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Purity Evaluation of Ta Metal Refined by Ar/Ar-H₂ Plasma Arc Melting
임재원,Kouji Mimura,Minoru Isshiki,최국선 대한금속·재료학회 2008 METALS AND MATERIALS International Vol.14 No.4
The refining effect of Ar/Ar-H₂ plasma arc melting (PAM) was investigated and the purity of Ta metals was evaluated by glow discharge mass spectrometry (GDMS). Most impurities in the Ta metals were removed by Ar/Ar-H₂ PAM, down to a few mass ppm levels, and the purities of respective Ta metals refined by Ar/Ar-20 % PAM were improved up to 5N5 (99.9995 %) and 5N7 (99.99972 %). It was also found that the deoxidation reaction under hydrogen plasma condition is enhanced by a remarkable decrease in the oxygen concentration of the Ta metal refined by Ar-H₂ PAM.
홍상휘,문지훈,Kouji Mimura,Makoto Mikami,Masahito Uchikoshi,Minoru Isshiki 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.2
We have investigated the effect of annealing in an O2 atmosphere on the electrical properties of high-quality ZnO single crystals grown by seeded chemical vapor transport (SCVT). A temperature dependent Hall-effect technique indicates that the dominant donor in as-grown ZnO crystals has an ED of 42.8 meV and ND value of 2.8 × 1017 cm−3. After heat treatment in the O2 atmosphere at 1000 oC for 5 h, the color of the crystal changed from an orange color to transparent, and the ND value decreased to 4.3 × 1016 cm−3, while the ED value did not change. It can be deduced that the dominant donor in as-grown ZnO single crystals is a donor type native defect, which has a donor binding energy of about 42.8 meV.
배준우,임재원,김선중,Kouji Mimura,Takamichi Miyazaki,Masahito Uchikoshi,Minoru Isshiki 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.3
ZrO2 dielectric layers were prepared by a two-step process, a deposition of pure Zr film with and without a negative substrate bias voltage and a subsequent oxidation of the Zr films. We focused on the effect of the negative substrate bias voltage on the Zr film deposition and the subsequent oxidation of the Zr films. As a result, the Zr film deposited at the substrate bias voltage of −50 V (Vs = −50 V) was found to have a high intensity peak of Zr (100) and a uniform and smooth surface. From the capacitance-voltage and currentvoltage measurements of the ZrO2 films, a high dielectric constant of 21 and the equivalent oxide thickness (EOT) of 2.6 nm were obtained on the oxidation layer of the Zr film deposited at Vs = −50 V. On the other hand, a low dielectric constant of 15 and the EOT of 3.6 nm was obtained on that of the Zr film deposited at Vs = 0 V. The leakage current density of the ZrO2 film (Vs = −50 V) was 5.69×10−4A/cm 2, and this value was much lower than the 1.21×10−4A/cm 2for the ZrO2 film (Vs = 0 V). It was found that the two-step process by subsequent oxidation after film deposition using a negative substrate bias voltage is useful for obtaining high-quality dielectric layers.
임재원,Good-Sun Choi,Dmitri Elanski,Kouji Mimura,Minoru Isshiki 한국자원공학회 2007 Geosystem engineering Vol.10 No.1
Recently, hydrogen plasma arc melting (HPAM) has been expected to be a practical melting and refining technique for metals and alloys. The effect of H2 addition to the Ar plasma gas on the purification of metals and alloys has been described by possible chemical reactions of impurities with activated hydrogen atoms on a molten metal as well as the increase in temperature of a metal surface. Trace impurity concentration of refined metals is determined using glow discharge mass spectrometry (GDMS). This method is used to determine trace elements quantitatively because GDMS is a direct solid-state analytical method that uses no chemical process and provides reliable quantitative concentrations for most elements below 0.01 ppm. We reviewed the refining effect of HPAM for several metals by trace impurity analysis using GDMS.