Enhancement of Thermoelectric Properties in n-type Cu0.01Bi2Te2.3+xSe0.7 (0 ≤ x ≤ 0.7) Compounds with Te-excess

Song Yi Back,조현용,김진희,안경한,이종수 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.2

The fine control of antisite defects for Bi2Te3-based materials is necessary to improve their thermoelectric performanceusing the optimization of a carrier concentration. In this work, we attempted to tune the n-type carrier concentration byforming antisite TeBidefects under a Te-rich condition for Cu0.01Bi2Te2.3+xSe0.7 samples (0 ≤ x ≤ 0.7). The electrical resistivitydecreases with increasing the amount of excess Te in the sample of Cu0.01Bi2Te2.3+xSe0.7, which is originated fromthe increase in the electron carrier concentration for the Te-excess samples. The highest power factor of 2.72 mW/m K2 isobtained at 323 K for Cu0.01Bi2Te2.4Se0.7,which is enhanced by ~ 20% compared to the x = 0 sample. The highest ZT of 0.92is achieved at 473 K for Cu0.01Bi2Te2.4Se0.7,which is 11% higher than that of x = 0 sample (ZT = 0.83). We demonstrate thatthe optimization of n-type carrier concentration by forming antisite TeBidefects in n-type Bi2Te3-based materials should beeffective for enhancing their thermoelectric performance.

Silicon Nanocanyon: One-Step Bottom-Up Fabrication of Black Silicon via in-Lasing Hydrophobic Self-Clustering of Silicon Nanocrystals for Sustainable Optoelectronics

Back, Seunghyun,Kim, Seongbeom,Kwon, Seung-Gab,Park, Jong Eun,Park, Song Yi,Kim, Jin Young,Kang, Bongchul American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.42

<P>We report a novel one-step bottom-up fabrication method for multiscale-structured black Si, which is characterized by randomly distributed microscale Si layers covered with sub-100 nm protrusions with submicron boundary grooves. The unique multiscale structure, suggested as a “nanocanyon,” effectively minimizes light reflection over a broad spectrum by diversifying the scattering routes from the nanotextured surface to the wide distributed boundary micronanoscale grooves. This structure was achieved by hydrophobic clustering and local aggregation of instantaneously melted Si nanocrystals on a glass substrate under laser irradiation. This method can replace the complicated conventional silicon processes, such as patterning for selective Si formation, texturing for improved absorption, and doping for modifying the electrical properties, because the proposed method obviates the need for photolithography, chemical etching, vacuum processes, and expensive wafers. Finally, black Si photosensor arrays were successfully demonstrated by a low-cost solution process and a laser growth sintering technique for microchannel fabrication. The results show the great potential of the proposed fabrication method for low-cost and sustainable production of highly sensitive optoelectronics and as an alternative to conventional wafer-based photosensor manufacturing techniques.</P> [FIG OMISSION]</BR>

Statistically Analysis of Clumps Formed in Turbulent Molecular Clouds

Chan Yi Song,Dongsu Ryu,Jongsoo Kim,Chang Hyun Back 한국천문학회 2005 天文學會報 Vol.30 No.1

Thermoelectric Properties and Chemical Potential Tuning by K- and Se-Coalloying in (Pb0.5Sn0.5)1-xKxTe0.95Se0.05

Dianta Ginting,Chan-Chieh Lin,Gareoung Kim,Song Yi Back,Bora Won,조현용,Jae Hyun Yun,Hyeon Seob So,Hosun Lee,Byung-Kyu Yu,Sung-Jin Kim,Jong-Soo Rhyee 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.3

Topological crystal insulator (TCI) and topological Dirac semimetals have topologically nontrivial surface and bulk state,respectively. The parent compound of Pb 0.5 Sn 0.5 Te exhibiting TCI band inversion has particle-hole symmetry owing to thegapless Dirac band implying a strong electron–hole bipolar compensation in Seebeck coeffi cient. We recently reported thatweak perturbation of TCI state can enhance thermoelectric performance signifi cantly due to highly dispersive and degeneratedenergy bands. It is a great interest that the further increase of chemical potential has benefi ciary to thermoelectric performancein the vicinity of topological phase transition. Here we investigate the thermoelectric properties of the co-doping eff ect by Kand Se in (Pb 0.5 Sn 0.5 ) 1− x K x Te 0.95 Se 0.05 ( x = 0.0, 0.005, 0.010, 0.015, 0.02) compounds. K-doping increases the band gap from0.15 eV (Pb 0.5 Sn 0.5 Te) to 0.21 eV ( x = 0.05) as well as increasing chemical potential resulting in the suppression of bipolardiff usion eff ect. In spite of the suppression of bipolar diff usion eff ect by K-doping, the power factor in K-doped compoundis decreased signifi cantly than the one of non-doped Pb 0.5 Sn 0.5 Te 0.95 Se 0.05 compound. It indicates that when we increasechemical potential further on the breaking of topological band inversion, the thermoelectric performance is deterioratedbecause the chemical potential resides far from the linear band dispersions which become conventional material. The ZTfor the K-doped (Pb 0.5 Sn 0.5 ) 1− x K x Te 0.95 Se 0.05 is obtained as 0.91 at 750 K for x = 0.017 which is increased as much as 99%comparing to the pristine compound Pb 0.5 Sn 0.5 Te but it is reduced value (51.5%) comparing to those of Pb 0.5 Sn 0.5 Te 0.95 Se 0.05compound. We believe that this research is valuable on the confi rmation that the weak perturbation of topological state andappropriate chemical potential tuning are important criteria in high thermoelectric performance.

Enhancement of thermoelectric properties in CuI-doped Bi₂Te_2.7Se_0.3 by hot-deformation

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>

Long-Term Stable Recombination Layer for Tandem Polymer Solar Cells Using Self-Doped Conducting Polymers

Lee, Jinho,Kang, Hongkyu,Kee, Seyoung,Lee, Seoung Ho,Jeong, Song Yi,Kim, Geunjin,Kim, Junghwan,Hong, Soonil,Back, Hyungcheol,Lee, Kwanghee American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.9

<P>Recently, the most efficient tandem polymer solar cells (PSCs) have used poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a p-type component of recombination layer (RL). However, its undesirable acidic nature, originating from insulating PSS, of PEDOT:PSS drastically reduces the lifetime of PSCs. Here, we demonstrate the efficient and stable tandem PSCs by introducing acid-free self-doped conducting polymer (SCP), combined with zinc oxide nanoparticles (ZnO NPs), as RL for PEDOT:PSS-free tandem PSCs. Moreover, we introduce an innovative and versatile nanocomposite system containing photoactive and p-type conjugated polyelectrolyte (p-CPE) into the tandem fabrication of an ideal self-organized recombination layer. In our new RL, highly conductive SCP facilitates charge transport and recombination process, and p-CPE helps to achieve nearly loss-free charge collection by increasing effective work function of indium tin oxide (ITO) and SCP. Because of the synergistic effect of extremely low electrical resistance, ohmic contact, and pH neutrality, tandem devices with our novel RL performed well, exhibiting a high power conversion efficiency of 10.2% and a prolonged lifetime. These findings provide a new insight for strategic design of RLs using SCPs to achieve efficient and stable tandem PSCs and enable us to review and extend the usefulness of SCPs in various electronics research fields.</P>

Possible Rashba band splitting and thermoelectric properties in CuI-doped Bi₂Te_2.7Se_0.3 bulk crystals

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>

원적외선 온열요법이 혈액투석 환자의 혈관통로 기능에 미치는 효과

최향미 ( Hyang Mi Choi ),최은덕 ( Eun Duck Choi ),장소형 ( So Hyeong Jang ),김은희 ( Eun Hee Kim ),최미정 ( Mi Jung Choi ),백송이 ( Song Yi Back ),한복희 ( Bok Hee Han ) 병원간호사회 2015 임상간호연구 Vol.21 No.2

Purpose: For hemodialysis, a vascular access which can maintain a certain speed for a long time is required. The prevention of the vascular access dysfunction is very important to decrease morbidity and to improvethe quality of life of patients receiving hemodialysis It is reported that far infrared heat increases the blood flow by expanding capillaries and micro-arteriovenouses. This study aimed to evaluate the effect of far infrared heat therapy as a new nursing intervention for maintaining vascular access function and improving the blood flow of patients receiving hemodialysis. Methods: The quasi-experimental research of nonequivalent control group pre-post test design was carried out for 59 patients receiving hemodialysis 3 times per week at K medical center. A far infrared heat was applied to the experimental group for 3 months. Results: The arteriovenous fistula blood flow of the experimental group (far infrared heat therapy group) increased significantly when compared to the control group (p=.047). However, static intra-access pressure ratio(SIAPR)was not different statistically (p=.101). Conclusion: The far infrared therapy could be considered as nursing intervention of choice as it demonstrated increase in the arteriovenous fistula blood flow in the patients receiving hemodialysis.