Faculty Profiles - KISODA Kenji

Published Papers - KISODA Kenji

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Raman spectroscopic study of phase transitions in undoped morphotropic PbZr1-xTixO3

Marco Deluca, Hideo Fukumura, Nobuhiko Tonari, Claudio Capiani, Noriyuki Hasuike, Kenji Kisoda, Carmen Galassi, Hiroshi Harima

JOURNAL OF RAMAN SPECTROSCOPY ( WILEY-BLACKWELL ) 42 ( 3 ) 488 - 495 2011.03 [Refereed]

Several PbZr1-xTixO3 (PZT) compositions in the proximity of the morphotropic phase boundary (MPB) were examined by means of Raman spectroscopy in the 15-800 K temperature range. Previous studies performed by other researchers using various techniques evidenced that, in the phase diagram of PZT, areas with rhombohedral/monoclinic and tetragonal/monoclinic phases coexist across the MPB. For these compositions, either long-range or short-range symmetry ordering of the monoclinic phase should be considered, so that no true rhombohedral-monoclinic-tetragonal phase boundary exists. In addition, the onset of antiferrodistortive phase transitions between high-T and low-T perovskite phases has been predicted by ab initio calculations and experimentally reported. In the present work, low-T and high-T Raman scattering spectra were collected on undoped PbZr1-xTixO3 with compositions x = 0.42, 0.45, 0.465, 0.48 and 0.53 in an attempt to clarify the current open issues on the phase diagram of PZT. Spectra clearly belonging to the respective phases were observed in the rhombohedral, monoclinic and tetragonal areas, thus confirming that monoclinic ordering is long-range only for a narrow range of compositions. Raman measurements at cryogenic temperatures allowed detecting all predicted low-T phases, including the tetragonal one. These results are in good agreement with both ab initio calculations and experimental results obtained by other authors on the same compositions. Copyright (C) 2010 John Wiley & Sons, Ltd.

Low temperature synthesis of ZnO thin films by spin-coating technique

Noriyuki Hasuike, Tomoe Harada, Toru Kiyohara, Koji Nishio, Kenji Kisoda, Hiroshi Harima

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 2 ( WILEY-V C H VERLAG GMBH ) 8 ( 2 ) 2011 [Refereed]

ZnO thin films were prepared by sol-gel spin-coating method with thermal annealing in O-2 atmosphere. The annealing temperature was varied in the range of 150 degrees C to 550 degrees C. ZnO thin films with wurtzite structure were synthesized in all the samples. The sample annealed at low temperature showed the smooth surface morphology, and it gradually became rough with increase in annealing temperature. Finally, the sample had porous structure due to the aggregation of ZnO grain. As this result, the transmittance decreased in the visible region by annealing at high temperature. Furthermore, Raman analysis indicated that the lattice defects such as O vacancy could be suppressed by annealing at low temperature. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Fabrication of ZnO/Zn1-xMgxO heterostructure thin films by sol-gel spin-coating method

Hasuike Noriyuki, Kiyohara Toru, Harada Tomoe, Kisoda Kenji, Harima Hiroshi

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 2 ( WILEY-V C H VERLAG GMBH ) 8 ( 2 ) 2011 [Refereed]

ZnO/Zn0.85Mg0.15O heterostructure thin films were prepared by sol-gel spin-coating method on sapphire (0001) substrate with different thickness of ZnO layer. X-ray diffraction patterns showed that all the samples were preferentially oriented in [0001] direction with no phase separation. Optical transmission spectra showed the clear band-edge absorption of ZnO and Zn0.85Mg0.15O layer, and the thickness of each layer was roughly estimated. Also, two UV emission peaks originated from each layer at 3.2 eV and 3.55 eV were observed in photoluminescence measurement. And, the emission peak at 3.2 eV of ZnO layer shifted to higher energy side with decrease in the thickness of ZnO layer. This result indicates that Mg ions slightly diffused to the ZnO layer in several nanometers of ZnO/Zn0.85Mg0.15O interface by thermal treatment in growth process. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Few-layer epitaxial graphene grown on vicinal 6H-SiC studied by deep ultraviolet Raman spectroscopy

Kenji Kisoda, Susumu Kamoi, Noriyuki Hasuike, Hiroshi Harima, Kouhei Morita, Satoru Tanaka, Akihiro Hashimoto

APPLIED PHYSICS LETTERS ( AMER INST PHYSICS ) 97 ( 3 ) 033108 2010.07

Few layer epitaxial graphenes (1.8-3.0 layers) grown on vicinal 6H-SiC (0001) were characterized by deep ultraviolet Raman spectroscopy. Shallow penetration depth of the probe laser enabled us to observe G-peak of graphene without subtraction of the SiC substrate signal from observed spectra. The G-peak was greatly shifted to higher frequency compared to that of graphite due to in-plane compressive stress deriving from the substrate. The frequency shift decreased with the number of graphene layers because of stress relaxation from layer to layer. Our experiment suggests that the stress is completely relaxed within five to six graphene layers. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3466150]

Raman scattering characterization of basic solid state physics p-type AlGaN layers

Jung Gon Kim, Hiroaki Yamamoto, Yasuhito Kamei, Noriyuki Hasuike, Hiroshi Harima, Kenji Kisoda, Masaya Ishida, Katsuki Furukawa, Mototaka Taneya

Physica Status Solidi (B) Basic Research 247 ( 7 ) 1725 - 1727 2010.07 [Refereed]

Mg-doped AlxGa1-xN layers were characterized by micro- scopic Raman scattering to study the activation process of dopant by thermal annealing and behavior of H impurities. Two types of samples, a monolayer and a device-like (laser diode) structure, were prepared for this study. Local vibrational modes (LVMs) related to H and Mg were clearly observed in the monolayer sample. The LVMs evidenced activation of Mg in Ga site with the release of H. Electronic Raman signal due to free hole was also observed in the annealed sample. In the device-like structure sample, the Mg-doped AlxGa1-xN clading layer showed similar results, though the signal was weaker than the monolayer sample. Interactions with neighboring layers may have influenced the layer properties. Composition of Al in the AlxGa1-xN layer was also determined from phonon frequencies in both samples, and the result well agreed with that of X-ray diffraction analysis. © 2010 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

Deep UV Raman Spectroscopy of Epitaxial Graphenes on Vicinal 6H-SiC Substrates

S. Kamoi, N. Hasuike, K. Kisoda, H. Harima, K. Morita, S. Tanaka, A. Hashimoto

SILICON CARBIDE AND RELATED MATERIALS 2009, PTS 1 AND 2 ( TRANS TECH PUBLICATIONS LTD ) 645-648 611 - + 2010 [Refereed]

We report microscopic Raman scattering studies of epitaxial graphene grown on SiC substrates using a deep-ultraviolet (UV) laser excitation at 266 nm to elucidate the interaction between the graphene layer and the substrate. The samples were grown on the Si-face of vicinal 6H-SiC (0001) substrates by sublimation of Si from SiC. The G band of the epitaxial graphene layer was clearly observed without any data manipulation. Increasing the number of graphene layers, the peak frequency of the G-band decreases linearly, while the peak width and the intensity increase. The G-band frequency of the graphene layers on SiC is higher than those of exfoliated graphene, which has been ascribed to compression from the substrate.

Micro-Raman study of BiFeO<inf>3</inf> thin films fabricated by chemical solution deposition using different Bi/Fe ratio precursors

T. Nakamura, H. Fukumura, N. Hasuike, H. Harima, Y. Nakamura, K. Kisoda, S. Nakashima, M. Okuyama

Acta Physica Polonica A 116 ( 1 ) 72 - 74 2009.07 [Refereed]

Chiral Sum Frequency Spectroscopy of Thin Films of Porphyrin J-Aggregates

Tetsuhiko Nagahara, Kenji Kisoda, Hiroshi Harima, Misako Aida, Taka-aki Ishibashi

JOURNAL OF PHYSICAL CHEMISTRY B ( AMER CHEMICAL SOC ) 113 ( 15 ) 5098 - 5103 2009.04

Thin films of chiral porphyrin J-aggregates have been studied by vibrationally and electronically doubly resonant sum frequency generation (SFG) spectroscopy. It was revealed that the chiral supramolecular structures of porphyrin aggregates in solutions were retained in the thin film samples, and their chirality was determined by using chiral vibrational SFG spectroscopy. Electronic resonance profiles of some vibrational bands in achiral and chiral SFG were different from each other, and both were distinct from electronic absorption spectra. To account for these peculiar profiles, we have proposed interference effects of Raman tensor components in achiral and chiral SFG susceptibilities, which is analogous to that of resonance Raman scattering.

Structural and electronic properties of ZnO polycrystals doped with Co

N. Hasuike, K. Nishio, H. Katoh, A. Suzuki, T. Isshiki, K. Kisoda, H. Harima

JOURNAL OF PHYSICS-CONDENSED MATTER ( IOP PUBLISHING LTD ) 21 ( 6 ) 064215 (5pp) 2009.02

Zn(1-x)Co(x)O samples were prepared by a standard solid- state reaction method. Zn(1-x)Co(x)O crystals in the wurtzite structure were obtained with a Co composition of up to 22.1%. The a- and c-axis lengths increased and decreased, respectively, with an increase in Co composition. Raman spectra showed systematic broadening of the E(2) (high) phonon mode associated with the increase in Co composition, and electronic transitions of Co in the oxygen tetrahedron were observed in optical absorption measurement. These results indicated systematic substitution of Co into the Zn sites. Furthermore, an additional broad absorption band at 2.4-3.3 eV corresponding to the charge transfer (CT) process (Co(2+) -> Co(1+)) was also observed. The Raman spectra showed strong enhancement of the LO phonon due to a resonant Raman process induced with the coupling of the LO phonon and a photo-excited carriers mediated CT gap. These results suggest the possibility of carrier-induced ferromagnetism based on double exchange interaction in Zn(1-x)Co(x)O by visible light irradiation.

Raman scattering study of multiferroic Ho3Fe5O12 thin films

H. Fukumura, N. Tonari, N. Hasuike, H. Harima, K. Kisoda, T. Koide, M. Seki, H. Tabata

JOURNAL OF PHYSICS-CONDENSED MATTER ( IOP PUBLISHING LTD ) 21 ( 6 ) 064221 (5pp) 2009.02

Ho3Fe5O12 crystallizes in a body-centered cubic lattice and shows no ferroelectricity because of its highly symmetric (centrosymmetric) crystal structure. However, in heteroepitaxially grown thin films, Ho3Fe5O12 may exhibit ferroelectricity because of lattice strains induced by the substrate. In this work, heteroepitaxial films of Ho3Fe5O12 were grown with different thicknesses of 50-160 nm and studied by x-ray diffraction and Raman scattering. The results were compared with those of bulk polycrystals to characterize residual strains. At room temperature, Raman spectra of films revealed a phonon frequency shift from those of bulk samples, showing lattice distortion. There was a difference in the lattice distortion scheme between the thinner and thicker films. Results of x-ray diffraction were well correlated with the Raman data. Raman measurements at 300-800 K showed the existence of lattice strain up to similar to 650 K. This suggests a remanent-polarization character of Ho3Fe5O12 films up to this temperature. Closeness between the magnetic ordering temperature T-N = 567 K and T-C similar to 650 K may bring us the ideal multiferroic material with an enhanced magnetoelectric effect at room temperature.

Spin-phonon coupling in multiferroic YbMnO3 studied by Raman scattering

H. Fukumura, N. Hasuike, H. Harima, K. Kisoda, K. Fukae, T. Yoshimura, N. Fujimura

JOURNAL OF PHYSICS-CONDENSED MATTER ( IOP PUBLISHING LTD ) 21 ( 6 ) 064218 (5pp) 2009.02

Hexagonal YbMnO3 bulk polycrystals were prepared and studied by Raman scattering in the temperature range of 15-300 K. A total of 15 phonon modes of A(1), E-1 and E-2 type were identified. Some E-2 phonon modes showed anomalous temperature variations in frequency at T-N similar to 80 K, suggesting a coupling between the spin and phonon systems below T-N. As another evidence of spin-phonon coupling, softening of an A(1)-phonon mode for the O-Mn vibration was observed at similar to T-N. Substitution of Mn by Al suggests this view.

Synthesis of TiO2 nanocrystals controlled by means of the size of magnetic elements and the level of doping with them

H. Nakano, N. Hasuike, K. Kisoda, K. Nishio, T. Isshiki, H. Harima

JOURNAL OF PHYSICS-CONDENSED MATTER ( IOP PUBLISHING LTD ) 21 ( 6 ) 064214 2009.02

TiO2 nanocrystals were synthesized by a hydrolysis method combined with a thermal treatment. TiO2 nanocrystals with rutile and anatase structure were selectively synthesized by controlling the pH level in the precursor solution, and the crystallite size was controlled by changing the reaction temperature. Moreover, Co-doped TiO2 nanocrystals with rutile structure were also synthesized by means of the addition of Co to the precursor solution. Secondary phases such as Co precipitates and Co oxide were not present in the sample tested, with [Co] < 10 mol%. With an increase in the Co doping level, the Eg-phonon signal at 447 cm(-1) was broadened and shifted to a lower frequency, indicating the incorporation of Co into the rutile TiO2 host lattice and lattice expansion. Optical absorption spectra showed that the absorption edge at similar to 3.0 eV corresponded to the band gap of rutile TiO2 and shifted to the lower energy side upon Co doping. These results indicated the possibility of band gap engineering of rutile TiO2 via Co doping. On the other hand, the charge transfer gap between O 2p and Co 3d orbitals was also observed for samples with Co, suggesting the possibility of photo- induced magnetism in rutile TiO2 nanocrystals, obtained by visible light irradiation.

Structural and electronic properties of Co-doped ZnO nanocrystals synthesized by co-precipitation method

Noriyuki Hasuike, Koji Nishio, Toshiyuki Isshiki, Kenji Kisoda, Hiroshi Harima

PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 6, NO 1 ( WILEY-V C H VERLAG GMBH ) 6 ( 1 ) 213 - + 2009

ZnO nanocrystals doped with Co were synthesized by co-precipitation method combined with post-thermal treatment. The synthesized crystals formed high-quality wurtzite ZnO crystal lattice with the dimension about 10 nm, substituting Co ions into Zn sites in the composition range of [Co] < 3.0%. The position of Co2+/1+ charge transfer (CT) level composed by O 2p and Co 3d orbitals was observed at 3.0 eV by optical absorption measurements. Raman spectra showed the enhancement of LO phonon due to resonant Raman effect caused by photo-excitation of free carriers mediated the CT level. And, Photoluminescence spectra showed UV emission at similar to 3.3 eV suppressed and shifted to higher energy side with increase in Co doping level, indicating increase in nonradiative recombination centers and the possibility of band-gap engineering in Zn1-xCoxO nanocrystals, respectively. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Raman Scattering Study of Stress Distribution around Dislocation in SiC

D. Matsuoka, H. Yamamoto, S. Nishino, N. Hasuike, K. Kisoda, H. Harima

SILICON CARBIDE AND RELATED MATERIALS 2007, PTS 1 AND 2 ( TRANS TECH PUBLICATIONS LTD ) 600-603 337 - + 2009

We have presented a combined method of microscopic measurements between Raman scattering and polarizing optical microscope to characterize inhomogeneous residual stress distributions around dislocations in 4H- and 6H-SiC wafers. First, stressed portions were found in wafers by an optical polarizing microscope under a crossed Nicole arrangement. Then, the portions were examined by Raman-imaging technique for lateral variations of phonon spectra. The residual stresses were quantified from the phonon-peak frequency shift using a known frequency-shift rate for 6H-SiC. Characterization to the depth direction was also conducted by surface etching with molten KOH. The stresses typically amounted to the order of 100 MPa. In a 4H-SiC homoepitaxial wafer sample, we observed threading dislocations transferred from the substrate to the epitaxial layer, and found that larger stress fields existed in the epitaxial layer than the substrate. We also observed stress distributions around compressively stressed sub-grain boundaries.

Effective catalyst on SiO2 in ethanol CVD for growth of single-walled carbon nanotubes

Toshiya Murakami, Yuki Hasebe, Kenji Kisoda, Koji Nishio, Toshiyuki Isshiki, Hiroshi Harima

DIAMOND AND RELATED MATERIALS ( ELSEVIER SCIENCE SA ) 17 ( 7-10 ) 1467 - 1470 2008.07

We have compared catalytic activity of Co and Fe in a growth process of single-walled carbon nanotube (SWNT) by chemical vapor deposition using ethanol as a carbon source and SiO2 as a catalyst-supporting material. Changes of the catalyst precursors (Co- and Fe acetate) in the growth process were carefully observed at three different stages: (i) after oxidation in air at 400 degrees C but before heating to the growth temperature (800 degrees C), (ii) after heating to the growth temperature in flowing Ar and H-2 but before starting the nanotube growth and (iii) after the growth process is over. During the growth of SWNT, the Co catalyst took the form of beta-Co, resulting in a high yield growth. On the contrary, the Fe catalyst formed a silicate, Fe2SiO4, showing a poor catalytic ability. Our result shows that chemical reactions between the catalyst precursors and their supporting materials sensitively affect the catalytic ability. (c) 2008 Elsevier B. V. All rights reserved.

Studies on the growth of pure double-walled carbon nanotube and its phonon spectra

Toshiya Murakami, Kazuyo Matsumoto, Kenji Kisoda, Ryoji Naito, Koji Nishio, Toshiyuki Isshiki, Hiroshi Harima

JOURNAL OF APPLIED PHYSICS ( AMER INST PHYSICS ) 103 ( 11 ) 114305 2008.06

Double-walled carbon nanotubes (DWCNTs) with a purity higher than 99% were synthesized by chemical vapor deposition, and their Raman spectra were observed at different excitation wavelengths lambda(ex). The spectra had a unique feature compared with single-walled carbon nanotubes (SWCNTs): the G-band shape was distinctly different from that of SWCNTs and showed a clear lambda(ex) dependence. The pure DWCNT samples showed complex radial breathing modes (RBM) spectra. The mode peaks were unambiguously classified into those for the inner and outer tubes by applying a simple analytic model considering the interwall interaction. After isolation treatment of the pure bundled samples, we observed RBM signals of DWCNTs having an identical inner tube with different outer tubes. The peculiar behavior of the G-band shape was interpreted by resonance enhancement of the outer tube. (C) 2008 American Institute of Physics.

Structural change of single-walled carbon nanotube induced by soft X-ray irradiation

Chihiro Itoh, Katsuya Uotome, Kenji Kisoda, Toshiya Murakami, Hiroshi Harima

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS ( ELSEVIER SCIENCE BV ) 266 ( 12-13 ) 2772 - 2775 2008.06

Single-walled carbon nanotubes (SWNTs) grown on Si(100) were irradiated with X-ray having the spectrum with a peak at 277 eV. We measured Raman scattering spectra of the samples before and after the irradiation at various fluences and found that the relative intensity of the defect-related band, D band, to the band of the tangential shear modes of the carbon atoms in a graphene sheet, G band, was enhanced by the irradiation. The fluence dependence of this intensity ratio, DIG, took a peak around the fluence of 7 x 10(13) cm(-2). Further X-ray irradiation reduced the DIG to around half of the maximum. Detail inspection of the low frequency Raman spectra revealed that the radial breathing modes of the SWNTs were modified by the irradiation. The result suggests that the X-ray irradiation gives rise to not only defect formation but also modification of the SWNT structure. (c) 2008 Elsevier B.V. All rights reserved.

Simultaneous observation of single-walled carbon nanotubes and catalyst particles on SiO2 substrate by transmission electron microscopy

Toshiya Murakami, Yuki Hasebe, Kengo Higashi, Kenji Kisoda, Koji Nishio, Toshiyuki Isshiki, Hiroshi Harima

JAPANESE JOURNAL OF APPLIED PHYSICS ( JAPAN SOC APPLIED PHYSICS ) 47 ( 1 ) 730 - 734 2008.01

Single-walled carbon nanotubes (SWNTs) were grown by catalytic chemical vapor deposition on SiO2 substrates. By thinning the substrate before growth, the morphologies of the SWNTs and their seed catalyst particles were simultaneously observed in the as-grown state by plan-view transmission electron microscopy (TEM). Analysis over a wide area of the substrate showed that the diameters of the SWNTs d and those of the catalyst particles D had different distributions. The catalytic activity was size-dependent: fine particles (D less than or similar to 4 nm) yielded the same diameter SWNTs (d similar to D), and intermediate sizes (similar to 4 < D less than or similar to 6 nm) yielded finer tubes (d < D), while larger particles (D greater than or similar to 6 nm) had no catalytic activity. We also found that the small catalyst particles with D of less than 5 nm that appeared during the growth process by chemical reactions with the carbon source mainly contributed to the growth of SWNTs.

Structural properties of nanometre-sized ZnO crystals doped with Co

N. Hasuike, R. Deguchi, H. Katoh, K. Kisoda, K. Nishio, T. Isshiki, H. Harima

JOURNAL OF PHYSICS-CONDENSED MATTER ( IOP PUBLISHING LTD ) 19 ( 36 ) 365223(8pages) 2007.09

Nanometre-sized ZnO crystals doped with Co were synthesized by a co-precipitation method combined with a thermal treatment. By changing the reaction temperature, we can control the crystallite size from roughly 10 nm particles to 20 nm x 200 nm nm rods grown along the hexagonal c-direction. X-ray diffraction and Raman scattering showed growth of high-quality wurtzite ZnO crystals incorporating Co systematically in the ZnO host lattice in the tested range of [ Co] < 3.0 mol%. Electronic transitions of Co in the oxygen tetrahedron were also observed in optical absorption, giving supporting evidence for systematic substitution of Co into the Zn site.

Observation of phonons in multiferroic BiFeO3 single crystals by Raman scattering

H. Fukumura, S. Matsui, H. Harima, T. Takahashi, T. Itoh, K. Kisoda, M. Tamada, Y. Noguchi, M. Miyayama

JOURNAL OF PHYSICS-CONDENSED MATTER ( IOP PUBLISHING LTD ) 19 ( 36 ) 365224(7pages) 2007.09

We have grown BiFeO3 bulk single crystals by a flux method and characterized the phonon spectra in detail by Raman scattering in the temperature range 4-1100 K. All the 13 Raman-active phonon modes predicted by group theory, 4A(1) + 9E, were observed at low temperature and successfully assigned by a polarized Raman measurement. Moreover, drastic spectral changes in the Raman spectra were observed at temperatures 600-700 K and 1000-1100 K. These features are discussed from the viewpoint of phonon coupling with the magnetic ordering and the structural phase transition, respectively.

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