Twisting the stacking of layered materials leads to rich new physics. A three-dimensional topological insulator film hosts two-dimensional gapless Dirac electrons on top and bottom surfaces, which, when the film is be...Twisting the stacking of layered materials leads to rich new physics. A three-dimensional topological insulator film hosts two-dimensional gapless Dirac electrons on top and bottom surfaces, which, when the film is below some critical thickness, will hybridize and open a gap in the surface state structure. The hybridization gap can be tuned by various parameters such as film thickness and inversion symmetry, according to the literature. The three-dimensional strong topological insulator Bi(Sb)Se(Te) family has layered structures composed of quintuple layers(QLs) stacked together by van der Waals interaction. Here we successfully grow twistedly stacked Sb_2Te_3 QLs and investigate the effect of twist angels on the hybridization gaps below the thickness limit. It is found that the hybridization gap can be tuned for films of three QLs, which may lead to quantum spin Hall states.Signatures of gap-closing are found in 3-QL films. The successful in situ application of this approach opens a new route to search for exotic physics in topological insulators.展开更多
Carbonaceous material has attracted much attention in the application of sodium-ion batteries(SIBs)anode.However,sluggish reaction kinetics and structure stability impede the application.Therefore,a stacked layered su...Carbonaceous material has attracted much attention in the application of sodium-ion batteries(SIBs)anode.However,sluggish reaction kinetics and structure stability impede the application.Therefore,a stacked layered sulfur-carbon complex with long-chain C–S_(x)–C bond(M-SC-S)is prepared.The layered structure ensures structural stability,and long-chain C–S_(x)–C bond expanding interlayer spacing boosts facile Na+diffusion.When assembled into cells,a high-quality solid-electrolyte interphase film would be formed due to a good match between the M-SC-S electrode and ether electrolyte.Moreover,an electrochemical activation process would happen between the Cu current collector and proper S-doped electrode material to in-situ form Cu_(2)S.The formation of Cu_(2)S in active material can not only provide more active sites for sodium storage and enhance pseudo-capacitance,but also reinforce the electrode/current collector interface and decrease the interfacial transfer resistance for rapid Na+kinetics.The synergistic effect of structure design and interface engineering optimizes the sodium storage system.Thus,the M-SC-S electrode delivers an excellent cyclic performance(321.6 mAh g^(−1)after 1000 cycles at 2 A g^(−1)with a capacity retention rate of 97.4%)and good rate capability(282.8 mAh g^(−1)after 4000 cycles even at a high current density of 10 A g^(−1)).The full cell also has an impressive cyclic performance(151.4 mAh g^(−1)after 500 cycles at 0.5 A g^(−1)).展开更多
Covalent organic frameworks(COFs) have been attracting growing concerns since the first report in2005. With the well-defined and ordered structures, COFs express big potential in mass transport, storage/separation and...Covalent organic frameworks(COFs) have been attracting growing concerns since the first report in2005. With the well-defined and ordered structures, COFs express big potential in mass transport, storage/separation and energy conversion applications. From the perspective of both theory and application,the construction of crystalline COFs with high quality and variety is highly worth to be devoted to. To give insight into the crystalline process of COFs and deeply understand the factors of COFs crystallization,this review was concentrated on the recent progress in construction of crystalline COFs. Accordingly, the types and crystallization process of COFs were summarized firstly. And then the factors on crystallinity and the measures for improving the crystallinity of COFs were classified and discussed in detail. Finally,the perspectives for the development of COFs in further was given at the end of this review.展开更多
Severe mechanical fractu re and unstable interphase,associated with the large volumetric expansion/contraction,significantly hinder the application of high-capacity SiO_(x)materials in lithium-ion batteries.Herein,we ...Severe mechanical fractu re and unstable interphase,associated with the large volumetric expansion/contraction,significantly hinder the application of high-capacity SiO_(x)materials in lithium-ion batteries.Herein,we report the design and facile synthesis of a layer stacked SiO_(x)microparticle(LS-SiO_(x))material,which presents a stacking structure of SiO_(x)layers with abundant disconnected interstices.This LS-SiO_(x)microparticle can effectively accommodate the volume expansion,while ensuring negligible particle expansion.More importantly,the interstices within SiO_(x)microparticle are disconnected from each other,which efficiently prevent the electrolyte from infiltration into the interior,achieving stable electrode/-electrolyte interface.Accordingly,the LS-SiO_(x)material without any coating delivers ultrahigh average Coulombic efficiency,outstanding cycling stability,and full-cell applicability.Only 6 cycles can attain>99.92%Coulombic efficiency and the capacity retention at 0.05 A g^(-1)for 100 cycles exceeds99%.After 800 cycles at 1 A g^(-1),the thickness swelling of LS-SiO_(x)electrode is as low as 0.87%.Moreover,the full cell with pure LS-SiO_(x)anode exhibits capacity retention of 91.2%after 300 cycles at 0.2 C.This work provides a novel concept and effective approach to rationally design silicon-based and other electrode materials with huge volume variation for electrochemical energy storage applications.展开更多
CONSPECTUS:Topotactic transformations between related crystal structures,involving etching,replacement,and intercalation,are increasingly recognized in the design and tuning of material properties.These transformation...CONSPECTUS:Topotactic transformations between related crystal structures,involving etching,replacement,and intercalation,are increasingly recognized in the design and tuning of material properties.These transformations reveal the fundamental principles of material structural changes,paving the way for creating novel materials with unique properties.Layered materials readily undergo structural or compositional changes due to their stacked atomic layers and bonding features.MAX phases,as nonvan der Waals(non-vdW)layered compounds,exhibit distinctive elemental compositions and bonding characters that make them suitable for topotactic transformations.A notable example is the typical transformation from MAX phases to MXenes,a new addition to two-dimensional(2D)materials,through Asite etching within MAX phases.In turn,the 2D structure of MXenes further promoted versatile topotactic transformations utilizing the interlayer space and tunable surfaces.This Account comprehensively reviews the topotactic transformation in MXenes and MAX phases,covering aspects from chemical etching to versatile chemical editing.We commence with an analysis of MAX phase degradation,examining the corrosion resistance of MAX phases in liquid metals and molten salts,which is crucial for their application as nuclear materials.This leads us to introduce the novel concept of precise A-site etching in MAX phases,which has paved the way for the groundbreaking discovery of 2D MXene.Given the important effect of etching methods on MXenes,we then delve into the various etching methods employed in preparing MXene and explore the detailed processes and mechanisms behind each method.Additionally,we highlight the recent advancements made by our research group regarding the Lewis acidic molten salt(LAMS)method.This method utilizes LAMSs as etching agents to selectively etch the A-site atomic layer,creating opportunities for the subsequent intercalation of atoms or anions to achieve isomorphous replacement of A-site atoms and surface modification with novel terminations.The strong oxidation ability of LAMSs also offers versatility in selectively etching A-site atomic species,particularly confined to the Al element.The LAMS method shows potential for synthesizing and controlling the structure of MXene and MAX phases,albeit with limitations.Its success depends on the properties of LAMSs,which must facilitate both etching and intercalation.However,some LAMSs are unsuitable due to their low redox potential,low boiling points,and instability at high temperatures.Therefore,we propose a versatile chemical scissor-mediated structural editing strategy.This strategy decouples etching from intercalation,using Lewis acidic cations or reduced metal atoms as chemical scissors to create space between MX sublayers,allowing atoms or anions to diffuse and enable topotactic transitions.This approach has facilitated the intercalation of various A-site atoms,expanded MXene surface termination options,and even enabled the conversion of 2D MXene into 3D MAX phases by combining termination removal with atom intercalation.Finally,we offer insights into the future of topotactic transformations in these materials,aiming to inspire further innovative progress in this field.A deeper understanding of the topotactic transformation process holds the promise of broadening the applications of layered materials,providing a solid foundation for advancements in related areas.展开更多
We present high-performance enhancement-mode AlGaN/GaN metal-oxide-semiconductor highelectron mobility transistors（MOS-HEMTs） by a fluorinated gate dielectric technique.A nanolaminate of an Al_2O_3/La_xAl_（1-x）O_3...We present high-performance enhancement-mode AlGaN/GaN metal-oxide-semiconductor highelectron mobility transistors（MOS-HEMTs） by a fluorinated gate dielectric technique.A nanolaminate of an Al_2O_3/La_xAl_（1-x）O_3/Al_2O_3 stack（x≈0.33） grown by atomic layer deposition is employed to avoid fluorine ions implantation into the scaled barrier layer.Fabricated enhancement-mode MOS-HEMTs exhibit an excellent performance as compared to those with the conventional dielectric-last technique,delivering a large maximum drain current of 916 mA/mm and simultaneously a high peak transconductance of 342 mS/mm.The balanced DC characteristics indicate that advanced gate stack dielectrics combined with buffered fluorine ions implantation have a great potential for high speed GaN E/D-mode integrated circuit applications.展开更多
基金Supported by the National Natural Science Foundation of China (Grant Nos.61804056 and 92065102)。
文摘Twisting the stacking of layered materials leads to rich new physics. A three-dimensional topological insulator film hosts two-dimensional gapless Dirac electrons on top and bottom surfaces, which, when the film is below some critical thickness, will hybridize and open a gap in the surface state structure. The hybridization gap can be tuned by various parameters such as film thickness and inversion symmetry, according to the literature. The three-dimensional strong topological insulator Bi(Sb)Se(Te) family has layered structures composed of quintuple layers(QLs) stacked together by van der Waals interaction. Here we successfully grow twistedly stacked Sb_2Te_3 QLs and investigate the effect of twist angels on the hybridization gaps below the thickness limit. It is found that the hybridization gap can be tuned for films of three QLs, which may lead to quantum spin Hall states.Signatures of gap-closing are found in 3-QL films. The successful in situ application of this approach opens a new route to search for exotic physics in topological insulators.
基金supported by the Key Research and Development Program of Wuhan(2025010102030005)the National Nature Science Foundation of Jiangsu Province(BK20221259)。
文摘Carbonaceous material has attracted much attention in the application of sodium-ion batteries(SIBs)anode.However,sluggish reaction kinetics and structure stability impede the application.Therefore,a stacked layered sulfur-carbon complex with long-chain C–S_(x)–C bond(M-SC-S)is prepared.The layered structure ensures structural stability,and long-chain C–S_(x)–C bond expanding interlayer spacing boosts facile Na+diffusion.When assembled into cells,a high-quality solid-electrolyte interphase film would be formed due to a good match between the M-SC-S electrode and ether electrolyte.Moreover,an electrochemical activation process would happen between the Cu current collector and proper S-doped electrode material to in-situ form Cu_(2)S.The formation of Cu_(2)S in active material can not only provide more active sites for sodium storage and enhance pseudo-capacitance,but also reinforce the electrode/current collector interface and decrease the interfacial transfer resistance for rapid Na+kinetics.The synergistic effect of structure design and interface engineering optimizes the sodium storage system.Thus,the M-SC-S electrode delivers an excellent cyclic performance(321.6 mAh g^(−1)after 1000 cycles at 2 A g^(−1)with a capacity retention rate of 97.4%)and good rate capability(282.8 mAh g^(−1)after 4000 cycles even at a high current density of 10 A g^(−1)).The full cell also has an impressive cyclic performance(151.4 mAh g^(−1)after 500 cycles at 0.5 A g^(−1)).
基金Natural Science Foundation of Shandong Province, China (No. ZR2021QB070)。
文摘Covalent organic frameworks(COFs) have been attracting growing concerns since the first report in2005. With the well-defined and ordered structures, COFs express big potential in mass transport, storage/separation and energy conversion applications. From the perspective of both theory and application,the construction of crystalline COFs with high quality and variety is highly worth to be devoted to. To give insight into the crystalline process of COFs and deeply understand the factors of COFs crystallization,this review was concentrated on the recent progress in construction of crystalline COFs. Accordingly, the types and crystallization process of COFs were summarized firstly. And then the factors on crystallinity and the measures for improving the crystallinity of COFs were classified and discussed in detail. Finally,the perspectives for the development of COFs in further was given at the end of this review.
基金the support of the National Natural Science Foundation of China(51634003)。
文摘Severe mechanical fractu re and unstable interphase,associated with the large volumetric expansion/contraction,significantly hinder the application of high-capacity SiO_(x)materials in lithium-ion batteries.Herein,we report the design and facile synthesis of a layer stacked SiO_(x)microparticle(LS-SiO_(x))material,which presents a stacking structure of SiO_(x)layers with abundant disconnected interstices.This LS-SiO_(x)microparticle can effectively accommodate the volume expansion,while ensuring negligible particle expansion.More importantly,the interstices within SiO_(x)microparticle are disconnected from each other,which efficiently prevent the electrolyte from infiltration into the interior,achieving stable electrode/-electrolyte interface.Accordingly,the LS-SiO_(x)material without any coating delivers ultrahigh average Coulombic efficiency,outstanding cycling stability,and full-cell applicability.Only 6 cycles can attain>99.92%Coulombic efficiency and the capacity retention at 0.05 A g^(-1)for 100 cycles exceeds99%.After 800 cycles at 1 A g^(-1),the thickness swelling of LS-SiO_(x)electrode is as low as 0.87%.Moreover,the full cell with pure LS-SiO_(x)anode exhibits capacity retention of 91.2%after 300 cycles at 0.2 C.This work provides a novel concept and effective approach to rationally design silicon-based and other electrode materials with huge volume variation for electrochemical energy storage applications.
基金supported by National Natural Science Foundation of China(Grant Number U23A2093 and 12435017)Ten-Thousand Talents Plan of Zhejiang Province(Grant Number 2022R51007)Ningbo Top-talent Team Program.
文摘CONSPECTUS:Topotactic transformations between related crystal structures,involving etching,replacement,and intercalation,are increasingly recognized in the design and tuning of material properties.These transformations reveal the fundamental principles of material structural changes,paving the way for creating novel materials with unique properties.Layered materials readily undergo structural or compositional changes due to their stacked atomic layers and bonding features.MAX phases,as nonvan der Waals(non-vdW)layered compounds,exhibit distinctive elemental compositions and bonding characters that make them suitable for topotactic transformations.A notable example is the typical transformation from MAX phases to MXenes,a new addition to two-dimensional(2D)materials,through Asite etching within MAX phases.In turn,the 2D structure of MXenes further promoted versatile topotactic transformations utilizing the interlayer space and tunable surfaces.This Account comprehensively reviews the topotactic transformation in MXenes and MAX phases,covering aspects from chemical etching to versatile chemical editing.We commence with an analysis of MAX phase degradation,examining the corrosion resistance of MAX phases in liquid metals and molten salts,which is crucial for their application as nuclear materials.This leads us to introduce the novel concept of precise A-site etching in MAX phases,which has paved the way for the groundbreaking discovery of 2D MXene.Given the important effect of etching methods on MXenes,we then delve into the various etching methods employed in preparing MXene and explore the detailed processes and mechanisms behind each method.Additionally,we highlight the recent advancements made by our research group regarding the Lewis acidic molten salt(LAMS)method.This method utilizes LAMSs as etching agents to selectively etch the A-site atomic layer,creating opportunities for the subsequent intercalation of atoms or anions to achieve isomorphous replacement of A-site atoms and surface modification with novel terminations.The strong oxidation ability of LAMSs also offers versatility in selectively etching A-site atomic species,particularly confined to the Al element.The LAMS method shows potential for synthesizing and controlling the structure of MXene and MAX phases,albeit with limitations.Its success depends on the properties of LAMSs,which must facilitate both etching and intercalation.However,some LAMSs are unsuitable due to their low redox potential,low boiling points,and instability at high temperatures.Therefore,we propose a versatile chemical scissor-mediated structural editing strategy.This strategy decouples etching from intercalation,using Lewis acidic cations or reduced metal atoms as chemical scissors to create space between MX sublayers,allowing atoms or anions to diffuse and enable topotactic transitions.This approach has facilitated the intercalation of various A-site atoms,expanded MXene surface termination options,and even enabled the conversion of 2D MXene into 3D MAX phases by combining termination removal with atom intercalation.Finally,we offer insights into the future of topotactic transformations in these materials,aiming to inspire further innovative progress in this field.A deeper understanding of the topotactic transformation process holds the promise of broadening the applications of layered materials,providing a solid foundation for advancements in related areas.
基金supported by the National Natural Science Foundation of China(Nos.61504125,61474101,61106130 61076120,61505181)the Natural Science Foundation of Jiangsu Province of China(Nos.BK20131072,BE2012007,BK2012516)
文摘We present high-performance enhancement-mode AlGaN/GaN metal-oxide-semiconductor highelectron mobility transistors（MOS-HEMTs） by a fluorinated gate dielectric technique.A nanolaminate of an Al_2O_3/La_xAl_（1-x）O_3/Al_2O_3 stack（x≈0.33） grown by atomic layer deposition is employed to avoid fluorine ions implantation into the scaled barrier layer.Fabricated enhancement-mode MOS-HEMTs exhibit an excellent performance as compared to those with the conventional dielectric-last technique,delivering a large maximum drain current of 916 mA/mm and simultaneously a high peak transconductance of 342 mS/mm.The balanced DC characteristics indicate that advanced gate stack dielectrics combined with buffered fluorine ions implantation have a great potential for high speed GaN E/D-mode integrated circuit applications.
