We present the electronic structure and electron energy loss spectroscopy (EELS) for uranium, niobium and U3Nb in which uranium is substituted by niobium. Comparing the electronic structures and optical properties for...We present the electronic structure and electron energy loss spectroscopy (EELS) for uranium, niobium and U3Nb in which uranium is substituted by niobium. Comparing the electronic structures and optical properties for uranium, niobium and U3Nb, we found that when niobium atom replaces uranium atom in the center lattice, density of state (DOS) of U3Nb shifts downward to low energy. Niobium affects DOS for f and d electrons more than that for p and s electrons. U3Nb is similar to uranium for the electronic energy loss spectra.展开更多
An ultra-high vacuum （UHV） compatible electron spectrometer employing a double toroidal analyzer has been de- veloped. It is designed to be combined with a custom-made scanning tunneling microscope （STM） to study ...An ultra-high vacuum （UHV） compatible electron spectrometer employing a double toroidal analyzer has been de- veloped. It is designed to be combined with a custom-made scanning tunneling microscope （STM） to study the spatially localized electron energy spectrum on a surface. A tip-sample system composed of a piezo-driven field-emission tungsten tip and a sample of highly ordered pyrolytic graphite （HOPG） is employed to test the performance of the spectrometer. Two-dimensional images of the energy-resolved and angle-dispersed electrons backscattered from the surface of HOPG are obtained, the performance is optimized and the spectrometer is calibrated. A complete electron energy loss spectrum covering the elastic peak to the secondary electron peaks for the HOPG surface, acquired at a tip voltage of -140 V and a sample current of 0.5 pA, is presented, demonstrating the viability of the spectrometer.展开更多
In this work the electronic structure and the impurity excess of the basal and rhombohedral twin grain boundaries are investigated, using electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectrosco...In this work the electronic structure and the impurity excess of the basal and rhombohedral twin grain boundaries are investigated, using electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS). The measurability of electronic structures of the twin grain boundaries are discussed by comparing theoretical density of states (DOS) from bulk material with interfacial DOS, obtained from local density functional theory (LDFT) calculations.展开更多
A novel instrument that integrates reflection high energy electron diffraction(RHEED),electron energy loss spectroscopy(EELS),and imaging is designed and simulated.Since it can correlate the structural,elemental,and s...A novel instrument that integrates reflection high energy electron diffraction(RHEED),electron energy loss spectroscopy(EELS),and imaging is designed and simulated.Since it can correlate the structural,elemental,and spatial information of the same surface region via the simultaneously acquired patterns of RHEED,EELS,and energy-filtered electron microscopy,it is named correlative reflection electron microscopy(c-REM).Our simulation demonstrates that the spatial resolution of this c-REM is lower than 50 nm,which meets the requirements for in-situ monitoring the structural and chemical evolution of surface in advanced material.展开更多
Phenomenon of localized surface plasmon excitation at nanostructured materials has attracted much attention in recent decades for their wide applications in single molecule detection,surface-enhanced Raman spectroscop...Phenomenon of localized surface plasmon excitation at nanostructured materials has attracted much attention in recent decades for their wide applications in single molecule detection,surface-enhanced Raman spectroscopy and nano-plasmonics.In addition to the excitation by external light field,an electron beam can also induce the local surface plasmon excitation.Nowadays,electron energy loss spectroscopy(EELS)technique has been increasingly employed in experiment to investigate the surface excitation characteristics of metallic nanoparticles.However,a present theoretical analysis tool for electromagnetic analysis based on the discrete dipole approximation(DDA)method can only treat the case of excitation by light field.In this work we extend the DDA method for the calculation of EELS spectrum for arbitary nanostructured materials.We have simulated EELS spectra for different incident locations of an electron beam on a single silver nanoparticle,the simulated results agree with an experimental measurement very well.The present method then provides a computation tool for study of the local surface plasmon excitation of metallic nanoparticles induced by an electron beam.展开更多
NIOBIUM and its oxides are a new kind of materials applied in technical fields, such as catalysis, microelectronics, ceramics and optical glass. In order to understand the surface structure and catalytic activity, muc...NIOBIUM and its oxides are a new kind of materials applied in technical fields, such as catalysis, microelectronics, ceramics and optical glass. In order to understand the surface structure and catalytic activity, much work has been done on the oxidation of niobium. These results indicated that the oxidation process of niobium surface, the distribution and the structure of niobium oxides on the surface are all closely related to the condition of the oxidation process. Due to the high activity of niobium and the complexity of niobium oxide species, up to now there has not been a clear picture of the structure and the forming condition of the niobium oxides. HREELS is a powerful tool to investigate vibrational and structural properties of surface, but the HREELS study of the oxidation of Nb single crystal by O<sub>2</sub> has never been reported before. In this note we investigated the oxidation of Nb（110） and the structure and adsorption properties of the oxide film using HREELS, UPS and AES.展开更多
本文介绍了近年来发展的四维电子能量损失谱(four-dimensional electron energy loss spectroscopy,4D-EELS)方法的原理及在界面晶格动力学研究方面的应用。详细阐述了四维电子能量损失谱数据采集的需求、方案设计、技术特点等,并对比...本文介绍了近年来发展的四维电子能量损失谱(four-dimensional electron energy loss spectroscopy,4D-EELS)方法的原理及在界面晶格动力学研究方面的应用。详细阐述了四维电子能量损失谱数据采集的需求、方案设计、技术特点等,并对比了该方法与其它散射谱学方法,尤其是振动谱学技术的主要优缺点。该方法的主要特点是在具有较高能量分辨率的同时,可以分别实现较高的空间、动量分辨能力,也可以通过调整实验参数灵活地在二者间取得平衡,从而将色散测量的空间分辨率提高至纳米量级。这一方法的发展使得声子色散的测量不再依赖于中子散射、同步辐射等大科学装置,也不再局限于大单晶样品的测量,能够实现对单个纳米结构甚至单原子尺寸的界面进行色散测量。展开更多
The morphologies, sizes, compositions and volume fractions of dendritic phases in in situ Ti-based metallic glass matrix composites （MGMCs） containing beryllium （Be） with the nominal composition of Tia7Zr19Cu5V12B...The morphologies, sizes, compositions and volume fractions of dendritic phases in in situ Ti-based metallic glass matrix composites （MGMCs） containing beryllium （Be） with the nominal composition of Tia7Zr19Cu5V12Be17 （mole fraction, %） were investigated using XRD, SEM, EBSD, TEM, EDS and three-dimensional reconstruction method. Moreover, visualized at the nanoscale, Be distribution is confirmed to be only present in the matrix using scanning transmission electron microscopy-electron energy loss spectroscopy （STEM-EELS）. Based on these findings, it has been obtained that the accurate chemical compositions are Wi28.3Zr19.7Cu8V6.4Be37.6 （mole fraction, %） for glass matrix and Wi62.nZr18.aCu2.6V16.6 （mole fraction, %） for the dendritic phases, and the volume fractions are 38.5% and 61.5%, respectively. It is believed that the results are of particular importance for the designing of Be-containing MGMCs.展开更多
基金Supported by the National Key Laboratory Foundation of China (9140C6601010804)Sichuan Provincial Key Laboratory for Applied Nuclear Technology in Geology Foundation (27-7).
文摘We present the electronic structure and electron energy loss spectroscopy (EELS) for uranium, niobium and U3Nb in which uranium is substituted by niobium. Comparing the electronic structures and optical properties for uranium, niobium and U3Nb, we found that when niobium atom replaces uranium atom in the center lattice, density of state (DOS) of U3Nb shifts downward to low energy. Niobium affects DOS for f and d electrons more than that for p and s electrons. U3Nb is similar to uranium for the electronic energy loss spectra.
基金supported by the National Basic Research Program of China (Grant No. 2010CB923301)the National Natural Science Foundation of China (GrantNos. 11327404 and 11174268)
文摘An ultra-high vacuum （UHV） compatible electron spectrometer employing a double toroidal analyzer has been de- veloped. It is designed to be combined with a custom-made scanning tunneling microscope （STM） to study the spatially localized electron energy spectrum on a surface. A tip-sample system composed of a piezo-driven field-emission tungsten tip and a sample of highly ordered pyrolytic graphite （HOPG） is employed to test the performance of the spectrometer. Two-dimensional images of the energy-resolved and angle-dispersed electrons backscattered from the surface of HOPG are obtained, the performance is optimized and the spectrometer is calibrated. A complete electron energy loss spectrum covering the elastic peak to the secondary electron peaks for the HOPG surface, acquired at a tip voltage of -140 V and a sample current of 0.5 pA, is presented, demonstrating the viability of the spectrometer.
文摘In this work the electronic structure and the impurity excess of the basal and rhombohedral twin grain boundaries are investigated, using electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS). The measurability of electronic structures of the twin grain boundaries are discussed by comparing theoretical density of states (DOS) from bulk material with interfacial DOS, obtained from local density functional theory (LDFT) calculations.
基金Project supported by the Shanghai Tech University and the National Natural Science Foundation of China(Grant No.11774039)。
文摘A novel instrument that integrates reflection high energy electron diffraction(RHEED),electron energy loss spectroscopy(EELS),and imaging is designed and simulated.Since it can correlate the structural,elemental,and spatial information of the same surface region via the simultaneously acquired patterns of RHEED,EELS,and energy-filtered electron microscopy,it is named correlative reflection electron microscopy(c-REM).Our simulation demonstrates that the spatial resolution of this c-REM is lower than 50 nm,which meets the requirements for in-situ monitoring the structural and chemical evolution of surface in advanced material.
基金supported by the National Natural Science Foundation of China (No.11574289)Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(2nd phase) (No.U1501501)+1 种基金"111" Project by Education Ministry of China"Materials research by Information Integration" Initiative (MI2I) Project of the Support Program for Starting Up Innovation Hub from Japan Science and Technology Agency (JST)
文摘Phenomenon of localized surface plasmon excitation at nanostructured materials has attracted much attention in recent decades for their wide applications in single molecule detection,surface-enhanced Raman spectroscopy and nano-plasmonics.In addition to the excitation by external light field,an electron beam can also induce the local surface plasmon excitation.Nowadays,electron energy loss spectroscopy(EELS)technique has been increasingly employed in experiment to investigate the surface excitation characteristics of metallic nanoparticles.However,a present theoretical analysis tool for electromagnetic analysis based on the discrete dipole approximation(DDA)method can only treat the case of excitation by light field.In this work we extend the DDA method for the calculation of EELS spectrum for arbitary nanostructured materials.We have simulated EELS spectra for different incident locations of an electron beam on a single silver nanoparticle,the simulated results agree with an experimental measurement very well.The present method then provides a computation tool for study of the local surface plasmon excitation of metallic nanoparticles induced by an electron beam.
文摘NIOBIUM and its oxides are a new kind of materials applied in technical fields, such as catalysis, microelectronics, ceramics and optical glass. In order to understand the surface structure and catalytic activity, much work has been done on the oxidation of niobium. These results indicated that the oxidation process of niobium surface, the distribution and the structure of niobium oxides on the surface are all closely related to the condition of the oxidation process. Due to the high activity of niobium and the complexity of niobium oxide species, up to now there has not been a clear picture of the structure and the forming condition of the niobium oxides. HREELS is a powerful tool to investigate vibrational and structural properties of surface, but the HREELS study of the oxidation of Nb single crystal by O<sub>2</sub> has never been reported before. In this note we investigated the oxidation of Nb（110） and the structure and adsorption properties of the oxide film using HREELS, UPS and AES.
文摘本文介绍了近年来发展的四维电子能量损失谱(four-dimensional electron energy loss spectroscopy,4D-EELS)方法的原理及在界面晶格动力学研究方面的应用。详细阐述了四维电子能量损失谱数据采集的需求、方案设计、技术特点等,并对比了该方法与其它散射谱学方法,尤其是振动谱学技术的主要优缺点。该方法的主要特点是在具有较高能量分辨率的同时,可以分别实现较高的空间、动量分辨能力,也可以通过调整实验参数灵活地在二者间取得平衡,从而将色散测量的空间分辨率提高至纳米量级。这一方法的发展使得声子色散的测量不再依赖于中子散射、同步辐射等大科学装置,也不再局限于大单晶样品的测量,能够实现对单个纳米结构甚至单原子尺寸的界面进行色散测量。
基金Project(11374028)supported by the National Natural Science Foundation of ChinaProject supported by the Cheung Kong Scholars Program of China
文摘The morphologies, sizes, compositions and volume fractions of dendritic phases in in situ Ti-based metallic glass matrix composites （MGMCs） containing beryllium （Be） with the nominal composition of Tia7Zr19Cu5V12Be17 （mole fraction, %） were investigated using XRD, SEM, EBSD, TEM, EDS and three-dimensional reconstruction method. Moreover, visualized at the nanoscale, Be distribution is confirmed to be only present in the matrix using scanning transmission electron microscopy-electron energy loss spectroscopy （STEM-EELS）. Based on these findings, it has been obtained that the accurate chemical compositions are Wi28.3Zr19.7Cu8V6.4Be37.6 （mole fraction, %） for glass matrix and Wi62.nZr18.aCu2.6V16.6 （mole fraction, %） for the dendritic phases, and the volume fractions are 38.5% and 61.5%, respectively. It is believed that the results are of particular importance for the designing of Be-containing MGMCs.
