To overcome the limitations of traditional single-crystal X-ray diffraction(SCXRD)for microcrystalline materials and the peak-overlapping issue of powder X-ray diffraction(PXRD),this study employed cryogenic continuou...To overcome the limitations of traditional single-crystal X-ray diffraction(SCXRD)for microcrystalline materials and the peak-overlapping issue of powder X-ray diffraction(PXRD),this study employed cryogenic continuous rotation electron diffraction(cryo-cRED)with a low-dose strategy to determine the crystal structure of CL30,a novel silicogermanate framework.It is confirmed that CL30 crystallizes in the C2/m space group and has layered topology composed of discontinuous zigzag chains connected by double four-membered ring(d4r)units,with fluoride anions(F^(-))occluded in the d4r units.In CL30,charge balance involves organic structure-directing agent(OSDA)cations,occluded F^(-),and terminal oxygen sites whose protonation state cannot be established from the present three dimensional(3D)ED data.F^(-)encapsulated in the d4r units contributes to charge compensation as the counter-anion to OSDA cations,rather than only balancing the framework charge.Although the refinement indices(R_(1)=0.29,wR_(2)=0.71)exceeded typical small-molecule crystallography standards,the structural model remained highly reliable,as supported by geometric restraints and validation.In electron diffraction,elevated R_(1) values are commonly attributed to the intrinsic factors of the technique,such as dynamic scattering,detector noise from scintillator-based detectors,and TEM stage instability(large spheres of confusion).This study introduces a new structural prototype to the silicogermanate family and establishes a feasible workflow for determining the structures of radiation-sensitive microcrystalline porous materials.展开更多
Space symmetry of prehnite, which occurs in cavities and veins within Skarn from the Tieshan iron mineral deposit,Daye,Hubei province,Central China,has been determined using selected area electron diffraction (SAED) a...Space symmetry of prehnite, which occurs in cavities and veins within Skarn from the Tieshan iron mineral deposit,Daye,Hubei province,Central China,has been determined using selected area electron diffraction (SAED) and convergent-beam electron diffraction (CBED) on the submicrometer scale.Our results confirm that the natural prehnite may have the structure with symmetry Pncm.The unit-cell parameters of investigated prehnite (a=0.458nm,b=0.555nm,and c=1.853nm) have been calculated by using the multicrystal diffraction rings of gold,the internal standard.展开更多
Surface segregation is studied via the evolution of reflection high-energy electron diffraction （RHEED） patterns under different values of As4 BEP for InGaAs films. When the As4 BEP is set to be zero, the RHEED patt...Surface segregation is studied via the evolution of reflection high-energy electron diffraction （RHEED） patterns under different values of As4 BEP for InGaAs films. When the As4 BEP is set to be zero, the RHEED pattern keeps a 4x3/（nx3） structure with increasing temperature, and surface segregation takes place until 470 ℃ The RHEED pattern develops into a metal-rich （4x2） structure as temperature increases to 495℃. The reason for this is that surface segregation makes the In inside the InGaAs film climb to its surface. With the temperature increasing up to 515℃, the RHEED pattern turns into a GaAs（2x4） structure due to In desorption. While the As4 BEP comes up to a specific value （1.33 x 10-4 Pa-1.33 x 10-3 Pa）, the surface temperature can delay the segregation and desorption. We find that As4 BEP has a big influence on surface desorption, while surface segregation is more strongly dependent on temperature than surface desorption.展开更多
The dependence of properties on the structure and morphology of semicrystalline polymers offers an effective way to tailor the properties of these materials through structure control. To this end, establishing the str...The dependence of properties on the structure and morphology of semicrystalline polymers offers an effective way to tailor the properties of these materials through structure control. To this end, establishing the structure and property relationship is of great importance. For a right characterization of the crystal structure, several techniques can be used. Among these techniques, electron diffraction has its advantage for determining the crystal structure related to specific formation condition since it can combine with bright and dark fields observation of the sample. This feature article describes the application of electron diffraction in determining the crystal structure of semicrystalline polymers with elaborately selected examples. We focus on how the electron diffraction can be used to disclose the crystal structure, mutual orientation of different crystals, as well as the disorders included in the polymer crystals.展开更多
Recent progress in ultrafast lasers,ultrafast X-rays and ultrafast electron beams has made it possible to watch the motion of atoms in real time through pumpprobe technique.In this review,we focus on how the molecular...Recent progress in ultrafast lasers,ultrafast X-rays and ultrafast electron beams has made it possible to watch the motion of atoms in real time through pumpprobe technique.In this review,we focus on how the molecular dynamics can be studied with ultrafast electron diffraction where the dynamics is initiated by a pumping laser and then probed by pulsed electron beams.This technique allows one to track the molecular dynamics with femtosecond time resolution and Angstr6m spatial resolution.We present the basic physics and latest development of this technique.Representative applications of ultrafast electron diffraction in studies of laser-induced molecular dynamics are also discussed.This table-top technique is complementary to X-ray free-electron laser and we expect it to have a strong impact in studies of chemical dynamics.展开更多
A method for semi-quantitative determination of thin film texture using electron diffrac- tion is described.The texture state of a zirconia thin film with a cubic structure has been determined in this way and is prese...A method for semi-quantitative determination of thin film texture using electron diffrac- tion is described.The texture state of a zirconia thin film with a cubic structure has been determined in this way and is presented as an example.展开更多
The selected area electron diffraction （SAED） pattern of magnetic iron oxide core/gold shell nanoparticles has been studied. For the composite particles with mean size less than 10 nm, their SAED pattern is found to...The selected area electron diffraction （SAED） pattern of magnetic iron oxide core/gold shell nanoparticles has been studied. For the composite particles with mean size less than 10 nm, their SAED pattern is found to be different from either the pattern of pure Fe oxide nanoparticles or that of pure Au particles. Based on the fact that the ring diameters of these composite particles fit the characteristic relation for the fcc structure, the Au atoms on surfaces of the concerned particles are supposed to pack in a way more tightly than they usually do in pure Au nanoparticles. The driving force for this is the coherency strain which enables the shell material at the heterostructured interface to adapt the lattice parameters of the core.展开更多
Five-fold twinned nanostructures are intrinsically strained or relaxed by extended defects to satisfy the space-filling requirement.Although both of metallic and semiconductor five-fold twinned nanostructures show inh...Five-fold twinned nanostructures are intrinsically strained or relaxed by extended defects to satisfy the space-filling requirement.Although both of metallic and semiconductor five-fold twinned nanostructures show inhomogeneity in their cross-sectional strain distribution,the evident strain concentration at twin boundaries in the semiconductor systems has been found in contrast to the metallic systems.Naturally,a problem is raised how the chemical bonding characteristics of various five-fold twinned nanosystems affects their strain-relieving defect structures.Here using three-dimensional(3D)electron diffraction mapping methodology,the intrinsic strain and the strain-relieving defects in a pentagonal Ag nanowire and a star-shaped boron carbide nanowire,both of them have basically equal radial twin-plane width about 30 nm,are nondestructively characterized.The non-uniform strain and defect distribution between the five single crystalline segments are found in both of the five-fold twinned nanowires.Diffraction intensity fine structure analysis for the boron carbide five-fold twinned nanowire indicates the presence of high-density of planar defects which are responsible for the accommodation of the intrinsic angular excess.However,for the Ag five-fold twinned nanowire,the star-disclination strain field is still present,although is partially relieved by the formation of localized stacking fault layers accompanied by partial dislocations.Energetic analysis suggests that the variety in the strain-relaxation ways for the two types of five-fold twinned nanowires could be ascribed to the large difference in shear modulus between the soft noble metal Ag and the superhard covalent compound boron carbide.展开更多
To integrate a terahertz pump into an ultrafast electron diffraction(UED)experiment has attracted much attention due to its potential to initiate and detect the structural dynamics both directly.However,the deflection...To integrate a terahertz pump into an ultrafast electron diffraction(UED)experiment has attracted much attention due to its potential to initiate and detect the structural dynamics both directly.However,the deflection of the electron probe by the electromagnetic field of the terahertz pump alters the incident angle of the electron probe on the sample,impeding it from recording structural information afterwards.In this article,we studied this issue by a theoretical simulation of the terahertz-induced deflection effect on the electron probe,and came up with several possible schemes to reduce such effect.As a result,a terahertz-pump-electron-probe UED experiment with a temporal resolution comparable to the terahertz period is realized.We also found that Me V UED was more suitable for such terahertz pump experiment.展开更多
Ultrafast electron diffraction （UED） technique has proven to be an innovative tool for providing new insights in lattice dynamics with unprecedented temporal and spatial sensitivities. In this article, we give a bri...Ultrafast electron diffraction （UED） technique has proven to be an innovative tool for providing new insights in lattice dynamics with unprecedented temporal and spatial sensitivities. In this article, we give a brief introduction of this technique using the proposed UED station in the Synergetic Extreme Condition User Facility （SECUF） as a prototype. We briefly discussed UED＇s functionality, working principle, design consideration, and main components. We also briefly reviewed several pioneer works with UED to study structure-function correlations in several research areas. With these efforts, we endeavor to raise the awareness of this tool among those researchers, who may not yet have realized the emerging opportunities offered by this technique.展开更多
The space group of PrCo_(12)B_6,compound has been determined using the convergent beam elec- tron diffraction method.The space group is found to be R3m.
Silicogermanate(JU110)with an interrupted open-framework has been synthesized by using a hydrothermal method using 1,1’-(1,4-phenylenebis(methylene))bis(1-methylpyrrolidin-1-ium)hydroxide as an organic structure-dire...Silicogermanate(JU110)with an interrupted open-framework has been synthesized by using a hydrothermal method using 1,1’-(1,4-phenylenebis(methylene))bis(1-methylpyrrolidin-1-ium)hydroxide as an organic structure-directing agent(OSDA).Silicon and fluoride anions were introduced to the concentrated-gel synthesis system,and different synthetic parameters influencing the synthesis were discussed.The structure of JU110 was characterised by using rotation electron diffraction(RED)and high-resolution powder X-ray diffraction.JU110 crystallizes in the space group Fm2m(No.42)with a=13.9117(2)Å,b=18.2980(3)Åand c=32.7800(6)Å.The structure is constructed by the sti layers found in the STI framework that are pillared by D4R/Ge7 units to form a large cavity,showing 10-ring openings along[100]and 9-ring openings along[110].Thermal stability studies showed that the framework was maintained with the loss of water molecules,but collapsed with the removal of charge-compensating cations.展开更多
A new borosilicate zeolite|N_(2)H_(36)C_(16)|[Si_(22)B_(2)O_(48)]·H_(2)O,denoted as EMM-26,has been synthesized by employing a linear dicationic organic structure directing agent 1,6-bis(N-methylpyrrolidinium)hex...A new borosilicate zeolite|N_(2)H_(36)C_(16)|[Si_(22)B_(2)O_(48)]·H_(2)O,denoted as EMM-26,has been synthesized by employing a linear dicationic organic structure directing agent 1,6-bis(N-methylpyrrolidinium)hexane(OSDA).EMM-26 has a novel zeolite framework and contains two-dimensional(2D)intersecting 10×10-ring channels.Its structure was solved from sub-micrometer sized crystals using rotation electron diffraction(RED)and refined against both the RED and synchrotron powder diffraction data.展开更多
Low-dose electron diffraction has been instrumental in determining the crystal structures of two compounds with metal-radical coordination frameworks{[Mn2^(Ⅱ)(NITIm)^(3)]CF^(3)SO_(3)·CH^(3)OH}n(1)and{[Mn_(2)^(Ⅱ...Low-dose electron diffraction has been instrumental in determining the crystal structures of two compounds with metal-radical coordination frameworks{[Mn2^(Ⅱ)(NITIm)^(3)]CF^(3)SO_(3)·CH^(3)OH}n(1)and{[Mn_(2)^(Ⅱ)(NITImMe_(2))_(3)]ClO_(4)}_(n)(2)that could never be grown to a crystal size large enough for single-crystal X-ray diffraction characterization.The compounds crystallize as nanocrystals upon addition of triflate(1)and perchlorate(2)anions and coordination of manganese(Ⅱ)with bis-chelate nitronyl nitroxide radicals NITImH(1)and NITImHMe_(2)(2)which are respectively 2-(2-imidazolyl)-and 2-(4,5-dimethylimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl.The two compounds have layered crystal structures in which cationic 2D metal-radical coordination polymers{[Mn2^(Ⅱ)(NITIm)_(3)]^(+)}_(n)(1)and{[Mn2^(Ⅱ)(NITImMe_(2))_(3)]^(+)}_(n)(2)are separated by layers of triflate(1)or perchlorate(2)anions.Magnetic measurements evidence a ferrimagnetic behavior within the 2D metal-radical sheets due to alternating antiferromagnetically coupled spins(S_(Mn)^(2+)=5/2 and S_(radical)=1/2).Both compounds exhibit a long-range 3D ordering of weak-ferromagnetic type due to spin canting with Curie temperatures T_(c)=45 K(1)and 40 K(2).This is associated with a field-induced metamagnetic transition from antiferromagnetic to ferromagnetic coupling of 2D metal-radical sheets.Studies of the crystal structures allows to rationalize how the molecular structure of nitronyl nitroxide radicals and of the counter-anions along with crystal packing affect the magnetic behavior related to interlayer distance and framework flexibility.These results are striking evidence that electron crystallography is a unique tool to solve structures of metal-organic compounds crystallizing as nanocrystals even with nitronyl nitroxide radical components too sensitive to typical electron doses.Overcoming the crystal size barrier,it allows the validation of chemical synthesis and the establishment of magneto-structural relationships fostering new advances in the design of molecule-based magnets.展开更多
Since the first discovery and description of materials,whose structures are not periodic,enormous efforts have been made in studying these aperiodic structures.With these efforts including the development of superspac...Since the first discovery and description of materials,whose structures are not periodic,enormous efforts have been made in studying these aperiodic structures.With these efforts including the development of superspace group theory and structure solution algorithms,numerous incommensurately modulated structures which represent the vast majority of known aperiodic structures have been determined with single crystal X-ray diffraction data.However,the determination of modulated structures remains very difficult for polycrystalline materials.Powder X-ray diffraction and electron microscopy techniques yield remarkable information for polycrystalline materials.By combining these two methods,modulated structures of polycrystalline materials that impede solution by conventional methods can be determined.The power of these methods is illustrated with the examples of the determination of modulated structures of polycrystalline materials.展开更多
In this study,the twinning-detwinning behavior and slip behavior of rolled AZ31 magnesium-alloy plates during a three-step intermittent dynamic compression process along the rolling direction(RD)and normal direction(N...In this study,the twinning-detwinning behavior and slip behavior of rolled AZ31 magnesium-alloy plates during a three-step intermittent dynamic compression process along the rolling direction(RD)and normal direction(ND),are investigated via quasi-in situ electron backscatter diffraction,and the causes of the twinning and detwinning behavior are explained according to Schmid law,local strain coordination,and slip trajectories.It is found that the twins are first nucleated and grow at a compressive strain of 3%along the RD.In addition to the Schmid factor(SF),the strain coordination factor(m’)also influences the selection of the twin variants during the twinning process,resulting in the nucleation of twins with a low SF.During the second and third steps of the application of continuous compressive strains with magnitudes and directions of 3%RD+3%ND and 3%RD+3%ND+2.5%ND,detwinning occurs to different extents.The observation of the detwinning behavior reveals that the order in which multiple twins within the same grain undergo complete detwinning is related to Schmid law and the strain concentration,with a low SF and a high strain concentration promoting complete detwinning.The interaction between slip dislocations and twin boundaries in the deformed grains as well as the pinning of dislocations at the tips of the {1012} tensile twins with a special structure result in incomplete detwinning.Understanding the microstructural evolution and twinning behavior of magnesium alloys under different deformation geometries is important for the development of high-strength and high-toughness magnesium alloys.展开更多
Zeolites have received great attention due to their wide applications in various fields such as catalysis,adsorp-tion/separation,ion exchange,etc.Determining the atomic crystal structure of zeolites is crucial to unde...Zeolites have received great attention due to their wide applications in various fields such as catalysis,adsorp-tion/separation,ion exchange,etc.Determining the atomic crystal structure of zeolites is crucial to understanding their functions and exploring their applications.Due to the difficulty of synthesizing large single crystals,the structures of many zeolites cannot be solved using conventional single-crystal X-ray diffraction(SCXRD)methods.Three-dimensional electron diffraction(3D ED)has witnessed rapid development during the past decade and has shown its powerful ability in the structure determination of zeolites.In this review,we will briefly introduce the history of 3D ED and summarize recent advances in the application of 3D ED for the analysis of zeolite structures,along with several typical examples in this research field.展开更多
Time-resolved MeV ultra-fast electron diffraction (UED) is a powerful tool for structure dynamics studies. In this paper, we present a design of a MeV UED facility based on a photocathode RF gun at Tsinghua University...Time-resolved MeV ultra-fast electron diffraction (UED) is a powerful tool for structure dynamics studies. In this paper, we present a design of a MeV UED facility based on a photocathode RF gun at Tsinghua University. Electron beam qualities are optimized with numerical simulations, indicating that resolutions of 250 fs and 0.01 , and bunch charge exceeding 105 electrons are expected with technically achievable machine parameters. Status of experiment preparation is also presented.展开更多
Enantiomorphic identification of chiral molecules is essential in organic chemistry and the pharmaceutical industry,as two enantiomorphic structures can show distinctively different properties.Here,we illustrate the a...Enantiomorphic identification of chiral molecules is essential in organic chemistry and the pharmaceutical industry,as two enantiomorphic structures can show distinctively different properties.Here,we illustrate the absolute structural determination of organic nanocrystals using zone-axis electron diffraction by taking advantage of electron multiple scattering.Two enantiomorphs are distinguished by comparing the reflection intensities of Friedel pairs in the zone-axis electron diffraction pattern,after confirming the absolute indices of reflections by locating relative positions of diffraction spots from two patterns that deviate from a certain angle.We demonstrate the protocol with successful applications in two chiral drug nanocrystals.展开更多
Different structure models of a long-period ordered phase in Fe-C martenstie formed during aging have been checked by computer simulation of electron diffraction(ED) patterns based on these models.The results showed t...Different structure models of a long-period ordered phase in Fe-C martenstie formed during aging have been checked by computer simulation of electron diffraction(ED) patterns based on these models.The results showed that the simulated ED pattern of γ'-FexC(Ⅱ) model proposed by the present authors is in good agreement with experimentally observed ED pattern.It was also confirmed that the incommensurate superperiod stems from the coexistence of several γ'-Fe_xC(H) phases with different superperiods.The Fe(144)C(24)(Fe6C) model proposed by Uwakweh et al.generated ED patterns remarkably different from the experimental ones.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.12374021)Beijing Natural Science Foundation (Grant No.1252031)。
文摘To overcome the limitations of traditional single-crystal X-ray diffraction(SCXRD)for microcrystalline materials and the peak-overlapping issue of powder X-ray diffraction(PXRD),this study employed cryogenic continuous rotation electron diffraction(cryo-cRED)with a low-dose strategy to determine the crystal structure of CL30,a novel silicogermanate framework.It is confirmed that CL30 crystallizes in the C2/m space group and has layered topology composed of discontinuous zigzag chains connected by double four-membered ring(d4r)units,with fluoride anions(F^(-))occluded in the d4r units.In CL30,charge balance involves organic structure-directing agent(OSDA)cations,occluded F^(-),and terminal oxygen sites whose protonation state cannot be established from the present three dimensional(3D)ED data.F^(-)encapsulated in the d4r units contributes to charge compensation as the counter-anion to OSDA cations,rather than only balancing the framework charge.Although the refinement indices(R_(1)=0.29,wR_(2)=0.71)exceeded typical small-molecule crystallography standards,the structural model remained highly reliable,as supported by geometric restraints and validation.In electron diffraction,elevated R_(1) values are commonly attributed to the intrinsic factors of the technique,such as dynamic scattering,detector noise from scintillator-based detectors,and TEM stage instability(large spheres of confusion).This study introduces a new structural prototype to the silicogermanate family and establishes a feasible workflow for determining the structures of radiation-sensitive microcrystalline porous materials.
文摘Space symmetry of prehnite, which occurs in cavities and veins within Skarn from the Tieshan iron mineral deposit,Daye,Hubei province,Central China,has been determined using selected area electron diffraction (SAED) and convergent-beam electron diffraction (CBED) on the submicrometer scale.Our results confirm that the natural prehnite may have the structure with symmetry Pncm.The unit-cell parameters of investigated prehnite (a=0.458nm,b=0.555nm,and c=1.853nm) have been calculated by using the multicrystal diffraction rings of gold,the internal standard.
基金supported by the National Natural Science Foundation of China (Grant No. 60866001)the Special Assistant to High-Level Personnel Research Projects of Guizhou Provincial Party Committee Organization Department of China (Grant No. TZJF- 2008-31)+3 种基金the Support Plan of New Century Excellent Talents of Ministry of Education, China (Grant No. NCET-08-0651)the Doctorate Foundation of the State Education Ministry of China (Grant No. 20105201110003)the Special Governor Fund of Outstanding Professionals in Science and Technology and Education of Guizhou Province, China (Grant No. 2009114)the Doctoral Foundation Projects of Guizhou College of Finance and Economics in 2010
文摘Surface segregation is studied via the evolution of reflection high-energy electron diffraction （RHEED） patterns under different values of As4 BEP for InGaAs films. When the As4 BEP is set to be zero, the RHEED pattern keeps a 4x3/（nx3） structure with increasing temperature, and surface segregation takes place until 470 ℃ The RHEED pattern develops into a metal-rich （4x2） structure as temperature increases to 495℃. The reason for this is that surface segregation makes the In inside the InGaAs film climb to its surface. With the temperature increasing up to 515℃, the RHEED pattern turns into a GaAs（2x4） structure due to In desorption. While the As4 BEP comes up to a specific value （1.33 x 10-4 Pa-1.33 x 10-3 Pa）, the surface temperature can delay the segregation and desorption. We find that As4 BEP has a big influence on surface desorption, while surface segregation is more strongly dependent on temperature than surface desorption.
基金supported by the National Natural Science Foundation of China (Nos. 50833006, 21274009,51221002 and 50973008)
文摘The dependence of properties on the structure and morphology of semicrystalline polymers offers an effective way to tailor the properties of these materials through structure control. To this end, establishing the structure and property relationship is of great importance. For a right characterization of the crystal structure, several techniques can be used. Among these techniques, electron diffraction has its advantage for determining the crystal structure related to specific formation condition since it can combine with bright and dark fields observation of the sample. This feature article describes the application of electron diffraction in determining the crystal structure of semicrystalline polymers with elaborately selected examples. We focus on how the electron diffraction can be used to disclose the crystal structure, mutual orientation of different crystals, as well as the disorders included in the polymer crystals.
基金The work was supported by the National Natural Science Foundation of China(No.11925505).
文摘Recent progress in ultrafast lasers,ultrafast X-rays and ultrafast electron beams has made it possible to watch the motion of atoms in real time through pumpprobe technique.In this review,we focus on how the molecular dynamics can be studied with ultrafast electron diffraction where the dynamics is initiated by a pumping laser and then probed by pulsed electron beams.This technique allows one to track the molecular dynamics with femtosecond time resolution and Angstr6m spatial resolution.We present the basic physics and latest development of this technique.Representative applications of ultrafast electron diffraction in studies of laser-induced molecular dynamics are also discussed.This table-top technique is complementary to X-ray free-electron laser and we expect it to have a strong impact in studies of chemical dynamics.
文摘A method for semi-quantitative determination of thin film texture using electron diffrac- tion is described.The texture state of a zirconia thin film with a cubic structure has been determined in this way and is presented as an example.
文摘The selected area electron diffraction （SAED） pattern of magnetic iron oxide core/gold shell nanoparticles has been studied. For the composite particles with mean size less than 10 nm, their SAED pattern is found to be different from either the pattern of pure Fe oxide nanoparticles or that of pure Au particles. Based on the fact that the ring diameters of these composite particles fit the characteristic relation for the fcc structure, the Au atoms on surfaces of the concerned particles are supposed to pack in a way more tightly than they usually do in pure Au nanoparticles. The driving force for this is the coherency strain which enables the shell material at the heterostructured interface to adapt the lattice parameters of the core.
基金National Natural Science Foundation of China(Grant Nos.51201015 and U1532262).
文摘Five-fold twinned nanostructures are intrinsically strained or relaxed by extended defects to satisfy the space-filling requirement.Although both of metallic and semiconductor five-fold twinned nanostructures show inhomogeneity in their cross-sectional strain distribution,the evident strain concentration at twin boundaries in the semiconductor systems has been found in contrast to the metallic systems.Naturally,a problem is raised how the chemical bonding characteristics of various five-fold twinned nanosystems affects their strain-relieving defect structures.Here using three-dimensional(3D)electron diffraction mapping methodology,the intrinsic strain and the strain-relieving defects in a pentagonal Ag nanowire and a star-shaped boron carbide nanowire,both of them have basically equal radial twin-plane width about 30 nm,are nondestructively characterized.The non-uniform strain and defect distribution between the five single crystalline segments are found in both of the five-fold twinned nanowires.Diffraction intensity fine structure analysis for the boron carbide five-fold twinned nanowire indicates the presence of high-density of planar defects which are responsible for the accommodation of the intrinsic angular excess.However,for the Ag five-fold twinned nanowire,the star-disclination strain field is still present,although is partially relieved by the formation of localized stacking fault layers accompanied by partial dislocations.Energetic analysis suggests that the variety in the strain-relaxation ways for the two types of five-fold twinned nanowires could be ascribed to the large difference in shear modulus between the soft noble metal Ag and the superhard covalent compound boron carbide.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774409,11827807,and92050106)supported by the Synergic Extreme Condition User Facility。
文摘To integrate a terahertz pump into an ultrafast electron diffraction(UED)experiment has attracted much attention due to its potential to initiate and detect the structural dynamics both directly.However,the deflection of the electron probe by the electromagnetic field of the terahertz pump alters the incident angle of the electron probe on the sample,impeding it from recording structural information afterwards.In this article,we studied this issue by a theoretical simulation of the terahertz-induced deflection effect on the electron probe,and came up with several possible schemes to reduce such effect.As a result,a terahertz-pump-electron-probe UED experiment with a temporal resolution comparable to the terahertz period is realized.We also found that Me V UED was more suitable for such terahertz pump experiment.
基金Project supported by the National Natural Science Foundation of China(Grant No.11774409)the National Basic Research Program of China(Grant No.2013CBA01501)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB16010200 and XDB07030300)
文摘Ultrafast electron diffraction （UED） technique has proven to be an innovative tool for providing new insights in lattice dynamics with unprecedented temporal and spatial sensitivities. In this article, we give a brief introduction of this technique using the proposed UED station in the Synergetic Extreme Condition User Facility （SECUF） as a prototype. We briefly discussed UED＇s functionality, working principle, design consideration, and main components. We also briefly reviewed several pioneer works with UED to study structure-function correlations in several research areas. With these efforts, we endeavor to raise the awareness of this tool among those researchers, who may not yet have realized the emerging opportunities offered by this technique.
文摘The space group of PrCo_(12)B_6,compound has been determined using the convergent beam elec- tron diffraction method.The space group is found to be R3m.
基金supported by the National Key Research and Development Program of China(Grant No.2016YFB0701100)the National Natural Science Foundation of China(Grant No.:21320102001 and 21621001)+2 种基金the 111 Project(B17020)financial support from the Swedish Research Council(VR),the Swedish Governmental Agency for Innovation Systems(VINNOVA)the Knut and Alice Wallenberg Foundation through the project grant 3DEM-NATUR.
文摘Silicogermanate(JU110)with an interrupted open-framework has been synthesized by using a hydrothermal method using 1,1’-(1,4-phenylenebis(methylene))bis(1-methylpyrrolidin-1-ium)hydroxide as an organic structure-directing agent(OSDA).Silicon and fluoride anions were introduced to the concentrated-gel synthesis system,and different synthetic parameters influencing the synthesis were discussed.The structure of JU110 was characterised by using rotation electron diffraction(RED)and high-resolution powder X-ray diffraction.JU110 crystallizes in the space group Fm2m(No.42)with a=13.9117(2)Å,b=18.2980(3)Åand c=32.7800(6)Å.The structure is constructed by the sti layers found in the STI framework that are pillared by D4R/Ge7 units to form a large cavity,showing 10-ring openings along[100]and 9-ring openings along[110].Thermal stability studies showed that the framework was maintained with the loss of water molecules,but collapsed with the removal of charge-compensating cations.
文摘A new borosilicate zeolite|N_(2)H_(36)C_(16)|[Si_(22)B_(2)O_(48)]·H_(2)O,denoted as EMM-26,has been synthesized by employing a linear dicationic organic structure directing agent 1,6-bis(N-methylpyrrolidinium)hexane(OSDA).EMM-26 has a novel zeolite framework and contains two-dimensional(2D)intersecting 10×10-ring channels.Its structure was solved from sub-micrometer sized crystals using rotation electron diffraction(RED)and refined against both the RED and synchrotron powder diffraction data.
基金supported by CNRS collaborative research program(PRC 2017-2019 No.1536)the Russian Science Foundation(grant No.21-73-20079)+6 种基金Magdesign Project(ANR-22-CE29-0018-03)Platforms of the Grenoble Instruct-ERIC center(ISBG,UAR 3518 CNRS-CEA-UGA-EMBL)within the Grenoble Partnership for Structural Biology(PSB)supported by FRISBI(ANR-10-INBS-0005-02)GRAL,financed within the University Grenoble Alpes graduate school(Ecoles Universitaires de Recherche)CBH-EUR-GS(ANR-17-EURE-0003)The IBS-ISBG electron microscope facility is supported by the Région Auvergne-Rhône-Alpes,Fondation pour la Recherche Médicale(FRM),Fonds FEDER and the GIS-Infrastructures en Biologie Santéet Agronomie(IBiSA)supported by Grant-in-Aid for Scientific Research(No.25220803 and 22H02053)CResCent(Chirality Research Center)in Hiroshima University(the MEXT program for promoting the enhancement of research universities,Japan)Core-to-Core Program,A.Advanced Research Networks.
文摘Low-dose electron diffraction has been instrumental in determining the crystal structures of two compounds with metal-radical coordination frameworks{[Mn2^(Ⅱ)(NITIm)^(3)]CF^(3)SO_(3)·CH^(3)OH}n(1)and{[Mn_(2)^(Ⅱ)(NITImMe_(2))_(3)]ClO_(4)}_(n)(2)that could never be grown to a crystal size large enough for single-crystal X-ray diffraction characterization.The compounds crystallize as nanocrystals upon addition of triflate(1)and perchlorate(2)anions and coordination of manganese(Ⅱ)with bis-chelate nitronyl nitroxide radicals NITImH(1)and NITImHMe_(2)(2)which are respectively 2-(2-imidazolyl)-and 2-(4,5-dimethylimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl.The two compounds have layered crystal structures in which cationic 2D metal-radical coordination polymers{[Mn2^(Ⅱ)(NITIm)_(3)]^(+)}_(n)(1)and{[Mn2^(Ⅱ)(NITImMe_(2))_(3)]^(+)}_(n)(2)are separated by layers of triflate(1)or perchlorate(2)anions.Magnetic measurements evidence a ferrimagnetic behavior within the 2D metal-radical sheets due to alternating antiferromagnetically coupled spins(S_(Mn)^(2+)=5/2 and S_(radical)=1/2).Both compounds exhibit a long-range 3D ordering of weak-ferromagnetic type due to spin canting with Curie temperatures T_(c)=45 K(1)and 40 K(2).This is associated with a field-induced metamagnetic transition from antiferromagnetic to ferromagnetic coupling of 2D metal-radical sheets.Studies of the crystal structures allows to rationalize how the molecular structure of nitronyl nitroxide radicals and of the counter-anions along with crystal packing affect the magnetic behavior related to interlayer distance and framework flexibility.These results are striking evidence that electron crystallography is a unique tool to solve structures of metal-organic compounds crystallizing as nanocrystals even with nitronyl nitroxide radical components too sensitive to typical electron doses.Overcoming the crystal size barrier,it allows the validation of chemical synthesis and the establishment of magneto-structural relationships fostering new advances in the design of molecule-based magnets.
基金supported by the Natural Science Foundation of China(21321001 and 21527803)the National Basic Research Program of China(2013CB8933402).
文摘Since the first discovery and description of materials,whose structures are not periodic,enormous efforts have been made in studying these aperiodic structures.With these efforts including the development of superspace group theory and structure solution algorithms,numerous incommensurately modulated structures which represent the vast majority of known aperiodic structures have been determined with single crystal X-ray diffraction data.However,the determination of modulated structures remains very difficult for polycrystalline materials.Powder X-ray diffraction and electron microscopy techniques yield remarkable information for polycrystalline materials.By combining these two methods,modulated structures of polycrystalline materials that impede solution by conventional methods can be determined.The power of these methods is illustrated with the examples of the determination of modulated structures of polycrystalline materials.
基金supported by the General Project of Liaoning Provincial Department of Education(NO:JYTMS20231199)Project of Liaoning Education Department(No:LKMZ20220462 and No:LJKMZ20220467)+1 种基金Basic scientific research project of Liaoning Provincial Department of Education(key research project)(No:JYTZD2023108)Liaoning Nature Fund Guidance Plan(No:42022-BS.179)。
文摘In this study,the twinning-detwinning behavior and slip behavior of rolled AZ31 magnesium-alloy plates during a three-step intermittent dynamic compression process along the rolling direction(RD)and normal direction(ND),are investigated via quasi-in situ electron backscatter diffraction,and the causes of the twinning and detwinning behavior are explained according to Schmid law,local strain coordination,and slip trajectories.It is found that the twins are first nucleated and grow at a compressive strain of 3%along the RD.In addition to the Schmid factor(SF),the strain coordination factor(m’)also influences the selection of the twin variants during the twinning process,resulting in the nucleation of twins with a low SF.During the second and third steps of the application of continuous compressive strains with magnitudes and directions of 3%RD+3%ND and 3%RD+3%ND+2.5%ND,detwinning occurs to different extents.The observation of the detwinning behavior reveals that the order in which multiple twins within the same grain undergo complete detwinning is related to Schmid law and the strain concentration,with a low SF and a high strain concentration promoting complete detwinning.The interaction between slip dislocations and twin boundaries in the deformed grains as well as the pinning of dislocations at the tips of the {1012} tensile twins with a special structure result in incomplete detwinning.Understanding the microstructural evolution and twinning behavior of magnesium alloys under different deformation geometries is important for the development of high-strength and high-toughness magnesium alloys.
基金supported by the National Key R&D Program of China(No.2022YFA1506000)the National Natural Science Foundation of China(No.22222108).
文摘Zeolites have received great attention due to their wide applications in various fields such as catalysis,adsorp-tion/separation,ion exchange,etc.Determining the atomic crystal structure of zeolites is crucial to understanding their functions and exploring their applications.Due to the difficulty of synthesizing large single crystals,the structures of many zeolites cannot be solved using conventional single-crystal X-ray diffraction(SCXRD)methods.Three-dimensional electron diffraction(3D ED)has witnessed rapid development during the past decade and has shown its powerful ability in the structure determination of zeolites.In this review,we will briefly introduce the history of 3D ED and summarize recent advances in the application of 3D ED for the analysis of zeolite structures,along with several typical examples in this research field.
基金Supported by NSFC (10735050,10875070)National Basic Research Program of China (973 Program)(2007CB815102)
文摘Time-resolved MeV ultra-fast electron diffraction (UED) is a powerful tool for structure dynamics studies. In this paper, we present a design of a MeV UED facility based on a photocathode RF gun at Tsinghua University. Electron beam qualities are optimized with numerical simulations, indicating that resolutions of 250 fs and 0.01 , and bunch charge exceeding 105 electrons are expected with technically achievable machine parameters. Status of experiment preparation is also presented.
基金support of the National Science Foundation of China[grant nos.22222108(Y.M.),12027804(Y.M.)]the Shanghai Science and Technology Plan[grant no.21DZ2260400(Y.M.)]+1 种基金gratefully acknowledge CℏEM,School of Physical Sciences and Technology,Shanghai-Tech University(grant no.EM02161943)for the support of their EM facilities and the Analytical Instrumentation Center(grant no.SPSTAIC10112914),School of Physical Sciences and Technology,ShanghaiTech University.
文摘Enantiomorphic identification of chiral molecules is essential in organic chemistry and the pharmaceutical industry,as two enantiomorphic structures can show distinctively different properties.Here,we illustrate the absolute structural determination of organic nanocrystals using zone-axis electron diffraction by taking advantage of electron multiple scattering.Two enantiomorphs are distinguished by comparing the reflection intensities of Friedel pairs in the zone-axis electron diffraction pattern,after confirming the absolute indices of reflections by locating relative positions of diffraction spots from two patterns that deviate from a certain angle.We demonstrate the protocol with successful applications in two chiral drug nanocrystals.
文摘Different structure models of a long-period ordered phase in Fe-C martenstie formed during aging have been checked by computer simulation of electron diffraction(ED) patterns based on these models.The results showed that the simulated ED pattern of γ'-FexC(Ⅱ) model proposed by the present authors is in good agreement with experimentally observed ED pattern.It was also confirmed that the incommensurate superperiod stems from the coexistence of several γ'-Fe_xC(H) phases with different superperiods.The Fe(144)C(24)(Fe6C) model proposed by Uwakweh et al.generated ED patterns remarkably different from the experimental ones.
