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Yoon S.,Seoul National University | Kwon O.-J.,Seoul National University | Jung M.-J.,Seoul National University | Yoo J.,Seoul National University | And 3 more authors.
Powder Diffraction | Year: 2011

Ca3-xSrxCo4O9 with different compositions (x = 0, 0.15, 0.3, and 0.45) were synthesized from stoichiometric mixtures of Co3O4, CaCO3, and SrCO3, and their unit-cell parameters were determined. The powders were mixed with silicon standard powder, and XRD patterns were collected and analyzed using TOPAS. The compounds were determined to be monoclinic with space group of P2. Unit-cell parameters changed from a = 4.8329(3) Å, b = 4.5727(1) Å, c = 10.8360(4) Å, and β = 98.093(7)° when x = 0, to a = 4.8432(1) Å, b = 4.6100(3) Å, c = 10.8668(3) Å, and β = 98.110(5)° when x = 0.3. An unidentified second phase was observed when x = 0.45. © 2011 International Centre for Diffraction Data.

Park J.-W.,Seoul National University | Kim K.-S.,Seoul National University | Hwang N.-M.,Seoul National University | Hwang N.-M.,Research Institute of Advanced Materials
Carbon | Year: 2016

A possibility for the new synthesis method of diamond nanoparticles is studied using a hot filament chemical vapor deposition (HFCVD) reactor. Considering the growth mechanism of diamonds at low pressure from the well-known observation of simultaneous diamond deposition and graphite etching without violating the second law of thermodynamics, diamond nanoparticles should be generated in the gas phase. To confirm the generation of diamond nanoparticles in the gas phase under the synthesis condition of diamond films by HFCVD, the transmission electron microscope (TEM) grid membrane was exposed for 3-15 s using a capturing apparatus and the grid membrane was observed by TEM. The number density of captured nanoparticles increased with increasing capture time whereas the size of them was changed only slightly. In addition, to confirm whether the nanoparticles are electrically charged or not, the electric bias was applied to the stainless steel plate placed below the holder of the TEM grid. The positive bias increased the number density of nanoparticles whereas the negative bias decreased it, indicating that nanoparticles are negatively charged. The TEM images showed that the captured nanoparticles had a diameter of 4-6 nm and 0.206 nm of crystalline lattice spacing, which indicates the {111} plane of diamond. © 2016 Elsevier Ltd.

Yang S.J.,Research Institute of Advanced Materials | Yang S.J.,Seoul National University | Park C.R.,Research Institute of Advanced Materials | Park C.R.,Seoul National University
Advanced Materials | Year: 2012

A straightforward method for significantly improving the moisture resistance of MOFs is described. In the proposed method, MOFs are subjected to thermal treatment, thus inducing the formation of an amorphous carbon coating on the MOF surfaces that prevents hydrolysis. This approach should open up new practical applications for MOFs in areas hitherto unexplored due to concerns regarding moisture sensitivity. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Im J.H.,Research Institute of Advanced Materials | Im J.H.,Seoul National University | Kang E.,Soongsil University | Yang S.J.,Research Institute of Advanced Materials | And 5 more authors.
Bulletin of the Korean Chemical Society | Year: 2014

Thermal degradation of titanium-containing metal-organic frameworks (MOFs; MIL-125 and MIL-125-NH2 at 350°C for 6 h in air produced TiO 2 nanoparticles of ca. 10 nm in diameter. Scanning electron and transmission electron microscope analyses indicated that those nanoparticles were aggregated randomly within each crystalline particle of their MOF precursors. The TiO2 nanoparticles prepared from MIL-125-NH 2 exhibited higher activity for the degradation of 4-chlorophenol under visible light.

Chang J.,Research Institute of Advanced Materials | Lee J.-W.,Research Institute of Advanced Materials | Kim S.-K.,Research Institute of Advanced Materials
Journal of Crystal Growth | Year: 2010

We successfully grew SrFeO3-δ thin films in a layer-by-layer manner by pulsed laser deposition (PLD). When the SrFeO3-δ films were directly grown on atomically flat Ti4+-terminated SrTiO3 (1 1 1) substrates, the oscillatory reflection-high-energy-electron-diffraction intensity was completely damped after its third oscillation. By contrast, the introduction of SrRuO3 buffer layers onto the SrTiO3 substrates allowed the SFO thin films to grow in a layer-by-layer manner over a far-extended thickness range. The probable mechanism of that growth is electronic reconstruction-reduced electrostatic potential divergence. With that result, the present study provides a means of growing pseudocubic (1 1 1)-oriented SrFeO3-δ heterointerfaces, making possible the fabrication of high-functionality oxide heterostructures. © 2009 Elsevier B.V. All rights reserved.

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