Transition metal phthalocyanines (TMPc) and relevant derivatives can act as pervasive molecules for their electronic, magnetic, and optical applications. Numerous researches based on TMPc are carried out, attempting t...Transition metal phthalocyanines (TMPc) and relevant derivatives can act as pervasive molecules for their electronic, magnetic, and optical applications. Numerous researches based on TMPc are carried out, attempting to synthesize novel two-dimensional (2D) metal-organic frameworks. Recently, some 2D poly-TMPc frameworks including FePc [J. Am. Chem. Soc. 133, 1203 (2011)], CoPc [Chem. Commun. 51, 2836 (2015)], and Ni-NiPc [J. Mater. Chem. A 6, 1188 (2018)] frameworks have been successfully synthesized experimentally. Meanwhile, potential applications in catalysis, gas storage, and spintronics were predicted by theoretical studies. Here, we propose a new kind of 2D poly-TMPc frameworks with kagome lattice (denoted as kag-TMPc) and systematically investigate their electronic and magnetic properties by employing first-principles calculations. We have demonstrated that the 2D kag-MnPc framework displays quite stable ferromagnetic ordering with Curie temperature about 125 K as indicated by Monte Carlo simulations based on Heisenberg model and prefers out-of-plane easy-magnetization axis. The 2D kag-CrPc framework is an ideal candidate for S=2 kagome antiferromagnet with RT3 magnetic order. Particularly, the investigations on optical absorption suggest that when the TMPc molecules are self-assembled into 2D kag- TMPc frameworks, their absorption wave bands are broadened, especially in visible region.展开更多
On-surface synthesis of semiconducting graphdiyne nanowires usually su er severe side re- actions owing to the high reactivity of the butadiynylene units at noble metal surfaces, limiting the production of isolated na...On-surface synthesis of semiconducting graphdiyne nanowires usually su er severe side re- actions owing to the high reactivity of the butadiynylene units at noble metal surfaces, limiting the production of isolated nanowires. In this work, we report the high-yield synthesis of branchless graphdiyne nanowires [-C≡C-Ph2-C≡C-]n via on-surface Ullmann coupling of 1,4-bis(4-bromophenyl)-1,3-butadiyne molecules with chemical vapor deposition method. Non-contact atomic force microscopy with single-bond resolution reveals that single gold adatoms act as e ective protecting groups for butadiynylene units by forming Au-π ligand bonds, preventing unwanted branched coupling reactions and enabling the synthesis of ultralong isolated graphdiyne nanowires. This study will stimulate further investigation on the role of various surface adatoms in protecting on-surface reactions.展开更多
Van der Waals stacking of two-dimensional crystals with rotation or mismatch in lattice constants gives rise to rich physical phenomena that are closely related to the strong correlations and band topology.Twisted gra...Van der Waals stacking of two-dimensional crystals with rotation or mismatch in lattice constants gives rise to rich physical phenomena that are closely related to the strong correlations and band topology.Twisted graphene and silicene heterobilayers have been theoretically predicted to host a tunable transport gap due to the mismatch of Dirac cones in the graphene and silicene layers.However,experimental realization of such twisted structure is challenging.Here,we report the formation of twisted graphene/silicene bilayers on Ru(0001)crystal via intercalation.Different moirépatterns form as single-crystalline graphene grows over different grains of the Ru surface.After silicon intercalation,graphene/silicene bilayers are observed with different twisting angles on top of different grains of the Ru substrate.Our work provides a new pathway towards construction of graphene based twisted heterobilayers.展开更多
The synthesis of antimonene, which is a promising group-V 2D material for both fundamental studies and technological applications, remains highly challenging. Thus far, it has been synthesized only by exfoliation or g...The synthesis of antimonene, which is a promising group-V 2D material for both fundamental studies and technological applications, remains highly challenging. Thus far, it has been synthesized only by exfoliation or growth on a few substrates. In this study, we show that thin layers of antimonene can be grown on Ag(111) by molecular beam epitaxy. High-resolution scanning tunneling microscopy combined with theoretical calculations revealed that the submonolayer Sb deposited on a Ag(111) surface forms a layer of AgSb2 surface alloy upon annealing. Further deposition of Sb on the AgSb2 surface alloy causes an epitaxial layer of Sb to form, which is identified as antimonene with a buckled honeycomb structure. More interestingly, the lattice constant of the epitaxial antimonene (5 /-) is much larger than that of freestanding antimonene, indicating a high tensile strain of more than 20%. This kind of large strain is expected to make the antimonene a highly promising candidate for room- temperature quantum spin Hall material.展开更多
Superconducting metal dichalcogenides(MDCs)present several similarities to the other layered SI1-perconductors like cuprates.The superconductivity in atomically thin MDCs has been demonstrated by recent experiments,ho...Superconducting metal dichalcogenides(MDCs)present several similarities to the other layered SI1-perconductors like cuprates.The superconductivity in atomically thin MDCs has been demonstrated by recent experiments,however,the investigation of the superconductivity intertwined with other or-ders are scarce.Investigating the pseudogap in atomic layers of MDCs may help to understand the superconducting mechanism for these true two dimensional(2D)superconducting systemns.Herein we report a pseudogap opening in the tunneling spectra of thin layers of SnSe2 epitaxially grown on highly oriented pyrolytic graphite(HOPG)with scanning tunneling microscopy/spectroscopy(STM/STS).A significant V-shaped pseudogap was observed to open near the Fermi level(Er)in the sTS.And at elevated temperatures,the gap gradually evolves to a shallow dip.Our experimental observations provide direct evidence of a pseudogap state in the electron-doped SnSe2 atomic layers on the HOPG surface,which may stimulate further exploration of the mechanism of superconductivity at 2D limit in MDCs.展开更多
基金the National Key Research Development Program of China (No.2016YFA0200604 and No.2017YFA0204904)the National Natural Science Foundation of China (No.21473174)+1 种基金the Fundamental Research Funds for the Central Universities (No.WK2340000074 and No.WK2060190084)The computational resources of Super-computing Center of University of Science and Technology of China, Supercomputing Center of Chinese Academy of Sciences, Tianjing, and Shanghai Supercomputer Centers are also acknowledged.
文摘Transition metal phthalocyanines (TMPc) and relevant derivatives can act as pervasive molecules for their electronic, magnetic, and optical applications. Numerous researches based on TMPc are carried out, attempting to synthesize novel two-dimensional (2D) metal-organic frameworks. Recently, some 2D poly-TMPc frameworks including FePc [J. Am. Chem. Soc. 133, 1203 (2011)], CoPc [Chem. Commun. 51, 2836 (2015)], and Ni-NiPc [J. Mater. Chem. A 6, 1188 (2018)] frameworks have been successfully synthesized experimentally. Meanwhile, potential applications in catalysis, gas storage, and spintronics were predicted by theoretical studies. Here, we propose a new kind of 2D poly-TMPc frameworks with kagome lattice (denoted as kag-TMPc) and systematically investigate their electronic and magnetic properties by employing first-principles calculations. We have demonstrated that the 2D kag-MnPc framework displays quite stable ferromagnetic ordering with Curie temperature about 125 K as indicated by Monte Carlo simulations based on Heisenberg model and prefers out-of-plane easy-magnetization axis. The 2D kag-CrPc framework is an ideal candidate for S=2 kagome antiferromagnet with RT3 magnetic order. Particularly, the investigations on optical absorption suggest that when the TMPc molecules are self-assembled into 2D kag- TMPc frameworks, their absorption wave bands are broadened, especially in visible region.
基金the National Key R&D Program of China(No.2016YFA0200603 No.2017YFA0205004)the Anhui Initiative in Quantum Information Technologies(AHY090300)+2 种基金the National Natural Science Foundation of China(No.21473174)the Fundamental Research Funds for the Central Universities(No.WK2060190084 and No.WK2340000082)Ai-di Zhao acknowledges a fellow-ship from the Youth Innovation Promotion Association of Chinese Academy of Science(2011322).
文摘On-surface synthesis of semiconducting graphdiyne nanowires usually su er severe side re- actions owing to the high reactivity of the butadiynylene units at noble metal surfaces, limiting the production of isolated nanowires. In this work, we report the high-yield synthesis of branchless graphdiyne nanowires [-C≡C-Ph2-C≡C-]n via on-surface Ullmann coupling of 1,4-bis(4-bromophenyl)-1,3-butadiyne molecules with chemical vapor deposition method. Non-contact atomic force microscopy with single-bond resolution reveals that single gold adatoms act as e ective protecting groups for butadiynylene units by forming Au-π ligand bonds, preventing unwanted branched coupling reactions and enabling the synthesis of ultralong isolated graphdiyne nanowires. This study will stimulate further investigation on the role of various surface adatoms in protecting on-surface reactions.
基金the Ministry of Science and Technology of China(Nos.2019YFA0308500 and 2018YFA0305800)the National Natural Science Foundation of China(Nos.61888102,51991340,and 52072401)the Chinese Academy of Sciences Project for Young Scientists in Basic Research(No.YSBR-003).
文摘Van der Waals stacking of two-dimensional crystals with rotation or mismatch in lattice constants gives rise to rich physical phenomena that are closely related to the strong correlations and band topology.Twisted graphene and silicene heterobilayers have been theoretically predicted to host a tunable transport gap due to the mismatch of Dirac cones in the graphene and silicene layers.However,experimental realization of such twisted structure is challenging.Here,we report the formation of twisted graphene/silicene bilayers on Ru(0001)crystal via intercalation.Different moirépatterns form as single-crystalline graphene grows over different grains of the Ru surface.After silicon intercalation,graphene/silicene bilayers are observed with different twisting angles on top of different grains of the Ru substrate.Our work provides a new pathway towards construction of graphene based twisted heterobilayers.
文摘The synthesis of antimonene, which is a promising group-V 2D material for both fundamental studies and technological applications, remains highly challenging. Thus far, it has been synthesized only by exfoliation or growth on a few substrates. In this study, we show that thin layers of antimonene can be grown on Ag(111) by molecular beam epitaxy. High-resolution scanning tunneling microscopy combined with theoretical calculations revealed that the submonolayer Sb deposited on a Ag(111) surface forms a layer of AgSb2 surface alloy upon annealing. Further deposition of Sb on the AgSb2 surface alloy causes an epitaxial layer of Sb to form, which is identified as antimonene with a buckled honeycomb structure. More interestingly, the lattice constant of the epitaxial antimonene (5 /-) is much larger than that of freestanding antimonene, indicating a high tensile strain of more than 20%. This kind of large strain is expected to make the antimonene a highly promising candidate for room- temperature quantum spin Hall material.
基金We thank Prof.Tao Wu for helpful discus.sion.This work was supported by the National Key R&D Program of China(Grant Nos.2016YFA0200603 and 2017YFA0205004)the"Strategic Priority Research Program"of CAS(Grant No.XDB01020100)+2 种基金the National Natural Science Foundation of China(Grant Nos.91321309,21421063,and 21473174)the Funda-mental Research Funds for the Central Science Advances Universi-ties(Nos.WK2060190027 and WK2060190084)A.Z.acknowledges a fellowship from the Youth Innovation Promotion Association of CAS(No.2011322)。
文摘Superconducting metal dichalcogenides(MDCs)present several similarities to the other layered SI1-perconductors like cuprates.The superconductivity in atomically thin MDCs has been demonstrated by recent experiments,however,the investigation of the superconductivity intertwined with other or-ders are scarce.Investigating the pseudogap in atomic layers of MDCs may help to understand the superconducting mechanism for these true two dimensional(2D)superconducting systemns.Herein we report a pseudogap opening in the tunneling spectra of thin layers of SnSe2 epitaxially grown on highly oriented pyrolytic graphite(HOPG)with scanning tunneling microscopy/spectroscopy(STM/STS).A significant V-shaped pseudogap was observed to open near the Fermi level(Er)in the sTS.And at elevated temperatures,the gap gradually evolves to a shallow dip.Our experimental observations provide direct evidence of a pseudogap state in the electron-doped SnSe2 atomic layers on the HOPG surface,which may stimulate further exploration of the mechanism of superconductivity at 2D limit in MDCs.