• Journal of the Korean Vacuum Society
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• v.20 no.5
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• pp.339-344
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• 2011

The Ohmic contact of Ti/Au metals on n-type ZnO thin film deposited on c-plane sapphire substrates by pulsed laser deposition was investigated by TLM (transfer length method) patterns. The Ti/Au metal films with thickness of 35 nm and 90 nm were deposited by electron-beam evaporator and thermal evaporator, respectively. By using the photo-lithography method, the $100{\times}100{\mu}m^2$ TLM patterns with $6{\sim}61{\mu}m$ gaps were formed. To improve the electrical properties as well as to decrease an interface states and stress between metal and semiconductor, the post-annelaing process was done in oxygen ambient by rapid thermal annealing system at temperature of $100{\sim}500^{\circ}C$ for 1 min. In this study, it appeared that the minimum specific contact resistivity shows about $1.1{\times}10^{-4}{\Omega}{\cdot}cm^2$ in $300^{\circ}C$ annealed sample, which may be originated from formation of oxygen vacancies of ZnO during an oxidation of Ti metal at the interface of Ohmic contacts.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.342-343
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• 2013

AlSb is a promising material for optical devices, particularly for high-frequency and nonlinear-optical applications. And AlSb offers significant potential for devices such as quantum-well lasers, laser diodes, and heterojunction bipolar transistors. In this work we study molecular beam epitaxy (MBE) growth of an unstrained AISb film on a GaAs substrate and identify the real-time monitoring capabilities of in situ spectroscopic ellipsometry (SE). The samples were fabricated on semi-insulating (0 0 1) GaAs substrates using MBE system. A rotating sample stage ensured uniform film growth. The substrate was first heated to $620^{\circ}C$ under As2 to remove surface oxides. A GaAs buffer layer approximately 200 nm- thick was then grown at $580^{\circ}C$. During the temperature changing process from $580^{\circ}C$ to $530^{\circ}C$, As2 flux is maintained with the shutter for Ga being closed and the reflection high-energy electron diffraction (RHEED) pattern remaining at ($2{\times}4$). Upon reaching the preset temperature of $530^{\circ}C$, As shutter was promptly closed with Sb shutter open, resulting in the change of RHEED pattern from ($2{\times}4$) to ($1{\times}3$). This was followed by the growth of AlSb while using a rotating-compensator SE with a charge-coupled-device (CCD) detector to obtain real-time SE spectra from 0.74 to 6.48 eV. Fig. 1 shows the real time measured SE spectra of AlSb on GaAs in growth process. In the Fig. 1 (a), a change of ellipsometric parameter ${\Delta}$ is observed. The ${\Delta}$ is the parameter which contains thickness information of the sample, and it changes in a periodic from 0 to 180o with growth. The significant change of ${\Delta}$ at~0.4 min means that the growth of AlSb on GaAs has been started. Fig. 1b shows the changes of dielectric function with time over the range 0.74~6.48 eV. These changes mean phase transition from pseudodielectric function of GaAs to AlSb at~0.44 min. Fig. 2 shows the observed RHEED patterns in the growth process. The observed RHEED pattern of GaAs is ($2{\times}4$), and the pattern changes into ($1{\times}3$) with starting the growth of AlSb. This means that the RHEED pattern is in agreement with the result of SE measurements. These data show the importance and sensitivity of SE for real-time monitoring for materials growth by MBE. We performed the real-time monitoring of AlSb growth by using SE measurements, and it is good agreement with the results of RHEED pattern. This fact proves the importance and the sensitivity of SE technique for the real-time monitoring of film growth by using ellipsometry. We believe that these results will be useful in a number of contexts including more accurate optical properties for high speed device engineering.

• Journal of Animal Science and Technology
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• v.44 no.1
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• pp.113-122
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• 2002

Beef loins that retailed in market were used as experimental samples. Some beef samples in raw state were packaged with PVDC as aerobic and vacuum condition. The other beef samples were cooked until core temperature arrived at 70$^{\circ}C$ and then packaged immediately in the same way of raw samples. After these samples were irradiated by electron beam 6kGy, irradiated samples were stored in refrigerator(2～4$^{\circ}C$). Identify and quantity of cholesterol oxides were analysed stored at 0 and 7 days, respectively. During the early stage of storage, 7$\beta$-hydroxycholesterol and 7-ketocholesterol were respectively produced from the raw meat samples, and the production of these chemicals were significantly higher (P$<$0.05) from the meats with aerobic packaging than those with vacuum packaging. With the passage of storage time, 7$\alpha$-hydroxycholesterol, 20$\alpha$-hydroxycholesterol, $\beta$-epoxide, $\beta$-epoxide and some other chemicals, which were not produced during the early stage of storage, were produced, Also, the production of these chemicals were significantly increased (P$<$0.05) with the passage of storage time. Cooked meat after irradiation and irradiated meat after cooking produced cholesterol on the 7th day of storage, although this chemical was not produced during the early stage of storage. Production of cholesterol oxides was significantly increased (P$<$0.05) with the passage of storage time for all treatments, and showed significantly lower value (P$<$0.05) with the vacuum packaging than aerobic packaging. Summarizing the aforementioned results, it was found that the production of cholesterol oxides was more easily affected by packaging condition than irradiation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.3
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• pp.578-584
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• 2017

$SiO_2$ buffer layer (100 nm) has been deposited on PET substrate by electron beam evaporation. And then, IZTO (In-Zn-Sn-O) thin film has been deposited on $SiO_2$/PET substrate with different RF power of 30 to 60 W, working pressure, 1 to 7 mTorr, by RF magnetron sputtering. Structural, electrical and optical properties of IZTO thin film have been analyzed with various RF powers and working pressures. IZTO thin film deposited on the process condition of 50 W and 3 mTorr exhibited the best characteristics, where figure of merit was $4.53{\times}10^{-3}{\Omega}^{-1}$, resistivity, $4.42{\times}10^{-4}{\Omega}-cm$, sheet resistance, $27.63{\Omega}/sq.$, average transmittance (400-800 nm), 81.24%. As a result of AFM, all the IZTO thin film has no defects such as pinhole and crack, and RMS surface roughness was 1.147 nm. Due to these characteristics, IZTO thin film deposited on $SiO_2$/PET structure was found to be a very compatible material that can be applied to the next generation flexible display device.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.1
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• pp.20-26
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• 2001

Titanium boride ($\textrn{TiB}_{x}$) films were deposited on (100) silicon substrates at the substrate temperature of $500^{\circ}C$ by means of the co-evaporation of titanium and boron evaporants during deposition. The co-evaporation method makes it possible to deposit the non-stoichiometric films with different boron-to-titanium ratio($0{\le}B/Ti \le 2.5$). The resistivity increases linearly as the boron-to-titanium ratio in the as-deposited films is increased. The surface roughness of $\textrn{TiB}_{x}$ films is changed as a function of the boron-to-titanium ratio. The XRD spectrum for pure titanium film shows a highly (002) preferred orientation. For B/Ti=0.59 ratio only a single TiB phase that shows a (111) preferred orientation is observed. However, the $\textrn{TiB}_{x}$ phase with the hexagonal structure of the $AlB_2$(C32) type appears as the boron concentration increase, and only a single $\textrn{TiB}_{x}$ phase is observed for $B/Ti \ge 2.0$ ratio. The $\textrn{TiB}_{x}$/Si samples reveal a tensile stress (3~$20{\times}^9$dyn/$\textrm{cm}^2$) in the overall composition of the films, although the magnitude of the residual stresses is depended on the nominal B/Ti ratio.

• Korean Journal of Materials Research
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• v.10 no.1
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• pp.77-82
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• 2000

A surface of polytetrafluoroethylene(PTFE) was modified with changing ion doses by 1 keV $Ar^+$ ion irradiation and Cu films having thickness $5000\;{\AA}$ were deposited on the modified PTFE. The SEM study showed that the surface texture of modified PTFE was in the form of cones whose height increased depending on ion doses. Through XPS spectra, it was found that the intensity of F ls peaks decreased with ion doses by preferential sputtering of F atoms and the C-C and / or C-F chains were formed by the crosslinking in the newly unstable chains. Cu films were deposited uniformly along the filaments formed on the modified PTFE. In x-ray diffraction (XRD) spectra of deposited Cu films on modified PTFE, a preferred orientation along (111) and (200) planes was found and the peak intensity of (111) plane increased as surface roughness of modified PTFE increased. The resistivity of Cu films was changed from $2.7{\mu}{\Omega}cm$ of unmodified PTFE to $4.3{\mu}{\Omega}cm$ of modified PTFE at ion dose of $1{\times}10^{16}/\textrm{cm}^2$ and the abrupt increase of resistivity in the modified PTFE at ion dose of $1{\times}10^{17}/\textrm{cm}^2$ was due to being cut off the film which resulted from the increased surface roughness.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.11-11
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• 2010

Thin-film-transistors (TFTs) that can be deposited at low temperature have recently attracted lots of applications such as sensors, solar cell and displays, because of the great flexible electronics and transparent. Transparent and flexible transistors are being required that high mobility and large-area uniformity at low temperature [1]. But, unfortunately most of TFT structures are used to be $SiO_2$ as gate dielectric layer. The $SiO_2$ has disadvantaged that it is required to high driving voltage to achieve the same operating efficiency compared with other high-k materials and its thickness is thicker than high-k materials [2]. To solve this problem, we find lots of high-k materials as $HfO_2$, $ZrO_2$, $SiN_x$, $TiO_2$, $Al_2O_3$. Among the High-k materials, $Al_2O_3$ is one of the outstanding materials due to its properties are high dielectric constant ( ~9 ), relatively low leakage current, wide bandgap ( 8.7 eV ) and good device stability. For the realization of flexible displays, all processes should be performed at very low temperatures, but low temperature $Al_2O_3$ grown by sputtering showed deteriorated electrical performance. Further decrease in growth temperature induces a high density of charge traps in the gate oxide/channel. This study investigated the effect of growth temperatures of ALD grown $Al_2O_3$ layers on the TFT device performance. The ALD deposition showed high conformal and defect-free dielectric layers at low temperature compared with other deposition equipments [2]. After ITO was wet-chemically etched with HCl : $HNO_3$ = 3:1, $Al_2O_3$ layer was deposited by ALD at various growth temperatures or lift-off process. Amorphous InGaZnO channel layers were deposited by rf magnetron sputtering at a working pressure of 3 mTorr and $O_2$/Ar (1/29 sccm). The electrodes were formed with electron-beam evaporated Ti (30 nm) and Au (70 nm) bilayer. The TFT devices were heat-treated in a furnace at $300^{\circ}C$ and nitrogen atmosphere for 1 hour by rapid thermal treatment. The electrical properties of the oxide TFTs were measured using semiconductor parameter analyzer (4145B), and LCR meter.

• Journal of the Korean Society of Food Science and Nutrition
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• v.38 no.1
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• pp.121-124
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• 2009

This study was conducted to investigate the reason for the increase in the antioxidant activity of cooking drip from Enteroctopus dofleini by gamma and electron-beam irradiation. To define the effect of irradiation on the antioxidant activity of polyphenol in cooking drip, polyphenol excluded cooking drip extracts were prepared with polyclar$^{TM}$. But, the antioxidant activity of the cooking drip extracts without polyphenol was still increased by both irradiations. Instead, the effect on the proteins in the cooking drips prepared by ammonium sulfate precipitation showed great increase in antioxidative activity by irradiation. From these results, it was concluded that the increase in the antioxidative activity in cooking drips by the irradiation was caused by the structural modification of proteins in the cooking drips.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.418-421
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• 2002

Fundamental study on quasi-monochromatic parallel radiography using a polycapillary plate and a plane-focus x-ray tube is described. The x-ray generator consists of a negative high-voltage power supply, a filament (hot cathode) power supply, and an x-ray tube. The negative high-voltage is applied to the cathode electrode, and the transmission type target (anode) is connected to the ground potential. The maximum voltage and current of the power supply were -100 kV (peak value) and 3.0 mA, respectively. In this experiment, the tube voltage was regulated from 20 to 25 kV, and the tube current was regulated by the filament temperature and ranged from 1.0 to 3.0 mA. The exposure time is controlled in order to obtain optimum film density, and the focal spot diameter was about 10 mm. The polycapillary plate is J5022-21 made by Hamamatsu Photonics Inc., and the outside and effective diameters are 87 and 77 mm, respectively. The thickness and the hole diameter of the polycapillary are 1.0 mm and 25 ${\mu}$m, respectively. The x-rays from the tube are formed into parallel beam by the polycapillary, and the radiogram is taken using an industrial x-ray film of Fuji IX 100 without using a screen. In the measurement of image resolution, we employed three brass spacers of 2, 30, and 60 mm in height. By the test chart, the resolution fell according to increases in the spacer height without using a polycapillary. In contrast, the resolution slightly fell with corresponding increases in the height by the polycapillary. In angiography, fine blood vessels of about 100 ${\mu}$m are clearly visible.

• Applied Chemistry for Engineering
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• v.3 no.1
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• pp.88-99
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• 1992

For the development of semiconducting photoelectrode to be more stable and efficient in the process of photoelectrolysis of the water, pure titanium rods were oxidized by anodic oxidation, furance oxidation and flame oxidation and used as electrodes. The Indium islands were formed by electrodeposition of "In" thin film on $TiO_2$ and Ti by electrodeposition. Also $A1_2O_3$ and NiO islands were coated on Ti by the electron-beam evaporation technique. The maximum photoelectrochemical conversion efficiency(${\eta}$) was 0.98% for flame oxidized electrode($1200^{\circ}C$ for 2min in air). Anodically oxidized electrodes have photoelectrochemical conversion efficiency of 0.14%. Furnace oxidized electrode($800^{\circ}C$ for 10min in air) has 0.57% of photoelectrochemical efficiency and shows a band-gap energy of about 2.9eV. The $In_2O_3$ coated $TiO_2$ exhibits 0.8% of photoelectrochemical efficiency but much higher value of ${\eta}$ was obtained with the Increase of applied blas voltage. However, $Al_2O_3$ or NiO coated $TiO_2$ shows much low value of ${\eta}$. The efficiency was dependent on the presence of the metallic interstitial compound $TiO_{0+x}$(x<0.33) at the metal-semiconductor interface and the thickness of the suboxide layer and the external rutile scale.