Keiichi Kohama

THICKNESS DEPENDENCE OF THE EPITAXIAL STRUCTURE OF VANADYL PHTHALOCYANINE FILM

We have studied the thickness dependence of the crystal structure in vanadyl phthalocyanine (VOPc) films epitaxially grown on KBr(100) surface. Optical second-harmonic generation observed in oblique incidence increases nearly quadratically with film thickness up to at least 64 nm and saturates, indicating a structural change from an epitaxial polar VO orientation to a nonpolar bulk crystal structure. The latter was assigned to monoclinic structure based on X-ray diffraction. Optical absorption spectra in visible and infrared regions and scanning electron microscopy also show the structural difference between the films thicker and thinner than about 80 nm.

Domain boundary structures in lanthanum lithium titanates

Perovskite-type lanthanum lithium titanate (LLTO) is attracting extensive interest because of its high intrinsic ionic conductivity. The material exhibits a complex microstructure with domains of various sizes and orientations that vary with the lithium content. Based on a systematic examination of both Li-poor and Li-rich LLTO compounds using state-of-the-art scanning transmission electron microscopy (STEM), we reveal the structures and composition of the domain boundaries (DBs) and consider their effect on Li-ion mobility and ionic conductivity, in the process positing the origin of the microstructural variations. DBs in this material are shown to consist essentially of two types: frequently occurring 90° rotation DBs and a much less common antiphase-type boundary. It is found that the 90° DBs are coherent interfaces consisting of interconnected steps that share La sites, with occupancies of La sites higher than in the domain interiors. The origin of microstructural variations in the two compounds is associated with different degrees of lattice mismatch strain at DBs in Li-poor and Li-rich materials. The lattice strain and associated O vacancies, as well as the high La occupancies, at DBs are expected to result in lower interdomain Li-ion mobility, which will have a deleterious effect on the overall ion conductivity.

Solid-state solar cells consisting of polythiophene-porphyrin composite films

Sandwich-type solid-state solar cells using polythiophene-porphyrin composite films were fabricated. A spin-coated film of poly(3-dodecylthiophene) (P3DT) was fabricated on a gold electrode. Next, an electropolymerized polythiophene film was superimposed on the surface of the spin-coated P3DT film by electrochemical polymerization of bithiophene (BiTh) with repeated redox cycles in the 0–+2 V region. Then, tetrathienylporphyrin (TThP) was further assembled on the polythiophene-modified electrode by using the same electrochemical polymerization procedure (1 or 10 cycles), to obtain polythiophene-porphyrin-modified gold electrodes. Finally, an aluminum electrode was deposited on the polythiophene-porphyrin modified gold electrode by vacuum deposition, forming the sandwich-type solid-state solar cells. The morphological characterizations of the films were carried out by scanning electron microscopy. The thickness of the organic layer decreased from ~5 µm m to ~3 µm by performing TThP polymerization. The amount of porphyrin moiety in the composite film was larger for the modified electrode after 10 cycles of electrochemical TThP polymerization than for that after 1 cycle of TThP polymerization. The resultant photocurrent increased with scanning cycle of TThP polymerization in the 400–600 nm region. The combination of polythiophene and porphyrin in the electrochemically modified electrode is one of the useful systems for photocurrent generation.

Cation ordering in A-site-deficient Li-ion conducting perovskites La(1−x)/3LixNbO3

Cation-deficient perovskites exhibit complex local atomic arrangements which cannot be adequately described by average crystal structure models. By combining reciprocal-space electron diffraction analysis and direct observations of atom positions using state-of-the-art scanning transmission electron microscopy, we clarify the nature of the cation ordering within A-site-deficient perovskite single crystals of La(1−x)/3LixNbO3 (x = 0 and x = 0.04). Both materials are found to have complex modulated crystal structures with two types of A-cation ordering, namely a long-range layer ordering in alternate (001)p planes and a short-range (intra-domain) columnar ordering within La-rich (001)p layers. The columnar ordering (occupational modulation) produces modulated displacements of Nb and O atoms. It is also found that substitution of even a small amount of Li for La can affect significantly the columnar ordering, leading to a series of structural and microstructural changes that are likely to have a deleterious effect on the Li-ion conductivity of this material.

Facile Fabrication and Photocurrent Generation Properties of Electrochemically Polymerized Fullerene–Poly(ethylene dioxythiophene) Composite Films

Fullerene–poly(ethylene dioxythiophene) (polyEDOT) composite films consisting of 3,4-ethyeledioxythiophene (EDOT) and a thiophene derivative of C60 fullerene (ThC60) or C60 fullerene were fabricated on a transparent indium–tin-oxide (ITO) electrode by electrochemical polymerization of the electrolyte solution of ThC60 (or C60) and EDOT. Incorporation of the C60 fullerene moiety in the polythiophene film was strongly suggested from absorption spectra of the composite film. We have found a higher degree of incorporation of the C60 fullerene moiety into the ThC60–polyEDOT film, as compared with the C60–polyEDOT film. In the presence of methylviologen as an electron acceptor, the as-prepared C60–polyEDOT and ThC60–polyEDOT composite films generated stable cathodic photocurrents in the 400–700 nm region with broad peaks. The photocurrent intensity and the internal photon-to-current quantum efficiency of the ThC60–polyEDOT composite film were considerably larger than those of C60–polyEDOT and polyEDOT films. The thiophene unit of ThC60 was confirmed to be quite effective for a stable incorporation of the C60 fullerene moiety in the film and a higher photocurrent generation.

Atomic level changes during capacity fade in highly oriented thin films of cathode material LiCoPO4

High-quality thin films with well-defined fast lithium ion diffusion pathways and minimal structural discontinuities are needed to develop high-performance electrodes for all-solid-state Li-ion batteries. Achieving this requires an understanding of the electrochemical processes and structural changes that take place within an electrode during charge/discharge. Here we report the successful synthesis of highly oriented olivine-structured LiCoPO4 thin films by chemical solution deposition onto Au(111)/Al2O3(0001) substrates. State-of-the-art scanning transition electron microscopy (STEM) and theoretical simulations are used to examine surface structures and the changes that occur during electrochemical cycling. As-synthesised films are found to be composed of nearly defect-free domains that are predominantly aligned with (210), (010) or (101) surfaces parallel to the substrate. High-angle annular dark field (HAADF)-STEM revealed the formation of considerable numbers of cation exchange (antisite) defects in the surface regions after only three cycles. Upon further electrochemical cycling, significant capacity fade, together with an increase in the concentration of cation exchange defects, was observed. Electron energy loss spectroscopy (EELS) revealed that formation of these defects is associated with oxygen loss and deformation of PO4 tetrahedra, leading to structural degradation detrimental to the electrochemical performance of thin-film LiCoPO4 electrodes.

Dependence of Off-Diagonal Components of χ(3) on Substrate Temperature of Epitaxially Grown Vanadyl Phthalocyanine Films

Single-crystalline vanadyl phthalocyanine films have been grown by the molecular beam epitaxy technique. The normalized off-diagonal ratio 3χ1221/χ1111 has been determined by circular-polarization third-harmonic generation measurement. It is revealed that the single-crystalline phase with 4mm symmetry can be distinguished from the C∞υ polycrystalline phase by circular-polarization third-harmonic generation measurement, and the quality of the epitaxial film can be quantitatively analyzed by the normalized off-diagonal ratio of 3χ1221/χ1111.

Anisotropy of ionic conduction in single-crystal Li x La(1− x )/3NbO3 solid electrolyte grown by directional solidification

The anisotropy of ionic conduction in a solid electrolyte (Li x La(1− x )/3NbO3) was experimentally confirmed for the first time. Ionic conduction measurements were carried out on the (100), (010), (001), (110), (111), and (112) planes of single-crystal ingots of Li x La(1− x )/3NbO3 grown by directional solidification. We found that the ionic conductivity in Li x La(1− x )/3NbO3 with x = 0.08 was 3.6 × 10−4 S cm−1 in the [100] and [010] directions, approximately 10 times higher than that in the [001] direction. Such anisotropy of the ionic conduction is discussed with respect to the characteristic layered structure of Li x La(1− x )/3NbO3.

Fabrication and Photocurrent Properties of Fullerene-Polyethylenedioxythiophene Composite Films

Department of Materials Physics and Chemistry, Graduate School of Engineering, Kyushu University, 744, Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan Department of Applied Chemistry, Faculty of Engineering, Kyushu University, 744, Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan Phone: +81-92-802-2816 E-mail: t-akitcm@mbox.nc.kyushu-u.ac.jp Center for Future Chemistry, Kyushu University, 744, Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan Battery & Cells Div., Secondary Battery Lab. III, Toyota Central R&D Labs., Inc., Nagakute, Aichi 480-1192, Japan Motohiro Special Research Lab., Toyota Central R&D Labs., Inc., Nagakute, Aichi 480-1192, Japan Hybrid Vehicle Material Engineering Div., Toyota Motor Corporation, Shizuoka, 410-1193, Japan Material Engineering Div. III, Toyota Motor Corporation, Shizuoka, 410-1193, Japan

Dye Sensitization Effect on Photocurrent Generation of Porphyrin-Polythiophene Composite Films

1Department of Materials Physics and Chemistry, Graduate School of Engineering, Kyushu University, 744, Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan 2Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744, Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan Phone: +81-92-802-2816 E-mail: t-akitcm@mbox.nc.kyushu-u.ac.jp 3Materials Department, Toyota Central R&D Laboratories, Inc., Aichi, 480-1192, Japan 4Hybrid Vehicle Material Engineering Div., Toyota Motor Corporation, Shizuoka, 410-1193, Japan