Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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The role of activated nitrogen species on double-folded screen nitriding process

Kim S., Lee J., Saito N., Takai O.

Journal of Physics: Conference Series Vol. 417 ( 1 ) 2013

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

As clean and energy saving surface hardening technology, plasma nitriding techniques have been evolved with object of higher performance in the last decades. Even though the diffusion of nitrogen inward to steel is occurred at the final step, solid diffusion from surface, energy transition from gas molecule of nitrogen to atomic or an activated state have many different steps depending on the plasma conditions, parameters and the design of each equipment. And this study made comparative on nitrogen sources transfer with conventional DC plasma nitriding and novel nitriding process using plasma diagnosis and metallurgical observation. With different vacuum pressure, gas ratio and new designed electrode (double-folded screen cathode electrode), it showed a different behavior of DC plasma nitriding including the nano-sized nitride on the outer surface of specimen due to nitrogen source of determining plasma species. In this study, plasma species was able to identify with optical emission spectroscopy (OES) studies. From these observations, we could understand better role of ions or neutral nitrogen species, like neutral nitrogen (N), N2+ and NHx radicals in plasma nitriding process with different parameters. And cutting layers of nitride specimen were showed the results due to a different species gas flow ratio or plasma conditions.

DOI： 10.1088/1742-6596/417/1/012023

Synthesis of gold nanoparticles by solution plasma sputtering in various solvents

Hu X., Takai O., Saito N.

Journal of Physics: Conference Series Vol. 417 ( 1 ) 2013

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

Gold clusters (average particle size is 1.5 nm) and nanoparticles (average particle size is 3.5 nm) with spherical morphology were fabricated by solution plasma sputtering in solution medium. This process was carried out in an open system under atmospheric pressure. During plasma region, rapid energetic radicals' bombardment, atom vapour diffusion, plasma expansion and medium condensation resulted in the formation of gold nanoparticles from its electrode wires. As-fabricated gold particles have well crystalline even for less than 1 nm cluster. Gold nanoparticles with average size about 3.5 nm gave obviously surface plasmon resonance band at near 511 nm. While surface plasmon resonance band was disappearing for 1.5 nm-cluster formed in liquid nitrogen.

DOI： 10.1088/1742-6596/417/1/012030

In situ preparation of gold nanoparticles in alginate gel matrix by solution plasma sputtering process

Watthanaphanit A., Panomsuwan G., Saito N.

Materials Research Society Symposium Proceedings Vol. 1569 2013

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

The rapid synthesis of gold nanoparticles (AuNPs) was done by solution plasma sputtering (SPS) process in the presence of a biopolymer, sodium alginate. We utilized the alginate polymer in order to meet three important requirements: (1) to promote the generation of plasma in liquid environment, (2) to provide colloidal stability, and (3) to render biocompatibility to the AuNPs. The effect of sodium alginate concentration (varied as 0.2, 0.5, and 0.9 %w/v) and plasma sputtering time on the particle size and the physical absorption property of the AuNPs were studied. The results indicated that preparation of AuNPs in alginate gel matrix was successful by the SPS process in one step without any reducing agents. This technique has high potential as a novel strategy to produce AuNPs suspended in alginate aqueous solution which is suitable for biomedical application. Copyright © Materials Research Society 2013.

DOI： 10.1557/opl.2013.766

Synthesis of Nanomaterials by Solution Plasma Processing

Takai, O; Bratescu, MA; Ueno, T; Saito, N

MICRO-NANO MECHATRONICS - NEW TRENDS IN MATERIAL, MEASUREMENT, CONTROL, MANUFACTURING AND THEIR APPLICATIONS IN BIOMEDICAL ENGINEERING page： 109 - 121 2013

Orientation control of textured SrTiO<inf>3</inf> thin films on platinized α-Al<inf>2</inf>O<inf>3</inf> (0 0 0 1) by an ion beam sputter deposition method

Panomsuwan G., Takai O., Saito N.

Journal of Physics D: Applied Physics Vol. 45 ( 49 ) 2012.12

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

SrTiO3 (STO) thin films were grown on Pt/Al2O 3 substrates without a Ti adhesion layer by an ion beam sputter deposition method in a range of growth temperatures between 600 and 750 °C. The effect of growth temperature on the film orientation was investigated by high-resolution x-ray diffraction, pole figure measurements and in-plane grazing incidence x-ray diffraction. The film orientation showed a strong dependence on the growth temperature. The films exhibited a predominant (1 1 0) orientation at a low growth temperature of 600 °C. With an increase in growth temperature to 750 °C, a highly (1 1 1)-textured STO film with two different orientation variants was achieved on the Pt/Al2O3 substrate. A narrow full-width at half-maximum of 0.12° for the rocking curve measured on 2 2 2 STO reflection and a six-fold symmetry from {1 0 0} STO and {1 1 0} STO pole figures were observed. Three-dimensional island growth mode was observed on the surfaces of all films, as investigated with an atomic force microscope. The evolution of grain shape and size was apparently found with an increase in growth temperature. The root-mean-square roughness of the STO film grown at 750 °C was raised to be about 4 nm due to the surface faceting of (1 1 1)-oriented grains. The growth mechanism of the (1 1 0)- and (1 1 1)-textured STO films on the Pt/Al2O3 substrates was also explained and discussed in detail. © 2012 IOP Publishing Ltd.

DOI： 10.1088/0022-3727/45/49/494003

Rapid sterilization of Escherichia coli by solution plasma process

Andreeva N., Ishizaki T., Baroch P., Saito N.

Japanese Journal of Applied Physics Vol. 51 ( 12 ) 2012.12

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

Solution plasma (SP), which is a discharge in the liquid phase, has the potential for rapid sterilization of water without chemical agents. The discharge showed a strong sterilization performance against Escherichia coli bacteria. The decimal value (D value) of the reduction time for E. coli by this system with an electrode distance of 1.0mm was estimated to be approximately 1.0 min. Our discharge system in the liquid phase caused no physical damage to the E. coli and only a small increase in the temperature of the aqueous solution. The UV light generated by the discharge was an important factor in the sterilization of E. coli. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.51.126201

15th International conference on thin films (ICTF-15)

Takai O., Saito N., Terashima C.

Journal of the Vacuum Society of Japan Vol. 55 ( 10 ) page： 464 - 468 2012.11

Synthesis and characteristics of Ag/Pt bimetallic nanocomposites by arc-discharge solution plasma processing

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

Nanotechnology Vol. 23 ( 39 ) 2012.10

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

Arc discharge in solution, generated by applying a high voltage of unipolar pulsed dc to electrodes of Ag and Pt, was used as a method to form Ag/Pt bimetallic nanocomposites via electrode erosion by the effects of the electric arc at the cathode (Ag rod) and the sputtering at the anode (Pt rod). Ag/Pt bimetallic nanocomposites were formed as colloidal particles dispersed in solution via the reduction of hydrogen radicals generated during discharge without the addition of chemical precursor or reducing agent. At a discharge time of 30s, the fine bimetallic nanoparticles with a mean particle size of approximately 5nm were observed by transmission electron microscopy (TEM). With increasing discharge time, the bimetallic nanoparticle size tended to increase by forming an agglomeration. The presence of the relatively small amount of Pt dispersed in the Ag matrix could be observed by the analytical mapping mode of energy-dispersive x-ray spectroscopy and high-resolution TEM. This demonstrated that the synthesized particle was in the form of a nanocomposite. No contamination of other chemical substances was detected by x-ray photoelectron spectroscopy. Hence, solution plasma could be a clean and simple process to effectively synthesize Ag/Pt bimetallic nanocomposites and it is expected to be widely applicable in the preparation of several types of nanoparticle. © 2012 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/23/39/395602

Rapid synthesis of ordered hexagonal mesoporous silica and their incorporation with Ag nanoparticles by solution plasma

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

Materials Research Bulletin Vol. 47 ( 10 ) page： 2726 - 2729 2012.10

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

Rapid synthesis of silica with ordered hexagonal mesopore arrangement was obtained using solution plasma process (SPP) by discharging the mixture of P123 triblock copolymer/TEOS in acid solution. SPP, moreover, was utilized for Ag nanoparticles (AgNPs) incorporation in silica framework as one-batch process using silver nitrate (AgNO 3) solution as precursor. The turbid silicate gel was clearly observed after discharge for 1 min and the white precipitate formed at 3 min. The mesopore with hexagonal arrangement and AgNPs were observed in mesoporous silica. Two regions of X-ray diffraction patterns (2θ < 2° and 2θ = 35-90°) corresponded to the mesoporous silica and Ag nanocrystal characteristics. Comparing with mesoporous silica prepared by a conventional sol-gel route, surface area and pore diameter of mesoporous silica prepared by solution plasma were observed to be larger. In addition, the increase in Ag loading resulted in the decrease in surface area with insignificant variation in the pore diameter of mesoporous silica. SPP could be successfully utilized not only to enhance gelation time but also to increase surface area and pore diameter of mesoporous silica. © 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.materresbull.2012.04.040

Enhanced memory window of Au/BaTiO <inf>3</inf>/SrTiO <inf>3</inf>/Si(001) MFIS structure with high c-axis orientation for non-volatile memory applications

Panomsuwan G., Takai O., Saito N.

Applied Physics A: Materials Science and Processing Vol. 108 ( 2 ) page： 337 - 342 2012.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics A: Materials Science and Processing

Metal-ferroelectric-insulator-semiconductor (MFIS) structures with BaTiO 3 (BTO) as a ferroelectric film and SrTiO 3 (STO) as an insulating buffer layer were fabricated on p-type Si(001) substrates using an ion beam sputter deposition technique. The effect of out-of-plane orientation on the electrical properties of the MFIS structures, including leakage current density and memory window behavior, were studied using the growth of the BTO ferroelectric film on Si substrate buffered by highly c-axis-oriented and randomoriented STO buffer layers. The experimental results show that the out-of-plane orientations of the BTO films were almost identical to those of the STO buffer layers. The MFIS structure with a high c-axis orientation exhibited a maximum clockwise capacitance-voltage memory window of 1.17 V with a low leakage current of 1.05 × 10 -7 A/cm 2 at an applied voltage of 4 V, which is a significant improvement compared to the MFIS structure with a random orientation. The difference in the electrical properties of the MFIS structures with both types of orientation is discussed in detail. The results obtained from this study indicate that the Au/BTO/STO/p-Si MFIS structure with high c-axis orientation has good potential for use in non-volatile memory applications. © Springer-Verlag 2012.

DOI： 10.1007/s00339-012-7011-6

Treatment of non-point sources by a thermal plasma system under DC partial transferred mode

Li O.L., Guo Y., Chang J.S., Urashima K., Saito N.

International Journal of Plasma Environmental Science and Technology Vol. 6 ( 1 ) page： 63 - 67 2012.7

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

Stormwater from urban areas is often accompanied with a variety of chemicals such as heavy metals, phosphorus, trace organic and hydrocarbons. Thermal plasma under DC transferred mode was proposed for decontamination of sediment carried by urban stormwater. After dredging, stormwater sediment/sludge accumulated in a stormwater detention pond was spread on top of a filter and the residues were transferred to a thermal plasma reactor. The reduction of total organic carbon (TOC) is 22% on average. Sediment was melted into slag with thermal plasma treatment under DC partial transferred operating mode. After treatment, the major compositions of the original stormwater sludge (e.g. sand (SiO 2) and calcite (CaCO 3)) decreased while other compositions such as KAlSi 3O 8, Fe 3O 4, NaCl and CaSO 4 were formed. The accumulated concentrations of C xH y, CO, CO 2, NO, NO 2, H 2S and SO 2 after a twohour thermal plasma treatment were 6100, 10000, 6200, 9700, 140, 40 and 27 ppm, respectively.

Study on the combustion inhibition of poly phenylene ether alloy

Yamashita T., Nakashima E., Takeda K., Saito N., Takai O.

Kobunshi Ronbunshu Vol. 69 ( 6 ) page： 297 - 299 2012.6

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

In this study, we evaluated the flame retardant properties of several chemical compounds to polyphenylene ether alloy. Some of them (metallic sulfide and a variety of carboxylate salts) are stronger than general flame retardants such as red phosphorus. Molybdenum disulfide is widely used as lubricant and sodium benzoate and disodium succinate are used as food additives. So it is a new insight that they have a significant effect on the flame retardancy of polyphenylene ether alloy. Molybdenum disulfide is a catalyst that degrades polyphenylene ether alloy. We also found a combinatorial effect when blending polyphenylene ether alloy with both molybdenum disulfide and sodium benzoate that show a stronger combustion inhibition than each single compound. ©2012, The Society of Polymer Science, Japan.

DOI： 10.1295/koron.69.297

Preparation and wettability examinations of transparent SiO<inf>2</inf> binder-added MgF<inf>2</inf> nanoparticle coatings covered with fluoro-alkyl silane self-assembled monolayer

Murata T., Hieda J., Saito N., Takai O.

Applied Optics Vol. 51 ( 13 ) page： 2298 - 2305 2012.5

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

SiO2-added MgF2 nanoparticle coatings with various surface roughness properties were formed on fused silica-glass substrates from autoclaved sols prepared at 100-180 °C. To give it hydrophobicity, we treated the samples with fluoro-alkyl silane (FAS) vapor to form self-assembled monolayers on the nanoparticle coating and we examined the wettability of the samples. The samples preserved good transparency even after the FAS treatment. The wettability examination revealed that higher autoclave temperatures produced a larger average MgF2 nanoparticle particle size, a larger surface roughness, and a higher contact angle and the roll-off angle. © 2012 Optical Society of America.

DOI： 10.1364/AO.51.002298

Active species generated by a pulsed arc electrohydraulic discharge plasma channel in contaminated water treatments

Li O.L., Takeuchi N., He Z., Guo Y., Yasuoka K., Chang J.S., Saito N.

Plasma Chemistry and Plasma Processing Vol. 32 ( 2 ) page： 343 - 358 2012.4

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

Pulsed arc electrohydraulic discharge (PAED) direct plasma technique was applied for various types of contaminated water treatment. The experimental system consists of a spark-gap switch type pulse power supply (0.5 kJ/pulse) and a 3 L stainless steel reactor with eccentrically configured rod-to-rod electrodes. The current and voltage waveforms are fundamentally different for different conductivity water. Double pulse current discharges were observed for pond water with relatively higher conductivity (637 mS/m) while a single pulse current discharge was observed for lake water with relatively lower conductivity (78 mS/m). From the optical emission spectrum and UV dosimeters, UV-A, UV-B, excited molecules and radicals including N 2*, O, H, OH, O3 etc. were observed during the discharge period. Both optical emission and UV intensities in pond water are slightly lower than lake water. The decay time of the UV-A, N 2*, OH, H and O radicals were around 0.6 ms, where the discharge period ended around 0.4 ms. The results indicate that the radicals existed longer than the discharge period. The pH, dissolved oxygen and conductivity were changed during the course of PAED treatment. The ions and radicals such as H·, O·, H +, OH· etc. generated by PAED may cause alterations density decay time and the active species in water were present for a longer period. The reduction of total organic carbon (TOC) in pond water reached 80% after 5 min of PAED treatment Based on local thermal plasma equilibrium (LTE) model, LTE thermal plasma chemical composition model for 1 mol water vapour was used to compare to present experiments. PAED discharge in contaminated pond water generated peak concentration of OH = 28% and O 2H = 0.012% mol in gas-phase and migrated to water-phase via gas-liquid interfaces generated by arc and micro-bubbles to form more stable O3, H2O 2, H2 and O 2. The model suggested that the reduction of TOC occurred in gas/plasma phases or liquid-phase side of gas liquid interfaces. © Springer Science+Business Media, LLC 2011.

DOI： 10.1007/s11090-011-9346-8

High sensitive detection of volatile organic compounds using superhydrophobic quartz crystal microbalance

Andreeva N., Ishizaki T., Baroch P., Saito N.

Sensors and Actuators, B: Chemical Vol. 164 ( 1 ) page： 15 - 21 2012.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical

A quartz crystal microbalance (QCM) chemical sensor coated with superhydrophobic film for detecting volatile organic compounds (VOCs) such as formaldehyde and toluene under ambient conditions was developed. The superhydrophobic film was deposited by means of microwave plasma enhanced chemical vapor deposition (MPECVD). The sensitivities of QCM sensor coated with superhydrophobic film to VOCs such as formaldehyde and toluene were investigated under ambient conditions. The sensitivity of the sensor to formaldehyde and toluene was considerably improved by the superhydrophobic surface modification. The surface modification promoted microscopic texturing to the film surface and thus increased the effective specific surface area of the sensor for the adsorption of formaldehyde and toluene. In addition, the adsorption of water molecules was minimized due to the superhydrophobic film deposited on the sensor surface, thus promoting the preferential adsorption of formaldehyde and toluene molecules on the QCM sensor coated with superhydrophobic film, compared to the conventional QCM sensor. Moreover, the adsorption mechanisms of formaldehyde-water and toluene-water molecules to the superhydrophobic film were discussed. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.snb.2012.01.051

Preparation of low molecular weight chitosan using solution plasma system

Prasertsung I., Damrongsakkul S., Terashima C., Saito N., Takai O.

Carbohydrate Polymers Vol. 87 ( 4 ) page： 2745 - 2749 2012.3

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

The solution plasma system was introduced to treat chitosan solution in order to prepare low molecular weight chitosan. The plasma treatment time was varied from 0 min to 300 min. The plasma-treated chitosan was characterized including viscosity, molecular weight by GPC, and chemical characteristics by FT-IR. The results showed that after treated with plasma for 15-60 min, the viscosity of chitosan solution and apparent molecular weight of chitosans were remarkably decreased, compared to those of untreated sample. Longer treatment time had less effect on both viscosity and molecular weight of samples. Eventually, long treatment time (>180 min) showed no influence on both viscosity and apparent molecular weight. This suggested that the degradation process of chitosan occurred during plasma treatment. FTIR analysis revealed that chemical structure of chitosan was not affected by solution plasma treatment. TOF-MS results showed that chitooligosaccharides with the degree of polymerization of 2-8 were also generated by solution plasma treatment. The results suggested that solution plasma system could be a potential method for the preparation of low molecular weight chitosan and chitooligosaccharides. © 2011 Elsevier Ltd.

DOI： 10.1016/j.carbpol.2011.11.055

Growth and characterization of highly c-axis textured SrTiO <inf>3</inf> thin films directly grown on Si(001) substrates by ion beam sputter deposition

Panomsuwan G., Cho S., Saito N., Takai O.

Crystal Research and Technology Vol. 47 ( 2 ) page： 187 - 194 2012.2

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

Highly c-axis textured SrTiO 3 (STO) thin films have been directly grown on Si(001) substrates using ion beam sputter deposition technique without any buffer layer. The substrate temperature was varied, while other parameters were fixed in order to study effect of substrate temperature on morphology and texture evolution of STO films. X-ray diffraction, pole figure analysis, atomic force microscope, and high-resolution electron microscopy were used to characterize and confirm quality and texture of the STO films. The experimental results show that optimum substrate temperature to achieve highly c-axis textured films is at 700 °C. The full width at half maximum (FWHM) of 002 STO was found to be 2° and fraction of (011) orientation was as low as 1%. The surface morphology was Volmer-Weber growth mode with a small roughness ∼1 nm. The lowest leakage current density (5.8 μA/cm 2 at 2 V) and the highest dielectric constant (Îμ STO ∼ 98) were found for highly c-axis textured films grown at 700 °C. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/crat.201100573

Rapid synthesis and structural characterization of well-defined gold clusters by solution plasma sputtering

Hu X., Cho S., Takai O., Saito N.

Crystal Growth and Design Vol. 12 ( 1 ) page： 119 - 123 2012.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Crystal Growth and Design

Ultrafine metal nanoparticles of a few nanometers in diameter exhibit size-dependent photonic and electric properties that are of interest for applications such as biosensors, catalysts, optics, and electronics. Chemical approaches and vacuum metal-vapor-condensation physical techniques were used to successfully synthesize gold nanoparticles. While it is difficult to obtain monodisperse and small sized gold nanoparticles without any reductant and polymer stabilizer or under vacuum conditions, in the present study, multiply twinned and near monodisperse gold clusters of diameter less than 2.0 nm were successfully fabricated for the first time by solution plasma sputtering in liquid nitrogen (LN 2) without any chemical additions (such as reductant and polymer stabilizer). Gold clusters formed in several microseconds simultaneously with solution plasma sputtering in an open system under atmospheric pressure. Gold clusters are identified to be well crystalline and multitwin-particles (MTPs) by high-resolution transmission electron microscopy. No surface plasmon resonance band was detected in the gold cluster aqueous solutions. Such MTPs with special corners and edges would be beneficial for tailoring catalytic properties at the nanoscale. The solution plasma sputtering method will have potential application in the future in the design and mass preparation of various multifunctional metal clusters. © 2011 American Chemical Society.

DOI： 10.1021/cg2008528

Effect of Sn<sup>4+</sup> additives on the microstructure and corrosion resistance of anodic coating formed on AZ31 magnesium alloy in alkaline solution

Salman S.A., Kuroda K., Saito N., Okido M.

Magnesium Technology page： 241 - 245 2012

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

Magnesium is the lightest structural metal with high specific strength and good mechanical properties. However, poor corrosion resistance limits its widespread use in many applications. Magnesium is usually treated with chromate conversion coatings. However, due to changing environmental regulations and pollution prevention requirements, a significant push exists to find new, alternative for poisonous Cr6+. Therefore, we aim to improve corrosion resistance of anodic coatings on AZ31 alloys using low cost non-chromate electrolyte. Anodizing was carried out in alkaline solutions with tin additives. The effect of tin additives on the coating film was characterized by SEM and XRD. The corrosion resistance was evaluated using anodic and cathodic polarizations and electrochemical impedance spectroscopy (EIS). Corrosion resistance property was improved with tin additives and the best anti-corrosion property was obtained with addition of 0.03 M Na 2SnO3.3H2O to anodizing solution.

DOI： 10.1002/9781118359228.ch45

Size-controlled gold nanoparticles synthesized in solution plasma

Bratescu M.A., Cho S.P., Takai O., Saito N.

Journal of Physical Chemistry C Vol. 115 ( 50 ) page： 24569 - 24576 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry C

Size-controlled gold nanoparticles (NPs) have been synthesized using an electrical discharge in a liquid environment, termed solution plasma processing (SPP). The gold NPs exhibit sizes from 1 to 2 to 10 nm when the solution pH was adjusted in the range from 12 to 3, respectively. The chemical environment surrounding the gold NPs depends on the preparation conditions and determines the electrostatic interaction among the nanoparticles, which alters their final size. Information obtained from XPS analysis, ToF-SIMS mass spectra, and UV-vis absorption spectroscopy were consistent and demonstrate that the gold NPs are partially oxidized on the surface, when synthesized in a pH 12 solution, and remain surrounded by gold chloride compounds when synthesized in a pH 3 solution. Plasma diagnostics shows that a high electron density contributes to generating a larger number of hydrogen radicals, which represent the main component in the reduction process of the gold ion into the neutral form. © 2011 American Chemical Society.

DOI： 10.1021/jp207447c

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