Organic fluorophores with dynamic conformations in the excited state have played a significant role in applications of organic functional dyes.Among them,dihydrophenazine-based dynamic fluorophores involving a photoin...Organic fluorophores with dynamic conformations in the excited state have played a significant role in applications of organic functional dyes.Among them,dihydrophenazine-based dynamic fluorophores involving a photoinduced structural planarization process in the excited state exhibited large Stokes shifts and conformation-dependent multicolor emissions.With the developments of synthetic strategies,precise modifications on dihydrophenazinebased scaffolds have successfully afforded a variety of precise molecular structures of varying sizes and compositions,which have delicately modulated their photophysical properties.Herein,this Perspective summarizes the precise modulations of dihydrophenazine-based dynamic fluorophores,including the development of the synthetic methodologies,and tailor-made molecular models to reveal the luminescence−structure relationships.展开更多
The electronic structures of PF and PF＋ are calculated with the high-level configuration interaction method. To improve the precision of calculations, the spin-orbit coupling effect, the scalar relativistic effect, a...The electronic structures of PF and PF＋ are calculated with the high-level configuration interaction method. To improve the precision of calculations, the spin-orbit coupling effect, the scalar relativistic effect, and the Davidson correction（q-Q） are also considered. The spectroscopic parameters of bound states are derived by the electronic structures of PF and PF＋, which are in good accordance with the measurements. The transition dipole moments of spin-allowed transitions are evaluated, and the radiative lifetimes of several A S states of PF and PF＋ are obtained.展开更多
Metal nanoclusters(NCs)are ultrasmall molecular aggregates consisting of dozens to hundreds of metal atoms consolidated by organic ligands,which represent an emerging area of nanoscience.Amide a myriad of metal NCs,co...Metal nanoclusters(NCs)are ultrasmall molecular aggregates consisting of dozens to hundreds of metal atoms consolidated by organic ligands,which represent an emerging area of nanoscience.Amide a myriad of metal NCs,copper NCs(CuNCs)comprise a low-cost,high-value subclass that has attracted great attention.The variable copper cores and diversity of protecting ligands have rendered CuNCs interesting molecular aggregates featuring structural and compositional versatility,hence showing distinctive properties and potential applications.In the present review,we have summarized the progress on atomically precise CuNCs that exhibit a range of appealing properties and applications in different fields.This review is expected to provide not only an overview of the current development on atomically precise CuNCs,but also possible directions for the future design of novel CuNCs for fundamental studies and practical applications.展开更多
A new type of air bearing with flexure structure is introduced. The new bearing is designed for precision mechanical engineering devices such as mechanical watch movement. The new design uses the flexure structure to ...A new type of air bearing with flexure structure is introduced. The new bearing is designed for precision mechanical engineering devices such as mechanical watch movement. The new design uses the flexure structure to provide 3D damping to absorb shocks from all directions. Two designs are presented： one has 12 T-shape slots in the radian direction while the other has 8 spiral slots in the radian direction. Both designs have flexure mountings on the axial directions. Based on the finite element analysis （FEA）, the new bearing can reduce the vibration （displacement） by as much as 8.37% and hence, can better protect the shafts.展开更多
To achieve highly selective synergistic chemotherapy attractive for clinical translation,the precise polymeric nano-prodrugs(PPD-NPs)were successfully constructed via the facile crosslinking reaction between p H-sensi...To achieve highly selective synergistic chemotherapy attractive for clinical translation,the precise polymeric nano-prodrugs(PPD-NPs)were successfully constructed via the facile crosslinking reaction between p H-sensitive poly(ortho ester)s and reduction-sensitive small molecule synergistic prodrug(Pt(IV)-1).PPD-NPs endowed the defined structure and high drug loading of cisplatin and demethylcantharidin(DMC).Moreover,PPD-NPs exhibited steady long-term storage and circulation via the crosslinked structure,suitable negative potentials and low critical micelle concentration(CMC),improved selective tumour accumulation and cellular internalization via dynamic size transition and surficial amino protonation at tumoural extracellular p H,promoted efficient disintegration and drug release at tumoural intracellular p H/glutathione,and enhanced cytotoxicity via the synergistic effect between cisplatin and DMC with the feed ratio of 1:2,achieving significant tumour suppression while decreasing the side effects.Thus,the dynamic crosslinked polymeric nano-prodrugs exhibit tremendous potential for clinically targeted synergistic cancer therapy.展开更多
In this paper, the technological progress on Chinese gravity exploration satellites is presented. Novel features such as ultra-stable structure, high accurate thermal control, drag-free and attitude control, micro-thr...In this paper, the technological progress on Chinese gravity exploration satellites is presented. Novel features such as ultra-stable structure, high accurate thermal control, drag-free and attitude control, micro-thrusters, aerodynamic configuration, the ability to perform micro-vibration analyses, microwave ranging system and mass center trimmer are described.展开更多
The structure stiffness of presses has great effects on the forming precision of workpieces, especially in near-net or net shape forming. Conventionally the stiffness specification of presses is empirically determined...The structure stiffness of presses has great effects on the forming precision of workpieces, especially in near-net or net shape forming. Conventionally the stiffness specification of presses is empirically determined, resulting in poor designs with insufficient or over sufficient stiffness of press structures. In this paper, an approach for the structure design of hydraulic presses is proposed, which is forming-precision-driven and can make presses costeffective by lightweight optimization. The approach consists of five steps:(1)the determination of the press stiffness specification in terms of the forming precision requirement of workpieces;(2)the conceptual design of the press structures according to the stiffness and workspace specifications, and the structure configuration of the press;(3)the prototype design of the press structures by equivalently converting the conceptual design to prototypes;(4)the selection of key structure parameters by sensitivity analysis of the prototype design; and(5)the optimization of the prototype design. The approach is demonstrated and validated through a case study of the structure design of a 100 MN hydraulic press.展开更多
CONSPECTUS:The global production of polymer products currently exceeds 400 megatons annually.To ensure effective and environmentally responsible use of this vast resource,optimizing the properties of the products is e...CONSPECTUS:The global production of polymer products currently exceeds 400 megatons annually.To ensure effective and environmentally responsible use of this vast resource,optimizing the properties of the products is essential.Achieving this requires precise control over the internal structure of the polymers.Depending on the materials used,polymers can exist in either amorphous or semicrystalline states.Processing is often performed from the melt state,and the cooling rate plays a critical role in determining whether amorphous or semicrystalline products are formed alongside other process parameters such as the pressure and shear rates.To understand the structure formation during processing,knowledge of the cooling rate dependence is therefore essential.As all of these processes are associated with thermal effects,calorimetry is universally applicable here.Achieving cooling rates that are comparable to those during processing has therefore long been a challenge for calorimetric measurement methods.With the introduction of MEMS-based chip sensors for calorimetry,significant progress has been made in reproducing conditions,such as those that occur during injection molding.These special calorimetric techniques are often summarized under the terms Fast Scanning Calorimetry(FSC)or Nanocalorimetry,alluding to nanogram samples.Investigations with controlled cooling rates of up to 1×10^(6)K/s are now possible with special chip sensors and allow the study of material properties under extreme conditions.Technological issues such as crystallization and nucleation processes under processrelevant conditions can be investigated in most cases with commercial devices that achieve cooling rates of 10^(4)K/s.The cooling rates to be considered in relation to various manufacturing processes are discussed here,and the functionality of corresponding chip calorimeters is briefly presented.Since calorimetry only provides general information on the processes taking place in the material,but not directly on the resulting structures,combinations of FSC and methods for structure elucidation,e.g.,microscopy,are also presented.The main part of this Account deals with contributions of FSC to the understanding of crystallization processes under conditions as they occur in different manufacturing processes.Not only the influence of the cooling rate during injection molding but also the multistage cooling by chill rolls during film production is considered.Thanks to the high scanning rate of FSC,needed to bypass crystallization in the low-supercooling temperature range where heterogeneous nucleation dominates,an important aspect of polymer structure formation-homogeneous crystal nucleation-has become accessible for direct observation.Homogeneous nucleation can occur not only during cooling but also during storage at temperatures close to or even below the glass transition temperature in the amorphous state.The possibilities of FSC for the generation and investigation of amorphous states are illustrated by an example.Finally,possible further developments of FSC and expected further applications of this fascinating technology are considered.展开更多
Element doping can break the crystal symmetry and realize the topological phase transition in quantum materials,which enables the precise modulation of energy band structure and microscopic dynamical interaction.Herei...Element doping can break the crystal symmetry and realize the topological phase transition in quantum materials,which enables the precise modulation of energy band structure and microscopic dynamical interaction.Herein,we have studied the ultrafast photocarrier dynamics in Zn-doped 3D topological Dirac semimetal Cd_(3)As_(2)utilizing time-resolved optical pump-terahertz probe spectroscopy.Comparing to the pristine Cd_(3)As_(2),we found that the relaxation time of the lightly doped alloy is slightly shorter,while that of the heavily doped alloy exhibits a significant prolongation.Pump-fluence-and temperature-dependent transient terahertz spectroscopy indicated that in pristine and lightly doped samples within nontrivial semimetal phase,the photocarrier dynamics are dominated by the cooling of Dirac fermions.In heavily doped alloy,however,the observed longer relaxation process can be attributed to interband electron-hole recombination,which is a result of doping-induced transition into a trivial semiconductor phase.Our investigation highlights that Zn-doping is an effective and flexible scheme for engineering the electronic structure and transient carrier relaxation dynamics in Cd_(3)As_(2),and offers a control knob for functional switching between diverse optoelectronic devices within the realm of practical applications.展开更多
Metal nanoclusters with accurate compositions and precise crystalline structures hold remarkable attention in serving as a unique model catalyst for well-defined correlations between structure and catalytic activity.M...Metal nanoclusters with accurate compositions and precise crystalline structures hold remarkable attention in serving as a unique model catalyst for well-defined correlations between structure and catalytic activity.More importantly,these metal nanoclusters exhibit strong quantum confinement effects,which differ from their larger nanoparticles in a number of catalytic reactions.This review focuses on recent advances of atomically precise metal nanoclusters for C_(1) compound conversion(C_(O),CO_(2),CH_(4),and HCOOH),including thermally-driven catalysis,photocatalysis,and electrocatalysis.The reaction mechanisms are discussed at an atomic-or even electron-level.It is anticipated that the progress in this research area could be extended to catalytic applications of metal nanoclusters in C_(1) chemistry.展开更多
It remains a significant challenge to develop a catalyst that merges the advantages of homogeneous and heterogeneous catalysis with high reactivity and great recyclability.Herein,an atomically precise Cu_(6)-NH_(2) na...It remains a significant challenge to develop a catalyst that merges the advantages of homogeneous and heterogeneous catalysis with high reactivity and great recyclability.Herein,an atomically precise Cu_(6)-NH_(2) nanocluster with distorted octahedral Cu_(6) core and NH_(2)-functionalized ligands has been developed as the first homo/heterogeneous catalyst to catalyze the cyclization reaction of propargylic amines with carbon dioxide(CO_(2))under mild conditions.As a homogeneous catalyst,Cu_(6)-NH_(2) shows excellent catalytic activity with high turnover frequency due to highly accessible active sites.The definite coordination geometry and homogeneity nature of active centers make it convenient to investigate the structure–activity relationship at the atomic level through experiments and theory calculations.In addition,the nanocluster exhibits excellent stability,great recrystallizability,and reusability in five catalytic cycles,in which its catalytic performance has no obvious decrease.Moreover,Cu_(6)-NH_(2) incorporates Lewis acid and base sites in metal and ligand,respectively,which can promote catalytic efficiency in a synergistic effect in the absence of any cocatalysts.Importantly,Cu_(6)-NH_(2) can realize direct conversion of CO_(2) in simulated flue gas into oxazolidinones with high efficiency.The metal-ligand cooperative effect and integrated advantages of homogeneous and heterogeneous catalysis would provide new perspectives to achieve advanced metal nanocluster catalysts for CO_(2) conversion.展开更多
Quantum dot(QD)-based memristors enable precise and energy-efficient neuromorphic computing through atomic-level control over electrical synapse performance.However,the stochastic nature of QD structures results in th...Quantum dot(QD)-based memristors enable precise and energy-efficient neuromorphic computing through atomic-level control over electrical synapse performance.However,the stochastic nature of QD structures results in the poor reliability of resistive switching in neuromorphic computing,limiting its practical applications.Here,we present a data-driven QD synthesis optimization loop to precisely engineer QD structures for reliable neuromorphic computing.By deeply integrating high-throughput density functional theory with machine learning,we establish a cross-scale screening platform for precise synthesis of QDs,enabling multi-dimension predictions from atomic-level structures to macroscopic electrical synaptic behaviors.Through the minimization of structural disorder,achieved by pure phase,uniform size distribution,and highly preferred orientation,QD-based memristors demonstrate a 57%reduction in switching voltage,a two-order-of-magnitude increase in the ON/OFF ratio,and endurance and retention degradation as low as 0.1%over 8.4×10^(7)s of continuous operation and 10^(5)rapid read cycles.Furthermore,the dynamic learning range and neuromorphic computing accuracy are improved by 477%and 27.8%(reaching 92.23%),respectively.These findings establish a scalable,data-driven strategy for rational design of QD-based memristors,advancing the development of next-generation reliable neuromorphic computing systems.展开更多
Atomically precise gold and/or silver nanoclusters play a key role in crystallography and coordination chemistry.Compared with gold nanoclusters,silver nanoclusters become unstable and difficult to crystallize due to ...Atomically precise gold and/or silver nanoclusters play a key role in crystallography and coordination chemistry.Compared with gold nanoclusters,silver nanoclusters become unstable and difficult to crystallize due to the high reactivity ofmetal silver.Herein,we report a silver nanocluster Ag_(213)(Adm-S)_(44)Cl_(33)(Ag_(213))coprotected by bulky thiolates and chlorides.The low surface thiolate coverage(about 45%)endows Ag_(213)with high catalytic activity.Supported on activated carbon,Ag_(213)nanoclusters exhibit excellent electrocatalytic oxygen reduction performance with Eonset and E_(1/2)values of 0.89 and 0.72 V,respectively,close to the values of commercial Pt/C catalyst.This is the first report on the electrocatalytic oxygen reduction reaction of nanoclusters with more than 100 silver atoms.Ag_(213)with the diameter of 2.75 nm comprises a core–shell structure Ag_(7)@Ag_(32)@Ag_(77)@Ag_(97).The strong plasmonic absorption band at 454 nm reveals the metallic nature of Ag_(213).Interestingly,halide is of importance.Chloride facilitates the formation of Ag_(213)and Ag_(56)(Adm-S)_(33)Cl_(16)(Ag_(56)^(Cl))while bromide can promote the formation of Ag_(56)(Adm-S)_(33)Br_(16)(Ag_(56)Br).This work provides an example for the study of largesized metal nanoclusters and nanocluster-based electrocatalysts.展开更多
基金financially supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.21790361 and 21871084)Shanghai Municipal Science and Technology Major Project(Grant No.2018SHZDZX03)+3 种基金the Fundamental Research Funds for the Central Universities,the Programme of Introducing Talents of Discipline to Universities(Grant No.B16017)Program of Shanghai Academic/Technology Research Leader(19XD1421100)the Shanghai Science and Technology Committee(Grant No.17520750100)the China Postdoctoral Science Foundation(2020M671018).
文摘Organic fluorophores with dynamic conformations in the excited state have played a significant role in applications of organic functional dyes.Among them,dihydrophenazine-based dynamic fluorophores involving a photoinduced structural planarization process in the excited state exhibited large Stokes shifts and conformation-dependent multicolor emissions.With the developments of synthetic strategies,precise modifications on dihydrophenazinebased scaffolds have successfully afforded a variety of precise molecular structures of varying sizes and compositions,which have delicately modulated their photophysical properties.Herein,this Perspective summarizes the precise modulations of dihydrophenazine-based dynamic fluorophores,including the development of the synthetic methodologies,and tailor-made molecular models to reveal the luminescence−structure relationships.
基金Supported by the National Natural Science Foundation of China under Grant No 11404180the Natural Science Foundation of Heilongjiang Province under Grant Nos F201335,A2015010,and A2015011the Postdoctoral Scientific Research Developmental Fund of Heilongjiang Province under Grant No LBH-Q14159
文摘The electronic structures of PF and PF＋ are calculated with the high-level configuration interaction method. To improve the precision of calculations, the spin-orbit coupling effect, the scalar relativistic effect, and the Davidson correction（q-Q） are also considered. The spectroscopic parameters of bound states are derived by the electronic structures of PF and PF＋, which are in good accordance with the measurements. The transition dipole moments of spin-allowed transitions are evaluated, and the radiative lifetimes of several A S states of PF and PF＋ are obtained.
基金Science,Technology and Innovation Committee of Shenzhen Municipality,Grant/Award Number:JCYJ20180507183413211RGC Senior Research Fellowship Scheme,Grant/Award Number:SRFS2021-5S01+4 种基金Hong Kong Research Grants Council,Grant/Award Number:PolyU153062/18PGuangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials,Grant/Award Number:2019B121205002Hong Kong Polytechnic University,Grant/Award Number:1-ZE1CResearch Institute for Smart Energy,Grant/Award Number:CDAQMiss Clarea Au for the Endowed Professorship in Energy,Grant/Award Number:847S。
文摘Metal nanoclusters(NCs)are ultrasmall molecular aggregates consisting of dozens to hundreds of metal atoms consolidated by organic ligands,which represent an emerging area of nanoscience.Amide a myriad of metal NCs,copper NCs(CuNCs)comprise a low-cost,high-value subclass that has attracted great attention.The variable copper cores and diversity of protecting ligands have rendered CuNCs interesting molecular aggregates featuring structural and compositional versatility,hence showing distinctive properties and potential applications.In the present review,we have summarized the progress on atomically precise CuNCs that exhibit a range of appealing properties and applications in different fields.This review is expected to provide not only an overview of the current development on atomically precise CuNCs,but also possible directions for the future design of novel CuNCs for fundamental studies and practical applications.
基金Selected from Proceedings of the 7th International Conference on Frontiers of DesignManufacturing(ICFDM'2006)This project is partially sup-ported by the Research Grant from the Hong Kong Watch Manufacturers Association the Federation of Hong Kong Watch TradeIndustry Technology Commission China(No.ITS/001/05).
文摘A new type of air bearing with flexure structure is introduced. The new bearing is designed for precision mechanical engineering devices such as mechanical watch movement. The new design uses the flexure structure to provide 3D damping to absorb shocks from all directions. Two designs are presented： one has 12 T-shape slots in the radian direction while the other has 8 spiral slots in the radian direction. Both designs have flexure mountings on the axial directions. Based on the finite element analysis （FEA）, the new bearing can reduce the vibration （displacement） by as much as 8.37% and hence, can better protect the shafts.
基金supported by the Anhui Engineering Technology Research center of Biochemical Pharmaceutical(Bengbu Medical College)the National Natural Science Foundation of China(No.51803001)the Research Foundation of Education Department of Anhui Province of China(No.KJ2018ZD003,KJ2018A0006 and KJ2019A0015)the Academic and Technology Introduction Project of Anhui University(AU02303203)。
文摘To achieve highly selective synergistic chemotherapy attractive for clinical translation,the precise polymeric nano-prodrugs(PPD-NPs)were successfully constructed via the facile crosslinking reaction between p H-sensitive poly(ortho ester)s and reduction-sensitive small molecule synergistic prodrug(Pt(IV)-1).PPD-NPs endowed the defined structure and high drug loading of cisplatin and demethylcantharidin(DMC).Moreover,PPD-NPs exhibited steady long-term storage and circulation via the crosslinked structure,suitable negative potentials and low critical micelle concentration(CMC),improved selective tumour accumulation and cellular internalization via dynamic size transition and surficial amino protonation at tumoural extracellular p H,promoted efficient disintegration and drug release at tumoural intracellular p H/glutathione,and enhanced cytotoxicity via the synergistic effect between cisplatin and DMC with the feed ratio of 1:2,achieving significant tumour suppression while decreasing the side effects.Thus,the dynamic crosslinked polymeric nano-prodrugs exhibit tremendous potential for clinically targeted synergistic cancer therapy.
基金support provided by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(51121004,41274041,51207033,and 11275055)
文摘In this paper, the technological progress on Chinese gravity exploration satellites is presented. Novel features such as ultra-stable structure, high accurate thermal control, drag-free and attitude control, micro-thrusters, aerodynamic configuration, the ability to perform micro-vibration analyses, microwave ranging system and mass center trimmer are described.
基金Supported by the National Natural Science Foundation of China(No.50805101 and No.51275347)the National Key S&T Special Projects of China on CNC Machine Tools and Fundamental Manufacturing Equipment(No.2010ZX04001-191 and No.2011ZX04002-032)the Science and Technology R&D Program of Tianjin(No.13JCZDJC35000 and No.12ZCDZGX45000)
文摘The structure stiffness of presses has great effects on the forming precision of workpieces, especially in near-net or net shape forming. Conventionally the stiffness specification of presses is empirically determined, resulting in poor designs with insufficient or over sufficient stiffness of press structures. In this paper, an approach for the structure design of hydraulic presses is proposed, which is forming-precision-driven and can make presses costeffective by lightweight optimization. The approach consists of five steps:(1)the determination of the press stiffness specification in terms of the forming precision requirement of workpieces;(2)the conceptual design of the press structures according to the stiffness and workspace specifications, and the structure configuration of the press;(3)the prototype design of the press structures by equivalently converting the conceptual design to prototypes;(4)the selection of key structure parameters by sensitivity analysis of the prototype design; and(5)the optimization of the prototype design. The approach is demonstrated and validated through a case study of the structure design of a 100 MN hydraulic press.
基金support by Wenzhou City’s key R&D project,“Unveiling the List and Assigning the Leader”(ZG2023044)Anhui Provence key R&D project(202304a05020081)the DFG SPP2122 project ZH 662/3−2 and Open Research Fund of the State Key Laboratory of Polymer Physics and Chemistry,Changchun Institute of Applied Chemistry,Chinese Academy of Sciences.
文摘CONSPECTUS:The global production of polymer products currently exceeds 400 megatons annually.To ensure effective and environmentally responsible use of this vast resource,optimizing the properties of the products is essential.Achieving this requires precise control over the internal structure of the polymers.Depending on the materials used,polymers can exist in either amorphous or semicrystalline states.Processing is often performed from the melt state,and the cooling rate plays a critical role in determining whether amorphous or semicrystalline products are formed alongside other process parameters such as the pressure and shear rates.To understand the structure formation during processing,knowledge of the cooling rate dependence is therefore essential.As all of these processes are associated with thermal effects,calorimetry is universally applicable here.Achieving cooling rates that are comparable to those during processing has therefore long been a challenge for calorimetric measurement methods.With the introduction of MEMS-based chip sensors for calorimetry,significant progress has been made in reproducing conditions,such as those that occur during injection molding.These special calorimetric techniques are often summarized under the terms Fast Scanning Calorimetry(FSC)or Nanocalorimetry,alluding to nanogram samples.Investigations with controlled cooling rates of up to 1×10^(6)K/s are now possible with special chip sensors and allow the study of material properties under extreme conditions.Technological issues such as crystallization and nucleation processes under processrelevant conditions can be investigated in most cases with commercial devices that achieve cooling rates of 10^(4)K/s.The cooling rates to be considered in relation to various manufacturing processes are discussed here,and the functionality of corresponding chip calorimeters is briefly presented.Since calorimetry only provides general information on the processes taking place in the material,but not directly on the resulting structures,combinations of FSC and methods for structure elucidation,e.g.,microscopy,are also presented.The main part of this Account deals with contributions of FSC to the understanding of crystallization processes under conditions as they occur in different manufacturing processes.Not only the influence of the cooling rate during injection molding but also the multistage cooling by chill rolls during film production is considered.Thanks to the high scanning rate of FSC,needed to bypass crystallization in the low-supercooling temperature range where heterogeneous nucleation dominates,an important aspect of polymer structure formation-homogeneous crystal nucleation-has become accessible for direct observation.Homogeneous nucleation can occur not only during cooling but also during storage at temperatures close to or even below the glass transition temperature in the amorphous state.The possibilities of FSC for the generation and investigation of amorphous states are illustrated by an example.Finally,possible further developments of FSC and expected further applications of this fascinating technology are considered.
基金National Natural Science Foundation of China(12404396,92150101,52225207,52350001)China Postdoctoral Science Foundation(2024M751932)Postdoctoral Fellowship Program of CPSF(GZB20240418)。
文摘Element doping can break the crystal symmetry and realize the topological phase transition in quantum materials,which enables the precise modulation of energy band structure and microscopic dynamical interaction.Herein,we have studied the ultrafast photocarrier dynamics in Zn-doped 3D topological Dirac semimetal Cd_(3)As_(2)utilizing time-resolved optical pump-terahertz probe spectroscopy.Comparing to the pristine Cd_(3)As_(2),we found that the relaxation time of the lightly doped alloy is slightly shorter,while that of the heavily doped alloy exhibits a significant prolongation.Pump-fluence-and temperature-dependent transient terahertz spectroscopy indicated that in pristine and lightly doped samples within nontrivial semimetal phase,the photocarrier dynamics are dominated by the cooling of Dirac fermions.In heavily doped alloy,however,the observed longer relaxation process can be attributed to interband electron-hole recombination,which is a result of doping-induced transition into a trivial semiconductor phase.Our investigation highlights that Zn-doping is an effective and flexible scheme for engineering the electronic structure and transient carrier relaxation dynamics in Cd_(3)As_(2),and offers a control knob for functional switching between diverse optoelectronic devices within the realm of practical applications.
基金The authors acknowledge financial supports from the National Key R&D Program of China(no.2018YFE0122600)the National Natural Science Foundation of China(no.21802070).
文摘Metal nanoclusters with accurate compositions and precise crystalline structures hold remarkable attention in serving as a unique model catalyst for well-defined correlations between structure and catalytic activity.More importantly,these metal nanoclusters exhibit strong quantum confinement effects,which differ from their larger nanoparticles in a number of catalytic reactions.This review focuses on recent advances of atomically precise metal nanoclusters for C_(1) compound conversion(C_(O),CO_(2),CH_(4),and HCOOH),including thermally-driven catalysis,photocatalysis,and electrocatalysis.The reaction mechanisms are discussed at an atomic-or even electron-level.It is anticipated that the progress in this research area could be extended to catalytic applications of metal nanoclusters in C_(1) chemistry.
基金financially supported by the National Natural Science Foundation of China(grant nos.92061201,21825106,21771163,and 22371263)the National Key R&D Program of China(grant no.2021YFA1200301)+1 种基金the Natural Science Foundation of Henan Province(grant no.232300421144)the Zhongyuan Thousand Talents(Zhongyuan Scholars)Program of Henan Province(grant no.234000510007).
文摘It remains a significant challenge to develop a catalyst that merges the advantages of homogeneous and heterogeneous catalysis with high reactivity and great recyclability.Herein,an atomically precise Cu_(6)-NH_(2) nanocluster with distorted octahedral Cu_(6) core and NH_(2)-functionalized ligands has been developed as the first homo/heterogeneous catalyst to catalyze the cyclization reaction of propargylic amines with carbon dioxide(CO_(2))under mild conditions.As a homogeneous catalyst,Cu_(6)-NH_(2) shows excellent catalytic activity with high turnover frequency due to highly accessible active sites.The definite coordination geometry and homogeneity nature of active centers make it convenient to investigate the structure–activity relationship at the atomic level through experiments and theory calculations.In addition,the nanocluster exhibits excellent stability,great recrystallizability,and reusability in five catalytic cycles,in which its catalytic performance has no obvious decrease.Moreover,Cu_(6)-NH_(2) incorporates Lewis acid and base sites in metal and ligand,respectively,which can promote catalytic efficiency in a synergistic effect in the absence of any cocatalysts.Importantly,Cu_(6)-NH_(2) can realize direct conversion of CO_(2) in simulated flue gas into oxazolidinones with high efficiency.The metal-ligand cooperative effect and integrated advantages of homogeneous and heterogeneous catalysis would provide new perspectives to achieve advanced metal nanocluster catalysts for CO_(2) conversion.
基金supported by the National Natural Science Foundation of China(51572205,52372159)the Natural Science Foundation Innovation Research Team of Hainan Province(524CXTD431)+1 种基金the National Science Fund for Distinguished Young Scholars of Hubei Province(201CFA067)the National Innovation and Entrepreneurship Training Program for College Students(S202510497020,202510497003,and S202510497010)。
文摘Quantum dot(QD)-based memristors enable precise and energy-efficient neuromorphic computing through atomic-level control over electrical synapse performance.However,the stochastic nature of QD structures results in the poor reliability of resistive switching in neuromorphic computing,limiting its practical applications.Here,we present a data-driven QD synthesis optimization loop to precisely engineer QD structures for reliable neuromorphic computing.By deeply integrating high-throughput density functional theory with machine learning,we establish a cross-scale screening platform for precise synthesis of QDs,enabling multi-dimension predictions from atomic-level structures to macroscopic electrical synaptic behaviors.Through the minimization of structural disorder,achieved by pure phase,uniform size distribution,and highly preferred orientation,QD-based memristors demonstrate a 57%reduction in switching voltage,a two-order-of-magnitude increase in the ON/OFF ratio,and endurance and retention degradation as low as 0.1%over 8.4×10^(7)s of continuous operation and 10^(5)rapid read cycles.Furthermore,the dynamic learning range and neuromorphic computing accuracy are improved by 477%and 27.8%(reaching 92.23%),respectively.These findings establish a scalable,data-driven strategy for rational design of QD-based memristors,advancing the development of next-generation reliable neuromorphic computing systems.
基金supported by the National Natural Science Foundation of China(grant nos.21771198,22071274,21821003).
文摘Atomically precise gold and/or silver nanoclusters play a key role in crystallography and coordination chemistry.Compared with gold nanoclusters,silver nanoclusters become unstable and difficult to crystallize due to the high reactivity ofmetal silver.Herein,we report a silver nanocluster Ag_(213)(Adm-S)_(44)Cl_(33)(Ag_(213))coprotected by bulky thiolates and chlorides.The low surface thiolate coverage(about 45%)endows Ag_(213)with high catalytic activity.Supported on activated carbon,Ag_(213)nanoclusters exhibit excellent electrocatalytic oxygen reduction performance with Eonset and E_(1/2)values of 0.89 and 0.72 V,respectively,close to the values of commercial Pt/C catalyst.This is the first report on the electrocatalytic oxygen reduction reaction of nanoclusters with more than 100 silver atoms.Ag_(213)with the diameter of 2.75 nm comprises a core–shell structure Ag_(7)@Ag_(32)@Ag_(77)@Ag_(97).The strong plasmonic absorption band at 454 nm reveals the metallic nature of Ag_(213).Interestingly,halide is of importance.Chloride facilitates the formation of Ag_(213)and Ag_(56)(Adm-S)_(33)Cl_(16)(Ag_(56)^(Cl))while bromide can promote the formation of Ag_(56)(Adm-S)_(33)Br_(16)(Ag_(56)Br).This work provides an example for the study of largesized metal nanoclusters and nanocluster-based electrocatalysts.
