Biomedical subjects

Kazuyoshi Tatsumi

Publications and source records attributed to Kazuyoshi Tatsumi.

4 recordsLinked to original sources

PubMed2006

Spectral restoration and energy resolution improvement of electron energy-loss spectra by Pixon reconstruction: II. Application to practical ELNES analysis of low SNR.

We applied Pixon deconvolution as introduced in Part I to several practical, examples of low signal-to-noise ratio (SNR), electron energy-loss spectra with a goal toward restoring their fine spectral features and/or improving the energy resolution. We demonstrate that by directly fitting the two-dimensional spectral data recorded on the CCD; the method enables us to reveal fine spectral structures. Consequently, Pixon reconstruction extends the ability to probe electronic states in very spatially localized areas, a capability currently unique to our method.

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PubMed2006

Spectral restoration and energy resolution improvement of electron energy-loss spectra by Pixon reconstruction: I. Principle and test examples.

We explore the use of the Pixon method, one of the highest performance image reconstruction methods available today, for the analysis of electron energy loss spectra (EELS). The method takes particular advantage of two-dimensional (2-D) CCD data, in which the data are blurred by a PRF (point-response-function as measured by the low-loss spectrum) both in the direction of energy dispersion and in the cross-dispersion direction. The Pixon method is used to simultaneously (i) deconvolve the PRF, increasing the spectral resolution, and (ii) fit the data in the cross-dispersion direction which efficiently combines the signal into a single parent spectrum. Relative to 1-D methods, we demonstrate that our 2-D treatment (i) more effectively detects weak features and (ii) allows EELS methods to be applied to much lower signal-to-noise ratio data. Both of these advantages are critical to the future development of EELS analysis.

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PubMed2006

Site-specific electronic structure analysis by channeling EELS and first-principles calculations.

Site-specific electronic structures were investigated by electron energy loss spectroscopy (EELS) under electron channeling conditions. The Al-K and Mn-L(2,3) electron energy loss near-edge structure (ELNES) of, respectively, NiAl2O4 and Mn3O4 were measured. Deconvolution of the raw spectra with the instrumental resolution function restored the blunt and hidden fine features, which allowed us to interpret the experimental spectral features by comparing with theoretical spectra obtained by first-principles calculations. The present method successfully revealed the electronic structures specific to the differently coordinated cationic sites.

Journal Article↗

PubMed2006

Peak assignments of ELNES and XANES using overlap population diagrams.

The usefulness of overlap population (OP) diagrams for peak assignments of an electron energy loss near-edge structure (ELNES) and an X-ray absorption near-edge structure (XANES) is demonstrated. Mg-K, L(2,3), and O-K edges of MgO are taken as examples. Theoretical calculations are performed using a first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method. A core-hole is included explicitly, and a large supercell is used to minimize artificial interactions among the core-holes in adjacent cells. All experimental spectra are quantitatively reproduced by the calculations. The OP diagrams for a selected pair of atomic orbitals are computed in order to provide proper assignments for each peak in ELNES and XANES. They are interpreted in terms of interactions among Mg-Mg and Mg-O bonds. Results are found to be consistent to our previous conclusion, which was obtained using a cluster method [T. Mizoguchi, et al., Phys. Rev. B 61 (2000) 2180]. The powerful combination of the OP diagram and a high-energy resolution ELNES to obtain fine electronic structures is also demonstrated.

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