Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

Division display 141 - 160 of about 355 ／ All the affair displays >>

Communication-In situ formation of anticorrosive Mg(OH)<inf>2</inf>/Carbon composite film on magnesium alloy by ascorbic acid-assisted hydrothermal process

Ishizaki T., Kamiyama N., Yamamoto E., Kumagai S., Sudare T., Saito N.

Journal of the Electrochemical Society Vol. 162 ( 14 ) page： C741 - C743 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the Electrochemical Society

An Mg(OH)2/carbon composite film was prepared on magnesium alloy AZ31 by an ascorbic acid (AA)-assisted hydrothermal method. All films were composed of crystalline brucite type Mg(OH)2. Film thickness decreased with an increase in the amount of AA added. X-ray photoelectron spectroscopy studies revealed that a peak component related to sp2-hybridized carbons contributed to improve film conductivity. Film resistivity decreased with an increase in C content. The film obtained from the aqueous solution containing 10 g/L of AA showed the lowest corrosion current density of all samples.

DOI： 10.1149/2.0351514jes

Direct deposition of gold nanoparticles on cellulose fiber by solution plasma process

Nemoto S., Watthanphanit A., Saito N.

Materials Research Society Symposium Proceedings Vol. 1723 page： 1 - 7 2015

From Cyano-aromatic Molecules to Nitrogen-doped Carbons by Solution Plasma for the Oxygen Reduction Reaction in Alkaline Medium

Panomsuwan G., Saito N., Ishizaki T.

Materials Today: Proceedings Vol. 2 ( 8 ) page： 4302 - 4308 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Today: Proceedings

Nitrogen-doped carbon nanoparticles (NCNPs) were synthesized by a solution plasma process followed by a thermal annealing at 900°C. Cyano-aromatic molecules, including cyanobenzene (C7H5N), 2-cyanopyridine (C6H4N2), and cyanopyrazine (C5H3N3), were used as single source precursors for the synthesis. The morphological features of NCNPs were governed by the aggregates and agglomerates of uniform nanosized particles (20-40nm). The structural analyses confirmed that NCNPs mainly exhibited a disordered amorphous carbon structure. The nitrogen doping contents determined from an X-ray photoelectron spectroscopy were found to be 0.58, 1.36, and 1.29 at% for NCNPs synthesized from cyanobenzene, 2-cyanopyridine, and cyanopyrazine, respectively. The improvements of oxygen reduction reaction activity and selectivity toward a four-electron pathway in an alkaline solution of NCNPs were correlated with the nitrogen doping content and nitrogen bonding state. The NCNPs also possessed excellent long-term durability and strong methanol tolerance in an alkaline solution compared to those of a commercial Pt/carbon catalyst.

DOI： 10.1016/j.matpr.2015.09.017

In situ solution plasma synthesis of mesoporous nanocarbon-supported bimetallic nanoparticles

Kang J., Saito N.

RSC Advances Vol. 5 ( 37 ) page： 29131 - 29134 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Herein, is reported a novel in situ one-step synthesis method of bimetallic nanoparticles (NPs) supported on carbon black, which can markedly prevent the aggregation and growth of NPs, resulting in a small particle size (average 5 nm), good dispersion, and high-electrocatalytic-activity. This journal is

DOI： 10.1039/c5ra04220h

Highly durable silica coated Pt/Cs with different surfactant types for proton exchange membrane fuel cell applications

Yaowarat W., Li O., Saito N.

RSC Advances Vol. 5 ( 55 ) page： 44258 - 44262 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Platinum supported on carbon Vulcan XC-72 (Pt/Cs) for application as a cathode in proton exchange membrane fuel cells (PEMFCs) was coated with silica layers by a sol-gel method with three types of surfactants with different charging properties. The three various types of surfactants (1) cationic surfactant (cetyltrimethylammonium bromide (CTAB)), (2) anionic surfactant (sodium dodecylbezenesulfonate (SDBS)), and (3) non-ionic surfactant (Pluronic 123 (P123)) were applied to prevent agglomeration of the Pt nanoparticles and prevent detachment of the Pt nanoparticles from the carbon supports during operation. The degree of improvement depended on the type of surfactant applied in the sol-gel method. The formation of silica layers by SDBS and P123 significantly improved the durability of the Pt/Cs catalysts under acid conditions. Silica coated Pt/Cs formed using SDBS and P123 showed improved durability after 500 cycles in a cyclic voltammetry test in 0.5 M sulfuric acid (H<inf>2</inf>SO<inf>4</inf>) by 27.3% and 22.7%, respectively.

DOI： 10.1039/c5ra03343h

Cellulose conversion to sugar alcohol by solution plasma processing

Watthanaphanit A., Lee H., Saito N.

Materials Research Society Symposium Proceedings Vol. 1745 page： 22 - 27 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

Cellulose was selectively converted to sugar alcohols (sorbitol and mannitol) over a supported-metal catalyst ruthenium on carbon (RuJC) by the application of plasma in cellulose aqueous suspension. Generally, conversion of cellulose to sugar alcohol should be done under H2 pressure and high temperature. The goal of using solution plasma process (SPP) in this study is to initiate "self-hydrogenation" by reactive hydrogen species generated from the plasma due to dissociation of water medium. The sugar alcohols were produced at room temperature and atmospheric pressure. Electrospray ionization mass spectrometric analysis indicates that the SPP is a potent tool to promote the conversion of cellulose to sugar alcohols.

DOI： 10.1557/opl.2015.787

A study on electron impact dissociative ionization of organosilicon precursors for plasma processing

Yun Y., Lee M., Inoue Y., Saito N., Takai O.

Journal of Nanoscience and Nanotechnology Vol. 14 ( 12 ) page： 9653 - 9656 2014.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Nanoscience and Nanotechnology

We discussed the electron impact dissociation behavior of the organosilicon molecules with methyl groups, based on the fragment pattern and molecular-orbital calculation of the bond dissociation energies for the molecules. From the calculation of bond dissociation energy of the organosilicon molecules, methyl groups, which bonded directly to the silicon atom, were found to have the weakest. Regarding the fragment patterns of the reactants investigated by a quadrupole mass spectrometer, the hexamethyldisiloxane was harder to dissociate than the trimethylmethoxysilane due to the strong Si-O bonding force, which also affected the dissociation in the plasma. From the above considerations, dissociation reactions by electron impact could be partly identified.

DOI： 10.1166/jnn.2014.10175

One-step facile synthesis of Pd nanoclusters supported on carbon and their electrochemical property

Shi J., Hu X., Zhang J., Tang W., Li H., Shen X., Saito N.

Progress in Natural Science: Materials International Vol. 24 ( 6 ) page： 593 - 598 2014.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Natural Science: Materials International

Well-crystallized Pd nanoclusters supported on Ketjen Black (KB) were successfully fabricated when Pd wires were served as an electrode pair by a solution plasma technique at atmospheric pressure. The synthesis of Pd nanoclusters was almost simultaneous with their dispersion on KB. Pd nanoclusters with the average diameter of about 2. nm were equably distributed on KB, and showed good electrochemical property corresponding to their obvious characteristic peaks. Multi-scan cyclic voltammetry and chronoamperometry clarified that as-prepared Pd nanoclusters have better electrochemical stability in alkaline solution than that of in acidic solution. Thus as-obtained Pd nanoclusters would become a promising electrocatalyst for fuel cells or Li-air batteries.

DOI： 10.1016/j.pnsc.2014.10.011

In situ solution plasma synthesis of nitrogen-doped carbon nanoparticles as metal-free electrocatalysts for the oxygen reduction reaction

Panomsuwan G., Chiba S., Kaneko Y., Saito N., Ishizaki T.

Journal of Materials Chemistry A Vol. 2 ( 43 ) page： 18677 - 18686 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Chemistry A

We report the in situ synthesis of nitrogen-doped carbon nanoparticles (NCNPs) by a solution plasma process without the addition of metal catalysts. Organic liquid mixtures of benzene and pyrazine were used as the precursors for the synthesis. The nitrogen-doping content can be easily controlled by changing the amount of pyrazine in the precursor. The NCNPs synthesized from the solution plasma process exhibit a turbostratic structure with highly uniform nanoscale particles. The nitrogen atoms can be homogeneously incorporated into the entire carbon structure due to the in situ doping during the growth and formation of the carbon particles. The electrochemical activity toward the oxygen reduction reaction (ORR) of the NCNPs in an alkaline medium reveals the improvement in terms of both the onset potential and current density as the nitrogen-doping content increases. The enhanced ORR activity of the NCNPS is mainly attributed to the presence of pyridinic-N and graphitic-N bonding configurations. They also possess long-term durability and excellent tolerance to methanol crossover effects. The results obtained in this study have demonstrated that the solution plasma process has great potential for the synthesis of metal-free nitrogen-doped carbon electrocatalysts for the ORR. We expect that this approach can be extended to the synthesis of other heteroatom-doped carbonaceous materials for a broad range of research applications in energy conversion and storage.

DOI： 10.1039/c4ta03010a

Solution plasma synthesis of nitrogen-doped carbon nanoballs as effective metal-free electrocatalysts for oxygen reduction reaction

Panomsuwan G., Chiba S., Saito N., Ishizaki T.

Prehospital and Disaster Medicine Vol. 1641 ( 4 ) 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Prehospital and Disaster Medicine

Nitrogen-doped carbons nanoballs were synthesized from an organic liquid precursor (a mixture of benzene and pyrazine) by solution plasma process. After synthesis, they were further annealed at 700 and 900 °C under N2 atmosphere. The nitrogen-doped carbon nanoballs before and after thermal annealing process exhibit a similar morphological feature, and their diameters are in the range between 20 and 40 nm. With higher annealing temperature, the graphitization of the nitrogen-doped carbon nanoballs increases. For the electrocatalytic activity in an alkaline solution, the limiting current density and onset potential for the ORR activity can be significantly improved for the samples after thermal annealing at 900 °C. We anticipate that solution plasma process will be a viable alternative way for synthesizing heteroatom-doped carbon electrocatalysts for broad application in the field of fuel cells, metal-air batteries, and supercapacitors.

DOI： 10.1557/opl.2014.319

Influence of the discharge time of solution plasma process on the formation of gold nanoparticles in alginate matrix

Watthanaphanit A., Heo Y.K., Saito N.

Journal of the Taiwan Institute of Chemical Engineers Vol. 45 ( 6 ) page： 3099 - 3103 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the Taiwan Institute of Chemical Engineers

Gold nanoparticles (AuNPs) stabilized in alginate matrix were synthesized by applying the plasma into alginate aqueous solution containing gold(III) chloride trihydrate precursor. Effect of the solution plasma process (SPP) discharge time on the physical properties, including shape and size, and the optical absorption properties of the synthesized AuNPs were investigated by varying the discharge times to be 0, 5, 10, 20 and 30. min. Results reveal that the increase in the discharge time leads to a size reduction of the AuNPs. Also, the particles tend to be more spherical. Appearance of the obtained AuNPs-alginate suspensions along with the change in their UV-vis absorption spectra intensity after samples were left standing for several time intervals suggest that alginate solution itself can act both as a stabilizer and a reducing agent for the AuNPs formation while the application of plasma helps to improve the controllability of shape and size of the synthesized particles. Furthermore, the method is simple, reproducible, and does not need any manipulative skill. Since the reducing agent is not required, the method is suitable for utilizing in biomedical application.

DOI： 10.1016/j.jtice.2014.09.001

Effect of growth temperature on structural and morphological evolution of epitaxial SrTiO<inf>3</inf> thin films grown on LaAlO<inf>3</inf> (001) substrates by ion beam sputter deposition

Panomsuwan G., Takai O., Saito N.

Vacuum Vol. 109 page： 175 - 179 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Vacuum

A series of epitaxial SrTiO3 (STO) thin films were grown on (001)-oriented LaAlO3 (LAO) substrates by ion beam sputter deposition (IBSD) at various growth temperatures in the range of 350-800 °C. Our results have shown that the growth temperature plays an essential role in influencing the structural and morphological evolution of the STO thin films. X-ray structural analysis demonstrates that the STO thin films are grown under in-plane compressive strain due to the effect of lattice mismatch. The out-of-plane lattice constant is found to decrease with increasing growth temperature. Atomic force microscopy observation reveals that the growth mode of STO thin films transforms from a three-dimensional island mode to a two-dimensional layer-by-layer mode at a sufficiently high growth temperature of 750 °C. We believe that high-quality epitaxial STO thin films with atomically flat surface prepared by IBSD in this study would be beneficial for the fabrication of perovskite STO-based superlattices. © 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.vacuum.2014.07.007

Hierarchical meso-macro structure porous carbon black as electrode materials in Li-air battery

Kang J., Li O.L., Saito N.

Journal of Power Sources Vol. 261 page： 156 - 161 2014.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Power Sources

A new class of hierarchical structure porous carbon black, carbon nanoballs (CNBs), was generated by solution plasma process (SPP) with benzene. The structural characterization revealed that CNBs have excellent meso-macro hierarchical pore structure, with an averaged diameter size of 14.5 nm and a total pore volume of 1.13 cm3 g-1. The CNBs are aggregated forming inter-connected pore channels in different directions on both the meso- and macrometer length scales. The discharge capacity of CNBs reached 3600 mAh g-1, which exceeded the capacity of Ketjen Black EC-600JD (a commercial carbon black with highest cell performance) by 30-40%. The excellent discharge capacity was contributed by the co-existence of high pore volume and meso-macro hierarchical porous structure. This new class carbon material exhibited higher discharge capacity compared to commercial porous carbon materials, and is possible to apply as the next generation of electrode materials in lithium-air (Li-air) battery. The structural and electrochemical properties accompanied with the synthesis mechanism of CNBs were discussed in details. © 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2014.03.072

Plasma-induced synthesis of CuO nanofibers and ZnO nanoflowers in water

Hu X., Zhang X., Shen X., Li H., Takai O., Saito N.

Plasma Chemistry and Plasma Processing Vol. 34 ( 5 ) page： 1129 - 1139 2014.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma Chemistry and Plasma Processing

Fiber-shaped cupric oxide (CuO) nanoparticles and flower-shaped ZnO nanoparticles were facilely synthesized by plasma-induced technique directly from copper and zinc electrode pair in water, respectively. The phase composition, morphologies and optical property of nanoparticles have been investigated by energy dispersive X-ray analysis, X-ray powder diffraction, transmission electron microscopy and UV-vis. The in situ analysis by an optical emission spectroscopy clarified the formation mechanism. Plasma was generated from the discharge between a metal electrode pair in water by a pulse direct current power. CuO and ZnO nanoparticles were synthesized via almost the same formation mechanism, which were prepared via the rapid energetic radicals' bombardment to electrodes' surface, atom vapour diffusion, plasma expansion, solution medium condensation, and in situ oxygen reaction and further growth. This novel plasma-induced technique will become a potential application in nanomaterials synthesis. © 2014 Springer Science+Business Media New York.

DOI： 10.1007/s11090-014-9546-0

X-ray analysis of strain distribution in two-step grown epitaxial SrTiO<inf>3</inf> thin films

Panomsuwan G., Takai O., Saito N.

Applied Physics Letters Vol. 105 ( 5 ) 2014.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Epitaxial SrTiO3 (STO) thin films were grown on (001)-oriented LaAlO3 (LAO) substrates using a two-step growth method by ion beam sputter deposition. An STO buffer layer was initially grown on the LAO substrate at a low temperature of 150°C prior to growing the STO main layer at 750°C. The thickness of the STO buffer layer was varied at 3, 6, and 10nm, while the total film thickness was kept constant at approximately 110nm. According to x-ray structural analysis, we show that the STO buffer layer plays an essential role in controlling the strain in the STO layer grown subsequently. It is found that the strains in the STO films are more relaxed with an increase in buffer layer thickness. Moreover, the strain distribution in two-step grown STO films becomes more homogeneous across the film thickness when compared to that in directly grown STO film. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4892827

Controlled crystalline orientation of SrTiO<inf>3</inf> thin films grown on Pt(1 1 1)/Ti/α-Al<inf>2</inf>O<inf>3</inf>(0 0 0 1) substrates: Effect of growth temperature and Ti layer thickness

Panomsuwan G., Takai O., Saito N.

Applied Surface Science Vol. 309 page： 95 - 105 2014.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

SrTiO3 (STO) thin films were grown on Pt(1 1 1)/Ti/α-Al2O3(0 0 0 1) substrates by ion beam sputter deposition. Growth temperature was varied between 600 and 750 °C, while Ti layer thickness was adjusted from 3 to 36 nm. Experimental results demonstrate that both the crystalline orientation and surface morphology are significantly dependent on change in the growth temperature and Ti layer thickness. From X-ray structural analysis, the STO thin films grown at 600 °C are perfectly (1 1 0)-oriented in spite of the change in Ti layer thickness. The STO thin films with a perfect (1 1 1) orientation are achievable at a sufficiently high growth temperature (≥700 °C) and a thin Ti layer (3-6 nm). Each crystalline orientation of STO thin films has a specific in-plane orientation relationship with respect to the Pt(1 1 1) layer. Flat-, rod-, and triangle-shaped grains are clearly observed from atomic force microscopy investigation, which are associated with the (1 1 0)-, (1 0 0)-, and (1 1 1)-oriented grains, respectively. Their grain orientations also show a good correlation with the X-ray structural analysis. The growth mechanism of each crystalline orientation can be described in term of surface diffusion, surface energy anisotropy, electrostatic, and role of TiOx seeds. © 2014 Elsevier B.V.

DOI： 10.1016/j.apsusc.2014.04.186

The role of the central Fe atom in the N<inf>4</inf>-macrocyclic structure for the enhancement of oxygen reduction reaction in a heteroatom nitrogen-carbon nanosphere

Kim D.W., Li O.L., Saito N.

Physical Chemistry Chemical Physics Vol. 16 ( 28 ) page： 14905 - 14911 2014.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

In the present work, we demonstrated the significance of a central transition metal, Fe, in a N4-macrocycle for the enhancement of ORR activity and other electrochemical properties. The catalysts were synthesized by a solution plasma process. Fe-phthalocyanine/benzene and phthalocyanine/benzene were chosen as the precursors of Fe-phthalocyanine based mesoporous carbon (FP-MCS) and phthalocyanine based mesoporous carbon (P-MCS) catalysts, respectively. The existence of Fe-N4 and N4 macrocyclic structures was confirmed by X-ray photoelectron spectroscopy. From the chemical bonding structure, FP-MCS demonstrated that the Me-N peaks increased as the amount of iron-phthalocyanine introduced in the experiment increased. The dominant active site was shifted from pyridinic nitrogen to Me-N when iron-phthalocyanine was present. The analysis of Tof-SIMS indicated that the relative intensity of FeN4Cy+ ions was approximately 50% of the total amount of ionized species of ∑FeN xCy+. Both XPS and Tof-SIMS results confirmed that the Fe-N4 site was the most favourable structure in the matrix. From CV measurements, the cathodic peak current corresponding to ORR activity slightly shifted from -0.19 V to -0.17 V when the active site changed from N4 to Fe-N4 macrocyclic structure. The current density increased more than 30% in the presence of iron. Based on the calculation of Koutecky-Levich plots, the electron transfer numbers for ORR reaction in P- and FP-MCSs were 3.25 and 3.98, respectively. These results clearly demonstrated that the presence of a Fe central ion in the N4-macrocyclic structure significantly enhanced the ORR and charge transfer number in ORR activities. © the Partner Organisations 2014.

DOI： 10.1039/c4cp01406e

Synthesis of mono-dispersed nanofluids using solution plasma

Heo Y., Bratescu M., Ueno T., Saito N.

Journal of Applied Physics Vol. 116 ( 2 ) 2014.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

Small-sized and well-dispersed gold nanoparticles (NPs) for nanofluidics have been synthesized by electrical discharge in liquid environment using termed solution plasma processing (SPP). Electrons and the hydrogen radicals are reducing the gold ions to the neutral form in plasma gas phase and liquid phase, respectively. The gold NPs have the smallest diameter of 4.9nm when the solution temperature was kept at 20°C. Nucleation and growth theory describe the evolution of the NP diameter right after the reduction reaction in function of the system temperature, NP surface energy, dispersion energy barrier, and nucleation rate. Negative charges on the NPs surface during and after SPP generate repulsive forces among the NPs avoiding their agglomeration in solution. Increasing the average energy in the SPP determines a decrease of the zeta potential and an increase of the NPs diameter. An important enhancement of the thermal conductivity of 9.4% was measured for the synthesized nanofluids containing NPs with the smallest size. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4887806

Growth of highly (100)-oriented SrTiO <inf>3</inf> thin films on Si(111) substrates without buffer layer

Panomsuwan G., Takai O., Saito N.

Journal of the American Ceramic Society Vol. 97 ( 5 ) page： 1383 - 1385 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the American Ceramic Society

The SrTiO3 (STO) thin films were directly grown on Si(111) substrates without buffer layer by an electron-cyclotron-resonance ion beam sputter deposition. The growth temperature was varied from 700°C to 850°C, while other parameters were kept unchanged. X-ray structural analysis demonstrates that the growth temperature has a strong influence in tuning degree of (100) orientation. The STO film grown at 800°C is found to be the highest degree of (100) orientation (98%) and a strong (100) fiber texture. For the surface morphology, the development of plate-shaped grains reveals a good correlation with the change in the degree of (100) orientation. Moreover, the leakage current-voltage characteristics of the Au/STO/Si(111) metal-insulator-semiconductor capacitors are investigated and discussed in considerable detail. © 2014 The American Ceramic Society.

DOI： 10.1111/jace.12912

Erratum: A phonon thermodynamics approach of gold nanofluids synthesized in solution plasma (Applied Physics Letters (2014) 104 (111902))

Heo Y., Antoaneta Bratescu M., Aburaya D., Saito N.

Applied Physics Letters Vol. 104 ( 14 ) 2014.4

　 PREV - NEXT 　

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18