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Cho, Hyunyong,Kim, Jin Hee,Back, Song Yi,Ahn, Kyunghan,Rhyee, Jong-Soo,Park, Su-Dong Elsevier 2018 Journal of alloys and compounds Vol.731 No.-
<P><B>Abstract</B></P> <P>We investigated the thermoelectric properties of CuI-doped Bi<SUB>2</SUB>Te<SUB>2.7</SUB>Se<SUB>0.3</SUB> compounds, fabricated by a repetitive hot-deformation process. The degree of texture of the materials was enhanced by the number of hot-deformation processings, and experimentally verified by X-ray diffraction measurements. Very interestingly, the enhanced texture induced by the hot-deformation produced a moderate reduction in electrical resistivity by improving electron mobility, while the Seebeck coefficient remained almost unchanged. The corresponding power factor at room temperature was significantly improved, from 3.1 mW m<SUP>−1</SUP> K<SUP>−2</SUP> to 4.1 mW m<SUP>−1</SUP> K<SUP>−2</SUP> after two successive hot-deformation processings, and consequently a high value of Z T of 1.07 was achieved at 423 K. This demonstrates that tuning the texture of Bi<SUB>2</SUB>Te<SUB>3</SUB> based materials by multiple hot-deformation processing steps can be an effective approach for increasing Z T .</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigated thermoelectric properties the CuI-doped Bi<SUB>2</SUB>Te<SUB>2.7</SUB>Se<SUB>0.3</SUB> by hot-deformation. </LI> <LI> Anisotropic texture is enhanced by hot deformation process. </LI> <LI> CuI doping and enhanced texture improves electron mobility. </LI> <LI> CuI doping is effective to increase power factor by increasing carrier density. </LI> <LI> It achieved high power factor and high ZT 1.07 at 423 K in n-type materials. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
조주희(Juhee Cho),이현용(Hyunyong Lee),오홍석(Hongseok Oh),조상욱(Sanguk Cho),윤중석(Joongseok Yoon),김덕근(Deokgeun Kim) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.11_2
Regulations regarding auto exhausts are currently being strengthened all around the world. Increases in the price of oil and natural gas, the growth of concerns about the finite nature of reserves, and increasing awareness of the environmental damage caused by burning fossil fuels have all stimulated interest in next generation cars. Unlike vehicles today, these automobiles address environmental concerns by producing less emissions and pollution, while still holding many economical benefits, like high efficiency. Major car manufacturers are focusing on the development of tile EV (Electric Vehicle). FCEV (Fuel Cell Electric Vehicle) and HEV (Hybrid Electric Vehicle). Because HEV makes up for the weak points of EV and FCEV, HEV research is most common and most vigorous. As the technology of battery and electric motors improves, these electrical vehicles can be put into practical use. This paper focuses on the trend and technologic features of the motor that drives the HEV.
백송이,Hyunyong Cho,Seokyeong Byeon,진현규,이종수 한국물리학회 2020 Current Applied Physics Vol.20 No.9
We investigate the thermoelectric properties on Ga-excess p-type GaxBi0.4Sb1.6Te3 compounds. Even though the random distribution of Ga-doping increases electrical resistivity giving rise to the decrease of power factor, the significant decrease of lattice thermal conductivity by the excess Ga-doping induces significant enhancement of ZT value (1.13 at 350 K) for the Ga x ¼ 0.03 doped compound. From the X-ray diffraction and elemental mapping by energy dispersive X-ray spectroscopy, we observed Sb and Ga phase separation leading to the phonon scattering. The Sb precipitation implies atomic defect in the matrix which can induce short wavelength phonon scattering. The synergetic phonon scatterings from various scattering sources such as point defect, alloy scattering, and grain boundary phonon scattering have an important role in the enhancement of thermoelectric performance.
Kim, Jin Hee,Cho, Hyunyong,Yun, Jae Hyun,Back, Song Yi,Lee, Chang-Hoon,Shim, Jihoon,Rhyee, Jong-Soo Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.806 No.-
<P><B>Abstract</B></P> <P>We investigated thermoelectric properties of the CuI-doped (CuI)<SUB> <I>x</I> </SUB>Bi<SUB>2</SUB>Te<SUB>2.7</SUB>Se<SUB>0.3</SUB> bulk crystals grown by the Bridgman method. From the formation energy calculation and lattice parameter expansion along the <I>c</I>-axis, we confirm that the Cu-atom intercalates at the van der Waals layer while iodine substitutes at the Te(2) site which donates two electrons per CuI doping. The band structure calculation in iodine doped bismuth telluride monolayer shows band splitting along the momentum direction implying the Rashba type band splitting near the Fermi level. The Seebeck coefficient as a function of Hall carrier concentration on the compounds does not follow the Pisarenko's relation, whereas it follows the Rashba type Seebeck coefficient. The theoretical fitting with the Rashba type Seebeck coefficient indicates that the Rashba energy is increased with increasing CuI doping concentration. Owing to the enhancement of power factor near room temperature and reduction of lattice thermal conductivity by atomic scattering of phonon, the CuI doped compound (CuI)<SUB> <I>x</I> </SUB>Bi<SUB>2</SUB>Te<SUB>2.7</SUB>Se<SUB>0.3</SUB> ( x = 0.3 mol.%) exhibited high Z T value over a wide temperature range.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZT of the CuI-doped Bi<SUB>2</SUB>Te<SUB>2.7</SUB>Se<SUB>0.3</SUB> is enhanced over a wide temperature range. </LI> <LI> Rashba band formation by Iodine doping is suggested by theoretical calculation. </LI> <LI> Seebeck coefficient behavior corresponds to the Rashba band expectation. </LI> <LI> Rashba band splitting enhances power factor. </LI> <LI> It guides new principle to increase thermoelectric performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>We investigated thermoelectric properties of the CuI-doped (CuI)xBi2Te2.7Se0.3 bulk crystals grown by the Bridgman method. From the formation energy calculation and lattice parameter expansion along the c-axis, we confirm that the Cu-atom intercalates at the van der Waals layer while Iodine substitutes at the Te(2) site which donate two electrons per CuI doping. The band structure calculation in Iodine doped Bismuth Telluride monolayer shows band splitting along the momentum direction implying Rashba type band splitting near the Fermi level. The Seebeck coefficient as a function of Hall carrier concentration on the compounds does not follow the Pisarenko's relation whereas it follows the Rashba type Seebeck coefficient. The theoretical fitting with the Rashba type Seebeck coefficient indicates that the Rashba energy is increased with increasing CuI doping concentration. Owing to the enhancement of power factor near room temperature and reduction of lattice thermal conductivity by atomic scattering of phonon, the CuI doped compound (CuI)xBi2Te2.7Se0.3 (x = 0.3 mol.%) exhibited high ZT value over a wide temperature range.[Figure] Electronic band structure calculation of Iodine doped [Bi2Te3]1- (left) and Seebeck coefficient S as a function of Hall carrier concentration nH of the (CuI)xBi2Te2.7Se0.3 (red circle) and CuxBi2Te2.7Se0.3 (blue triangle) compounds. Solid lines are the calculation results from the Seebeck coefficient by Rashba band splitting (right).</P> <P>[DISPLAY OMISSION]</P>
Solvent-Assisted Gel Printing for Micropatterning Thin Organic–Inorganic Hybrid Perovskite Films
Jeong, Beomjin,Hwang, Ihn,Cho, Sung Hwan,Kim, Eui Hyuk,Cha, Soonyoung,Lee, Jinseong,Kang, Han Sol,Cho, Suk Man,Choi, Hyunyong,Park, Cheolmin American Chemical Society 2016 ACS NANO Vol.10 No.9
<P>While tremendous efforts have been made for developing thin perovskite films suitable for a variety of potential photoelectric applications such as solar cells, field-effect transistors, and photodetectors, only a few works focus on the micropatterning of a perovskite film which is one of the most critical issues for large area and uniform microarrays of perovskite-based devices. Here we demonstrate a simple but robust method of micropatterning a thin perovskite film with controlled crystalline structure which guarantees to preserve its intrinsic photoelectric properties. A variety of micropatterns of a perovskite film are fabricated by either microimprinting or transfer-printing a thin spin-coated precursor film in soft-gel state with a topographically prepatterned elastomeric poly(dimethylsiloxane) (PDMS) mold, followed by thermal treatment for complete conversion of the precursor film to a perovskite one. The key materials development of our solvent assisted gel printing is to prepare a thin precursor film with a high-boiling temperature solvent, dimethyl sulfoxide. The residual solvent in the precursor gel film makes the film moldable upon microprinting with a patterned PDMS mold, leading to various perovskite micropatterns in resolution of a few micrometers over a large area. Our nondestructive micropatterning process does not harm the intrinsic photoelectric properties of a perovskite film, which allows for realizing arrays of parallel-type photodetectors containing micropatterns of a perovskite film with reliable photoconduction performance. The facile transfer of a micropatterned soft-gel precursor film on other substrates including mechanically flexible plastics can further broaden its applications to flexible photoelectric systems.</P>
Jang, Houk,Kim, Jaeseok,Kim, Min-Seok,Cho, Jeong Ho,Choi, Hyunyong,Ahn, Jong-Hyun American Chemical Society 2014 NANO LETTERS Vol.14 No.12
<P>The anomalous piezoresistance (a-PZR) effects, including giant PZR (GPZR) with large magnitude and inverse PZR of opposite, have exciting technological potentials for their integration into novel nanoelectromechanical systems. However, the nature of a-PZR effect and the associated kinetics have not been clearly determined yet. Even further, there are intense research debates whether the a-PZR effect actually exists or not; although numerous investigations have been conducted, the origin of the effect has not been clearly understood. This paper shows the existence of a-PZR and provides direct experimental evidence through the performance of well-established electrical measurements and terahertz spectroscopy on silicon nanomembranes (Si NMs). The clear inverse PZR behavior was observed in the Si NMs when the thickness was less than 40 nm and the magnitude of the PZR response linearly increased with the decreasing thickness. Observations combined with electrical and optical measurements strongly corroborate that the a-PZR effect originates from the carrier concentration changes via charge carrier trapping into strain-induced defect states.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-12/nl503186u/production/images/medium/nl-2014-03186u_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl503186u'>ACS Electronic Supporting Info</A></P>
백색왜성 PG1159-035 광도측정 데이터에 관한 통계적 패턴분석
박석윤,이순기,정현용,김규영,조한석,김석,박민우 충남대학교 기초과학연구소 2000 忠南科學硏究誌 Vol.27 No.2
This study approached the characteristic of dwarf star through time series analysis, and compared observations with the pattern of them, using ACF and Periodogram.
박석윤,정기영,박래현,이낙영,이석훈,이주호,김주한,김홍기,김종우,조한석,정현용,김재문,한상익,전양환,이민선 충남대학교 기초과학연구소 1999 忠南科學硏究誌 Vol.26 No.2
With the correct equipment, microvolt EEG signals can be recorded from the scalp. Their potential use for diagnosis of physiological and psychiatric diseases and for increasing our understanding of cognitive processes is being realized by current research in many fields. Our work focuses on the research for good EEG signal representations and on careful analysis classification results using statistical EEG analysis(SEEG).