Song Peng
Degree: PhD
Position: Assistant Professor
Affiliation: NTU-School of Electrical and Electronic Engineering
Research Type: Experiment
Email: peng.song@ntu.edu.sg
Research Interests:
2D and topological spintronic materials and devices
2D electronic device physics
Memory and computing devices strong
CA2DM Publications:
2020 |
Leng, Kai; Wang, Lin; Shao, Yan; Abdelwahab, Ibrahim; Grinblat, Gustavo; Verzhbitskiy, Ivan; Li, Runlai; Cai, Yongqing; Chi, Xiao; Fu, Wei; Song, Peng; Rusydi, Andrivo; Eda, Goki; Maier, Stefan A; Loh, Kian Ping Electron tunneling at the molecularly thin 2D perovskite and graphene van der Waals interface Journal Article NATURE COMMUNICATIONS, 11 (1), 2020, ISSN: 2041-1723. @article{ISI:000588063600006, title = {Electron tunneling at the molecularly thin 2D perovskite and graphene van der Waals interface}, author = {Kai Leng and Lin Wang and Yan Shao and Ibrahim Abdelwahab and Gustavo Grinblat and Ivan Verzhbitskiy and Runlai Li and Yongqing Cai and Xiao Chi and Wei Fu and Peng Song and Andrivo Rusydi and Goki Eda and Stefan A Maier and Kian Ping Loh}, doi = {10.1038/s41467-020-19331-6}, times_cited = {0}, issn = {2041-1723}, year = {2020}, date = {2020-10-30}, journal = {NATURE COMMUNICATIONS}, volume = {11}, number = {1}, publisher = {NATURE RESEARCH}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Quasi-two-dimensional perovskites have emerged as a new material platform for optoelectronics on account of its intrinsic stability. A major bottleneck to device performance is the high charge injection barrier caused by organic molecular layers on its basal plane, thus the best performing device currently relies on edge contact. Herein, by leveraging on van der Waals coupling and energy level matching between two-dimensional Ruddlesden-Popper perovskite and graphene, we show that the plane-contacted perovskite and graphene interface presents a lower barrier than gold for charge injection. Electron tunneling across the interface occurs via a gate-tunable, direct tunneling-to-field emission mechanism with increasing bias, and photoinduced charge transfer occurs at femtosecond timescale (similar to 50fs). Field effect transistors fabricated on molecularly thin Ruddlesden-Popper perovskite using graphene contact exhibit electron mobilities ranging from 0.1 to 0.018 cm(2)V(-1)s(-1) between 1.7 to 200K. Scanning tunneling spectroscopy studies reveal layer-dependent tunneling barrier and domain size on few-layered Ruddlesden-Popper perovskite.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Quasi-two-dimensional perovskites have emerged as a new material platform for optoelectronics on account of its intrinsic stability. A major bottleneck to device performance is the high charge injection barrier caused by organic molecular layers on its basal plane, thus the best performing device currently relies on edge contact. Herein, by leveraging on van der Waals coupling and energy level matching between two-dimensional Ruddlesden-Popper perovskite and graphene, we show that the plane-contacted perovskite and graphene interface presents a lower barrier than gold for charge injection. Electron tunneling across the interface occurs via a gate-tunable, direct tunneling-to-field emission mechanism with increasing bias, and photoinduced charge transfer occurs at femtosecond timescale (similar to 50fs). Field effect transistors fabricated on molecularly thin Ruddlesden-Popper perovskite using graphene contact exhibit electron mobilities ranging from 0.1 to 0.018 cm(2)V(-1)s(-1) between 1.7 to 200K. Scanning tunneling spectroscopy studies reveal layer-dependent tunneling barrier and domain size on few-layered Ruddlesden-Popper perovskite. |
Li, Jing; Song, Peng; Zhao, Jinpei; Vaklinova, Kristina; Zhao, Xiaoxu; Li, Zejun; Qiu, Zhizhan; Wang, Zihao; Lin, Li; Zhao, Meng; Herng, Tun Seng; Zuo, Yuxin; Jonhson, Win; Yu, Wei; Hai, Xiao; Lyu, Pin; Xu, Haomin; Yang, Huimin; Chen, Cheng; Pennycook, Stephen J; Ding, Jun; Teng, Jinghua; Neto, Castro A H; Novoselov, Kostya S; Lu, Jiong Printable two-dimensional superconducting monolayers Journal Article NATURE MATERIALS, 20 (2), pp. 181-+, 2020, ISSN: 1476-1122. @article{ISI:000584012400003, title = {Printable two-dimensional superconducting monolayers}, author = {Jing Li and Peng Song and Jinpei Zhao and Kristina Vaklinova and Xiaoxu Zhao and Zejun Li and Zhizhan Qiu and Zihao Wang and Li Lin and Meng Zhao and Tun Seng Herng and Yuxin Zuo and Win Jonhson and Wei Yu and Xiao Hai and Pin Lyu and Haomin Xu and Huimin Yang and Cheng Chen and Stephen J Pennycook and Jun Ding and Jinghua Teng and Castro A H Neto and Kostya S Novoselov and Jiong Lu}, doi = {10.1038/s41563-020-00831-1}, times_cited = {0}, issn = {1476-1122}, year = {2020}, date = {2020-10-26}, journal = {NATURE MATERIALS}, volume = {20}, number = {2}, pages = {181-+}, publisher = {NATURE RESEARCH}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {A mild electrochemical exfoliation method has been developed to obtain large-size two-dimensional superconductor monolayers with high crystallinity and production yield, which enables the easy fabrication of twisted van der Waals heterostructures and printed films.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A mild electrochemical exfoliation method has been developed to obtain large-size two-dimensional superconductor monolayers with high crystallinity and production yield, which enables the easy fabrication of twisted van der Waals heterostructures and printed films. |
Fu, Wei; Zhao, Xiaoxu; Wang, Ke; Chen, Zhi; Leng, Kai; Fu, Deyi; Song, Peng; Wang, Hai; Deng, Longjiang; Pennycook, Stephen J; Zhang, Gang; Peng, Bo; Loh, Kian Ping An Anomalous Magneto-Optic Effect in Epitaxial Indium Selenide Layers Journal Article NANO LETTERS, 20 (7), pp. 5330-5338, 2020, ISSN: 1530-6984. @article{ISI:000548893200083, title = {An Anomalous Magneto-Optic Effect in Epitaxial Indium Selenide Layers}, author = {Wei Fu and Xiaoxu Zhao and Ke Wang and Zhi Chen and Kai Leng and Deyi Fu and Peng Song and Hai Wang and Longjiang Deng and Stephen J Pennycook and Gang Zhang and Bo Peng and Kian Ping Loh}, doi = {10.1021/acs.nanolett.0c01704}, times_cited = {0}, issn = {1530-6984}, year = {2020}, date = {2020-07-08}, journal = {NANO LETTERS}, volume = {20}, number = {7}, pages = {5330-5338}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Single-phonon modes offer potential applications in quantum phonon optics, but the phonon density of states of most materials consist of mixed contributions from coupled phonons. Here, using theoretical calculations and magneto-Raman measurements, we report two single-phonon vibration modes originating from the breathing and opposite out-of-plane vibrations of InSe layers. These single-phonon vibrations exhibit an anticorrelated scattering rotations of the polarization axis under an applied vertical magnetic field; such an anomalous magneto-optical behavior is due to the reverse bond polarizations of two quantum atomic vibrations, which induce different symmetry for the corresponding Raman selection rules. A 180 degrees (+90 degrees and -90 degrees) integrated scattering rotation angle of two single-phonon modes was achieved when the magnetic field was swept from 0 to 6 T. This work demonstrates new ways to manipulate the magneto-optic effect through phonon polarity-based symmetry control and opens avenues for exploring single-phonon-vibration-based nanomechanical oscillators and magneto-phononcoupled physics.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Single-phonon modes offer potential applications in quantum phonon optics, but the phonon density of states of most materials consist of mixed contributions from coupled phonons. Here, using theoretical calculations and magneto-Raman measurements, we report two single-phonon vibration modes originating from the breathing and opposite out-of-plane vibrations of InSe layers. These single-phonon vibrations exhibit an anticorrelated scattering rotations of the polarization axis under an applied vertical magnetic field; such an anomalous magneto-optical behavior is due to the reverse bond polarizations of two quantum atomic vibrations, which induce different symmetry for the corresponding Raman selection rules. A 180 degrees (+90 degrees and -90 degrees) integrated scattering rotation angle of two single-phonon modes was achieved when the magnetic field was swept from 0 to 6 T. This work demonstrates new ways to manipulate the magneto-optic effect through phonon polarity-based symmetry control and opens avenues for exploring single-phonon-vibration-based nanomechanical oscillators and magneto-phononcoupled physics. |
Zhao, Xiaoxu; Song, Peng; Wang, Chengcai; Riis-Jensen, Anders C; Fu, Wei; Deng, Ya; Wan, Dongyang; Kang, Lixing; Ning, Shoucong; Dan, Jiadong; Venkatesan, T; Liu, Zheng; Zhou, Wu; Thygesen, Kristian S; Luo, Xin; Pennycook, Stephen J; Loh, Kian Ping Engineering covalently bonded 2D layered materials by self-intercalation Journal Article NATURE, 581 (7807), pp. 171-+, 2020, ISSN: 0028-0836. @article{ISI:000532836000027, title = {Engineering covalently bonded 2D layered materials by self-intercalation}, author = {Xiaoxu Zhao and Peng Song and Chengcai Wang and Anders C Riis-Jensen and Wei Fu and Ya Deng and Dongyang Wan and Lixing Kang and Shoucong Ning and Jiadong Dan and T Venkatesan and Zheng Liu and Wu Zhou and Kristian S Thygesen and Xin Luo and Stephen J Pennycook and Kian Ping Loh}, doi = {10.1038/s41586-020-2241-9}, times_cited = {0}, issn = {0028-0836}, year = {2020}, date = {2020-05-01}, journal = {NATURE}, volume = {581}, number = {7807}, pages = {171-+}, publisher = {NATURE RESEARCH}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Two-dimensional (2D) materials(1-5) offer a unique platform from which to explore the physics of topology and many-body phenomena. New properties can be generated by filling the van der Waals gap of 2D materials with intercalants(6,7); however, post-growth intercalation has usually been limited to alkali metals(8-10). Here we show that the self-intercalation of native atoms(11,12) into bilayer transition metal dichalcogenides during growth generates a class of ultrathin, covalently bonded materials, which we name ic-2D. The stoichiometry of these materials is defined by periodic occupancy patterns of the octahedral vacancy sites in the van der Waals gap, and their properties can be tuned by varying the coverage and the spatial arrangement of the filled sites(7,13). By performing growth under high metal chemical potential(14,15) we can access a range of tantalum-intercalated TaS(Se)(y), including 25% Ta-intercalated Ta9S16, 33.3% Ta-intercalated Ta7S12, 50% Ta-intercalated Ta10S16, 66.7% Ta-intercalated Ta8Se12 (which forms a Kagome lattice) and 100% Ta-intercalated Ta9Se12. Ferromagnetic order was detected in some of these intercalated phases. We also demonstrate that self-intercalated V11S16, In11Se16 and FexTey can be grown under metal-rich conditions. Our work establishes self-intercalation as an approach through which to grow a new class of 2D materials with stoichiometry- or composition-dependent properties.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Two-dimensional (2D) materials(1-5) offer a unique platform from which to explore the physics of topology and many-body phenomena. New properties can be generated by filling the van der Waals gap of 2D materials with intercalants(6,7); however, post-growth intercalation has usually been limited to alkali metals(8-10). Here we show that the self-intercalation of native atoms(11,12) into bilayer transition metal dichalcogenides during growth generates a class of ultrathin, covalently bonded materials, which we name ic-2D. The stoichiometry of these materials is defined by periodic occupancy patterns of the octahedral vacancy sites in the van der Waals gap, and their properties can be tuned by varying the coverage and the spatial arrangement of the filled sites(7,13). By performing growth under high metal chemical potential(14,15) we can access a range of tantalum-intercalated TaS(Se)(y), including 25% Ta-intercalated Ta9S16, 33.3% Ta-intercalated Ta7S12, 50% Ta-intercalated Ta10S16, 66.7% Ta-intercalated Ta8Se12 (which forms a Kagome lattice) and 100% Ta-intercalated Ta9Se12. Ferromagnetic order was detected in some of these intercalated phases. We also demonstrate that self-intercalated V11S16, In11Se16 and FexTey can be grown under metal-rich conditions. Our work establishes self-intercalation as an approach through which to grow a new class of 2D materials with stoichiometry- or composition-dependent properties. |
Fu, Wei; Qiao, Jingsi; Zhao, Xiaoxu; Chen, Yu; Fu, Deyi; Yu, Wei; Leng, Kai; Song, Peng; Chen, Zhi; Yu, Ting; Pennycook, Stephen J; Quek, Su Ying; Loh, Kian Ping Room Temperature Commensurate Charge Density Wave on Epitaxially Grown Bilayer 2H-Tantalum Sulfide on Hexagonal Boron Nitride Journal Article 27 ACS NANO, 14 (4), pp. 3917-3926, 2020, ISSN: 1936-0851. @article{ISI:000529895500017, title = {Room Temperature Commensurate Charge Density Wave on Epitaxially Grown Bilayer 2H-Tantalum Sulfide on Hexagonal Boron Nitride}, author = {Wei Fu and Jingsi Qiao and Xiaoxu Zhao and Yu Chen and Deyi Fu and Wei Yu and Kai Leng and Peng Song and Zhi Chen and Ting Yu and Stephen J Pennycook and Su Ying Quek and Kian Ping Loh}, doi = {10.1021/acsnano.0c00303}, times_cited = {27}, issn = {1936-0851}, year = {2020}, date = {2020-04-28}, journal = {ACS NANO}, volume = {14}, number = {4}, pages = {3917-3926}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The breaking of multiple symmetries by periodic lattice distortion at a commensurate charge density wave (CDW) state is expected to give rise to intriguing interesting properties. However, accessing the commensurate CDW state on bulk TaS, crystals typically requires cryogenic temperatures (77 K), which precludes practical applications. Here, we found that heteroepitaxial growth of a 2H-tantalum disulfide bilayer on a hexagonal-boron nitride (h-BN) substrate produces a robust commensurate CDW order at room temperature, characterized by a Moire superlattice of 3 X 3 TaS2 on a 4 X 4 h-BN unit cell. The CDW order is confirmed by scanning transmission electron microscopy and Raman measurements. Theoretical calculations reveal that the stabilizing energy for the CDW phase of the monolayer and bilayer 2H-TaS2-on-h-BN substrates arises primarily from interfacial electrostatic interactions and, to a lesser extent, interfacial strain. Our work shows that engineering interfacial electrostatic interactions in an ultrathin van der Waals heterostructure constitutes an effective way to enhance CDW order in two-dimensional materials.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The breaking of multiple symmetries by periodic lattice distortion at a commensurate charge density wave (CDW) state is expected to give rise to intriguing interesting properties. However, accessing the commensurate CDW state on bulk TaS, crystals typically requires cryogenic temperatures (77 K), which precludes practical applications. Here, we found that heteroepitaxial growth of a 2H-tantalum disulfide bilayer on a hexagonal-boron nitride (h-BN) substrate produces a robust commensurate CDW order at room temperature, characterized by a Moire superlattice of 3 X 3 TaS2 on a 4 X 4 h-BN unit cell. The CDW order is confirmed by scanning transmission electron microscopy and Raman measurements. Theoretical calculations reveal that the stabilizing energy for the CDW phase of the monolayer and bilayer 2H-TaS2-on-h-BN substrates arises primarily from interfacial electrostatic interactions and, to a lesser extent, interfacial strain. Our work shows that engineering interfacial electrostatic interactions in an ultrathin van der Waals heterostructure constitutes an effective way to enhance CDW order in two-dimensional materials. |
Song, Peng; Hsu, Chuang-Han; Vignale, Giovanni; Zhao, Meng; Liu, Jiawei; Deng, Yujun; Fu, Wei; Liu, Yanpeng; Zhang, Yuanbo; Lin, Hsin; Pereira, Vitor M; Loh, Kian Ping Coexistence of large conventional and planar spin Hall effect with long spin diffusion length in a low-symmetry semimetal at room temperature Journal Article NATURE MATERIALS, 19 (3), pp. 292-+, 2020, ISSN: 1476-1122. @article{ISI:000510823100005, title = {Coexistence of large conventional and planar spin Hall effect with long spin diffusion length in a low-symmetry semimetal at room temperature}, author = {Peng Song and Chuang-Han Hsu and Giovanni Vignale and Meng Zhao and Jiawei Liu and Yujun Deng and Wei Fu and Yanpeng Liu and Yuanbo Zhang and Hsin Lin and Vitor M Pereira and Kian Ping Loh}, doi = {10.1038/s41563-019-0600-4}, times_cited = {0}, issn = {1476-1122}, year = {2020}, date = {2020-02-03}, journal = {NATURE MATERIALS}, volume = {19}, number = {3}, pages = {292-+}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {A large spin Hall angle and long spin diffusion length are found in the low-symmetry, few-layer semimetal MoTe2 at room temperature, thus identifying this material as an excellent candidate for simultaneous spin generation, transport and detection.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A large spin Hall angle and long spin diffusion length are found in the low-symmetry, few-layer semimetal MoTe2 at room temperature, thus identifying this material as an excellent candidate for simultaneous spin generation, transport and detection. |
2018 |
Zhao, Meng; Song, Peng; Teng, Jinghua Electrically and Optically Tunable Responses in Graphene/Transition-Metal-Dichalcogenide Heterostructures Journal Article ACS APPLIED MATERIALS & INTERFACES, 10 (50), pp. 44102-44108, 2018, ISSN: 1944-8244. @article{ISI:000454383500089, title = {Electrically and Optically Tunable Responses in Graphene/Transition-Metal-Dichalcogenide Heterostructures}, author = {Meng Zhao and Peng Song and Jinghua Teng}, doi = {10.1021/acsami.8b12588}, times_cited = {0}, issn = {1944-8244}, year = {2018}, date = {2018-12-19}, journal = {ACS APPLIED MATERIALS & INTERFACES}, volume = {10}, number = {50}, pages = {44102-44108}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Heterostructures involving layered two-dimensional (2D) transition metal dichalcogenides (TMDCs) are not only fundamentally interesting to explore emerging properties at atomically thin limit, but also technically important to achieve novel optoelectronic devices. However, achieving tunable optoelectronic properties and clarifying interlayer processes (charge transfer, energy transfer) in 2D heterostructures have remained part of the key challenges so far. Here, by fabricating heterostructures of graphene and monolayer TMDCs (n-type MoS2 and p-type WSe2), we demonstrate both electrically and optically tunable responses of the heterostructures, revealing the critical interface processes between graphene and TMDCs. In MoS2/graphene heterostructures, electron transfer from MoS2 to graphene is observed, and gate-tunable interface relaxation induces the electrically controlled photoluminescence (PL), whereas in WSe2/graphene heterostructures, electron transfer from graphene to WSe2 is observed, and the PL is tuned by carrier density, which can be controlled by the gate voltage. The interlayer process can also be modulated by laser intensity, which enables photoinduced doping on graphene and optically tunable electrical characteristics of graphene. Combining the tunable Fermi level of graphene and strong light matter interaction of monolayer TMDCs, our demonstrations are important for the design of multifunctional and efficient optoelectronic devices with TMDC/graphene heterostructures.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Heterostructures involving layered two-dimensional (2D) transition metal dichalcogenides (TMDCs) are not only fundamentally interesting to explore emerging properties at atomically thin limit, but also technically important to achieve novel optoelectronic devices. However, achieving tunable optoelectronic properties and clarifying interlayer processes (charge transfer, energy transfer) in 2D heterostructures have remained part of the key challenges so far. Here, by fabricating heterostructures of graphene and monolayer TMDCs (n-type MoS2 and p-type WSe2), we demonstrate both electrically and optically tunable responses of the heterostructures, revealing the critical interface processes between graphene and TMDCs. In MoS2/graphene heterostructures, electron transfer from MoS2 to graphene is observed, and gate-tunable interface relaxation induces the electrically controlled photoluminescence (PL), whereas in WSe2/graphene heterostructures, electron transfer from graphene to WSe2 is observed, and the PL is tuned by carrier density, which can be controlled by the gate voltage. The interlayer process can also be modulated by laser intensity, which enables photoinduced doping on graphene and optically tunable electrical characteristics of graphene. Combining the tunable Fermi level of graphene and strong light matter interaction of monolayer TMDCs, our demonstrations are important for the design of multifunctional and efficient optoelectronic devices with TMDC/graphene heterostructures. |
Song, Peng; Hsu, Chuanghan; Zhao, Meng; Zhao, Xiaoxu; Chang, Tay-Rong; Teng, Jinghua; Lin, Hsin; Loh, Kian Ping Few-layer 1T′ MoTe2 as gapless semimetal with thickness dependent carrier transport Journal Article 2D MATERIALS, 5 (3), 2018, ISSN: 2053-1583. @article{ISI:000435144800001, title = {Few-layer 1T′ MoTe_{2} as gapless semimetal with thickness dependent carrier transport}, author = {Peng Song and Chuanghan Hsu and Meng Zhao and Xiaoxu Zhao and Tay-Rong Chang and Jinghua Teng and Hsin Lin and Kian Ping Loh}, doi = {10.1088/2053-1583/aac78d}, times_cited = {0}, issn = {2053-1583}, year = {2018}, date = {2018-07-01}, journal = {2D MATERIALS}, volume = {5}, number = {3}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {Semimetal MoTe2 can be a type II Weyl semimetal in the bulk, but monolayer of this material is predicted to be quantum spin hall insulators. This dramatic change in electronic properties with number of layers is an excellent example of the dimensional effects of quantum transport. However, a detailed experimental study of the carrier transport and band structure of ultrathin semimetal MoTe2 is lacking so far. We performed magneto-transport measurements to study the conduction behavior and quantum phase coherence of 1T' MoTe2 as a function of its thickness. We show that due to a unique two-band transport mechanism (synergetic contribution from electron conduction and hole conduction), the conduction behavior of 1T ' MoTe2 changes from metallic to p-type unipolar, and finally to ambipolar as the thickness decreases, suggesting that this effect can be used in devices by effectively controlling the thickness. Our transport studies, optical measurements and first-principles electronic structure calculations reveal that 1T' MoTe2 remains gapless down to a few (similar to 2-3) layers. Despite being gapless, 1T ' MoTe2 exhibits metal-insulator transition at 3-layer thickness, due to enhanced carrier localization effect.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Semimetal MoTe2 can be a type II Weyl semimetal in the bulk, but monolayer of this material is predicted to be quantum spin hall insulators. This dramatic change in electronic properties with number of layers is an excellent example of the dimensional effects of quantum transport. However, a detailed experimental study of the carrier transport and band structure of ultrathin semimetal MoTe2 is lacking so far. We performed magneto-transport measurements to study the conduction behavior and quantum phase coherence of 1T' MoTe2 as a function of its thickness. We show that due to a unique two-band transport mechanism (synergetic contribution from electron conduction and hole conduction), the conduction behavior of 1T ' MoTe2 changes from metallic to p-type unipolar, and finally to ambipolar as the thickness decreases, suggesting that this effect can be used in devices by effectively controlling the thickness. Our transport studies, optical measurements and first-principles electronic structure calculations reveal that 1T' MoTe2 remains gapless down to a few (similar to 2-3) layers. Despite being gapless, 1T ' MoTe2 exhibits metal-insulator transition at 3-layer thickness, due to enhanced carrier localization effect. |
Song, Peng; Guerin, Sarah; Tan, Sherman Jun Rong; Annadata, Harshini Venkata; Yu, Xiaojiang; Scully, Micheal; Han, Ying Mei; Roemer, Max; Loh, Kian Ping; Thompson, Damien; Nijhuis, Christian A Stable Molecular Diodes Based on π-π Interactions of the Molecular Frontier Orbitals with Graphene Electrodes Journal Article ADVANCED MATERIALS, 30 (10), 2018, ISSN: 0935-9648. @article{ISI:000426720400028, title = {Stable Molecular Diodes Based on π-π Interactions of the Molecular Frontier Orbitals with Graphene Electrodes}, author = {Peng Song and Sarah Guerin and Sherman Jun Rong Tan and Harshini Venkata Annadata and Xiaojiang Yu and Micheal Scully and Ying Mei Han and Max Roemer and Kian Ping Loh and Damien Thompson and Christian A Nijhuis}, doi = {10.1002/adma.201706322}, times_cited = {0}, issn = {0935-9648}, year = {2018}, date = {2018-03-08}, journal = {ADVANCED MATERIALS}, volume = {30}, number = {10}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {In molecular electronics, it is important to control the strength of the molecule-electrode interaction to balance the trade-off between electronic coupling strength and broadening of the molecular frontier orbitals: too strong coupling results in severe broadening of the molecular orbitals while the molecular orbitals cannot follow the changes in the Fermi levels under applied bias when the coupling is too weak. Here, a platform based on graphene bottom electrodes to which molecules can bind via pi-pi interactions is reported. These interactions are strong enough to induce electronic function (rectification) while minimizing broadening of the molecular frontier orbitals. Molecular tunnel junctions are fabricated based on self-assembled monolayers (SAMs) of Fc(CH2)(11)X (Fc = ferrocenyl, X = NH2, Br, or H) on graphene bottom electrodes contacted to eutectic alloy of gallium and indium top electrodes. The Fc units interact more strongly with graphene than the X units resulting in SAMs with the Fc at the bottom of the SAM. The molecular diodes perform well with rectification ratios of 30-40, and they are stable against bias stressing under ambient conditions. Thus, tunnel junctions based on graphene with pi-pi molecule-electrode coupling are promising platforms to fabricate stable and well-performing molecular diodes.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In molecular electronics, it is important to control the strength of the molecule-electrode interaction to balance the trade-off between electronic coupling strength and broadening of the molecular frontier orbitals: too strong coupling results in severe broadening of the molecular orbitals while the molecular orbitals cannot follow the changes in the Fermi levels under applied bias when the coupling is too weak. Here, a platform based on graphene bottom electrodes to which molecules can bind via pi-pi interactions is reported. These interactions are strong enough to induce electronic function (rectification) while minimizing broadening of the molecular frontier orbitals. Molecular tunnel junctions are fabricated based on self-assembled monolayers (SAMs) of Fc(CH2)(11)X (Fc = ferrocenyl, X = NH2, Br, or H) on graphene bottom electrodes contacted to eutectic alloy of gallium and indium top electrodes. The Fc units interact more strongly with graphene than the X units resulting in SAMs with the Fc at the bottom of the SAM. The molecular diodes perform well with rectification ratios of 30-40, and they are stable against bias stressing under ambient conditions. Thus, tunnel junctions based on graphene with pi-pi molecule-electrode coupling are promising platforms to fabricate stable and well-performing molecular diodes. |
Ren, Tianhua; Song, Peng; Chen, Jianyi; Loh, Klan Ping Whisper Gallery Modes in Monolayer Tungsten Disulfide-Hexagonal Boron Nitride Optical Cavity Journal Article ACS PHOTONICS, 5 (2), pp. 353-358, 2018, ISSN: 2330-4022. @article{ISI:000426142800015, title = {Whisper Gallery Modes in Monolayer Tungsten Disulfide-Hexagonal Boron Nitride Optical Cavity}, author = {Tianhua Ren and Peng Song and Jianyi Chen and Klan Ping Loh}, doi = {10.1021/acsphotonics.7b01245}, times_cited = {0}, issn = {2330-4022}, year = {2018}, date = {2018-02-01}, journal = {ACS PHOTONICS}, volume = {5}, number = {2}, pages = {353-358}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {There are strong interests in constructing nanolasers using two-dimensional transition metal dichalcogenides (TMDs) due to their strong light matter interactions and high optical gain. However, most cavity designs based on transfer of exfoliated TMDs on silicon oxide are not optimized since monolayer emitters are located far from where the photonic mode reaches maximum intensity. By taking advantage of the excellent dielectric properties of hexagonal boron nitride (h-BN), we design a new microdisk optical cavity fabricated from a van der Waals (VdW) stacked h-BN/WS2/hBN. The heterostructure is patterned into microdisk cavities characterized by whispering gallery modes (WGMs). The emission intensity of the WS2, trion is enhanced by 2.9 times that of exciton in the heterostructure, giving rise to whisper gallery modes with resonance intensities that show nonlinear power dependence. A Rayleigh scatterer directs the cavity emission to vertical collection. Such VdW heterostructure provides an atomically smooth interface that is ideal for low loss photon propagation, giving a Q factor of 1200.}, keywords = {}, pubstate = {published}, tppubtype = {article} } There are strong interests in constructing nanolasers using two-dimensional transition metal dichalcogenides (TMDs) due to their strong light matter interactions and high optical gain. However, most cavity designs based on transfer of exfoliated TMDs on silicon oxide are not optimized since monolayer emitters are located far from where the photonic mode reaches maximum intensity. By taking advantage of the excellent dielectric properties of hexagonal boron nitride (h-BN), we design a new microdisk optical cavity fabricated from a van der Waals (VdW) stacked h-BN/WS2/hBN. The heterostructure is patterned into microdisk cavities characterized by whispering gallery modes (WGMs). The emission intensity of the WS2, trion is enhanced by 2.9 times that of exciton in the heterostructure, giving rise to whisper gallery modes with resonance intensities that show nonlinear power dependence. A Rayleigh scatterer directs the cavity emission to vertical collection. Such VdW heterostructure provides an atomically smooth interface that is ideal for low loss photon propagation, giving a Q factor of 1200. |
Zhao, Xiaoxu; Fu, Deyi; Ding, Zijing; Zhang, Yu-Yang; Wan, Dongyang; Tan, Sherman J R; Chen, Zhongxin; Leng, Kai; Dan, Jiadong; Fu, Wei; Geng, Dechao; Song, Peng; Du, Yonghua; Venkatesan, T; Pantelides, Sokrates T; Pennycook, Stephen J; Zhou, Wu; Loh, Kian Ping Mo-Terminated Edge Reconstructions in Nanoporous Molybdenum Disulfide Film Journal Article NANO LETTERS, 18 (1), pp. 482-490, 2018, ISSN: 1530-6984. @article{ISI:000420000000065, title = {Mo-Terminated Edge Reconstructions in Nanoporous Molybdenum Disulfide Film}, author = {Xiaoxu Zhao and Deyi Fu and Zijing Ding and Yu-Yang Zhang and Dongyang Wan and Sherman J R Tan and Zhongxin Chen and Kai Leng and Jiadong Dan and Wei Fu and Dechao Geng and Peng Song and Yonghua Du and T Venkatesan and Sokrates T Pantelides and Stephen J Pennycook and Wu Zhou and Kian Ping Loh}, doi = {10.1021/acs.nanolett.7b04426}, times_cited = {2}, issn = {1530-6984}, year = {2018}, date = {2018-01-01}, journal = {NANO LETTERS}, volume = {18}, number = {1}, pages = {482-490}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The catalytic and magnetic properties of molybdenum disulfide (MoS2) are significantly enhanced by the presence of edge sites. One way to obtain a high density of edge sites in a two-dimensional (2D) film is by introducing porosity. However, the large-scale bottom-up synthesis of a porous 2D MoS2 film remains challenging and the correlation of growth conditions to the atomic structures of the edges is not well understood. Here, using molecular beam epitaxy, we prepare wafer-scale nanoporous MoS2 films under conditions of high Mo flux and study their catalytic and magnetic properties. Atomic-resolution electron microscopy imaging of the pores reveals two new types of reconstructed Mo-terminated edges, namely, a distorted 1T (DT) edge and the Mo-Klein edge. Nanoporous MoS2 films are magnetic up to 400 K, which is attributed to the presence of Mo-terminated edges with unpaired electrons, as confirmed by density functional theory calculation. The small hydrogen adsorption free energy at these Mo-terminated edges leads to excellent activity for the hydrogen evolution reaction.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The catalytic and magnetic properties of molybdenum disulfide (MoS2) are significantly enhanced by the presence of edge sites. One way to obtain a high density of edge sites in a two-dimensional (2D) film is by introducing porosity. However, the large-scale bottom-up synthesis of a porous 2D MoS2 film remains challenging and the correlation of growth conditions to the atomic structures of the edges is not well understood. Here, using molecular beam epitaxy, we prepare wafer-scale nanoporous MoS2 films under conditions of high Mo flux and study their catalytic and magnetic properties. Atomic-resolution electron microscopy imaging of the pores reveals two new types of reconstructed Mo-terminated edges, namely, a distorted 1T (DT) edge and the Mo-Klein edge. Nanoporous MoS2 films are magnetic up to 400 K, which is attributed to the presence of Mo-terminated edges with unpaired electrons, as confirmed by density functional theory calculation. The small hydrogen adsorption free energy at these Mo-terminated edges leads to excellent activity for the hydrogen evolution reaction. |
2017 |
Peng, Bo; Li, Qi; Liang, Xiao; Song, Peng; Li, Jian; He, Keliang; Fu, Deyi; Li, Yue; Shen, Chao; Wang, Hailong; Wang, Chuangtang; Liu, Tao; Zhang, Li; Lu, Haipeng; Wang, Xin; Zhao, Jianhua; Xie, Jianliang; Wu, Mingzhong; Bi, Lei; Deng, Longjiang; Loh, Kian Ping Valley Polarization of Trions and Magnetoresistance in Heterostructures of MoS2 and Yttrium Iron Garnet Journal Article ACS NANO, 11 (12), pp. 12257-12265, 2017, ISSN: 1936-0851. @article{ISI:000418990200052, title = {Valley Polarization of Trions and Magnetoresistance in Heterostructures of MoS_{2} and Yttrium Iron Garnet}, author = {Bo Peng and Qi Li and Xiao Liang and Peng Song and Jian Li and Keliang He and Deyi Fu and Yue Li and Chao Shen and Hailong Wang and Chuangtang Wang and Tao Liu and Li Zhang and Haipeng Lu and Xin Wang and Jianhua Zhao and Jianliang Xie and Mingzhong Wu and Lei Bi and Longjiang Deng and Kian Ping Loh}, doi = {10.1021/acsnano.7b05743}, times_cited = {2}, issn = {1936-0851}, year = {2017}, date = {2017-12-01}, journal = {ACS NANO}, volume = {11}, number = {12}, pages = {12257-12265}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Manipulation of spin degree of freedom (DOF) of electrons is the fundamental aspect of spintronic and valleytronic devices. Two-dimensional transition metal dichalcogenides (2D TMDCs) exhibit an emerging valley pseudospin, in which spin-up (-down) electrons are distributed in a +K (-K) valley. This valley polarization gives a DOF for spintronic and valleytronic devices. Recently, magnetic exchange interactions between graphene and magnetic insulator yttrium iron garnet (YIG) have been exploited. However, the physics of 2D TMDCs with YIG have not been shown before. Here we demonstrate strong many-body effects in a heterostructure geometry comprising a MoS2 monolayer and YIG. High-order trions are directly identified by mapping absorption and photoluminescence at 12 K. The electron doping density is up to similar to 10'3 cm(-2), resulting in a large splitting of similar to 40 meV between trions and excitons. The trions exhibit a high circular polarization of similar to 80% under optical pumping by circularly polarized light at similar to 1.96 eV; it is confirmed experimentally that both phonon scattering and electron-hole exchange interaction contribute to the valley depolarization with temperature; importantly, a magnetoresistance (MR) behavior in the MoS2 monolayer was observed, and a giant MR ratio of similar to 30% is achieved, which is 1 order of magnitude larger than the reported ratio in MoS2/CoFe2O4 heterostructures. Our experimental results confirm that the giant MR behaviors are attributed to the interfacial spin accumulation due to YIG substrates. Our work provides an insight into spin manipulation in a heterostructure of monolayer materials and magnetic substrates.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Manipulation of spin degree of freedom (DOF) of electrons is the fundamental aspect of spintronic and valleytronic devices. Two-dimensional transition metal dichalcogenides (2D TMDCs) exhibit an emerging valley pseudospin, in which spin-up (-down) electrons are distributed in a +K (-K) valley. This valley polarization gives a DOF for spintronic and valleytronic devices. Recently, magnetic exchange interactions between graphene and magnetic insulator yttrium iron garnet (YIG) have been exploited. However, the physics of 2D TMDCs with YIG have not been shown before. Here we demonstrate strong many-body effects in a heterostructure geometry comprising a MoS2 monolayer and YIG. High-order trions are directly identified by mapping absorption and photoluminescence at 12 K. The electron doping density is up to similar to 10'3 cm(-2), resulting in a large splitting of similar to 40 meV between trions and excitons. The trions exhibit a high circular polarization of similar to 80% under optical pumping by circularly polarized light at similar to 1.96 eV; it is confirmed experimentally that both phonon scattering and electron-hole exchange interaction contribute to the valley depolarization with temperature; importantly, a magnetoresistance (MR) behavior in the MoS2 monolayer was observed, and a giant MR ratio of similar to 30% is achieved, which is 1 order of magnitude larger than the reported ratio in MoS2/CoFe2O4 heterostructures. Our experimental results confirm that the giant MR behaviors are attributed to the interfacial spin accumulation due to YIG substrates. Our work provides an insight into spin manipulation in a heterostructure of monolayer materials and magnetic substrates. |
Fu, Deyi; Zhao, Xiaoxu; Zhang, Yu-Yang; Li, Linjun; Xu, Hai; Jang, A-Rang; Yoon, Seong In; Song, Peng; Poh, Sock Mui; Ren, Tianhua; Ding, Zijing; Fu, Wei; Shin, Tae Joo; Shin, Hyeon Suk; Pantelides, Sokrates T; Zhou, Wu; Loh, Kian Ping Molecular Beam Epitaxy of Highly Crystalline Monolayer Molybdenum Disulfide on Hexagonal Boron Nitride Journal Article JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 139 (27), pp. 9392-9400, 2017, ISSN: 0002-7863. @article{ISI:000405642400044, title = {Molecular Beam Epitaxy of Highly Crystalline Monolayer Molybdenum Disulfide on Hexagonal Boron Nitride}, author = {Deyi Fu and Xiaoxu Zhao and Yu-Yang Zhang and Linjun Li and Hai Xu and A-Rang Jang and Seong In Yoon and Peng Song and Sock Mui Poh and Tianhua Ren and Zijing Ding and Wei Fu and Tae Joo Shin and Hyeon Suk Shin and Sokrates T Pantelides and Wu Zhou and Kian Ping Loh}, doi = {10.1021/jacs.7b05131}, times_cited = {0}, issn = {0002-7863}, year = {2017}, date = {2017-07-12}, journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, volume = {139}, number = {27}, pages = {9392-9400}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Atomically thin molybdenum disulfide (MoS2), a direct-band-gap semiconductor, is promising for applications in electronics and optoelectronics, but the scalable synthesis of highly crystalline film remains challenging. Here we report the successful epitaxial growth of a continuous, uniform, highly crystalline monolayer MoS2 film on hexagonal boron nitride (h-BN) by molecular beam epitaxy. Atomic force microscopy and electron microscopy studies reveal that MoS2 grown on h-BN primarily consists of two types of nucleation grains (0 aligned and 60 degrees antialigned domains). By adopting a high growth temperature and ultralow precursor flux, the formation of 60 degrees antialigned grains is largely suppressed. The resulting perfectly aligned grains merge seamlessly into a highly crystalline film. Large-scale monolayer MoS2 film can be grown on a 2 in. h-BN/sapphire wafer, for which surface morphology and Raman mapping confirm good spatial uniformity. Our study represents a significant step in the scalable synthesis of highly crystalline MoS2 films on atomically flat surfaces and paves the way to large-scale applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Atomically thin molybdenum disulfide (MoS2), a direct-band-gap semiconductor, is promising for applications in electronics and optoelectronics, but the scalable synthesis of highly crystalline film remains challenging. Here we report the successful epitaxial growth of a continuous, uniform, highly crystalline monolayer MoS2 film on hexagonal boron nitride (h-BN) by molecular beam epitaxy. Atomic force microscopy and electron microscopy studies reveal that MoS2 grown on h-BN primarily consists of two types of nucleation grains (0 aligned and 60 degrees antialigned domains). By adopting a high growth temperature and ultralow precursor flux, the formation of 60 degrees antialigned grains is largely suppressed. The resulting perfectly aligned grains merge seamlessly into a highly crystalline film. Large-scale monolayer MoS2 film can be grown on a 2 in. h-BN/sapphire wafer, for which surface morphology and Raman mapping confirm good spatial uniformity. Our study represents a significant step in the scalable synthesis of highly crystalline MoS2 films on atomically flat surfaces and paves the way to large-scale applications. |
Song, Peng; Thompson, Damien; Annadata, Harshini V; Guerin, Sarah; Loh, Kian Ping; Nijhuis, Christian A Supramolecular Structure of the Monolayer Triggers Odd-Even Effects in the Tunneling Rates across Noncovalent Junctions on Graphene Journal Article JOURNAL OF PHYSICAL CHEMISTRY C, 121 (8), pp. 4172-4180, 2017, ISSN: 1932-7447. @article{ISI:000395616200008, title = {Supramolecular Structure of the Monolayer Triggers Odd-Even Effects in the Tunneling Rates across Noncovalent Junctions on Graphene}, author = {Peng Song and Damien Thompson and Harshini V Annadata and Sarah Guerin and Kian Ping Loh and Christian A Nijhuis}, doi = {10.1021/acs.jpcc.6b12949}, times_cited = {2}, issn = {1932-7447}, year = {2017}, date = {2017-03-02}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {121}, number = {8}, pages = {4172-4180}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Molecular electronics aims to control charge transport at the molecular level, but it is not always clear which factors are important to control because it is difficult to distinguish interface effects from molecular effects. Investigating so-called "odd-even" effects in molecular tunnel junctions provides an opportunity to study molecular effects while keeping the nature of the molecule electrode interactions unchanged. Odd-even effects in charge tunneling rates have been observed in self-assembled monolayer (SAM)-based tunnel junctions with strong covalent molecule-bottom electrode interactions, but it is not clear whether these odd even effects originate from the intrinsic properties of the SAM or strong molecule-electrode interactions. Herein, we report tunnel junctions based on SAMs that form on graphene through weak noncovalent interactions (i.e., van der Waals interactions) and also form a van der Waals contact with the top electrode. We found that odd-even effects in charge tunneling rates persist in these junctions with only noncovalent interfaces. AC impedance spectroscopy measurements and molecular dynamics calculations indicate that the odd-even effects of charge transport rates mainly arise from intrinsic properties of the SAM packing, and thus these effects should be considered as a general design rule in future SAM -based junctions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Molecular electronics aims to control charge transport at the molecular level, but it is not always clear which factors are important to control because it is difficult to distinguish interface effects from molecular effects. Investigating so-called "odd-even" effects in molecular tunnel junctions provides an opportunity to study molecular effects while keeping the nature of the molecule electrode interactions unchanged. Odd-even effects in charge tunneling rates have been observed in self-assembled monolayer (SAM)-based tunnel junctions with strong covalent molecule-bottom electrode interactions, but it is not clear whether these odd even effects originate from the intrinsic properties of the SAM or strong molecule-electrode interactions. Herein, we report tunnel junctions based on SAMs that form on graphene through weak noncovalent interactions (i.e., van der Waals interactions) and also form a van der Waals contact with the top electrode. We found that odd-even effects in charge tunneling rates persist in these junctions with only noncovalent interfaces. AC impedance spectroscopy measurements and molecular dynamics calculations indicate that the odd-even effects of charge transport rates mainly arise from intrinsic properties of the SAM packing, and thus these effects should be considered as a general design rule in future SAM -based junctions. |
Geng, Dechao; Zhao, Xiaoxu; Li, Linjun; Song, Peng; Tian, Bingbing; Liu, Wei; Chen, Jianyi; Shi, Dong; Lin, Ming; Zhou, Wu; Loh, Kian Ping Controlled growth of ultrathin Mo2C superconducting crystals on liquid Cu surface Journal Article 2D MATERIALS, 4 (1), 2017, ISSN: 2053-1583. @article{ISI:000391612000001, title = {Controlled growth of ultrathin Mo_{2}C superconducting crystals on liquid Cu surface}, author = {Dechao Geng and Xiaoxu Zhao and Linjun Li and Peng Song and Bingbing Tian and Wei Liu and Jianyi Chen and Dong Shi and Ming Lin and Wu Zhou and Kian Ping Loh}, doi = {10.1088/2053-1583/aa51b7}, times_cited = {0}, issn = {2053-1583}, year = {2017}, date = {2017-03-01}, journal = {2D MATERIALS}, volume = {4}, number = {1}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {Exhibiting thickness-dependent change in the critical temperature (T-c) for the onset of superconductivity, Mo2C has emerged as an important new member in the family of two-dimensional atomic crystals. Controllable growth in terms of morphology and thickness is necessary to elucidate its intrinsic properties at the 2D limit. Here we demonstrate the chemical vapor deposition of ultrathin Mo2C crystals on liquid Cu surface where the morphology of the crystals can be controlled by tuning the carbon supersaturation. A unique staggered carbon vacancy ordering is discovered in Mo2C crystals having particular geometries. Thickness engineering of the crystal can be achieved by controlling the thickness of the Cu catalyst layer, which affords a facile route to grow ultrathin 2D samples. Ultrathin Mo2C crystals so obtained, have been characterized using aberration corrected scanning transmission electron microscopy annular dark field imaging, where the co-existence of both AA and AB stacking modes is observed. The high crystallinity of the Mo2C crystals synthesized in this work is attested by its characteristic sharp superconducting transition.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Exhibiting thickness-dependent change in the critical temperature (T-c) for the onset of superconductivity, Mo2C has emerged as an important new member in the family of two-dimensional atomic crystals. Controllable growth in terms of morphology and thickness is necessary to elucidate its intrinsic properties at the 2D limit. Here we demonstrate the chemical vapor deposition of ultrathin Mo2C crystals on liquid Cu surface where the morphology of the crystals can be controlled by tuning the carbon supersaturation. A unique staggered carbon vacancy ordering is discovered in Mo2C crystals having particular geometries. Thickness engineering of the crystal can be achieved by controlling the thickness of the Cu catalyst layer, which affords a facile route to grow ultrathin 2D samples. Ultrathin Mo2C crystals so obtained, have been characterized using aberration corrected scanning transmission electron microscopy annular dark field imaging, where the co-existence of both AA and AB stacking modes is observed. The high crystallinity of the Mo2C crystals synthesized in this work is attested by its characteristic sharp superconducting transition. |