Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Sou Ryuzaki Last modified date:2021.07.13

Assistant Professor / Department of Fundamental Organic Chemistry / Institute for Materials Chemistry and Engineering


Papers
1. N. Saito, S. Ryuzaki, Y. Tsuji, Y. Noguchi, P. Wang, D. Tanaka, Y. Arima, K. Okamoto, K. Yoshizawa, K. Tamada., Effect of chemically induced permittivity changes on the plasmonic properties of metal nanoparticles, Communications Materials, https://doi.org/10.1038/s43246-021-00159-6, 2, 54, 1-8, 2021.06, Understanding chemical effects on the plasmonic properties of a metal nanomaterial due to the surface molecules on that metal is of great importance in the field of plasmonics and these effects have yet to be completely elucidated. Here, we report mechanisms of the chemically induced change in the electronic state at the metal-ligand interface of silver nanoparticles due to the ligand molecules, and the effect of this change on the plasmonic properties of those nanoparticles. It was found that changes in the electron density of states at the metal-ligand interface cause alterations in the induced and permanent dipole moments, and eventually to the permittivity at the interface, when the wave function near the Fermi level is localized at the interface. These alterations play a key role in determining the plasmonic properties of silver nanoparticles. The present findings provide a more precise understanding of the interconnection between the electronic states at the metal-organic interface and the plasmonic properties of the metal..
2. S. Ryuzaki, T. Yasui, M. Tsutsui, K. Yokota, Y. Komoto, P. Paisrisarn, N. Kaji, D. Ito, K. Tamada, T. Ochiya, M. Taniguchi, Y. Baba, and T. Kawai., Rapid Discrimination of Extracellular Vesicles by Shape Distribution Analysis, ANALYTICAL CHEMISTRY, 10.1021/acs.analchem.1c00258, 93, 18, 7037-7044, 2021.05, A rapid and simple cancer detection method independent of cancer type is an important technology for cancer diagnosis. Although the expression profiles of biological molecules contained in cancer cell-derived extracellular vesicles (EVs) are considered candidates for discrimination indexes to identify any cancerous cells in the body, it takes a certain amount of time to examine these expression profiles. Here, we report the shape distributions of EVs suspended in a solution and the potential of these distributions as a discrimination index to discriminate cancer cells. Distribution analysis is achieved by low-aspect-ratio nanopore devices that enable us to rapidly analyze EV shapes individually in solution, and the present results reveal a dependence of EV shape distribution on the type of cells (cultured liver, breast, and colorectal cancer cells and cultured normal breast cells) secreting EVs. The findings in this study provide realizability and experimental basis for a simple method to discriminate several types of cancerous cells based on rapid analyses of EV shape distributions..
3. M. Tsutsui, S. Ryuzaki, K. Yokota, H. Yuhui, T. Washio, K. Tamada, and T. Kawai., Field effect control of translocation dynamic in surround-gate nanopores, Communications Materials, https://doi.org/10.1038/s43246-021-00132-3, 2, 29, 1-9, 2021.03, Controlling the fast electrophoresis of nano-objects in solid-state nanopores is a critical issue for achieving electrical analysis of single-particles by ionic current. In particular, it is crucial to slow-down the translocation dynamics of nanoparticles. We herein report that a focused electric field and associated water flow in a surround-gate nanopore can be used to trap and manipulate a nanoscale object. We fine-control the electroosmosis-induced water flow by modulating the wall surface potential via gate voltage. We find that a nanoparticle can be captured in the vicinity of the conduit by balancing the counteracting electrophoretic and hydrodynamic drag forces. By creating a subtle force imbalance, in addition, we also demonstrate a gate-controllable motion of single-particles moving at an extremely slow
speed of several tens of nanometers per second. The present method may be useful in singlemolecule detection by solid-state nanopores and nanochannels..
4. Takekuma, Haruka; Leng, Junfu; Tateishi, Kazutaka; Xu, Yang; Chan, Yinthai; Ryuzaki, Sou; Wang, Pangpang; Okamoto, Koichi; Tamada, Kaoru, Layer Number-Dependent Enhanced Photoluminescence from a Quantum Dot Metamaterial Optical Resonator, ACS APPLIED ELECTRONIC MATERIALS, 10.1021/acsaelm.0c01011, 3, 1, 468-475, 2021.01.
5. Ryuzaki, Sou; Matsuda, Rintaro; Taniguchi, Masateru, Pore Structures for High-Throughput Nanopore Devices, MICROMACHINES, 10.3390/mi11100893, 11, 10, 2020.10.
6. Okamoto, Koichi; Okura, Kota; Wang, Pangpang; Ryuzaki, Sou; Tamada, Kaoru, Flexibly tunable surface plasmon resonance by strong mode coupling using a random metal nanohemisphere on mirror, NANOPHOTONICS, 10.1515/nanoph-2020-0118, 9, 10, 3409-3418, 2020.09.
7. Matsuda, Rintaro; Ryuzaki, Sou; Okamoto, Koichi; Arima, Yusuke; Tsutsui, Makusu; Taniguchi, Masateru; Tamada, Kaoru, Finite-difference time-domain simulations of inverted cone-shaped plasmonic nanopore structures, JOURNAL OF APPLIED PHYSICS, 10.1063/5.0010418, 127, 24, 2020.06.
8. Haruka Takekuma, Kyohei Tagomori, Shuhei Shinohara, Shihomi Masuda, Yang Xu, Yinthai Chan, Pangpang Wang, Soh Ryuzaki, Koichi Okamoto, Kaoru Tamada, How to make microscale pores on a self-assembled Ag nanoparticle monolayer, Colloids and Interface Science Communications, 10.1016/j.colcom.2019.100175, 30, 2019.05, In this short communication, we report a procedure for the fabrication of microscale pores on a rigid self-assembled Ag nanoparticle monolayer with nanothickness. Here, condensed water droplets on a hydrophobic substrate are used as a pore formation template for Langmuir-Schaefer film deposition. The optical properties of the Ag nanoparticle monolayer were influenced by the porous structure, e.g., the localized surface plasmon resonance (LSPR) peak was weakened and broadened for the porous monolayer compared with the homogeneous monolayer, even though the number of particles on the substrate should be the same between them. The pores obtained by this method were robust and could be used as a mask for metal deposition or local fluorescence imaging. This environmentally friendly technique can provide a micropatterned surface with a minimal cytotoxicity, which has high potential for LSPR mediated biosensing and bioimaging applications..
9. Pangpang Wang, Soh Ryuzaki, Lumei Gao, Shuhei Shinohara, Noboru Saito, Koichi Okamoto, Kaoru Tamada, Sunao Yamada, Comparison of the mechanical strength of a monolayer of silver nanoparticles both in the freestanding state and on a soft substrate, Journal of Applied Physics, 10.1063/1.5063567, 125, 13, 2019.04, A 7-nm-thick monolayer comprising myristate-capped silver nanoparticles (AgNPs) was fabricated by first drop casting an AgNP solution on the surface of a 10-100 μl water drop placed on a solid substrate. With the natural evaporation of the water, a monolayer slowly descended onto the substrate, the latter containing an array of 2.5-μm-diameter and 200-nm-deep holes, and finally formed circular freestanding monolayers in the holes. Nanoindentation measurement based on atomic force microscopy was carried out on the circular freestanding monolayer at its center, and the extending and retracting force-indentation curves were recorded to analyze further the mechanical properties of the monolayer. The force-indentation curves were evidently nonlinear, and so a two-term continuum-mechanics theory was used to interpret the results. By fitting the force-indentation curves using a two-term equation, the prestress and Young’s modulus of the freestanding AgNP monolayer were obtained as approximately 0.05 N/m and several gigapascals, respectively, which are consistent with the results reported in the literature. For comparison, we also studied the mechanical responses of AgNP monolayers and bilayers on a soft polydimethylsiloxane (PDMS) substrate by using nanoindentation. Because the AgNP monolayer was stiffer than the PDMS substrate, it was possible to measure the mechanical response of the former despite it being only 7 nm thick. The mechanical strength of the freestanding AgNP monolayers was considered to be dominated by the attractive interactions between the interdigitated hydrocarbon chains of the myristate..
10. Kazutaka Tateishi, Pangpang Wang, Soh Ryuzaki, Mitsuru Funato, Yoichi Kawakami, Koichi Okamoto, Kaoru Tamada, Micro-photoluminescence mapping of light emissions from aluminum-coated InGaN/GaN quantum wells, Applied Physics Express, 10.7567/1882-0786/ab0911, 12, 5, 2019.01, Micro-photoluminescence (PL) mapping was investigated for Al-coated InGaN/GaN quantum wells (QWs), which showed huge PL enhancement by the surface plasmon (SP) resonance. The obtained images show inhomogeneity at the micro-meter scale; in addition, the region with lower PL intensities tend to have a longer PL wavelength for bare QWs. This correlation changed with an Al coating, positive correlations were observed in an area with a relatively short peak wavelength with blue-shift. Conversely, negative correlations were observed at longer peak wavelengths. These results suggest that the quantum-confined Stark effect (QCSE) was screened by the enhanced electrical-field of the SP resonance..
11. Ayumi Ishijima, Pangpang Wang, Soh Ryuzaki, Koichi Okamoto, Kaoru Tamada, Comparison of LSPR-mediated enhanced fluorescence excited by S- and P-polarized light on a two-dimensionally assembled silver nanoparticle sheet, Applied Physics Letters, 10.1063/1.5056211, 113, 17, 2018.10, Localized surface plasmon resonance (LSPR) excited by an oblique incidence of S- and P-polarized light to a two-dimensionally assembled silver nanoparticle sheet was investigated via enhanced fluorescence under total internal reflection fluorescence (TIRF) microscopy. The finite-difference-time-domain simulation demonstrated that the S-polarized light induced a strong plasmon coupling at a nanogap between the particles, which eventually led to a highly confined, strong, and "flattened" electric field on the entire surface. In contrast, the LSPR field excited by P-polarized light was located on the individual particles, having a relatively long tail in the axial direction (low confinement). The LSPR-mediated fluorescence appeared stronger under P-polarized light than under S-polarized light in the experiments using cyanine dye solutions, while the opposite result was obtained for the fluorescence bead snapshot (diameter: 200 nm). Magnified images of the single beads taken by a super-resolution digital CMOS camera (65 nm/pixel) revealed improved lateral resolution when S-polarized light was used on both the silver nanoparticle sheet and glass under TIRF microscopy..
12. Priastuti Wulandari, Yolla Sukma Handayani, Rachmat Hidayat, Pangpang Wang, Soh Ryuzaki, Koichi Okamoto, Kaoru Tamada, Surface plasmon resonance effect of silver nanoparticles on the enhanced efficiency of inverted hybrid organic-inorganic solar cell, Journal of Nonlinear Optical Physics and Materials, 10.1142/S0218863518500170, 27, 2, 2018.06, We investigate the effects of silver nanoparticles capped by 1-octanethiol (AgSC8) incorporated into the active layer of regioregular poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) in the fabrication of an inverted hybrid solar cell. The localized surface plasmon resonance (LSPR) excited in AgSC8 is expected to enhance the photon absorption as well as improve the efficiency of exciton generation and dissociation in this type of solar cell. The measured UV-visible absorption spectra show that photoactive polymer (P3HT:PCBM) layers with 2.09wt.% and 3.34wt.% AgSC8 incorporations remain homogeneous, while it appears aggregated with 5.02wt.% AgSC8 incorporation. Under the illumination of 100mW/cm
2
simulated solar irradiation, the fabricated device exhibits an increased open circuit voltage (Voc) from 0.327V to 0.665V for the case with 3.34wt.% AgSC8 incorporation and an improved device power conversion efficiency (PCE) from 1.01% to 1.92%. These results suggest the favorably role of AgSC8 in photo-generation of exciton and its dissociation at the LSPR frequency of AgSC8. The decrease of short circuit current density (Jsc) from 10.316mA/cm
2to8.668mA/cm
2 nevertheless implies reduced conductivity due to AgSC8 incorporation..
13. Noboru Saito, Sou Ryuzaki, Pangpang Wang, Susie Park, Nobuyuki Sakai, Tetsu Tatsuma, Koichi Okamoto, Kaoru Tamada, Durability improvements of two-dimensional metal nanoparticle sheets by molecular cross-linked structures between nanoparticles, Japanese Journal of Applied Physics, 10.7567/JJAP.57.03EG10, 57, 3, 2018.03, The durability of two-dimensional metal nanoparticle sheets is a crucial factor for realizing next-generation optoelectronic devices based on plasmonics such as organic light-emitting diodes. Here, we report improvements in the durability of Ag nanoparticle sheets by forming alkanedithiol (DT16) cross-linked structures between the nanoparticles. The cross-linked structures in a sheet were fabricated by the self-assembly of DT16-capped Ag nanoparticles with 10% coverage (AgDT16). The durabilities for thermal, organic solvent, and oxidation reactions of AgDT16 sheets were found to be improved owing to the cross-linked structures by comparing Ag nanoparticle sheets without the cross-linked structures. The absorbance spectra revealed that the Ag nanoparticle sheets without the structure are markedly damaged by each durability test, whereas the AgDT16 sheets remain. The molecular cross-linked structures between nanoparticles in two-dimansional metal nanoparticle sheets were found to have the potential to play a key role in the realization of plasmonic optoelectronic devices including metal nanoparticles..
14. Shihomi Masuda, Yuhki Yanase, Eiji Usukura, Sou Ryuzaki, Pangpang Wang, Koichi Okamoto, Thasaneeya Kuboki, Satoru Kidoaki, Kaoru Tamada, High-resolution imaging of a cell-attached nanointerface using a gold-nanoparticle two-dimensional sheet, Scientific reports, 10.1038/s41598-017-04000-4, 7, 1, 2017.12, This paper proposes a simple, effective, non-scanning method for the visualization of a cell-attached nanointerface. The method uses localized surface plasmon resonance (LSPR) excited homogeneously on a two-dimensional (2D) self-assembled gold-nanoparticle sheet. The LSPR of the gold-nanoparticle sheet provides high-contrast interfacial images due to the confined light within a region a few tens of nanometers from the particles and the enhancement of fluorescence. Test experiments on rat basophilic leukemia (RBL-2H3) cells with fluorescence-labeled actin filaments revealed high axial and lateral resolution even under a regular epifluorescence microscope, which produced higher quality images than those captured under a total internal reflection fluorescence (TIRF) microscope. This non-scanning-type, high-resolution imaging method will be an effective tool for monitoring interfacial phenomena that exhibit relatively rapid reaction kinetics in various cellular and molecular dynamics..
15. Noboru Saito, Pangpang Wang, Koichi Okamoto, Sou Ryuzaki, Kaoru Tamada, Large patternable metal nanoparticle sheets by photo/e-beam lithography, Nanotechnology, 10.1088/1361-6528/aa8930, 28, 43, 2017.10, Techniques for micro/nano-scale patterning of large metal nanoparticle sheets can potentially be used to realize high-performance photoelectronic devices because the sheets provide greatly enhanced electrical fields around the nanoparticles due to localized surface plasmon resonances. However, no single metal nanoparticle sheet currently exists with sufficient durability for conventional lithographical processes. Here, we report large photo and/or e-beam lithographic patternable metal nanoparticle sheets with improved durability by incorporating molecular cross-linked structures between nanoparticles. The cross-linked structures were easily formed by a one-step chemical reaction; immersing a single nanoparticle sheet consisting of core metals, to which capping molecules ionically bond, in a dithiol ethanol solution. The ligand exchange reaction processes were discussed in detail, and we demonstrated 20 μm wide line and space patterns, and a 170 nm wide line of the silver nanoparticle sheets..
16. Kazutaka Tateishi, Pangpang Wang, Sou Ryuzaki, Mitsuru Funato, Yoichi Kawakami, Koichi Okamoto, Kaoru Tamada, Micro-photoluminescence mapping of surface plasmon enhanced light emissions from InGaN/GaN quantum wells, Applied Physics Letters, 10.1063/1.4998798, 111, 17, 2017.10, We conducted photoluminescence (PL) mapping to elucidate the detailed mechanism of PL enhancement based on the energy transfer from excitons to surface plasmon polaritons (SPPs) in silver-coated InGaN quantum wells (QWs). The PL mapping for bare InGaN QWs showed positive or negative correlations between the PL peak intensity and wavelength. These correlations are normally caused by exciton localization and the quantum confined Stark effect, respectively; however, they did not appear in the silver-coated region of the InGaN QWs, and the wavelength distribution shifted into shorter wavelengths due to the SP-induced PL enhancement. These results suggest that the energy transfer from the excitons to the SPPs should be much faster than that in the exciton localization and charge screening processes of the piezoelectric field in QWs..
17. Zhen Yu Juang, Chien Chih Tseng, Yumeng Shi, Wen Pin Hsieh, Sou Ryuzaki, Noboru Saito, Chia En Hsiung, Wen Hao Chang, Yenny Hernandez, Yu Han, Kaoru Tamada, Lain Jong Li, Graphene-Au nanoparticle based vertical heterostructures
A novel route towards high-ZT Thermoelectric devices, Nano Energy, 10.1016/j.nanoen.2017.06.004, 38, 385-391, 2017.08, Monolayer graphene exhibits impressive in-plane thermal conductivity (> 1000 W m–1 K–1). However, the out-of-plane thermal transport is limited due to the weak van der Waals interaction, indicating the possibility of constructing a vertical thermoelectric (TE) device. Here, we propose a cross-plane TE device based on the vertical heterostructures of few-layer graphene and gold nanoparticles (AuNPs) on Si substrates, where the incorporation of AuNPs further inhibits the phonon transport and enhances the electrical conductivity along vertical direction. A measurable Seebeck voltage is produced vertically between top graphene and bottom Si when the device is put on a hot surface and the figure of merit ZT is estimated as 1 at room temperature from the transient Harman method. The polarity of the output voltage is determined by the carrier polarity of the substrate. The device concept is also applicable to a flexible and transparent substrate as demonstrated..
18. Sou Ryuzaki, Makusu Tsutsui, Yuhui He, Kazumichi Yokota, Akihide Arima, Takanori Morikawa, Masateru Taniguchi, Tomoji Kawai, Rapid structural analysis of nanomaterials in aqueous solutions, Nanotechnology, 10.1088/1361-6528/aa5e66, 28, 15, 2017.03, Rapid structural analysis of nanoscale matter in a liquid environment represents innovative technologies that reveal the identities and functions of biologically important molecules. However, there is currently no method with high spatio-temporal resolution that can scan individual particles in solutions to gain structural information. Here we report the development of a nanopore platform realizing quantitative structural analysis for suspended nanomaterials in
solutions with a high z-axis and xy-plane spatial resolution of 35.8±1.1 and 12 nm, respectively. We used a low thickness-to-diameter aspect ratio pore architecture for achieving cross sectional areas of analyte (i.e. tomograms). Combining this with multiphysics simulation methods to translate ionic current data into tomograms, we demonstrated rapid structural analysis of single polystyrene (Pst) beads and single dumbbell-like Pst beads in aqueous solutions..
19. Soh Ryuzaki, Jun Onoe, Photoexcited carrier dynamics in organic solar cells, Organic Solar Cells Materials, Devices, Interfaces, and Modeling, 10.1201/b18072, 143-166, 2017.01, Understanding the photoexcited carrier dynamics in organic photovoltaic (OPV) cells helps us to improve their power conversion efficiency (η) for practical use because some breakthroughs in the recent decade have been based on bulk-heterojunctions (BHJs) between donor (D) and acceptor (A) materials. The BHJ plays a role of increasing the D-A interface area involving photocarrier generation regions, and thus the number of photocarriers increases at the interfaces [1,2]. Although the BHJ can improve the η of OPV cells by up to ca. 8%, the improving rate of η does not significantly increase [3-5]. This is presumably because there are still major unclear points for BHJ as follows: (1) the nanostructure of the BHJ schematic illustration has been shown) and (2) the reproducibility of BHJ fabrication. Figure 6.1 schematically illustrates typical structures of (a) a D-A hetero doublelayered OPV cell and (b) a BHJ-OPV cell. As shown in Figure 6.1b, because the BHJ is fabricated by coevaporation of donor and acceptor materials or by spin-coating conductive polymers, the D-A interface thus formed is too complex to analyze and reproduce the nanostructure compared to that of a double-layered heterojunction [2,6]. These facts make it difficult to discuss the photoexcited carrier dynamics at the BHJ D-A interface. Accordingly, the reason why the BHJ improves the η has been unclear so far..
20. Akihide Arima, Makusu Tsutsui, Yuhui He, Sou Ryuzaki, Masateru Taniguchi, Electrical trapping mechanism of single-microparticles in a pore sensor, AIP Advances, 10.1063/1.4967214, 6, 11, 2016.11, Nanopore sensing via resistive pulse technique are utilized as a potent tool to characterize physical and chemical property of single -molecules and -particles. In this article, we studied the influence of particle trajectory to the ionic conductance through a pore. We performed the optical/electrical simultaneous sensing of electrophoretic capture dynamics of single-particles at a pore using a microchannel/nanopore system. We detected ionic current drops synchronous to a fluorescently dyed particle being electrophoretically drawn and become immobilized at a pore in the optical imaging. We also identified anomalous trapping events wherein particles were captured at nanoscale pin-holes formed unintentionally in a SiN membrane that gave rise to relatively small current drops. This method is expected to be a useful platform for testing novel nanopore sensor design wherein current behaves in unpredictable manner..
21. Koichi Okamoto, Daisuke Tanaka, Ryo Degawa, Xinheng Li, Pangpang Wang, Sou Ryuzaki, Kaoru Tamada, Electromagnetically induced transparency of a plasmonic metamaterial light absorber based on multilayered metallic nanoparticle sheets, Scientific reports, 10.1038/srep36165, 6, 2016.11, In this study, we observed the peak splitting of absorption spectra for two-dimensional sheets of silver nanoparticles due to the electromagnetically induced transparency (EIT) effect. This unique optical phenomenon was observed for the multilayered nanosheets up to 20 layers on a metal substrate, while this phenomenon was not observed on a transparent substrate. The wavelength and intensities of the split peaks depend on the number of layers, and the experimental results were well reproduced by the calculation of the Transfer-Matrix method by employing the effective medium approximation. The Ag nanosheets used in this study can act as a plasmonic metamaterial light absorber, which has a such large oscillator strength. This phenomenon is a fundamental optical property of a thin film on a metal substrate but has never been observed because native materials do not have a large oscillator strength. This new type of EIT effect using a plasmonic metamaterial light absorber presents the potential for the development of future optic and photonic technologies..
22. Pangpang Wang, Daisuke Tanaka, Soh Ryuzaki, Shohei Araki, Koichi Okamoto, Kaoru Tamada, Silver nanoparticles with tunable work functions, Applied Physics Letters, 10.1063/1.4933253, 107, 15, 2015.10, To improve the efficiencies of electronic devices, materials with variable work functions are required to decrease the energy level differences at the interfaces between working layers. Here, we report a method to obtain silver nanoparticles with tunable work functions, which have the same silver core of 5 nm in diameter and are capped by myristates and 1-octanethoilates self-assembled monolayers, respectively. The silver nanoparticles capped by organic molecules can form a uniform two-dimensional sheet at air-water interface, and the sheet can be transferred on various hydrophobic substrates. The surface potential of the two-dimensional nanoparticle sheet was measured in terms of Kelvin probe force microscopy, and the work function of the sheet was then calculated from the surface potential value by comparing with a reference material. The exchange of the capping molecules results in a work function change of approximately 150-250 meV without affecting their hydrophobicity. We systematically discussed the origin of the work function difference and found it should come mainly from the anchor groups of the ligand molecules. The organic molecule capped nanoparticles with tunable work functions have a potential for the applications in organic electronic devices..
23. Sou Ryuzaki, Jakob A.S. Meyer, Søren Petersen, Kasper Nørgaard, Tue Hassenkam, Bo W. Laursen, Local charge transport properties of hydrazine reduced monolayer graphene oxide sheets prepared under pressure condition, Applied Physics Letters, 10.1063/1.4895072, 105, 9, 2014.09, Charge transport properties of chemically reduced graphene oxide (RGO) sheets prepared by treatment with hydrazine were examined using conductive atomic force microscopy. The current-voltage (I-V) characteristics of monolayer RGO sheets prepared under atmospheric pressure followed an exponentially increase due to 2D variable-range hopping conduction through small graphene domains in an RGO sheet containing defect regions of residual sp3carbon clusters bonded to oxygen groups, whereas RGO sheets prepared in a closed container under moderate pressure showed linear I-V characteristics with a conductivity of 267.2-537.5S/m. It was found that the chemical reduction under pressure results in larger graphene domains (sp2networks) in the RGO sheets when compared to that prepared under atmospheric pressure, indicating that the present reduction of GO sheets under the pressure is one of the effective methods to make well-reduced GO sheets..
24. Yuhui He, Makusu Tsutsui, Sou Ryuzaki, Kazumichi Yokota, Masateru Taniguchi, Tomoji Kawai, Graphene/hexagonal boron nitride/graphene nanopore for electrical detection of single molecules, NPG Asia Materials, 10.1038/am.2014.29, 6, 6, 2014.06, Graphene nanopore device, since its proposal, has witnessed tremendous progress toward the goal of single-molecule detection. However, one central challenge of preparing electrodes with nanometer precision on the graphene remains unsolved. Here we show theoretically the feasibility of graphene/hexagonal BN (h-BN)/graphene structure where top graphene layer acts as one electrical contact while the bottom layer as the other. Based on quantum chemistry/nonequilibrium Green's function investigation, we give clear physical pictures why ABC stacking of the above heterogeneous layers results in excellent insulating of the top and bottom graphene electrodes. On the other hand, when the target molecule is inside the nanopore the background conductance through the h-BN dielectric will not keep decreasing even though more layers of h-BN are inside the nanopore. The mechanism is illustrated as that the presence of the molecule will enhance the vertical transmission through the h-BN dielectric via quantum interference. We employ a single-level molecule model, and show quantitatively that the discussed effect can be utilized as a powerful signal amplifier for the molecule conductance, thus enhancing the measurability of single molecules by 3-4 orders..
25. Soh Ryuzaki, Jun Onoe, Anomaly in the electric resistivity of one-dimensional uneven peanut-shaped C60 polymer film at a low temperature, Applied Physics Letters, 10.1063/1.4869120, 104, 11, 2014.03, We performed in situ four-probe measurements of the current-voltage characteristics of one-dimensional (1D) uneven peanut-shaped C60 polymer films in the temperature range 30-350 K under ultrahigh vacuum conditions (2 × 10-7 Pa). Arrhenius plots of the film resistance with respect to temperature showed two different electron-conduction mechanisms. While electrons are conducted via a thermal excitation hopping at temperatures above 160 K, the resistivity of the 1D polymer film exhibits an anomalous behavior that becomes fluctuated at a given value in the temperature range 40-90 K and decreases at temperatures below 40 K..
26. Soh Ryuzaki, Jun Onoe, Photo-generated carrier dynamics in the vicinity of the donor/acceptor interface of organic solar cells, Electronics and Communications in Japan, 10.1002/ecj.11542, 96, 8, 1-8, 2013.08, Change in electronic states before and after photo-irradiation at a Donor/Acceptor (D/A) interface in organic solar cells consisting of zinc-porphyrin and fullerene films has been examined using in situ impedance spectroscopy (IS), which makes it possible to non-destructively measure a built-in potential (Vbi) of both D and A films at the D/A interface. The accumulation of photo-generated carriers in the vicinity of the D/A interface was found to increase the Vbi of both D [Zn(OEP)] and A [C60] films at the interface. In addition, it was noted that the sum of Vbi obtained on photo-irradiation was in good agreement with the open-circuit voltage (VOC), of which the origin is still unsolved for organic solar cells. Thus, the charge accumulation of photo-generated carriers in the vicinity of the D/A interface plays a key role in determining V OC..
27. Masayuki Furuhashi, Yukihiro Okamoto, Daisuke Onoshima, Takahito Ohshiro, Sou Ryuzaki, Kazumichi Yokota, Makusu Tsutsui, Masateru Taniguchi, Kazuhiko Nakatani, Yoshinobu Baba, Tomoji Kawai, High speed DNA denaturation using microheating devices, Applied Physics Letters, 10.1063/1.4813552, 103, 2, 2013.07, Denaturation is a first step for further treatment of DNA and is expected to be carried out rapidly on an integrated chip. A microheater is a promising device for the denaturation because of easiness for fabrication and operation. In the present study, we fabricated a microheater and thermometers on a coverslip and investigated response of temperature to application of voltage. In addition, our experiment and simulation proved local heating at an aimed area. Finally, we demonstrated denaturation of DNA in buffer solution, the result of which proved that the DNA around the heater denatured within 60 ms..
28. Makusu Tsutsui, Yoichi Maeda, Yuhui He, Sadato Hongo, Soh Ryuzaki, Satoyuki Kawano, Tomoji Kawai, Masateru Taniguchi, Trapping and identifying single-nanoparticles using a low-aspect-ratio nanopore, Applied Physics Letters, 10.1063/1.4813084, 103, 1, 2013.07, Manipulation of particles and molecules in fluid is a fundamental technology in biosensors. Here, we report electrical trapping and identification of single-nanoparticles using a low-aspect-ratio nanopore. Particle trapping and detrapping are implemented through a control of the cross-membrane electrophoretic voltage. This electrical method is found to enable placing an individual nanoparticle in vicinity of a lithographically-defined nanopore by virtue of the balance between the two counteracting factors, electrostatic and electroosmotic forces. We also demonstrate identification of trapped nanoparticles by the ionic current through the particle-pore gap space. This technique may find applications in electrode-embedded nanopore sensors..
29. Sou Ryuzaki, Jun Onoe, In situ nondestructive impedance spectroscopic study of nanostructured heterojunction organic photovoltaic cells, Japanese journal of applied physics, 10.7567/JJAP.52.06GD03, 52, 6 PART 2, 2013.06, The equivalent circuit model of the heterojunction organic photovoltaic (OPV) cells consisting of 20-nm-thick zinc-octaethylporphyrin [Zn(OEP)] and 30 nm-thick C60 films respectively used as donor and acceptor layers has been determined using impedance spectroscopy under dark and illumination (100mW/cm2, AM1.5) conditions. Under dark condition, the equivalent circuit consisting of a series resistance and two-RC (R: resistance, C: capacitance) circuits corresponding to individual layers well reproduced the impedance spectra. On the other hand, the four-RC circuit model, in which the additional two RC circuits corresponded to individual films in the vicinity of the Zn(OEP)/C60 interface, could explain the impedance spectra obtained under illumination condition..
30. Sou Ryuzaki, Masahiro Nishiyama, Jun Onoe, Electron transport properties of air-exposed one-dimensional uneven peanut-shaped C60 polymer films, Diamond and Related Materials, 10.1016/j.diamond.2012.12.004, 33, 12-15, 2013.01, The electron transport properties of an air-exposed one-dimensional (1D) uneven peanutshaped C60 polymer film were investigated by examining the temperature dependence (30-350 K) of the current-voltage (I-V) characteristics under ultrahigh vacuum conditions. Arrhenius plots of the resistance as a function of temperature showed two different electron conduction mechanisms. At temperatures above 140 K, it was found that electrons are conducted via a thermal excitation hopping mechanism, and the activation energy changed discontinuously from 124 to 99 meV at ca. 190 K because of a change in the 1D polymer chain-chain interactions. On the other hand, at temperatures below 100 K, the electron conduction behavior is consistent with a 2D variable-range hopping mechanism..
31. Sou Ryuzaki, Jun Onoe, Photo-generated carrier dynamics in the vicinity of the donor/acceptor interface of organic solar cells, IEEJ Transactions on Electronics, Information and Systems, 10.1541/ieejeiss.132.1291, 132, 8, 1291-1296, 2012, Change in electronic states before and after photo-irradiation at a Donor/Accepter (D/A) interface in organic solar cells consisting of Zinc-porphyrin and fullerene films has been examined using in situ impedance spectroscopy (IS), which makes it possible to non-destructively measure a built-in potential (Vbi) of both D and A films at the D/A interface. Charge accumulation of photo-generated carriers in the vicinity of the D/A interface was found to enlarge the Vbi of both D [Zn(OEP)] and A [C60] films at the interface. In addition, it was noted that the sum of Vbi upon photo-irradiation was in good agreement with the open-circuit voltage (VOC), the origin of which has still remained unsolved for organic solar cells. It was thus found that charge accumulation of photo-generated carriers in the vicinity of the D/A interface plays a key role in determining VOC..
32. Sou Ryuzaki, Jun Onoe, Influence of charge accumulation of photogenerated carriers in the vicinity of donor/acceptor interface on the open-circuit voltage of zinc-porphyrin/ C60 heterojunction organic photovoltaic cells, Journal of Physics D: Applied Physics, 10.1088/0022-3727/44/26/265102, 44, 26, 2011.07, The correlation between open-circuit voltage (VOC) and built-in potential (Vbi) upon photo-irradiation in the vicinity of the donor/acceptor (D/A) interface in zinc-octaethylporphyrin [Zn(OEP)]/C 60 heterojunction photovoltaic (OPV) cells is investigated by examining the capacitance-voltage (C-V) characteristics. Charge accumulation of photogenerated carriers in the vicinity of the D/A interface is found to enlarge Vbi of both D [Zn(OEP)] and A (C60) films in the vicinity of the interface. In addition, it is noted that VOC is in good agreement with the sum of Vbi of each film in the vicinity of the D/A interface. This suggests that charge accumulation of photogenerated carriers in the vicinity of the D/A interface plays a key role in determining V OC for solar cells..
33. Sou Ryuzaki, Toshihiro Kai, Yasunori Toda, Satoru Adachi, Jun Onoe, Effects of inter-molecular charge-transfer excitons on the external quantum efficiency of zinc-porphyrin/C60 heterojunction photovoltaic cells, Journal of Physics D: Applied Physics, 10.1088/0022-3727/44/14/145103, 44, 14, 2011.04, We have examined the structural effects of zinc-octaethylporphyrin [Zn(OEP)] films used as a donor on the external quantum efficiency (EQE) of organic heterojunction photovoltaic (OPV) cells [ITO/Zn(OEP)/C60/Al], and investigated what exactly causes the improvement of EQE. When the structure of the Zn(OEP) films changed from amorphous to crystalline, the maximum EQE increased from 36% to 42%, which is greater than that of around 35% for previously reported OPV cells using buffer materials (Peumans and Forrest 2001 Appl. Phys. Lett. 79 126). The crystallization of Zn(OEP) films is found to increase the number of inter-molecular charge-transfer (IMCT) excitons and to enlarge the mobility of carriers and IMCT excitons, thus significantly improving the EQE of the photoabsorption band under illumination due to the IMCT excitons..
34. S. Ryuzaki, J. Onoe, X-ray diffraction and scanning electron microscopic studies on the crystal structure and surface/interface morphology of zinc-octaethylporphyrin films on an indium tin oxide substrate spin coated with 3,4-polyethylenedioxythiophene
polystyrenesulfonate, Journal of Applied Physics, 10.1063/1.3182723, 106, 2, 2009.08, The crystal structure and surface/interface morphology of zinc-octaethylporphyrin [Zn(OEP)] films deposited on an indium tin oxide (ITO) substrate spin coated with 3,4- polyethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS) have been investigated using x-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. XRD results indicated that there are two kinds of grains with their sizes of approximately 20 nm that is independent of film thickness and substrate temperature. One has a diffraction plane with an interplanar distance of 1.12 nm and with its orientation parallel to the substrate, whereas the other has a diffraction plane with an interplanar distance of 1.24 nm and with that inclined mainly by 60° to the substrate. The abundant ratio of the two grains was controlled to some extent by varying film thickness and substrate temperature. Cross-sectional SEM images showed that a part of Zn(OEP) molecules are incorporated into PEDOT:PSS for its film thickness smaller than 130 nm, while that Zn(OEP) whiskers begin to grow for its film thickness exceeding 130 nm..
35. S. Ryuzaki, T. Hasegawa, J. Onoe, X-ray diffraction and infrared multiple-angle incidence resolution spectroscopic studies on the crystal structure and molecular orientation of zinc-porphyrin thin films on a SiO2/Si substrate, Journal of Applied Physics, 10.1063/1.3143105, 105, 11, 2009.07, The crystal structure and molecular orientation of zinc-octaethylporphyrin [Zn(OEP)] thin films deposited on a SiO2 /Si (111) substrate have been investigated using x-ray diffraction (XRD) and infrared multiple-angle incidence resolution spectroscopy (MAIRS), respectively. XRD results show that the Zn(OEP) thin films have two kinds of crystallites with a diffraction plane (2θ=7.9°) parallel to the substrate and with that (2θ=7.1°) inclined mainly by 60°-70° to the substrate. Comparison with simulated XRD results of the Zn(OEP) single crystal indicates that the diffraction angle of 2θ=7.9° is consistent with that of the (01 1-) plane of the single crystal, while the angle of 2θ=7.1° is slightly different from that of 7.3° corresponding to the (010) plane of the single crystal. On the other hand, MAIRS results demonstrate that Zn(OEP) molecules in the crystallite corresponding to 2θ=7.9° are inclined by 52.2±0.9° to the substrate, which is in a good agreement with that of ca. 50° estimated from the Zn(OEP) single crystal structure. In addition, these crystalline sizes are estimated to be approximately 20 nm and independent of film thickness. Accordingly, it can be concluded from the XRD and MAIRS results that the Zn(OEP) films have two kinds of grains. One has the single crystal structure, in which Zn(OEP) molecules are inclined by 52.2°±0.9° to the substrate. On the other hand, the other has a crystal structure close to the single crystal, in which Zn(OEP) molecules would be inclined by 10°-20° to the substrate..
36. Y. Toda, S. Ryuzaki, J. Onoe, Femtosecond carrier dynamics in electron-beam-irradiated C60 film, Applied Physics Letters, 10.1063/1.2838347, 92, 9, 2008.03, Time-resolved temperature-dependent transmission changes were measured for both pristine C60 and electron-beam-irradiated C60 polymer films using an optical pump-probe technique. Only the signals obtained for the C60 polymer show a temperature-dependent slow decay, which appears in the low temperature region below ∼60 K. This slow decay component exhibits a monotonic increase in both relaxation time and amplitude with decreasing temperature, providing evidence of gap formation associated with ordering fluctuations..
37. Soh Ryuzaki, J. Onoe, The crystallinity and surface morphology of zinc octaethylporphyrin thin films on an indium-tin-oxide substrate, Journal of Applied Physics, 10.1063/1.2838204, 103, 3, 2008.02, The crystallinity and surface morphology of zinc octaethylporphyrin, Zn(OEP), thin films (20 nm thick) deposited on an indium-tin-oxide substrate have been investigated using x-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD and SEM results show that the Zn(OEP) film formed at room temperature (RT) was amorphous and its surface morphology was smooth, whereas the film deposited at 473 K was crystalline and its surface morphology became rough compared to that formed at RT. On the other hand, when the Zn(OEP) film formed at RT was subsequently annealed at 473 K for 1 min, the film was crystallized as well as formed at 473 K but its surface morphology was maintained to be smooth..
38. Sou Ryuzaki, Tomohiko Ishii, Jun Onoe, In situ X-ray photoelectron spectroscopic study of metalloporphyrin- fullerene alternative-deposited thin films, Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 10.1143/JJAP.46.5363, 46, 8 A, 5363-5366, 2007.08, In situ X-ray photoelectron spectra (XPS) of metal-octaethylporphyrin [Pd(OEP), Cu(OEP), and Zn(OEP)] and C60 alternative-deposited films on a silicon substrate are presented for the fabrication of high-performance organic thin-film photovoltaic (PV) cells. XPS results indicated that only Zn(PEP) and C60 alternative-deposited films have a layered structure, whereas the other films have a mixed structure. This may be due to the difference in molecular symmetry between the anti-and syn-configurations of M(OEP): Zn(OEP) has a syn-configuration that can be stacked on a C60 film, whereas the other M(OEP)s have an anti-configuration that is difficult to be stacked on the film..