Takao Tsurui

Phonon confinement effect of silicon nanowires synthesized by laser ablation

A gradual downshift and asymmetric broadening of the Si optical phonon peak were observed by Raman scattering measurements of continuously thermally oxidized silicon nanowires (SiNWs) synthesized by laser ablation. This downshift and broadening can be interpreted by the phonon confinement effect. Further thermal oxidation produced a reverse change; namely, an upshift of the optical phonon peak. This is considered to be due to compressive stress since this stress was relieved by removing the oxide layers formed around the SiNW cores, resulting in a downshift of the optical phonon peak.

Phonon confinement and self-limiting oxidation effect of silicon nanowires synthesized by laser ablation

The phonon confinement and self-limiting oxidation effects of silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The size of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs’ surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement, while excess oxidation causes an upshift due to compressive stress. The compressive stress retarded the oxidation of the SiNWs by self-limiting oxidation effect. This result shows that the Si core diameter can be controlled by compressive stress.

Doping and hydrogen passivation of boron in silicon nanowires synthesized by laser ablation

Local vibrational modes of boron (B) in silicon nanowires (SiNWs) synthesized by laser ablation were observed at about 618 and 640cm−1 by Raman scattering measurements. Boron doping was performed during the growth of SiNWs. Fano [Phys. Rev. 124, 1866 (1961)] broadening was also observed in the Si optical phonon peak. These results prove that B atoms were doped in the SiNWs. Hydrogen (H) passivation of B acceptors in the SiNWs was also investigated. A broad peak was observed at around 650–680cm−1 after hydrogenation, demonstrating that B dopants were passivated by the formation of the well-known H–B passivation centers.

Phosphorus doping and hydrogen passivation of donors and defects in silicon nanowires synthesized by laser ablation

Phosphorus (P) doping was performed during the synthesis of silicon nanowires (SiNWs) by laser ablation. At least three types of signals were observed by electron spin resonance (ESR) at 4.2K. Phosphorus doping into substitutional sites of crystalline Si in SiNWs was demonstrated by the detection of an ESR signal with a g value of 1.998, which corresponds to conduction electrons in crystalline Si, and by an energy-dispersive x-ray spectroscopy spectrum of the PKα line. The ESR results also revealed the presence of defects. These defects were partially passivated by hydrogen and oxygen atoms.

Direct observations of La ordering and domain structures in La0.61Li0.17TiO3 by high resolution electron microscopy

La0.61Li0.17TiO3 microstructures have been studied by high resolution electron microscopy. A local lattice distortion occurs in the vicinity of the domain boundary region due to the twin with an angle of 89°. The average domain size of La0.61Li0.17TiO3 is greater than 20 nm. The domain size and structures of La0.61Li0.17TiO3 differ greatly from those of La-poor compounds, such as La0.55Li0.35TiO3. At a nanoscopic level, microdomains of 20–100 nm in size construct a two-dimensional structure in La-rich compounds, while microdomains of 5–10 nm in size construct a three-dimensional structure in La-poor compounds. In addition, the Li-ion conduction mechanisms for La-rich and La-poor compounds are two- and three-dimensional, respectively.

Synthesis of silicon nanowires using laser ablation method and their manipulation by electron beam

Abstract Size control of silicon nanowires (SiNWs) synthesized by laser ablation of a Si target with iron or nickel as catalysts were investigated by changing the synthesis parameters such as the content of catalyst in targets and laser power during synthesis. The diameter and length of SiNWs significantly depended on the synthesis parameters, i.e. the size of SiNWs can be controlled by the synthesis parameters. Manipulation of SiNWs was also performed during the observation of scanning electron microscope. By changing the degree of charge-up for free-standing adjacent intertwined SiNWs at an edge of Si substrate, the distance and speed of opening motion of them can be controlled. This motion is probably caused by the Coulomb repulsive interaction between them.

Proton Transport and Microstructure Properties in Superlattice Thin Films Fabricated by Pulsed Laser Deposition

Superlattice thin films of the perovskite-type oxide proton conductor SrZr0.95Y0.05O3/SrTiO3 was fabricated by pulsed laser deposition. Their structural and proton transport properties were reported. X-ray diffraction analysis and selected area electron diffraction revealed that the thin films were epitaxially grown on MgO(001) substrate. High-density edge dislocations and a columnar structure were observed in the films by high-resolution electron microscopy. The in-plane electrical conductivity of the thin films was determined by impedance spectroscopy. The contribution of proton transport to the total conductivity of the films was confirmed by H2O/D2O exchange measurement. The conductivity of superlattice films was increased by introducing heterointerfaces. The high activation energy (Ea=1.0 eV) was explained by the grain-boundary effect of the columnar structure in the films.

Hierarchy of dynamic structure of super-ionic conducting glass CuI–Cu2MoO4

Abstract A composite glass, CuI–Cu 2 MoO 4 , has an ionic conductivity at room temperature, corresponding to ionic liquid conductivity. Pulsed neutron scattering and XAFS measurements show that the main framework of the sample is constructed from [MoO 4 ]-tetrahedra and [MoO 6 ]-octahedra. Cu + ions in the glass are bound to 2 O atoms or 4 I atoms. he atomic motion below 20 meV in the sample measured at room temperature is close to that of the α-CuI crystalline state near its melting point. In addition to the Boson peak, above 200 K, quasielastic neutron scattering due to the local diffusion of Cu + ions is found at energies 5 meV. The long-range translational diffusion of the Cu + ions in the sample is directly demonstrated by high resolution quasielastic neutron scattering results. The broadening is less than 100 μeV. The hierarchic static and dynamic structure of the sample is shown to control the properties of the super-ionic conducting glass, CuI–Cu 2 MoO 4 .

High-Pressure Synthesis of a Novel PbFeO 3

A novel perovskite-type oxide PbFeO3 was successfully synthesized under a pressure as high as 7GPa, and the crystal structure, oxidation state, thermal stability, magnetic and dielectric properties were investigated. PbFeO3 possesses an orthorhombic perovskite unit cell and there is no phase transition between room temperature and 570 K. This compound decomposes into Pb2Fe2O5 in the vicinity of 740 K in air. According to XPS, it was found that this compound includes the Pb2+, Pb4+, and Fe3+ ions.

Phonon Confinement and Impurity Doping in Silicon Nanowires Synthesized by Laser Ablation

The effect of phonon confinement and impurity doping in silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The diameter of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs’ surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement. Boron doping was also performed during the growth of SiNWs. Local vibrational modes of boron (B) in silicon nanowires (SiNWs) synthesized by laser ablation were observed at about 618 and 640 cm–1 by Raman scattering measurements. Fano broadening due to coupling between discrete optical phonons and the continuum of interband hole excitations was also observed in the Si optical phonon peak. These results prove that B atoms were doped in the SiNWs.