• Progress in Medical Physics
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• v.12 no.1
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• pp.95-102
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• 2001

The intracavitary cones were designed which were made of stainless steel and have scratched inside cone to be generated electron scatter and designed to be attached easily to the LINAC collimator and controlled cones length to be contacted smoothly between the patient and the cone tip. Two types of intracavitary cones were designed. One is the straight end cones with circular opening on the distal end and the other is 30 degree beveled end cones with elliptical opening on the distal end. Each type of intracavitary cone ranged in daimeter from 2.5 cm to 3.5 cm and required a separate set of lower trimmer annulias cone diameter. The film phantom was designed with an internal cassette that accurately aligned the film edge with the film phantom surface. Film optical density data were measured by photodensitometer(Wellhofer 700i) Dosimetry measurements were made to commission the LINAC for 6 - 20 MeV electron using the intracavitary cones. Isodose curves were measured for all energy and cones combinations. Output is defined as the maximum dose per MU along the clinical central axis in water at 113 cm SSD. Calibration output, defined to be the output for the 15cm$\times$15cm diameter straight cone, was adjusted to 1.00 cGy/MU at each energy according to the TG-21 protocol.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.344-344
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• 2014

Transparent amorphous oxide semiconductors such as a In-Ga-Zn-O (a-IGZO) have advantages for large area electronic devices; e.g., uniform deposition at a large area, optical transparency, a smooth surface, and large electron mobility >10 cm2/Vs, which is more than an order of magnitude larger than that of hydrogen amorphous silicon (a-Si;H).1) Thin film transistors (TFTs) that employ amorphous oxide semiconductors such as ZnO, In-Ga-Zn-O, or Hf-In-Zn-O (HIZO) are currently subject of intensive study owing to their high potential for application in flat panel displays. The device fabrication process involves a series of thin film deposition and photolithographic patterning steps. In order to minimize contamination, the substrates usually undergo a cleaning procedure using deionized water, before and after the growth of thin films by sputtering methods. The devices structure were fabricated top-contact gate TFTs using the a-IGZO films on the plastic substrates. The channel width and length were 80 and 20 um, respectively. The source and drain electrode regions were defined by photolithography and wet etching process. The electrodes consisting of Ti(15 nm)/Al(120 nm)/Ti(15nm) trilayers were deposited by direct current sputtering. The 30 nm thickness active IGZO layer deposited by rf magnetron sputtering at room temperature. The deposition condition is as follows: a rf power 200 W, a pressure of 5 mtorr, 10% of oxygen [O2/(O2+Ar)=0.1], and room temperature. A 9-nm-thick Al2O3 layer was formed as a first, third gate insulator by ALD deposition. A 290-nm-thick SS6908 organic dielectrics formed as second gate insulator by spin-coating. The schematic structure of the IGZO TFT is top gate contact geometry device structure for typical TFTs fabricated in this study. Drain current (IDS) versus drain-source voltage (VDS) output characteristics curve of a IGZO TFTs fabricated using the 3-layer gate insulator on a plastic substrate and log(IDS)-gate voltage (VG) characteristics for typical IGZO TFTs. The TFTs device has a channel width (W) of $80{\mu}m$ and a channel length (L) of $20{\mu}m$. The IDS-VDS curves showed well-defined transistor characteristics with saturation effects at VG>-10 V and VDS>-20 V for the inkjet printing IGZO device. The carrier charge mobility was determined to be 15.18 cm^2 V-1s-1 with FET threshold voltage of -3 V and on/off current ratio 10^9.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.271-272
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• 2012

Bulk Metallic Glasses (BMGs or amorphous alloy) exhibit high strength and good corrosion resistance. Applications of thin films and micro parts of BMGs have been used a lot since its inception in the research of BMGs. However, Application and fabrication of BMGs are limited to make structural materials. Thin films of BMGs which is sputtered on the surface of structural materials by sputtering process is used to improve limits about application of BMGs. In order to investigate the difference of properties between designed alloys and thin films, we identified that thin films deposited on the surface that have the characteristic of the amorphous films and the composition of designed alloys. Zr-Cu (Cu=30, 35, 38, 40, 50 at.%) and Zr-Cu-Al (Al=10 at.% fixed, Cu=26, 30, 34, 38 at.%) alloys were fabricated with Zr (99.7% purity), Cu (99.997% purity), and Al (99.99% purity) as melting 5 times by arc melting method before rods 2mm in diameter was manufactured. In order to analyze GFA (Glass Forming Ability), rods were observed by Optical Microscopy and SEM and $T_g$, $T_x$, ($T_x$ is crystallization temperature and $T_g$ is the glass transition temperature) and Tm were measured by DTA and DSC. Powder was manufactured by Gas Atomizer and target was sintered using powder in large supercooled liquid region ($=T_x-T_g$) by SPS(Spark Plasma Sintering). Amorphous foil was prepared by RSP process with 5 gram alloy button. The composition of the foil and sputtered thin film was analyzed by EDS and EPMA. In the result of DSC curve, binary alloys ($Zr_{62}Cu_{38}$, $Zr_{60}Cu_{40}$, $Zr_{50}Cu_{50}$) and ternary alloys ($Zr_{64}Al_{10}Cu_{26}$, $Zr_{56}Al_{10}Cu_{34}$, $Zr_{52}Al_{10}Cu_{38}$) have $T_g$ except for $Zr_{70}Cu_{30}$ and $Zr_{60}Al_{10}Cu_{30}$. The compositions with $T_g$ made into powders. Figure shows XRD data of thin film showed similar hollow peak.

• Korean Journal of Optics and Photonics
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• v.17 no.3
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• pp.278-284
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• 2006

We have fabricated and measured electrooptic modulator using coupled stack InAs/InGaAs quantum dots. The height of the quantum dot is 16 nm and quantum dots are stacked including an InGaAs capping layer. The peak wavelength of photoluminescence is 1260 nm at room temperature and 1158 nm at 12 K. The operation characteristics of the quantum dots show high modulation efficiency of electrooptic modulator at 1550 nm compared to that of existing III-V bulk and MQW type semiconductor. The measured switching voltage ($V\pi$) is 540 and 600 mV, for TE mode and TM mode, respectively. From the results, the modulation efficiency can be determined as 333.3 and $300^{\circ}/V{\cdot}mm$ for TE and TM modes. The results reported here may lead to the design and fabrication of a novel electrooptic modulator with low switching voltage and high efficiency.

• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.248-253
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• 2005

We designed and fabricated a compact multi-mode interference (MMI) wavelength demultiplexer using the concept of 'Improved Quasi-State' modes. The output power and extinction ratio were improved by utilizing modal phase error which is specially occurred in low-index contrast. For a designed demultiplexer, the mode propagation analysis with effective index approximation shows significant improvement of extinction ratio to -25 dB for both $1.31{\mu}m\;and\;1.51{\mu}m$ wavelength region and the split-length was reduced about 1/5 of other MMI devices. The fabricated device shows successful characteristics for both 1.31 and $1.55{\mu}m$ wavelengths. These results demonstrate the potential of low-index materials system and the embossing process for photonic integrated circuits.

• Korean Journal of Optics and Photonics
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• v.18 no.1
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• pp.1-7
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• 2007

Filter colorimeters have a set of spectral bands for which spectral responsivity is the same as the color matching function defined by CIE (Commission Internationale de I'Eclairage). We have designed a set of color matching function filters denoted by $\bar{x}-filter,\;\bar{y}-filter,\;and\;\bar{z}-filter$. Because the $\bar{x}-function$ has two transmission bands, two $\bar{x}-filters$ are designed to cover the $\bar{x}-function$. To design the filters, we developed a nonlinear least square fit program which determines the thickness of the color glasses by minimizing its spectral mismatch value ($f{_1}'$) to below 3 %. The design has been validated by fabrication of the $\bar{y}-bar$ filter, of which $f{_1}'$ was measured to be 2.8 %. Considering a LCD flat panel display as a device under test, we have calculated the systematic error of the colorimetric measurement using the designed filters.

• Korean Journal of Optics and Photonics
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• v.23 no.3
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• pp.124-127
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• 2012

We designed and fabricated dichroic filters for high-power fiber lasers to protect the pumping laser diode from counterpropagating laser beams. The transmittance at laser diode wavelengths of 905 nm~925 nm was designed to be less than 0.1% and the transmittance at the fiber laser or Brillouin scattering wavelengths of 1020 nm ~ 1100 nm was designed to be more than 99.9%. Since oxide materials have good adhesion to the $SiO_2$ substrate, $SiO_2/Ta_2O_5$ were used as coating materials. The filter was fabricated according to our optimized design and its characteristics were compared with the theoretical design. As a result, the transmittance at laser diode wavelengths of 905 nm~925 nm was measured to be less than 0.1%, and the transmittance at the fiber laser or Brillouin scattering wavelengths of 1020 nm~1100 nm was measured to be more than 95.5%, which coincided well with the theoretical design considering processing errors. The filter was found to operate well over 1W of input laser power.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.588-588
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• 2013

Nanoscale noble-metals have attracted enormous attention from researchers in various fields of study because of their unusual optical properties as well as novel chemical properties. They have possible uses in diverse applications such as devices, transistors, optoelectronics, information storages, and energy converters. It is well-known that nanoparticles of noble-metals such as silver and gold show strong absorption bands in the visible region due to their surface-plasmon oscillation modes of conductive electrons. Silver nanocubes stand out from various types of Silver nanostructures (e.g., spheres, rods, bars, belts, and wires) due to their superior performance in a range of applications involvinglocalized surface plasmon resonance, surface-enhanced Raman scattering, and biosensing. In addition, extensive efforts have been devoted to the investigation of Gold-based nanocomposites to achieve high catalytic performances and utilization efficiencies. Furthermore, as the catalytic reactivity of Silver nanostructures depends highly on their morphology, hollow Gold nanoparticles having void interiors may offer additional catalytic advantages due to their increased surface areas. Especially, hollow nanospheres possess structurally tunable features such as shell thickness, interior cavity size, and chemical composition, leading to relatively high surface areas, low densities, and reduced costs compared with their solid counterparts. Thus, hollow-structured noblemetal nanoparticles can be applied to nanometer-sized chemical reactors, efficient catalysts, energy-storage media, and small containers to encapsulate multi-functional active materials. Silver nanocubes dispersed in water have been transformed into Ag@Au nanoboxes, which show highly enhanced catalytic properties, by adding $HAuCl_4$. By using this concept, $SiO_2$-coated Ag@Au nanoboxes have been synthesized via galvanic replacement of $SiO_2$-coated Ag nanocubes. They have lower catalytic ability but more stability than Ag@Au nanoboxes do. Thus, they could be recycled. $SiO_2$-coated Ag@Au nanoboxes have been found to catalyze the degradation of 4-nitrophenol efficiently in the presence of $NaBH_4$. By changing the amount of the added noble metal salt to control the molar ratio Au to Ag, we could tune the catalytic properties of the nanostructures in the reduction of the dyes. The catalytic ability of $SiO_2$-coated Ag@Au nanoboxes has been found to be much more efficient than $SiO_2$-coated Ag nanocubes. Catalytic performances were affected noteworthily by the metals, sizes, and shapes of noble-metal nanostructures.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.4
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• pp.164-167
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• 2010

Bulk GaN single crystal with 1.5 mm thickness was successfully grown by hydride vapor phase epitaxy (HVPE) technique. Free-standing GaN substrates of $10{\times}10,\;15{\times}15$ mm size were fabricate after lift-off of sapphire substrate and their optical properties were characterized properties for device applications. X-ray diffraction patterns showed (002) and (004) peak, and the FWHM of the X-ray rocking curve (XRC) measurement in (002) was 98 arcsec. A sharp photoluminescence spectrum at 363 nm was observed and defect spectrum at visible range was not detected. The hexagonal-shaped etch-pits are formed on the GaN surface in $200^{\circ}C\;H_3PO_4$ at 5 minutes. The defect density calculated from observed etch-pits on surface was around $5{\times}10^6/cm^2$. This indicates that the fabricated GaN substrates can be used for applications in the field of optodevice, and high power electronics.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.1
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• pp.43-52
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• 2010

Glass was fabricated by using refused coal ore obtained from Dogye coal mine in Samchuk. We additionally used soda ash and calcium carbonate as raw materials to make a glass with the chemical composition of soda-lime glass. And the properties of glass were measured when limestone was used as natural raw materials instead of calcium carbonate as chemical raw materials. Transparent glass was fabricated by melting raw materials at $1550^{\circ}C$ for 1 hr in an electrical furnace. The various kinds of glass samples were fabricated according to the kinds of refused coal ore and glass cullet. The optical properties of transmittance and color chromaticity were measured by UV/VIS/NIR spectrometer and the thermal properties of thermal expansion coefficient and softening point were measured. Transparent glass with the transmittance of over 70% in visible range was fabricated by using normal refused coal ore and black colored glass with the transmittance of 0~35% was fabricated by using shel1 type refused coal ore. Therefore, it is concluded that refused coal ore can be used for raw materials to manufacture secondary glass products such as a glass tile and foamed glass panel for construction material.