Rutile TiO2 （001） quantum dots （or nano-marks） in different shapes were used to imitate uncleaved material surfaces or materials with rough surfaces. By numerical integration of the equation of motion of cantileve...Rutile TiO2 （001） quantum dots （or nano-marks） in different shapes were used to imitate uncleaved material surfaces or materials with rough surfaces. By numerical integration of the equation of motion of cantilever for silicon tip scanning along the [110] direction over the rutile TiO2 （001） quantum dots in ultra high vacuum （UHV）, scanning routes were explored to achieve atomic resolution from frequency shift image. The tip-surface interaction forces were calculated from Lennard-Jones （12-6） potential by the Hamaker summation method. The calculated results showed that atomic resolution could be achieved by frequency shift image for TiO2 （001） surfaces of rhombohedral quantum dot scanning in a vertical route, and spherical cap quantum dot scanning in a superposition route.2007 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V.展开更多
Heterogeneous catalysts are the most important catalysts in industrial reactions. Nanocatalysts, with size ranging from hundreds of nanometers to the atomic scale, possess activities that are closely connected to thei...Heterogeneous catalysts are the most important catalysts in industrial reactions. Nanocatalysts, with size ranging from hundreds of nanometers to the atomic scale, possess activities that are closely connected to their structural characteristics such as particle size, surface morphology, and three-dimensional topography. Recently, the development of advanced analytical transmission electron microscopy（TEM） techniques, especially quantitative high-angle annular darkfield（HAADF） imaging and high-energy resolution spectroscopy analysis in scanning transmission electron microscopy（STEM） at the atomic scale, strengthens the power of（S）TEM in analyzing the structural/chemical information of heterogeneous catalysts. Three-dimensional reconstruction from two-dimensional projected images and the real-time recording of structural evolution during catalytic reactions using in-situ（S）TEM methods further broaden the scope of（S）TEM observation. The atomic-scale structural information obtained from high-resolution（S）TEM has proven to be of significance for better understanding and designing of new catalysts with enhanced performance.展开更多
Reaction dynamics in gases at operating temperatures at the atomic level are the basis of heterogeneous gas-solid catalyst reactions and are crucial to the catalyst function.Supported noble metal nanocatalysts such as...Reaction dynamics in gases at operating temperatures at the atomic level are the basis of heterogeneous gas-solid catalyst reactions and are crucial to the catalyst function.Supported noble metal nanocatalysts such as platinum are of interest in fuel cells and as diesel oxidation catalysts for pollution control,and practical ruthenium nanocatalysts are explored for ammonia synthesis.Graphite and graphitic carbons are of interest as supports for the nanocatalysts.Despite considerable literature on the catalytic processes on graphite and graphitic supports,reaction dynamics of the nanocatalysts on the supports in different reactive gas environments and operating temperatures at the single atom level are not well understood.Here we present real time in-situ observations and analyses of reaction dynamics of Pt in oxidation,and practical Ru nanocatalysts in ammonia synthesis,on graphite and related supports under controlled reaction environments using a novel in-situ environmental(scanning) transmission electron microscope with single atom resolution.By recording snapshots of the reaction dynamics,the behaviour of the catalysts is imaged.The images reveal single metal atoms,clusters of a few atoms on the graphitic supports and the support function.These all play key roles in the mobility,sintering and growth of the catalysts.The experimental findings provide new structural insights into atomic scale reaction dynamics,morphology and stability of the nanocatalysts.展开更多
Atomic single-molecule imaging has drawn extensive attention for exploring different behaviors and properties of small molecules.However,current techniques still face challenges,due to the thermal activity and beam se...Atomic single-molecule imaging has drawn extensive attention for exploring different behaviors and properties of small molecules.However,current techniques still face challenges,due to the thermal activity and beam sensitivity of small molecules.Recently,ångström-level spatial resolution for single molecules was successfully demonstrated using different imaging methods,including scanning tunneling microscopy,atomic force microscopy,cryogenic and transmission electron microscopy.In this perspective,we focus on different confinement strategies in these single-molecule imaging techniques,and summarize the recent studies of the structures and behaviors of single molecules.Especially,a new concept of spatial confinement at room temperature has been achieved by using microporous materials,such as zeolites,which has made it possible to fix and visualize the configurations of single molecule inside channels.In outlook,we describe what progress we can make along such a confinement strategy,and what new perspectives and discoveries we may find beyond our imagination.展开更多
The common ways to activate a chemical reaction are by heat,electric current,or light.However,mechanochemistry,where the chemical reaction is activated by applied mechanical force,is less common and only poorly unders...The common ways to activate a chemical reaction are by heat,electric current,or light.However,mechanochemistry,where the chemical reaction is activated by applied mechanical force,is less common and only poorly understood at the atomic scale.Here we report a tip-induced activation of chemical reaction of carbon monoxide to dioxide on oxidized rutile TiO_(2)(110)surface.The activation is studied by atomic force microscopy,Kelvin probe force microscopy under ultrahigh-vacuum and liquid nitrogen temperature conditions,and density functional theory(DFT)modeling.The reaction is inferred from hysteretic behavior of frequency shift signal further supported by vector force mapping of vertical and lateral forces needed to trigger the chemical reaction with torque motion of carbon monoxide towards an oxygen adatom.The reaction is found to proceed stochastically at very small tip-sample distances.Furthermore,the local contact potential difference reveals the atomic-scale charge redistribution in the reactants required to unlock the reaction.Our results open up new insights into the mechanochemistry on metal oxide surfaces at the atomic scale.展开更多
Amorphous materials such as glass,polymer and amorphous alloy have broad applications ranging from daily life to extreme conditions due to their unique properties in elasticity,strength and electrical resistivity.A be...Amorphous materials such as glass,polymer and amorphous alloy have broad applications ranging from daily life to extreme conditions due to their unique properties in elasticity,strength and electrical resistivity.A better understanding of atomic structure of amorphous materials will provide invaluable information for their further engineering and applications.However,experimentally determining the three-dimensional(3D)atomic structure of amorphous materials has been a long-standing problem.Due to the disordered atomic arrangement,amorphous materials do not have any translational and rotational symmetry at long-range scale.Conventional characterization methods,such as the scattering and the microscopy imaging,can only provide the statistic structural information which is averaged over the macroscopic region.The knowledge of the 3D atomic structure of amorphous materials is limited.Recently atomic resolution electron tomography(AET)has proven an increasingly powerful tool for atomic scale structural characterization without any crystalline assumptions,which opens a door to determine the 3D structure of various amorphous materials.In this review,we summarize the state-of-art characterization methods for the exploration of atomic structures of amorphous materials in the past few decades,including X-ray/neutron diffraction,nano-beam and angstrom-beam electron diffraction,fluctuation electron microscopy,high-resolution scanning/transmission electron microscopy,and atom probe tomography.From experimental data and theoretical descriptions,3D structures of various amorphous materials have been built up.Particularly,we introduce the principles and recent progress of AET,and highlight the most recent groundbreaking feat accomplished by AET,i.e.,the first experimental determination of all 3D atomic positions in a multi-component glass-forming alloy and the 3D atomic packing in amorphous solids.We also discuss the new opportunities and challenges for characterizing the chemical and structural defects in amorphous materials.展开更多
CrTaO_(4)has been found to play a pivotal role in the protection of refractory high-entropy alloys(RHEAs)from high-temperature oxidation and thermal attack due to its high melting point,low thermal conductivity,close ...CrTaO_(4)has been found to play a pivotal role in the protection of refractory high-entropy alloys(RHEAs)from high-temperature oxidation and thermal attack due to its high melting point,low thermal conductivity,close thermal expansion coefficient(TEC)to RHEAs.These appealing properties enable CrTaO_(4)as a new type of protective scale material for high-temperature applications such as in air breathing jet engines.For such engine applications,CaO-MgO-Al_(2)O_(3)-SiO_(2)(CMAS)corrosion is a critical issue.However,the corrosion behavior of CrTaO_(4)under CMAS attack remains unknown so far.Here,the corrosion resistance of CrTaO_(4)to molten CMAS is comprehensively studied.It is demonstrated that the CMAS corrosion resistance is significantly superior over commercial yttria-stabilized zirconia and the commonly investigated thermal barrier coating materials.Element and phase compositional analyses indicate dense and CMAS corrosion-resistant layers are established between CMAS and the CrTaO_(4)substrate.The interface reaction between the CrTaO_(4)substrate and CMAS at 1250 and 1300℃gives rise to a dense layer composed of CaTa_(2)O_(6) and Mg(Cr,Al)_(2)O_(4)spinel just beneath the molten CMAS.At 1350℃,a phase composition gradient layer,composed of crystalline phases CaTa_(2)O_(6)/CaTa_(2)O_(6)+Mg(Cr,Al)_(2)O_(4)/CaTa_(2)O_(6)+Cr2O_(3),is formed.With increased calcium consumption due to more Ca-containing crystalline phase formation upon elevating temperature,the Ca/Si ratio in CMAS melt declines,thereby increasing the viscosity of the melt and mitigating the penetration of CMAS into the CrTaO_(4)substrate.展开更多
High-entropy carbide ceramics(HECCs)exhibit superior properties compared to their constituent bi-nary compounds.However,high synthesis and sintering temperature are main obstacles that limit their widespread applicati...High-entropy carbide ceramics(HECCs)exhibit superior properties compared to their constituent bi-nary compounds.However,high synthesis and sintering temperature are main obstacles that limit their widespread applications.To address this issue,compositional and particle size controllable high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb02Ta_(0.2))C_(x) powders were successfully prepared by a sugar hydrogel combined with the carbothermal reduction method.Owing to the introduction of carbon vacancy,the temperature for the formation of single-phase solid solution of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(x) powders was decreased,and the addition of nitrogen decreased the densification temperature of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(0.95) ceramic by 200℃.In addition,the flexural strength and fracture toughness of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(0.95) ceramic were improved by 29%and 30%,respectively,compared with those without nitrogen doping.Atomic-resolution high angle annular dark field scanning transmission electron microscopy(HAADF-STEM)and energy dispersive spectroscopy(EDS)mapping re-veal that the segregation of N and small cation Ti as well as large lattice strains are responsible for the enhanced mechanical properties.Furthermore,with the introduction of nitrogen,the onset oxidation tem-perature(OOT)was increased,while the parabolic oxidation rate constant was decreased,revealing the beneficial effect of nitrogen doping on oxidation resistance.These results demonstrate that nitrogen dop-ing can not only improve the mechanical properties of HECCs but also enhance the oxidation resistance,which paves the way for the wide application of HECCs.展开更多
Three-dimensional(3D)structural analysis is an important field in physical and biological sciences.There exist two groups of electron microscopy methods that are capable of providing 3D structural information of an ob...Three-dimensional(3D)structural analysis is an important field in physical and biological sciences.There exist two groups of electron microscopy methods that are capable of providing 3D structural information of an object,i.e.,electron tomography and depth sectioning.Electron tomography is capable of resolving atoms in all three dimensions,but the accuracy in atomic positions is low and the object size that can be reconstructed is limited.Depth sectioning methods give high positional accuracy in the imaging plane,but the spatial resolution in the third dimension is low.In this work,electron tomography and depth sectioning are combined to form a method called multiple-section local-orbital tomography,or nLOT in short.The nLOT method provides high spatial resolution and high positional accuracy in all three dimensions.The object size that can be reconstructed is extended to a million atoms.The present method establishes a foundation for the widespread application of atomic electron tomography.展开更多
Cryogenic electron microscopy(cryo-EM)has extensively boosted structural biology research since the“resolution revolution”in the year of 2013 which was soon awarded the Nobel Prize in Chemistry in 2017.The advances ...Cryogenic electron microscopy(cryo-EM)has extensively boosted structural biology research since the“resolution revolution”in the year of 2013 which was soon awarded the Nobel Prize in Chemistry in 2017.The advances in camera techniques and software algorithms enabled cryoEM to routinely characterize the three-dimensional structures of biomolecules at near-atomic resolution.Biomolecules are basically sensitive to electron irradiation damage,which can be minimized at cryo-temperature.This principle has inspired material scientists to characterize electron beam-or air-sensitive materials by cryo-EM,such as the electrodes in the lithium-ion battery,metal-organic frameworks(MOFs),covalent-organic frameworks(COFs)and zeolites.In addition,the reaction systems can be fast-frozen at vitreous ice in cryoEM,which correspondingly preserves the materials at the close-to-native state.Herein,we summarized the development and applications of both the cryo-EM technique and other emerging cryo-techniques in materials science,and energy storage and conversion.Cryo-EM techniques,capable of the direct observation of sensitive materials and electrochemical reaction processes,will greatly renew our understanding of materials science and related mechanisms.展开更多
As a new type of iron-based superconductor, CaKFe_(4)As_(4) has recently been demonstrated to be a promising platform for observing Majorana zero modes (MZMs). The surface of CaKFe_(4)As_(4) plays an important role in...As a new type of iron-based superconductor, CaKFe_(4)As_(4) has recently been demonstrated to be a promising platform for observing Majorana zero modes (MZMs). The surface of CaKFe_(4)As_(4) plays an important role in realizing the MZM since it hosts superconducting topological surface states. However, due to the complicated crystal structure, the terminal surface of CaKFe_(4)As_(4) has not been determined yet. Here, by using scanning tunneling microscopy/spectroscopy (STM/S), we find that there are two types of surface structure in CaKFe_(4)As_(4). Bias-dependent atomic resolution images show an evolvement from 2–√×2–√ superstructure with respect to the As lattice into 1 × 1 when the tip is brought close to the surface, revealing the sublattice of missing As atoms. Together with the first-principles calculations, we show that the surface As layer has a buckled structure. Our findings provide insight to future surface study of CaKFe_(4)As_(4) as well as other iron-pnictide superconductors.展开更多
文摘Rutile TiO2 （001） quantum dots （or nano-marks） in different shapes were used to imitate uncleaved material surfaces or materials with rough surfaces. By numerical integration of the equation of motion of cantilever for silicon tip scanning along the [110] direction over the rutile TiO2 （001） quantum dots in ultra high vacuum （UHV）, scanning routes were explored to achieve atomic resolution from frequency shift image. The tip-surface interaction forces were calculated from Lennard-Jones （12-6） potential by the Hamaker summation method. The calculated results showed that atomic resolution could be achieved by frequency shift image for TiO2 （001） surfaces of rhombohedral quantum dot scanning in a vertical route, and spherical cap quantum dot scanning in a superposition route.2007 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V.
基金Project supported by the Natural Science Foundation of China(Grant No.51622211)the Pioneer Hundred Talents Program of Chinese Academy of Sciences
文摘Heterogeneous catalysts are the most important catalysts in industrial reactions. Nanocatalysts, with size ranging from hundreds of nanometers to the atomic scale, possess activities that are closely connected to their structural characteristics such as particle size, surface morphology, and three-dimensional topography. Recently, the development of advanced analytical transmission electron microscopy（TEM） techniques, especially quantitative high-angle annular darkfield（HAADF） imaging and high-energy resolution spectroscopy analysis in scanning transmission electron microscopy（STEM） at the atomic scale, strengthens the power of（S）TEM in analyzing the structural/chemical information of heterogeneous catalysts. Three-dimensional reconstruction from two-dimensional projected images and the real-time recording of structural evolution during catalytic reactions using in-situ（S）TEM methods further broaden the scope of（S）TEM observation. The atomic-scale structural information obtained from high-resolution（S）TEM has proven to be of significance for better understanding and designing of new catalysts with enhanced performance.
基金the Engineering and Physical Science Research Council(EPSRC),U.K.for the award of a research grant EP/J0118058/1 and postdoctoral research assistantships(PDRAs) to M.R.W.and R.W.M.from the grant。
文摘Reaction dynamics in gases at operating temperatures at the atomic level are the basis of heterogeneous gas-solid catalyst reactions and are crucial to the catalyst function.Supported noble metal nanocatalysts such as platinum are of interest in fuel cells and as diesel oxidation catalysts for pollution control,and practical ruthenium nanocatalysts are explored for ammonia synthesis.Graphite and graphitic carbons are of interest as supports for the nanocatalysts.Despite considerable literature on the catalytic processes on graphite and graphitic supports,reaction dynamics of the nanocatalysts on the supports in different reactive gas environments and operating temperatures at the single atom level are not well understood.Here we present real time in-situ observations and analyses of reaction dynamics of Pt in oxidation,and practical Ru nanocatalysts in ammonia synthesis,on graphite and related supports under controlled reaction environments using a novel in-situ environmental(scanning) transmission electron microscope with single atom resolution.By recording snapshots of the reaction dynamics,the behaviour of the catalysts is imaged.The images reveal single metal atoms,clusters of a few atoms on the graphitic supports and the support function.These all play key roles in the mobility,sintering and growth of the catalysts.The experimental findings provide new structural insights into atomic scale reaction dynamics,morphology and stability of the nanocatalysts.
基金supported by National Natural Science Foundation of China(T2322019,22275133,22204116)Suzhou Science and Technology Development Plan(ZXL2023179)+2 种基金Natural Science Foundation of Jiangsu Province(BK20220484,BK20200851)Suzhou Key Laboratory of Functional Nano&Soft Materials,Collaborative Innovation Center of Suzhou Nano Science&Technologythe 111 Project,Joint International Research Laboratory of Carbon-Based Functional Materials and Devices.
文摘Atomic single-molecule imaging has drawn extensive attention for exploring different behaviors and properties of small molecules.However,current techniques still face challenges,due to the thermal activity and beam sensitivity of small molecules.Recently,ångström-level spatial resolution for single molecules was successfully demonstrated using different imaging methods,including scanning tunneling microscopy,atomic force microscopy,cryogenic and transmission electron microscopy.In this perspective,we focus on different confinement strategies in these single-molecule imaging techniques,and summarize the recent studies of the structures and behaviors of single molecules.Especially,a new concept of spatial confinement at room temperature has been achieved by using microporous materials,such as zeolites,which has made it possible to fix and visualize the configurations of single molecule inside channels.In outlook,we describe what progress we can make along such a confinement strategy,and what new perspectives and discoveries we may find beyond our imagination.
基金supported by a Grant-in-Aid for Scientific Research from Japan Society for the Promotion of Science(JSPS)from the Ministry of Education,Culture,Sports,Science,and Technology of Japan(Nos.JP16H06327,JP17H01061,A21J103560,and JP22H00282)supported by the International Joint Research Promotion Program of Osaka University(Nos.J171013014,J171013007,J181013004,J181013006,Ja1999001,Ja19990011,and A21J103560)+1 种基金JSPSthe National Natural Science Foundation of China(No.J191053055)supported by APVV-21-0272,VEGA-2/0070/21,VEGA-2/0125/20,VEGA-2/0131/23,and H2020 TREX GA No.952165 projects。
文摘The common ways to activate a chemical reaction are by heat,electric current,or light.However,mechanochemistry,where the chemical reaction is activated by applied mechanical force,is less common and only poorly understood at the atomic scale.Here we report a tip-induced activation of chemical reaction of carbon monoxide to dioxide on oxidized rutile TiO_(2)(110)surface.The activation is studied by atomic force microscopy,Kelvin probe force microscopy under ultrahigh-vacuum and liquid nitrogen temperature conditions,and density functional theory(DFT)modeling.The reaction is inferred from hysteretic behavior of frequency shift signal further supported by vector force mapping of vertical and lateral forces needed to trigger the chemical reaction with torque motion of carbon monoxide towards an oxygen adatom.The reaction is found to proceed stochastically at very small tip-sample distances.Furthermore,the local contact potential difference reveals the atomic-scale charge redistribution in the reactants required to unlock the reaction.Our results open up new insights into the mechanochemistry on metal oxide surfaces at the atomic scale.
基金supported by the National Natural Science Foundation of China(22172003)High-performance Computing Platform of Peking University.
文摘Amorphous materials such as glass,polymer and amorphous alloy have broad applications ranging from daily life to extreme conditions due to their unique properties in elasticity,strength and electrical resistivity.A better understanding of atomic structure of amorphous materials will provide invaluable information for their further engineering and applications.However,experimentally determining the three-dimensional(3D)atomic structure of amorphous materials has been a long-standing problem.Due to the disordered atomic arrangement,amorphous materials do not have any translational and rotational symmetry at long-range scale.Conventional characterization methods,such as the scattering and the microscopy imaging,can only provide the statistic structural information which is averaged over the macroscopic region.The knowledge of the 3D atomic structure of amorphous materials is limited.Recently atomic resolution electron tomography(AET)has proven an increasingly powerful tool for atomic scale structural characterization without any crystalline assumptions,which opens a door to determine the 3D structure of various amorphous materials.In this review,we summarize the state-of-art characterization methods for the exploration of atomic structures of amorphous materials in the past few decades,including X-ray/neutron diffraction,nano-beam and angstrom-beam electron diffraction,fluctuation electron microscopy,high-resolution scanning/transmission electron microscopy,and atom probe tomography.From experimental data and theoretical descriptions,3D structures of various amorphous materials have been built up.Particularly,we introduce the principles and recent progress of AET,and highlight the most recent groundbreaking feat accomplished by AET,i.e.,the first experimental determination of all 3D atomic positions in a multi-component glass-forming alloy and the 3D atomic packing in amorphous solids.We also discuss the new opportunities and challenges for characterizing the chemical and structural defects in amorphous materials.
基金supported by the National Natural Science Foundation of China(Nos.U23A20562 and 52302074).
文摘CrTaO_(4)has been found to play a pivotal role in the protection of refractory high-entropy alloys(RHEAs)from high-temperature oxidation and thermal attack due to its high melting point,low thermal conductivity,close thermal expansion coefficient(TEC)to RHEAs.These appealing properties enable CrTaO_(4)as a new type of protective scale material for high-temperature applications such as in air breathing jet engines.For such engine applications,CaO-MgO-Al_(2)O_(3)-SiO_(2)(CMAS)corrosion is a critical issue.However,the corrosion behavior of CrTaO_(4)under CMAS attack remains unknown so far.Here,the corrosion resistance of CrTaO_(4)to molten CMAS is comprehensively studied.It is demonstrated that the CMAS corrosion resistance is significantly superior over commercial yttria-stabilized zirconia and the commonly investigated thermal barrier coating materials.Element and phase compositional analyses indicate dense and CMAS corrosion-resistant layers are established between CMAS and the CrTaO_(4)substrate.The interface reaction between the CrTaO_(4)substrate and CMAS at 1250 and 1300℃gives rise to a dense layer composed of CaTa_(2)O_(6) and Mg(Cr,Al)_(2)O_(4)spinel just beneath the molten CMAS.At 1350℃,a phase composition gradient layer,composed of crystalline phases CaTa_(2)O_(6)/CaTa_(2)O_(6)+Mg(Cr,Al)_(2)O_(4)/CaTa_(2)O_(6)+Cr2O_(3),is formed.With increased calcium consumption due to more Ca-containing crystalline phase formation upon elevating temperature,the Ca/Si ratio in CMAS melt declines,thereby increasing the viscosity of the melt and mitigating the penetration of CMAS into the CrTaO_(4)substrate.
基金supported by the National Natural Science Foundation of China(Nos.52272060,51902067,51872066 and 52002001)the Key Program of National Natural Science Foundation of China(No.52032003)+6 种基金the China Postdoctoral Sci-ence Foundation(Nos.2019M651282 and 2022T150157)the Hei-longjiang Provincial Postdoctoral Science Foundation(Nos.LBH-Z19022 and LBH-TZ2207)Heilongjiang Touyan Innovation Team Program,the Shanghai Aerospace Science and Technology Innova-tion Fund(No.SAST2019-012)the Fundamental Research Funds for the Central Universities(No.FRFCU5710051022)the Science Foundation of National Key Laboratory of Science and Tech-nology on Advanced Composites in Special Environments(No.JCKYS2022603C011)the Domestic Visiting and Studying Project for Outstanding Young Key Talents in Universities of Anhui Province(No.gxgnfx2021131)Young and Middle-aged Top Talent Project of Anhui Polytechnic University.
文摘High-entropy carbide ceramics(HECCs)exhibit superior properties compared to their constituent bi-nary compounds.However,high synthesis and sintering temperature are main obstacles that limit their widespread applications.To address this issue,compositional and particle size controllable high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb02Ta_(0.2))C_(x) powders were successfully prepared by a sugar hydrogel combined with the carbothermal reduction method.Owing to the introduction of carbon vacancy,the temperature for the formation of single-phase solid solution of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(x) powders was decreased,and the addition of nitrogen decreased the densification temperature of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(0.95) ceramic by 200℃.In addition,the flexural strength and fracture toughness of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(0.95) ceramic were improved by 29%and 30%,respectively,compared with those without nitrogen doping.Atomic-resolution high angle annular dark field scanning transmission electron microscopy(HAADF-STEM)and energy dispersive spectroscopy(EDS)mapping re-veal that the segregation of N and small cation Ti as well as large lattice strains are responsible for the enhanced mechanical properties.Furthermore,with the introduction of nitrogen,the onset oxidation tem-perature(OOT)was increased,while the parabolic oxidation rate constant was decreased,revealing the beneficial effect of nitrogen doping on oxidation resistance.These results demonstrate that nitrogen dop-ing can not only improve the mechanical properties of HECCs but also enhance the oxidation resistance,which paves the way for the wide application of HECCs.
基金supported by Basic Science Center Project of the National Natural Science Foundation of China(52388201)the National Natural Science Foundation of China(51525102)。
文摘Three-dimensional(3D)structural analysis is an important field in physical and biological sciences.There exist two groups of electron microscopy methods that are capable of providing 3D structural information of an object,i.e.,electron tomography and depth sectioning.Electron tomography is capable of resolving atoms in all three dimensions,but the accuracy in atomic positions is low and the object size that can be reconstructed is limited.Depth sectioning methods give high positional accuracy in the imaging plane,but the spatial resolution in the third dimension is low.In this work,electron tomography and depth sectioning are combined to form a method called multiple-section local-orbital tomography,or nLOT in short.The nLOT method provides high spatial resolution and high positional accuracy in all three dimensions.The object size that can be reconstructed is extended to a million atoms.The present method establishes a foundation for the widespread application of atomic electron tomography.
基金supported by the National Natural Science Foundation of China(52171219 and 91963113)。
文摘Cryogenic electron microscopy(cryo-EM)has extensively boosted structural biology research since the“resolution revolution”in the year of 2013 which was soon awarded the Nobel Prize in Chemistry in 2017.The advances in camera techniques and software algorithms enabled cryoEM to routinely characterize the three-dimensional structures of biomolecules at near-atomic resolution.Biomolecules are basically sensitive to electron irradiation damage,which can be minimized at cryo-temperature.This principle has inspired material scientists to characterize electron beam-or air-sensitive materials by cryo-EM,such as the electrodes in the lithium-ion battery,metal-organic frameworks(MOFs),covalent-organic frameworks(COFs)and zeolites.In addition,the reaction systems can be fast-frozen at vitreous ice in cryoEM,which correspondingly preserves the materials at the close-to-native state.Herein,we summarized the development and applications of both the cryo-EM technique and other emerging cryo-techniques in materials science,and energy storage and conversion.Cryo-EM techniques,capable of the direct observation of sensitive materials and electrochemical reaction processes,will greatly renew our understanding of materials science and related mechanisms.
基金We thank Min Ouyang and Wu Zhou for helpful discussion. This work is supported by the National Key Research and Development Program of China (Nos. 2019YFA0308500 and 2018YFA0305800)the National Natural Science Foundation of China (Nos. 51922011, 51991340, and 61888102)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences (No. XDB28000000)A portion of the research was performed in CAS Key Laboratory of Vacuum Physics. G. H. C. is supported by Funds for the Central Universities and the National Key Research and Development Program of China (Nos. 2019FZA3004, 2017YFA0303002, and 2016YFA0300202).
文摘As a new type of iron-based superconductor, CaKFe_(4)As_(4) has recently been demonstrated to be a promising platform for observing Majorana zero modes (MZMs). The surface of CaKFe_(4)As_(4) plays an important role in realizing the MZM since it hosts superconducting topological surface states. However, due to the complicated crystal structure, the terminal surface of CaKFe_(4)As_(4) has not been determined yet. Here, by using scanning tunneling microscopy/spectroscopy (STM/S), we find that there are two types of surface structure in CaKFe_(4)As_(4). Bias-dependent atomic resolution images show an evolvement from 2–√×2–√ superstructure with respect to the As lattice into 1 × 1 when the tip is brought close to the surface, revealing the sublattice of missing As atoms. Together with the first-principles calculations, we show that the surface As layer has a buckled structure. Our findings provide insight to future surface study of CaKFe_(4)As_(4) as well as other iron-pnictide superconductors.
