Takashi Ikuta

Wave field restoration using three-dimensional Fourier filtering method.

A wave field restoration method in transmission electron microscopy (TEM) was mathematically derived based on a three-dimensional (3D) image formation theory. Wave field restoration using this method together with spherical aberration correction was experimentally confirmed in through-focus images of amorphous tungsten thin film, and the resolution of the reconstructed phase image was successfully improved from the Scherzer resolution limit to the information limit. In an application of this method to a crystalline sample, the surface structure of Au(110) was observed in a profile-imaging mode. The processed phase image showed quantitatively the atomic relaxation of the topmost layer.

Active image processing

This paper describes a new concept of active modulation image processing and also shows a simple real-time linear image processing apparatus based on this concept. The apparatus contains a vibrating mirror and a combination of the CCD image sensor camera and the video frame integrator, which are used as the image translator and the bipolar weighted integrator with object images, respectively. Experimental results with the Laplacian operation and image restoration under the basis of a pseudo-Wiener filter show that the present image processing technique has practical potential.

High Contrast Observation of Magnetic Domain with High Voltage SEM

The analysis and experiments on the observation of the type II magnetic contrast in a backscattered electron image by using a high voltage scanning electron microscope are described. Although the reduction in the spatial resolution of the magnetic contrast due to the enlargement of the diffusion area of the penetrating electron probe is unavoidable, this approach of using a high voltage scanning electron microscope is very effective for increasing the magnetic contrast, and it seems a very useful means of studying the magnetic materials for practical use such as Mn-Zn ferrite and others.

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.

Development of a parallel detection and processing system using a multidetector array for wave field restoration in scanning transmission electron microscopy.

A parallel image detection and image processing system for scanning transmission electron microscopy was developed using a multidetector array consisting of a multianode photomultiplier tube arranged in an 8 x 8 square array. The system enables the taking of 64 images simultaneously from different scattered directions with a scanning time of 2.6 s. Using the 64 images, phase and amplitude contrast images of gold particles on an amorphous carbon thin film could be separately reconstructed by applying respective 8 shaped bandpass Fourier filters for each image and multiplying the phase and amplitude reconstructing factors.

Real-time lock-in imaging by a newly developed high-speed image-processing charge coupled device video camera

Real-time lock-in imaging with high-frequency modulation (up to 16 kHz) was successfully performed at high spatial resolution (640×480 pixels) using a newly developed high-speed image-processing charge coupled device (CCD) video camera. To achieve high-resolution lock-in imaging, the high-speed image-processing CCD video camera incorporates a high-definition TV image sensor that uses a high-definition frame-interline-transfer (FIT) CCD architecture. A novel FIT-CCD driving method, in which vertical CCD shift registers are utilized as a temporary frame memory, enables lock-in imaging at a modulation frequency in excess of the video frame rate (30 Hz). Furthermore, since the high-speed image-processing CCD video camera has a function for subtracting images taken with high-frequency modulation, a lock-in image with no background contrast can be observed in real time. The phase detection function for lock-in imaging, when coupled with real-time image processing using the high-speed image-processing CCD video ...

Theoretical background of defocus image modulation processing (DIMP) based on three dimensional optical transfer functions (3D-OTFs)

Summary Defocus-image modulation processing (DIMP), where a bipolar weighted image integration of the observed defocus series is performed, is one of the most promising approaches for real-time observation of spherical-aberration-free phase and amplitude images with a transmission electron microscope. DIMP can be extended to hollow-cone illumination (HCI) to improve the resolution of the electron microscope significantly, which has been already confirmed in the experiment using an optical microscope. In this paper, the theoretical background of DIMP is investigated by using 3D-OTFs in 3D-Fourier space. First, 3D-OTFs are derived under coherent illumination and the filtering characteristics of the DIMP are interpreted using the 3D-OTFs. Then the bipolar weighting functions used in DIMP are obtained by inverse Fourier transform of the filter functions in 3D-Fourier space under axial and hollow-cone illuminations.

Phase reconstruction in annular bright-field scanning transmission electron microscopy

A novel technique for reconstructing the phase shifts of electron waves was applied to Cs-corrected scanning transmission electron microscopy (STEM). To realize this method, a new STEM system equipped with an annular aperture, annularly arrayed detectors and an arrayed image processor has been developed and evaluated in experiments. We show a reconstructed phase image of graphite particles and demonstrate that this new method works effectively for high-resolution phase imaging.

Development of a novel CCD video camera incorporated with operational function for real-time image processing

Abstract A real-time image processing CCD video camera has been developed, which enables two successive images either to be added or subtracted each other in real-time, i.e. in period of one video field (1/60 s). This camera has been originally designed for real-time observation of the spherical aberration free image with a defocus image modulation processing (DIMP) electron microscope (EM) newly constructed. The visualization of a rotating disk demonstrates this novel CCD video camera enables the real-time image processing.