Papers by Keyword: EELS

Abstract: CBED and EELS are most common methods to determine the thickness of the TEM specimen. In this work, specimen thickness of He-ion irradiated Al is measured respectively by CBED and EELS under 200kV. The helium concentration and the atomic displacement damage level are 2000appm and 0.2dpa, respectively. The CBED results show that the measurements of extinction distance match the calculations of effective extinction distance considering the deviation vector of the crystal. Moreover, it is proven by modeling analysis that He-ion irradiation does not affect the thickness measurements of extinction distance. Compared with CBED, the specimen thickness, measured by EELS, is larger, and may be attributed to the decrease of the zero-loss peak due to a part of elastic scattering electronsloss and the larger inelastic scattering mean free path selected. The EELS measurement error is less than 20%,consistent with the accuracy (about 20%) byK. Iakoubovskiiet al.

Abstract: Silicene is becoming one of the most important two-dimensional materials. In this work, EEL Spectra were calculated for α-silicene (flat), and β-silicene (low-buckled, and theoretically the most stable). Band structures were determined using the semi-empirical Tight-Binding Method considering second nearest neighbors, sp³ model, Harrison's rule, and Slater-Koster parameterization. The dielectric function was calculated within the Random Phase Approximation and a space discretization scheme. We found that, compared to bulk Si, additional resonances appear which are red-shifted. Buckling gives rise to a richer structure at low energy.

Abstract: The analysis of Auger electron and electron energy-loss spectra was developed to determine an elastic modulus and a relative permittivity of the diamond and tetrahedral amorphous carbon layers (both on the substrate of NiTi alloy), the graphite and graphite-like carbon layers in a carbon/oxidization/ TiNi systems. The description of line-shape carbon Auger spectrum is based on the convolution of two-conduction electron and one-core electron spectral densities. It was concluded that the comparisons of the experimental and theoretical Auger spectra were determined the quantitative assessment of the electron-electron repulsion, which allow us to calculate the relative permittivity of the layer. The analysis of electron plasmon losses was applied to determine the values of plasma energies of the layers. Such parameter values were as then applied to calculate the values of nanoscale properties. The results demonstrated that the property values of the carbon layers were in good agreement with that reported in literature.

Abstract: Silicon polymorphs have been prepared by means of scratching or indentation of Si(100) surfaces. Different indenter types have been used in order to validate the independence of silicon polymorph formation from indenter geometry. The formation of silicon polymorphs could be verified by registering the loading-displacement curves. Related to the maximum loads applied, only the formation of the meta-stable silicon phases SI-III, Si-IV and Si-XII has been observed, what has been verified by Raman spectroscopy. Four different ways of the preparation of electron transparent samples are presented and compared. Finally, a first electron energy loss spectrum of certain silicon polymorphs is shown.

Abstract: The electron energy loss spectroscopy (EELS) of pure Ti, TiNi, Ni3Ti and pure Ni has been acquired and d-electron occupancy of both Ti and Ni in the metals has been measured from the white-line intensity. It is found that the change of d-electron occupancy of Ni is very small in all metals, but the d-electron occupancy of Ti in Ni3Ti increases considerable large relative to pure Ti. The change of d-electron occupancy is discussed in terms of charge transfer mechanism, local charge neutrality (LCN) approximation, and hybridization.

Abstract: Growth of high quality GaN/AlN heterostructures by plasma assisted molecular beam epitaxy (PAMBE) is possible with excess of Ga on the surface. During growth of AlN this additional Ga acts as surfactant and improves mobility of the Al adatoms on the growing surface, at the possible cost of Ga segregation and creation of mixed AlGaN interlayer. Scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) were used to determine chemical composition of high crystallographic quality GaN-AlN multilayer structure. It was shown that segregation occurs at AlN-GaN heterointerfaces, while GaN-AlN interfaces have abrupt stepwise change of the chemical composition. HRTEM results show creation of trench defects at the periphery of growing AlN islands in the case of nonoptimized growth.

Abstract: χThe nanostructure of Fischer-Tropsch (FT) Fe carbides are investigated using aberration-corrected high-resolution transmission electron microscopy (TEM). The plasma-generated Fe carbides are analyzed just after synthesis, following reduction via a H2 treatment step and once used as FT catalyst and deactivated. The as-produced nanoparticles (NPs) are seen to be abundantly covered with graphitic and amorphous carbon. Using the extended information limit from the spherical aberration-corrected TEM, the NPs could be indexed as a mixture of NPs in the θ-Fe3C and χ–Fe₅C₂ phases. The reduction treatment exposed the NPs by removing most of the carbonaceous spe_{Subscript text}cies while retaining the χ–Fe₅C₂. Fe-carbides NPs submitted to conditions typical to FT synthesis develop a Fe₃O4 shell which eventually consumes the NPs up to a point where 3-4 nm residual carbide is left at the center of the particle. _{Subscript text}Various mechanisms explaining the formation of such a microstructure are discussed.

Abstract: SiO2/4H-SiC interfaces are examined by high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and spatially resolved electron energy-loss spectroscopy (EELS). HRTEM and HAADF-STEM images of SiO2/4H-SiC interfaces reveal that abrupt interfaces are formed irrespective of the fabrication conditions. Transition regions around the interfaces reported by Zheleva et al. were not observed. Using EELS, profiles of the C/Si and O/Si ratios across an interface were measured. Our measurements did not reveal a C-rich region on the SiC side of the interface, which was reported by Zheleva et al.

Abstract: We developed a new method to quantify the He atoms in the SiC/SiC Composites Irradiation Behaviour in Fusion Reactor Environment Conditions. We focus on the cavities measurements of the energy shift of the He K-edge of the electron energy loss spectrum. The method is based on mapping the density of He atoms inside the measured bubbles. Combining with the number density and the average diameter of the cavities, we are able to distinguish and estimate the amount of He atoms in the cavities and in the matrix, respectively. We found that small bubbles contain much higher density of He atoms than the larger ones. At irradiation temperature above 1000oC, all the He atoms are trapped inside the bubbles. On the contrary, it is not the case at the lower irradiation temperature.

Abstract: The dielectric properties of the intermetallic cubic Laves phase compound YFe2 were determined by analyzing the low loss region of the EELS spectrum in a transmission electron microscope. From these data, the optical joint density of states (OJDS) was obtained by Kramers-Kronig analysis. Since maxima observed in the OJDS spectra are assigned to interband transitions; these spectra can be interpreted on the basis of numerical calculations performed with the Wien2k code, using the Fully-Linearized-Augmented-Plane wave (FLAPW) method within the Local-Spin-Density Approximation. Comparison between experimental results and theory shows good agreement.