Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Gold nanoparticle synthesis using three-dimensionally integrated micro-solution plasmas

Shirafuji T., Ueda J., Nakamura A., Cho S.P., Saito N., Takai O.

Japanese Journal of Applied Physics Vol. 52 ( 12 ) 2013.12

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

Three-dimensionally integrated micro-solution plasmas (3D IMSPs), in which microplasmas are generated in gas bubbles in an aqueous solution held in a porous dielectric material, have been applied to gold nanoparticle synthesis. Conventional solution plasma processes require additional chemicals to increase the electrical conductivity of the aqueous solution for generating plasmas. In contrast to this, 3D IMSPs have been found to generate plasmas without such a procedure when the aqueous solution has a low electrical conductivity as in the case of HAuCl4 for gold nanoparticle synthesis. The gold nanoparticle synthesis has been confirmed through the observation of optical absorption due to the plasmon resonance at 550 nm, and also through the characterization of their size, crystallinity, and composition by transmission electron microscopy and energy dispersive X-ray spectroscopy. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.126202

Degradation of β-chitosan by solution plasma process (SPP)

Prasertsung I., Damrongsakkul S., Saito N.

Polymer Degradation and Stability Vol. 98 ( 10 ) page： 2089 - 2093 2013.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Degradation and Stability

In this work, the solution plasma process (SPP) is used to treat β-chitosan solutions in order to induce the degradation of chitosan. The effects of solution plasma on the properties of chitosan solutions are investigated. The treatment time was varied from 0 to 300 min. The plasma-treated chitosan was characterized by the following methods; molecular weight by GPC, viscosity, crystal structure by XRD, chemical characteristics by FT-IR, solubility by UV-vis spectrophotometer, and fractional analysis. The results showed that after treatment with plasma for 15-120 min, the viscosity of the chitosan solution and apparent molecular weight of chitosans decreased remarkably, when compared to those of untreated sample. Longer treatment times had less effect on both viscosity and molecular weight of the samples. This suggested that the degradation process of chitosan occurred during plasma treatment. The XRD analysis showed that the crystallinity of chitosan was destroyed, resulting in amorphous structure. FT-IR analysis revealed that chemical structure of chitosan was not affected by solution plasma treatment. The %yield of water-soluble chitosan was increased with increasing plasma treatment time. These results implied that solution plasma process is able to induce the degradation of chitosan solutions. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymdegradstab.2013.07.001

Highly efficient treatment of industrial wastewater by solution plasma with low environmental load

Cai L., Wu Y., Wu Y., Yamauti S., Saito N.

Water Science and Technology Vol. 68 ( 4 ) page： 923 - 928 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Water Science and Technology

Advanced oxidation techniques are efficient processes to dispose of organic contaminants in industrial wastewater with low secondary pollution. The solution plasma technique was featured as an advanced oxidation technique with low secondary pollution and high efficiency. However, the solution plasma technique reported previously could only treat wastewater of less than 200 mL owing to the limited plasma generated by only one pair of electrodes. In this work, multiple pairs of electrodes were installed at the bottom of the reaction vessel to generate plasma for decomposing methylene blue trihydrate (MB) and methyl orange (MO) solutions with a batch amount of 18 L/batch. The solution plasma technique was compared with direct ozonation in decomposition of MB and MO wastewater. A surprising phenomenon is that MO was more readily decomposed than MB by using direct ozonation, whereas the removal of MO was too low, and MB was more readily decomposed than MO by using the solution plasma technique. © IWA Publishing 2013.

DOI： 10.2166/wst.2013.321

Epitaxial growth of (111)-oriented BaTiO<inf>3</inf>/SrTiO<inf>3</inf> perovskite superlattices on Pt(111)/Ti/Al<inf>2</inf>O<inf>3</inf>(0001) substrates

Panomsuwan G., Takai O., Saito N.

Applied Physics Letters Vol. 103 ( 11 ) 2013.9

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

Symmetric BaTiO3/SrTiO3 (BTO/STO) superlattices (SLs) were epitaxially grown on Pt(111)/Ti/Al2O3(0001) substrates with various modulation periods (Λ = 4.8 - 48 nm) using double ion beam sputter deposition. The BTO/STO SLs exhibit high (111) orientation with two in-plane orientation variants related by a 180° rotation along the [111]Pt axis. The BTO layer is under an in-plane compressive state, whereas the STO layer is under an in-plane tensile state due to the effect of lattice mismatch. A remarkable enhancement of dielectric constant is observed for the SL with relatively small modulation period, which is attributed to both the interlayer biaxial strain effect and the Maxwell-Wagner effect. © 2013 AIP Publishing LLC.

DOI： 10.1063/1.4820780

Generation of three-dimensionally integrated micro solution plasmas and its application to decomposition of organic contaminants in water

Shirafuji T., Himeno Y., Saito N., Takai O.

Journal of Photopolymer Science and Technology Vol. 26 ( 4 ) page： 507 - 511 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Photopolymer Science and Technology

Three-dimensionally integrated micro solution plasmas were generated in gas bubbles in porous dielectric materials filled with gas/liquid mixed medium. The methylene blue molecules in aqueous solution were decomposed by the treatment with the three-dimensionally integrated micro solution plasmas. Decomposition efficiency was 16 times higher than conventional solution plasma in the case of applied voltage of 5 kV. With decreasing applied voltage from 5 to 2 kV, the decomposition efficiency was improved up to 360% in comparison to that of 5 kV, while reduction in the decomposition rate was 40%. © 2013 SPST.

DOI： 10.2494/photopolymer.26.507

Solution plasma synthesis process of carbon nano particles in organic solutions

Li H., Kang J., Urashima K., Saito N.

International Journal of Plasma Environmental Science and Technology Vol. 7 ( 1 ) page： 31 - 36 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Plasma Environmental Science and Technology

In this study, solution plasma process (SPP) was applied to synthesis carbon nanoparticles in organic solution. In the SPP process, carbon nanoparticles were formed by carbon atoms supplied by two different groups of organic solutions, sugar and aromatic hydrocarbon solutions. Glucose, sucrose and fructose were used as sugar solution, whereas benzene and toluene were applied for the aromatic hydrocarbon solutions. Within the same group of solution, the carbon structure and size distribution were found to be similar. On average, 100 ml sugar solution produced 15 mg of carbon by weight. The particles included hemisphere and sphere in shape, with a size distribution between 100 - 600 nm. For aromatic hydrocarbon solutions, 930 and 1000 mg of carbon could be generated, respectively, from 100 ml of pure toluene and benzene. The particles were spherical shape with a size distribution of 20 - 30 nm. Fundamental characteristics of plasma discharge including voltage and current waveforms, as well as active species generated were compared. The discharge in sugar solution occurred in three different phases: pre-discharge, the initiation and the formation of discharge, whereas the discharge in benzene happened in two main steps: pre-discharging and the formation of discharge. From the optical emission spectrum, the major active species obtained from sugar solution were Hα (656 nm), followed by atomic O (777 nm), Hβ (486 nm) and relatively low intensity of atomic C (247 nm). For benzene and toluene solutions, the majority active species were observed to be C2 (513 nm) and CH (431 nm) and followed by Hα (656 nm). The results indicated pure benzene might be suitable solution applied for the synthesis of carbon nanoparticles in solution plasma process.

Crosslinking of a gelatin solutions induced by pulsed electrical discharges in solutions

Prasertsung I., Damrongsakkul S., Saito N.

Plasma Processes and Polymers Vol. 10 ( 9 ) page： 792 - 797 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma Processes and Polymers

This study uses discharges in solutions for the treatment of gelatin solutions in order to generate crosslinking. The effects of plasma on the properties of gelatin solutions were investigated, the latter including viscosity, amino acid contents, chemical analyses, and gel strengths. The results show that, after short duration plasma treatments (5-10 min), the viscosity of the gelatin solutions increased, while the concentration of OH · free radicals decreased. After adding ethanol to the gelatin solutions, a greater increase in viscosity, and a greater decrease in free radicals were found. This suggests that ethanol provides more free radicals that can promote the crosslinking of the gelatin solution during the plasma treatment, resulting in higher viscosity. The gel strength of the gelatin was greatly enhanced by the plasma treatment of the solution. The results regarding the free amino acid contents showed that the crosslinking degree of plasma-treated gelatin was higher than that of the untreated gelatin. FTIR measurements show that after plasma treatment, the IR bands at 1 668 and 1 558 cm-1, corresponding to the amide I and II groups of gelatin, shifted to higher wavenumbers, i.e. 1 672 and 1 564 cm-1, respectively. This suggests that crosslinking has occurred between gelatin molecules. The results show that discharges in solutions may be able to induce crosslinking reactions in the gelatin. Electrical discharges in solutions can be chemical-free, alternative crosslinking methods. Electrical discharges are investigated for the treatment of gelatin solutions as potential crosslinking, non-toxic methods. Plasmas were found to induce crosslinking of gelatin molecules, as demonstrated by the increased viscosity, decreased free amino contents, and increased gel strength. The addition of ethanol in gelatin solutions enhanced the crosslinking; this is because ethanol provides more free radicals necessary for crosslinking reactions. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/ppap.201200148

Synthesis of structure-controlled carbon nano spheres by solution plasma process

Kang J., Li O., Saito N.

Carbon Vol. 60 page： 292 - 298 2013.8

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

Structure-controlled carbon nanospheres (CNSs) were synthesized by an innovative plasma in liquid method, termed solution plasma processing (SPP). CNSs were formed by using benzene as a carbon precursor. Typically, 500 mg of CNSs were obtained from 100 ml of benzene with 20 min of treatment. The average diameters of CNSs increased from 20 to 100 nm when the pulse frequency of the bipolar power supply adjusted from 25 to 65 kHz. The TEM images showed that CNSs synthesized at 25-50 kHz consisted of amorphous carbon, while CNSs generated at 65 kHz were composed of continuous short range graphite with turbostratic structure. X-ray diffraction (XRD) patterns and TEM images showed that CNSs synthesized at 25-50 kHz had a low graphitization degree, while CNSs synthesized at 65 kHz consisted of graphite sheets with regular and ordering structure in basal planes. The increase of D/G intensity ratio in Raman spectroscopy confirmed the transition from amorphous carbon to nanocrystalline-graphite (NCG) with increasing pulse frequency. The resistivity of CNSs also increased with increasing pulse frequency. CNSs synthesized at 65 kHz have shown similar degree of resistivity as other commercial carbon black materials. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2013.04.040

A simple synthesis method for nano-metal catalyst supported on mesoporous carbon: The solution plasma process

Kang J., Li O., Saito N.

Nanoscale Vol. 5 ( 15 ) page： 6874 - 6882 2013.7

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

High-electrocatalytic-activity noble nanoparticles (NPs) supported on carbon nanoballs (CNBs) were synthesized using an innovative plasma-in-liquid method, which is known as solution plasma processing (SPP). This technique uses a one-step method for the synthesis of NPs on carbon materials. CNBs are formed using benzene as a carbon precursor while gold (Au) or platinum (Pt) nanoparticles are generated instantaneously via sputtering from metal electrodes. The synthesized NP/CNBs were annealed at 850 °C in order to increase the conductivity of the material. The results of structural characterizations reveal that the Au and Pt NPs are smaller than 10 nm and have a uniform size distribution, and these NPs are successfully loaded onto highly mesoporous CNBs that have an average pore diameter between 13 and 16 nm. In the results from cyclic voltammetry measurements, the Au/CNBs and Pt/CNBs show clear peaks corresponding to the oxidation and reduction features in the catalytic reactions. Apart from noble nanoparticles, SPP can also be used to synthesize various kinds of NPs including bimetallic NPs loaded on spherical carbon supports by changing the working electrodes. The proposed mechanism for the synthesis is discussed in detail. This method shows potential to be a candidate for the next-generation synthesis of NP/carbon in the future. © 2013 The Royal Society of Chemistry.

DOI： 10.1039/c3nr01229h

One-step synthesis of gold bimetallic nanoparticles with various metal-compositions

Bratescu M., Takai O., Saito N.

Journal of Alloys and Compounds Vol. 562 page： 74 - 83 2013.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

A rapid, one-step process for the synthesis of bimetallic nanoparticles by simultaneous metal reduction and gold erosion in an aqueous solution discharge was investigated. Gold bimetallic nanoparticles were obtained by alloying gold with various types of metals belonging to one of the following categories: divalent sp metals, trivalent sp metals, 3d or 4d metals. The composition of the various gold bimetallic nanoparticles obtained depends on electrochemical factors, charge transfer between gold and other metal, and initial concentration of metal in solution. Transmission electron microscopy and energy dispersive spectroscopy show that the gold bimetallic nanoparticles were of mixed pattern, with sizes of between 5 and 20 nm. A red-shift of the surface plasmon resonance band in the case of the bimetallic nanoparticles Au-Fe, Au-Ga, and Au-In, and a blue-shift of the plasmon band of the Au-Ag nanoparticles was observed. In addition, the interaction of gold bimetallic nanoparticles with unpaired electrons, provided by a stable free radical molecule, was highest for those NPs obtained by alloying gold with a 3d metal. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2013.02.033

Effect of polymer concentration on the depolymerization of sodium alginate by the solution plasma process

Watthanaphanit A., Saito N.

Polymer Degradation and Stability Vol. 98 ( 5 ) page： 1072 - 1080 2013.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Degradation and Stability

Depolymerization of alginate was accessed, for the first time, by the plasma treatment in solution called solution plasma process (SPP). The process was done by applying an electrical discharge into a reactor containing sodium alginate aqueous solution. The key of the production is the generation of reactive species induced by the plasma in a liquid environment that can lead to the scission of polymer chains. Effect of polymer concentration on the SPP processing parameters and the depolymerization efficiency were studied. Three concentrations of sodium alginate solutions, i.e., 0.2, 0.5, and 0.9 %w/v, were prepared. The results showed that increasing concentration of the alginate solution decreased the applied voltage required for the generation of plasma. Optical emission spectra demonstrated that the generation of reactive species was the highest at the lowest alginate concentration (i.e. 0.2 %w/v). Therefore, molecular weight reduction of this concentration after the SPP was more remarkable than the others. The most significant species required for the depolymerization of alginate was the reactive hydrogen species. Molecular weight distributions (MWD) of the obtained low molecular weight alginates (LMALGs) for all concentrations were narrow. Furthermore, reduction trends of molecular weight and viscosity of alginate with varying operation times indicated that the depolymerization of alginate in aqueous solution by the SPP was affected by the combined contribution of two factors: (1) the amount of reactive species generated during the process and (2) the degree of chain entanglement of the polymers. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymdegradstab.2013.01.011

Solution plasma sputtering processes for the synthesis of PtAu/C catalysts for Li-Air batteries

Terashima C., Iwai Y., Cho S.P., Ueno T., Zettsu N., Saito N., Takai O.

International Journal of Electrochemical Science Vol. 8 ( 4 ) page： 5407 - 5420 2013.4

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Electrochemical Science

Clean, nanosized PtAu/C catalysts were fabricated, using a simple one-step synthesis technique that involved sputtering discharge in liquid, and did not require the use of chemical species such as surfactants and/or reductants. This solution plasma sputtering was driven by a pulsed power supply, and was performed on the discharge between Pt and Au targets in a liquid dispersion of carbon black. Fine PtAu nanoparticles with an average diameter of 5.7 nm were uniformly deposited on the carbon support. The production and composition of the PtAu nanoparticles could be controlled via changes in the sputtering conditions. The Au-rich Pt19Au81/C (atomic %) catalysts provided higher specific capacity, even in carbonate-based electrolyte Li-air batteries, reducing the amount of Li2CO3 that was deposited on the bare carbon. © 2013 by ESG.

Facile fabrication of PtAu alloy clusters using solution plasma sputtering and their electrocatalytic activity

Hu X., Shen X., Takai O., Saito N.

Journal of Alloys and Compounds Vol. 552 page： 351 - 355 2013.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

Well-crystallized PtAu alloy clusters of about 2.0 nm in mean diameter are successfully fabricated via a one-step route of solution plasma sputtering at atmospheric pressure. The solution plasma provides a novel reaction field with highly energetic state for the formation of PtAu alloy clusters. The synergetic effects of rapid energetic radicals' bombardment, atom vapor diffusion, plasma expansion and solution medium condensation resulted in the formation of PtAu alloy clusters with various relative atom amount ratios. PtAu alloy clusters are highly dispersive in water for a long time without any polymeric stabilizer. As-fabricated PtAu alloy clusters show well electrocatalytic activity. PtAu alloy clusters are easily collected and well re-dispersed in various organic solvents for various potential applications. And PtAu alloy clusters supported on carbon were successfully fabricated by a one-step route. These results imply that this novel process will have potential application in future in the design and mass production of various multifunctional metal and/or alloy clusters. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2012.08.033

Fabrication and characterization of epitaxial SrTiO <inf>3</inf>/Nb-doped SrTiO <inf>3</inf> superlattices by double ECR ion beam sputter deposition

Panomsuwan G., Takai O., Saito N.

Vacuum Vol. 89 ( 1 ) page： 35 - 39 2013.3

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

Epitaxial oxide superlattices (SLs) of SrTiO 3 (STO) and Nb-doped SrTiO 3(STNO) were fabricated on LaAlO 3 (LAO) (001) substrates by an ion beam sputter deposition (IBSD) system having double electron cyclotron resonance (ECR) ion guns. The [STO x/STNO y] 10 SLs were epitaxially grown at different stacking sequences (x = 6 nm, y = 1-6 nm) and maintained the periodicity z of 10. Structural properties and surface morphology are found to be strongly dependent on the STNO sublayer thickness (y). Highly strained SLs with two-dimensional growth mode is observed at smaller STNO sublayer thickness (y = 1 nm). With increasing to a critical thickness (y = 4 nm), the SLs are freely strained and transformed to three-dimensional growth mode. The results demonstrate that the double ECR-IBSD is a versatile technique for the growth of high-quality oxide SLs. © 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.vacuum.2012.08.011

Growth of highly (110)- and (111)-textured SrTiO<inf>3</inf> thin films on Pt(111)/α-Al<inf>2</inf>O<inf>3</inf>(0001) substrates by ECR ion beam sputter deposition

Panomsuwan G., Takai O., Saito N.

Solid State Communications Vol. 158 page： 65 - 69 2013.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Solid State Communications

SrTiO3 (STO) thin films were directly grown on Pt(111)/α-Al2O3(0001) substrates without Ti buffer layer using electron cyclotron resonance ion beam sputter deposition. Highly (110)- and (111)-textured STO films were obtained at 600 and 750 °C, respectively. The structural, morphological and electrical properties of both textured films were studied and compared. From high-resolution X-ray diffraction data and in-plane pole figure analysis, highly (110)-textured STO film was found to contain three orientation variants related by a 120°in-plane rotation, while highly (111)-textured STO film had two orientation variants related by a 180°in-plane rotation. The presence of rod- and triangular-shaped grains was observed for the (110)- and (111)-textured film surfaces, respectively. Their grain orientations were also consistent with the structural analysis. The leakage current characteristics of Pt/STO/Pt capacitors were found to follow the Schottky emission and Poole-Frenkel conduction mechanisms. A larger dielectric constant of (111)-textured film (320 at 100 kHz) was obtained in comparison with that of (110)-textured film (238 at 100 kHz) due to the effect of biaxial in-plane tensile strain and larger grain size. © 2013 Elsevier Ltd.

DOI： 10.1016/j.ssc.2012.12.026

Nanomechanical properties of amorphous and polycrystalline SrTiO <inf>3</inf> transparent thin films prepared by ion beam sputtering

Panomsuwan G., Takai O., Saito N.

Journal of Materials Engineering and Performance Vol. 22 ( 3 ) page： 863 - 868 2013.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Engineering and Performance

Transparent SrTiO3 thin films were deposited on glass substrates by ion beam sputtering at various substrate temperatures. The structural characteristic of the deposited films shows the transition from amorphous phase to polycrystalline phase at 600 C. The films exhibit a good transparency in the visible region (∼80-85%) and a relatively smooth surface. The calculated band gaps for amorphous and polycrystalline films were ∼4.20 and ∼3.84 eV, respectively. The refractive index of the films increases with increasing the substrate temperature, and the extinction coefficient of the films in the visible region is in the order of 10-3, indicating low optical loss. The nanomechanical properties of the films were investigated using nanoindentation technique. Young's modulus and hardness for all films are found to be increased with the increase of substrate temperature. © 2012 ASM International.

DOI： 10.1007/s11665-012-0320-2

Discharge time dependence of a solution plasma process for colloidal copper nanoparticle synthesis and particle characteristics

Pootawang P., Saito N., Lee S.Y.

Nanotechnology Vol. 24 ( 5 ) 2013.2

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

In this study, we investigate a new synthetic route, termed the solution plasma process, for the synthesis of colloidal copper nanoparticles (CuNPs) in the presence of an amide and acid capping agent. Gelatin and ascorbic acid were selected as the capping agents to protect the particles against coalescence and oxidation side reaction. Using a high voltage power supply, CuNPs were rapidly formed by 1 min after the discharge. The size and shape of the CuNPs were dependent on the discharge time and were clearly influenced by the effect of the capping agents under two characteristics of the discharge medium (pH and temperature). With a long discharge time, the CuNP size tended to decrease with the formation of anisotropic particle morphologies: spherical, cubic, hexagonal, triangular and rod-like shapes. The decrease in CuNP size as a function of discharge time could be explained by the dissolution of CuNPs in a lower pH solution. After 5 min discharge the capping agent evidently allowed the protection of the synthesized CuNPs against oxidation with the presence of anisotropic CuNP shapes. It is demonstrated that the CuNP shape could be tuned from spherical to anisotropic shapes without the undesirable oxidation by adjusting the discharge time of the solution plasma. These advantages are valuable for material engineering to design the properties of Cu-based nanoparticles for the desired applications. © 2013 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/24/5/055604

Optical and mechanical properties of transparent SrTiO<inf>3</inf> thin films deposited by ECR ion beam sputter deposition

Panomsuwan G., Takai O., Saito N.

Physica Status Solidi (A) Applications and Materials Science Vol. 210 ( 2 ) page： 311 - 319 2013.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (A) Applications and Materials Science

SrTiO3 (STO) thin films have been deposited on glass substrates by electron cyclotron resonance (ECR) ion beam sputter deposition at different substrate temperatures (100-600 °C). The structural characteristics of the deposited films show a transition from amorphous phase to polycrystalline phase at 600 °C. The films exhibit good transparency with an interference pattern in the visible region and a very smooth surface without cracks. The refractive index of the films increases with an increase of the substrate temperature, and their dispersion was analyzed by a single-oscillator model. The extinction coefficient of the films in the visible region is of the order of 10 -3-10-2. The estimated values of the direct and indirect bandgap energies for the polycrystalline STO film are 3.80 and 3.32 eV, respectively. Its density is almost identical to the bulk STO single crystal, which is relatively high in comparison with those prepared by other techniques. The mechanical stability of the films is also improved with an increase of substrate temperature. Young's modulus and hardness of the polycrystalline STO film are 194.1 ± 15.5 and 22.5 ± 2.0 GPa, respectively. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.201228077

Simple synthesis of platinum nanoparticles by plasma sputtering in water

Hu X., Takai O., Saito N.

Japanese Journal of Applied Physics Vol. 52 ( 1 PART2 ) 2013.1

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

We applied a novel method of plasma sputtering in water for simple and fast preparation of carbon-supported platinum nanoparticles at atmospheric pressure from platinum wire electrodes without using any stabilizers, chemical reductant, plasma-generating gas, or salt solution in an open system. Upon plasma sputtering, special waveforms of voltage and current were obtained using a pulsed power supply. The obtained emission spectra clarified that platinum atoms were formed in the plasma region from the electrode surface owing to bombardment of the surface by highly energetic electrons and radicals derived from plasma. Thus, carbon-supported 2 nm and highly dispersed platinum nanoparticles were successfully synthesized by this fast and simple plasma sputtering method. Highly crystallized platinum nanoparticles show good electrocatalytic activity. This plasma sputtering technique has shown a potential application to the synthesis of other metal nanoparticles. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.01AN05

Gold nanoparticles supported on SrTiO<inf>3</inf> by solution plasma sputter deposition for enhancing UV- and visible-light photocatalytic efficiency

Panomsuwan G., Zettsu N., Saito N.

Materials Research Society Symposium Proceedings Vol. 1509 page： 80 - 85 2013

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

Gold (Au) nanoparticles were synthesized and deposited on the perovskite SrTiO3 (STO) via a one-step solution plasma sputter deposition (SPSD) without any reducing reagents at ambient condition. Good dispersion of the Au nanoparticles deposited on the STO surface was clearly observed. The synthesized Au nanoparticles were well-crystallized with a spherical shape and preferably exhibited multiply twinned structure. An average diameter of Au nanoparicles was estimated to be 6.1 ± 1.4 nm by transmission electron microscopy. Enhanced photocatalytic activity was found for the Au-STO when compared to the pure STO, as investigated from the degradation of methylene blue solution under ultraviolet and visible light irradiation. The SPSD seems to be a rapid and facile approach to prepare the Au nanoparticles supported on the metal oxide for photocatalytic applications. © 2013 Materials Research Society.

DOI： 10.1557/opl.2013.729

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