• 대한금속재료학회지
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• 제50권6호
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• pp.445-448
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• 2012

We studied the effect of temperature and reaction time by investigating the various temperatures and reaction times in the reduction of molybdenum oxide ($MoO_3$) to molybdenum (Mo) powder in hydrogen gas. We also studied the effect of the reaction of reduction according to the various hydrogen gas flow rates. We surveyed the reduction from molybdenum oxide to molybdenum powder in hydrogen gas and checked two temperature ranges, one from $400^{\circ}C$ to $600^{\circ}C$ and the other from $700^{\circ}C$ to $900^{\circ}C$. We found that the reaction ratio of molybdenum oxide increased with an increasing temperature and also increased with an increasing reaction time, but hydrogen gas did not influence the reduction ratio of molybdenum oxide. We examined molybdenum powders fabricated by ball milling for two hours, using with X-ray diffraction (XRD) and a scanning electron microscopy (SEM).

• 열처리공학회지
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• 제24권1호
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• pp.31-36
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• 2011

$TiO_2$ films were deposited on a glass substrate with RF magnetron sputtering and then surface of $TiO_2$ films were electron beam irradiated in a vacuum condition to investigate the effect of electron bombardment on the thin film crystallization, surface roughness and gas sensitivity for hydrogen. $TiO_2$ films that electron beam irradiated at 450eV were amorphous phase, while the films irradiated at 900 eV show the anatase (101) diffraction peak in XRD pattern. AFM measurements show that the roughness is depend on the electron irradiation energy. As increase the hydrogen gas concentration and operation temperature, the gas sensitivity of $TiO_2$ and $TiO_2$/ZnO films is increased proportionally and $TiO_2$ films that electron beam irradiated at 900 eV show the higher sensitivity than the films were irradiated at 450eV. From the XRD pattern and AFM observation, it is supposed that the crystallization and rough surface promote the hydrogen gas sensitivity of $TiO_2$ films.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.250-250
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• 2011

Zinc oxide (ZnO) structures have great potential in many applications. Currently, the most commonly used method to grow ZnO nanostructres are the vapor transport method (VPT). The morphology of the ZnO structures largely related to the growth conditions, including growth temperature, distance between the substrate and source, and gas ambient. Previously ZnO nanosturecutres with high crystallinity were obtained at the growth temperature of 800$^{\circ}C$, in the argon and oxygen gas ambient. In this study, we report the properties of the ZnO nanostructures, which were synthesized on Au-catalyzed Si substrate by VPT, using a mixture of ZnO and graphite powders as source material under the different condition, including gas ratio of argon/oxygen and distance between substrate and source at the growth temperature of 800$^{\circ}C$. The structural and optical properties of the ZnO nanostructures were investigated by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and photoluminescence (PL).

• Bulletin of the Korean Chemical Society
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• 제32권5호
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• pp.1579-1582
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• 2011

Alumina particles wrapped in few-layer graphene sheets were prepared by calcining aluminum nitride powders under a mixed gas flow of carbon monoxide and argon. The graphene sheets were characterized by powder X-ray diffraction (XRD), Raman spectroscopy, electron energy loss spectroscopy, and high-resolution transmission electron microscopy. The few-layer graphene sheets, which wrapped around the alumina particles, did not exhibit any diffraction peaks in the XRD patterns but did show three characteristic bands (D, G, and 2D bands) in the Raman spectra. The dye-sensitized solar cell (DSSC) with the alumina particles wrapped in few-layer graphene sheets exhibited significantly improved overall energy-conversion efficiency, compared to conventional DSSC, due to longer electron lifetime.

• 한국표면공학회지
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• 제50권4호
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• pp.296-300
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• 2017

NiO nanofibers with Au nanoparticles were synthesized by sol-gel and electrospinning techniques, in which the reduction process by ultraviolet exposure is included for the growth of Au nanoparticles in the electrospinning solution. FE-SEM(Field Emission Scanning Electron Microscopy), TEM(Transmission Electron Microscopy) revealed that the synthesized nanofibers had the diameter of approximately 200 nm. X-ray diffraction showed the successful formation of Au-decorated NiO nanofibers. Gas sensing tests of Au-decorated NiO nanofibers were performed using reducing gases of CO, and $C_6H_6$, $C_7H_8$, $C_2H_5OH$. Compared to as-synthesized NiO nanofibers, the response of Au-loaded NiO nanofibers to CO gas was found to be about 3.4 times increased. On the other hand, the response increases were only 1.1-1.3 times for $C_6H_6$, $C_7H_8$, and $C_2H_5OH$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1304-1307
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• 1997

A hydrogen gas sensor utilizing Pt/$SnO_2$ system was fabricated by the pressed pellet method. The crystal structure, direction of the crystal, crystal size and microstructure between the catalyst and the support ($SnO_2$) were characterized with Electron Diffraction Analysis, Transmission Electron Microscopy, Scanning Electron Microscopy. After the reactor with a Pt/$SnO_2$ sample was run with a flow rate of 30sccm (a mixture of $0.5%H_2$ in $N_2$) for a while, the resistance of $SnO_2$ was saturated, but the $SnO_2$ kept absorbing $H_2$ gas. $H_2$ gas sensing properties of Pt/$SnO_2$ were investigated at several temperatures. As a result, it was observed that Pt/$SnO_2$ has high sensitivity at $300^{\circ}C$ and $400^{\circ}C$.

• The Korean Journal of Ceramics
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• 제4권1호
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• pp.20-24
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• 1998

Thin films of diamond-like carbon(DLC) can be successfully deposited by using a magnetron plasma chemical vapor deposition (CVD) method with an rf(13.56 MHz) plasma of $C_dH_8$. Plasma characteristics are analyzed as a function of the magnetic field. As the magnetic field increases, both electron temperature ($T_e$) and density ($n_e$)increase, but the negative dc self-bias voltage (-$V_{ab}$) decreases, irrespective of gas pressures in the range of 1~7 mTorr. High deposition rates have been obtained even at low gas pressures, which may be attributed to the increased mean free path of electrons in the magentron plasma. Effects of rf power and additive gas on the structural properties of DLC films aer also examined by using various technique namely, TED(transmissio electron diffraction) microanalysis, FTIR, and Raman spectroscopies.

• 한국분말재료학회지
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• 제6권2호
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• pp.171-177
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• 1999

Ti-45.2at.%Ni-5at.%Cu and Ti-40.2at.%Ni-10atat.%Cu alloy powders were fabricated by gas atomization process. The microstructures, Shape, hardness and phase transformation behaviors of the powders were investigated by means of optical microscopy, scanning electron microscopy, micro-hardness measurement, x-ray diffraction analyses and differential scanning calorimetry. The hardness of the Ti-Ni-XCu alloy powders decreased as Cu-content increased. The x-ray diffraction analyses were carried out for powders without heat treatment, and those that treated at 85$0^{\circ}C$ for an hour in a vaccum state($10^5$ torr) and then quenched into ice water. The intensity of B$19^t$ phase increased with heat treating. The monoclinic B$19^t$ martensite was formed in the Ti-Ni-XCu alloy powders during cooling.

• 방사선산업학회지
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• 제7권2_3호
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• pp.167-170
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• 2013

Lignin can be a valuable natural chemical resource. Structurally, lignin is a three-dimensional polymer made up of condensed C-C bonds and some ether linkages, most of which are not readily degraded. In this study, lignin carbonization under various electron beam pretreatment conditions was characterized through a thermogravimetric analysis (TGA), X-ray diffraction (XRD) and Raman spectroscopy. Lignin stabilization was controlled by various doses of electron beam irradiation corresponding to 50, 100, 200, 500 and 1,000 kGy; the carbonization process was performed under a nitrogen gas atmosphere at $1000^{\circ}C$ for 1 h. The TGA results showed that a 1,000 kGy lignin dose increased the residue weight from 39.96% to 45.23%, compared to non-irradiated lignin. This observation is in agreement with the XRD and Raman spectroscopy results, in which the two theta degrees and the degree of crystallization were improved by increasing the electron beam irradiation.

• 한국재료학회지
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• 제15권10호
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• pp.621-625
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• 2005

Effects of rf power, pressure, sputtering gas composition, and substrate temperature on the deposition rate of the $WC_x$ coatings were investigated. The effects of rf power and sputtering gas composition on the hardness and corrosion resistance of the $WC_x$ coatings deposited by reactive sputtering were also investigated. X-ray diffraction (XRD) and Auger electron spectroscopy (AES) analyses were performed to determine the structures and compositions of the films, respectively. The hardnesses of the films were investigated using a nanoindenter, scanning electron microscopy, ana a salt-spray test, respectively. The deposition rate of the films was proportional to rf power and inversely proportional to the $CH_4$ content of $Ar/CH_4$ sputtering gas. The deposition rate linearly increased with increasing chamber pressure. The hardness of the $WC_x$ coatings Increased as rf power increased. The highest hardness was obtained at a $Ar/CH_4$ concentration of $10 vol.\%$ in the sputtering gas. The hardness of the $WC_x$ film deposited under optimal conditions was found to be much higher than that of the electroplated chromium film, although the corrosion resistance of the former was slightly lower than that of the latter.