Published Papers - KISODA Kenji

Raman scattering studies on multiferroic YMnO3

H. Fukumura, S. Matsui, H. Harima, K. Kisoda, T. Takahashi, T. Yoshimura, N. Fujimura

JOURNAL OF PHYSICS-CONDENSED MATTER ( IOP PUBLISHING LTD )  19 ( 36 ) 365239(9pages)   2007.09

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YMnO3 is a multiferroic material in which ferroelectric and antiferromagnetic ordering can coexist. We have studied a YMnO3 bulk crystal in detail by Raman scattering in a wide temperature range of 15-1200 K, with comparison to a previous experiment at room temperature and a theoretical prediction for Raman- active phonon modes. In the low- temperature ferroelectric phase, the observed phonon spectra showed anomalous temperature variation at the Neel temperature, T-N similar to 80 K, suggesting a coupling between the spin and phonon systems below T-N. Furthermore, spectra for the high- temperature paraelectric phase, reported here for the first time, showed a sudden change at the Curie temperature T-C > 900 K, suggesting an abrupt structural phase change from the ferroelectric to the paraelectric phase.

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Raman and photoluminescence from dispersed single walled carbon nanotubes

T. Murakami, K. Kisoda, T. Tokuda, K. Matsumoto, H. Harima, K. Mitikami, T. Isshiki

DIAMOND AND RELATED MATERIALS ( ELSEVIER SCIENCE SA )  16 ( 4-7 ) 1192 - 1194   2007.04

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We have grown single walled carbon nanotubes (SWNTs) by catalytic chemical vapor deposition and optically characterized them after dispersing in an aqueous solution with centrifugal purification. Defect-induced band observed in Raman spectra drastically decreased in intensity after the centrifugal process, showing a good separation of by-products such as defective nanotubes and amorphous carbons. Radial breathing modes of the dispersed SWNTs showed frequency up-shift by 2-3 cm(-1) from those of bundled SWNTs as an evidence of isolation. The effect of inter-tube interaction on the electronic transition energy was traced by time-resolved PL measurement. The effect of aggregation process was much smaller than that estimated previously for bundling. It suggests that the aggregated samples are still well dispersed like those in aqueous solution. (c) 2007 Elsevier B.V All rights reserved.

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Synthesis and Raman study of double-walled carbon nanotubes

Kazuyo Matsumoto, Toshiya Murakami, Toshiyuki Isshiki, Kenji Kisoda, Hiroshi Harima

DIAMOND AND RELATED MATERIALS ( ELSEVIER SCIENCE SA )  16 ( 4-7 ) 1188 - 1191   2007.04

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Almost 100% pure double-walled carbon nanotube (DWNT) was successfully synthesized by optimizing the catalyst composition of Co/Fe/ Mo in a chemical vapor deposition (CVD) growth system with a post-growth purification process. The Raman scattering spectra of the product showed characteristic features of DWNT. The radial breathing modes were analyzed well by a simple analytic model considering the interwall interaction. (c) 2006 Elsevier B.V All rights reserved.

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Raman scattering study of multiferroic BiFeO3 single crystal

H. Fukumura, H. Harima, K. Kisoda, M. Tamada, Y. Noguchi, M. Miyayama

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS ( ELSEVIER SCIENCE BV )  310 ( 2 ) E367 - E369   2007.03

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Raman scattering spectra of bulk BiFeO3 single crystals have been measured in the temperature range of 4-1200 K. All Raman active phonon modes predicted by the group theory were observed at 4 K and assigned by a polarized measurement. Moreover, we have found drastic changes of Raman spectra at 600-700 and 1000-1100 K. These changes were discussed in combination with magnetic ordering and structural phase transition. (c) 2006 Elsevier B.V. All rights reserved.

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Spin-coupled phonons in multiferroic YbMnO3 epitaxial films by Raman scattering

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

12TH INTERNATIONAL CONFERENCE ON PHONON SCATTERING IN CONDENSED MATTER (PHONONS 2007) ( IOP PUBLISHING LTD )  92   012126(4pages)   2007

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YbMnO3 epitaxial thin films were investigated by Raman scattering in the temperature range of 15-300K. We successfully observed some phonon modes (5A(1)+6E(2)) at 15K with mode assignment based on polarized Raman study. Furthermore, an E-2 mode at 253 cm(-1) which affected Mn-O-Mn bond angles showed anomalous temperature variation in frequency at temperature below similar to 80K. It suggested a spin-phonon coupling that occurred below T-N.

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Temperature measurement of GaN-based blue-violet laser diodes in operation by Raman microprobe

Kenji Takahashi, Daisuke Matsuoka, Hiroshi Harima, Kenji Kisoda, Yuhzoh Tsuda, Takayuki Yuasa, Mototaka Taneya

PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4 NO 7 2007 ( WILEY-V C H VERLAG GMBH )  4 ( 7 ) 2802 - +   2007

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Blue-violet GaN-based laser diodes have been characterized by microscopic Raman scattering to obtain temperature distributions in the chip during operation. The local temperature increased steeply in the vicinity of the light-emitting layer at distance < similar to 20 pun. At injection current I = 120 mA with laser output of 150 mW, the local temperature at the light emitting layer was about 50 degrees C higher than that of the chip mount, 25 degrees C.

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Catalytic mechanism of a Fe-Co bimetallic system for efficient growth of single-walled carbon nanotubes on Si/SiO2 substrates

Toshiya Murakami, Kazuya Mitikami, Satoru Ishigaki, Kazuyo Matsumoto, Koji Nishio, Toshiyuki Isshiki, Hiroshi Harima, Kenji Kisoda

JOURNAL OF APPLIED PHYSICS ( AMER INST PHYSICS )  100 ( 9 ) 094303(4pages)   2006.11

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Single-walled carbon nanotubes (SWCNTs)were grown on Si/SiO2 substrates by catalytic chemical vapor deposition using ethanol as a carbon source. We found that a bimetallic catalyst, Fe-Co, worked efficiently in growing SWCNTs in contrast to Fe or Co catalyst only. The underlying mechanism was carefully studied by observing the catalyst-substrate interactions by transmission electron microscopy. It is shown that preferential diffusion of Fe into a SiO2 layer occurs in the bimetallic case, which suppresses aggregation of nanometer-sized Co particles that play key roles in growing SWCNTs. (c) 2006 American Institute of Physics.

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Influence of the growth morphology of single-walled carbon nanotubes on gas sensing performance

W. Wongwiriyapan, S. Honda, H. Konishi, T. Mizuta, T. Ohmori, Y. Kishimoto, T. Ito, T. Maekawa, K. Suzuki, H. Ishikawa, T. Murakami, K. Kisoda, H. Harima, K. Oura, M. Katayama

Nanotechnology   17 ( 17 ) 4424 - 4430   2006.08  [Refereed]

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We investigated the impact of the growth morphology of single-walled carbon nanotubes (SWNTs) on gas sensing performance. An SWNT film was directly synthesized on alumina substrate by thermal chemical vapour deposition. Different morphologies of the SWNTs in terms of density, diameter distribution and orientation were obtained by varying the growth temperature. Vertically aligned SWNTs with a high density were grown at 750°C, while horizontally lying SWNT networks with a low density were grown in the temperature range 800-950°C. The sensor response of the resultant SWNTs to NO2 was characterized at room temperature. It was found that the density of SWNTs strongly dominates sensor performance
the SWNT networks with the lowest density exhibited the highest sensor sensitivity. This was evidenced by characterization of density-controlled SWNTs synthesized using different thicknesses of an Fe/Al multilayer catalyst. The high sensor sensitivity for low-density SWNT networks is likely to be attributed to suppression of the formation of SWNT bundles and reduction of narrow-band-gap conduction paths, resulting in the enhancement of the adsorption probability and chemical gating efficiency of gas molecules on SWNTs. © IOP Publishing Ltd.

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Direct growth of single-walled carbon nanotubes on W tip apex

Winadda Wongwiriyapan, Shin-Ichi Honda, Tomoaki Mizuta, Takafumi Ohmori, Toshiya Murakami, Kenji Kisoda, Hiroshi Harima, Jung-Goo Lee, Hirotaro Mori, Kenjiro Oura, Mitsuhiro Katayama

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers   45 ( 3 A ) 1880 - 1882   2006.03  [Refereed]

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We demonstrated the direct growth of single-walled carbon nanotubes (SWNTs) on a W tip by Fe/Al catalyst-assisted chemical vapor deposition (CVD). A high-purity network of SWNTs with diameters of 0.9-3.7 nm was grown on the W tip. Under optimum CVD conditions, the growth of isolated SWNTs protruding from the W tip apex was achieved. We found that the circumference of the tip region affected the morphology of the resultant SWNTs. The direct growth method provides a potential application of SWNTs to a novel tip for scanning tunnelling microscopy (STM). © 2006 The Japan Society of Applied Physics.

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Raman study on the process of Si advanced integrated circuits

S. Nishibe, T. Sasaki, H. Harima, K. Kisoda, T. Yamazaki, W. S. Yoo

14th IEEE International Conference on Advanced Thermal Processing of Semiconductors, RTP 2006     211 - 215   2006  [Refereed]

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Precise control of fabrication processing is a key point for future integration technology of Si devices. Reliable characterization of Si wafers at each fabrication process is indispensable. Raman scattering has high-potential as a technique for non-contact and nondestructive characterization which yields valuable information on Si-based materials. Here, a patterned Si wafer for a modern electronic device is characterized by Raman microprobe to study the effect of different processes on residual stress, as well as other physical aspects. © 2006 IEEE.

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Raman scattering from In0.2Ga0.8N/GaN superlattices

Kenji Kisoda, Kohji Hirakura, Hiroshi Harima

PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 3, NO 6 ( WILEY-VCH, INC )  3 ( 6 ) 1997 - 2000   2006

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We have performed Raman scattering experiments on high quality In0.2Ga0.8N/GaN superlattices(SLs). The A(1) LO phonon mode from the In0.2Ga0.8N layer was observed in the Mg doped SL. This was attributable to manifestation of a resonance enhancement via acceptor levels formed by magnesium doping. The peak frequency of the A, LO mode shifted to high frequency side with the excitation energy. The frequency shift suggested that the composition of indium was fluctuated along the growth direction in the InGaN layer. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Direct growth of single-walled carbon nanotube networks on alumina substrate: A novel route to ultrasensitive gas sensor fabrication

Winadda Wongwiriyapan, Shin-Ichi Honda, Hirofumi Konishi, Tomoaki Mizuta, Takafumi Ohmori, Tatsuya Ito, Toru Maekawa, Kengo Suzuki, Hiroshi Ishikawa, Toshiya Murakami, Kenji Kisoda, Hiroshi Harima, Kenjiro Oura, Mitsuhiro Katayama

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers   44 ( 11 ) 8227 - 8230   2005.11  [Refereed]

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We explored structural and electrical properties of single-walled carbon nanotube (SWNT) networks directly grown on alumina substrates. The netlike SWNTs were uniformly grown on the substrate at a high quality. From the Raman spectroscopy analysis it was found that the as-grown SWNT networks were a mixture of metallic and semiconducting SWNTs, while the SWNT networks after their electrical breakdown exhibited a predominance of the semiconducting property. The direct growth method and subsequent electrical breakdown facilitated high-throughput production of practical ultrasensitive sensors for pollutant gases with a high sensitivity, which was demonstrated by NO 2 detection. © 2005 The Japan Society of Applied Physics.

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Growth of single-walled carbon nanotubes rooted from Fe/Al nanoparticle array

W Wongwiriyapan, M Katayama, T Ikuno, N Yamauchi, T Mizuta, T Murakami, S Honda, K Oura, K Kisoda, H Harima

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS ( JAPAN SOC APPLIED PHYSICS )  44 ( 1A ) 457 - 460   2005.01

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We explored the growth of single-walled carbon nanotubes (SWNTs) from nanoparticle array made of an Fe/Al multilayer catalyst by thermal chemical vapor deposition. Fe nanoparticles with a high number density and a narrow size distribution (1-5 nm) were efficiently formed by annealing the Fe/Al thin layer, resulting in the high-yield growth of SWNTs. Moreover, it was found that isolated SWNTs are rooted from patterned Fe/Al islands. The SWNTs bridged between electrodes exhibited semiconducting and metallic properties.

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Raman scattering studies on ZnO doped with Ga and N (codoping), and magnetic impurities

N Hasuike, H Fukumura, H Harima, K Kisoda, H Matsui, H Saeki, H Tabata

JOURNAL OF PHYSICS-CONDENSED MATTER ( IOP PUBLISHING LTD )  16 ( 48 ) S5807 - S5810   2004.12

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ZnO layers doped simultaneously with Ga and N (codoping), and magnetic elements (V, Co) were characterized by Raman scattering to study their structural stability. Five impurity modes were observed in range 200-900 cm(-1) in the doped samples, and showed characteristic variation with the doping level. It is shown that these modes can be used as a good measure of lattice defects induced by doping. The Raman spectra showed that the magnetic elements were incorporated up to 5 mol% without serious deterioration in crystallinity.

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Optical studies on GaN-based spintronics materials

N Hasuike, H Fukumura, H Harima, K Kisoda, M Hashimoto, YK Zhou, H Asahi

JOURNAL OF PHYSICS-CONDENSED MATTER ( IOP PUBLISHING LTD )  16 ( 48 ) S5811 - S5814   2004.12

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Structural properties of GaN layers doped with magnetic impurities (Mn, Cr) were investigated by Raman scattering. In the case of Mn-doping, an impurity mode was observed at around 585 cm(-1) with concentrations of Mn up to 1-2%. This mode was assigned to a local vibrational mode of Mn substituting the Ga site, and interpreted as spectral evidence of a uniform solid solution in the samples. For Cr-doping, good crystalline quality was also confirmed up to [Cr] = 3-5%. Cr is more miscible in GaN than Mn. Resonance enhancement of LO phonon signal was observed in GaCrN layers when excited by a deep UV laser at 266 nm (4.7 eV). This indicates generation of photo-carriers.

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Raman study of SWNTs grown by CCVD method on SiC

T Murakami, T Sako, H Harima, K Kisoda, K Mitikami, T Isshiki

THIN SOLID FILMS ( ELSEVIER SCIENCE SA )  464   319 - 322   2004.10

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Single-walled carbon nanotubes (SWNTs) were grown on both the Si- and C-faces of a 6H-SiC substrate by catalytic chemical vapor deposition (CCVD) using ethanol as the carbon source. Raman scattering measurements showed that uniform SWNTs grew on the Si face. Furthermore, SWNTs grown on the Si face showed larger intensity ratio of G-band to D-band (G/D ratio) than those grown on the C face. These results mean that growth of high quality SWNTs is promoted on the Si face in SiC substrates. This is probably attributed to the more reactive nature of the C face with the catalyst compared to the Si face. (C) 2004 Elsevier B.V. All rights reserved.

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Ohmic contact formation on p-type GaN using Pd/Mo electrode without alloying process

E Kurimoto, M Hangyo, H Harima, K Takatani, M Ishida, M Taneya, K Kisoda

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS ( JAPAN SOC APPLIED PHYSICS )  43 ( 10 ) 6988 - 6991   2004.10  [Refereed]

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Ohmic contact formation on a p-GaN layer with a specific contact resistance of rho(c) = 5 x 10(-4) Omegacm(2) has been achieved using a Pd/Mo electrode without the use of an alloying process. rho(c) was reduced to 2 x 10(-4) Omegacm(2) by annealing in vacuum at 500degreesC. The Pd/Mo electrode showed much improved ohmic-contact characteristics than the Ni/Mo electrode. Characterization by micro-Raman scattering revealed that the hole concentration increased in the p-GaN layer just under the Pd/Mo electrode with increasing annealing temperature. This cannot be explained by the removal of hydrogen. A decrease in the density of hole traps and an increase in the density of active acceptors, such as Ga vacancies, are considered to be the most significant contributing factors.

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Metal valence structures and magnetic interactions in halogen-bridged 1-D Ni-Pd mixed-metal complexes studied by C-13 and H-1 solid state NMR

N Kimura, A Josako, M Kano, K Kisoda, T Manabe, M Yamashita, R Ikeda

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN ( CHEMICAL SOC JAPAN )  77 ( 10 ) 1815 - 1819   2004.10

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C-13 NMR spectra at room temperature and the temperature dependences of H-1 T-1 in the solid state were measured in [Ni1-xPdxX(chxn)(2)]X-2 (X: Cl, Br; chxn: 1R,2R-cyclohexanedianline; 0.0 less than or equal to x less than or equal to 1.0), where anti ferromagnetically coupled paramagnetic -X-Ni3+-X-Ni3+-X- chains were formed at x = 0.00, while the mixed-valence -X-Pd2+-X-Pd4+-X- state was made at x = 1.00. C-13 signals at alpha-carbons in chxn coordinating to Pd atoms showed a doublet assignable to Pd2+ and Pd-4+ in x = 1.00, while, with a slight decrease of x from 1.00, a clear broadening and a shift to low-field of signals, indicating conversion into the averaged Pd3+ state, were observed. This can be explained by the fluctuation of the Pd valency caused by neighboring paramagnetic Ni3+ sites introduced in small amounts in the 1-D chain. The x dependences of the chemical shifts of beta- and gamma-carbons are also attributable to the effect from a partial mixing of the paramagnetic Pd3+ sites. The values of H-1 T-1 and its temperature dependence observed in the ranges of 100-300 K and x less than or equal to 0.13 for [Ni1-xPdxBr(chxn)(2)]Br-2 could be explained by a model of strong exchange interactions between Ni3+ and Pd3+ as well as Ni3+ sites. Gradual changes in the T-1 value and slope with increasing x from 0.00 to 0.93 are attributabte to the variation of the exchange interaction value, which depends upon the number of Ni-Ni pairs.

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Spectroscopic observation of oxidation process in InN

E Kurimoto, M Hangyo, H Harima, M Yoshimoto, T Yamaguchi, T Araki, Y Nanishi, K Kisoda

APPLIED PHYSICS LETTERS ( AMER INST PHYSICS )  84 ( 2 ) 212 - 214   2004.01

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Spectroscopic observations of high-quality wurtzite InN have shown that oxygen is easily incorporated in the crystal by thermal treatments in the air. Incorporation of oxygen may play a key role in determining the apparent properties of InN including the bandgap and the lattice constant. It is shown that Raman scattering is a sensitive tool to probe the oxygen incorporation process and associated deterioration in crystallinity. (C) 2004 American Institute of Physics.

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Anisotropy of electron mobility in n-type 15R-SiC studied by Raman scattering

E Kurimoto, M Hangyo, H Harima, K Kisoda, T Nishiguchi, S Nishino, S Nakashima, M Katsuno, N Ohtani

SILICON CARBIDE AND RELATED MATERIALS 2003, PRTS 1 AND 2 ( TRANS TECH PUBLICATIONS LTD )  457-460   621 - 624   2004  [Refereed]

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LO-phonon-plasmon coupled modes in n-type 15R-SiC bulk crystals with free carrier concentration of n = 10(16) similar to 10(18) cm(-3) were observed by Raman scattering. The axial-type mode for which the plasma oscillation and atomic displacements occur along the c-axis, and the planar-type mode for which these oscillations occur in the c- plane, were separately observed. A spectral line-shape analysis was done using three adjustable parameters for free carrier concentration, plasmon damping rate and phonon damping rate. Carrier mobilities parallel and perpendicular to the c-axis (mu(perpendicular to) and mu(ll), respectively) were evaluated from the results, showing a weak anisotropy mu(perpendicular to)/mu(ll) = 1.8 +/- 0.3. This result is in agreement with a previous Hall measurement, and is qualitatively similar to the case of n-type 6H-SiC.