Masami Terauchi

Production of zigzag-type BN nanotubes and BN cones by thermal annealing

Abstract Boron nitride nanotubes (BNT) and boron nitride cones (BN cones) were produced by thermal annealing of a mixed powder of β-rhombohedral boron and hexagonal boron nitride (h-BN) at 1200°C under lithium vapor. The BNTs were found to grow from the edge of h-BN particles along one of 〈10 1 0〉 directions of the particles. The BNTs consist of zigzag-type layers whose 〈10 1 0〉 direction is parallel to the tube axis. The BN cones with an apex angle of about 20° were discovered. It was revealed that the BN cones were not formed by a helically wound conical BN layer but by a pile of monolayer BN cones.

Electron Energy-Loss Spectra of Carbon Nanotubes

Carbon nanotubes were investigated by means of electron energy-loss spectroscopy. Two peaks due to the π plasmon and the π+σ plasmon were observed. The energy of the π+σ plasmon peaks varied from 22.0 eV to 24.5 eV, which roughly agrees with the average plasmon energy of graphite. A shoulder due to single electron excitations was observed at 13 eV, which was not observed in graphite. There were two kinds of nanotubes which exhibited their respective π plasmon peaks at 5.2 eV and 6.4 eV. The peaks in the dielectric function obtained by Kramers-Kronig analysis of the spectra were broader than those of graphite probably due to the curving of the graphitic sheets.

Electron energy-loss spectra of single-shell carbon nanotubes

Transmission electron energy-loss spectra of single-shell carbon nanotubes were measured and compared with those of multishell carbon nanotubes and graphite. Two peaks due to the π plasmon and the π+σ plasmon were observed at 5.8 eV and 20.6 eV, respectively. The energy of the π plasmon takes a value between those of two kinds of multishell tubes. The energy of the π+σ plasmon is lower than those of multishell tubes and graphite by 2 eV and 6 eV, respectively. The 1s→π* and 1s→σ* transition peaks of the single-shell tubes are much broader than those of the multishell tubes and graphite. The reason for the broadening may be due to the strong curving of the graphitic sheets.

Convergent-beam and small-area-parallel-beam electron diffraction of icosahedral quasicrystals of a melt-quenched Al-Mn alloy

Abstract Intensity distribution in convergent-beam electron diffraction (CBED) patterns obtained from icosahedral quasicrystas of a melt-quenched Al-Mn alloy reveal that the quasicrystals do not have fivefold, threefold and twofold rotation axes and have no inversion center, although ordinary diffraction patterns obtained thus far showed these rotation symmetries. CBED patterns taken from specimen areas of about 3 nm in diameter show a deviation in geometry in spot positions from the fivefold rotation symmetry. Ring patterns due to higher-order Laue zone reflections are not observed in CBED patterns. Kikuchi bands are composed of two sub-bands in the five equivalent directions, and each band has a different intensity profile. Parallel-beam (3 × 10-5 rad) electron diffraction patterns obtained from specimen areas less than 100 nm in diameter also show a deviation from the fivefold symmetry in spot positions and make clear that each Bragg reflection consists of many fine spots which show no fivefold symmetry. It is proven experimentally that all the observed reflections occur already in the approximation of kinematical diffraction, although their intensities may be modified by dynamical diffraction effect.

High energy-resolution electron energy-loss spectroscopy study of the dielectric properties of bulk and nanoparticle LaB6 in the near-infrared region

The dielectric properties of LaB(6) crystals and the plasmonic behavior of LaB(6) nanoparticles, which have been applied to solar heat-shielding filters, were studied by high energy-resolution electron energy-loss spectroscopy (HR-EELS). An EELS spectrum of a LaB(6) crystal showed a peak at 2.0 eV, which was attributed to volume plasmon excitation of carrier electrons. EELS spectra of single LaB(6) nanoparticles showed peaks at 1.1-1.4 eV depending on the dielectric effect from the substrates. The peaks were assigned to dipole oscillation excitations. These peak energies almost coincided with the peak energy of optical absorption of a heat-shielding filter with LaB(6) nanoparticles. On the other hand, those energies were a smaller than a dipole oscillation energy predicted using the dielectric function of bulk LaB(6) crystal. It is suggested that the lower energy than expected is due to an excitation at 1.2 eV, which was observed for oxidized LaB(6) area.

Electron Microscope Study of Decagonal Quasicrystals of Al70Ni15Fe15

Decagonal quasicrystals of an Al70Ni15Fe15 alloy were investigated by transmission electron microscopy. Dark-field image studies revealed that there exist inversion domains and the domain boundaries accompany the antiphase shift of c/2. High-resolution image studies revealed that specific pentagonal atom clusters exist and that all the clusters in a domain have the same sense of polarity and those in the neighboring domains have the opposite sense. A preliminary structural model for explaining the high-resolution image was generated by the section method.

Development of wavelength-dispersive soft X-ray emission spectrometers for transmission electron microscopes—an introduction of valence electron spectroscopy for transmission electron microscopy

Two types of wavelength-dispersive soft X-ray spectrometers, a high-dispersion type and a conventional one, for transmission electron microscopes were constructed. Those spectrometers were used to study the electronic states of valence electrons (bonding electrons). Both spectrometers extended the acceptable energy regions to higher than 2000 eV. The best energy resolution of 0.08 eV was obtained for an Al L-emission spectrum by using the high-dispersion type spectrometer. By using the spectrometer, C K-emission of carbon allotropes, Cu L-emission of Cu(1-x)Zn(x) alloys and Pt M-emission spectra were presented. The FWHM value of 12 eV was obtained for the Pt Malpha-emission peak. The performance of the conventional one was also presented for ZnS and a section specimen of a multilayer device. W-M and Si-K emissions were clearly resolved. Soft X-ray emission spectroscopy based on transmission electron microscopy (TEM) has an advantage for obtaining spectra from a single crystalline specimen with a defined crystal setting. As an example of anisotropic soft X-ray emission, C K-emission spectra of single crystalline graphite with different crystal settings were presented. From the spectra, density of states of pi- and sigma-bondings were separately derived. These results demonstrated a method to analyse the electronic states of valence electrons of materials in the nanometre scale based on TEM.

Hybridized Microcrystals Composed of Metal Fine Particles and π-Conjugated Organic Microcrystals

We have successfully prepared hybridized microcrystals composed of polydiacetylene microcrystals and silver fine particles by means of the co-reprecipitation method, and investigated their hybridized structure and optical properties. It was revealed experimentally for the first time that the core domain of metal fine particles may interact optoelectronically with the shell layer of polydiacetylene in the hybridized microcrystals to give different electronic states from those of the original compounds.

Electron energy-loss spectroscopy study of the metal-insulator transition in VO2

Electron energy-loss spectra of VO2 have been measured from perfect single crystalline areas of 100–180 nm diameter in the metallic and insulating phases. A sharp peak has been observed at 1.2 eV in the valence electron excitation spectra of the metallic phase but not in those of the insulating phase. We assign the peak to an interband transition or d-d transition by inspecting the dielectric function derived from the present loss function with the help of an energy band diagram already given, although an excitation at about 1 eV already observed by optical measurement was assigned to the excitation of a free-carrier plasmon. The peak due to the O 1s → V 3d(t2g) transition in the O 1s excitation spectra decreased in intensity but increased in the full width at half-maximum (FWHM) at the transition from the metallic phase to the insulating phase. These changes are considered to have been due to the fact that the d\varparallel band splits into the upper unoccupied and lower occupied d\varparallel bands and the upper d\varparallel band rises above the π* band in the insulating phase, but that the d\varparallel band is unsplit and located within the π* band in the metallic phase.

ɛ‐TiO, a Novel Stable Polymorph of Titanium Monoxide

For the Ti/O system, three titanium monoxide (TiO) phases (α, β, and γ) with defective NaCl-type structures and a high-temperature hexagonal phase (H) have been known for decades. In this work, single crystals of a novel polymorph, ɛ-TiO, were synthesized by using a bismuth flux. X-ray diffraction (XRD) revealed a hexagonal crystal structure (a=4.9936(3) Å, c=2.8773(2) Å, P6‾ 2m) that is isotypic with ɛ-TaN. While the Ti atoms are surrounded by trigonal prismatic (sixfold coordination) and trigonal planar (threefold coordination) arrangements of O atoms, the O atoms are found in a pseudo-square-pyramidal arrangement of Ti atoms. First-principles calculations of the formation enthalpy and the electron and phonon density of states and crystal orbital Hamilton population (COHP) analysis revealed that ɛ-TiO is more stable than α-TiO, which had previously been regarded as the most stable phase at low temperatures.