Tadahiro Yokosawa

Carbon nanofilm with a new structure and property

We have prepared a carbon film of nanometer thickness, which is called here a carbon nanofilm (CNF), starting from the oxidation of graphite. The structure and thickness of the CNF are determined by high-resolution transmission electron microscopy and electron diffraction. The structure is of a new type (S.G.: P3), in which carbon six-membered-ring planes are stacked with the sequence of ...AA.... According to electron energy loss spectroscopy, a substantial amount of oxygen is detected but the molar ratio of oxygen to carbon is possibly decreased to less than 0.1. The CNF changes from an insulator to a semiconductor when reduced on heating at 250°C.

Single graphene sheet detected in a carbon nanofilm

In order to clarify the existence of a single sheet of carbon six-membered-ring plane (graphene) this letter presents a method by which the stacking number of the sheets in a carbon nanofilm (CNF) can be exactly counted, based on the quantitative analysis of electron diffraction intensity. Using the method we can detect a single graphene sheet in a CNF.

Formation of an Al-Co Decagonal Quasicrystal from a τ 2-Inflated Al 13Co 4 Approximant

A model for the formation of an Al-Co decagonal quasicrystal with space group \(P\overline{10}m2\) from a τ 2 -inflated monoclinic Al 13 Co 4 approximant is constructed on the basis of the observation of high-resolution electron microscope images. It is shown that star- and crown-shaped structural units of the Al-Co decagonal quasicrystal are formed by combining elongated hexagon tiles or the basic structural unit of τ 2 -Al 13 Co 4 .

Formation of a superlattice order from a fundamental-lattice decagonal quasicrystal of Al72Ni20Co8

A structural change of an Al 72 Ni 20 Co 8 decagonal quasicrystal into the S1-type superlattice ordered phase has been observed at about 450°C by in-situ high-resolution electron microscopy. The Al...

Structural variations in local areas of an Al70Ni15Fe15 decagonal quasicrystal and the interpretation by the 1-nm column-pair scheme

Abstract Structural variations in local areas such as the star-shaped and butterfly-shaped tiles of a noncentrosymmetric decagonal quasicrystal of Al 70 Ni 15 Fe 15 have been investigated by using the high-angle annular dark-field scanning transmission electron microscope method. It has been demonstrated that the variations of the star-shaped and butterfly-shaped tiles in Al 70 Ni 15 Fe 15 are uniquely decomposed into the 1-nm column-pairs [Saitoh et al., J. Phys. Soc. Jpn. 68 (1999) 2886], which is the basic structural unit of the τ 2 -inflated Al 13 Co 4 approximant.

Diffuse Phase Transition and Anisotropic Evolution of Nanodomains in Nd0.2Sr0.8MnO3

We investigated the crystal structures of single-crystal Nd 0.2 Sr 0.8 MnO 3 by means of synchrotron x-ray diffraction measurement and transmission electron microscopy. We observed the coexistence of distinct crystal-structural phases, i.e., tetragonal (orbital ordered) and cubic (orbital disordered) phases, over a significantly wide range of temperatures. The ratio of these phases varied continuously with temperature. These indicate that the crystal exhibits a diffuse phase transition of the 3 z 2 - r 2 -type orbital ordering. Moreover, we observed the anisotropic evolution of the orbital-ordered nanodomains in the cubic phase. This specific nature of the phase transition probably originates from the competition between the orbital order and disorder.

Magnetocrystalline anisotropy behavior in the multiferroic BiMnO3 examined by Lorentz transmission electron microscopy

We investigated magnetic domain structures of a multiferroic manganite, BiMnO3, by Lorentz transmission electron microscopy. Ferromagnetic domains were observed below ∼105 K, close to the ferromagnetic Curie temperature, TC. The spontaneous magnetization aligns distinctly along the [010] direction, suggesting that the magnetic easy direction is along the b axis. Inflection and merging of the domain walls was observed at twin boundaries. This indicates pinning of the magnetic domain walls at crystallographic twin boundaries. Furthermore, we observed narrow magnetic domain walls, suggesting strong magnetocrystalline anisotropy.

In-Situ HREM Observation of the Structural Change from a Fundamental-Lattice Decagonal Quasicrystal of Al72Ni20Co8 to the S1 Type Superlattice Phase

A structural change of an Al 72 Ni 20 Co 8 decagonal quasicrystal into the S1-type superlattice ordered phase has been observed at about 400°C by in-situ high-resolution electron microscopy. It is considered that the formation of the S1-type superlattice order is attributed to the structural change of the atom cluster with 2 nm diameter from mirror symmetric one to fivefold symmetric one and the disappearance of 1.2-nm intercluster bonds.

Structural Study of an Al–Co Approximant by High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy

It has been discovered by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) that a melt-quenched Al 73 Co 27 alloy forms a new approximant. The approximant is composed of the Penrose skinny and fat rhombi with a 2 nm edge length, which are arranged periodically in one direction but disordered in the direction perpendicular to the periodic direction. It has been clarified that rocket- and butterfly-shaped tiles, which are constructed by the basic structural units of τ 2 -Al 13 Co 4 (the 1-nm column pairs) [K. Saitoh et al. : J. Phys. Soc. Jpn. 68 (1999) 2886], appear at the skinny tile and over the skinny and fat tiles, respectively. The structural relationship between the skinny and fat tiles and the 1-nm column pairs has been clarified for the first time. It has been revealed that the tiling of the skinny and fat rhombi in the present approximant, including the disordered feature of the tiling, is formed by a network of the 1-nm column pairs.

Space-Group Determination of Monoclinic ad Orthorhombic Al_ Co_4 Approximants by the Convergent-Beam Electron Diffraction Method : Condensed Mater: Structure, etc.

Space groups of monoclinic and orthorhombic Al 13 Co 4 approximants have been determined to be C 2/ m and P n m n , respectively, by the convergent-beam electron diffraction method. These space groups agree with those assumed in an X-ray structure analysis [Freiburg et al .: Mater. Sci. Forum 228–231 (1996) 583] and a conventional electron diffraction method [Ma and Kuo: Metall. Trans. 23A (1992) 1121].