light-absorbing layer in solar cell. In this step, workfunction and Fermi energy difference could be precisely considered for Schottky and hetero junction device, respectively. In this presentation, we introduce the strategy to obtain high performance solar cell fabricated using PbS NQDs below the size of the Bohr radius. The PbS NQDs with various diameters were synthesized using methods established by Hines with a few modifications. PbS NQDs solids were assembled using layer-by-layer spin-coating method. Subsequent ligand-exchange was carried out using 1,2-ethanedithiol (EDT) to reduce inter-NQDs distance. Finally, Schottky junction solar cells were fabricated on ITO-coated glass and 150 nm-thick Al was deposited on the top of PbS NQDs solids as a top electrode using thermal evaporation technique. To evaluate the solar cell performance, current-voltage (I-V) measurement were performed under AM 1.5G solar spectrum at 1 sun intensity. As a result, we could achieve the power conversion efficiency of 3.33% at Schottky junction solar cell. This result indicates that high performance solar cell is successfully fabricated by optimizing the all steps as mentioned above in this work.