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MBE growth of ZnO Epilayers with Annealed Initial Zn Layers and its Properties
Ghun Sik Kim,Min Su Kim,Do Yeob Kim,Su Min Jeon,Min Young Cho,Hyun Young Choi,Jae Min Lim,Ji Hoon Kim,Dong-Yul Lee,Joo In Lee,Sung Dong Park,Eundo Kim,Myong Hyo Jung,Do-Weon Hwang,Jae-Young Leem 한국진공학회 2009 한국진공학회 학술발표회초록집 Vol.37 No.-
Kim, Ghun Sik,Lee, Byung Yong,Ham, Hyung Chul,Han, Jonghee,Nam, Suk Woo,Moon, Jooho,Yoon, Sung Pil Pergamon Press 2019 International journal of hydrogen energy Vol.44 No.1
<P><B>Abstract</B></P> <P>Biofuels such as sewage gas and landfill gas, which can be used as fuels in solid oxide fuel cells, have suitable composition of CH<SUB>4</SUB> and CO<SUB>2</SUB> for dry reforming. We developed an Sr<SUB>0.92</SUB>Y<SUB>0.08</SUB>Ti<SUB>1−x</SUB>Ru<SUB>x</SUB>O<SUB>3−d</SUB> material as an anode for solid oxide fuel cells that use biofuels as a direct fuel and show an excellent performance in dry reforming. The Pechini method was used to synthesize the material using ruthenium substitution in the titanium site of an Sr<SUB>0.92</SUB>Y<SUB>0.08</SUB>TiO<SUB>3−d</SUB> (SYT) material. X-ray diffraction analysis confirmed that the perovskite phase of the synthesized catalyst was maintained. Ruthenium-loaded catalysts were prepared by coprecipitating ruthenium onto SYT to compare with the Sr<SUB>0.92</SUB>Y<SUB>0.08</SUB>Ti<SUB>1−x</SUB>Ru<SUB>x</SUB>O<SUB>3−d</SUB>. The differences between Sr<SUB>0.92</SUB>Y<SUB>0.08</SUB>Ti<SUB>1−x</SUB>Ru<SUB>x</SUB>O<SUB>3−d</SUB> and ruthenium-loaded SYT materials during methane dry reforming and the thermal stability during long-term operation were evaluated. In particular, SYTRu10 exhibited higher methane conversion and carbon dioxide conversion than Ru10-loaded SYT at the temperature range of 600–900 °C and stable performance even in long-term operation. X-ray fluorescence and Brunauer–Emmett–Teller measurements were performed to measure the composition of the catalysts and the specific surface area, pore size, and pore volume of the catalysts. X-ray photoelectron spectroscopy and temperature-programmed reduction were used to investigate the state and behavior of ruthenium. Furthermore, transmission electron microscopy was performed to analyze the shape of the catalyst before and after the reaction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High and stable CH<SUB>4</SUB> dry reforming activity for Ru-doped Sr<SUB>0.92</SUB>Y<SUB>0.08</SUB>TiO<SUB>3−d</SUB> (SYT) perovskite catalyst. </LI> <LI> Comparison of dry reforming performance between Ru-doped SYT and Ru-loaded SYT. </LI> <LI> Effect of the Ru exsolution phenomenon in the Ru-doped SYT during the dry reforming of CH<SUB>4</SUB>. </LI> </UL> </P>
Effects of thermal annealing in oxygen plasma for buffer layers on properties of ZnO thin films.
Kim, Ghun Sik,Kim, Min Su,Choi, Hyun Young,Cho, Min Young,Yim, Kwang Gug,Leem, Jae-Young American Scientific Publishers 2011 Journal of Nanoscience and Nanotechnology Vol.11 No.10
<P>ZnO thin films with ZnO buffer layers were grown by plasma-assisted molecular beam epitaxy (PA-MBE) on p-type Si(100) substrates. Before the growth of the ZnO thin films, the ZnO buffer layers were deposited on the Si substrates for 20 minutes and then annealed at the different substrate temperature ranging from 600 to 800 degrees C in oxygen plasma. The structural and optical properties of the ZnO thin films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and room-temperature (RT) photoluminescence (PL). A narrower full width at half maximum (FWHM) of the XRD spectra for ZnO(002) and a larger grain are observed in the samples with the thermal annealed buffer layers in oxygen plasma, compared to those of the as-grown sample. The surface morphology of the samples is changed from rugged to flat surface. In the PL spectra, near-band edge emission (NBEE) at 3.2 eV (380 nm) and deep-level emission (DLE) around 1.77 to 2.75 eV (700 to 450 nm) are observed. By increasing the annealing temperatures up to 800 degrees C, the PL intensity of the NBEE peak is higher than that of the as-grown sample. These results imply that the structural and optical properties of ZnO thin films are improved by the annealing process.</P>
Hermawan, Erik,Sang Lee, Gyun,Sik Kim, Ghun,Chul Ham, Hyung,Han, Jonghee,Pil Yoon, Sung Elsevier 2017 CERAMICS INTERNATIONAL Vol.43 No.13
<P><B>Abstract</B></P> <P>A densification process based on chemical/electrochemical vapor deposition (CVD/EVD) was successfully performed to produce a dense and gas-tight YSZ electrolyte on a metal support for solid oxide fuel cell applications. Micro Ni/YSZ (7:3wt%) was deposited by screen printing and YSZ was deposited by an atmospheric plasma spray (APS) process on a metal support prior to the CVD/EVD refinement process. The initial nitrogen permeation flux through the YSZ layer prepared by the APS process was in the range of 1.8–2.7×10<SUP>−7</SUP> mol/scm<SUP>2</SUP> at 25°C, which shows that residual pores/pinholes existed in the YSZ layer. After YSZ density refinement by the CVD/EVD process, a dense and gas-tight YSZ layer can be obtained after five hours of deposition. An additional 4–7µm of YSZ was observed after the refinement process was finished. The average film growth rate during CVD/EVD was approximately 1.14µm/h. From XRD analysis, the YSZ layer prepared after CVD/EVD showed a dominant cubic structure; nonetheless, a secondary phase was also observed. From the SEM and elemental mapping analyses, the YSZ layers showed a homogeneous distribution on the surface of the metal support. The present results showed that the CVD/EVD process is capable of refining the YSZ electrolyte density/tightness by plugging residual pores/pinholes, along with increasing the YSZ thickness, for application in metal-supported solid oxide fuel cells.</P>