Quantitative phase imaging(QPI)enables non-invasive cellular analysis by utilizing cell thickness and refractive index as intrinsic probes,revolutionizing label-free microscopy in cellular research.Differential phase ...Quantitative phase imaging(QPI)enables non-invasive cellular analysis by utilizing cell thickness and refractive index as intrinsic probes,revolutionizing label-free microscopy in cellular research.Differential phase contrast(DPC),a non-interferometric QPI technique,requires only four intensity images under asymmetric illumination to recover the phase of a sample,offering the advantages of being label-free,non-coherent and highly robust.Its phase reconstruction result relies on precise modeling of the phase transfer function(PTF).However,in real optical systems,the PTF will deviate from its theoretical ideal due to the unknown wavefront aberrations,which will lead to significant artifacts and distortions in the reconstructed phase.We propose an aberration-corrected DPC(ACDPC)method that utilizes three intensity images under annular illumination to jointly retrieve the aberration and the phase,achieving high-quality QPI with minimal raw data.By employing three annular illuminations precisely matched to the numerical aperture of the objective lens,the object information is transmitted into the acquired intensity with a high signal-to-noise ratio.Phase retrieval is achieved by an iterative deconvolution algorithm that uses simulated annealing to estimate the aberration and further employs regularized deconvolution to reconstruct the phase,ultimately obtaining a refined complex pupil function and an aberration-corrected quantitative phase.We demonstrate that ACDPC is robust to multi-order aberrations without any priori knowledge,and can effectively retrieve and correct system aberrations to obtain high-quality quantitative phase.Experimental results show that ACDPC can clearly reproduce subcellular structures such as vesicles and lipid droplets with higher resolution than conventional DPC,which opens up new possibilities for more accurate subcellular structure analysis in cell biology.展开更多
Lattice,charge,orbital,and spin are the four fundamental degrees of freedom in condensed matter,of which the interactive coupling derives tremendous novel physical phenomena,such as high-temperature superconductivity...Lattice,charge,orbital,and spin are the four fundamental degrees of freedom in condensed matter,of which the interactive coupling derives tremendous novel physical phenomena,such as high-temperature superconductivity（high-T_c SC） and colossal magnetoresistance（CMR） in strongly correlated electronic system.Direct experimental observation of these freedoms is essential to understanding the structure-property relationship and the physics behind it,and also indispensable for designing new materials and devices.Scanning transmission electron microscopy（STEM） integrating multiple techniques of structure imaging and spectrum analysis,is a comprehensive platform for providing structural,chemical and electronic information of materials with a high spatial resolution.Benefiting from the development of aberration correctors,STEM has taken a big breakthrough towards sub-angstrom resolution in last decade and always steps forward to improve the capability of material characterization;many improvements have been achieved in recent years,thereby giving an indepth insight into material research.Here,we present a brief review of the recent advances of STEM by some representative examples of perovskite transition metal oxides;atomic-scale mapping of ferroelectric polarization,octahedral distortions and rotations,valence state,coordination and spin ordering are presented.We expect that this brief introduction about the current capability of STEM could facilitate the understanding of the relationship between functional properties and these fundamental degrees of freedom in complex oxides.展开更多
On the basis of a state-of-the-art aberration-corrected transmission electron microscope, the spherical aberration coefficient CSof the objective lens can be tuned to either a positive or a negative value. The use of ...On the basis of a state-of-the-art aberration-corrected transmission electron microscope, the spherical aberration coefficient CSof the objective lens can be tuned to either a positive or a negative value. The use of a negative value of CS combined with an overfocus setting of the objective lens leads to the development of the negative CSimaging（NCSI） technique. Images obtained using the NCSI technique show superior contrast and signal intensity at atomic column positions than the corresponding positive CSimages, especially for weakly scattering oxygen columns that are in close proximity to strongly scattering cation columns in oxides. Based on the images obtained under the NCSI condition, quantification of the image contrast allows measurements of the atom positions with a precision of a few picometers and the local chemistry on atomic scale. In the present review, we discuss firstly the benefits of the NCSI technique in studies of oxide materials,and then show a procedure for quantitative analysis of the image based on the absolute value of contrast. In the last part,examples are given for the application of the quantitative high-resolution transmission electron microscopy（HRTEM） to the study of electric dipoles of oxide ferroelectrics and atomic-scale chemistry of interfaces.展开更多
Nanoscale zero-valent iron （nZVI） possesses unique chemistry and capability for the separation and transformation of a growing number of environmental contaminants. A nZVI particle consists of two nanoscale componen...Nanoscale zero-valent iron （nZVI） possesses unique chemistry and capability for the separation and transformation of a growing number of environmental contaminants. A nZVI particle consists of two nanoscale components, an iron （oxyhydr）oxides shell and a metallic iron core. This classical ＂core-shell＂ structure offers nZVI with unique and multifaceted reactivity of sorption, complexation, reduction and precipita- tion due to its strong small particle size for engineering deployment, large surface area, abundant reactive sites and electron-donating capacity for enhanced chemical activity. For over two decades, research has been steadily expanding our understanding on the reaction mechanisms and engineering performance of nZVI for soil and groundwater remediation, and more recently for wastewater treatment.展开更多
Aberration-corrected scanning transmission electron microscopy was employed to investigate the microstructures and secondary phases in LaBaCo2O5.5＋δ（LBCO） thin films grown on SrTiO3 （STO） substrates. The as-grow...Aberration-corrected scanning transmission electron microscopy was employed to investigate the microstructures and secondary phases in LaBaCo2O5.5＋δ（LBCO） thin films grown on SrTiO3 （STO） substrates. The as-grown films showed an epitaxial growth on the substrates with atomically sharp interfaces and orientation relationships of [100]LBCO//[100]STO and （001）LBCO//（001）STO. Secondary phases were observed in the films, which strongly depended on the sample fabrication conditions. In the film prepared at a temperature of 900 ℃, nano-scale CoO pillars nucleated on the substrate, and grew along the [001] direction of the film. In the film grown at a temperature of 1000 ℃, isolated nano-scale C0304 particles appeared, which promoted the growth of {111 } twinning structures in the film. The orientation relationships and the interfaces between the secondary phases and the films were illustrated, and the growth mechanism of the film was discussed.展开更多
The oxidation chemistry of two-dimensional transition metal carbide MXenes has brought new research significance to their protection and application.However,the oxidation behavior and degradation mechanism of MXenes,i...The oxidation chemistry of two-dimensional transition metal carbide MXenes has brought new research significance to their protection and application.However,the oxidation behavior and degradation mechanism of MXenes,in particular with time under oxygen conditions at room tem-perature,remain largely unexplored.Here,several experimental and theo-retical techniques are used to determine a very early stage of the oxidation mechanism of HF-etched Ti3C2Tx(a major member of MXenes and Tx=surface functional groups)in an oxygen environment at room temper-ature.Aberration-corrected environmental transmission electron micros-copy coupled with reactive molecular dynamics simulations show that the crystal plane-dependent oxidation rate of Ti3C2Tx and oxide expansion are attributed to differences in the coordination and charge of superficial Ti atoms,and the existence of the channels between neighboring MXene layers on the different crystal planes.The complementary x-ray photoelec-tron spectroscopy and Raman spectroscopy analyses indicate that the ana-tase and a tiny fraction of brookite TiO2 successively precipitate from the amorphous region of oxidized Ti3C2Tx,grow irregularly and transform to rutile TiO2.Our study reveals the early-stage structural evolution of MXenes in the presence of oxygen and facilitates further tailoring of the MXene per-formance employing oxidation strategy.展开更多
As an innovative development of single-atom catalysts(SACs),single-cluster catalysts(SCCs)such as dualatom catalysts have attracted considerable interest due to their excellent performance in catalysis.As one of the m...As an innovative development of single-atom catalysts(SACs),single-cluster catalysts(SCCs)such as dualatom catalysts have attracted considerable interest due to their excellent performance in catalysis.As one of the most powerful and visualizable tools,scanning transmission electron microscopy(STEM)has been widely applied in the characterization of SCCs.Herein,the nitrogen-doped carbonsupported FeFe and CoFe,two representative examples of homonuclear and heteronuclear SCCs,are characterized by STEM.Furthermore,an image processing program is developed to analyze the STEM images and to obtain the locations of atoms,as well as the projected distances between atoms in possible dual-atom pairs.The dimer distances of both CoFe and FeFe catalysts exhibit a trimodal distribution,which can correspond to the energy-favorable atomic structures of the theoretical simulations.Our work offers an avenue for directly revealing the possible atomic configurations of dual-atom sites in SCCs via big data statistics of STEM images and strong theoretical simulations.展开更多
The structure and properties of CeO2 surfaces have been intensively studied due to their importance in a lot of surface-related applications. Since most of surface techniques probe the structure information inside the...The structure and properties of CeO2 surfaces have been intensively studied due to their importance in a lot of surface-related applications. Since most of surface techniques probe the structure information inside the outermost surface plane, the subsurface structure information has been elusive in many studies. Using the profile imaging with aberration-corrected transmission electron microscopy, the structure information in both the outermost layer and the sublayers of the CeO2（100） surface has been obtained. In addition to the normal structures that have been reported before, where the surface is Ce-or O-terminated, a metastable surface has been discovered. In the new structure, there is an atomic layer reversal between the outermost layer and the sublayer, giving a structure with O as the outermost layer for the stoichiometry of normal Ce-terminated surface. The charge redistribution for the polarity compensation has also been changed relative to the normal surface.展开更多
The behavior of oxygen on ceria surfaces is closely related with the applications of ceria as a catalyst and oxygen conductor in solid-oxide fuel cells. Here, the atomic configurations of oxygen adatoms and vacancies ...The behavior of oxygen on ceria surfaces is closely related with the applications of ceria as a catalyst and oxygen conductor in solid-oxide fuel cells. Here, the atomic configurations of oxygen adatoms and vacancies on the(110) surface of CeO_2 have been studied combining aberration-corrected transmission electron microscopy and first-principles calculations. The oxygen adatoms were estimated to be located on top of Ce atoms with 50% coverage, forming a c(2×2) reconstruction. The oxygen vacancies can form stable configuration, with the Ce atoms partly reduced.展开更多
Optically imaging atomic nuclei is a long-sought goal for scientific and applied research,but it has never been realized so far.We integrate aberration-corrected scanning transmission electron microscopy(STEM),the bre...Optically imaging atomic nuclei is a long-sought goal for scientific and applied research,but it has never been realized so far.We integrate aberration-corrected scanning transmission electron microscopy(STEM),the bremsstrahlung generation of X-ray photons,and the energy-dispersive X-ray spectroscopic(EDS)receiving and mapping of the photons into a new microscopy method of optical imaging,by which atomic nuclei of different materials are successfully imaged with X-ray photons.Moreover,this imaging method is shown to be workable with different STEM instruments and be capable of distinguishing atomic nuclei of different elements and resolving imaged size differences of atomic nuclei with the order of magnitude as small as 1 pm.Therefore,it is a general method that can image atomic nuclei and their evolutions in materials science,chemistry and physics.展开更多
基金supported by the National Natural Science Foundation of China(62305162,62227818,62361136588)China Postdoctoral Science Foundation(2023TQ0160,2023M731683)+5 种基金Nanjing University of Science and Technology independent research project(30923010305)National Key Research and Development Program of China(2024YFE0101300)Biomedical Competition Foundation of Jiangsu Province(BE2022847)Key National Industrial Technology Cooperation Foundation of Jiangsu Province(BZ2022039)Fundamental Research Funds for the Central Universities(2023102001)Open Research Fund of Jiangsu Key Laboratory of Spectral Imaging&Intelligent Sense(JSGP202105,JSGP202201,JSGPCXZNGZ202401)。
文摘Quantitative phase imaging(QPI)enables non-invasive cellular analysis by utilizing cell thickness and refractive index as intrinsic probes,revolutionizing label-free microscopy in cellular research.Differential phase contrast(DPC),a non-interferometric QPI technique,requires only four intensity images under asymmetric illumination to recover the phase of a sample,offering the advantages of being label-free,non-coherent and highly robust.Its phase reconstruction result relies on precise modeling of the phase transfer function(PTF).However,in real optical systems,the PTF will deviate from its theoretical ideal due to the unknown wavefront aberrations,which will lead to significant artifacts and distortions in the reconstructed phase.We propose an aberration-corrected DPC(ACDPC)method that utilizes three intensity images under annular illumination to jointly retrieve the aberration and the phase,achieving high-quality QPI with minimal raw data.By employing three annular illuminations precisely matched to the numerical aperture of the objective lens,the object information is transmitted into the acquired intensity with a high signal-to-noise ratio.Phase retrieval is achieved by an iterative deconvolution algorithm that uses simulated annealing to estimate the aberration and further employs regularized deconvolution to reconstruct the phase,ultimately obtaining a refined complex pupil function and an aberration-corrected quantitative phase.We demonstrate that ACDPC is robust to multi-order aberrations without any priori knowledge,and can effectively retrieve and correct system aberrations to obtain high-quality quantitative phase.Experimental results show that ACDPC can clearly reproduce subcellular structures such as vesicles and lipid droplets with higher resolution than conventional DPC,which opens up new possibilities for more accurate subcellular structure analysis in cell biology.
基金Project supported by the National Key Basic Research ProjectChina(Grant No.2014CB921002)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB07030200)the National Natural Science Foundation of China(Grant Nos.51522212 and 51421002)
文摘Lattice,charge,orbital,and spin are the four fundamental degrees of freedom in condensed matter,of which the interactive coupling derives tremendous novel physical phenomena,such as high-temperature superconductivity（high-T_c SC） and colossal magnetoresistance（CMR） in strongly correlated electronic system.Direct experimental observation of these freedoms is essential to understanding the structure-property relationship and the physics behind it,and also indispensable for designing new materials and devices.Scanning transmission electron microscopy（STEM） integrating multiple techniques of structure imaging and spectrum analysis,is a comprehensive platform for providing structural,chemical and electronic information of materials with a high spatial resolution.Benefiting from the development of aberration correctors,STEM has taken a big breakthrough towards sub-angstrom resolution in last decade and always steps forward to improve the capability of material characterization;many improvements have been achieved in recent years,thereby giving an indepth insight into material research.Here,we present a brief review of the recent advances of STEM by some representative examples of perovskite transition metal oxides;atomic-scale mapping of ferroelectric polarization,octahedral distortions and rotations,valence state,coordination and spin ordering are presented.We expect that this brief introduction about the current capability of STEM could facilitate the understanding of the relationship between functional properties and these fundamental degrees of freedom in complex oxides.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51390472 and 51471169)the National Basic Research Program of China(Grant No.2015CB654903)
文摘On the basis of a state-of-the-art aberration-corrected transmission electron microscope, the spherical aberration coefficient CSof the objective lens can be tuned to either a positive or a negative value. The use of a negative value of CS combined with an overfocus setting of the objective lens leads to the development of the negative CSimaging（NCSI） technique. Images obtained using the NCSI technique show superior contrast and signal intensity at atomic column positions than the corresponding positive CSimages, especially for weakly scattering oxygen columns that are in close proximity to strongly scattering cation columns in oxides. Based on the images obtained under the NCSI condition, quantification of the image contrast allows measurements of the atom positions with a precision of a few picometers and the local chemistry on atomic scale. In the present review, we discuss firstly the benefits of the NCSI technique in studies of oxide materials,and then show a procedure for quantitative analysis of the image based on the absolute value of contrast. In the last part,examples are given for the application of the quantitative high-resolution transmission electron microscopy（HRTEM） to the study of electric dipoles of oxide ferroelectrics and atomic-scale chemistry of interfaces.
基金supported by the National Natural Science Foundation of China (Nos. 51578398 and 41772243)the National Postdoctoral Program for Innovative Talents (No. BX201700172)
文摘Nanoscale zero-valent iron （nZVI） possesses unique chemistry and capability for the separation and transformation of a growing number of environmental contaminants. A nZVI particle consists of two nanoscale components, an iron （oxyhydr）oxides shell and a metallic iron core. This classical ＂core-shell＂ structure offers nZVI with unique and multifaceted reactivity of sorption, complexation, reduction and precipita- tion due to its strong small particle size for engineering deployment, large surface area, abundant reactive sites and electron-donating capacity for enhanced chemical activity. For over two decades, research has been steadily expanding our understanding on the reaction mechanisms and engineering performance of nZVI for soil and groundwater remediation, and more recently for wastewater treatment.
基金financially supported by the National Natural Science Foundation of China (Nos. 51501143, 51202185 and 51390472)the National Basic Research Program of China (No. 2015CB654903)Fundamental Research Funds for the Central Universities, China Postdoctoral Science Foundation (No. 2015M572554)
文摘Aberration-corrected scanning transmission electron microscopy was employed to investigate the microstructures and secondary phases in LaBaCo2O5.5＋δ（LBCO） thin films grown on SrTiO3 （STO） substrates. The as-grown films showed an epitaxial growth on the substrates with atomically sharp interfaces and orientation relationships of [100]LBCO//[100]STO and （001）LBCO//（001）STO. Secondary phases were observed in the films, which strongly depended on the sample fabrication conditions. In the film prepared at a temperature of 900 ℃, nano-scale CoO pillars nucleated on the substrate, and grew along the [001] direction of the film. In the film grown at a temperature of 1000 ℃, isolated nano-scale C0304 particles appeared, which promoted the growth of {111 } twinning structures in the film. The orientation relationships and the interfaces between the secondary phases and the films were illustrated, and the growth mechanism of the film was discussed.
基金appreciate the support from the National Natural Science Foundation of China(Grant Nos.52061003,52174368,U20A20274)the Natural Science Foundation of Yunnan Province(Grant No.202301AT070209).
文摘The oxidation chemistry of two-dimensional transition metal carbide MXenes has brought new research significance to their protection and application.However,the oxidation behavior and degradation mechanism of MXenes,in particular with time under oxygen conditions at room tem-perature,remain largely unexplored.Here,several experimental and theo-retical techniques are used to determine a very early stage of the oxidation mechanism of HF-etched Ti3C2Tx(a major member of MXenes and Tx=surface functional groups)in an oxygen environment at room temper-ature.Aberration-corrected environmental transmission electron micros-copy coupled with reactive molecular dynamics simulations show that the crystal plane-dependent oxidation rate of Ti3C2Tx and oxide expansion are attributed to differences in the coordination and charge of superficial Ti atoms,and the existence of the channels between neighboring MXene layers on the different crystal planes.The complementary x-ray photoelec-tron spectroscopy and Raman spectroscopy analyses indicate that the ana-tase and a tiny fraction of brookite TiO2 successively precipitate from the amorphous region of oxidized Ti3C2Tx,grow irregularly and transform to rutile TiO2.Our study reveals the early-stage structural evolution of MXenes in the presence of oxygen and facilitates further tailoring of the MXene per-formance employing oxidation strategy.
基金supported by the National Key Research and Development Project(2022YFA1503900,2022YFA1503000,and 2022YFA1203400)Shenzhen Fundamental Research Funding(JCYJ20210324115809026,JCYJ20220818100212027,and JCYJ20200109141216566)+7 种基金Shenzhen Science and Technology Program(KQTD20190929173815000)Guangdong scientific program with contract no.2019QN01L057Guangdong Innovative and Entrepreneurial Research Team Program(2019ZT08C044)to Gu Msupported by the National Natural Science Foundation of China(22033005)to Li Jpartially sponsored by Guangdong Provincial Key Laboratory of Catalysis(2020B121201002).support from Presidential fund and Development and Reform Commission of Shenzhen Municipalitysupported by the Center for Computational Science and Engineering at SUSTechthe CHEM high-performance supercomputer cluster(CHEMHPC)located at the Department of Chemistry,SUSTech。
文摘As an innovative development of single-atom catalysts(SACs),single-cluster catalysts(SCCs)such as dualatom catalysts have attracted considerable interest due to their excellent performance in catalysis.As one of the most powerful and visualizable tools,scanning transmission electron microscopy(STEM)has been widely applied in the characterization of SCCs.Herein,the nitrogen-doped carbonsupported FeFe and CoFe,two representative examples of homonuclear and heteronuclear SCCs,are characterized by STEM.Furthermore,an image processing program is developed to analyze the STEM images and to obtain the locations of atoms,as well as the projected distances between atoms in possible dual-atom pairs.The dimer distances of both CoFe and FeFe catalysts exhibit a trimodal distribution,which can correspond to the energy-favorable atomic structures of the theoretical simulations.Our work offers an avenue for directly revealing the possible atomic configurations of dual-atom sites in SCCs via big data statistics of STEM images and strong theoretical simulations.
基金supported by the National natural Science Foundation of China(51525102,51390475,51371102 and 21673277)the National Basic Research Program of China(2015CB654902)
文摘The structure and properties of CeO2 surfaces have been intensively studied due to their importance in a lot of surface-related applications. Since most of surface techniques probe the structure information inside the outermost surface plane, the subsurface structure information has been elusive in many studies. Using the profile imaging with aberration-corrected transmission electron microscopy, the structure information in both the outermost layer and the sublayers of the CeO2（100） surface has been obtained. In addition to the normal structures that have been reported before, where the surface is Ce-or O-terminated, a metastable surface has been discovered. In the new structure, there is an atomic layer reversal between the outermost layer and the sublayer, giving a structure with O as the outermost layer for the stoichiometry of normal Ce-terminated surface. The charge redistribution for the polarity compensation has also been changed relative to the normal surface.
基金supported by the National Natural Science Foundation of China(Grant Nos.51525102,51390475,51371102&21673277)National Basic Research Program of China(Grant No.2015CB654902)
文摘The behavior of oxygen on ceria surfaces is closely related with the applications of ceria as a catalyst and oxygen conductor in solid-oxide fuel cells. Here, the atomic configurations of oxygen adatoms and vacancies on the(110) surface of CeO_2 have been studied combining aberration-corrected transmission electron microscopy and first-principles calculations. The oxygen adatoms were estimated to be located on top of Ce atoms with 50% coverage, forming a c(2×2) reconstruction. The oxygen vacancies can form stable configuration, with the Ce atoms partly reduced.
基金financially supported by the National Key R&D Program of China(2017YFA0700104)the National Science Fund for Distinguished Young Scholars(51825102)+1 种基金the National Natural Science Foundation of China(51971157,51671145 and 51761165012)Tianjin Science Fund for Distinguished Young Scholars(19JCJQJC61800)。
文摘Optically imaging atomic nuclei is a long-sought goal for scientific and applied research,but it has never been realized so far.We integrate aberration-corrected scanning transmission electron microscopy(STEM),the bremsstrahlung generation of X-ray photons,and the energy-dispersive X-ray spectroscopic(EDS)receiving and mapping of the photons into a new microscopy method of optical imaging,by which atomic nuclei of different materials are successfully imaged with X-ray photons.Moreover,this imaging method is shown to be workable with different STEM instruments and be capable of distinguishing atomic nuclei of different elements and resolving imaged size differences of atomic nuclei with the order of magnitude as small as 1 pm.Therefore,it is a general method that can image atomic nuclei and their evolutions in materials science,chemistry and physics.
