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Probing temperature-dependent interlayer coupling in a MoS2/h-BN heterostructure

Nano Research 2020年第2期13卷 576-582页

作者： Hamin Park Gwang Hyuk Shin Khang June Lee sung-yool choi School of Electrical Engineering Centerfor Advanced Materials Discovery towards 3D Display KAISTDaejeon 34141Republic of Korea

Stacking of atomically thin layers of two-dimensional materials has revealed extraordinary physical phenomena owing to van der Waals(vdW)interaction at the interface.However,most of the studies focused on the transition metal dichalcogenide(TMD)/TMD heterostructure,while the interlayer coupling of the TMD/hexagonal boron nitride(h-BN)heterostructure has not been extensively explored despite its importance.In this study,the temperature-dependent interlayer coupling is demonstrated in a heterostructure of molybdenum disulfide(MoS2)and h-BN.The interface between MoS2 and the insulating substrate exerts a significant spectroscopic impact on MoS2 through substrate-induced local strain,charged impurity,and vdW interactions.Under non-resonant conditions,temperature-dependent peak shifts in Raman and photoluminescence(PL)spectra of MoS2 reveal the evolution of interlayer coupling.Phonon frequencies and PL peak energies at different temperatures demonstrate how substrate-induced strain,impurity,and vdW interactions at the interface influence phonon vibration and excitonic transition of MoS2.Under resonant conditions at low temperature,anomalous Raman modes appear in the MoS2/h-BN heterostructure because of the enhanced electron-phonon coupling and vdW interactions.The anomalous Raman modes are quantitatively investigated by the deconvolution of the resonance Raman spectra and described by interlayer coupling at low temperature,in agreement with complementary indications from the temperature-dependent evolution of non-resonant Raman and PL spectra.

关键词： van der Waals heterostructures interlayer coupling Raman spectroscopy excitonic resonance photoluminescence

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Zero-static-power nonvolatile logic-in-memory circuits for flexible electronics

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Nano Research 2017年第7期10卷 2459-2470页

作者： Byung ChulJang Sang Yoon Yang Hyejeong seong sung Kyu Kim Junhwan choi sung Gap Im sung-yool choi School of Electrical Engineering Graphene/2D Materials Research Center Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea Department of Chemical and Biomolecular Engineering Graphene/2D Materials Research Center Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea Department of Materials Science and Engineering Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea

Flexible logic circuits and memory with ultra-low static power consumption are in great demand for battery-powered flexible electronic systems. Here, we show that a flexible nonvolatile logic-in-memory circuit enabling normally-off computing can be implemented using a poly（1,3,5-trivinyl-l,3,5-trimethyl cyclotrisiloxane）（pV3D3）-based memristor array. Although memristive logic-in-memory circuits have been previously reported, the requirements of additional components and the large variation of memristors have limited demonstrations to simple gates within a few operation cycles on rigid substrates only. Using memristor-aided logic （MAGIC） architecture requiring only memristors and pV3D3-memristor with good uniformity on a flexible substrate, for the first time, we experimentally demonstrated our implementation of MAGIC-NOT and -NOR gates during multiple cycles and even under bent conditions. Other functions, such as OR, AND, NAND, and a half adder, are also realized by combinations of NOT and NOR gates within a crossbar array. This research advances the development of novel computing architecture with zero static power consumption for battery- powered flexible electronic systems.

关键词： memristor,memristive logic circuit,flexible nonvolatilelogic-in-memory circuit,normally-off computing,memristor-aided logic（MAGIC） architecture

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Effective shape-controlled growth of monolayer MoS2 flakes by powder-based chemical vapor deposition

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Nano Research 2017年第1期10卷 255-262页

作者： Sang Yoon Yang Gi Woong Shim Seung-Bum Seo sung-yool choi Graphene Research Center (GRC) Center for Advanced Materials Discovery for 3D Displays (CAMD3) School of Electrical EngineeringKorea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea

In the recent years, transition-metal dichalcogenides such as MoS2 have attracted considerable attention owing to their unique structure and electronic properties. Chemical vapor deposition （CVD） is a popular method for producing MoS2 flakes with different shapes. Here, we report an effective method for achieving a broad range of shape evolution in CVD-grown monolayer MoS2 flakes. By controlling the S and MoO3 temperatures, the shape of the monolayer MoS2 flakes was varied from hexagonal to triangular via intermediate shapes such as truncated and multi-apex triangles. The shape evolution of the MoS2 flakes can be explained by introducing the term “nominal Mo：S ratio”, which refers to the amount of loaded MoO3 and evaporated S powders. By using the nominal Mo：S ratio, we predicted the potential reaction atmosphere and effectively controlled the actual proportion of MoO3-x with respect to S in the growth region, along with the growth temperature. From the systematic investigation of the behavior of the shape evolution, we developed a shape-evolution diagram, which can be used as a practical guide for producing CVD-grown MoS2 flakes with desired shapes

关键词： molybdenum disulfide,CVD growth,shape evolution,diagram,growth condition

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Atomically thin heterostructure with gap-mode plasmon for overcoming trade-off between photoresponsivity and response time

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Nano Research 2021年第5期14卷 1305-1310页

作者： Khang June Lee Cheolmin Park Hyeok Jun Jin Gwang Hyuk Shin sung-yool choi School of Electrical Engineering Center for Advanced Materials Discovery towards 3D DisplaysKorea Advanced Institute of Science and Technology291 Daehak-roYuseong-guDaejeon34141Republic of Korea

Two-dimensional(2D)materials have recently provided a new perspective on optoelectronics because of their unique layered structure and excellent physical properties.However,their potential use as optoelectric devices has been limited by the trade-off between photoresponsivity and response time.Here,based on a vertically stacked atomically thin p-n junction,we propose a gap-mode plasmon structure that simultaneously enables enhanced responsivity and rapid photodetection.The atomically thin 2D materials act as a spacer for enhancing the gap-mode plasmons,and their short transit length in the vertical direction allows fast photocarrier transport.We demonstrate a high responsivity of up to 8.67 A/W with a high operation speed that exceeds 35 MHz under a 30 nW laser power.Spectral photocurrent,absorption,and a numerical simulation are used to verify the effectiveness of the gap-mode plasmons in the device.We believe that the design strategy proposed in this study can pave the way for a platform to overcome the trade-off between responsivity and response time.

关键词： atomically thin heterostructure gap-mode plasmons photodetectors high responsivity fast response time

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Graphene electrode with tunable charge transport in thin-film transistors

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Nano Research 2018年第1期11卷 274-286页

作者： Ick-Joon Park Tae In Kim In-Tak Cho Chang-Woo Song Ji-Woong Yang Hongkeun Park Woo-Seok Cheong sung Gap Im Jong-Ho Lee sung-yool choi School of Electrical Engineering GrapheneY2D Materials Research Center Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea Department of Electrical Engineering Seoul National University Seou108826 Republic of Korea Electronics and Telecommunications Research Institute Daejeon 34129 Republic of Korea Department of Chemical and Biomolecular Engineering Graphene/2D Materials Research Center Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea

Graphene, a single atomic layer of sp2-hybridized carbon, has immense potential as a transparent conducting material in electronic applications owing to its superior properties, including optical transparency and high conductivity. Particularly, the tunable work function of graphene enables the integration of graphene electrodes with various electronic devices. To achieve high performance in graphene-based devices, effective charge transport between the graphene electrode and the semiconducting material needs to be optimized; this is closely related to the modulation of the Schottky barrier （SB）. In this study, we investigate the ~nable charge transport properties as a function of graphene doping in n-channel thin-film transistors （TFTs） in terms of the electrical characteristics and low-frequency noise （LFN） behaviors. Alkali metal carbonates tuned the work function of graphene, resulting in a dramatic decrease in the SB and an improvement of the carrier injection in n-channel TFTs. The electrical performance of the TFTs was evaluated by extraction of the field-effect mobilities and ratio of contact resistance to total resistance. Furthermore, the level of contact noise created by the barrier height fluctuation and relative contribution of channel noise and contact noise in the TFTs was investigated by LFN measurements to demonstrate the ~nable charge transport. Our findings therefore provide new insights into the tunable charge transport mechanism in graphene-based devices and reveal the immense potential of graphene as electrodes in high performance flexible and transparent displays.

关键词： charge transport,graphene doping,Schottky barrier,work function,contact property,low-frequency noise

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Thermal deformation of aluminum alloy casting materials for tire mold by numerical analysis

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中国有色金属学会会刊：英文版 2012年第S3期22卷 859-863页

作者： Hee-sung YOON Je-Se choi yool-Kwon OH Department of Advanced Parts and Materials Engineering Chosun University Department of Mechatronics Engineering Chosun University

Thermal deformation of aluminum alloy casting materials for manufacturing the tire mold was numerically investigated.The AC7A and AC4C casting material was selected as casting material and the metal casting device was used in order to manufacture the mold product of automobile tire in the actual industrial field.The temperature distribution and the cooling time of casting materials were numerically calculated by finite element analysis (FEA).Also,the thermal deformation such as displacement and stress distribution was calculated from the temperature results.The thermal deformation was closely related to the temperature difference between the surface and inside of the casting.The numerical analysis results reveal that the thermal deformation of AC7A casting material is higher than that of AC4C casting material.Also,the thermal deformation results at the central part are larger than that on the side of casting because of the shrinkage caused by the cooling speed difference.

关键词： thermal deformation finite element analysis AC7A casting material AC4C casting material

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动脉自旋标记灌注加权成像有助于预测胶质母细胞瘤分子生物学标志物与生存

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国际医学放射学杂志 2020年第2期 252-252页

作者： R.E.yool T.J.Yun I.Hwang E.K.Hong K.M.Kang S.H.choi 高珍 Institute of Radiation Medicine Seoul National University Medical Research Center

目的预测胶质母细胞瘤(GBM)病人的无进展生存(PFS)和总生存(OS),以及早期识别与预后相关的分子生物标志物具有临床重要性。本研究探讨动脉自旋标记灌注加

关键词：灌注加权成像动脉自旋标记生物学标志物胶质母细胞瘤

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