• Journal of the Korean Magnetics Society
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• v.16 no.3
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• pp.163-167
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• 2006

Ultrasonic irradiation in a solution during the chemical reaction may accelerate the rate of the reaction and the crystallization at low temperature. We have synthesized nanometer sized magnetite particles using coprecipitation method, sonochemical method without surfactant, and sonochemical method with surfactant, in order to investigate the effect of ultrasonic irradiation and surfactant on the coprecipitates of metal ions. The size of the magnetite nanoparticles prepared by coprecipitation method, and sonochemical method without surfactant showed broad distributions. But we got uniform nanoparticles using a sonochemical method with oleic acid. The average size of the particles can be controlled by the ratio $R=[H_2O]/[surfactant]$. The size of the magnetite nanoparticles prepared by this method showed narrow distributions. We have characterized the nanoparticles using an X-ray diffraction (XRD), a superconducting quantum interference device (SQUID), and atomic force microscope (AFM). The size and distribution of the magnetite nanoparticles were measured by dynamic light scattering (DLS) method.

• Journal of Korean Ophthalmic Optics Society
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• v.9 no.1
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• pp.35-41
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• 2004

This study investigated the crystal growth, crystalline structure and the basic optical properties of $PbSnSe/BaF_2$ epilayers. The PbSnSe epilayer was grown on $BaF_2$(111) insulating substrates using a hot wall epitaxy (HWE) technique. It was found from the analysis of X-ray diffraction patterns that $PbSnSe/BaF_2$ epilayer was grown single crystal with a rock-salt structure oriented along [111] the growth direction. Using Rutherford back scattering, the atomic ratios of the PbSnSe was found to be proper stoichiometric. The best values for the full width at half maximum (FWHM) of the DCXRD was 162 arcsec for PbSnSe epilayer. The epilayer-thickness dependence of the FWHM of the DCXRD shows that the quality of the $PbSnSe/BaF_2$ is as expected. The dielectric function ${\varepsilon}(E)$ of a semiconductor is closely related to its electronic energy band structure and such relation can be drawn from features around the critical points(CPs) in the optical spectra. The real and imaginary parts(${\varepsilon}1$ and ${\varepsilon}2$) of the dielectric function ${\varepsilon}$ of PbSe were measured, and the observed spectra reveal distinct structures at energies of the E1, E2 and E3 CPs. These data are analyzed using a theoretical model known as the model dielectric function (MDF). The optical constants related to dielectric function such as the complex refractive index ($n^*=n+ik$), absorption coefficient (${\alpha}$) and normal-incidence reflectivity (R) are also presented for $PbSnSe/BaF_2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.249-249
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• 2009

We have grown large area BSTO($(Ba_{1-x}Sr_x)TiO_3$) thin films (x=0.4) on 2 inch diameter MgO (001) single crystal substrates using a pulse laser deposition(PLD) system. Substrate temperature and oxygen pressure in the deposition chamber, and the laser optics for ablating a target have been controlled to obtain the uniform thickness and preferred orientation of the films. Results of x-ray diffraction and rocking curve analysis revealed that the BSTO films were grown on MgO substrates with a preferred orientation (002), and the full width half maximum of the rocking curve was measured to be 0.86 degree at optimum condition. Roughness of the films have been measured to be $3.42{\AA}$ rms by using atomic force microscopy. We have successfully deposited the large area BSTO thin films of $4000{\AA}$ thickness on 50 mm diameter MgO substrates.

• Journal of the Korean Vacuum Society
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• v.10 no.3
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• pp.380-386
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• 2001

A nuclear microprobe system with adjustable precision object slits and a magnetic quadrupole doublet was designed by the beam optics simulation using a first order matrix formalism, and installed in a $30^{\circ}$ beam line connected with KIGAM 1.7 MV Tandem VDG Accelerator. Demagnification factors for x and y axis are calculated to be 25 and 4.9, respectively, and a minimum beam spot side is expected to be about 5 $\mu\textrm{m}$ for 3 MeV proton beams with a current of about 1 nA. A multi-purpose octagonal target chamber has been built to facilitate MeV ion-beam analytical techniques of PIXE, RBS, ERDA, and ion beam micro-machining. It contains X-ray and particle detectors, a zoom microscope, a Faraday cup, a 4-axis sample manipulator and a high vacuum pumping system. The system performance of the nuclear microprobe is now being tested, and automatic manipulator control and data acquisition system will be installed for routine applications of micro ion-beam analytical techniques.

• Korean Journal of Optics and Photonics
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• v.25 no.4
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• pp.216-220
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• 2014

We have synthesized a $CaMgSi_2O_6:Eu^{2+}$ blue phosphor via a solid-state reaction method. The $CaMgSi_2O_6:Eu^{2+}$ phosphor has monoclinic structure with a space group of C2/c (15), and an emission band peaking at 450 nm (blue) due to the $4f^7-4f^65d$ transition of the $Eu^{2+}ion$. The emission intensity at $100^{\circ}C$ is 54% of the value at room temperature. A white LED was fabricated by integrating a UV LED (400 nm) with our blue phosphor plus two commercial green and red phosphors. The white LED shows a color temperature of 3500 K with a color rendering index of 87 (x = 0.3936, y = 0.3605), and a luminous efficiency of 18 lm/W. The white LED shows a luminance maintenance of 97% after operation at 350 mA for 400 hours at $85^{\circ}C$.

• Journal of the Korean Solar Energy Society
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• v.31 no.2
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• pp.82-88
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• 2011

The artificial increase in the solar intensity incident on solar cells using lenses or mirrors can allow solar cells to generate equivalent power with a lower cost. There are two types of concentration optics for solar energy conversion. One is to use mirrors, and the other is to use Fresnel lenses. The gains that can be achieved with a Fresnel lens or a parabolic mirror are compared. The result showed the gains are comparable and the two configurations were developed competitively. In application areas of Fresnel lenses as solar concentrators, several variations of design were devised and tested. Some PV systems still use commercially available flat Fresnel lenses as concentrators. A convex linear Fresnel lens to improve the concentration ratio and the efficiency is devised and flat linear Fresnel lens in thermal energy collection is utilized. In this study, we designed and optimized flat Fresnel lens and the 'light pipe' to develop 500X concentrated solar PV system. In the process, we compare the transmission efficiencies according to groove types. We performed rigorous ray tracing simulation of the flat Fresnel lenses. The computer aided simulation showed the 'grooves in case' has the better efficiency than that of 'grooves out case'. Based on the ray-trace results we designed and manufactured sample Fresnel lenses. The optical performance were measured and compared with ray-trace results. Finally, the optical efficiency was measured to be above 75%. All the design and manufacturing were performed based on that InGaP/InGaAs/Ge triple junction solar cell is used to convert the photon energy to electrical power. Field test will be made and analyzed in the near future.

• Journal of the Korean Magnetics Society
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• v.17 no.2
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• pp.71-75
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• 2007

Ultrasonic irradiation in a solution during the chemical reaction may accelerate the rate of the reaction and the crystallization at low temperature. We have synthesized nanometer sized zinc ferrite particles using chemical co-precipitation technique through a sonochemical method with surfactant such as oleic acid. The thermal behaviour of the zinc ferrite was determined by the thermoanalytical techniques (TGA-DSC). Powder X-ray diffraction measurements show that the samples have the spinel structure. Magnetic properties measurement were performed using a superconducting quantum interference device (SQUID) magnetometer.

• Journal of the Korean Society of Radiology
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• v.12 no.1
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• pp.17-22
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• 2018

Multilayer mirrors are optical elements that can replace single crystal optical elements such as silicon or germanium, and they have artificial diffraction plane of a thickness of several nanometers. We examined the first Bragg angle and the reduction of reflectivity by variation of layer thickness in a W/Si multilayer mirror of small d-spacing. A W/Si multilayer mirror for an incidence angle of $0.55^{\circ}$ and an energy of 17.5 keV was designed and showed a maximum reflectivity of 72.67%. When the thickness of tungsten or silicon layer was simultaneously changed, the first Bragg angle was shifted and the reflectivity was reduced. When there was a change in thickness for one layer of W/Si multilayer, no change in the reflectivity was showed but the unevenness of the envelope was observed. Reduction of reflectivity was also observed at random Gaussian thickness variations. It is possible to predict the tolerance of multilayer mirror by examining the reflectivity degradation according to the thickness change in the W/Si multilayer mirror of small d-spacing.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.420-420
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• 2012

ZnO seed layer were deposited on quartz substrate by sol-gel method and prism-like Al-doped ZnO nanorods (AZO nanorods) were grown on ZnO seed layer by hydrothermal method with various Al concentration ranging from 0 to 2.0 at.%. Structural and optical properties of the AZO nanorods were investigated by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), photoluminescence (PL). The diameter of the AZO nanorods was smaller than undoped ZnO nanorods and its diameter of the AZO nanorods decreased with increasing Al concentration. In XRD spectrum, it was observed that stress and full width at half maximum (FWHM) of the AZO nanorods decreased and the 'c' lattice constant increased as the Al concentration increased. From undoped ZnO nanorods, it was observed that the green-red emission peak of deep-level emission (DLE) in PL spectra. However, after Al doping, not only a broad green emission peak but also a blue emission peak of DLE were observed.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.285-285
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• 2011

EUVL (Extreme Ultra Violet Lithography) is one of competitive lithographic technologies for sub-30nm fabrication of nano-scale Si devices that can possibly replace the conventional photolithography used to make today's microcircuits. Among the core EUVL technologies, mask fabrication is of considerable importance since the use of new reflective optics having a completely different configuration compared to those of conventional photolithography. Therefore new materials and new mask fabrication process are required for high performance EUVL mask fabrication. This study investigated the etching properties of SnO2 (Tin Oxide) as a new absorber material for EUVL binary mask. The EUVL mask structure used for etching is SnO2 (absorber layer) / Ru (capping / etch stop layer) / Mo-Si multilayer (reflective layer) / Si (substrate). Since the Ru etch stop layer should not be etched, infinitely high selectivity of SnO2 layer to Ru ESL is required. To obtain infinitely high etch selectivity and very low LER (line edge roughness) values, etch parameters of gas flow ratio, top electrode power, dc self - bias voltage (Vdc), and etch time were varied in inductively coupled Cl2/Ar plasmas. For certain process window, infinitely high etch selectivity of SnO2 to Ru ESL could be obtained by optimizing the process parameters. Etch characteristics were measured by on scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses. Detailed mechanisms for ultra-high etch selectivity will be discussed.