• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.175-175
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• 2003

ZnO 박막은 그 동안 어려운 문제로 여겨진 p형 도핑방법이 점차 알려 지면서 발광소자 적용 가능성이 주목받고 있다. ZnO는 발광 스펙트럼(PL) 피크의 날카로움, 높은 exciton 결합에너지, 습식식각의 가능, 벽개면 형성의 용이함 및 동종 기판 적용 가능 등의 본질적인 장점을 지니고 있어 재현성있는 p형 도핑방법 기술이 확립된다면 이를 이용한 발광소자 적용 시 기존의 질화물계에 비하여 우수한 소자 제조 가능성이 있다. 이에 따라 국내외에서 ZnO 박막제조에 관련된 많은 연구들이 진행되고 있다. 특히 ZnO 박막을 발광소자로 적용하기 위해서는 고품질의 에피탁시 박막을 성장시켜야 하며 이를 위하여 MBE, MOCVD, PLD법 등 다양한 에피탁시 박막증착이 시도되고 있다. 또한 보다 양질의 ZnO 박막을 성장시키기 위해 적절한 단결정 기판 및 버퍼층의 탐색과 각 기판에 따른 ZnO 박막의 물성평가 작업도 국내외의 여러 연구그룹에서 진행되고 있다.

• Korean Journal of Materials Research
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• v.25 no.6
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• pp.265-268
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• 2015

ZnO micro/nanocrystals at large scale were synthesized through the thermal evaporation of Al-Zn mixtures under air atmosphere. The effect of synthetic temperature and time on the morphology of the micro/nanocrystals was examined. It was found that the temperature and time affected the morphology of the ZnO crystals. At temperatures below $900^{\circ}C$, no crystals were synthesized. At a temperature of $1000^{\circ}C$, ZnO crystals with a rod shape were synthesized. With an increase in temperature from $1000^{\circ}C$ to $1100^{\circ}C$, the morphology of the crystals changed from rod shape to wire and granular shapes. As the time increased from 2 h to 3 h at $1000^{\circ}C$, tetrapod-shaped ZnO crystals started to form. XRD patterns showed that the ZnO crystals had a hexagonal wurtzite structure. EDX analysis revealed that the ZnO crystals had high purity. It is believed that the ZnO nanowires were grown via a vapor-solid mechanism because no catalyst particles were observed at the tips of the micro/nanocrystals in the SEM images.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.155-156
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• 2006

Single crystalline ZnO fims were successfully grown on r-plane sapphire substrate by plasma-assisted molecular beam epitaxy. Epitaxial relationship between the ZnO film and the-r-plane sapphire was determined to be [-1101]$Al_2O_3\;{\parallel}$ [0001]ZnO, [11-20]$Al_2O_3\;{\parallel}$ [-1100]ZnO based on the in-situ RHEED analysis and confirmed again by HRXRD measurements. Grown (11-20) ZnO films showed faceted structure along the <0001> direction and the RMS roughness was about 4 nm.

• Metals and materials international
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• v.24 no.6
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• pp.1241-1248
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• 2018

The reactive wetting behaviors of molten Zn-Al-Mg alloys on MnO- and amorphous (a-) $SiO_2$-covered steel sheets were investigated by the sessile drop method, as a function of the Al and Mg contents in the alloys. The sessile drop tests were carried out at $460^{\circ}C$ and the variation in the contact angles (${\theta}_c$) of alloys containing 0.2-2.5 wt% Al and 0-3.0 wt% Mg was monitored for 20 s. For all the alloys, the MnO-covered steel substrate exhibited reactive wetting whereas the $a-SiO_2$-covered steel exhibited nonreactive, nonwetting (${\theta}_c>90^{\circ}$) behavior. The MnO layer was rapidly removed by Al and Mg contained in the alloys. The wetting of the MnO-covered steel sheet significantly improved upon increasing the Mg content but decreased upon increasing the Al content, indicating that the surface tension of the alloy droplet is the main factor controlling its wettability. Although the reactions of Al and Mg in molten alloys with the $a-SiO_2$ layer were found to be sluggish, the wettability of Zn-Al-Mg alloys on the $a-SiO_2$ layer improved upon increasing the Al and Mg contents. These results suggest that the wetting of advanced high-strength steel sheets, the surface oxide layer of which consists of a mixture of MnO and $SiO_2$, with Zn-Al-Mg alloys could be most effectively improved by increasing the Mg content of the alloys.

• Journal of Magnetics
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• v.13 no.1
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• pp.19-22
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• 2008

ZnO nanotips, grown on c-$Al_2O_3$ and quartz, were implanted variously with 200 keV Fe or Mn ions to a dose level of $5{\times}10^{16}cm^{-2}$. The magnetic properties of these samples were measured using a superconducting quantum interference device (SQUID) magnetometer. Fe-implanted ZnO nanotips grown on c-$Al_2O_3$ showed a coercive field width of 209 Oe and a remanent field of 12% of the saturation magnetization ($2.3{\times}10^{-5}emu$) at 300K for a sample annealed at $700^{\circ}C$ for 20 minutes. The field-cooled and the zero-field-cooled magnetization measurements also showed evidence of ferromagnetism in this sample with an estimated Curie temperature of around 350 K. The Mn-implanted ZnO nanotips grown on c-$Al_2O_3$ showed superparamagnetism resulting from the dominance of a spin-glass phase. The ZnO nanotips grown on quartz and implanted with Fe or Mn showed signs of ferromagnetism, but neither was consistent.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.314-314
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• 2008

The low temperature sintering and the dielectric properties of $Al_2O_3/SiO_2$-zinc borosilicate glass composites were investigated in the view of the application for LTCC. When the sintering was conducted at $900^{\circ}C$ $ZnAl_2O_4$ and $ZnB_2O_4$ compounds formed at the $Al_2O_3$-rich and the $SiO_2$-rich compositions, respectively. The reaction between ZBS glass and $Al_2O_3/SiO_2$ caused the formation of these compounds. The $Al_2O_3/SiO_2$ ratio affected the dielectric properties. The excellent dielectric properties, i.e., Q$\times$f value= 40,000 GHz and ${\varepsilon}_r$=4.5, were obtained in the $Al_2O_3/SiO_2$-ZBS glass system and fabricated the LTCC substrate materials.

• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.560-565
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• 2003

M-doped (M=Al, Ni) ZnO thermoelectric materials were fully densified at low temperatures of 800∼1,000$^{\circ}C$ and their sintering characteristics and microstructural features were investigated. Electron microscopic analysis showed that the addition of NiO promoted tile formation of solid solution and caused actively grain growth. The addition of A1$_2$O$_3$ prevented the evaporation of pure ZnO at grain boundaries and suppressed the grain growth by the formation of secondary phase. In case of the addition of A1$_2$O$_3$ together with NiO, the specimen showed an excellent microstructure and also the SEM-EBSP (Electron Back-scattered Diffraction Pattern) analysis confirmed that it shows a superior grain boundary distribution to the others specimens. These microstructural characteristics induced by the addition of A1$_2$O$_3$ together with NiO may increase the electrical conductivity by the increase in carrier concentration and decrease the thermal conductivity by the phonon scattering effect and, consequently, improve the thermoelectric property.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.245-246
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• 2012

Al 농도를 0 부터 2 at.% 까지 조절하여 도핑된 $Cd_{0.5}Zn_{0.5}O$ 박막을 석영 기판 위에 성장하였다. Al 도핑된 $Cd_{0.5}Zn_{0.5}O$ 박막의 구조적, 광학적 특성을 조사하기 위해 field-emission scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), 그리고 ultraviolet-visible (UV) spectroscopy을 사용하였다. 광학적 밴드갭은 Al 도핑 농도가 증가함에 따라 2.874 (0 at.%), 2.874 (0.5 at.%), 3.029 (1.0 at.%), 3.038 (1.5 at.%), 3.081 eV (2.0 at.%)로 증가하였다. Urbach energy는 도핑 농도에 따라 각각 464 (0 at.%), 585 (0.5 at.%), 571 (1.0 at.%), 600 (1.5 at.%), 470 meV (2.0 at.%)이었다. 또한, Al 농도가 증가함에 따라 $Cd_{0.5}Zn_{0.5}O$ 박막의 표면, 구조적 및 광학적 특성이 크게 변화되었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.969-972
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• 2004

Al doped Zinc Oxide(ZnO:Al) films, which is widely used as a transparent conductor in optoelectronic devices such as solar cell, liquid crystal display, plasma display panel, thermal heater, and other sensors, were prepared by using the capacitively coupled DC magnetron sputtering method. In this paper the effect of doping amounts of $Al_2O_3$ on the electrical, optical and morphological properties were investigated experimentally, The results show that the structural and electrical properties of the film are highly affected by the doping. The optimum growth conditions were obtained for films doped with 2 wt% of Al203 which exhibit a resistivity of $8.5{\times}10^{-4}{\Omega}-cm$ associated with a transmittance of 91.7 % for 840 nm in film thickness in the wavelength range of the visible spectrum.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.6
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• pp.905-912
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• 2011

In this study, the novel concept catalytic reactor was designed for water-gas shift reaction (WGS) under high pressure. The novel concept catalytic reactor was composed of an autoclave, the catalyst, and liquid water. Cu-ZnO/$Al_2O_3$ as the low temperature shift catalyst was used for WGS reaction. WGS in the novel concept catalytic reactor was carried out at the ranges of 150~$250^{\circ}C$ and 30~50 atm. The liquid water was filled at the bottom of the autoclave catalytic reactor and the catalyst of pellet type was located at the gas-liquid water interface. It was concluded that WGS reaction occurred over the surface of catalysts partially wetted with liquid water. The conversion of CO for WGS was also controlled with changing content of Cu and ZnO used as the catalytic active components. Meanwhile, the catalyst of honey comb type coated with Cu-ZnO/$Al_2O_3$ was used in order to increase the contact area between wet-surface of catalyst and the reactants of gas phase. It was confirmed from these experiments that $H_2$/CO ratio of the simulated coal gas increased from 0.5 to 0.8 by WGS at gas-liquid water interface over the wet surface of honey comb type catalyst at $250^{\circ}C$ and 50 atm.