Nanoscale defects such as dislocations have a significant impact on the phonon thermal transport properties in non-metallic materials.To unravel these effects,an understanding of defect phonon modes is essential.Herei...Nanoscale defects such as dislocations have a significant impact on the phonon thermal transport properties in non-metallic materials.To unravel these effects,an understanding of defect phonon modes is essential.Herein,at the atomic scale,the localized phonons of individual dislocations at a Si/Ge interface are measured via monochromated electron energy loss spectroscopy in a scanning transmission electron microscope.These modes are then correlated with the local microstructure,further revealing the dislocation effects on the local thermal transport properties.The dislocation causes a phonon redshift of several milli-electron-volts within about two to four nanometers of the core,where both the strain field and Ge segregation play roles.With the presence of dislocation,the local interfacial thermal conductance can be either enhanced or reduced,depending on the complex interaction and competition between lattice disorder(dislocation)and element disorder(heterointerface mixing and Ge-segregation)at the interface.These findings provide valuable insights to improve the thermal properties of thermoelectric generators and thermal management systems through proper defect engineering.展开更多
Imaging the doping elements is doped TiO2 thin film. But it is critical for understanding the photocatalytic activity of still a challenge to characterize the interactions between the dopants and the TiO2 lattice at t...Imaging the doping elements is doped TiO2 thin film. But it is critical for understanding the photocatalytic activity of still a challenge to characterize the interactions between the dopants and the TiO2 lattice at the atomic level. Here, we use high angle annular dark- field/annular bright-field scanning transmission electron microscope （HAADF/ABF-STEM） combined with electron energy loss spectroscopy （EELS） to directly image the individual Cr atoms doped in anatase TiO2（001） thin film from [100] direction. The Cr dopants, which are clearly imaged through the atomic-resolution EELS mappings while can not be seen by HADDF/ABF-STEM, occupy both the substitutional sites of Ti atoms and the interstitial sites of TiO2 matrix. Most of them preferentially locate at the substitutional sites of Ti atoms. These results provide the direct evidence for the doping structure of Cr-doped A- TiO2 thin film at the atomic level and also prove the EELS mapping is an excellent technique for characterizing the doped materials.展开更多
Steve Pennycook is a pioneer in the application of high-resolution scanning transmission electron microscopy(STEM)and in particular the use of annular dark-field(ADF)imaging.Here we show how a general framework for 4D...Steve Pennycook is a pioneer in the application of high-resolution scanning transmission electron microscopy(STEM)and in particular the use of annular dark-field(ADF)imaging.Here we show how a general framework for 4D STEM allows clear links to be made between ADF imaging and the emerging methods for reconstructing images from 4D STEM data sets.We show that both ADF imaging and ptychographical reconstruction can be thought of in terms of integrating over the overlap regions of diffracted discs in the detector plane.This approach allows the similarities in parts of their transfer functions to be understood,though we note that the transfer functions for ptychographic imaging cannot be used as a measure of information transfer.We also show that conditions of partial spatial and temporal coherence affect ADF imaging and ptychography similarly,showing that achromatic interference can always contribute to the image in both cases,leading to a robustness to partial temporal coherence that has enabled high-resolution imaging.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52125307)the National Key R&D Program of China(Grant No.2021YFB3501500)the support from the New Cornerstone Science Foundation through the XPLORER PRIZE。
文摘Nanoscale defects such as dislocations have a significant impact on the phonon thermal transport properties in non-metallic materials.To unravel these effects,an understanding of defect phonon modes is essential.Herein,at the atomic scale,the localized phonons of individual dislocations at a Si/Ge interface are measured via monochromated electron energy loss spectroscopy in a scanning transmission electron microscope.These modes are then correlated with the local microstructure,further revealing the dislocation effects on the local thermal transport properties.The dislocation causes a phonon redshift of several milli-electron-volts within about two to four nanometers of the core,where both the strain field and Ge segregation play roles.With the presence of dislocation,the local interfacial thermal conductance can be either enhanced or reduced,depending on the complex interaction and competition between lattice disorder(dislocation)and element disorder(heterointerface mixing and Ge-segregation)at the interface.These findings provide valuable insights to improve the thermal properties of thermoelectric generators and thermal management systems through proper defect engineering.
基金supported by the Ministry of Science and Technology of China(No.2016YFA0200603 and No.2013CB834605)the"Strategic Priority Research Program"of CAS(No.XDB01020100)+1 种基金the National Natural Science Foundation of China(No.91421313,No.21421063,and No.21573207)Anhui Provincial Natural Science Foundation(1708085MA06)
文摘Imaging the doping elements is doped TiO2 thin film. But it is critical for understanding the photocatalytic activity of still a challenge to characterize the interactions between the dopants and the TiO2 lattice at the atomic level. Here, we use high angle annular dark- field/annular bright-field scanning transmission electron microscope （HAADF/ABF-STEM） combined with electron energy loss spectroscopy （EELS） to directly image the individual Cr atoms doped in anatase TiO2（001） thin film from [100] direction. The Cr dopants, which are clearly imaged through the atomic-resolution EELS mappings while can not be seen by HADDF/ABF-STEM, occupy both the substitutional sites of Ti atoms and the interstitial sites of TiO2 matrix. Most of them preferentially locate at the substitutional sites of Ti atoms. These results provide the direct evidence for the doping structure of Cr-doped A- TiO2 thin film at the atomic level and also prove the EELS mapping is an excellent technique for characterizing the doped materials.
基金funding from the European Research Council(ERC)under the European Union’s Horizon 2020 Research and Innovation Programme via Grant Agreement No.802123-HDEM(TJP)from the UK Engineering and Physical Sciences Research Council(EPSRC)via grant EP/M010708/1(PDN).
文摘Steve Pennycook is a pioneer in the application of high-resolution scanning transmission electron microscopy(STEM)and in particular the use of annular dark-field(ADF)imaging.Here we show how a general framework for 4D STEM allows clear links to be made between ADF imaging and the emerging methods for reconstructing images from 4D STEM data sets.We show that both ADF imaging and ptychographical reconstruction can be thought of in terms of integrating over the overlap regions of diffracted discs in the detector plane.This approach allows the similarities in parts of their transfer functions to be understood,though we note that the transfer functions for ptychographic imaging cannot be used as a measure of information transfer.We also show that conditions of partial spatial and temporal coherence affect ADF imaging and ptychography similarly,showing that achromatic interference can always contribute to the image in both cases,leading to a robustness to partial temporal coherence that has enabled high-resolution imaging.
