Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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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 Open Access

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)) Open Access

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

Applied Physics Letters Vol. 104 ( 14 ) 2014.4

A phonon thermodynamics approach of gold nanofluids synthesized in solution plasma

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

Applied Physics Letters Vol. 104 ( 11 ) 2014.3

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

The phonon thermodynamics theory for liquids was applied to explain the thermal characteristics of gold nanofluids synthesized by a simple, one-step, and chemical-free method using an electrical discharge in a liquid environment termed solution plasma process. The specific heat capacity of nanofluids was measured with a differential scanning calorimeter using the ratio between the differential heat flow rate and the heating rate. The decrease of the specific heat capacity with 10% of gold nanofluids relative to water was explained by the decrease of Frenkel relaxation time with 22%, considering a solid-like state model of liquids. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4868872

Depolymerization of chitosan-metal complexes via a solution plasma technique

Pornsunthorntawee O., Katepetch C., Vanichvattanadecha C., Saito N., Rujiravanit R.

Carbohydrate Polymers Vol. 102 ( 1 ) page： 504 - 512 2014.2

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

Chitosan-metal complexes were depolymerized under acidic conditions using a solution plasma system. Four different types of metal ions, including Ag +, Zn2+, Cu2+, and Fe3+ ions, were added to the chitosan solution at a metal-to-chitosan molar ratio of 1:8. The depolymerization rate was affected by the types of metal ions that form complexes with chitosan. The complexation of chitosan with Cu2+ or Fe3+ ions strongly promoted the depolymerization rate of chitosan using a solution plasma treatment. However, chitosan-Ag+ and chitosan-Zn2+ complexes exhibited no change in the depolymerization rate compared to chitosan. After plasma treatment of the chitosan-metal complexes, the depolymerized chitosan products were separated into water-insoluble and water-soluble fractions. The water-soluble fraction containing low-molecular-weight chitosan was obtained in a yield of less than 57% for the depolymerization of chitosan-Fe3+ complex with the plasma treatment time of 180 min. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbpol.2013.11.025

A novel one-step synthesis of gold nanoparticles in an alginate gel matrix by solution plasma sputtering

Watthanaphanit A., Panomsuwan G., Saito N.

RSC Advances Vol. 4 ( 4 ) page： 1622 - 1629 2014

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

We report a novel strategy to produce stable colloidal gold nanoparticles (AuNPs) in alginate aqueous solution which can be done in one step and without any chemicals. The AuNPs were produced by applying a voltage across a pair of gold electrodes which were immersed in alginate aqueous solution. Since the generation of AuNPs was caused by the sputtering of gold electrodes, the process was named the solution plasma sputtering (SPS) process. We utilize the alginate polymer in order to meet three important requirements: (1) to promote the generation of plasma in a liquid environment, (2) to endow biocompatibility to the AuNPs, and (3) to provide colloidal stability to the AuNPs-alginate aqueous suspensions. The alginate concentrations were varied as 0.2, 0.5, and 0.9 %w/v. The concentration-dependent effect on the particle size of AuNPs, the physical absorption property and the stability of the AuNPs-alginate suspensions were studied. Results indicate that preparation of chemical-free colloidal AuNPs-alginate aqueous suspension is successful by the SPS process. The obtained colloidal suspensions were stable and able to retain their strong plasmon absorption bands within a reasonable time period. As a consequence, this is a high-potential technique to produce AuNPs suspended in alginate aqueous solution appropriate for biomedical applications. © 2014 The Royal Society of Chemistry.

DOI： 10.1039/c3ra45029e

Solution plasma exfoliation of graphene flakes from graphite electrodes

Lee H., Bratescu M., Ueno T., Saito N.

RSC Advances Vol. 4 ( 93 ) page： 51758 - 51765 2014

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

Graphene flakes were successfully produced by a simple method named a solution plasma process. The plasma was generated between two carbon electrode tips which were immersed in distilled water. The production approach is a continuous energy accumulation induced by focusing of plasma streamers on the surface of electrodes. This focused energy produces thermal gradient zones where a proper energy level is produced. Concisely, the energy is enough to extract graphene layers from the graphite structure but not enough to break covalent C-C bonds within the graphene sheets. Optical emission spectroscopy results showed the decomposition of carbon from the graphite electrodes with different intensities for the carbon species. Transmission electron microscopy images confirmed the hexagonal honeycomb structure of the graphene flakes. Furthermore, broadening of the 2D band in the Raman spectra revealed that the graphene flakes were disordered multilayers. This journal is

DOI： 10.1039/c4ra03253e

Solution plasma synthesis process of tungsten carbide on N-doped carbon nanocomposite with enhanced catalytic ORR activity and durability

Kim D., Li O., Pootawang P., Saito N.

RSC Advances Vol. 4 ( 32 ) page： 16813 - 16819 2014

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

In this study, the enhancement of ORR activity and durability by an N-doped carbon nanocomposite on tungsten carbide (WC) nanoparticles was reported. The nanocomposite of tungsten carbide on two different carbon matrices, pure carbon matrix (WC/C) and N-doped carbon matrix (WC/N-C), was at first prepared by a simple discharge process in the mixture of benzene/dodecane and pyrrole/dodecane. The nanoparticles of tungsten carbide were formed via the sputtering effect of tungsten electrodes during discharge. The results of TEM and XRD demonstrated that tungsten carbide nanoparticles with a mean size of 6 nm were evenly dispersed on both carbon matrices. The results of cyclic voltammetry measurements showed that both obtained metal/carbon matrices promoted a significant oxygen reduction reaction (ORR) in alkaline solution. The ORR potential of tungsten carbide/carbon matrix and nitrogen-doped carbon were -0.29 V and -0.36 V, respectively. The enhancement of ORR activity in WC/N-C was attributed to the combined catalytic effects of WC and N in the carbon matrix. Although the ORR activity of WC/N-C was still incomparable with commercial Pt/C, the durability of the catalyst was significant higher than that of Pt/C in a methanol environment. The catalyst did not exhibit an evident change of initial current after 4000 s. Therefore, the inexpensive N-doped WC/C nanocomposite might be a promising and highly durable catalytic material for cathodes in fuel cell applications. © 2014 the Partner Organisations.

DOI： 10.1039/c4ra02380c

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.

Materials Research Society Symposium Proceedings Vol. 1641 2014

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

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. © 2014 Materials Research Society.

DOI： 10.1557/opl.2014.319

Charge doping of large-area graphene by gold-alloy nanoparticles

Bratescu M., Saito N.

Journal of Physical Chemistry C Vol. 117 ( 50 ) page： 26804 - 26810 2013.12

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

We present a facile, one-step, and surfactant-free method for direct synthesis and loading of stable gold and gold-alloy nanoparticles (NPs) on large-area graphene using an electrical discharge in a liquid environment, termed solution plasma. We observed a charge doping of graphene by the gold NPs, which depends on the particles' chemical composition, even if the NPs contain a few percent of trivalent sp metals, such as indium (In) or gallium (Ga). Raman and electron energy loss spectroscopy (EELS) methods show that graphene is doped with electrons (n-type) in the case of gold NPs and with holes (p-type) in the case of gold-alloy NPs. The Raman band shift indicates that the amount of the transferred electrons from the gold NPs to graphene is -2 × 10 -4 electrons per unit cell. The gold-alloy NPs receive from graphene (2 and 4) × 10-5 electrons per unit cell if the gold NPs contain In and Ga, respectively. In the EELS spectra, the decrease in the intensity of the 1s-π* transition and the shift of the π* peak to higher energy confirm the depopulation of the antibonding states caused by the electron transfer from graphene to the gold-alloy NPs. © 2013 American Chemical Society.

DOI： 10.1021/jp409368c

Functionalization of multiwalled carbon nanotubes by solution plasma processing in ammonia aqueous solution and preparation of composite material with polyamide 6

Shirafuji T., Noguchi Y., Yamamoto T., Hieda J., Saito N., Takai O., Tsuchimoto A., Nojima K., Okabe Y.

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

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

Solution plasma processing (SPP) has been performed on multiwalled carbon nanotubes (MWCNTs) in ammonia aqueous solution. The MWCNTs, which do not disperse in aqueous solution, uniformly dispersed after the SPP. Only 2 h was required to obtain 10 g of the dispersed MWCNTs, while 7 days and additional chemicals were required for 185mg in a previous study. The X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy of the SPP-treated MWCNTs revealed that nitrogen- and oxygen-containing groups are formed on the MWCNTs. Serious damage to the MWCNT structure was not observed in the Raman spectrum or transmission electron microscopy images of the SPP-treated MWCNTs. The composite materials prepared using polyamide 6 with the SPP-treated MWCNTs showed better tensile, bending, and impact strength than those prepared with nontreated MWCNTs. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.125101

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

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