Yoshifumi Taniguchi

Development of real-time defocus-modulation-type active image processing (DMAIP) for spherical-aberration-free TEM observation

Abstract A new technique for spherical-aberration-free observations under Transmission Electron Microscope (TEM) by real-time defocus-modulation-type active image processing (DMAIP) has been developed. This technique is based on a sophisticated accelerating-voltage modulation which enables both rapid through-focusing and functionized irradiation-time control to be performed. The functionized irradiation-time control which we have newly developed for the present DMAIP, is as follows: The through-focusing, Δƒ(t), is controlled so that the irradiation time of the primary beam per unit defocus value, dt/dΔƒ, is proportional to the weighting function, W(Δƒ), at each defocus value, Δƒ. The simple accumulation of the image signal per unit time, i(Δf(t), expressed by the integral, ∫i(Δƒ(t)) dt, is proved to lead to the real-time DMAIP. The driving signal for the accelerating-voltage modulation was simply supplied to the feedback circuit of the high-voltage stabilizing unit of the TEM, and the processed images were successively displayed on a cathode ray tube (CRT) in real time at the video-frame rate ( 4 30 s). The experimental confirmation has been made through the Thon-diagramming technique with a commercial type TEM, the JEM-200CX. The Thon diagram constructed from these real-time processed images have clearly revealed that the spherical aberration of the objective lens has been successfully corrected in the range of intermediate spatial frequency (

Spherical-aberration-free observation of TEM images by defocus-modulation image processing

Abstract Defocus-modulation image processing has been applied to correct the spherical aberration in transmission electron microscopic images. The correction procedure is performed by off-line integration of through-focus images with bipolar weighting functions. An electron microscope with a field emission gun, the HF-2000, was used in this experiment. The Thon diagrams constructed by plotting the power spectra of the processed images as a function of virtual defocus value clearly demonstrate that the spherical aberration was corrected very well, leading to the marked improvement of the resolution from 3.7 to 5.8 nm -1 . As a novel approach to assess the information limit more accurately, we have represented the Thon diagrams for the amplitude and phase components separately. The presented results reveal that this approach is of practical use even for thicker samples which cannot be treated as weak phase objects.

Spherical-aberration-free observation of profile images of the Au(011) surface by defocus-modulation image processing

Abstract Spherical-aberration-free profile images of a reconstructed Au(011) surface have been successfully observed by a high-resolution transmission electron microscope combined with defocus-modulation image processing. In the processed images, both surface shape and lattice image were seen more clearly than in the original images, demonstrating the high potential of the processing for determining atom positions. Some of the intensity peaks observed at the topmost layer of the 2 × 1 missing-row reconstructed surface have shifted in ∾0.02 nm toward the surface as predicted by LEED experiments, but one of them has been displaced outward ∾0.05 nm. Using through-focus images calculated by a dynamical electron diffraction theory and an image formation theory, computer simulations of the image processing were performed. By comparison with the simulated results, the displacements of the lattice image are confirmed to be due not to the effect of remaining spherical aberration or an artifact of processing but to the displacement of atoms in the crystal.