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Hydrogen incorporation induced the octahedral symmetry variation in VO<sub>2</sub> films
Lee, Dooyong,Kim, Hyegyeong,Kim, Ji Woong,Lee, Ik Jae,Kim, Yooseok,Yun, Hyung-Joong,Lee, Jouhahn,Park, Sungkyun Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.396 No.-
<P><B>Abstract</B></P> <P>This study examined the microscopic aspects of macroscopic physical property variations of hydrogen annealed VO<SUB>2</SUB> films, deposited on Al<SUB>2</SUB>O<SUB>3</SUB>(0001) substrates by RF magnetron sputtering. The temperature-dependent electrical resistivity showed that the as-grown film exhibited a metal-insulator-transition (MIT) at 55.20°C and 49.26°C during heating and cooling, respectively. On the other hand, no MIT was observed for the film annealed under a hydrogen environment. Spectroscopic measurements during the <I>in-situ</I> hydrogenation process showed that hydrogen annealing (∼0.3mbar, up to 300°C) promoted the V<SUP>3+</SUP> state above 100°C. Raman spectroscopy and X-ray diffraction confirmed that the as-grown film changed from a monoclinic to rutile structure during hydrogen annealing. In addition, the shift of the (020) diffraction peak position of the hydrogen-annealed film to a lower angle compare to that of the known rutile VO<SUB>2</SUB> film was attributed to the expansion of the unit cell. In addition, local structure analysis showed that an increase in octahedral symmetry after hydrogen annealing is one of the main explanations for the metallic characteristics of the hydrogen-annealed film.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Metal-insulator-transition disappeared after hydrogenation. </LI> <LI> Hydrogen incorporated into VO2 occurred at the low temperature (∼100°C). </LI> <LI> Hydrogen incorporation causes structural change from monoclinic to rutile. </LI> <LI> Reduced octahedron symmetry with hydrogen incorporation is related to the vanishing MIT characteristics. </LI> </UL> </P>
Lee, Dooyong,Kim, Jiwoong,Cho, Chang-Woo,Bae, Jong-Seong,Won, Jonghan,Lee, Jouhahn,Park, Sungkyun Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.447 No.-
<P><B>Abstract</B></P> <P>The asymmetric response of the cation distribution on [001] oriented CoFe<SUB>2</SUB>O<SUB>4</SUB> films were examined. Depending on the deposition temperature and substrates (MgO(0 0 1) or SrTiO<SUB>3</SUB>(0 0 1)), the films exhibited a range of compressive or tensile strain states along the out-of-plane. With increases in deposition temperature, the initial compressive (tensile) strain for the films grown on MgO(0 0 1) (SrTiO<SUB>3</SUB>(0 0 1)) was reduced. Furthermore, the out-of-plane (in-plane) magnetic anisotropy of the film grown on MgO(0 0 1) (SrTiO<SUB>3</SUB>(0 0 1)) decreased with increasing deposition temperature. The uniaxial magnetic anisotropy energy calculation based on the magnetic anisotropy (crystalline and shape) and strain of films confirmed that the strain reduction with increasing deposition temperature is the main source of the uniaxial magnetic anisotropy reduction, regardless of the sign of the strain. X-ray photoelectron spectroscopy explained the saturation magnetization variation by the cation distribution depending on the strain state. Furthermore, the calculated magnetic moment based on the cation distribution were well matched for the high crystalline films.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Epitaxial strain is reduced as the growth temperature is increased. </LI> <LI> Out-of-plane tensile trained films exhibit in-plane magnetic anisotropy. </LI> <LI> Uniaxial magnetic anisotropy energy decreases with decreasing out-of-plane strain. </LI> <LI> Depending on the strain state the opposite behavior of the cation distribution occurred. </LI> <LI> Variation of the saturation magnetization is related to the cation distribution. </LI> </UL> </P>
Lee, Dooyong,Williams, D.J.,Vogel, S.C.,Proffen, Th,Thompson, J.D.,Daemen, L.L.,Park, Sungkyun Elsevier 2016 Current Applied Physics Vol.16 No.9
<P>A series of transition metal NixCo1-x(N(CN)(2))(2) dicyanamide molecular magnet, 0 <= x <= 1, was chemically synthesized. Structure and magnetic properties were investigated by IR spectroscopy, neutron powder diffraction and temperature-dependent magnetization measurement. The neutron powder diffraction measurement established that all samples showed the rutile structure with Pnnm space group. The detailed Rietveld refinement results revealed a systematic decrease of unit-cell volume with increasing Ni content. We also observed a concurrent increase of the Curie temperature with Ni content due to the increase of superexchange interaction. (C) 2016 Elsevier B.V. All rights reserved.</P>
A case of acute organic solvent poisoning during epoxy coating
Sujin Lee,Inah Kim,Dooyong Park,Jaechul Song,Sang Gil Lee 대한직업환경의학회 2019 대한직업환경의학회지 Vol.31 No.-
Background: In the construction industry, maintaining health and safety of workers often challenging. Among the workers at construction sites, painters are at particular risk of respiratory diseases and neurotoxicity. However, in Korea there is weak enforcement of workers" health and safety practices in the construction industry in Korea. Poisonings frequently occur at (semi)closed construction sites. In this study, we report a case of acute organic solvent poisoning during construction site painting. Case presentation: A 71-year-old man was found unconscious at a construction site and immediately transferred to the emergency room. The consciousness level was "stupor state" and the body temperature was hypothermic, at 32 degrees (Celsius). There were no acute brain or cardiac lesions that would have accounted for the faintness. In addition, blood and urine tests did not indicate a cause of loss of consciousness. He had been painting epoxy to waterproof the basement floor before fainting. According to exposure simulation, the patient was overexposed to various organic solvents, such as approximately 316–624 ppm toluene during the work before fainting. Considering the ventilation status of the workplace and the status of no protection, it is considered that exposure through the respiratory tract was considerable. Conclusions: The patient in this case lost consciousness during the epoxy coating in a semi-enclosed space. It can be judged as a result of acute poisoning caused by organic solvent exposure and considered to be highly related to work environment.
The effect of fe2+ state in electrical property variations of sn‐doped hematite powders
Song, Sehwan,Kim, Jiwoong,Lee, Dooyong,Lee, Jisung,Min, Taewon,Chae, Jong‐,Ah,Bae, Jong‐,Seong,Lee, Jaekwang,Lee, Jeong‐,Soo,Park, Sungkyun Wiley-Blackwell 2017 Journal of the American Ceramic Society Vol.100 No.9