Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investi...Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investigation of its electronic structure are critical. Here we report the electronic structure of 1T'-MoTe2 films grown by molecular beam epitaxy(MBE).Growth of the 1T'-MoTe2 film depends critically on the substrate temperature, and successful growth of the film is indicated by streaky stripes in the reflection high energy electron diffraction(RHEED) and sharp diffraction spots in the low energy electron diffraction(LEED). Angle-resolved photoemission spectroscopy(ARPES) measurements reveal a metallic behavior in the as-grown film with an overlap between the conduction and valence bands. First principles calculation suggests that a suitable tensile strain along the a-axis direction is needed to induce a gap to make it an insulator. Our work not only reports the electronic structure of MBE grown 1T'-MoTe2 films, but also provides insights for strain engineering to make it possible for quantum spin Hall effect.展开更多
Enzyme-powered micro/nanomotors(EMNMs)represent cutting-edge research taking advantage of enzymes as biocatalysts to provide a driving force for micro/nanomotors.Up to now,EMNMs have been designed to be powered by cat...Enzyme-powered micro/nanomotors(EMNMs)represent cutting-edge research taking advantage of enzymes as biocatalysts to provide a driving force for micro/nanomotors.Up to now,EMNMs have been designed to be powered by catalase,urease,lipase,collagenase,compound enzymes,etc.They not only have good biocompatibility and biosafety but also possess the unique ability to utilize physiologically relevant fuel to achieve autonomous propulsion through in vivo catalytic reactions.This innovation has opened exciting possibilities for medical applications of EMNMs.Given the fact that the human body is naturally abundant with substrates available for enzymatic reactions,EMNMs can effectively exploit the complex microenvironment associated with diseases,enabling the diagnosis and treatment of various medical conditions.In this review,we first introduce different kinds of EMNMs applied in specific environments for the diagnosis and treatment of diseases,while highlighting their advancements for revolutionizing healthcare practices.Then,we address the challenges faced in this rapidly evolving field,and at last,the potential future development directions are discussed.As the potential of EMNMs becomes increasingly evident,continued research and exploration are essential to unlock their full capabilities and to ensure their successful integration into clinical applications.展开更多
PtTe2 and PtSe2 with trigonal structure have attracted extensive research interests since the discovery of type-II Dirac fermions in the bulk crystals. The evolution of the electronic structure from bulk 3D topologica...PtTe2 and PtSe2 with trigonal structure have attracted extensive research interests since the discovery of type-II Dirac fermions in the bulk crystals. The evolution of the electronic structure from bulk 3D topological semimetal to 2D atomic thin films is an important scientific question. While a transition from 3D type-II Dirac semimetal in the bulk to 2D semiconductor in monolayer(ML) film has been reported for PtSe2, so far the evolution of electronic structure of atomically thin PtTe2 films still remains unexplored.Here we report a systematic angle-resolved photoemission spectroscopy(ARPES) study of the electronic structure of high quality PtTe2 films grown by molecular beam epitaxy with thickness from 2 ML to 6 ML.ARPES measurements show that PtTe2 films still remain metallic even down to 2 ML thickness, which is in sharp contrast to the semiconducting property of few layer PtSe2 films. Moreover, a transition from 2D metal to 3D type-II Dirac semimetal occurs at film thickness of 4–6 ML. In addition, Spin-ARPES measurements reveal helical spin textures induced by local Rashba effect in the bulk PtTe2 crystal, suggesting that similar hidden spin is also expected in few monolayer PtTe2 films. Our work reveals the transition from2D metal to 3D topological semimetal and provides new opportunities for investigating metallic 2D films with local Rashba effect.展开更多
Numerous exotic properties have been discovered in Dirac Semimetals(DSMs) and Weyl Semimetals(WSMs). In a given DSM/WSM, the Dirac/Weyl nodes usually coexist with other bulk states, making their respective contributio...Numerous exotic properties have been discovered in Dirac Semimetals(DSMs) and Weyl Semimetals(WSMs). In a given DSM/WSM, the Dirac/Weyl nodes usually coexist with other bulk states, making their respective contribution elusive. In this work, we distinguish the role of bulk states from the tilted Dirac nodes on the transport properties in DSMs. Specifically, we applied pressure to a type-II DSM material, PtTe2, and studied its pressure modified electronic and lattice structure systematically by using in situ transport measurements and X-ray diffraction(XRD). A pressure-induced transition at about 20 GPa is revealed in the transport properties, while the layered lattice structure is robust against pressure as illustrated in XRD measurement results.Density functional theory(DFT) calculations suggest that this is originated from the Lifshitz transition in the bulk states. Our findings provide evidence to identify the bulk states' influence on transport from the topologically-protected DSM states in the DSM material.展开更多
基金Project supported by the National Basic Research Program of China(Grant Nos.2016YFA0301004 and 2015CB921001)the National Natural Science Foundation of China(Grant Nos.11334006,11725418,and 11674188)
文摘Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investigation of its electronic structure are critical. Here we report the electronic structure of 1T'-MoTe2 films grown by molecular beam epitaxy(MBE).Growth of the 1T'-MoTe2 film depends critically on the substrate temperature, and successful growth of the film is indicated by streaky stripes in the reflection high energy electron diffraction(RHEED) and sharp diffraction spots in the low energy electron diffraction(LEED). Angle-resolved photoemission spectroscopy(ARPES) measurements reveal a metallic behavior in the as-grown film with an overlap between the conduction and valence bands. First principles calculation suggests that a suitable tensile strain along the a-axis direction is needed to induce a gap to make it an insulator. Our work not only reports the electronic structure of MBE grown 1T'-MoTe2 films, but also provides insights for strain engineering to make it possible for quantum spin Hall effect.
基金support by the Young Taishan Scholars Program of Shandong Province(Grant No.tsqn202306272)National Key Research and Development Project of China(Grant No.2023YFFO715101)+5 种基金National Natural Science Foundation of China(Grant No.22307050)Natural Science Foundation of Shandong Province(Grant No.ZR2023QB292,ZR2024YQ068,2024HWYQ-062)the Leading Project of Science and Technology of Yantai Development Zone(Grant No.2021RC016)CFG and RLR acknowledge funding from Fundaçao para a Ciencia e Tecnologia(FCT)Grants 10.54499/2022.05711.CEECIND/CP1718/CT0012(CFG)and 10.54499/2022.05737.PTDC(CFG,RLR)as well as TERM RES Hub–Scientific Infrastructure for Tissue Engineering and Regenerative Medicine,reference PINFRA/22190/2016(Norte-01-0145-FEDER-022190).
文摘Enzyme-powered micro/nanomotors(EMNMs)represent cutting-edge research taking advantage of enzymes as biocatalysts to provide a driving force for micro/nanomotors.Up to now,EMNMs have been designed to be powered by catalase,urease,lipase,collagenase,compound enzymes,etc.They not only have good biocompatibility and biosafety but also possess the unique ability to utilize physiologically relevant fuel to achieve autonomous propulsion through in vivo catalytic reactions.This innovation has opened exciting possibilities for medical applications of EMNMs.Given the fact that the human body is naturally abundant with substrates available for enzymatic reactions,EMNMs can effectively exploit the complex microenvironment associated with diseases,enabling the diagnosis and treatment of various medical conditions.In this review,we first introduce different kinds of EMNMs applied in specific environments for the diagnosis and treatment of diseases,while highlighting their advancements for revolutionizing healthcare practices.Then,we address the challenges faced in this rapidly evolving field,and at last,the potential future development directions are discussed.As the potential of EMNMs becomes increasingly evident,continued research and exploration are essential to unlock their full capabilities and to ensure their successful integration into clinical applications.
基金supported by the National Natural Science Foundation of China(11725418 and 11334006)the National Basic Research Program of China(2016YFA0301004,2016YFA0301001,and 2015CB921001)+1 种基金Science Challenge Project(TZ2016004)Beijing Advanced Innovation Center for Future Chip(ICFC)
文摘PtTe2 and PtSe2 with trigonal structure have attracted extensive research interests since the discovery of type-II Dirac fermions in the bulk crystals. The evolution of the electronic structure from bulk 3D topological semimetal to 2D atomic thin films is an important scientific question. While a transition from 3D type-II Dirac semimetal in the bulk to 2D semiconductor in monolayer(ML) film has been reported for PtSe2, so far the evolution of electronic structure of atomically thin PtTe2 films still remains unexplored.Here we report a systematic angle-resolved photoemission spectroscopy(ARPES) study of the electronic structure of high quality PtTe2 films grown by molecular beam epitaxy with thickness from 2 ML to 6 ML.ARPES measurements show that PtTe2 films still remain metallic even down to 2 ML thickness, which is in sharp contrast to the semiconducting property of few layer PtSe2 films. Moreover, a transition from 2D metal to 3D type-II Dirac semimetal occurs at film thickness of 4–6 ML. In addition, Spin-ARPES measurements reveal helical spin textures induced by local Rashba effect in the bulk PtTe2 crystal, suggesting that similar hidden spin is also expected in few monolayer PtTe2 films. Our work reveals the transition from2D metal to 3D topological semimetal and provides new opportunities for investigating metallic 2D films with local Rashba effect.
基金supported by the National Key Research Program of China(Grant No.2016YFA0300702)the National Basic Research Program of China(Grant No.2014CB921104)+5 种基金the Shanghai Municipal Natural Science Foundation(Grant Nos.18JC1411400,18ZR1403200,and 17ZR1442400)the National Natural Science Foundation of China(Grant No.U1530402)the National Natural Science Foundation of China(Grant No.11674188)China Postdoctoral Science Foundation(Grant No.2017M610221)Shanghai Sailing Program(Grant No.17YF1429000)the National Postdoctoral Program for Innovative Talents(Grant No.BX201600036)
文摘Numerous exotic properties have been discovered in Dirac Semimetals(DSMs) and Weyl Semimetals(WSMs). In a given DSM/WSM, the Dirac/Weyl nodes usually coexist with other bulk states, making their respective contribution elusive. In this work, we distinguish the role of bulk states from the tilted Dirac nodes on the transport properties in DSMs. Specifically, we applied pressure to a type-II DSM material, PtTe2, and studied its pressure modified electronic and lattice structure systematically by using in situ transport measurements and X-ray diffraction(XRD). A pressure-induced transition at about 20 GPa is revealed in the transport properties, while the layered lattice structure is robust against pressure as illustrated in XRD measurement results.Density functional theory(DFT) calculations suggest that this is originated from the Lifshitz transition in the bulk states. Our findings provide evidence to identify the bulk states' influence on transport from the topologically-protected DSM states in the DSM material.
