The catalyst of Pt/SnO2 was prepared by the impregnation method. The catalytic activities of Pt/SnO2 catalysts pretreated under several conditions were investigated for the combustion of ethyl acetate. The activity was degraded by the heat-treatment in a reducing atmosphere, and was recovered to some extent by the reoxidation treatment. The interface between platinum particles and SnO2 particles were observed by TEM so as to elucidate the cause of the change in catalytic activity. In the Pt/SnO2 catalyst reduced in hydrogen, the particles with core-shell structure were clearly observed. On the other hand, the redispersion of platinum particles was confirmed in the reoxidized Pt/SnO2 catalyst. Thus, it was verified that the catalytic activities of Pt/SnO2 were strongly related with their nano structure. The analogous structural change proceeded in the other precious metal catalysts such as Ru/SnO2, Pd/SnO2, and Rh/SnO2.
It is well known that the catalytic activity of Au nanoparticle changes significantly depending on the size of the Au particle. It is also suggested that the interface structure between the Au and support metal oxides is important for the catalytic properties. Thus, in order to elucidate the mechanism of catalysis by Au, it is indispensable to clarify the structure of the interface between Au nanoparticle and metal oxide support in atomic scale. We present some recent results concerning the structure of Au catalysts obtained by electron microscopy.
Platinum supported on titanium dioxide (Pt/TiO2) exhibits remarkably high activity towards the decomposition reaction of organic molecules. Recently the size of Pt clusters has been reduced to less than 1nm. In contrast, the size of TiO2 support particles has been kept at sub-micron sizes to ensure stability at high temperature. The surface has also been modified to form a heterogeneous nanostructure. Although these complex nanocatalysts can be visualized by transmission electron microscopy, switching between several accelerating voltages improves the reproducibility and reliability of the results. Here we report a progressive electron microscopy study of such heterogeneous catalysts using accelerating voltages of 80kV to 1MV. Switching voltages is also essential for estimating the beam effect when performing environmental transmission electron microscopy (ETEM). We present EM images of Pt/TiO2 photocatalysts by advanced ETEM taken over this range of accelerating voltages. In the 80keV TEM image, selective lattice imaging of the Pt nanoparticle was achieved. In addition, greater contrast was obtained in comparison with a conventional 200keV image. On the other hand, a 300keV accelerating voltage provided clearer lattice imaging of the TiO2 supporting particles. In the 1MeV TEM image, surface steps and defect structures of TiO2 were successfully visualized.
In gaseous atmosphere at high temperature, the catalyst material changes the structure and the property. For the research and development of catalysts, it is of vital importance to clarify mechanisms of solid-gas reactions at high temperature. On the other hand, ETEM (Environmental Transmission Electron Microscope) have been developed by a lot of researchers.In this paper, we introduce the feature of our ETEM and observation results of catalysts (Platinum on carbon, Platinum on CeO2).
To analyze atomic arrangements on the surfaces and interfaces of solids in gases, especially during catalytic reactions, we have recently introduced a high-resolution environmental transmission electron microscope (ETEM) with the Cs corrector of the objective lens in Osaka University. The ETEM is equipped with an environmental cell (E-cell) for higher resolution observation of specimens under higher gas pressures. We can observe specimens under stable and reproducible gas environments by the well-designed evacuation system. The Cs-corrected ETEM can be applied for characterizing 1) the properties of nanomaterials in real environments such as metal nanoparticle catalysts in reaction gases and 2) the synthesis processes of nanomaterials such as the chemical vapor growth of carbon nanotubes in gases at high temperature. The ETEM can be used as a standard scanning transmission electron microscope (STEM) as well as a standard transmission electron microscope (TEM) with the Cs corrector of the objective lens after quick evacuation of gases from the E-cell.
Recent trends have pushed the scientific instruments associated with electron microscopy toward computer-controlled and automatic operation. It could be very effective under such circumstances to apply mathematical treatments suitable for the microscopic and spectroscopic data characteristics and extract information embedded thereby as much as possible, particularly for noise reduction, resolution improvement and statistical information extraction. In the present article several signal and image processing techniques, their features and application examples, which have been done by the present author are introduced.
This paper reports the recent topics related to the phase transformations in functional materials, which were studied by using techniques of in situ transmission electron microscopy. We herein focused on the relationship between lattice imperfection and magnetization in a ferromagnetic shape memory alloy, and the microscopic mechanism of the peculiar domain switching phenomenon which was recently discovered in a layered manganite. The in situ experiments were carried by using special equipments that applied magnetic/electric fields to the specimens inside the microscope. The complex microstructures produced by the phase transformations were analyzed by complementarily using electron holography, Lorentz microscopy, dark-field image observations, and such other techniques.
Neurons generate a tremendous number of synaptic connections to realize complex brain functions, such as cognition, learning, and motor control. Synapses are specialized cell-to-cell junctions and provide a structural basis for signal transduction between neurons. A variety of protein molecules, including membrane receptors, scaffolding proteins, and signal processing molecules, are known to accumulate at synapses and information about transport, incorporation and stabilization of these molecules is indispensable for the understanding of synaptic functions. Imaging of synapses in live neurons revealed the process of synapse formation and maturation, and also provided the evidences of dynamics molecular redistribution in response to synaptic activity. In this review, I will introduce recent findings related to the topic of synapse formation and remodeling with special emphasis on imaging of GFP-tagged synaptic molecules in living neurons.
Carbon nanotubes (CNTs) and graphene derived from SiC(0001) and (0001) substrates respectively were investigated by transmission electron microscopy (TEM).
Formation of well-aligned and highly-dense CNT films by surface decomposition of SiC(0001) were firstly found. Growth mechanism of the CNTs was shown by clarifying the relationship between the diameter and number of the layer. Transmission electron diffraction patterns revealed that zigzag-type CNTs are selectively formed by the present method.
Successively, atomic-scale structures of the interface between graphene and SiC(0001) have been investigated using high-resolution TEM observation combined with a first principles calculation. Our analysis revealed the presence of a metastable transitional structure formed by decomposition of a single SiC bilayer as well as fully-packed honeycomb graphene as the interface structure. The results of our calculation clarified that the difference in the interface structures should strongly influence the electronic states. A formation process of graphene layers on SiC (0001) were also revealed by high-resolution TEM as following: Initially, nucleation occurs at SiC steps, covering them with a few layers of graphene. These curved graphene layers stand almost perpendicularly on the lower terrace. Graphene subsequently grows over the terrace region. The growth is often pinned by lattice defects of the SiC substrate.
Current approaches to restore the partial loss of organ function, stem cell transplantation therapy and tissue engineering technologies have been developed as a cure for various diseases, injury and aging. The ultimate goal of regenerative therapy is to develop fully functioning bioengineered organs which work in cooperation with surrounding tissues and can replace to dysfunctional organs. In current research on whole-tooth regenerative therapy, a basic strategy is being pursued in which a bioengineered tooth germ is induced to develop into a fully functional tooth. Previously, we developed a three-dimensional organ-germ method for the reconstitution a bioengineered organ germ. Recently, we successfully demonstrated that our bioengineered tooth germ could develop a fully functioning tooth, which has hardness for masticatory potential, the functional responsibility against a mechanical stress, and perceptive potentials of neural fibers. These results represented that the bioengineered tooth germ could develop a fully functioning regenerated tooth and an organ replacement regenerative therapy using a bioengineered organ germ might be feasible.
Light elements are of central importance in a wide range of materials and devices. However, direct imaging of light elements at atomic resolution has been an outstanding challenge for the popular and otherwise highly successful technique of scanning transmission electron microscopy. Recently, a new imaging mode, called annular bright field (ABF) imaging, has been found to give direct and robust imaging of both light and heavy elements simultaneously.This new imaging mode is reviewed and compared with other scanning transmission electron microscopy imaging modes.The basic principles of image formation are discussed, with particular emphasis on what makes light elements visible. Example applications, including the direct visualization of hydrogen within a crystalline environment, are presented.
Confocal imaging in scanning transmission electron microscopy (STEM) is a new technique for performing depth sectioning of specimens in a transmission electron microscope. This is called scanning confocal electron microscopy (SCEM). In the present work, we have developed two base technologies, 3D specimen scanning system and annular dark field (ADF) confocal imaging optics, to realize SCEM practically, and performed depth sectioning with depth resolution less than 100nm using a conventional transmission electron microscope JEM-2100F. And, it was demonstrated that 3D reconstruction could be obtained by SCEM for the first time. Furthermore, ADF-SCEM using a JEM-2200MCO machine equipped with aberration correctors in its probe-forming and imaging lenses was performed, and about 20nm in depth resolution was achieved. This paper aims at introducing a principle and outline of ADF-SCEM and showing some experimental results.
Devices that enable simultaneous and the same axis observation of histocytochemically labeled ultrastructure by fluorescence probes are desired for more detailed biomedical experiments and understanding of the functional molecular morphology. We have developed a hybrid microscope equipped with both fluorescent optical microscope and scanning electron microscope. In this article, we will briefly review the trial processes of the FL-SEM development, and show some examples obtained by the instrument. Fluolid, a novel fluorescent substance that is favorable for utilizing in the hybrid microscope, is also mentioned.
An ultra-precise positioning system for X-ray interferometer was developed for phase-contrast X-ray imaging. 30-picoradian rotational stability of the positioning tables was attained by increasing the mechanical rigidity of the tables, suppressing the drift rotation by feedback systems, and decreasing the mechanical vibration from the floor by an active air-suspension. The stability makes it possible to perform detailed three-dimensional observations of biomedical samples.
We discuss the detection of a single spin by monitoring the tunneling current of the scanning tunneling microscope (STM). First example is the detection of a single spin by the observation of the Kondo resonance feature, which is formed by a single spin placed in the conductance electrons and appeared as a sharp feature at the Fermi level in the differential conductance plot. When investigated on a double-decker bis(phthalocyaninato)terbium(III) complex (TbPc2) adsorbed on an Au(111) surface, the dI/dV curve of the tunneling current recorded onto a TbPc2 molecule shows a Kondo peak whose origin is an unpaired spin of a π-orbital of a Pc ligand. Next the detection of a single spin by monitoring the high-frequency component of the tunneling current in the presence of a magnetic field. For a submonolayer oxide thin film on the Si(111)-7×7 surface, it was demonstrated that a spin signal synchronized with the Larmor precession of the electron spin associated with a dangling bond can be detected. With site-specific measurement, it was found that the spin signal appears on the bright Si adatom in which oxygen atoms occupy the backbonds and weakened the metallic nature of the Si(111)- 7×7 surface. The measured Larmor frequency corresponded to g~2.00.