van der Waals(vdW)layered α-In_(2)Se_(3)possesses stable ferroelectricity even down to monolayer,showing great promise in emerging ferroelectric semiconductor non-volatile memory and in-memory computing.Deciphering t...van der Waals(vdW)layered α-In_(2)Se_(3)possesses stable ferroelectricity even down to monolayer,showing great promise in emerging ferroelectric semiconductor non-volatile memory and in-memory computing.Deciphering the atomistic mechanisms governing its complex phase transition occurring in devices,such as thermal budget during fabrication or cycling,is of critical importance for device performance improvement yet remains challenging due to the intricate polymorphism and low interchange barriers.Here,we directly visualize the unique atomic-level in-plane directional phase transition in 2H-αIn_(2)Se_(3)that initiates from the In-Se octahedral framework,and is driven by the migrations of indium ions(in octahedrons)and vacancies(in vdW-gap),revealing a novel intralayer and interlayer indium atoms and vacancies rearrangement pathway.We demonstrate that each In-Se octahedral configuration evolves into two non-layered In-Se tetrahedral frameworks,ultimately coalescing a novel non-layered 6H-type In_(2)Se_(3)phase with the cation sites might be occupied by 1/3 vacancies and 2/3 indium atoms.Our results provide detailed microscopic insights on the phase transition dynamics of the ferroelectric 2H-α In_(2)Se_(3)in response to the thermal stimulus,and may offer guidelines for the precise controlling of specific In_(2)Se_(3)phases and the reliability improvement of ferroelectric In_(2)Se_(3)-based nanodevices.展开更多
The chiral behavior of phonons has been verified in achiral van der Waals(vdW)layered hexagonal lattices but lacks of experimental evidences in achiral orthorhombic materials like vdW-layered MX(M=Ge,Sn;X=Se,S).Here,w...The chiral behavior of phonons has been verified in achiral van der Waals(vdW)layered hexagonal lattices but lacks of experimental evidences in achiral orthorhombic materials like vdW-layered MX(M=Ge,Sn;X=Se,S).Here,we choose SnSe as a model anisotropic MX candidate and explore the optical activity with linearly/circularly polarized Raman spectroscopy along the specified crystal axes by combining with spherical aberration-corrected transmission electron microscopy.Interestingly,besides the robust deflection of linearly polarized photons,we observe the inherent circularlike vibration behavior featuring the chirality of phonon in this orthorhombic lattice,which gives a max degree of circular polarization of~80%by referring to the B_(3g) mode of MX.Our findings not only extend chiral phonons to orthorhombic lattices as theoretically predicted for promising applications in polarized optics,spintronics and phonon filters,but also may provide a strategy for exploring the chiral phonons in anisotropic vdWlayered materials.展开更多
基金supported from the National Natural Science Foundation of China(Nos.62274061 and 12134003)the National Key Research Project of China(No.2022YFA1402902)+5 种基金the Natural Science Foundation of Chongqing,China(No.CSTB2023NSCQ-MSX0975)the East China Normal University Multifunctional Platform for Innovation(004)the Innovation Foundation of Central University,Natural Science Foundation of Shanghai(No.25ZR1403003)the Foundational Research Funds for the Central Universities(No.YBNLTS2024-022)the Postdoctoral Fellowship Program of CPSF(No.GZB20250144)the Open Fund of State Key Laboratory of Infrared Physics(No.SITP-NLISTZD-2024-06).
文摘van der Waals(vdW)layered α-In_(2)Se_(3)possesses stable ferroelectricity even down to monolayer,showing great promise in emerging ferroelectric semiconductor non-volatile memory and in-memory computing.Deciphering the atomistic mechanisms governing its complex phase transition occurring in devices,such as thermal budget during fabrication or cycling,is of critical importance for device performance improvement yet remains challenging due to the intricate polymorphism and low interchange barriers.Here,we directly visualize the unique atomic-level in-plane directional phase transition in 2H-αIn_(2)Se_(3)that initiates from the In-Se octahedral framework,and is driven by the migrations of indium ions(in octahedrons)and vacancies(in vdW-gap),revealing a novel intralayer and interlayer indium atoms and vacancies rearrangement pathway.We demonstrate that each In-Se octahedral configuration evolves into two non-layered In-Se tetrahedral frameworks,ultimately coalescing a novel non-layered 6H-type In_(2)Se_(3)phase with the cation sites might be occupied by 1/3 vacancies and 2/3 indium atoms.Our results provide detailed microscopic insights on the phase transition dynamics of the ferroelectric 2H-α In_(2)Se_(3)in response to the thermal stimulus,and may offer guidelines for the precise controlling of specific In_(2)Se_(3)phases and the reliability improvement of ferroelectric In_(2)Se_(3)-based nanodevices.
基金financially supported by the National Natural Science Foundation of China(Nos.62274061 and 12134003)the National Key Research Project of China(No.2022YFA1402902)+4 种基金the Natural Science Foundation of Shanghai(No.25ZR1403003)the Space Application System of China Manned Space Program,the East China Normal University Multifunctional Platform for Innovation(004)the Foundational Research Funds for the Central Universities(No.YBNLTS2024-022)the Open Fund of State Key Laboratory of Infrared Physics(No.SITP-NLIST-ZD-2024-06)the Postdoctoral Fellowship Program of CPSF(No.GZB20250144).
文摘The chiral behavior of phonons has been verified in achiral van der Waals(vdW)layered hexagonal lattices but lacks of experimental evidences in achiral orthorhombic materials like vdW-layered MX(M=Ge,Sn;X=Se,S).Here,we choose SnSe as a model anisotropic MX candidate and explore the optical activity with linearly/circularly polarized Raman spectroscopy along the specified crystal axes by combining with spherical aberration-corrected transmission electron microscopy.Interestingly,besides the robust deflection of linearly polarized photons,we observe the inherent circularlike vibration behavior featuring the chirality of phonon in this orthorhombic lattice,which gives a max degree of circular polarization of~80%by referring to the B_(3g) mode of MX.Our findings not only extend chiral phonons to orthorhombic lattices as theoretically predicted for promising applications in polarized optics,spintronics and phonon filters,but also may provide a strategy for exploring the chiral phonons in anisotropic vdWlayered materials.
