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1,431 results on '"Kim, Sang-il"'

118. Characteristics of Rhombohedral (3R) Structure of α-In2Se3 Nanosheets by Mechanical Exfoliation.

Author

Seo, Dong Hyun, Kim, Ju Won, Seong, Jin-Hoo, Lee, Hyo-Chang, Kim, Sang-il, and Kim, TaeWan

Abstract

The mechanically exfoliated ultrathin 3R α-In2Se3 nanosheets were transferred onto a SiO2/Si substrate. Using atomic force microscopy, it was confirmed that the transferred α-In2Se3 transferred had a thickness of 15–120 nm. The thickness-dependence of Raman peaks of E 2 , A 1 1 , E 4 , and A 1 2 was observed from the Raman spectra. Moreover, the measured photoluminescence peak values in the range of 869–895 nm indicate a blue shift as the thickness decreases. The field-effect transistor based on α-In2Se3 exhibited an n-type semiconductor behavior. From the transfer curve at gate voltage of 10 V, the derived values of the mobility and ON/OFF ratio are 24.26 cm2 V− 1 s− 1 and 1.84, respectively. In addition, it was confirmed that the 3R α-In2Se3 layers had a high photoresponsivity of up to approximately 34,500 A/W under illumination (λ = 750 nm). [ABSTRACT FROM AUTHOR]

Published
2024
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126. Realizing High Thermoelectric Performance in n‐Type Se‐Free Bi2Te3 Materials by Spontaneous Incorporation of FeTe2 Nanoinclusions

Author

Rahman, Jamil Ur, primary, Nam, Woo Hyun, additional, Jung, Yong‐Jae, additional, Won, Jong Ho, additional, Oh, Jong‐Min, additional, Van Du, Nguyen, additional, Rahman, Gul, additional, García‐Suárez, Víctor M., additional, He, Ran, additional, Nielsch, Kornelius, additional, Cho, Jung Young, additional, Seo, Won‐Seon, additional, Roh, Jong Wook, additional, Kim, Sang‐il, additional, Lee, Soonil, additional, Lee, Kyu Hyoung, additional, Kim, Hyun Sik, additional, and Shin, Weon Ho, additional

Published
2023
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140. Enhanced thermoelectric performance of TiS2via large thermal conductivity reduction by solid solution alloying with TiSe2

Author

Park, Sanghyun, Roh, Jong Wook, Park, Joontae, Cho, Hyungyu, Kang, Seung Min, Park, Okmin, Kim, Hyun-Sik, and Kim, Sang-il

Abstract

TiS2is a transition metal dichalcogenide with semiconducting transport properties, and is considered a potential thermoelectric material owing to its relatively low lattice thermal conductivity originated from van der Waals stacking. In this study, the evolution of electrical and thermal transport properties of TiS2by solid solution alloying with TiSe2are investigated systematically regarding thermoelectric properties. A series of solid solution compositions of Ti(S1 − xSex)2(x= 0, 0.1, 0.2, 0.3, 0.4, and 0.5) polycrystalline samples was synthesized by a conventional solid-state reaction, wherein no secondary phase was formed. As xincreased, the electrical conductivity and carrier concentration gradually increased, while the Seebeck coefficient decreased. Consequently, the power factor decreased. On the other hand, the lattice thermal conductivity is reduced largely to 0.96 W/mK for x= 0.5 at 300 K, compared to 2.3 W/mK for the pristine TiS2sample. Consequently, the thermoelectric figure of merit zTof TiS2was enhanced by solid solution allying with TiSe2, despite deterioration of the electrical transport properties. The maximum zTof 0.41 was observed for x= 0.4 (Ti(S0.6Se0.4)2) at 500 K.

Published
2024
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145. Enhanced Thermoelectric Properties in Highly Co-Doped Bi2Se3 by Density-of-State Effective Mass Increase.

Author

Kang, Seung Min, Lee, Kyu Hyoung, Roh, Jong Wook, Cho, Hyungyu, Park, Sanghyun, Park, Joontae, and Kim, Sang-il

Subjects
DOPING agents (Chemistry), CARRIER density, ELECTRIC conductivity, PHONON scattering, THERMAL conductivity
Abstract

Bi2Se3 alloys are promising thermoelectric materials for use at near room temperature. In this study, we investigated the thermoelectric transport properties of Co-doped Bi2Se3, Bi2−xCoxSe3 (x = 0 , 0.03, 0.06, 0.09, and 0.12) polycrystalline alloys. The electrical conductivity of Bi2Se3 increased with Co doping as the electron concentration increased. The power factor increased by 83% (1.17 mW/mK2) with the Co doping compared with 0.64 mW/mK2 for pristine Bi2Se3 at room temperature. The density-of-states effective mass significantly increased to 0.30 m 0 (free electron mass) by high Co doping of x =0.12 compared to 0.14 m 0 for pristine Bi2Se3. The total thermal conductivity of the Co-doped samples increased owing to the increase in electronic thermal conductivity, despite the systematic decrease in the lattice thermal conductivity caused by Co doping due to additional phonon scattering. Nevertheless, an enhancement in z T was observed for all the Co-doped samples. The maximum z T value of 0.39 in highly Co-doped Bi1.88Co0.12Se3 is observed at 520K, which is 18% higher than that of pristine Bi2Se3. The z T value of the Co-doped sample could be further increased with the decrease in carrier concentration, which could be attained with the decrease in total thermal conductivity owing to the decreased electronic thermal conductivity while maintaining a high power factor originating from the increased effective mass. [ABSTRACT FROM AUTHOR]

Published
2024
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146. Influence of elevated temperature on the microhardness and microstructure of carbon fiber reinforced polymers.

Author

Lee, Se Woong, Han, Seulgi, Kim, Sang-il, and Choi, Sungmo

Subjects
HIGH temperatures, CARBON fiber-reinforced plastics, MICROSTRUCTURE, SURFACE defects, EPOXY resins
Abstract

Carbon fiber-reinforced polymer (CFRP) has attracted attention for the reinforcement and retrofitting of concrete structures. Thus, their degradation in elevated temperatures is important feature to investigate. Herein, influence of elevated temperatures on microstructure and microhardness properties of different types of CFRP was investigated. A series of CFRP plate-, sheet-, and bar-type samples were fired at 150, 250, 350, and 450°C. Crystal structural properties of epoxy resin matrices and carbon fibers in the CFRP composites were examined using X-ray diffraction analysis. An increase in surface defects was observed for the fired CFRP plates and bars; however, there was no significant difference between the microstructures of the fired CFRP sheets. Hardness of CFRP plates fired at 150 and 250°C substantially decreased from 0.67 to 0.62 and 0.47 GPa, respectively, compared to that of unfired CFRP plate. Similarly, hardness of CFRP bars fired at 150, 250, and 350°C decreased from 2.09 to 1.73, 1.63, and 0.62 GPa, which is reduced by 17, 22, and 70%, respectively, compared to that of unfired CFRP bar. Decrease in hardness is attributed to several factors, such as mechanical degradation in the resin matrix, fiber/matrix debonding, and an increase in microcracks on the surface. [ABSTRACT FROM AUTHOR]

Published
2023
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