Takayoshi Tanji

Observation of magnetic‐domain states of barium ferrite particles by electron holography

Magnetic domain states of completely isolated particles of barium ferrite between 0.1 and 2 μm in size are investigated by electron holography. Phase distribution is reconstructed digitally by the Fourier transform method and converted to interference micrographs. In the interference micrographs single magnetic‐domain particles are observed directly and clearly for the first time. Furthermore, it is found that single‐domain and two‐domain particles coexist down to sizes as small as about 0.1 μm.

Phase‐shifting electron holography by beam tilting

A phase‐shifting method to directly measure the amplitude and phase distribution of specimen in an electron holographic microscope without the introduction of large number of carrier fringes is proposed. The initial phase of electron holograms is shifted by tilting the incident electron beam with a digital voltage/current supply. Several holograms of a specimen with properly different phase shifts are recorded digitally and used to calculate the amplitude and phase distributions of the specimen. Experimental result of observing the phase distribution of a cubic MgO crystal is shown.

Improvement of windowed type environmental-cell transmission electron microscope for in situ observation of gas-solid interactions

We have developed an improved, windowed type environmental-cell (E-cell) transmission electron microscope (TEM) for in situ observation of gas-solid interactions, such as catalytic reactions at atmospheric pressure. Our E-cell TEM includes a compact E-cell specimen holder with mechanical stability, resulting in smoother introduction of the desired gases compared with previous E-cell TEMs. In addition, the gas control unit was simplified by omitting the pressure control function of the TEM pre-evacuation chamber. This simplification was due to the successful development of remarkably tough thin carbon films as the window material. These films, with a thickness of <10 nm, were found to withstand pressure differences >2 atm. Appropriate arrangement of the specimen position inside the E-cell provided quantitatively analyzable TEM images, with no disturbances caused by the windowed films. As an application, we used this E-cell TEM to observe the dynamic shape change in a catalytic gold nanoparticle supported on TiO(2) during the oxidation of CO gas.

Development of an environmental high-voltage electron microscope for reaction science

Environmental transmission electron microscopy and ultra-high resolution electron microscopic observation using aberration correctors have recently emerged as topics of great interest. The former method is an extension of the so-called in situ electron microscopy that has been performed since the 1970s. Current research in this area has been focusing on dynamic observation with atomic resolution under gaseous atmospheres and in liquids. Since 2007, Nagoya University has been developing a new 1-MV high voltage (scanning) transmission electron microscope that can be used to observe nanomaterials under conditions that include the presence of gases, liquids and illuminating lights, and it can be also used to perform mechanical operations to nanometre-sized areas as well as electron tomography and elemental analysis by electron energy loss spectroscopy. The new instrument has been used to image and analyse various types of samples including biological ones.

Interferometry using convergent electron diffracted beams plus an electron biprism (CBED + EBI)

Abstract A method of interferometry which interferes convergent electron beams by means of an electron biprism, CBED + EBI, is presented. The method requires an electron biprism which is placed below the specimen and in between any two or more convergent beams. The biprism compensates the convergent beams deviation angle by means of an applied potential. When overlaid the diffracted beams interfere to produce an interferogram. Theoretical and practical descriptions of the CBED + EBI method are presented, as well as some of its special features such as its ability to interfere high spatial frequency beams, to produce high contrast fringes and to measure the electron beams coherency.

Interference of three electron waves by two biprisms and its application to direct visualization of electromagnetic fields in small regions

We present a method for the interference of three electron waves and its application to direct visualization of pure phase objects such as electromagnetic microfields. Using a transmission electron microscope equipped with a field-emission electron gun and two electron biprisms, an object wave and two reference waves at either side of the object wave are superposed to produce a new type of interference pattern. In this pattern, equal-phase lines of the object wave are directly displayed as intensity modulation of periodic interference fringes. An electric field around a latex particle, induced by electron-beam irradiation, has been observed. The electric charge of the particle is estimated, from observed phase shift, to be 6.4×10−17 C, which is equal to about 400 electrons. A change of the electric field around charged alumina particles at high temperatures has been observed dynamically. Magnetic flux lines emerging from a barium ferrite particle are also visualized.

Effect of Dispersion of Nanosize Platinum Particles on Electrical Conduction Properties of Proton-Conducting Oxide SrZr0.9Y0.1O3 − α

Nanosize effects have gradually become emphasized in the description of ion conduction properties of solids. The authors demonstrate a nanoionics effect that occurs in a proton-conducting perovskite upon dispersing fine platinum particles in the oxide. Both the ionic and hole conductivities are lost when the volume fraction of dispersed platinum exceeds a threshold value, resulting in an enormous reduction in both conductivities. These experimental results are discussed in accordance with a percolation model: the boundary layer, where charge carriers are suppressed by a space charge layer effect, blocks the bulk conduction of both protonic and electron-hole charge carriers.

Dynamic observation of magnetic domains by on-line real-time electron holography

Abstract Dynamic behavior of magnetic domains in a thin permalloy film has been observed by on-line real-time electron holography. Electron holograms formed in a transmission electron microscope equipped with an electron biprism are detected by a TV camera and transferred to a liquid-crystal spatial light modulator (LC-SLM) located at the output port of a Mach-Zehnder interferometer. Interference micrographs, where magnetic flux lines are directly visualized, are obtained by superimposing a plane wave onto an object wave reconstructed from the hologram in the LC-SLM. Using this system, dynamic behavior of magnetic domains in the magnetization or demagnetization processes is clearly observed.

Sparse modeling of EELS and EDX spectral imaging data by nonnegative matrix factorization.

Advances in scanning transmission electron microscopy (STEM) techniques have enabled us to automatically obtain electron energy-loss (EELS)/energy-dispersive X-ray (EDX) spectral datasets from a specified region of interest (ROI) at an arbitrary step width, called spectral imaging (SI). Instead of manually identifying the potential constituent chemical components from the ROI and determining the chemical state of each spectral component from the SI data stored in a huge three-dimensional matrix, it is more effective and efficient to use a statistical approach for the automatic resolution and extraction of the underlying chemical components. Among many different statistical approaches, we adopt a non-negative matrix factorization (NMF) technique, mainly because of the natural assumption of non-negative values in the spectra and cardinalities of chemical components, which are always positive in actual data. This paper proposes a new NMF model with two penalty terms: (i) an automatic relevance determination (ARD) prior, which optimizes the number of components, and (ii) a soft orthogonal constraint, which clearly resolves each spectrum component. For the factorization, we further propose a fast optimization algorithm based on hierarchical alternating least-squares. Numerical experiments using both phantom and real STEM-EDX/EELS SI datasets demonstrate that the ARD prior successfully identifies the correct number of physically meaningful components. The soft orthogonal constraint is also shown to be effective, particularly for STEM-EELS SI data, where neither the spatial nor spectral entries in the matrices are sparse.

Realization of a mixed type of interferometry using convergent-beam electron diffraction and an electron biprism

Abstract A new method of interferometry has been realized using a transmission electron microscope with a stable field emission gun, electron biprism and specimen holder. The method involves interfering diffracted beams from a crystal by use of an electron biprism. The interferograms produced provide information about the crystal. Use of a small electron probe affords structural information about the crystal at the atomic level.