Papers by Keyword: EELS

Abstract: The paper presents metrology of the growth and characterization of 3d metal monolayer films on silicon. EELS analysis of plasmon peaks during the layer-by-layer growth of Co films on Si(111) demonstrate that thickness measurement of the monolayer films is possible on base of spectra decomposition with interface and film plasmon peak extracting. Results of the resistivity measurement of Co films on Si(111) with different state of the surface correlate with growth mechanism of the films on AES data. AFM-pictures show replication of step surface relief versus the thickness demonstrating growth of the smooth Fe nanofilm on Si(100).

Abstract: SrTiO3 bicrystals with various types of grain boundaries were prepared by joining two single crystals at high temperature. By using the bicrystals, we examined their current-voltage characteristics across single grain boundaries from a viewpoint of point defect segregation in the vicinity of the grain boundaries. Current-voltage property in SrTiO3 bicrystals was confirmed to show a cooling rate dependency from annealing temperature, indicating that cation vacancies accumulate due to grain boundary oxidation. The theoretical results obtained by ab-initio calculation clearly showed that the formation energy of Sr vacancies is the lowest comparing with Ti and O vacancies in oxidized atomosphere. The formation of a double Schottky barrier (DSB) in n-type SrTiO3 is considered to be closely related to the accumulation of the charged Sr vacancies. Meanwhile, by using three types of low angle boundaries, the excess charges related to one grain boundary dislocation par unit length was estimated. In this study, we summarized our results obtained in our group.

Abstract: Energetic nitrogen ion was injected into a TiO2 photocatalyst in order to investigate the optimal local concentration of doped nitrogen for visible-light response. N+-implanted TiO2 samples promoted the photocatalytic activity under visible-light irradiation. N K-edge XANES of the highest activity sample indicated that N replaces the O sites near the surface, whereas in the samples of higher N+ fluence, N−O and/or N−N species formed. Depth-resolved N K-edge ELNES revealed the two types of N, depending on the concentration, and we found the local N concentration effective for visible-light response was less than ∼1 at%. Further, the spatial distributions of the different chemical states of N by energy-filtering TEM (FETEM) supported these findings.

Abstract: The structure of melt-spun and crystallized Mg-10%Ni and Mg-10%Ni-5%La alloys is studied using HRTEM, coupled with ED and EELS techniques, for specimens subjected to hydrogenation and dehydrogenation. The presence of nano-sized (5-10nm) Mg2Ni grains dispersed in the matrix of Mg nano-grains is observed before hydrogenation. This structure is almost preserved after hydrogenation and dehydrogenation at 300°C. In the hydrogenated specimen, nanoboundaries lying between MgH2 and Mg2NiH4 nano-grains are observed. They appear to provide main routes for the hydrogen transport in these nanostructured materials.

Abstract: High Resolution Transmission Electron Microscope and Electron Energy Loss Spectroscopy and have been used to characterize the structure and chemical composition of niobium carbonitrides in the ferrite of a Fe-Nb-C-N model alloy at different precipitation stages. Experiments seem to indicate the coexistence of two types of precipitates: pure niobium nitrides and mixed sub-stoichiometric niobium carbonitrides. In order to predict the chemical composition of these precipitates, a thermodynamical formalism has been developed to evaluate (i) the nucleation and growth rates (classical nucleation theory) and (ii) the chemical composition of nuclei and existing precipitates. A model based on the numerical resolution of former equations, is used to compute precipitates size distribution evolution at a given temperature. The predicted compositions are in very good agreement with experimental results.

Abstract: Niobium is a strong carbide forming element which is often used in microalloyed steels to control the grain size during thermomechanical treatments and to provide strengthening through precipitation processes. A detailed microscopic investigation is one of the keys for understanding the first stages of the precipitation sequence, thus Transmission Electron Microscopy (TEM) is required. The main difficulty of TEM studies is due to the nanometre scale dimensions of the particles, which makes their detection, structural and chemical characterization delicate. Model Fe- (Nb0.06%,C0.05%) and Fe-(Nb0.05%,C0.03%,N0.03%) ferritic alloys subjected to isothermal annealing treatments have been investigated. High Resolution TEM (HRTEM) and conventional TEM (CTEM) were used to characterise the morphology, nature and location of precipitates. Volume fraction measurements and a statistical approach to the determination of precipitate size histograms have been investigated using Energy Filtered TEM (EFTEM) and High Angle Annular Dark Field (HAADF) imaging. Chemical compositions were quantified by Electron Energy Loss Spectroscopy (EELS). The evolution of precipitate composition with time and temperature is compared with previous simulations obtained from new thermodynamic models based on equilibrium boundary conditions.

Abstract: In core-level electron energy loss spectroscopy (EELS) for anisotropic systems, the applied electric field is determined by the momentum transfer vector q, therefore the collection solid angle range for the scattering electrons and sample orientation will affect the measured EELS spectra.. Using the spatially resolved C 1s core excitation in carbon nanotube as an example, we show that the EELS measurement can be understood by a simple dipole theory of anisotropic core loss spectroscopy which decomposes the spectral contribution in terms of orientationelly averaged isotropic spectrum and linear dichrotic spectrum. In addition, we point out the Magic Angle (MA) conditions that allow the direct determination of the averaged spectra acquired independent of the exact sample orientation.

Abstract: A novel EELS technique was developed to study bonding of grain boundary in many kinds of steels. We measured the normalized intensities of Fe white lines and calculated the occupancies of 3d states of iron, and then analyzed the relationship of the occupancies of 3d states of iron and the fracture property of the steels. We found that if the grain boundary has a different occupancy of 3d state of iron from that of the bulk, the steel tends to have an intergranular fracture, whereas if the grain boundary has almost the same occupancy of 3d state as the bulk, the steel tends to have a transgranular fracture. Our result shows that the difference in the occupancy of 3d state between bulk and grain boundary can be used to study the fracture mode at grain boundary in steel.