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2496 Carbon-free Mn-doped LiFePO4 cathode for highly transparent thin-film batteries 이현석,김상태,Narendra Singh Parmar,송종한,정경윤,Kwang-Bum Kim,최지원, 2019.09 Journal of power sources 434 , (226713~226720) The search for transparent battery cathodes primarily focuses on patterned electrodes with feature sizes below the optical absorption limit. This significantly limits the electrode capacity, as a large electrode area remains unused to maintain transparency. Herein, we report transparent olivine LiFe0.77Mn0.23PO4 thin-film electrodes discovered through high-throughput continuous-composition-spread sputtering. After investigating six different Mn doping ratios, we found the optimal Mn-doped olivine composition with an enhanced discharge capacity of 45.7 μA h/cm2∙μm without using excessive nanosized features or carbon coating. The thin-film electrode exhibits a clear redox activity for both Fe3+/2+ and Mn3+/2+, resulting in an enhanced average voltage over LiFePO4 composition. A 250-nm-thick film exhibits an optical transmittance of over 80% in the visible region. The results in this study demonstrates that transparent cathode thin films can be developed based on phospho-olivines via doping strategies with high-throughput continuous-composition-spread sputtering methods. 보기
2495 Composition-dependent topological-insulator properties of epitaxial (Bi1-xSbx)2(Te1-ySey)3 thin films 이미림,조성원,이연진,이수연, 2019.09 Journal of alloys and compounds 800 , (81~87) Due to strong spin-orbit coupling (SOC), topological insulators (TIs) have attracted much interest in developing novel energy-efficient electronic devices. (Bi1-xSbx)2(Te1-ySey)3 (BSTS) has been regarded as a prototypical TI because of the dominance of the surface channel in carrier transport. Nevertheless, the effect of the composition of BSTS on SOC has not been explored, which is important for the application in novel electronic devices. In this work, BSTS thin films with systematically varying compositions are examined to release composition-dependent maps for the bulk carrier density, the dominance of the surface states in carrier transport, and the strength of SOC. The maps show that the regions for optimizing each property are located in separate positions, with a narrow overlap between them. These results imply that a stringent control in composition of the BSTS thin film is required in order to take advantage of the spin-momentum-locked surface channel of TI in novel electronic devices. 보기
2494 Double layered dielectric elastomer by vapor encapsulation casting for highly deformable and strongly adhesive triboelectric materials Hai Bo Xu,김정훈,김상태,황희재,Deepam Maurya,최덕균,강종윤,송현철, 2019.08 Nano energy 62 , (144~153) Triboelectric generators (TEG), based on contact electrification and electro-static induction, has received a significant attention because of their numerous applications. To improve the electrified surface charge density in TEG, increasing the surface area of dielectric materials or forming internal hollow structures are typically employed to increase capacitance. However, the fabrication processes of such structures are complex and time-consuming. Here, we provide a facile and cost-effective synthesis method for the porous PDMS based TEG via a novel vapor encapsulation casting (VEC). The double dielectric layer composed of the porous and dense PDMS layers are formed in-site through VEC. The thickness and the thickness ratio of the double dielectric layer can be precisely controlled by adjusting the uncured PDMS thickness and vapor penetration depth. The double dielectric layer TEG (DTEG) exhibits the improved harvesting performance because the porous dielectric layer increases the capacitance and compressibility, while the dense layer passivates the fully open pores which reduce the charging surface area as completely opening through the dielectric layer without contacting the bottom electrode. We obtain the maximum output voltage of 345 V and short circuit current of 3 μA/cm2 from DTEG having 0.95 porous thickness ratio, resulting 330% enhancement in the power output as compared to the dense PDMS based TEG. We further investigate the performance of DTEG under various operating conditions. We also demonstrate the operation of Bluetooth distance/temperature sensors using capacitors charged by DTEG. 보기
2493 A first-principles study of the structural and electronic properties of the epitaxial Ge(1?1?1)/La2O3(0?0?1) heterostructure 류카이,고은정,황철성,최정혜, 2019.07 Journal of physics D, applied physics 52, 36 , (365101-1~365101-7) The effects of the atomic configuration of the epitaxial Ge(1 1 1)/La2O3(0 0 1) interface on the electrical properties of the structure were studied using first-principles calculations. The interface stability of this heterostructure is susceptible to the atomic configuration of the interface. The Ge–O-bonded interface without interfacial gap states is generally more stable than the Ge–La-bonded interface, which involves interfacial gap states. The band alignment is affected by the charge transfer depending on the interface atomic configuration, and the band bending across the La2O3 region was observed due to the electronic dipole inside the La2O3. 보기
2492 III-V on silicon avalanche photodiodes by heteroepitaxy Yuan Yuan,정대환,Keye Sun,Jiyuan Zheng,Andrew Jones,John Bowers,Joe Campbell, 2019.07 Optics letters 44, 14 , (3538~3541) 보기
2491 Gate-Tunable and Programmable n?InGaAs/Black Phosphorus Heterojunction Diodes 이영수,엄두승,임성동,이호찬,김민수,Tzu-Yi Yang,Yu-Lun Chueh,김형준,고현협, 2019.07 ACS Applied Materials & Interfaces 11 , (23382~23391) Semiconductor heterostructures have enabled numerous applications in diodes, photodetectors, junction field-effect transistors, and memory devices. Two-dimensional (2D) materials and III–V compound semiconductors are two representative materials providing excellent heterojunction platforms for the fabrication of heterostructure devices. The marriage between these semiconductors with completely different crystal structures may enable a new heterojunction with unprecedented physical properties. In this study, we demonstrate a multifunctional heterostructure device based on 2D black phosphorus and n-InGaAs nanomembrane semiconductors that exhibit gate-tunable, photoresponsive, and programmable diode characteristics. The device exhibits clear rectification with a large gate-tunable forward current, which displays rectification and switching with a maximum rectification ratio of 4600 and an on/off ratio exceeding 105, respectively. The device also offers nonvolatile memory properties, including large hysteresis and stable retention of storage charges. By combining the memory and gate-tunable rectifying properties, the rectification ratio of the device can be controlled and memorized from 0.06 to 400. Moreover, the device can generate three different electrical signals by combining a photoresponsivity of 0.704 A/W with the gate-tunable property, offering potential applications, for example, multiple logic operator. This work presents a heterostructure design based on 2D and III–V compound semiconductors, showing unique physical properties for the development of multifunctional heterostructure devices. 보기
2490 Long-range chiral exchange interaction in synthetic antiferromagnets 한동수,이규준,Jan-Philipp Hanke,Yuriy Mokrousov,김경환,유우석,Youri L. W. van Hees,김태완,Reinoud Lavrijsen,유천열,Henk J. M. Swagten,정명화,Mathias Klaui, 2019.07 Nature materials 18 , (703~708) The exchange interaction governs static and dynamic magnetism. This fundamental interaction comes in two flavours—symmetric and antisymmetric. The symmetric interaction leads to ferro- and antiferromagnetism, and the antisymmetric interaction has attracted significant interest owing to its major role in promoting topologically non-trivial spin textures that promise fast, energy-efficient devices. So far, the antisymmetric exchange interaction has been found to be rather short ranged and limited to a single magnetic layer. Here we report a long-range antisymmetric interlayer exchange interaction in perpendicularly magnetized synthetic antiferromagnets with parallel and antiparallel magnetization alignments. Asymmetric hysteresis loops under an in-plane field reveal a unidirectional and chiral nature of this interaction, which results in canted magnetic structures. We explain our results by considering spin–orbit coupling combined with reduced symmetry in multilayers. Our discovery of a long-range chiral interaction provides an additional handle to engineer magnetic structures and could enable three-dimensional topological structures. 보기
2489 Optimization of device design for low cost and high efficiency planar monolithic perovskite/silicon tandem solar cells Chan Ul Kim,Jae Choul Yu,Eui Dae Jung,In Young Choi,Hyungmin Lee,Wonjin Park,김인호,이도권,Kuen Kee Hong,Myoung Hoon Song,Kyoung Jin Choi, 2019.06 Nano energy 60 , (213~221) Perovskite/silicon hybrid tandem solar cells are very close to commercialization owing to their low cost and relatively high efficiency compared to tandem cells based on III-V compound semiconductors. However, most hybrid tandem cell research is based on n-type heterojunction Si cells, which occupy only a small fraction of the total solar market. Here, we propose a new method for optimizing the design of low-cost and high-efficiency monolithic tandem cells based on p-type homojunction Si cells by realizing lossless current matching by simultaneously controlling the band gap energy and thickness of the perovskite film. In addition, systematic studies have been conducted to determine the optimal hole transport layer applicable to the tandem cell from the viewpoint of band alignment and process compatibility, in order to reduce the open-circuit voltage loss. Optimized tandem cells, which were fabricated with a 310 nm thick perovskite layer of (FAPbI3)0.8(MAPbBr3)0.2 and a hole transport layer of poly(triaryl amine), had a significantly increased efficiency of 21.19% compared to semi-transparent stand-alone perovskite (13.4%) and Si cells (12.8%). Our tandem cell represented the highest efficiency increment among all monolithic perovskite/Si tandem cells as well as the highest efficiency among monolithic perovskite/Si tandem cells based on p-type homojunction Si cells with Al back-surface fields. The design rules suggested in this study could also be applicable to different types of perovskite/Si tandem cells. 보기
2488 +Iron hexacyanocobaltate metal-organic framework: Highly reversible and stationary electrode material with rich borders for lithium-ion batteries 장개강,Rajender S. Varma,Ho Won Jang,최지원,Mohammadreza Shokouhimehr, 2019.06 Journal of alloys and compounds 791 , (911~917) Metal-organic frameworks (MOFs) are attractive electrode material candidates for lithium-ion batteries (LIBs) and are garnering significant interest due to their tunable pore size and intriguing electrochemical properties. A border-rich iron (Fe3+) hexacyanocobaltate (FeHCCo) MOF is synthesized via a facile and low-cost co-precipitation method and evaluated as a cathode material for LIBs. The MOF delivered reversible capacities corresponding to 136 and 57 mAh g−1 at 0.63 and 6.25C, respectively. Furthermore, a lithiation capacity of 116 mAh g−1 at 1.25C was maintained with a Coulombic efficiency of 99.6%. The high electrochemical performance can be attributed to the highly reversible open-framework crystal texture of border-rich FeHCCo, which may provide new insights on the application of MOFs as viable electrode materials in rechargeable LIBs. 보기
2487 Domain epitaxy of crystalline BeO films on GaN and ZnO substrates Seung Min Lee,Jung Hwan Yum,Eric S. Larsen,Shahab Shervin,Weijie Wang,Jae-Hyun Ryou,Christopher W. Bielawski,이우철,김성근,Jungwoo Oh, 2019.06 Journal of the American Ceramic Society 102, 6 , (3745~3752) 해킹의 위험이 있는 문자가 감지되었습니다. 보기