Yoshitaka Aoyama

Dependence of beam broadening on detection angle in scanning transmission electron microtomography

It has been shown that scanning transmission electron microtomography (STEMT) is quite effective for observing specimens with thicknesses on the order of micrometers in three dimensions (3D). In STEMT, the specimen is scanned using a focused electron beam, and the electrons from the convergence point are detected at the detector placed at a certain detection angle. Until recently, a wide detection angle corresponding to the mode often called the dark-field (DF) mode was mainly used. Although the detection angle can vary and is one of the crucial experimental factors in STEMT, its effect on 3D reconstruction has never been discussed from either an experimental or a theoretical viewpoint. Moreover, the effectiveness of another mode of electron tomography, transmission electron microtomography (TEMT), is not clear. In the present study, a polymeric specimen, an acrylonitrile butadiene styrene resin, with a thickness of ~1 mum and a fixed volume was observed using three different modes, namely, TEMT, small detection-angle STEMT referred to as bright-field STEMT, and DF-STEMT, in order to examine their advantages and disadvantages by observing multiple scattering of electrons inside the specimen.

Observation of the Three-Dimensional Structure of Actin Bundles Formed with Polycations

Three-dimensional structures of actin bundles formed with polycations were observed by using transmission electron microtomography and atomic force microscopy. We found, for the first time, that the cross-sectional morphology of actin bundles depends on the polycation species and ionic strength, while it is insensitive to the degree of polymerization and concentration of polycation. Actin bundles formed with poly-N-[3-(dimethylamino)propyl] acrylamide methyl chloride quaternary show a ribbon-like cross-sectional morphology in low salt concentrations that changes to cylindrical cross-sectional morphology with hexagonal packing of the actin filaments in high salt concentrations. Contrastingly, actin bundles formed with poly-L-lysine show triangular cross-sectional morphology with hexagonal packing of the actin filaments. These variations in cross-sectional morphology are discussed in terms of anisotropy in the electrostatic energy barrier.

Near Shadowless EDS Tomography for Sliced Sample Realized by X-ray Collection with One Large Sized SDD Detector

Three-dimensional (3D) elemental mapping by energy dispersive X-ray spectroscopy (EDS) is getting popular for characterizations of samples having 3D structures to be solved such as semiconducting devices or blended polymers, since the method enables us to see the atomic species and 3D distribution of sample simultaneously. For the reconstruction of the 3D elemental maps, the EDS tomography is developed combining electron tomography and the two dimensional (2D) elemental mapping by EDS [1]. In the previous X-ray detection system composed of two EDS detectors, the detectors locates symmetrically with respect to the tilt axis of the sample holder. Therefore, some portion of the generated X-rays are blocked by the sample holder or supporting mesh in specific tilting angle range. The shadowing on the configuration may make artifacts in resulting 3D elemental maps. In order to avoid this problem, it is necessary to correct the measured intensity of EDS maps after the acquisition, according to the expected or pre-measured detection efficiency.

Rapid 3D Reconstruction in the EDS Tomography by using Iterative Series Reduction (ISER) Method

Energy Dispersive X-ray Spectroscopy (EDS) is widely used to obtain the elemental maps of a sample. EDS Tomography is a method to reconstruct three-dimensional (3D) elemental maps from a set of twodimensional (2D) EDS elemental maps. The maps can be obtained by a transmission electron microscope (TEM) equipped with EDS detector. The high accelerating voltages of TEM is necessary to obtain the transparent image and elemental maps. On the other hand, many 2D elemental maps, forming a tilt series map, are necessary to reconstruct 3D elemental maps. Therefore, the electron beam damage is serious in EDS Tomography, and a method to reduce the number of elemental maps is sought-after.