Iwao Hashimoto

Effect of small crystal tilt on atomic-resolution high-angle annular dark field STEM imaging

Using a slightly tilted convergent electron beam, high-angle annular dark field scanning transmission electron microscopy observations have been performed of a [0 11]-oriented Si crystal. A small tilt of the crystal zone axis with respect to the coma-axis of the probe-forming lens causes a difference in intensity between bright spots of a Si dumbbell. The semiangle of the beam probe and the tilting angle with respect to the specimen hormal were determined by means of convergent beam micro-diffraction. The simulation using these parameters accounts for the image contrasts satisfactorily.

Effect of chromatic aberration on atomic-resolved spherical aberration corrected STEM images

The effect of the chromatic aberration (C(c)) coefficient in a spherical aberration (C(s))- corrected electromagnetic lens on high-resolution high-angle annular dark field (HAADF) scanning transmission electron microscope (STEM) images is explored in detail. A new method for precise determination of the C(c) coefficient is demonstrated, requiring measurement of an atomic-resolution one-frame through-focal HAADF STEM image. This method is robust with respect to instrumental drift, sample thickness, all lens parameters except C(c), and experimental noise. It is also demonstrated that semi-quantitative structural analysis on the nanometer scale can be achieved by comparing experimental C(s)- corrected HAADF STEM images with their corresponding simulated images when the effects of the C(c) coefficient and spatial incoherence are included.

Extended dynamical HAADF STEM image simulation using the Bloch-wave method.

An extended method is proposed for the precise simulation of high-angle annular dark-field (HAADF) scanning transmission electron-microscope (STEM) images for materials containing elements with large atomic numbers and for thick specimens. The approach combines a previously reported method utilizing two kinds of optical potential [Watanabe, Yamazaki, Hashimoto & Shiojiri (2001). Phys. Rev. B, 64, 115432] with a representation of a crystal sliced into multiple layers. The validity of the method is demonstrated by simulated images for elements with the diamond structure (Si, Ge and alpha-Sn) and for the perovskite BaTiO3.

Rate control of cell sheet recovery by incorporating hydrophilic pattern in thermoresponsive cell culture dish

Thready stripe-polyacrylamide (PAAm) pattern was fabricated on a thermoresponsive poly(N-isopropylacrylamide) (PIPAAm) surface, and their surface properties were characterized. A PIPAAm surface spin-coated with positive photoresist was irradiated through a 5 µm/5 µm or a 10 µm/10-µm black and white striped photomask, resulting in the radical polymerization of AAm on the photoirradiated area. After staining with Alexa488 bovine serum albumin, the stripe-patterned surface was clearly observed and the patterned surface was also observed by a phase contrast image of an atomic force microscope. NIH-3T3 (3T3) single cells were able to be cultured at 37°C on the patterned surfaces as well as on a PIPAAm surface without pattern, and the detachment of adhered cells was more rapidly from the patterned surface after reducing temperature. Furthermore, the rate of detachment of 3T3 confluent cell sheet on the patterned surface was accelerated, compared with on a conventional PIPAAm surface under the static condition. The rate control of cell sheet recovery should contribute the preservations of cell phenotype and biological functions of cell sheet for applying to clinical trials.

Imaging of light and heavy atomic columns by spherical aberration corrected middle-angle bright-field STEM.

Simultaneous detection of both light and heavy atomic columns is theoretically and experimentally explored with spherical aberration (C(s))-corrected middle-angle bright-field (MABF) scanning transmission electron microscopy (STEM). Optimized MABF STEM visualizes both light O atomic columns and heavy Sr and Ti-O atomic columns for SrTiO₃(001) as distinct bright spots and dark spots with characteristic bright rings, respectively, over practical ranges of the probe-forming lens defocus and sample thickness, although medium-heavy Ti-O atomic columns appear as blurred dark spots. The difference in contrast between heavy and light atomic columns is greater than that of annular BF STEM images. The formation of distinctive bright and dark spots is interpreted simply as the difference in the degrees of localization and inelastic absorption of channeling electrons in individual atomic columns by analyses of convergent wave fields inside the crystal in both real and reciprocal space. In addition, Bloch wave expansion of MABF STEM images suggests that bright rings are formed mainly by 2p-like convergent Bloch wave fields localized on heavy atomic columns.

Lattice imaging in low-angle and high-angle bright-field scanning transmission electron microscopy

Atomic resolution low-angle bright-field (LABF) scanning transmission electron-microscope (STEM) images and high-angle bright-field (HABF) STEM images of [011]-orientated Si have been experimentally obtained together with high-angle annular dark-field (HAADF) STEM images. The contrast formation mechanisms of the LABF STEM and HABF STEM images are examined in comparison with HAADF STEM images. The HABF STEM images independent of defocus and thickness have spatial resolution comparable with HAADF STEM images, and are shown to be given as a simple convolution under the non-dispersion approximation of localized Bloch waves.

Characteristics of Defects in Quenched β-Brass

Defects in quenched β-brass have been studied by transmission electron microscopy. Irregularly-shaped dislocation loops are formed heterogeneously along antiphase domain boundaries. Isolated black spot defects are also formed inside antiphase domains besides these loops and their density is about 3×10 19 /m 3 . The process of ordering by vacancy mechanism and clustering of quenched-in vacancies have been examined by means of the Monte Carlo simulation by taking into account both quenching rate and binding energy of vacancies. It is shown that excess vacancies aggregate along an antiphase domain boundary in the course of ordering during quenching. A possibility of the formation of black spot defects is also discussed on the basis of the above simulation.

Effect of convergent beam semiangle on image intensity in HAADF STEM images

In this study, we experimentally and theoretically show that the intensities of bright spots in a spherical aberration (C(s))-uncorrected high-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) image of [011]-oriented Co(3)O(4), which has two different numbers of Co atoms in the projected atomic columns, are reversed with increasing sample thickness. However, C(s)-corrected HAADF STEM images produce intensities that correctly depend on the average number of atoms in the projected atomic columns. From an analysis based on the Bloch-wave theorem, it is found that an insufficient semiangle of the incident convergent beam yields intensities that do not depend on the average atomic number in the atomic columns.

Quantitative structural analysis of twin boundary in α-Zn7Sb2O12 using HAADF STEM method

The structure and composition of the 1/4{110} twin boundary in alpha-Zn7Sb2O12 have been determined by using quantitative high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) analysis. The noise in the experimental HAADF STEM images is reduced by using the maximum entropy method and average processing, and the parameters used in dynamical simulations are experimentally determined. From the analysis, it has been found that octahedral sites in the twin boundary slightly shift parallel to the [110] direction, and a reduction of the Sb concentration at the octahedral sites on the plane adjacent to the twin boundary was detected. The reduction was measured from three regions in the same twin boundary, and the Sb concentrations were 4 +/- 3, 8 +/- 3 and 19 +/-2 at% from 33 at%.

Precise measurement of local strain fields with energy-unfiltered convergent-beam electron diffraction.

A simple and robust method to precisely determine local strain fields using energy-unfiltered convergent-beam electron diffraction is presented. This method involves the subtraction of background intensity, the extraction of higher-order Laue-zone lines by tracing using a Radon transformation and a system of analytical strain determination without the need for an optimization routine such as chi2-based minimization. As an example, the measurement of residual strain in a silicon-on-insulator wafer is demonstrated. It is found from micro-Raman spectroscopy analysis that, at the nanometre scale, this measurement succeeds with an accuracy of 0.06%.