Structural characteristics of Alo.55 Gao.45N epilayer were investigated by high resolution x-ray diffraction（HRXRD）and transmission electron microscopy（TEM）;the epilayer was grown on GaN/sapphire substrates using ...Structural characteristics of Alo.55 Gao.45N epilayer were investigated by high resolution x-ray diffraction（HRXRD）and transmission electron microscopy（TEM）;the epilayer was grown on GaN/sapphire substrates using a high-temperature A1 N interlayer by metal organic chemical vapor deposition technique.The mosaic characteristics including tilt,twist,heterogeneous strain,and correlation lengths were extracted by symmetric and asymmetric XRD rocking curves as well as reciprocal space map（RSM）.According to Williamson-Hall plots,the vertical coherence length of AlGaN epilayer was calculated,which is consistent with the thickness of AlGaN layer measured by cross section TEM.Besides,the lateral coherence length was determined from RSM as well.Deducing from the tilt and twist results,the screw-type and edge-type dislocation densities are 1.0×10~8 cm^（-2） and 1.8×10^（10） cm^（-2）,which agree with the results observed from TEM.展开更多
This paper studies the microstructural and magnetic properties of LaFe11.5Si1.5 compound by means of highresolution transmission electron microscope and bulk magnetometry measurements. The crystalline structure is acc...This paper studies the microstructural and magnetic properties of LaFe11.5Si1.5 compound by means of highresolution transmission electron microscope and bulk magnetometry measurements. The crystalline structure is accompanied with the noncrystalline and nanocrystalline structures. This characteristic is the reflection of the crystalline process held by quenching. The inverse susceptibilities diverge and deviate from Curie-Weiss law under low applied magnetic fields. This paper proposes the possible mechanism between the anomalous susceptibilities and microstructure, and offers a perspective on the magnetic properties of metastable intermetallic compounds.展开更多
Scanning transmission electron microscopy（STEM） has been shown as powerful tools for material characterization,especially after the appearance of aberration-corrector which greatly enhances the resolution of STEM. H...Scanning transmission electron microscopy（STEM） has been shown as powerful tools for material characterization,especially after the appearance of aberration-corrector which greatly enhances the resolution of STEM. High angle annular dark field（HAADF） and annular bright field（ABF） imaging of the aberration-corrected STEM are widely used due to their high-resolution capabilities and easily interpretable image contrasts. However, HAADF mode of the STEM is still limited in detecting light elements due to the weak electron-scattering power. ABF mode of the STEM could detect light and heavy elements simultaneously, providing unprecedented opportunities for probing unknown structures of materials. Atomiclevel structure investigation of materials has been achieved by means of these imaging modes, which is invaluable in many fields for either improving properties of materials or developing new materials. This paper aims to provide a introduction of HAADF and ABF imaging techniques and reviews their applications in characterization of cathode materials, study of electrochemical reaction mechanisms, and exploring the effective design of lithium-ion batteries（LIBs）. The future prospects of the STEM are also discussed.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
This paper reports that InAs/In0.53Ga0.47As/AlAs resonant tunnelling diodes have been grown on InP substrates by molecular beam epitaxy. Peak to valley current ratio of these devices is 17 at 300K. A peak current dens...This paper reports that InAs/In0.53Ga0.47As/AlAs resonant tunnelling diodes have been grown on InP substrates by molecular beam epitaxy. Peak to valley current ratio of these devices is 17 at 300K. A peak current density of 3kA/cm^2 has been obtained for diodes with AlAs barriers of ten monolayers, and an Ino.53Ga0.47As well of eight monolayers with four monolayers of InAs insert layer. The effects of growth interruption for smoothing potential barrier interfaces have been investigated by high resolution transmission electron microscope.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
基金Project supported by the National Key Research and Development Project of China(Grant No.2016YFB0400100)the Hi-tech Research Project of China(Grant Nos.2014AA032605 and 2015AA033305)+5 种基金the National Natural Science Foundation of China(Grant Nos.61274003,61422401,51461135002,and61334009)the Natural Science Foundation of Jiangsu Province,China(Grant Nos.BY2013077,BK20141320,and BE2015111)the Project of Green Young and Golden Phenix of Yangzhou City,the Postdoctoral Sustentation Fund of Jiangsu Province,China(Grant No.1501143B)the Project of Shandong Provinceial Higher Educational Science and Technology Program,China(Grant No.J13LN08)the Solid State Lighting and Energy-saving Electronics Collaborative Innovation Center,Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)Research Funds from NJU–Yangzhou Institute of Opto-electronics
文摘Structural characteristics of Alo.55 Gao.45N epilayer were investigated by high resolution x-ray diffraction（HRXRD）and transmission electron microscopy（TEM）;the epilayer was grown on GaN/sapphire substrates using a high-temperature A1 N interlayer by metal organic chemical vapor deposition technique.The mosaic characteristics including tilt,twist,heterogeneous strain,and correlation lengths were extracted by symmetric and asymmetric XRD rocking curves as well as reciprocal space map（RSM）.According to Williamson-Hall plots,the vertical coherence length of AlGaN epilayer was calculated,which is consistent with the thickness of AlGaN layer measured by cross section TEM.Besides,the lateral coherence length was determined from RSM as well.Deducing from the tilt and twist results,the screw-type and edge-type dislocation densities are 1.0×10~8 cm^（-2） and 1.8×10^（10） cm^（-2）,which agree with the results observed from TEM.
基金Project supported by the National Natural Science Foundation of China (Grant No 50801015)the National High Technology Research and Development Program of China (Grant No 2007AA03Z458)
文摘This paper studies the microstructural and magnetic properties of LaFe11.5Si1.5 compound by means of highresolution transmission electron microscope and bulk magnetometry measurements. The crystalline structure is accompanied with the noncrystalline and nanocrystalline structures. This characteristic is the reflection of the crystalline process held by quenching. The inverse susceptibilities diverge and deviate from Curie-Weiss law under low applied magnetic fields. This paper proposes the possible mechanism between the anomalous susceptibilities and microstructure, and offers a perspective on the magnetic properties of metastable intermetallic compounds.
基金supported by the National Basic Research Program of China(Grant No.2014CB921002)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB07030200)the National Natural Science Foundation of China(Grant Nos.51522212,51421002,and 51672307)
文摘Scanning transmission electron microscopy（STEM） has been shown as powerful tools for material characterization,especially after the appearance of aberration-corrector which greatly enhances the resolution of STEM. High angle annular dark field（HAADF） and annular bright field（ABF） imaging of the aberration-corrected STEM are widely used due to their high-resolution capabilities and easily interpretable image contrasts. However, HAADF mode of the STEM is still limited in detecting light elements due to the weak electron-scattering power. ABF mode of the STEM could detect light and heavy elements simultaneously, providing unprecedented opportunities for probing unknown structures of materials. Atomiclevel structure investigation of materials has been achieved by means of these imaging modes, which is invaluable in many fields for either improving properties of materials or developing new materials. This paper aims to provide a introduction of HAADF and ABF imaging techniques and reviews their applications in characterization of cathode materials, study of electrochemical reaction mechanisms, and exploring the effective design of lithium-ion batteries（LIBs）. The future prospects of the STEM are also discussed.
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.
文摘This paper reports that InAs/In0.53Ga0.47As/AlAs resonant tunnelling diodes have been grown on InP substrates by molecular beam epitaxy. Peak to valley current ratio of these devices is 17 at 300K. A peak current density of 3kA/cm^2 has been obtained for diodes with AlAs barriers of ten monolayers, and an Ino.53Ga0.47As well of eight monolayers with four monolayers of InAs insert layer. The effects of growth interruption for smoothing potential barrier interfaces have been investigated by high resolution transmission electron microscope.
基金sponsored by the National Basic Research Program of China(973 Program)under grant no.2015CB351905the National Natural Science Foundation of China(no.61504019)+3 种基金China Postdoctoral Science Foundation(no.2015M580783)Scientific Research Start-up Foundation of University of Electronic Science and Technology of China(Y02002010301082)the Technology Innovative Research Team of Sichuan Province of China(no.2015TD0005)the Fundamental Research Funds for the Central Universities of China(no.ZYGX2015J140)
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.
