Kiyokazu Yoshida

Some Applications of an Ultra-High Voltage Electron Microscope on Materials Science

Fundamental problems for application of a 3 MV-class electron microscope have been examined at 2 MV on various materials such as aluminum, copper, 18-8 type stainless steel and gold as follows: (a) The maximum observable thickness of these specimens at 2 MV is generally 12~13 times larger than those at 0.1 MV. And thus, it is expected that processes of various phenomena in most materials can be continuously observed as same as in bulk specimens by the electron microscopy. (b) The anomalous transmission of electrons clearly occurs at the symmetry position of 111 reflections at 2 MV even in aluminum. (c) Total amount of secondary defects due to electron irradiation damage strongly depends not only on the order of reflections but also on deviation from the Bragg condition. When the anomalous transmission at the symmetry position occurs, the amount of defects shows the maximum value at the symmetry position of reflections. (d) Utility of capsules are examined on determination of the liquid structure and oxidizing processes of aluminum.

International telemicroscopy with a 3 MV ultrahigh voltage electron microscope.

The ability for remote microscope operation via a network connection was added recently to the ultrahigh voltage electron microscope (UHVEM) in Osaka University, and used successfully for the observation of thick biological samples across the Pacific Ocean by researchers at the National Center for Microscopy and Imaging Research (NCMIR) at the University of California San Diego. High-quality images at video rate were transferred by a satellite link and control signals were transmitted by an ISDN connecting the workstations at both sites. Most microscope functions operated from the console of the UHVEM were replicated on the graphical user interface of the remote workstation. By clicking on icons or in boxes in the display window with a mouse, the researcher could operate the UHVEM from the remote-site. The total delay time for sending images and returning control signals was about 0.7 s, which did not interfere significantly with the smooth operation of the instrument. Researchers at the remote site were able to record images on film in the microscope which were later sent to San Diego.

Shrinkage of Grown-in Defects in Czochralski Silicon During Thermal Annealing in Vacuum

We examined the effect of thermal annealing in vacuum on the behavior of dual-type octahedral void defects in Czochralski silicon. We found that the smaller void shrinks first at about 1100°C and that during the shrinkage of the smaller void to extinction, the bigger void maintains its structure and size. In addition, we found that shrinkage of the smaller void begins from the adjacent region between the two voids. We believe that the effect of minimizing the surface energy first takes place selectively in the smaller void and that after the extinction of the smaller void, the effect of minimizing the surface energy takes place in the bigger void.

Position control of electron energy loss spectrum in case of accelerating-voltage fluctuation

In the parallel detection EELS, the fluctuation effect of the accelerating voltage is compensated both by the open loop and negative feedback controls. The fundamental frequency components of the AC power line and the excitation of Cockcroft-Walton circuit are canceled by applying the inverse-phase signal to the deflection coil, while the effect from the drift and the higher-order ripples is controlled by the negative feedback. The energy resolution is increased from 9.3 eV to 5.7 eV by the open loop control and can be improved up to 3.8 eV by the negative feedback. As the loop gain increases, the resolution increases at first, but then decreases. This decrease results from the shot noise of electron beam and the phase shift of the feedback loop. It is theoretically shown that the optimum condition to the loop gain and the bandwidth exists for the feedback control.

Lorentzian-like image blur of gold nanoparticles on thick amorphous silicon films in ultra-high-voltage transmission electron microscopy

We quantitatively analyzed the contrast degradation and blur of 20-nm gold nanoparticles adsorbed on the top of amorphous silicon films of thicknesses of 0.54, 1.09, 1.63 and 2.2 μm in bright-field transmission electron microscope (TEM) images taken at accelerating voltages of 0.5, 1, 2 and 3 MeV. The thickness dependence of the transmission was well explained and consistent with our calculations. The blur function, derived by assuming that the TEM image of a thick specimen can be reproduced by convolving the TEM image of a very thin specimen with it, was found to be expressed by a two-dimensional Lorentzian function. Considering the two characteristics of the Lorentzian function, a sharp peak around the center and a long tail, we concluded that, for TEM observations of thick specimens, the image contrast is degraded predominantly by inelastic scattering and the image is blurred predominantly by multiple elastic scattering.

An autofocus method using quasi-Gaussian fitting of image sharpness in ultra-high-voltage electron microscopy

An accurate method using image sharpness to determine the best focusing is proposed for ultra-high-voltage electron microscopy. This method maximizes image sharpness for adjusting the focus. Five images with different defocus values are used to calculate the image sharpness. To obtain the best focus value that produces greatest image sharpness, fitting the quasi-Gaussian function to five image sharpness is a suitable alternative. This method, which maximizes image sharpness, gives better accuracy than the wobbler method for the ultra-high-voltage electron microscope. The focusing area can be selected without moving the field of view, because the focusing area can be selected at almost any area in the image.

Grooved fluorescent plate for parallel-detection electron energy loss spectroscopy in ultra-high-voltage electron microscopy

Abstract The fluorescent plates in parallel-detection electron-energy-loss spectroscopy are studied from the viewpoint of the spatial resolution and the background of spectra. The self-supporting fluorescent plate is proposed in order to reduce the backscattered electrons from the supporting substrate of the fluorescent plate. Many fine grooves are cut on the thin Si plate and are filled with phosphor powder. This “grooved fluorescent plate” is effective to suppress the blur of spectra although the intensity decreases slightly.

Electron energy dependence of characteristics of fluorescent plates for ultrahigh-voltage electron microscopes.

The characteristics of fluorescent plates for high energy electron beams (0.5-2.0 MeV) are examined. The thickness and the optical transparency of plates strongly affect the luminous broadening and intensity. The spatial luminous broadening in fluorescent plates is measured and is simply represented by the rise width of a knife edge image. When the thickness is much smaller than the range of incident electrons, the rise width is 1/4-1/5 of the thickness in the case of YAG single crystal plates that are transparent for light, while the rise width is nearly equal to the thickness for the packed P22 powder plates that are opaque for light. To suppress the luminous broadening under 50 microm, the thickness of YAG plates has to be thinner than 250 microm in the energy region around 2 MeV. Under the same condition of the rise width, the luminous intensity of YAG plates is twice as high as that of the P22 plates.

Electron Microscope Study of Some Diffusion Phenomena in Metals

Successive stages of sintering processes among metal powders have been observed with a 3MV-class electron microscope, and the following facts are clarified: (a) Recovery process easily occurs in small powders. (b) In the adjacent powders contacted with the recovered one, recrystallization starts from the contact point. In this case, the recovered powder plays as a seed crystal so that the crystal orientations of adjacent powders are coincided with that of the recovered one. (c) Dislocation structures in small powders lastly exist. This fact is related to decrease of the sintering temperature. Electron microscope measurements of the enhanced precipitation along the lattice imperfections have also been examined on grain boundaries and dislocation lines.

Scientific Grid Activities and PKI Deployment in the Cybermedia Center, Osaka University

The Cybermedia Center (CMC), Osaka University, is a research institution that offers knowledge and technology resources obtained from advanced researches in the areas of large-scale computation, information and communication, multimedia content and education. Currently, CMC is involved in Japanese national Grid projects such as JGN II (Japan Gigabit Network), NAREGI and BioGrid. Not limited to Japan, CMC also actively takes part in international activities such as PRAGMA. In these projects and international collaborations, CMC has developed a Grid system that allows scientists to perform their analysis by remote-controlling the worlds largest ultra-high voltage electron microscope located in Osaka University. In another undertaking, CMC has assumed a leadership role in BioGrid by sharing its experiences and knowledge on the system development for the area of biology.In this paper, we will give an overview of the BioGrid project and introduce the progress of the Telescience unit, which collaborates with the Telescience Project led by the National Center for Microscopy and Imaging Research (NCMIR). Furthermore, CMC collaborates with seven Computing Centers in Japan, NAREGI and National Institute of Informatics to deploy PKI base authentication infrastructure. The current status of this project and future collaboration with Grid Projects will be delineated in this paper.