The principle, imaging condition and experimental method for obtaining high resolution composition contrast in secondary electron image were described. A new technique of specimen preparation for secondary electron co...The principle, imaging condition and experimental method for obtaining high resolution composition contrast in secondary electron image were described. A new technique of specimen preparation for secondary electron composition contrast observation was introduced and discussed. By using multilayer P+Si1-xGex/pSi heterojunction internal photoemission infrared detector as an example, the applications of secondary electron composition contrast imaging in microstructure studies on heterojunction semiconducting materials and devices were stated. The characteristics of the image were compared with the ordinary transmission electron diffraction contrast image. The prospects of applications of the imaging method in heterojunction semiconductor devices and multilayer materials are also discussed.展开更多
Biomass in karst terrain has rarely been measured because the steep mountainous limestone terrain has limited the ability to sample woody plants.Satellite observation, especially at high spatial resolution, is an impo...Biomass in karst terrain has rarely been measured because the steep mountainous limestone terrain has limited the ability to sample woody plants.Satellite observation, especially at high spatial resolution, is an important surrogate for the quantification of the biomass of karst forests and shrublands. In this study, an artificial neural network(ANN) model was built using Pléiades satellite imagery and field biomass measurements to estimate the aboveground biomass(AGB) in the Houzhai River Watershed, which is a typical plateau karst basin in Central Guizhou Province, Southwestern China. A back-propagation ANN model was also developed.Seven vegetation indices, two spectral bands of Pléiades imagery, one geomorphological parameter,and land use/land cover were selected as model inputs. AGB was chosen as an output. The AGB estimated by the allometric functions in 78 quadrats was utilized as training data(54 quadrats, 70%),validation data(12 quadrats, 15%), and testing data(12 quadrats, 15%). Data-model comparison showed that the ANN model performed well with an absolute root mean square error of 11.85 t/ha, which was 9.88%of the average AGB. Based on the newly developed ANN model, an AGB map of the Houzhai River Watershed was produced. The average predicted AGB of the secondary evergreen and deciduous broadleaved mixed forest, which is the dominant forest type in the watershed, was 120.57 t/ha. The average AGBs of the large distributed shrubland,tussock, and farmland were 38.27, 9.76, and 11.69 t/ha, respectively. The spatial distribution pattern ofthe AGB estimated by the new ANN model in the karst basin was consistent with that of the field investigation. The model can be used to estimate the regional AGB of karst landscapes that are distributed widely over the Yun-Gui Plateau.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
High resolution Fresnel zone plates for nanoscale three-dimensional imaging of materials by both soft and hard x-rays are increasingly needed by the broad applications in nanoscience and nanotechnology.When the outmos...High resolution Fresnel zone plates for nanoscale three-dimensional imaging of materials by both soft and hard x-rays are increasingly needed by the broad applications in nanoscience and nanotechnology.When the outmost zone-width is shrinking down to 50 nm or even below,patterning the zone plates with high aspect ratio by electron beam lithography still remains a challenge because of the proximity effect.The uneven charge distribution in the exposed resist is still frequently observed even after standard proximity effect correction(PEC),because of the large variety in the line width.This work develops a new strategy,nicknamed as local proximity effect correction(LPEC),efficiently modifying the deposited energy over the whole zone plate on the top of proximity effect correction.By this way,50 nm zone plates with the aspect ratio from 4:1 up to 15:1 and the duty cycle close to 0.5 have been fabricated.Their imaging capability in soft(1.3 keV)and hard(9 keV)x-ray,respectively,has been demonstrated in Shanghai Synchrotron Radiation Facility(SSRF)with the resolution of 50 nm.The local proximity effect correction developed in this work should also be generally significant for the generation of zone plates with high resolutions beyond 50 nm.展开更多
The crystal structure of the minor phase, named superstructure II, existing in multiferroic compound BiMnO3 has been studied by electron diffraction and high-resolution transmission electron microscopy. Domains of maj...The crystal structure of the minor phase, named superstructure II, existing in multiferroic compound BiMnO3 has been studied by electron diffraction and high-resolution transmission electron microscopy. Domains of major and minor phases coexisting in BiMnO3 were observed in high-resolution electron microscope images. The unit cell of minor phase was determined to be triclinic with the size 4×4×4 times as large as the distorted perovskite subcell. The [111] and [101] projected structure maps of the minor phase have been derived from the corresponding images by means of the image processing. A possible rough three-dimensional （3D） structure model was proposed based on the 3D structural information extracted from the two projected structure maps. Since there is no inversion centre in the proposed model, the minor phase may contribute to the ferroelectric property of BiMnO3.展开更多
透射电子显微镜(transmission electron microscope,TEM)具有超高的空间分辨率,是化学、材料科学、物理学、生物科学等领域最重要的研究手段之一.影响TEM空间分辨率的因素众多,不仅包括电镜自身结构和成像原理等,还有样品性质等原因.为...透射电子显微镜(transmission electron microscope,TEM)具有超高的空间分辨率,是化学、材料科学、物理学、生物科学等领域最重要的研究手段之一.影响TEM空间分辨率的因素众多,不仅包括电镜自身结构和成像原理等,还有样品性质等原因.为系统且全面地了解TEM分辨率的涵义、原理与应用,本文通过回顾TEM空间分辨率的发展历史,从理论上厘清了TEM空间分辨率的概念、物理涵义、影响因素和适用范围;从电镜装置角度,分别概述了电子枪、磁透镜、图像探测器和电镜内外部环境对空间分辨率的影响规律,以及单色器、像差校正器和新型图像探测器的发展现状;从实际应用角度,重点介绍了样品过厚、电子束损伤、积碳和原子振动等降低空间分辨率的作用机理及解决途径.本文可为非电子显微学研究者们正确使用TEM提供参考.展开更多
原子级分辨率的成像表征对探究材料结构与性质间的联系具有重大意义。应用像差校正的高分辨电子显微成像技术(high⁃resolution transmission electron microscopy,HRTEM)可以实现亚埃尺度分辨率的图像表征,但电子束辐照敏感材料受限于...原子级分辨率的成像表征对探究材料结构与性质间的联系具有重大意义。应用像差校正的高分辨电子显微成像技术(high⁃resolution transmission electron microscopy,HRTEM)可以实现亚埃尺度分辨率的图像表征,但电子束辐照敏感材料受限于辐照引起的结构损伤,无法用常规辐照剂量进行HRTEM成像表征。将出射波重构(exit wave reconstruction,EWR)技术应用于辐照敏感材料,一方面可以解决HRTEM图像中衬度反转的问题并提高图像分辨率至信息极限;另一方面,通过算法实现对信息的充分利用,适合于从低剂量数据中提取有效信息。采用低剂量EWR技术可以实现电子束敏感材料的原子级分辨率图像,为研究电子束辐照敏感材料提供更多可能性,也使针对出射波重构技术的研究具有更大的应用前景与科学意义。展开更多
文摘The principle, imaging condition and experimental method for obtaining high resolution composition contrast in secondary electron image were described. A new technique of specimen preparation for secondary electron composition contrast observation was introduced and discussed. By using multilayer P+Si1-xGex/pSi heterojunction internal photoemission infrared detector as an example, the applications of secondary electron composition contrast imaging in microstructure studies on heterojunction semiconducting materials and devices were stated. The characteristics of the image were compared with the ordinary transmission electron diffraction contrast image. The prospects of applications of the imaging method in heterojunction semiconductor devices and multilayer materials are also discussed.
基金supported by the National Key R and D Program of China(2016YFC0502101)the National Basic Research Program of China(2013CB956704)the Opening Fund of the State Key Laboratory of Environmental Geochemistry(SKLEG2017911)
文摘Biomass in karst terrain has rarely been measured because the steep mountainous limestone terrain has limited the ability to sample woody plants.Satellite observation, especially at high spatial resolution, is an important surrogate for the quantification of the biomass of karst forests and shrublands. In this study, an artificial neural network(ANN) model was built using Pléiades satellite imagery and field biomass measurements to estimate the aboveground biomass(AGB) in the Houzhai River Watershed, which is a typical plateau karst basin in Central Guizhou Province, Southwestern China. A back-propagation ANN model was also developed.Seven vegetation indices, two spectral bands of Pléiades imagery, one geomorphological parameter,and land use/land cover were selected as model inputs. AGB was chosen as an output. The AGB estimated by the allometric functions in 78 quadrats was utilized as training data(54 quadrats, 70%),validation data(12 quadrats, 15%), and testing data(12 quadrats, 15%). Data-model comparison showed that the ANN model performed well with an absolute root mean square error of 11.85 t/ha, which was 9.88%of the average AGB. Based on the newly developed ANN model, an AGB map of the Houzhai River Watershed was produced. The average predicted AGB of the secondary evergreen and deciduous broadleaved mixed forest, which is the dominant forest type in the watershed, was 120.57 t/ha. The average AGBs of the large distributed shrubland,tussock, and farmland were 38.27, 9.76, and 11.69 t/ha, respectively. The spatial distribution pattern ofthe AGB estimated by the new ANN model in the karst basin was consistent with that of the field investigation. The model can be used to estimate the regional AGB of karst landscapes that are distributed widely over the Yun-Gui Plateau.
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Project supported by the National Natural Science Foundation of China(Grant No.U1732104)China Postdoctoral Science Foundation(Grant No.2017M611443)Shanghai STCSM2019-11-20 Grant,China(Grant No.19142202700)。
文摘High resolution Fresnel zone plates for nanoscale three-dimensional imaging of materials by both soft and hard x-rays are increasingly needed by the broad applications in nanoscience and nanotechnology.When the outmost zone-width is shrinking down to 50 nm or even below,patterning the zone plates with high aspect ratio by electron beam lithography still remains a challenge because of the proximity effect.The uneven charge distribution in the exposed resist is still frequently observed even after standard proximity effect correction(PEC),because of the large variety in the line width.This work develops a new strategy,nicknamed as local proximity effect correction(LPEC),efficiently modifying the deposited energy over the whole zone plate on the top of proximity effect correction.By this way,50 nm zone plates with the aspect ratio from 4:1 up to 15:1 and the duty cycle close to 0.5 have been fabricated.Their imaging capability in soft(1.3 keV)and hard(9 keV)x-ray,respectively,has been demonstrated in Shanghai Synchrotron Radiation Facility(SSRF)with the resolution of 50 nm.The local proximity effect correction developed in this work should also be generally significant for the generation of zone plates with high resolutions beyond 50 nm.
基金supported by the National Natural Science Foundation of China (Grant No 50672124)Ministry of Science and Technology (MOST) of China (Grant Nos 2005CB724402 and 2007CB925003)
文摘The crystal structure of the minor phase, named superstructure II, existing in multiferroic compound BiMnO3 has been studied by electron diffraction and high-resolution transmission electron microscopy. Domains of major and minor phases coexisting in BiMnO3 were observed in high-resolution electron microscope images. The unit cell of minor phase was determined to be triclinic with the size 4×4×4 times as large as the distorted perovskite subcell. The [111] and [101] projected structure maps of the minor phase have been derived from the corresponding images by means of the image processing. A possible rough three-dimensional （3D） structure model was proposed based on the 3D structural information extracted from the two projected structure maps. Since there is no inversion centre in the proposed model, the minor phase may contribute to the ferroelectric property of BiMnO3.
文摘透射电子显微镜(transmission electron microscope,TEM)具有超高的空间分辨率,是化学、材料科学、物理学、生物科学等领域最重要的研究手段之一.影响TEM空间分辨率的因素众多,不仅包括电镜自身结构和成像原理等,还有样品性质等原因.为系统且全面地了解TEM分辨率的涵义、原理与应用,本文通过回顾TEM空间分辨率的发展历史,从理论上厘清了TEM空间分辨率的概念、物理涵义、影响因素和适用范围;从电镜装置角度,分别概述了电子枪、磁透镜、图像探测器和电镜内外部环境对空间分辨率的影响规律,以及单色器、像差校正器和新型图像探测器的发展现状;从实际应用角度,重点介绍了样品过厚、电子束损伤、积碳和原子振动等降低空间分辨率的作用机理及解决途径.本文可为非电子显微学研究者们正确使用TEM提供参考.
