Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
KAORU TAMADA Last modified date:2021.04.23

Senior Vice President / Department of Fundamental Organic Chemistry / Institute for Materials Chemistry and Engineering


Papers
1. Chun Chieh Chang, Ting Yun Chen, Ting Wei Lin, Junfu Leng, Kaoru Tamada, Ya Ju Lee, Flexible and Ultranarrow Transmissive Color Filters by Simultaneous Excitations of Triple Resonant Eigenmodes in Hybrid Metallic-Optical Tamm State Devices , ACS Photonics, 10.1021/acsphotonics.0c01, 8, 2, 540-549, 2021.04.
2. Haruka Takekuma, Junfu Leng, Kazutaka Tateishi, Yang Xu, Yinthai Chan, Sou Ryuzaki, Pangpang Wang, Koichi Okamoto, Kaoru Tamada, 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.
3. Shihomi Masuda, Thasaneeya Kuboki, Satoru Kidoaki, Shi Ting Lee, Sou Ryuzaki, Koichi Okamoto, Yusuke Arima, Kaoru Tamada, High Axial and Lateral Resolutions on Self-Assembled Gold Nanoparticle Metasurfaces for Live-Cell Imaging, ACS Applied Nano Materials, 10.1021/acsanm.0c02300, 3, 11, 11135-11142, 2020.11, A plasmonic metasurface composed of homogeneously self-assembled gold nanoparticles can provide high-contrast fluorescence images confined to the nanointerface. In this study, we successfully demonstrated real-time, high-spatiotemporal-resolution imaging of adhered Venus-paxillin-3T3 live cells under a widefield microscope, where not only a high axial resolution but also a high lateral resolution down to the theoretical limit were confirmed through nascent cluster formation of paxillin. The improved lateral resolution on the sheet could be interpreted as the characteristic of localized surface plasmon resonance (LSPR)-mediated enhanced fluorescence and the metasurface acting as a nanothickness plane light emitter. We also found minimized photobleaching, owing to the increase in the emission efficiency via plasmon-exciton coupling. This simple nanomaterial-based technique will be a powerful tool to enhance interfacial signals and improve the quality of live-cell images, not only under widefield microscopes but also in combination with various super-resolution microscope
systems in the future..
4. Koichi Okamoto, Kota Okura, Pangpang Wang, Sou Ryuzaki, Kaoru Tamada, 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, We propose a unique random metal nanohemisphere on mirror (NHoM) structure to tune the surface plasmon (SP) resonance in a flexible manner. The SP resonance peak was split into two peaks owing to the strong coupling between the SP mode in the metal nanohemisphere and the mirror image mode generated in the metal substrate. This phenomenon is based on the fact that the strong coupling and the induced electromagnetic effects are similar to those pertaining to the Rabi splitting, Fano resonance, and electromagnetically induced transparency, thus providing quantum effect analogies. These phenomena have recently attracted increased attention and have been studied with nanocavities fabricated with top-down nanotechnologies. Compared with previous reports, NHoM structures can be fabricated in a much easier manner and are tunable in rather wider wavelength regions without nanofabrication technologies. The SP resonance peaks were enhanced, sharpened dramatically, and tuned flexibly, based on the optimization of the thickness of the spacer layer between the metal hemisphere and metal substrate. Experimental results were reproduced and were explained based on finite difference time domain (FDTD) simulations. These phenomena have never been observed previously on similar nanosphere on mirror (NSoM) because nanohemispherical structures were required. The NHoM nanocavity structure has a quality factor >200 that is surprisingly high for the localized SP mode of nanoparticles. Flexible tuning of the SP resonance with the use of NHoM is envisaged to lead to the development of new applications and technologies in the field of plasmonics and nanophotonics..
5. Rintaro Matsuda, Sou Ryuzaki, Koichi Okamoto, Yusuke Arima, Makusu Tsutsui, Masateru Taniguchi, Kaoru Tamada, Finite-difference time-domain simulations of inverted cone-shaped plasmonic nanopore structures, Journal of Applied Physics, 10.1063/5.0010418, 127, 24, 2020.06, Plasmonic nanopore structures have been expected to play a key role in next-generation nanopore devices because plasmonic-enhanced electric fields inside nanopores potentially enable the measurement of surface-enhanced Raman scattering (SERS) spectra of a single analyte passing through a nanopore. However, sufficient enhancement of the electric field inside a nanopore for SERS measurements has not been obtained. Here, we report finite-difference time-domain simulation studies of inverted cone-shaped plasmonic nanopore structures, which maximally show an ∼1000 times stronger SERS enhancement factor than that of a conventional cylindrical plasmonic nanopore structure. The enhancement was found to be achieved via nanofocusing and structural effects, causing a 1.3 and 4.7 times stronger plasmonic-enhanced electric field than that of a cylindrical structure, respectively. The present study suggests a high potential of inverted cone shapes as plasmonic nanopore structures for SERS measurement of an analyte passing through a nanopore..
6. Jing Kai Huang, Noboru Saito, Yichen Cai, Yi Wan, Chia Chin Cheng, Mengliu Li, Junjie Shi, Kaoru Tamada, Vincent C. Tung, Sean Li, Lain Jong Li, Steam-Assisted Chemical Vapor Deposition of Zeolitic Imidazolate Framework, ACS Materials Letters, 10.1021/acsmaterialslett.0c00026, 2, 5, 485-491, 2020.05, Direct growth of metal-organic frameworks (MOFs) on substrates is a prerequisite to incorporating them into functional platforms and microdevices. Nevertheless, available reports mostly rely on the solvent-based routes, typically altered from processes for powder synthesis which are obstacles to the nanofabrication. Besides, although few vapor-phase growth approaches were presented, the proposed procedures required multiple steps, such as matrix deposition and post-conversion, to obtain desired MOF films on substrates. Here, we demonstrate a steam-assisted chemical vapor deposition (CVD) method to directly synthesize highly crystalline ZIF-67 thin films at the temperature <125°C. With a slow deposition rate, the ZIF-67 forms a highly oriented thin film on a c-plane sapphire substrate, indicating the growth is epitaxial. Furthermore, we demonstrate the integration of directly grown CVD ZIF-67 as the active material of chemiresistors onto microelectronic chips. The ZIF-67 chemiresistors exhibit responses to the gas molecules, which are capable of diffusing into the cage of ZIF-67 at room temperature. The proposed synthesis method of ZIF-67 thin films is simple, scalable, cost-effective, and promising for numerous applications..
7. J. Leng, Y. Xu, Y-T. Chan, P. Wang, S. Ryuzaki, K. Okamoto & K. Tamada, Tuning the Emission Colors of Self-Assembled Quantum Dot Monolayers via One-Step Heat Treatment for Display Applications, ACS Appl. Nano Mater., 10.1021/acsanm.9b02358, 3, 3214-3222, 2020.02.
8. Naoto Takeshima, Kosuke Sugawa, Masaki Noguchi, Hironobu Tahara, Shota Jin, Kouichi Takase, Joe Otsuki, Kaoru Tamada, Synthesis of Ag nanoprisms with precisely-tuned localized surface plasmon wavelengths by sequential irradiation of light of two different wavelengths, Chemistry Letters, 10.1246/cl.190888, 49, 3, 240-243, 2020.01, Synthesis of anisotropic Ag nanoprisms (AgPRs) contributes to the development of high performance plasmonic devices. The localized surface plasmon resonance wavelength of AgPRs was successfully tuned within 500600 nm by sequential irradiation of 470-nm and 525-nm light to the Ag nanospheres for predetermined periods of time. We have clarified the mechanism in which the AgPRs are synthesized by the first irradiation, which act as the seeds for the growth in the second irradiation with remaining Ag nanospheres being consumed..
9. Junfu Leng, Tian Wang, Xiaofei Zhao, Evon Woan Yuann Ong, Baisheng Zhu, Jun De Andrew Ng, Ying Chieh Wong, Khoong Hong Khoo, Kaoru Tamada, Zhi Kuang Tan, Thermodynamic Control in the Synthesis of Quantum-Confined Blue-Emitting CsPbBr3 Perovskite Nanostrips, Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.9b03873, 11, 6, 2036-2043, 2020.03, Size control is critical in the synthesis of quantum-confined semiconductor nanocrystals, otherwise known as quantum dots. The achievement of size-uniformity and narrow spectral line-width in quantum dots conventionally relies on a very precise kinetic control of the reactions, where reaction time plays a significant role in defining the final crystal sizes and distribution. Here, we show that synthesis of quantum-confined perovskite nanostrips could be achieved through a thermodynamically controlled reaction, using a low-temperature and ligand-rich approach. The nanostrip growth proceeds through an initial one-dimensional (1D) nanorod stage, followed by the lateral widening of the rod to form a two-dimensional (2D) nanostrip. The spectral characteristics of the final product remain unchanged after prolonged reaction, indicating no signs of crystal ripening and confirming the thermodynamic nature of this reaction. The CsPbBr3 perovskite nanostrips were highly uniform and emit at a deep-blue wavelength of 462 nm with a remarkably narrow line-width of 13 nm. This corresponds to color coordinates of (0.136, 0.049) on the CIE 1931 color space, which fulfils the stringent Rec. 2020 standard for next-generation color displays. The well-passivated nanostrips also possess negligible defects and provide a near-unity photoluminescence quantum yield at 94%. Crucially, the achievement of blue emission through a pure-halide perovskite circumvents the problems of spectral instability that are frequently experienced in mixed-halide perovskite systems. The convenience and scalability of our thermodynamic approach, coupled with the excellent optical attributes, would likely enable these quantum-confined perovskite systems to be the preferred method toward color control in trichromatic display applications..
10. 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..
11. 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, 134301, 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..
12. 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..
13. Koichi Okamoto, Kazutaka Tateishi, Kaoru Tamada, Mitsuru Funato, Yoichi Kawakami, Micro-photoluminescence mapping of surface plasmon-coupled emission from InGaN/GaN quantum wells, Japanese Journal of Applied Physics, 10.7567/1347-4065/ab07ae, 58, SC, 2019.01, Micro-photoluminescence (PL) mapping was investigated to elucidate the detailed mechanism of surface plasmon (SP)-enhanced emissions from InGaN/GaN quantum wells (QWs) with Ag or Al coating. The PL wavelengths were obviously red-shifted with Ag films, while the PL peak wavelengths were not changed with Al coating. The relationship between the PL peak intensity and the PL wavelength at each pixel showed a positive or negative correlation for the uncoated part of the InGaN/GaN QWs with blue or green emission, respectively. We found that these correlations disappeared in the Ag-coated regions. These results suggest that the energy transfer from the excitons to the SPs should be much faster than that in the exciton localization and charge screening processes of the piezoelectric field in QWs. These effects were not observed for the Al-coated regions because the mechanism of PL enhancement should be quite different as we have suggested previously..
14. 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, 171602, 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..
15. Shihomi Masuda, Salomé Mielke, Federico Amadei, Akihisa Yamamoto, Pangpang Wang, Takashi Taniguchi, Kenichi Yoshikawa, Kaoru Tamada, Motomu Tanaka, Nonlinear Viscoelasticity of Highly Ordered, Two-Dimensional Assemblies of Metal Nanoparticles Confined at the Air/Water Interface, Langmuir, 10.1021/acs.langmuir.8b02713, 34, 43, 13025-13034, 2018.10, In this study, we investigated the viscoelastic properties of metal nanoparticle monolayers at the air/water interface by dilational rheology under periodic oscillation of surface area. Au nanoparticles capped with oleylamine form a stable, dense monolayer on a Langmuir film balance. The stress response function of a nanoparticle monolayer was first analyzed using the classical Kelvin-Voigt model, yielding the spring constant and viscosity. The obtained results suggest that the monolayer of nanoparticles is predominantly elastic, forming a two-dimensional physical gel. As the global shape of the signal exhibited a clear nonlinearity, we further analyzed the data with the higher modes in the Fourier series expansion. The imaginary part of the higher mode signal was stronger than the real part, suggesting that the dissipative term mainly causes the nonlinearity. Intriguingly, the response function measured at larger strain amplitude became asymmetric, accompanied by the emergence of even modes. The significance of interactions between nanoparticles was quantitatively assessed by calculating the potential of mean force, indicating that the lateral correlation could reach up to the distance much larger than the particle diameter. The influence of surface chemical functions and core metal has also been examined by using Au nanoparticles capped with partially fluorinated alkanethiolate and Ag nanoparticles capped with myristic acid. The combination of dilational rheology and correlation analyses can help us precisely control two-dimensional colloidal assembly of metal nanoparticles with fine-adjustable localized surface plasmon resonance..
16. 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/cm2 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/cm2to8.668mA/cm2 nevertheless implies reduced conductivity due to AgSC8 incorporation..
17. Noboru Saito, Soh 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, Part 1: Regular Papers & Short Notes, 10.7567/JJAP.57.03EG10, 57, 3, 03EG10, 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..
18. Shuhei Shinohara, Namsoon Eom, E. Jen Teh, Kaoru Tamada, Drew Parsons, Vincent S.J. Craig, The Role of Citric Acid in the Stabilization of Nanoparticles and Colloidal Particles in the Environment
Measurement of Surface Forces between Hafnium Oxide Surfaces in the Presence of Citric Acid, Langmuir, 10.1021/acs.langmuir.7b03116, 34, 8, 2595-2605, 2018.02, The interactions between colloidal particles and nanoparticles determine solution stability and the structures formed when the particles are unstable to flocculation. Therefore, knowledge of the interparticle interactions is important for understanding the transport, dissolution, and fate of particles in the environment. The interactions between particles are governed by the surface properties of the particles, which are altered when species adsorb to the surface. The important interactions in the environment are almost never those between the bare particles but rather those between particles that have been modified by the adsorption of natural organic materials. Citric acid is important in this regard not only because it is present in soil but also as a model of humic and fulvic acids. Here we have studied the surface forces between the model metal oxide surface hafnia in the presence of citric acid in order to understand the stability of colloidal particles and nanoparticles. We find that citric acid stabilizes the particles over a wide range of pH at low to moderate ionic strength. At high ionic strength, colloidal particles will flocculate due to a secondary minimum, resulting in aggregates that are dense and easily redispersed. In contrast, nanoparticles stabilized by citric acid remain stable at high ionic strengths and therefore exist in solution as individual particles; this will contribute to their dispersion in the environment and the uptake of nanoparticles by mammalian cells..
19. Mamoru Tamura, Koichi Okamoto, Kaoru Tamada, Takuya Iida, Stochastic approach to simulation of evaporation-triggered multiple self-assembly of mixed metal nanoparticles and their variable superradiance, Applied Physics Letters, 10.1063/1.5005830, 112, 3, 33106, 2018.01, We developed a design principle for the evaporation-triggered heterogeneous assembly of different kinds of metal nanoparticles in a two-dimensional environment. A dynamic Monte Carlo simulation shows the formation of island structures of gold nanoparticles (gold islands) surrounded by smaller silver nanoparticles (silver matrix) during the evaporation of organic solvent from the dispersion liquid on the water surface. Our developed principle revealed the spontaneous change in multiple interactions between gold and silver nanoparticles owing to the presence or the absence of solvation repulsion, which plays a crucial role in the formation of gold islands in the silver matrix. Not only the randomly arranged gold islands, but also the surrounding silver matrix phase contributed to the wavelength-tunable light scattering enhanced by a factor of 102 due to the superradiance effect. These results will pave the way for the design of multicolored optical devices based on random plasmonics via controlled interparticle interactions..
20. Eiji Usukura, Yuhki Yanase, Ayumi Ishijima, Thasaneeya Kuboki, Satoru Kidoaki, Koichi Okamoto, Kaoru Tamada, LSPR-mediated high axial-resolution fluorescence imaging on a silver nanoparticle sheet, PLoS One, 10.1371/journal.pone.0189708, 12, 12, 2017.12, This paper reports our original technique for visualizing cell-attached nanointerfaces with extremely high axial resolution using homogeneously excited localized surface plasmon resonance (LSPR) on self-assembled silver nanoparticle sheets. The LSPR sheet can confine and enhance the fluorescence at the nanointerface, which provides high signal-to-noise ratio images of focal adhesion at the cell-attached interface. The advantage of this LSPR-assisted technique is its usability, which provides comparable or higher-quality nanointerfacial images than TIRF microscopy, even under epifluorescence microscopy. We also report the cytotoxicity of silver nanoparticles, as determined via morphological analysis of adherent cells on the sheet..
21. Shihomi Masuda, Yuhki Yanase, Eiji Usukura, Soh 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..
22. Noboru Saito, Pangpang Wang, Koichi Okamoto, Soh Ryuzaki, Kaoru Tamada, Large patternable metal nanoparticle sheets by photo/e-beam lithography, Nanotechnology, 10.1088/1361-6528/aa8930, 28, 43, 435705, 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..
23. Kazutaka Tateishi, Pangpang Wang, Soh 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..
24. Koichi Okamoto, Mitsuru Funato, Yoichi Kawakami, Kaoru Tamada, High-efficiency light emission by means of exciton–surface-plasmon coupling, Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 10.1016/j.jphotochemrev.2017.05.005, 32, 58-77, 2017.09, Coupling between surface plasmons (SPs) and excitons can be used to enhance the emission efficiencies of light-emitting materials and devices. This approach had been theoretically predicted and, in 2004, was experimentally demonstrated by our group for enhancing the visible emission from InGaN/GaN quantum wells (QWs). Exciton–SP coupling increases the spontaneous emission rates of the excited states, causes a relative reduction in nonradiative relaxation, and ultimately increases the internal quantum efficiencies (IQEs) of such devices. Here, we present a brief history of the increases in emission efficiency that have been achieved and the underlying mechanism thereof. This method has the potential to enable the development of high-efficiency light-emitting diodes (LEDs), eventually leading to the replacement of fluorescent lights with solid-state light sources. After the initial discovery of this phenomenon, many device structures were proposed and reported; however, their emission efficiencies have thus far remained insufficient for practical application. Here, we also present recent progress on device applications and the current problems that must be solved. Finally, we explain the future possibilities regarding the extension of SP-enhanced light emission over a broader wavelength region, from the deep ultraviolet (UV) to the infrared (IR)..
25. Zhen Yu Juang, Chien Chih Tseng, Yumeng Shi, Wen Pin Hsieh, Soh 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..
26. S. Masuda, Y. Yanase, E. Usukura, S. Ryuzaki, K. Okamoto, KUBOKI THASANEEYA, S. Kidoaki, Kaoru Tamada, High-resolution imaging of a cell- attached nanointerface using a gold-nanoparticle two-dimensional sheet, Sci. Rep., 7, 3720, 1-10, 2017.07, 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..
27. Masaki Matsubara, Warren Stevenson, Jun Yabuki, Xiangbing Zeng, Haoliang Dong, Kazunobu Kojima, Shigefusa F. Chichibu, Kaoru Tamada, Atsushi Muramatsu, Goran Ungar, Kiyoshi Kanie, A Low-Symmetry Cubic Mesophase of Dendronized CdS Nanoparticles and Their Structure-Dependent Photoluminescence, Chem, 10.1016/j.chempr.2017.05.001, 2, 6, 860-876, 2017.06, A liquid crystal (LC) phase with P213 symmetry, the lowest so far in a cubic LC, was obtained in a system of CdS quantum dots (QDs) modified with a two-layer corona of aliphatic thiols (inner) and LC aromatic dendrons (outer). We propose that the unusual low symmetry of this cubic mesophase is a result of the multi-layered corona, which prefers to adopt an anisotropic radial profile because of the combination of long and short “bristles.” The anisotropic distribution of dendrons (long bristles) in the P213 phase is thought to facilitate π-π interaction among the aromatic moieties. The interaction gives rise to non-radiative exciton energy-transfer pathways that induce photoluminescence quenching of the CdS QDs. This is believed to be the first example of structure-dependent emission-quenching behavior..
28. Z-Y. Juang, C-C Tseng, Y. Shi, W-P Hsieh, Sou Ryuzaki, N. Saito, C.-E Hsiung, Y. Hernandez, Y. Han, Kaoru Tamada, L-J L, Graphene-Au nanoparticle based vertical heterostructures: A novel route towards high-ZT Thermoelectric devices, Nano Energy, 38, 385-391, 2017.04.
29. Yuhei Terada, Hirokazu Seto, Yu Hoshino, Tatsuya Murakami, Shuhei Shinohara, Kaoru Tamada, Yoshiko Miura, SPR study for analysis of a water-soluble glycopolymer interface and molecular recognition properties, Polymer Journal, 10.1038/pj.2016.99, 49, 2, 255-262, 2017.02, Glycopolymers consisting of mannose and acrylamide with different mannose incorporation ratios (10 and 100%) were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization, and the polymer layers were prepared on a gold substrate. The detailed polymer layer structure and molecular recognition properties were analyzed by the surface plasmon resonance (SPR) technique. The glycopolymers formed pancake-like thin layers with thicknesses of ∼2 nm in air and were swollen in the aqueous solution. The molecular recognition against concanavalin A (ConA) was also analyzed by SPR. Binding constants between glycopolymers and ConA were large enough to suggest multivalent effects. Binding rate constants of ConA to glycopolymers were in the same order; however, the dissociation rate constant was lower in the glycopolymer with a mannose ratio of 100% because of the high local mannose density near the binding point of ConA..
30. K. Okamoto, M. Funato, Y. Kawakami, N. Okada, K. Tadatomo, Kaoru Tamada, Plasmonics toward high-efficiency LEDs from the visible to the deep-UV region, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXI 2017 Light-Emitting Diodes Materials, Devices, and Applications for Solid State Lighting XXI, 10.1117/12.2249589, 10124, 2017, The surface plasmon (SP) resonance was used to increase the emission efficiencies toward high efficiency light-emitting diodes (LEDs). We obtained the enhancements of the electroluminescence from the fabricated plasmonic LED device structure by employing the very thin p+-GaN layer. The further enhancements should be achievable by optimization of the metal and device structures. Next important challenge is to extend this method from the visible to the deep UV region. By using Aluminum, we obtained the enhancements of emissions at ∼260 nm from AlGaN/AlN quantum wells. We succeeded to control the SP resonance by using the various metal nanostructures. These localized SP resonance spectra in the deep-UV regions presented here would be useful to enhance deep UV emissions of super wide bandgap materials such as AlGaN/AlN. We believe that our approaches based on ultra-deep UV plasmonics would bring high efficiency ultra-deep UV light sources..
31. Koichi Okamoto, Daisuke Tanaka, Ryo Degawa, Xinheng Li, Pangpang Wang, Soh 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..
32. K. Okamoto, D. Tanaka, R. Degawa, X. Li, PANGPANG WANG, Sou Ryuzaki, Kaoru Tamada, Electromagnetically induced transparency of a plasmonic metamaterial light absorber based on multilayered metallic nanoparticle sheets, Sci. Rep. , 6, 36165, 2016.09.
33. Ryo Degawa, Pangpang Wang, Daisuke Tanaka, Susie Park, Nobuyuki Sakai, Tetsu Tatsuma, Koichi Okamoto, Kaoru Tamada, Colorimetric Detection of an Airborne Remote Photocatalytic Reaction Using a Stratified Ag Nanoparticle Sheet, Langmuir, 10.1021/acs.langmuir.6b01521, 32, 32, 8154-8162, 2016.08, Photocatalysts are practically used for decomposition of harmful and fouling organic compounds. Among the photocatalytic reactions, remote oxidation via airborne species is a relatively slow process, so that a sensitive technique for its detection has been awaiting. Here, we investigated an airborne remote photocatalytic reaction of a TiO2 photocatalyst modified with Pt nanoparticles as co-catalysts via the color change caused by a decomposition of a multilayered silver nanoparticle sheet. The silver nanoparticle sheet fabricated by the Langmuir-Schaefer method on a gold substrate exhibits a unique multicolor depending upon the number of layers. The color originates from multiple light trapping in the stratified sheets that has a metamaterial characteristic along with an intra- and interlayer coupling of localized surface plasmon resonance (LSPR). The stepwise decomposition of the sheets was confirmed by the colorimetric data, which exhibited not only a monotonic decrease but also a maximized absorption of light when the film thickness reached the optimal thickness for light trapping or when the oxidation of the Ag core started. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and surface plasmon resonance (SPR) spectroscopy data provided a complete view of the decomposition process of this inorganic-organic nanocomposite film, and simulation by the transfer-matrix method explained a simultaneous plasmonic response rationally. The influence of the humidity and gas flow rate on the airborne remote photocatalytic reaction kinetics was examined by this colorimetric detection method, and it suggests that H2O in air plays an essential role in the reaction..
34. Kwang Sup Lee, Chantal Andraud, Kaoru Tamada, Konstantin Sokolov, Kenneth T. Kotz, Gang Zheng, Feature issue introduction
Biophotonic materials and applications, Optical Materials Express, 10.1364/OME.6.001747, 6, 5, 1747-1750, 2016.05, Biophotonics can be defined as the interplay of light and biological matter. The percolation of new optical technology into the realm of biology has literally shed new light into the inner workings of biological systems. This has revealed new applications for optics in biology. In a parallel trend, biomolecules have also been investigated for their optical applications. Materials are playing a central role in the development of biophotonics. New materials, fabrication methods, and structures are enabling new biosensors, contrast agents, imaging strategies, and assay methods. Similarly, biologic materials themselves can be used in photonic devices. In this context, two open-access, rapid-publication journals from The Optical Society of America, Optical Materials Express and Biomedical Optics Express, will publish a joint feature issue covering advances in biophotonics materials..
35. Kwang Sup Lee, Chantal Andraud, Kaoru Tamada, Konstanting Sokolov, Kenneth T. Kotz, Gang Zheng, Feature issue introduction
Biophotonic materials and applications, Biomedical Optics Express, 10.1364/BOE.7.002078, 7, 5, 2078-2081, 2016.05, Biophotonics can be defined as the interplay of light and biological matter. The percolation of new optical technology into the realm of biology has literally shed new light into the inner workings of biological systems. This has revealed new applications for optics in biology. In a parallel trend, biomolecules have been investigated for their optical applications. Materials are playing a central role in the development of biophotonics. New materials, fabrication methods, and structures are enabling new biosensors, contrast agents, imaging strategies, and assay methods. Similarly, biologic materials themselves can be used in photonic devices. In this context, two open-access, rapid-publication journals from The Optical Society of America (OSA), Optical Materials Express and Biomedical Optics Express, will publish a joint feature issue covering advances in biophotonics materials..
36. Ryo degawa, Pangpang Wang, Daisuke Tanaka, S. Park, N.Sakai, T. Tatsuma, Koichi Okamoto, Kaoru Tamada, Colorimetric detection of an airborne remote photocatalytic reaction using a stratified Ag nanoparticle Sheet, Langmuir, 32, 8154-8162, 2016.04.
37. K. Lee, C. Andraud, Kaoru Tamada, K. Sokolov, K. Kotz, . Zheng, Feature issue introduction: biophotonic materials and applications, Opt. Mater. Express , 6, 1747 , 2016.04.
38. Makoto Yamamoto, Shuhei Shinohara, Kaoru Tamada, Hisao Ishii, Yutaka Noguchi, Observation of ambipolar switching in a silver nanoparticle single-electron transistor with multiple molecular floating gates, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.7567/JJAP.55.03DC02, 55, 3, 2016.03, Ambipolar switching behavior was observed in a silver nanoparticle (AgNP)-based single-electron transistor (SET) with tetra-tert-butyl copper phthalocyanine (ttbCuPc) as a molecular floating gate. DepenDing on the wavelength of the incident light, the stability diagram shifted to the negative and positive directions along the gate voltage axis. These results were explained by the photoinduced charging of ttbCuPc molecules in the vicinity of AgNPs. Moreover, multiple device states were induced by the light irradiation at a wavelength of 600 nm, suggesting that multiple ttbCuPc molecules individually worked as a floating gate..
39. Makoto Yamamoto, Shuhei Shinohara, Kaoru Tamada, Hisao Ishii, Yutaka Noguchi, Observation of ambipolar switching in a silver nanoparticle single-electron transistor with multiple molecular floating gates, Japanese Journal of Applied Physics, 55, 03DC02-1-03DC02-6, 2016.01.
40. Pangpang Wang, Daisuke Tanaka, Shohei Araki, K. Okamoto, Kaoru Tamada, Silver nanoparticles with tunable work functions, Applied Physics Letters, 107, 151601-1-151601-5, 2015.10.
41. 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..
42. Shuhei Shinohara, Daisuke Tanaka, Koichi Okamoto, Kaoru Tamada, Colorimetric plasmon sensors with multilayered metallic nanoparticle sheets, Phys. Chem. Chem. Phys., 17, 18606-18612, 2015.07.
43. Shuhei Shinohara, Daisuke Tanaka, Koichi Okamoto, Kaoru Tamada, Colorimetric plasmon sensors with multilayered metallic nanoparticle sheets, Physical Chemistry Chemical Physics, 10.1039/c5cp02564h, 17, 28, 18606-18612, 2015.07, Colorimetric plasmon sensors for naked-eye detection of molecular recognition events have been proposed. Here, 3-layered Ag nanoparticle (NP) sheets on a Au substrate fabricated using the Langmuir-Schaefer method were utilized as the detection substrates. A drastic color change was observed following the binding of Au NPs via avidin-biotin interactions at less than 30% surface coverage. The color change was attributed not only to the localized surface plasmon resonance (LSPR) of the adsorbed Au NPs but also to the multiple light trapping effect derived from the stratified Au and Ag NPs, as predicted by a finite-difference time-domain (FDTD) simulation. This plasmonic multi-color has great potential in the development of simple and highly sensitive diagnostic systems..
44. Daisuke Tanaka, Keisuke Imazu, Jinwoo Sung, Cheolmin Park, K. Okamoto, Kaoru Tamada, Characteristics of localized surface plasmons excited on mixed monolayers composed of self-assembled Ag and Au nanoparticles, Nanoscale, DOI: 10.1039/c5nr03601a, 7, 15310-15320, 2015.06.
45. Kazutaka Tateishi, M. Funato, Y. Kawakami, Koichi Okamoto, Kaoru Tamada, Highly Enhanced Green Emission from InGaN Quantum Wells due to Surface Plasmon Resonance on Aluminum Films, Appl. Phys. Lett, 106, 121112 , 2015.03.
46. Kazutaka Tateishi, Mitsuru Funato, Yoichi Kawakami, Koichi Okamoto, Kaoru Tamada, Highly enhanced green emission from InGaN quantum wells due to surface plasmon resonance on aluminum films, Applied Physics Letters, 10.1063/1.4916392, 106, 12, 2015.03, Photoluminescence (PL) from InGaN/GaN quantum wells was highly enhanced by the surface plasmon (SP) resonance on aluminum thin films. The enhancement ratio of green emission reached 80, which was much larger than the previously reported enhancements on silver films. The resulting large enhancement should be attributed to an ∼20-fold enhancement of the excitation efficiency and ∼4-fold enhancement of the emission efficiency by the excitation and emission spectra. The temperature dependence of the PL intensities and the time-resolved PL measurements were also performed to understand the detailed mechanism. We concluded that the resonance between the excitation light and the SP on the Al surface should improve the excitation efficiency, i.e., the light absorption efficiency. This result suggests that the Al films have an extraordinary photon confinement effect, which are unique properties of plasmonics with Al and should be useful for new and wider applications..
47. Priastuti Wulandari, Takeshi Nagahiro, Nobuko Fukuoda, Yasuo Kimura, Michio Niwano, Kaoru Tamada, Characterization of citrates on gold and silver nanoparticles, J. Colloid Inter. Sci., 438, 244, 2015.01.
48. Daisuke Tanaka, Keisuke Imazu, Jinwoo Sung, Cheolmin Park, Koichi Okamoto, Kaoru Tamada, Characteristics of localized surface plasmons excited on mixed monolayers composed of self-assembled Ag and Au nanoparticles, Nanoscale, 10.1039/c5nr03601a, 7, 37, 15310-15320, 2015.01, The fundamental characteristics of localized surface plasmon resonance (LSPR) excited on mixed monolayers composed of self-assembled Ag and Au nanoparticles (AgNPs and AuNPs, respectively) were investigated. Mixed monolayered films were fabricated at the air-water interface at different mixing ratios. The films retained their phase-segregated morphologies in which AuNPs formed several 10 to 100 nm island domains in a homogeneous AgNP matrix phase. The LSPR bands originating from the self-assembled domains shifted to longer wavelengths as the domain size increased, as predicted by a finite-difference time-domain (FDTD) simulation. The FDTD simulation also revealed that even an alternating-lattice-structured two-dimensional (2D) AgNP/AuNP film retained two isolated LSPR bands, revealing that the plasmon resonances excited on each particle did not couple even in a continuous 2D sheet, unlike in the homologous NP system. The fluorescence quenching test of Cy3 and Cy5 dyes confirmed that the independent functions of AuNPs and AgNPs remained in the mixed films, whereas the AuNPs exhibited significantly higher quenching efficiency for the Cy3 dye compared with AgNPs due to the overlap of the excitation/emission bands of the dyes with the AuNP LSPR band. Various applications can be considered using this nanoheterostructured plasmonic assembly to excite spatially designed, high-density LSPR on macroscopic surfaces..
49. Priastuti Wulandari, Takeshi Nagahiro, Nobuko Fukada, Yasuo Kimura, Michio Niwano, Kaoru Tamada, Characterization of citrates on gold and silver nanoparticles, Journal of Colloid and Interface Science, 10.1016/j.jcis.2014.09.078, 438, 244-248, 2015.01, In this paper, we report different coordinations of citrates on gold (AuNP) and silver (AgNP) nanoparticles, as determined using Fourier transform infrared spectroscopy (FTIR) and molecular orbital (MO) calculations. AuNPs and AgNPs are found to have completely different interactions with the carboxylate anchoring groups, as indicated by their unique asymmetric stretching vibrations in the FTIR spectra. The νas (COO-) of citrate exhibits a high-frequency shift resulting from the formation of a unidentate coordination on AuNPs, whereas this vibration exhibits a low-frequency shift as a result of ionic bond formation on AgNPs, as predicted from the MO calculations of the corresponding metal complex salts. The enhancement in the IR signals when their vibration direction was perpendicular to the nanoparticle surface revealed the influence of localized surface plasmons excited on the metal nanoparticles..
50. PANGPANG WANG, Koichi Okamoto, Kaoru Tamada, Tuning the work functions of two-dimensional silver nanoparticle sheets using local oxidation nanolithography, Adv. Mater. Interfaces, 1400268, 2014.12.
51. Pangpang Wang, Koichi Okamoto, Kaoru Tamada, Tuning the work functions of 2D silver nanoparticle sheets using local oxidation nanolithography, Advanced Materials Interfaces, 10.1002/admi.201400268, 1, 9, 2014.12, Nanometer scale patterning on 2D self-assembled silver nanoparticle sheets using local oxidation nanolithography (LON) is successfully conducted. The patterns written by means of this method exhibit not only topological changes but also changes in the contact potential difference. The silver nanoparticle sheet as an adjusted work function film, which is patternable by LON, has great potential for nano-optoelectronic device applications..
52. Akira Baba, Keisuke Imazu, Akihito Yoshida, Daisuke Tanaka, Kaoru Tamada, Surface plasmon resonance properties of silver nanoparticle 2D sheets on metal gratings, SpringerPlus, 3, 284, 2014.06.
53. E. Usukura, S. Shinohara, K. Okamoto, J. Lim, K. Char, K. Tamada, Highly confined, enhanced surface fluorescence imaging with two-dimensional silver nanoparticle sheets, Applied Physics Letters, 104, 121906, 2014.03.
54. Eiji Usukura, Shuhei Shinohara, Koichi Okamoto, Jaehoon Lim, Kookheon Char, Kaoru Tamada, Highly confined, enhanced surface fluorescence imaging with two-dimensional silver nanoparticle sheets, Applied Physics Letters, 10.1063/1.4869560, 104, 12, 2014.03, A method of obtaining highly confined, enhanced surface fluorescence imaging is proposed using two-dimensional (2D) silver nanoparticle (AgMy) sheets. This technique is based on the localized surface plasmon resonance excited homogeneously on a 2D silver nanoparticle sheet. The AgMy sheets are fabricated at the air-water interface by self-assembly and transferred onto hydrophobic glass substrates. These sheets can enhance the fluorescence only when the excitation wavelength overlaps with the plasmon resonance wavelength. To confirm the validity of this technique, two separate test experiments are performed. One is the epifluorescence microscope imaging of a quantum dot 2D sheet on the AgMy 2D sheet with a SiO2 spacer layer, where the fluorescence is maximized with the 20 nm SiO2 layer, determined by the Förster resonance energy transfer distances. The second experiment is the imaging of a single fluorescence bead with a total internal reflection fluorescent microscope. We confirmed that the AgMy sheet provides a 4-fold increase in fluorescence with a 160-nm spatial resolution at 30 ms/frame snapshot. The AgMy sheet will be a powerful tool for high sensitivity and high-resolution real time bioimaging at nanointerfaces..
55. Daisuke Tanaka, Shuhei Shinohara, Eiji Usukura, Pangpang Wang, Koichi Okamoto, Kaoru Tamada, High-sensitivity surface plasmon resonance sensors utilizing high-refractive-index silver nanoparticle sheets, Japanese journal of applied physics, 10.7567/JJAP.53.01AF01, 53, 1 PART 2, 2014.02, We propose an idea for improving the angular sensitivity of Kretschmann-type surface plasmon resonance (SPR) sensors through the use of highrefractive- index silver nanoparticle (AgNP) sheets on metal substrates. According to Fresnel simulations, the angular sensitivity will be improved threefold by using the multilayered AgNP coating on gold or silver substrates. We confirmed the validity of this method by a model measurement with a SiO 2 sputtered film, which has a refractive index similar to that of organic or biological molecules. This simple technique will contribute to realizing a high-sensitivity SPR sensor, especially for the detection of small molecules..
56. Makoto Yamamoto, Rieko Ueda, Toshifumi Terui, Keisuke Imazu, Kaoru Tamada, Takeshi Sakano, Kenji Matsuda, Hisao Ishii, Yutaka Noguchi, Wavelength dependence and multiple-induced states in photoresponses of copper phthalocyanine-doped gold nanoparticle single-electron device, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.7567/JJAP.53.01AC02, 53, 1 PART 2, 2014.02, We have proposed a gold nanoparticle (GNP)-based single-electron transistor (SET) doped with a dye molecule, where the molecule works as a photoresponsive floating gate. Here, we examined the source-drain current (ISD) at a constant drain voltage under light irradiation with various wavelengths ranging from 400 to 700 nm. Current change was enhanced at the wavelengths of 600 and 700nm, corresponding to the optical absorption band of the doped molecule (copper phthalocyanine: CuPc). Moreover, several peaks appear in the histograms of ISD during light irradiation, indicating that multiple discrete states were induced in the device. The results suggest that the current change was initiated by the light absorption of CuPc and multiple CuPc molecules near the GNP working as a floating gate. Molecular doping can activate advanced device functions in GNP-based SETs..
57. Musubu Ichikawa, Kenji Ishida, Hisao Ishii, Kotaro Kajikawa, Masakazu Nakamura, Kaoru Tamada, Yuji Yoshida, Recent advances in molecular electronics and bioelectronics, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.7567/JJAP.53.01A001, 53, 1, 2014.01.
58. Akira Baba, Keisuke Imazu, Akihito Yoshida, Daisuke Tanaka, Kaoru Tamada, Surface plasmon resonance properties of silver nanoparticle 2D sheets on metal gratings, SpringerPlus, 10.1186/2193-1801-3-284, 3, 1, 1-10, 2014.01, Grating-coupled propagating surface plasmons associated with silver-nanoparticle 2D crystalline sheets exhibit sensitive plasmonic resonance tuning. Multilayered silver-nanoparticle 2D crystalline sheets are fabricated on gold or silver grating surfaces by the Langmuir- Blodgett method. We show that the deposition of Ag crystalline nanosheets on Au or Ag grating surfaces causes a drastic change in propagating surface plasmon resonance (SPR) both in angle measurements at fixed wavelengths and in fixed incident-angle mode by irradiation of white light. The dielectric constant of the multilayered silver nanosheet is estimated by a rigorous coupled-wave analysis. We find that the dielectric constant drastically increases as the number of silver-nanosheet layers increases. The experimentally obtained SP dispersions of Ag crystalline nanosheets on Au and Ag gratings are compared with the calculated SP dispersion curves. The drastic change in the surface plasmon resonance caused by the deposition of Ag-nanoparticle 2D crystalline sheets on metal grating surfaces suggests the potential for applications in highly sensitive sensors or for plasmonic devices requiring greatly enhanced electric fields..
59. Yutaka Noguchi, Makoto Yamamoto, Hisao Ishii, Rieko Ueda, Toshifumi Terui, Keisuke Imazu, Kaoru Tamada, Takeshi Sakano, Kenji Matsuda, Photoresponses in gold nanoparticle single-electron transistors with molecular floating gates, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.7567/JJAP.52.110102, 52, 11 PART 1, 2013.11, We have proposed a simple method of activating advanced functions in single-electron transistors (SETs) based on the specific properties of individual molecules. As a prototype, we fabricated a copper phthalocyanine (CuPc)-doped SET. The device consists of a gold-nanoparticle (GNP)-based SET doped with CuPc as a photoresponsive floating gate. In this paper, we report the details of the photoresponses of the CuPc-doped SET, such as conductance switching, sensitivity to the wavelength of the incident light, and multiple induced states..
60. Yutaka Noguchi, Makoto Yamamoto, Hisao Ishii, Reiko Ueda, Toshifumi Terui, Keisuke Imazu, Kaoru Tamada, Takeshi Sakano, Keiji Matsuda, Photoresponses in gold nanoparticle single-electron transistors with molecular floating gates, Jpn. J. Appl. Phys., 52, 110102, 2013.10.
61. D. Tanaka, S. Shinohara, E. Usukura, P. Wang, Koichi Okamoto, K. Tamada, High-sensitivity surface plasmon resonance sensors utilizing high-refractive-index silver nanoparticle sheets, Japanese Journal of Applied Physics , 01AF01 , 2013.10.
62. M. Yamamoto, R. Ueda, T. Terui, K. Imazu, K. Tamada, T. Sakano, K. Matsuda, H. Ishii, Y. Noguchi, Wavelength dependence and multiple-induced states in photoresponses of copper phthalocyanine-doped gold nanoparticle single-electron device, Japanese Journal of Applied Physics , 53, 01AC02, 2013.10.
63. Koichi Okamoto, Brian Lin, Keisuke Imazu, Akihito Yoshida, Koji Toma, Mana Toma, Kaoru Tamada, Tuning Colors of Silver Nanoparticle Sheets by Multilayered Crystalline Structures on Metal Substrates, Plasmonics, 10.1007/s11468-012-9437-2, 8, 2, 581-590, 2013.06, We report a new concept of tuning plasmonic colors of two-dimensional crystalline silver nanoparticle sheets with layer-by-layer structures. The multilayered crystalline sheets fabricated by the Langmuir-Schaefer method keep the localized surface plasmon resonance bands at the same position (λmax = 465 nm) on quartz, while they change their colors drastically on metal substrates depending on the number of layers (one to five layers). The response of the absorption spectra was absolutely nonlinear, with maximum absorption for two or three layers. The obtained results were well reproduced by the finite difference time domain simulation. The simulation confirmed that these plasmonic colors originate not only from near-field coupling of plasmon resonance but also far-field nano-optics of the multilayered silver nanoparticle sheets..
64. Koichi Okamoto, Brian Lin, Keisuke Imazu, Akihito Yoshida, Koji Toma, Mana Toma, Kaoru Tamada, Tuning colors of silver nanoparticle sheets by multilayered crystalline structures on metal substrates, Plasmonics, 8, 581, 2013.04.
65. Kaoru Tamada, Shinobu Yokokawa, Gemini SAMs, Handbook of Biofunctional Surfaces, 10.4032/9789814364188, 31-57, 2013.04, In this chapter, we report our effort to fabricate "gemini"-structured cationic self-assembled monolayers (SAMs) composed of quaternary ammonium (QA) sulfur derivatives. In these gemini SAMs, two molecules bearing resembling molecular structures are chemically combined, where the orientation and distance between QA groups are specified by covalent bondings with an ethylene spacer. We found that l-tartaric acid, a probe molecule with two carboxyl groups having the same distance as the ethylene unit, exhibits a strong affinity to the gemini surface. We also found that chiral surfaces fabricated by immobilization of tartaric acid enantiomers (l, d, or meso) on the gemini surface has potential for optical resolution of a racemate via a preferential crystal growth at solid-liquid interface..
66. Xiaoying Xu, Mitsuru Futano, Yoichi Kawakami, Koichi Okamoto, Kaoru Tamada, Grain size dependence of surface plasmon enhanced photoluminescence, Optical Express, 2013.02.
67. Xiaoying Xu, Mitsuru Funato, Yoichi Kawakami, Koichi Okamoto, Kaoru Tamada, Grain size dependence of surface plasmon enhanced photoluminescence, Optics Express, 10.1364/OE.21.003145, 21, 3, 3145-3151, 2013.02, Photoluminescence (PL) in the InGaN quantum well based lightemitting diodes (LED) is greatly mediated through the coupling with the Surface Plasmons (SPs) at the interface of the sputtered Ag film. SPs coupled PL is independently tuned through controlling the grain size of the sputtered Ag films. The grain size of ∼50 nm exhibits the maximum light extraction efficiency (LEE) at the wavelength of 460 nm. This grain size agrees with the periodic lattice constant of the grating structure in the calculation, where the momentum mismatch between the SPs and the radiative light can be compensated..
68. Akihito Yoshida, Keisuke Imazu, Xinheng Li, Koichi Okamoto, Kaoru Tamada, Spectroscopic properties of multilayered gold nanoparticle 2D sheets, Langmuir, 10.1021/la303533f, 28, 49, 17153-17158, 2012.12, We report the fabrication technique and optical properties of multilayered two-dimensional (2D) gold nanoparticle sheets ("Au nanosheet"). The 2D crystalline monolayer sheet composed of Au nanoparticles shows an absorption peak originating from a localized surface plasmon resonance (LSPR). It was found that the absorption spectra dramatically change when the monolayers are assembled into the multilayers on different substrates (quartz or Au). In the case of the multilayers on Au thin film (d = 200 nm), the LSPR peak is shifted to longer wavelength at the near-IR region by increasing the number of layers. The absorbance also depends on the layer number and shows the nonlinear behavior. On the other hand, the multilayers on quartz substrate show neither such LSPR peak shift nor nonlinear response of absorbance. The layer number dependence on metal surfaces can be interpreted as the combined effects between the near-field coupling of the LSPR and the far-field optics of the stratified metamaterial films, as proposed in our previous study. We also report the spectroscopic properties of hybrid multilayers composed of two kinds of monolayers, i.e., Au nanosheet and Ag nanosheet. The combination of the different metal nanoparticle sheets realizes more flexible plasmonic color tuning..
69. Akihito Yoshida, Keisuke Imazu, Xinheng Li, Koichi Okamoto, Kaoru Tamada, Spectroscopic Properties of Multilayered Gold Nanoparticles 2D Sheets, Langmuir, 28, 17153, 2012.11.
70. Makoto Yamamoto, Toshifumi Teruo, Reiko Ueda, Keisuke Imazu, Kaoru Tamada, Takeshi Sakano, Kenji Matsuda, Hisao Ishii, Yutaka Noguchi, Photoinduced conductance switching in a dye-doped gold nanoparticle transistor, Applied Physics Letters, 101, 023103, 2012.07.
71. Makoto Yamamoto, Toshifumi Terui, Rieko Ueda, Keisuke Imazu, Kaoru Tamada, Takeshi Sakano, Kenji Matsuda, Hisao Ishii, Yutaka Noguchi, Photoinduced conductance switching in a dye-doped gold nanoparticle transistor, Applied Physics Letters, 10.1063/1.4733612, 101, 2, 2012.07, Photoinduced conductance switching was demonstrated in a copper phthalocyanine (CuPc)-doped gold nanoparticle (GNP) transistor formed in a nanogap electrode with a back gate structure. Two specific states were reversibly induced in conductance of the CuPc-doped devices by light irradiation and applied voltages. The probability of occurrence of conductance switching decreased with a reduction in the number of incident photons. In addition, conductance switching was not observed in the devices before CuPc doping. Conductance switching originates from change in the local potential of GNPs, possibly induced by a charge-state bistability of an individual CuPc molecule worked as a floating gate..
72. Yoshikazu Kumashiro, Yasuhiro Ikezoe, Tomohiro Hayashi, Youichi Okabayashi, Kaoru Tamada, Masayuki Yamato, Teruo Okano, Masahiko Hara, Temperature-modulated adsorption of poly(N-isopropylacrylamide)-grafted ferritin on solid substrate, Colloids and Surfaces B: Biointerfaces, 10.1016/j.colsurfb.2012.02.028, 95, 57-64, 2012.06, Ferritin grafted with temperature-responsive poly(N-isopropylacrylamide) (PIPAAm-ferritin) was synthesized by a coupling reaction using PIPAAm and ferritin for obtaining stimuli-responsive biomaterials. The hydrodynamic diameter of PIPAAm-ferritins in aqueous solution increased at 37°C at a higher protein concentration (>0.2. mg/mL) because of the intermolecular aggregation through the hydrophobic interaction of PIPAAm chains. On the other hand, PIPAAm-ferritins at a lower concentration (<0.2. mg/mL) were unable to increase their size even at 37°C. The adsorption kinetics of PIPAAm-ferritins on hydrophobically modified Si substrate were evaluated with a quartz crystal microbalance in 10. mmol/L Bis-Tris/HCl buffer (pH 5.8) with and without poly(oxyethylene) sorbitan monolaurate (TWEEN 20) (0.05. wt%) as a surfactant. Although the adsorption of PIPAAm-ferritins on hydrophobic Si substrate at 25°C in the buffer with TWEEN 20 was hardly observed, PIPAAm-ferritins were considerably adsorbed on the substrate at 37°C, indicating that the hydrophobic interaction between the substrate and PIPAAm grafts on the ferritins after the destruction of the hydrophobic interaction between the protein and the substrate by TWEEN 20..
73. Yoshikazu Kumashiro, Yasuhiro Ikezoe, Tomohiro Hayashi, Youichi Okabayashi, Kaoru Tamada, Masayuki Yamato, Teruo Okano, Masahiko Hara, Temperature-modulated adsorption of poly(N-isopropylacrylamide)- grafted ferritin on solid substrate, Colloids and Surfaces B: Biointerfaces, 95, 57, 2012.04.
74. Nobuko Fukuda, Naoyuki Ishida, Kenichi Nomura, Tong Wang, Kaoru Tamada, Hirobumi Ushijima, Analysis of adsorption and binding behaviors of silver nanoparticles onto a pyridyl-terminated surface using XPS and AFM, Langmuir, 10.1021/la2032785, 27, 21, 12916-12922, 2011.11, In this study, we analyzed adsorption and binding behaviors of citrate-capped silver nanoparticles (AgNPs) on a pyridyl-terminated surface using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Adsorption of the AgNPs onto the pyridyl-terminated silicon wafer surface was completed through pH-controlled sol immersion. The adsorption occurred predominantly at a pH less than the pKb value of the pyridyl group and more than the pKa1 of citric acid, indicating that the driving force behind adsorption was electrostatic interaction. Adsorption of citrate onto the pyridyl group also occurred at pKa1 < pH < pK b without AgNPs. According to XPS in the N1s region, larger deprotonation from the pyridinium-formed pyridyl groups was demonstrated subsequent to adsorption of the AgNPs. The deprotonation from the pyridinium indicates the formation of the neutral pyridyl group as the counterpart of hydrogen bonding with the carboxyl group of citrate. The binding state between the pyridyl group and citrate surrounding AgNPs is expected to be kept stable through hydrogen bonding and van der Waals force derived from the AgNPs approach to the pyridyl surface..
75. Jungmok You, Akihito Yoshida, June Seok Heo, Han Soo Kim, Hyun Ok Kim, Kaoru Tamada, Eunkyoung Kim, Protein coverage on polymer nanolayers leading to mesenchymal stem cell patterning, Physical Chemistry Chemical Physics, 10.1039/c1cp21732a, 13, 39, 17625-17632, 2011.10, Interactions of gelatin and albumin with a photo-reactive diphenylamino-s-triazine bridged p-phenylene vinylene polymer (DTOPV) were examined by using surface plasmon resonance (SPR) spectroscopy to explore the effect of the polymer structure on protein coverage of DTOPV nanofilms. The SPR data revealed a significant increase of gelatin adsorption on UV-DTOPV nanofilms, while the adsorption of albumin was decreased by UV exposure in the time frame of the experiment. We also found that the selective adsorption of these proteins was highly dependent on the protein concentration; the highest selectivity of protein adsorption was obtained at the lowest concentration (3.5 μg ml -1), while no selective adsorption was confirmed at high concentrations (350 and 1000 μg ml -1). The selective attachment of mesenchymal stem cells (MSCs) was directly correlated with the selective adsorption of these proteins onto DTOPV nanofilms. The MSCs attachment onto UV-DTOPV films was promoted with only small mass coverage of gelatin, which led to MSC patterning onto the patterned DTOPV nanofilms successfully. The role of cell adhesion proteins that we found in this study will be a clue to elucidate the complex response of biomolecules on functional polymer nanolayers, and contribute to build up biocompatible surfaces on various advanced materials for the sake of cell engineering and medical implants. This journal is.
76. Nobuko Fukuda, Naoyuki Ishida, Kenichi Nomura, Tong Wang, Kaoru Tamada, Hirobumi Ushijima, Analysis of Adsorption and Binding Behaviors of Silver Nanoparticles onto a Pyridyl-Terminated Surface Using XPS and AFM, Langmuir, 27, 12916-12922, 2011.06.
77. Jungmok You, Akihito Yoshida, June Seok Heo, Han-Soo Kim, Hyun Ok Kim, Kaoru Tamada, Eunkyoung Kim, Protein coverage on polymer nanolayers leading to mesenchymal stem cell patterning, Physical Chemistry Chemical Physics, 13, 39, 17625-17632, 2011.06.
78. Kim HW, Jung J, Han MN, Lim S, Tamada K, Hara M, Kawai M, Kim Y, Kuk Y , One-Dimensional Molecular Zippers , J. Am. Chem. Soc., 10.1021/ja2031486, 133, 24, 9236-9238, 2011.04.
79. Mana Toma, Koji Toma, Kanae Michioka, Yasuhiro Ikezoe, Daiki Obara, Koichi Okamoto and Kaoru Tamada, Collective plasmon modes excited on a silver nanoparticle 2D crystalline sheet, Phys. Chem. Chem. Phys., 10.1039/c0cp02953j, 13, 7459-7466, 2011.02.
80. Kim HW, Han, M, Shin HJ, Lim S , Oh Y, Tamada K , Hara M , Kim Y, Kawai M, Kuk Y, Control of Molecular Rotors by Selection of Anchoring Sites , Phys. Rev. Lett., 10.1103/PhysRevLett.106.146101, 106, 14, 146101, 2011.01.
81. Satoshi Katano, Koji Toma, Mana Toma, Kaoru Tamada and Yoichi Uehara, Nanoscale coupling of photons to vibrational excitation of Ag nanoparticle 2D array studied by scanning tunneling microscope light emission spectroscopy, Phys. Chem. Chem. Phys., 10.1039/c0cp01005g, 12, 44, 14749-14753, 2010.08.
82. T. Nagahiro, K. Ishibashi, Y. Kimura, M. Niwano, T. Hayashi, Y. Ikezoe, M. Hara, T. Tatsuma, K. Tamada, Ag nanoparticle sheet as a marker of lateral remote photocatalytic reaction, Nanoscale, 10.1039/b9nr00240e, 2, 107-113, 2009.11.
83. Himadri Acharya, Jinwoo Sung, Byeong Hyeok Sohn, Dong Ha Kim, Kaoru Tamada, Cheolmin Park, Tunable surface plasmon band of position selective Ag and Au nanoparticles in thin block copolymer micelle films, Chemistry of Materials, 10.1021/cm901245g, 21, 18, 4248-4255, 2009.09, The manuscript describes a novel method to fabricate a thin composite film based on spin coating in which surface plasmon bands of Au and Ag nanoparticles are effectively coupled with each other because of position-selective deposition of both nanoparticles on a self-assembled block copolymer structure. Simple solution blending and subsequent spin coating of Au nanoparticles (NPs) and a block copolymer micelles containing Ag NPs in the core regions offers a facile route for controlling coupled surface plasmon band (SPB) of the two NPs over 100 nm in wavelength in thin solid films. Effective coupling of two individual SPBs relies upon the self-assembled composite structure where Ag and Au NPs are preferentially located in the core and corona regions of the micelles, respectively, allowing not only a controlled interparticle distance but also homogeneous dispersion of the NPs throughout film..
84. T. Nagahiro, H. Akiyama, M. Hara, K. Tamada, Photoisomerization of azobenzene containing self-assembled monolayers investigated by Kelvin probe work function measurements, J. Electron Spectroscopy and Related Phenomena, 172, 1-3, 128-133, 2009.07.
85. X. Li, K. Tamada, A. Baba, M. Hara, pH controlled two dimensional gold nanoparticle aggregates for systematic study of local surface plasmon coupling, J. Nanoscience and Nanotechnology, 9, 1, 408-416, 2009.07.
86. Tamada K, Michioka K, Li X , Ikezoe Y, Saito M, Otsuka K, Bioapplication of plasmonic nanosheet, ORGANIC PHOTONIC MATERIALS AND DEVICES XI, Proceedings of SPIE-The International Society for Optical Engineering, 10.1117/12.814977, 7213, 2009.07.
87. H. Acharya, J. Sung, B.-H. Sohn, D.H. Kim, K. Tamada, C. Park, Tunable Surface Plasmon Band of Position Selective Ag and Au Nanoparticles in Thin Block Copolymer Micelle Films, Chem. Mater. , 21, 4248-4255, 2009.07.
88. Takeshi Nagahiro, Haruhisa Akiyama, Masahiko Hara, Kaoru Tamada, Photoisomerization of azobenzene containing self-assembled monolayers investigated by Kelvin probe work function measurements, Journal of Electron Spectroscopy and Related Phenomena, 10.1016/j.elspec.2009.02.009, 172, 1-3, 128-133, 2009.05, Photoisomerization of asymmetric azobenzene disulfide self-assembled monolayer (SAM) on gold was characterized by the Kelvin probe work function measurements in ambient atmosphere. The reversible changes in work function between trans and cis azobenzene SAMs are reasonably interpreted by the molecular dipole moments normal to the surface based on the molecular conformational models. The different para-substituents of azobenzene with electron donating and electron-withdrawing properties induce opposite responses in work function against UV-vis photoirradiation, which is a direct evidence of functional SAMs being effective for the energy-level alignment at the organic/electrode interface. The Kelvin probe measurements in atmosphere eventually provide the work function value equivalent to that determined by ultraviolet photoelectron spectroscopy (UPS) in ultrahigh vacuum in our previous study..
89. Xinheng Li, Kaoru Tamada, Baba Iakira, Masahiko Hara, pH-controlled two dimensional gold nanoparticle aggregates for systematic study of local surface plasmon coupling, Journal of Nanoscience and Nanotechnology, 10.1166/jnn.2009.J066, 9, 1, 408-416, 2009.01, We report a way of using citrates, ionic capping molecules on gold nanoparticles, as a 'tuner" to adjust the charge density on the particles by solution pH, in correlation with their association constants (pKa). We have synthesized 10% biotin-capped gold nanoparticles with 90% citrates covering on the remaining surfaces. The controlled electrostatic repulsion force between the particles determines the distance between the particles on substrate, i.e., the surface density of the particles, even for the case of immobilization via biotin-avidin reaction. Thus the density of gold nanoparticles on surface was varied in a wide range systematically, especially to high density, and the optical response of two dimensional particle aggregates was investigated to discuss the effect of local plasmon coupling. The UV-vis-Near-IR reflection absorption spectrum of the particle aggregates at low pH (pH
90. Yasuhiro Ikezoe, Yoshikazu Kumashiro, Kaoru Tamada, Takuro Matsui, Ichiro Yamashita, Kiyotaka Shiba, Masahiko Hara, Growth of giant two-dimensional crystal of protein molecules from a three-phase contact line, Langmuir, 10.1021/la802104f, 24, 22, 12836-12841, 2008.11, A novel method to fabricate a two-dimensional (2D) crystal of protein molecules has been developed. The method enables us to control both the position of nucleation and the direction of the crystal growth. The crystal obtained using a protein molecule, ferritin, was found to be composed of a number of densely packed single crystal domains with an unprecedentedly large size of approximately 100 μm2. This method also reveals characteristic behavior of the spatiotemporal evolution of the crystal; for example, "fusion" of the crystal domains, which is never observed in an ordinary crystal composed of atoms or ions, was demonstrated. Our approach could have potential in fabricating extraordinarily large and highly ordered nanoparticle arrays of organic or inorganic materials..
91. Lloyd F.N. Ah Qune, H. Akiyama, T. Nagahiro, Kaoru Tamada, Andrew T.S. Wee, Reversible work function changes induced by photoisomerization of asymmetric azobenzene dithiol self-assembled monolayers on gold, Applied Physics Letters, 10.1063/1.2969468, 93, 8, 2008.09, We measured reversible changes in the work function (Δ φAu) of gold substrates modified by asymmetric azobenzene dithiol self-assembled monolayers (SAMs) following photoisomerization and thermal recovery of the azo unit. The azobenzene derivative SAMs were photoisomerized to cis form by UV irradiation. Δ φAu was monitored in real time during thermal recovery to trans form by ultraviolet photoelectron spectroscopy using a synchrotron light source. Changing the substituted functional group in the p′ position of the azobenzene from electron donating to electron withdrawing resulted in opposite responses of Δ φAu against photoisomerization. Hence, a direct correlation between Δ φAu and changes in molecular dipole moments was obtained..
92. Priastuti Wulandari, Takeshi Nagahiro, Kanae Michioka, Kaoru Tamada, Ken ichi Ishibashi, Yasuo Kimura, Michio Niwano, Coordination of carboxylate on metal nanoparticles characterized by Fourier transform infrared spectroscopy, Chemistry Letters, 10.1246/cl.2008.888, 37, 8, 888-889, 2008.08, The coordination of carboxylate capping agents on silver and gold nanoparticles is investigated by Fourier transform infrared spectroscopy (FTIR). The shift of carboxylate stretching frequency confirmed that carboxylate bound on gold nanoparticle forms unidentate coordination, while that on silver nanoparticle shows ionic bonding. The different coordinations on gold and silver NPs are reasonably interpreted by molecular orbital (MO) calculation based on metal carboxylate molecules..
93. Ishii N, Fitrilawati F, Manna A, Akiyama H, Tamada Y, Tamada K, Gold nanoparticles used as a carrier enhance production of anti-hapten IgG in rabbit: A study with azobenzene-dye as a hapten presented on the entire surface of gold nanoparticles, Bioscience Biotechnology and Biochemistry, 72, 1, 124-131, 2008.07.
94. Qune, LFNA, Makino K, Tamada K, Chen W , Wee ATS, Selective adsorption of L-tartaric acid on gemini-type self-assembled monolayers., J. Phys. Chem. C, 112, 8, 3049-3053, 2008.07.
95. L.F.N.A. Qune, K. Tamada, M. Hara, Self-Assembling Properties of 11-Ferrocenyl-1-Undecanethiol on Highly Oriented Pyrolitic Graphite Characterized by Scanning Tunneling Microscopy, e-Journal of Surface Science and Nanotechnology, 6, 119-123, 2008.07.
96. P. Wulandari, T. Nagahiro, K. Michioka, K. Tamada*, K. Ishibashi, Y. Kimura, M. Niwano, Coordination of Carboxylate on Metal Nanoparticles Characterized by Fourier Transform Infrared Spectroscopy, Chem. Lett., 37, 8, 888-889, 2008.07.
97. C.-D. Keum, N. Ishii, K. Michioka, K. Tamada, M. Hara, M. Furusawa, H. Fukushima, A Gram Scale Synthesis of Monodispersed Silver Nanoparticles Capped by Carboxylate and Their Ligand Exchange, J. Nonlinear Optical Physics & Materials, 17, 131-142, 2008.07.
98. P. Wulandari, X. Li, K. Tamada, M. Hara, Conformational Study and Citrates Adsorbed on Gold Nanoparticles Using Fourier Transform Infrared Spectroscopy, J. Nonlinear Optical Physics & Materials, 17, 185-192, 2008.07.
99. L.F.N.A.Qune, H. Akiyama, T. Nagahiro, K. Tamada, A.T.S. Wee, Reversible work function changes induced by photoisomerization of asymmetric azobenzene dithiol self-assembled monolayers on gold, Apply. Phys. Lett., 93, 083109-1-083109-3, 2008.07.
100. Y. Ikezoe, Y. Kumashiro, K. Tamada, T. Matsui, I. Yamashita, K. Shiba, M. Hara, Growth of giant two-dimensional crystals of protein molecules from a three-phase contact line, Langmuir, 24, 22, 12836-12841, 2008.07.
101. Y. Kumashiro, Y. Ikezoe, K. Tamada, and M. Hara, Dynamic Interfacial Properties of Poly(ethylene glycol)-Modified Ferritin at the Solid/Liquid, J. Phys. Chem. B, 112, 8291-8297, 2008.07.
102. Yoshikazu Kumashiro, Yasuhiro Ikezoe, Kaoru Tamada, Masahiko Hara, Dynamic interfacial properties of polyethylene glycol-modified ferritin at the solid/liquid interface, Journal of Physical Chemistry B, 10.1021/jp7104506, 112, 28, 8291-8297, 2008.07, Poly(ethylene glycol)-modified ferritins (PEG-ferritins) with various molecular weights were synthesized by the grafting method, and their dynamic interfacial properties at the solid/liquid interface were investigated. The number of PEG grafted to ferritins was controlled by the amount of 1,1′-carbonyldiimidazole-modified PEG adding to the reaction solution. The adsorption kinetics and energy dissipation of PEG-ferritins onto bare Si substrate and amino-modified Si substrate were investigated with a quartz crystal microbalance (QCM) in 10 mM bis-Tris/HCl buffer (pH 5.8), while their morphologies were characterized by scanning electron microscopy (SEM). The adsorption dynamics of PEG-ferritins onto amino-modified Si substrate were quite different from those of unmodified ferritin, which can be reasonably interpreted by the desorption capability of PEG-ferritins on the surface attributed to amphiphilicity and the high-chain mobility of PEG chains..
103. Chang Dae Keum, Noriyuki Ishii, Kanae Michioka, Priastuti Wulandari, Kaoru Tamada, Masahiko Furusawa, Hitoshi Fukushima, A gram scale synthesis of monodispersed silver nanoparticles capped by carboxylates and their ligand exchange, Journal of Nonlinear Optical Physics and Materials, 10.1142/S0218863508004093, 17, 2, 131-142, 2008.06, In this paper, we report a simple yet powerful synthetic method for obtaining monodispersed silver nanoparticles by direct thermal decomposition of two materials - one is silver acetate as a source of the metal core and the other is myristic acid as a capping agent. The reaction was performed at 250°C, the boiling point of myristic acid, without additional solvent. The nucleation and growth of the particles were monitored by dynamic light scattering in order to optimize the reaction time. By this simple procedure, we could obtain uniformly sized Ag nanoparticles with the average diameter of 4.8 ± 0.1 nm. Although the particles were synthesized at high temperature, the ligand exchange between myristates and alkanethiolates can be achieved at room temperature. Significant characteristics of Ag nanoparticles attributed to localized surface plasmons were investigated..
104. Priastuti Wulandari, Xinheng Li, Kaoru Tamada, Masahiko Hara, Conformational study of citrates adsorbed on gold nanoparticles using fourier transform infrared spectroscopy, Journal of Nonlinear Optical Physics and Materials, 10.1142/S0218863508004032, 17, 2, 185-192, 2008.06, We investigated the structure of citrates adsorbed on Au nanoparticles (AuNPs) synthesized by the Frens method by Fourier transformed infrared spectroscopy (FTIR). We found that physisorbed citrates are stable enough to stay on the surface of AuNPs during purification. The FT-IR spectra of citrates on AuNPs are quite uniquely different from bulk citrates, suggesting the formation of coordination bond between carboxylate group and gold. The shifts of carboxylate vibration modes on AuNPs are larger than that on flat Au substrates, as expected from the stronger dipole field on AuNPs compared with that on flat substrates..
105. Lloyd F.N. Ah Qune, Kaoru Tamada, Masahiko Hara, Self-assembling properties of 11-ferrocenyl-1-undecanethiol on highly oriented pyrolitic graphite characterized by scanning tunneling microscopy, e-Journal of Surface Science and Nanotechnology, 10.1380/ejssnt.2008.119, 6, 119-123, 2008.04, Molecular resolution scanning tunneling microscope (STM) images the spontaneous self-assembly of 11-ferrocenyl-1-undecanethiol ((C5H 5)Fe(C5H4)(CH2)11-SH) forming a large striped-phase on highly oriented pyrolitic graphite (HOPG) at a phenyloctane-HOPG interface. In the image, the alkyl chains lying flat on HOPG appear as bundles in groups of five in the moiré pattern due to lattice mismatch with the underlying HOPG. The ferrocene units appearing as either fuzzy or ring-like structures suggest the random rotation of cyclopentadienyl (Cp) rings sandwiching the central iron ion of the ferrocene moieties with their principal axis either oblique or perpendicular to the HOPG. The ferrocene moieties are more clearly resolved in a mixed film with octanethiol, where the fuzzy or ring-like structures of the ferrocene units are asymmetrically distant from the sulfur head-groups forming alternating rows in the phase segregated image. Both molecules can be clearly distinguished by the length of the molecular rows..
106. Noriyuki Ishii, Fitri Fitrilawati, Abhijit Manna, Haruhisa Akiyama, Yasushi Tamada, Kaoru Tamada, Gold nanoparticles used as a carrier enhance production of anti-hapten IgG in rabbit
A study with azobenzene-dye as a hapten presented on the entire surface of gold nanoparticles, Bioscience, Biotechnology and Biochemistry, 10.1271/bbb.70499, 72, 1, 124-131, 2008.02, The azobenzene moiety, well-known not only for its reversible cis-to-trans photoisomerization but also as a hapten, does not induce antibodies on its own, but it reacts with antibodies raised against conjugates with protein carriers. Hence we selected azobenzene dye as an indicator to assess the possibility of having gold nano-particles act as an immunological carrier instead of protein carriers. In rabbits, we confirmed an in vivo response against azobenzene dye presented on the entire surface of gold nanoparticles (azo-nanoparticles), where the gold nanoparticles appeared to play a role as a carrier for the hapten. A high yield of immunoglobulin G (IgG) against the azobenzene derivative took place in rabbits injected with azo-nanoparticles, whereas no increase in IgG was recognized in other rabbits treated solely with chemically equivalent azobenzene dye instead of azo-nanoparticles. Electron microscopy and surface plasmon resonance spectroscopy indicated that the IgG obtained specifically recognized the difference between the isomer conformations of the azobenzene moiety..
107. Lloyd F.N. Ah Qune, Kenji Makino, Kaoru Tamada, Wei Chen, Andrew T.S. Wee, Selective adsorption of L-tartaric acid on gemini-type self-assembled monolayers, Journal of Physical Chemistry C, 10.1021/jp076785d, 112, 8, 3049-3053, 2008.02, Synchrotron photoelectron spectroscopy and X-ray absorption spectroscopy studies of cationic self-assembled monolayers (SAMs) of quaternary ammonium (QA) sulfur derivates prepared on gold substrates were performed to investigate the adsorption mechanism of L-tartaric acid on a gemini-structured didodecyl dithiol (HS-gQA-SH). Using soft X-rays from a synchrotron light source, the carboxylate (deprotonated carboxylic acid) of L-tartaric acid was found to undergo an exchange reaction with the native bromide counterion of HS-gQA-SH-SAM. We also report the first soft XPS spectra of the bromide counterion of the QA. These results indicate the necessary chemical architecture via distance matching for exchange reactions to occur between complex molecules and point the way to more effective molecular recognition systems..
108. Megumi Sadaie, Naoki Nishikawa, Yoshikazu Kumashiro, Yasunori Ikezawa, Yuuki Kumagai, Kenji Marino, Satomi Ohnishi, Kaoru Tamada, Masahiko Hara, Quantitative friction map on surface composed of β-cyclodextrin monolayer, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.1143/JJAP.46.7838, 46, 12, 7838-7845, 2007.12, Our developing method "quantitative friction map" enables us to compare the spatial distribution of friction forces on the surface among separately scanned samples sensitively. We applied this technique to evaluate the friction acting between mono-[6-deoxy-6-[(mercaptoethyl)amino]]-β- cyclodextrin (β-CD-EA-SH) and OH-terminated C11 alkanethiol (OH-C11-SH) self-assembled monolayers (SAMs) in terms of symmetric and asymmetric features. The friction acting between symmetric β-CD-EA-SH SAMs is significantly larger than that acting between asymmetric β-CD-EA-SH SAM vs OH-C11-SH SAM and symmetric OH-C11-SH SAMs, although all the surfaces are commonly composed of hydroxyl terminated groups. The different frictional forces on these surfaces are closely correlated with the different adhesion forces, in which symmetric β-CD-EA-SH SAMs exhibited 1.5- and 1.3-fold larger pull-off force than β-CD-EA-SH SAM vs OH-C11-SH SAM and symmetric OH-C11-SH SAM vs OH-C11-SH SAM, respectively. Both force data can be explained by the "specific interactions" between glucose units on cyclodextrin heads rather than the deformation of the SAM by cantilever scanning..
109. Kaoru Tamada, Fumio Nakamura, Masateru Ito, Xinheng Li, Akira Baba, SPR-based DNA detection with metal nanoparticles, Plasmonics, 10.1007/s11468-007-9035-x, 2, 4, 185-191, 2007.12, In this short review paper, we summarize some of our ideas to utilize gold nanoparticles for the enhancement of surface plasmon resonance signals on DNA microarray. The hybridization of target-DNA capped gold nanoparticles with probe DNA on surface provides ca. ten times stronger optical contrast compared with that of target-DNA molecules. Our simulation result based on the Maxwell-Garnet theory explains well our experimental data and proves a potential of metallic nanoparticles for the substantial sensitivity enhancements for biosensor application in DNA diagnostics and bio-affinity studies, which leads to the fabrication of high resolution DNA microarrays..
110. Masateru Ito, Fumio Nakamura, Akira Baba, Kaoru Tamada, Hirobumi Ushijima, King Hang Aaron Lau, Abhijit Manna, Wolfgang Knoll, Enhancement of surface plasmon resonance signals by gold nanoparticles on high-density DNA microarrays, Journal of Physical Chemistry C, 10.1021/jp070524m, 111, 31, 11653-11662, 2007.08, We have developed a new methodology to fabricate high-resolution DNA microarrays (2500 dots/cm2) in combination with microcontact printing (μCP) and surface plasmon resonance (SPR) imaging. A novel COOHterminated PEG-disulfide with para-carborane (p-carborane) was synthesized as an initiator chemically bound to a gold substrate for surface coupling reactions with NH 2-terminated DNA. The hybridization between target DNA immobilized on gold nanoparticles and probe DNA arrayed on flat gold substrates was successfully demonstrated by SPR imaging, where nonspecific adsorption was not observed at the array background. The gold nanoparticles on the array give quite high contrast even at low surface coverage with gold nanoparticles (∼10%) by the enhancement effect of optical signals based on nanoscale phenomena. This enhancement effect can be well described by the simulation based on the Maxwell-Garnett theory for the effective dielectric constants and Fresnel's equation..
111. Khor HL, Kuan Y, Kukula H, Tamada K, Knoll W, Moeller M , Hutmacher D, Response of cells on surface-induced nanopatterns: Fibroblasts and mesenchymal progenitor cells, Biomacromolecules, 8, 5, 1530-1540, 2007.07.
112. Ito M, Nakamura F, Baba A, Tamada K, Ushijima H, Lau KHA , Manna A, Knoll W, Enhancement of surface plasmon resonance signals by gold nanoparticles on high-density DNA microarrays, J. Phys. Chem. C, 111, 31, 11653-11662, 2007.07.
113. Sadaie M, Nishikawa N, Kumashiro Y, Ikezawa Y, Kumagai Y , Makino K, Ohnishi S, Tamada K, Hara M., Quantitative friction map on surface composed of beta-cyclodextrin monolayer, Jpn. J. Appl. Phys. PART 1, 46, 12, 7838-7845, 2007.07.
114. Nao Terasaki, Noritaka Yamamoto, Kaoru Tamada, Mineyuki Hattori, Takashi Hiraga, Akihiko Tohri, Ikutaro Sato, Masako Iwai, Michinao Iwai, Shunpei Taguchi, Isao Enami, Yasunori Inoue, Yoshinori Yamanoi, Tetsu Yonezawa, Katsuya Mizuno, Masaki Murata, Hiroshi Nishihara, Satoshi Yoneyama, Makoto Minakata, Tsutomu Ohmori, Makoto Sakai, Masaaki Fujii, Bio-photosensor
Cyanobacterial photosystem I coupled with transistor via molecular wire, Biochimica et Biophysica Acta - Bioenergetics, 10.1016/j.bbabio.2006.11.008, 1767, 6, 653-659, 2007.06, We report on the first successful output of electrons directly from photosystem I (PSI) of thermophilic cyanobacteria to the gate of a field-effect transistor (FET) by bypassing electron flow via a newly designed molecular wire, i.e., artificial vitamin K1, and a gold nanoparticle; in short, this newly manufactured photosensor employs a bio-functional unit as the core of the device. Photo-electrons generated by the irradiation of molecular complexes composed of reconstituted PSI on the gate were found to control the FET. This PSI-bio-photosensor can be used to interpret gradation in images. This PSI-FET system is moreover sufficiently stable for use exceeding a period of 1 year..
115. Hwei Ling Khor, Yujun Kuan, Hildegard Kukula, Kaoru Tamada, Wolfgang Knoll, Martin Moeller, Dietmar W. Hutmacher, Response of cells on surface-induced nanopatterns
Fibroblasts and mesenchymal progenitor cells, Biomacromolecules, 10.1021/bm0611533, 8, 5, 1530-1540, 2007.05, Ultrathin films of a poly(styrene)-block-poly(2-vinylpyrindine) diblock copolymer (PS-b-P2VP) and poly(styrene)-block-poly(4-vinylpyrindine) diblock copolymer (PS-b-P4VP) were used to form surface-induced nanopattern (SINPAT) on mica. Surface interaction controlled microphase separation led to the formation of chemically heterogeneous surface nanopatterns on dry ultrathin films. Two distinct nanopatterned surfaces, namely, wormlike and dotlike patterns, were used to investigate the influence of topography in the nanometer range on cell adhesion, proliferation, and migration. Atomic force microscopy was used to confirm that SINPAT was stable under cell culture conditions. Fibroblasts and mesenchymal progenitor cells were cultured on the nanopatterned surfaces. Phase contrast and confocal laser microscopy showed that fibroblasts and mesenchymal progenitor cells preferred the densely spaced wormlike patterns. Atomic force microscopy showed that the cells remodelled the extracellular matrix differently as they migrate over the two distinctly different nanopatterns..
116. Kaoru Tamada, Fumio Nakamura, Masateru Ito, Xinheng Li, Akira Baba, SPR-based DNA detection with metal nanoparticles, Plasmonics, 2, 4, 185-191, 2007.01.
117. Chun Wei Lee, Keke Zhang, H. Tantang, Anup Lohani, S. G. Mhaisalkar, Lain Jong Li, T. Nagahiro, Kaoru Tamada, Y. Chen, Tuning of electrical characteristics in networked carbon nanotube field-effect transistors using thiolated molecules, Applied Physics Letters, 10.1063/1.2772181, 91, 10, 2007, The authors examine the effects of adsorption of four thiolated molecules (HS- C10 H21, HS- C11 H22 OH, HS- C10 H20 COOH, and HS- C2 H4 C4 F9) on the electrical characteristics of single-walled carbon nanotube network FETs (SNFETs). Work function of the electrodes was measured before and after molecule adsorption. Schottky barrier energy extraction for SNFETs was also performed and the results provide direct evidence that the device characteristics of SNFETs after SAM adsorption are altered primarily due to the change in energy-level alignment between the Au and SWNTs, which thus provides an effective methodology for the tuning and performance optimization of these devices in a controllable way..
118. Yasuyuki Yokota, Akira Miyazaki, Ken Ichi Fukui, Toshiaki Enoki, Kaoru Tamada, Masahiko Hara, Dynamic and collective electrochemical responses of tetrathiafulvalene derivative self-assembled monolayers, Journal of Physical Chemistry B, 10.1021/jp062285t, 110, 41, 20401-20408, 2006.10, Electroactive tetrathiafulvalene (TTF)-containing alkanethiol self-assembled monolayers (SAMs) were designed and synthesized to elucidate the relationship between electrochemical responses and film structures. Two TTF derivative molecules having one alkanethiol chain (1) and two alkanethiol chains (2) were utilized to modulate the molecular packing arrangements in the SAMs, and the formation and structure of the SAMs were characterized by surface plasmon resonance spectroscopy (SPR). SPR measurements in various contacting media demonstrated loose packing of SAM 1 and close packing of SAM 2 due to the different space fillings of the molecules. Two successive one-electron redox waves were observed for both SAMs by cyclic voltammetry. The peak widths of the redox waves were strongly dependent on the oxidation states of the TTF moieties, the packing arrangement of the SAMs, and the contacting medium. We found that TTF-based SAMs exhibited collective electrochemical responses induced by dynamic structural changes, depending on the degree of freedom for the component molecules in the SAMs. These results imply that the molecular design, taking into account the electrochemical responses, extends the available range of molecular-based functionalities in TTF-based SAMs..
119. Xinheng Li, Kaoru Tamada, Akira Baba, Wolfgang Knoll, Masahiko Hara, Estimation of dielectric function of biotin-capped gold nanoparticles via signal enhancement on surface plasmon resonance, Journal of Physical Chemistry B Materials, 10.1021/jp062004h, 110, 32, 15755-15762, 2006.08, Biotin-capped gold nanoparticles assembled on flat gold with volume fraction/are studied by surface plasmon resonance (SPR) spectroscopy and atomic force microscopy (AFM) in order to estimate the dielectric function of the gold nanoparticles based on the Maxwell-Garnett (MG) theory. The complex dielectric function (∈′, ∈″) of the spherical nanoparticles at three representative wavelengths in the vis-near-IR region, i.e., λ = 543, 632.8, and 1152 nm, is estimated for a surface homogeneously covered with nanoparticles in order to discuss the wavelength dependence of the dielectric function. The SPR response of a surface covered with particles in 2D aggregates is also analyzed. The experimental SPR curve of the particle aggregates deviates from the theoretical predictions, suggesting dipole interactions between particles..
120. Megumi Sadaie, Naoki Nishikawa, Satomi Ohnishi, Kaoru Tamada, Kiyoshi Yase, Masahiko Hara, Studies of human hair by friction force microscopy with the hair-model-probe, Colloids and Surfaces B: Biointerfaces, 10.1016/j.colsurfb.2006.06.004, 51, 2, 120-129, 2006.08, We employed a cantilever modified with a self-assembled monolayer (SAM) as a "hair-model-probe" for friction force microscopy (FFM) to measure friction acting between hair and hair-like surfaces. The "hair-model-probe" was prepared by forming a SAM of octadecanethiol on a gold-coated cantilever. We investigated frictional properties of human hair at both root and tip, and the dependency on applied load, influence of scanning direction, and local frictional distribution. The friction coefficient of the hair tip was greater than that of the hair root. Load dependency of friction at the hair tip was clearly observed, while friction at the hair root was less dependent on applied load. At the hair root, an anisotropic frictional property was observed: friction force along the long axis of the hair fiber was about 1.5-2 times larger than that along the short axis. Atomic force microscopy (AFM) images showed striations on the cuticle cells that have about 6 nm depth and their long axis oriented in the direction of the hair fiber. The frictional distribution images revealed that the local areas showing strong shear corresponded to striations. Since such distribution of friction was not observed at the hair tip, it is suggested that the anisotropic frictional property at the hair root was caused mainly by the striations. The frictional distribution in regions that excluded the striations also showed the anisotropic frictional property that friction parallel to the long axis of the hair fiber is greater than that along the short axis. This result suggests that the orientation of fatty acid molecules comprising the fat layer (F-layer) may also contribute to the anisotropic frictional property. We have concluded that loss of the F-layer is a dominant cause of strong friction detected at the hair tip, and at the striations of the hair root..
121. Shinobu Yokokawa, Kaoru Tamada, Masahiko Hara, Formation of chiral surface with enantiomeric tartaric acid on gemini-structured self-assembled monolayers, Journal of Nanoscience and Nanotechnology, 10.1166/jnn.2006.242, 6, 6, 1772-1778, 2006.06, Chiral surfaces were prepared by L, D, and Meso-tartaric acids (TAs) adsorbed on geministructured self-assembled monolayers (SAMs) composed of ethylenebis [(12-mercaptododecyl) dimethyl ammonium bromide] (HS-gQA-SH). The formation and structure of the chiral surfaces were characterized by surface plasmon resonance spectroscopy (SPR) and Fourier transform infraredreflection adsorption spectroscopy (FTIR-RAS). The thickness of enantiomeric TA layers on the HS-gQA-SH SAM was estimated to be c.a. 5-6 Å regardless of their chirality, in good agreement with the height of TA molecules anchoring on the surface with two COOH groups. All the TAs on the HS-gQA-SH SAM exhibit the same ionization state independent of their chirality in their vibration bands of carboxyiic groups. We attempted a second-layer adsorption of the enantiomeric TAs on L-TA monomolecular layer (L-TA SAM) precomposed on the HS-gQA-SH. A strong affinity between first and second TA layers resulted in the film growth when their chirality is identical (i.e., L-TA on L-TA SAM). We found the structure of second L-TA layer was completely different from that of the first layer, where a crystalline-like L-TA phase was found as a predominant component. Our results imply a preferential crystalline growth of chiral molecules on the same chiral surface, which may lead to a work for optical resolution into two enantiomers at a solid-liquid interface..
122. Fumio Nakamura, Masateru Ito, Ablihito Manna, Kaoru Tamada, Masahiko Hara, Wolfgang Knoll, Observation of hybridization on a DNA array by surface plasmon resonace imaging using Au nanoparticles, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.1143/JJAP.45.1026, 45, 2 A, 1026-1029, 2006.02, To realize the sensitive detection of DNA hybridization, DNA-modified Au nanoparticles (DNA-AuNPs) containing single-and double-stranded portions were prepared. The hybridization of a target DNA using the DNA-AuNPs on a DNA self-assembled monolayer (DNA-SAM) was monitored in situ by surface plasmon resonance (SPR) imaging. A sandwich type hybridization (DNA-SAM/target DNA/DNA-AuNP) experiment was carried out in order to enhance the hybridization signal. SPR imaging results strongly indicate that the hybridization signal is enhanced several times compared to the case of target DNA hybridization..
123. Nobuko Fukuda, Jun Young Kim, Takashi Fukuda, Hirobumi Ushijima, Kaoru Tamada, Synthesis and optical characterization of novel imidazole-based Azo materials, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.1143/JJAP.45.460, 45, 1 B, 460-464, 2006.01, We synthesized novel imidazole-based azo compounds and their optical properties were investigated. In the course of recrystallization, pink-orange and violet products were obtained. The violet one shows poor solubility for most organic solvents except polar aprotic solvents such as dimethylsulfoxide (DMSO) and dimethylfolmamide (DMF). The spectra of NMR in DMSO-d6 and UV-vis absorption spectra in DMSO for both products were found to be identical. However, there were differences in FT-IR absorption spectra. The violet solid compound exhibited broad bands that could be attributed to N-H⋯N hydrogen bonding. These results show that the violet product consists of an aggregation of molecules formed via intermolecular hydrogen bonding. Additionally, imidazole-based azo copolymers containing liquid crystalline side chain groups were also synthesized. The photoinduced birefringence of these copolymers was observed by irradiation of a linearly polarized 532 nm laser beam as a pumping light. It was confirmed that the material exhibited photoisomerization properties and the observed birefringence was attributed to photoinduced molecular reorientation. Moreover, the dipolar effect in photoinduced birefringence was briefly discussed..
124. Nobuko Fukuda, Makoto Fujimaki, Koichi Awazu, Kaoru Tamada, Kiyoslii Yase, High sensitive optical detection of bio-chemicals onto a silicon oxide surface based on waveguide mode, 2005 MRS Fall Meeting Nanoparticles and Nanostructures in Sensors and Catalysis, 900, 470-475, 2005.12, This work presents high sensitive detection of specific adsorption of proteins onto a silicon oxide (SiOx) surface modified by molecules with a biotinyl-end group. We fabricated a SiOx waveguide by sputtering onto a thin gold film and measured the incident angle-dependence of reflectivity using a polarized He-Ne laser under total internal reflection condition. When the s-polarized light was irradiated to the SiOx waveguide (760 nm) coupled with a prism, the incident angle-dependence of reflectivity showed narrow dips due to excitation of the waveguide mode. The waveguide surface was modified by the molecules with the biotinyl-end group as a protein probe. Specific adsorption of streptavidin in a PBS buffer solution was monitored through time course of the reflectivity change at a constant incident angle, where the waveguide mode was excited. As compared with conventional SPR system using a gold surface, high sensitive detection of the specific adsorption was achieved. Additionally, we fabricated micro-patterned arrays of biotinyl-end layers onto the SiOx waveguide surface by micro-contact printing (μCP). Then we observed the specific adsorption behavior on the micro-patterned arrays by the imaging based on the waveguide mode using a CCD camera..
125. F. Fitrilawati, R. Renu, C. Baskar, L. G. Xu, H. S O Chan, S. Valiyaveettil, Kaoru Tamada, W. Knoll, Langmuir-blodgett-kuhn and self-assembled films of asymmetrically substituted poly(paraphenylene), Langmuir, 10.1021/la0505667, 21, 26, 12146-12152, 2005.12, Asymmetrically substituted poly(paraphenylene) (PhPPP) with hydrophilic and hydrophobic side chains was investigated. The polymer behavior at the air-water interface was studied on the basis of surface pressure-area (π-A) isotherms and compression/expansion hysteresis measurements. PhPPP can form stable monolayers with an area per repeat unit of A = 0.20 ± 0.02 nm2 and a collapse pressure in the range of π = 25 mN/m. Then, Langmuir-Blodgett-Kuhn (LBK) films of PhPPP were prepared by horizontally and vertically transferring the Langmuir monolayers onto hydrophilic solid substrates at π = 12 mN/m. Cross-section analysis of the AFM tapping-mode topography images of a single transferred monolayer reveals a thickness of d0 = 0.9 ± 0.1 nm. Taking into account the obtained monolayer thickness, curvefitting calculations of angular scan data of LB monolayers measured using surface plasmon resonance (SPR) spectroscopy lead to a value for the refractive index of n = 1.78 ± 0.02 at λ = 632.8 nm. Next, the spontaneous formation of a PhPPP monolayer by adsorption from solution was studied ex situ by atomic force microscopy and UV-vis spectroscopy and in situ by using SPR spectroscopy. Stable self-assembled monolayers of PhPPP can be formed on hydrophilic surfaces with a thickness similar to that of the monolayer obtained using the LB method. The characterization results confirmed the amphiphilic character and the self-assembly properties of PhPPP, as well as the possibility of preparing homogeneous monolayer and multilayer films..
126. Soichi Otsuki, Koji Ohta, Kaoru Tamada, Shin Ichi Wakida, Thickness measurements on transparent substrates based on reflection ellipsometry. I. Optical effects of high-refractive-index additional layers, Applied Optics, 10.1364/AO.44.005910, 44, 28, 5910-5918, 2005.10, Theoretical studies were conducted for thickness measurements using transparent substrates on the external and internal reflection configurations. For three-phase systems consisting of ambient, film, and substrate, the refractive index of the substrate could be optimized to obtain the high sensitivity of an ellipsometric quantity Δ to the film thickness and the small susceptibility of Δ to errors in the incident angle. It was shown that the combination of an ordinary glass substrate and an additional dielectric layer with an appropriate layer thickness works as a synthetic high-index single substrate (SHIS). The optical effect of the combination was approximately described by use of the effective refractive index of SHIS. A method to select the refractive index of the additional layer was also given..
127. Soichi Otsuki, Kaoru Tamada, S. Wakida, Wavelength-scanning surface plasmon resonance imaging, Applied Optics, 10.1364/AO.44.003468, 44, 17, 3468-3472, 2005.06, A new surface plasmon resonance (SPR) imaging technique was proposed. After measurements were conducted at varying wavelengths, the wavelength affording the minimum brightness (SPR wavelength) was determined at each pixel of the image. A two-dimensional map of the SPR wavelength could be converted to a thickness profile by use of a nonlinear calibration curve, which was obtained by Fresnel calculation. An array of protein thin layers on a gold film was evaluated in air to present the layers' surface structure in nanometer scale..
128. Soichi Otsuki, Kaoru Tamada, Shin Ichi Wakida, Two-dimensional thickness measurements based on internal reflection ellipsometry, Applied Optics, 10.1364/AO.44.001410, 44, 8, 1410-1415, 2005.03, An imaging ellipsometer technique on internal reflection geometry that can measure the thickness distribution of a thin film possessing an assumed refractive index is described. Because a prism is used for the internal reflection geometry, it was theoretically predicted that angular derivation from the normal incidence on the prism surface affects only the ^ value by a factor of 0.97 at maximum. Measurements were carried out for an optical system of silica substrate-TiO2 layer-silica layer-protein film-air, with a thin-film array of dried protein as the sample film. Thickness of the protein films was two-dimensionally estimated only from the measured map of the A value by use of the simulated relationship between the thickness and the A value. The thickness map obtained was coincident on the whole with the results according to a mechanical scanning. The detection limit was approximately ±0.2 nm. These findings validate the optical effect of a high-index additional layer to improve the sensitivity and precision of thickness measurements of the sample film on transparent substrates..
129. Masateru Ito, Tian Xin Wei, Peng Lei Chen, Haruhisa Akiyama, Mutsuyoshi Matsumoto, Kaoru Tamada, Yoshinori Yamamoto, A novel method for creation of free volume in a one-component self-assembled monolayer. Dramatic size effect of para-carborane, Journal of Materials Chemistry, 10.1039/b411121d, 15, 4, 478-483, 2005.01, We fabricated the self-assembled monolayers (SAMs) composed of 4-(12-(10-mercaptodecyl)-1,12-dicarba-closo-dodecaborane)-4′-octyloxy azobenzene and 4-(10-mercaptodecyloxy)-4′-octyloxyazobenzene on a gold surface, and performed photoswitching experiments. The SAM including p-carborane exhibited a much higher and more reversible photochemical response in comparison with the SAM in the absence of the p-carborane. This result suggests that the free volume of the azobenzene moiety to change its conformation is increased due to the size effect of the p-carborane..
130. H. L. Khor, Y. J. Kuan, D. W. Hutmacher, Kaoru Tamada, W. Knoll, Cell adhesion and migration in response to nano-patterned surfaces formed by diblock copolymers, Transactions - 7th World Biomaterials Congress Transactions - 7th World Biomaterials Congress, 2004.12, The cell adhesion and migration behavior on different nanopatterned surfaces was investigated to determine the effect of different nano-topography on cell function. The adsorption of extracellular matrix protein like fibronectin, on different nanopatterned surfaces, was performed by using immunofluorescence and contact angle measurements. The initial cell adhesion strength on the different substrates was studied by the use of laser tweezers. The live imaging of cell migration on the different substrates with cells transfected with EYFP-alpha-tubulin vector was studied. The initial cell culture on coated and plain mica strips demonstrated that hMSC displayed more of a polar morphology with long filopodium extensions on worm-like patterned substrates..
131. King Hang Aaron Lau, Le Shon Tan, Kaoru Tamada, Melissa S. Sander, Wolfgang Knoll, Highly sensitive detection of processes occurring inside nanoporous anodic alumina templates
A waveguide optical study, Journal of Physical Chemistry B Materials, 10.1021/jp0498567, 108, 30, 10812-10818, 2004.07, We have applied nanoporous anodic alumina films as planar optical waveguides and studied changes in the effective dielectric constants of these thin films due to various processes occurring in the pores. We demonstrate the potential of the porous anodic alumina waveguide for high sensitivity (bio-) chemical sensing with bovine serum albumin adsorption and desorption at various pH values, with subangstrom sensitivity in the effective thickness of protein adsorbed. We also monitored pore widening (alumina dissolution) with subangstrom sensitivity, which is conceptually the reverse of detecting conformal film deposition on pore surfaces. Furthermore, we monitored the exchange of pore-filling media between phosphate buffer solution and ethanol, which produces qualitatively the same response as complete pore filling with other materials by various deposition techniques. Thus porous anodic alumina films may be employed simultaneously as deposition templates and as highly sensitive detectors of processes within the pores..
132. Wolfgang Knoll, Ming Yong Han, Xinheng Li, Jose Luis Hernandez-Lopez, Abhijit Manna, Klaus Müllen, Fumio Nakamura, Lifang Niu, Rudolf Robelek, Evelyne L. Schmid, Kaoru Tamada, Xinhua Zhong, Nanoscopic building blocks from polymers, metals, and semiconductors for hybrid architectures, Journal of Nonlinear Optical Physics and Materials, 10.1142/S0218863504001815, 13, 2, 229-241, 2004.06, This paper describes some of our efforts in the area of nanostructured thin film architectures. The resulting interfacial hybrid assemblies are built from (1) organic/polymeric objects based on dendrimer systems, from (2) surface-functionalized Au nanoparticles, and (3) from a variety of semiconducting quantum dots. Dendrimers as polymeric building blocks with a strictly monodisperse particle size distribution in the nanometer range can be functionalized in the core, the scaffold, or at the periphery, thus offering interesting hybrid materials for a wide range of applications. The combination with Au clusters and their local surface plasmon resonances suggests new strategies for optoelectronic devices or unconventional bio-sensor platforms. The possibility of tuning the luminescent properties of semiconducting nanoparticles by size or compositional bandgap engineering complements the assembly kit with building blocks for supramolecular thin film nanocomposite materials..
133. Chang Dae Keum, Takashi Fukuda, Him Matsuda, Kaoru Tamada, Facile photofabrication of stable, submicrometer-wide, electrically conductive patterns, Advanced Materials, 16, 8, 696-699+666, 2004.04, A fabrication method for submicrometor-wide electric conductive patterns using Ag nanoparticle/polymer composites on furan-functionalized substrates (see Figure) is reported. A 180 nm wide (full width at half maximum) photofabricatcd pattern has been achieved, well below the wavelength of incident light. After anneating at 200°C for 40 min. the pattern worked as an electric wire with a resistivity of -8 × 104 Ω cm..
134. Tianxin Wei, Kaoru Tamada, Shinobu Yokokawa, Eisuke Ito, Kiyoshi Yase, Masahiko Hara, Fabrication and characterization of novel mixed-valence pentaamminechlororuthenium(III) hexacyanoruthenate(II) coordination compound self-assembled film, Chemistry Letters, 10.1246/cl.2004.164, 33, 2, 164-165, 2004.02, Functional self-assembled film of a class II mixed-valence coordination compound, pentaamminechlororuthenium(III) hexacyanoruthenate(II) (Na[NH 3]5Ru(III)-CN-Ru(II)(CN)5), was fabricated and characterized by surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS) and phase modulation infrared reflection-absorption spectroscopy (PMIR-RAS)..
135. Chang Dae Keum, Takashi Fukuda, Hiro Matsuda, Kaoru Tamada, Submicron-wide pattern of silver wire stabilized on functionalized substrates, Molecular Crystals and Liquid Crystals, 10.1080/15421400490506450, 425, 27-39, 2004, A stable submicron-wide electric conductive pattern consists of silver nanoparticles/polymer composite is established via photolithographic procedure, in which the introduction of furan-functionalized surface for the chemical anchoring of the pattern was a significant contrivance. Due to the strong anchoring between narrow-patterned film and the treated substrate, submicron-wide patterns stands up well against the development and annealing process. Approximately 180 nm-wide nanopattern has been achieved by the irradiation of 488 nm light. The width is well below the dimension of the incident light wavelength. Time dependence of the electric resistance of the composite thin film during annealing process has been measured at 200°C, and an optimum annealing time was found. The achieved volume resistivity after the optimum annealing was evaluated as ∼8 × 10-4 Ohm-cm that was determined by four-probe measurements..
136. Shinobu Yokokawa, Masahiko Hara, Kaoru Tamada, Eisuke Ito, Cationic Self-assembled Monolayers Composed of Gemini-structured Sulfur Compounds on Gold
A New Approach to Control Ionic Functions on Surfaces, Proceedings of the 13th Korea-Japan Joint Forum on Organic Materials for Electronics and Photonics Molecular Crystals and Liquid Crystals, 10.1080/15421400390263875, 407, PART 3, 2003.12, Cationic self-assembled monolayers (SAMs) composed of quaternary ammonium (QA) sulfur derivatives have been synthesized to control a position and a distance between charged head groups on gold substrates. Three molecules bearing resembling molecular structures, "gemini"-structured didodecyl dithiol (HS-gQA-SH), didodecyl disulfide (QA-SS-QA), and gemini-structured didodecyl disulfide (gQA-SS-gQA), were utilized in this study, and the formation and structure of the SAMs were characterized by surface plasmon resonance spectroscopy (SPR)..
137. Takashi Fukuda, Chang Dae Keum, Hiro Matsuda, Kiyoshi Yase, Kaoru Tamada, Photo-induced surface relief on Azo polymer for optical component fabrication, Proceedings of SPIE - The International Society for Optical Engineering, 10.1117/12.508289, 5183, 155-162, 2003.12, With respect to the manufacturing of optical elements, facile and effective fabrication method is proposed. It is developed in connection with photo-induced surface relief (PSR) formation phenomenon that occurs on the azobenzene functionalized polymer film. Purely optically inscribed surface relief structures have been used as a plastic mold for manufacturing of its replica. At least a hundred times replication process has been achieved using thermosetting resin without any deterioration. This method has many merits not only from a technical viewpoint but also from a economical efficiency. In this report, first the PSR phenomenon is explained and then several examples for optical component fabrication are demonstrated. photo-induced surface relief (PSR), azobenzene polymer film, optical patterning, polymer mold (template), replication, thermosetting resin, UV curable resin, optical elements, kinoform, laser pattern generator..
138. Akira Baba, Jörn Lübben, Kaoru Tamada, Wolfgang Knoll, Optical Properties of Ultrathin Poly(3,4-ethylenedioxythiophene) Films at Several Doping Levels Studied by In Situ Electrochemical Surface Plasmon Resonance Spectroscopy, Langmuir, 10.1021/la034848n, 19, 21, 9058-9064, 2003.10, In this paper, we report on in situ optical/electrochemical investigations using a combination of surface plasmon resonance spectroscopy and electrochemistry in order to determine the complex dielectric constants of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films. The PEDOT films were deposited by in situ electropolymerization. The film thickness was monitored by a quartz crystal microbalance. In the electrochemical surface plasmon resonance (EC-SPR) measurements, three wavelengths corresponding to interband and intraband electronic transition regions were used in order to investigate electrochromic properties. The optical conductivity was also determined by EC-SPR measurement with a near-infrared laser wavelength which corresponds to the region outside the anomalous dispersion..
139. Jianjiang Hu, Chao Yin, Hai Quan Mao, Kaoru Tamada, Wolfgang Knoll, Functionalization of poly(ethylene terephthalate) film by pulsed plasma deposition of maleic anhydride, Advanced Functional Materials, 10.1002/adfm.200304384, 13, 9, 692-697, 2003.09, Poly(ethylene terephthalate) (PET) films have been functionalized with carboxyl groups by pulsed plasma polymerization of maleic anhydride (MA). The preserved anhydride groups of MA were converted to carboxyl groups by subsequent hydrolysis. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to determine the chemical composition of the deposited MA plasma polymers. Atomic force microscopy (AFM) observations visually confirmed the coverage of the PET surface with plasma polymers after water treatment of the processed PET substrate, and the functionality in the XPS spectra of samples before and after water treatment indicated the persistence of functional groups and the good adhesion of the deposited layers on the PET substrate. In accordance with FTIR and XPS results, the density of carboxyl groups increased with decreasing plasma duty cycle. Compared with the pristine PET substrate, a higher roughness was observed on the modified PET surface by AFM. The roughness decreased sharply with decreasing plasma duty cycle..
140. Shinobu Yokokawa, Kaoru Tamada, Eisuke Ito, Masahiko Hara, Cationic self-assembled monolayers composed of gemini-structured dithiol on gold
A new concept for molecular recognition because of the distance between adsorption sites, Journal of Physical Chemistry B Materials, 10.1021/jp027375m, 107, 15, 3544-3551, 2003.04, Cationic self-assembled monolayers (SAMs) composed of quaternary ammonium (QA) sulfur derivatives have been synthesized to control the distance between charged headgroups on gold substrates. Two molecules bearing resembling molecular structures, "gemini"-structured didodecyl dithiol (HS-gQA-SH) and didodecyl disulfide (QA-SS-QA), were utilized in this study, and the formation and structure of the SAMs were characterized by surface plasmon resonance spectroscopy (SPR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared-reflection adsorption spectroscopy (FTIR-RAS). In the HS-gQA-SH SAM, the orientation and distance between QA groups are specified by the covalent bonding with ethylene spacer, while those of the QA-SS-QA SAM are determined by the electric repulsion between charged headgroups, that is, QA groups in the QA-SS-QA SAM are more randomly located, being more distant than with those in the HS-gQA-SH SAM. We found that L-tartaric acid, a probe molecule with two carboxyl groups having the distance of an ethylene unit, exhibits a strong affinity on the HS-gQA-SH SAM. In contrast, no specific binding was observed on the QA-SS-QA SAM. These results imply the possibility to build up a molecular recognition system on surfaces because of the control of the distance between the charged headgroups by using the gemini-structured molecular design..
141. Kaoru Tamada, Haruhisa Akiyama, Tian Xin Wei, Seung Ae Kim, Photoisomerization reaction of unsymmetrical azobenzene disulfide self-assembled monolayers
Modification of azobenzene dyes to improve thermal endurance for photoreaction, Langmuir, 10.1021/la0258493, 19, 6, 2306-2312, 2003.03, Recently we have developed an unsymmetrical azobenzene disulfide with a short alkyl side chain, 4-hexyl-4′-(12-(dodecyldithio)-dodecyloxy)azobenzene (C6AzSSC12), aiming of a high efficiency in photoisomerization in SAMs on planar gold surfaces (Tamada, K.; et al. Langmuir 2002, 18, 5239). In this paper, we introduce an additional modification on the molecule to improve the thermal endurance for the photoreaction by attachment of a methyl group to the azobenzene ring, thus avoiding dye aggregation sterically. A "methyl-derivatized" azobenzenethiol (C6Az(Me)SH) SAM revealed a significant improvement in their photoreactivity compared with an unmodified azobenzenethiol (C6AzSH) SAM due to the steric effect of the methyl group. A "methyl-derivatized" unsymmetrical azobenzene disulfide (C6Az(Me)SSC12) SAM exhibited quite a similar photoresponse to that of C6AzSSC12 SAM before heat treatment owing to the free volume given by the unsymmetrical structure; however, only the C6Az(Me)SSC12 SAM could retain high photoreactivity in phase-segregated domains formed by annealing, unlike the C6AzSSC12 SAM. The C6Az(Me)SH and C6Az(Me)SSC12 SAMs exhibited a reaction kinetics different from that of C6AzSSC12 SAM due to a different quantum yield and the molecular tilt angle of the azobenzene unit. The C6Az(Me)SH SAM exhibited a typical character of "congested surface", where the reaction rate from cis to trans was faster, while that from trans to cis was slower compared with those of C6Az(Me)SSC12 SAM..
142. Shinobu Yokokawa, Masahiko Hara, Kaoru Tamada, Eisuke Ito, Cationic self-assembled monolayers composed of gemini-structured sulfur compounds on gold
A new approach to control ionic functions on surfaces, Molecular Crystals and Liquid Crystals, 10.1080/744819020, 407, 2003.01, Cationic self-assembled monolayers (SAMs) composed of quaternary ammonium (QA) sulfur derivatives have been synthesized to control a position and a distance between charged head groups on gold substrates. Three molecules bearing resembling molecular structures, "gemini"-structured didodecyl dithiol (HS-gQA-SH), didodecyl disulfide (QA-SS-QA), and gemini-structured didodecyl disulfide (gQA-SS-gQA), were utilized in this study, and the formation and structure of the SAMs were characterized by surface plasmon resonance spectroscopy (SPR)..
143. Abhijit Manna, Peng Lei Chen, Haruhisa Akiyama, Tian Xin Wei, Kaoru Tamada, Wolfgang Knoll, Optimized photoisomerization on gold nanoparticles capped by unsymmetrical azobenzene disulfides, Chemistry of Materials, 10.1021/cm0207696, 15, 1, 20-28, 2003.01, Gold nanoparticles capped by an unsymmetrical azobenzene disulfide, 4-hexyl-4′-(12-(dodecyldithio)dodecyloxy)azobenzene (C6AzSSC12), were synthesized in order to investigate the efficiency of azobenzene photoisomerization on colloidal gold surfaces. The nanoparticles were synthesized by a two-step method to avoid the direct contact of azobenzene units with a reducing agent. The average size of the particles was determined to be ∼5.2 ± 1.3 nm from transmission electron microscope (TEM) images. The CH2 antisymmetric (∼2919 cm-1) and symmetric (∼2850 cm-1) stretching bands in the FTIR spectra of the nanocomposite confirmed the all-trans conformation of alkyl chains in the C6AzSSC12 on the colloidal gold. The photoisomerization reaction of the C6AzSSC12-capped gold nanoparticles was studied by UV-vis absorption spectroscopy in toluene. The reaction kinetics was identical to that of the free C6AzSSC12 molecules dissolved in toluene, with no deviations from a first-order plot for both trans-to-cis and cis-to-trans photoisomerization, suggesting no steric hindrance throughout the whole reaction process. The free volume guaranteed by the 50% dilution of the dye functions due to the unsymmetrical disulfide structures, as well as their noncompact molecular tails owing to the assembly on the curved colloidal gold, must be responsible for such a highly efficient photoreaction. Sedimentation of the nanoparticles arose in toluene subsequent to the photoisomerization of the capping azobenzene molecules from trans to cis isomers. This phenomenon can be interpreted as resulting from differences in the degree of solvation between the azobenzene isomers..
144. Haruhisa Akiyama, Kaoru Tamada, Jun'ichi Nagasawa, Koji Abe, Takashi Tamaki, Photoreactivity in self-assembled monolayers formed from asymmetric disulfides having para-substituted azobenzenes, Journal of Physical Chemistry B, 10.1021/jp026103g, 107, 1, 130-135, 2003.01, Asymmetric dialkyl disulfides with a para-substituted azobenzene (i.e., 4-substituted 4′-(12-(dodecyldithio)-dodecyloxy)azobenzenes) produced photoresponsive self-assembled monolayers (SAMs) on gold (111) surfaces. Infrared reflection absorption (IR-RA) spectroscopy and reflection ultraviolet (UV) and visible (vis) light absorption spectroscopy gave information on the molecular orientational order of the adsorbates in the SAMs. The photoreactivity was investigated using dynamic contact-angle measurements with a Wilhelmy-type surface balance. The structure and photoreactivity of the SAMs were dependent on the substituent at the para position of an azobenzene moiety. Relatively ordered structures in the methylene parts and the photoisomerization of azobenzene moieties were observed for the SAMs formed from the hexyl- and the nonsubstituted azobenzene disulfides. However, a less-ordered SAM structure was seen for the cyanoazobenzene disulfide SAM, and the photoresponse is rather unstable..
145. Ryota Yuge, Akira Miyazaki, Toshiaki Enoki, Kaoru Tamada, Fumio Nakamura, Masahiko Hara, Intercalation effect of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimetane having strong electron affinity in self-assembled monolayers composed of charge transfer complex prepared by coadsorption and layer-by-layer adsorption methods, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 41, 12, 7462-7468, 2002.12, Charge transfer (CT) complex self-assembled monolayers (SAMs) on a gold substrate are prepared using layer-by-layer adsorption and coadsorption methods with mercapto-methyl-tetrathiafulvalene (TTF-CH2SH) and strong acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF4), in comparison with TTF-CH2SH/TCNQ SAMs consisting of moderate acceptor TCNQ. The layer-by-layer method yields TTF-CH2SH/TCNQF4 SAMs with the coexistence of neutral TCNQF4 and anionic TCNQF4
-, where the TCNQF4
- anions are laid on the TTF layer with the TTF-CH2SH molecules standing perpendicular to the gold substrate. The neutral TCNQF4 molecules are stacked above the TCNQF4
- anion layer. This is in contrast to the fact that TCNQ having intermediate strength of acceptor character does not yield any CT SAMs when using the layer-by-layer technique. In the coadsorption method, TTF-CH2SH/TCNQF4 SAMs are formed, where all the TCNQF4 molecules are completely reduced as TCNQF4
- anions, similar to those in bulk TTF-TCNQF4 crystals. Taking into account that TTF-CH2SH/TCNQ SAMs have the same fractional value (0.6) of the degree of charge transfer to that of bulk TTF-TCNQ crystal, the coadsorption technique can reproduce the electronic structure of the bulk CT complex in the 2D SAMs. The coadsorbed SAMs have an intercalation structure, where acceptor molecules are intercalated into the interstitials of TTF-CH2SH/Au units with the molecular axes of both acceptor and donor molecules parallel to each other. Such a donor/acceptor molecular arrangement can provide a favorable situation in the charge transfer between the two ingredients, resulting in the similar electronic structure to that of bulk CT crystals..
146. Ryota Yuge, Akira Miyazaki, Toshiaki Enoki, Kaoru Tamada, Fumio Nakamura, Masahiko Hara, Fabrication of TTF-TCNQ charge-transfer complex self-assembled monolayers
Comparison between the coadsorption method and the layer-by-layer adsorption method, Journal of Physical Chemistry B, 10.1021/jp0135757, 106, 27, 6894-6901, 2002.07, We propose a novel technique to fabricate self-assembled monolayers (SAMs) of 2D charge-transfer complexes by coadsorption of thiol-functionalized tetrathiafulvalene derivatives (TTF-CH2SH) with 7,7,8,8-tetracyano-quinodimethane (TCNQ) on a gold substrate. For the "coadsorption" method, the gold substrates are immersed into the TTF-CH2SH and TCNQ mixed acetonitrile solution under optimum conditions for TTF-TCNQ bulk crystalline growth. TTF-CH2SH/TCNQ SAMs are also prepared by the conventional "layer-by-layer" adsorption method to compare the film properties with those of the coadsorbed SAMs, where the gold substrates are exposed to TCNQ solution after TTF-CH2SH (single component) SAM formation. For both TTF-CH2SH/TCNQ SAMs, the adsorption process and the optical thickness are characterized by surface plasmon resonance (SPR) measurements. The coadsorbed TTF-CH2SH/TCNQ SAMs form slightly thicker films (15.9 Å) than do the SAMs prepared by the layer-by-layer adsorption method (15.1 Å) because they incorporate the TCNQ molecules more efficiently in the film. The FTIR-RAS data reveal that all TCNQ molecules in the coadsorbed SAMs are in the mixed valence state, whereas no intermolecular charge transfer is present in the SAMs prepared by the layer-by-layer adsorption method. From the C≡N absorption bands in the IR spectra, the degree of charge transfer is estimated to ≃0.6 for the coadsorbed SAMs, which is comparable to the value for the bulk TTF-TCNQ crystals..
147. Kaoru Tamada, Haruhisa Akiyama, Tian Xin Wei, Photoisomerization reaction of unsymmetrical azobenzene disulfide self-assembled monolayers studied by surface plasmon spectroscopy
Influences of side chain length and contacting medium, Langmuir, 10.1021/la0157667, 18, 13, 5239-5246, 2002.06, We report the characteristics of azobenzene-containing self-assembled monolayers (SAMs) which are designed and synthesized for surface photoisomerization reactions. The photoreactive SAMs were composed of unsymmetrical azobenzene disulfides, in which the free volumes for photoreaction of azobenzene moieties are guaranteed by 50% dilution of dye functions at the molecular level on the surface. The photoswitching reaction was monitored in situ through the change of optical film thickness by means of surface plasmon spectroscopy. The influences of alkyl side chain length and contacting medium on the photoreaction were also investigated. The profile of the trans to cis photoisomerization reaction by UV light irradiation exhibited a clear deviation from first-order kinetics, suggesting a steric hindrance effect on the photoreaction process..
148. Ryota Yuge, Akira Miyazaki, Toshiaki Enoki, Kaoru Tamada, Fumio Nakamura, Masahiko Hara, Electrochemical properties of self-assembled monolayers composed of TTF derivative, Molecular Crystals and Liquid Crystals, 10.1080/10587250290089365, 377, 395-398, 2002, We prepared self-assembled monolayers (SAMs) composed of tetrathiafulvalene (TTF) derivative modified on gold substrate and investigate their electrochemical properties by cyclic voltammogram (CV). The first and second oxidation peaks were observed at E11/2= 0.40 V and E21/2 = 0.81 V, respectively. The peak current was observed to be proportional to the scan rate, suggesting the feature of modified SAMs molecules. The result indicates that TTF-thiolate SAMs on gold electrode have electronic structure similar to hulk TTF molecules..
149. T. Ederth, Kaoru Tamada, P. M. Claesson, R. Valiokas, R. Colorado, M. Graupe, O. E. Shmakova, T. R. Lee, Force measurements between semifluorinated thiolate self-assembled monolayers
Long-range hydrophobic interactions and surface charge, Journal of Colloid and Interface Science, 10.1006/jcis.2000.7318, 235, 2, 391-397, 2001.03, Long-range interactions between self-assembled monolayers (SAMs) of semifluorinated alkanethiols have been studied by direct force measurements in water and aqueous NaCl solutions. SAMs prepared from three different thiols, with identical fluorinated head groups but varying hydrocarbon spacer lengths, were investigated: CF3(CF2)9(CH2)xSH, where x = 2, 11, or 17. Force measurements show that the interactions in water and electrolyte solutions are composed of both double-layer interactions emerging from what appears to be charges adsorbed onto the surfaces and long-range "hydrophobic" attractions, in excess of the expected van der Waals forces. The three investigated thiols produce similar results in force measurements, though the contact angles with water are slightly different. The "hydrophobic" attraction has the form of step-like attractive discontinuities in the force profiles at separations ranging from 20 to 40 nm, caused by bridging of microscopic bubbles residing at the surfaces. The shape or range of these discontinuities are not significantly affected by replacement of the water with either 1 mM or 1 M NaCl solutions. The origin of the charges causing the electrostatic double-layer interaction is unclear, but some possible causes are discussed..
150. Kaoru Tamada, T. Ishida, W. Knoll, H. Fukushima, R. Colorado, M. Graupe, O. E. Shmakova, T. R. Lee, Molecular packing of semifluorinated alkanethiol self-assembled monolayers on gold
Influence of alkyl spacer length, Langmuir, 10.1021/la001212c, 17, 6, 1913-1921, 2001.03, The structures of semifluorinated alkanethiol self-assembled monolayers (SAMs) generated by the adsorption of CF3(CF2)9(CH2)nSH (F10HnSH, n = 2, 6, 11, 17, 33) onto gold were investigated with atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and surface plasmon resonance spectroscopy. Images obtained by AFM of the F10H2SH SAM showed a remarkably ordered 2D hexagonal lattice with a lattice constant, a = 5.9 ± 0.1 Å, on Au(111)/mica. As the total number of carbon atoms in the alkyl spacer groups (n) was increased, the flourocarbon adlayer structure appeared more disordered in the AFM images; however, the thicknesses of the fluorocarbon layers estimated from the C 1s (CF3), C 1s (CF2), and F 1s XPS signal intensities were indistinguishable in all of the SAMs. In contrast, the C 1s (CH2) signals revealed that the tilt angles of the alkyl spacer groups depended strongly on n. We utilized a contrast variation SPR technique with various contacting media for an independent determination of the refractive indices and the film thicknesses of the semifluorinated SAMs. The obtained data were consistent with our AFM and XPS results, which show that the longer alkyl chains pack more densely than the shorter ones in these SAMs..
151. H. Fukushima, S. Seki, T. Nishikawa, H. Takiguchi, Kaoru Tamada, K. Abe, R. Colorado, M. Graupe, O. E. Shmakova, T. R. Lee, Microstructure, wettability, and thermal stability of semifluorinated self-assembled monolayers (SAMs) on gold, Journal of Physical Chemistry B, 104, 31, 7417-7423, 2000.08, The microstructure, wettability, and thermal stability of self-assembled monolayers (SAMs) on gold generated from semifluorinated alkanethiols F(CF2)10(CH2)nSH, where n = 2, 6, 11, 17, and 33 (F10HnSH), were examined by polarization modulation infrared reflection absoprtion spectroscopy (PM-IRRAS) and dynamic contact angle measurements. Analysis by PM-IRRAS revealed that the length of the methylene spacer (Hn) influenced the tilt angle of the fluorocarbon segments in the semifluorinated SAMs. As the length of the methylene spacer was increased, the tilt angle of the perfluorocarbon moiety increased with respect to the surface normal. The longer methylene spacers (Hn,n = 11, 17, and 33) exhibited well-ordered trans-extended conformations as indicated by the position of the antisymmetric methylene band Shortening the length of the methylene spacer to n = 6, however, led to a decrease in conformational order Dynamic contact angle measurements, using the Wilhelmy plate method showed that the semifluorinated SAMs were poorly wet by both water (average θa = 120°) and hexadecane (average θa = 81°). The wettability varied with the length of the methylene spacer; in particular, both the thinnest and the thickest semifluorinated SAMs (derived from F10H2SH and F10H33SH, respectively) exhibited relatively low dynamic contact angle values. In addition, the thermal stability of the semifluorinated SAMs was found to increase as the length of the methylene spacer was increased. Overall, these films exhibited remarkable resistance to thermal degradation (e.g., SAMs derived from F10H33SH sustained a relatively high contact angles after incubation at 150 °C for 1 h in air)..
152. Koji Abe, Hiroshi Takiguchi, Kaoru Tamada, Dynamic contact angle measurement of Au(111)-thiol self-assembled monolayers by the Wilhelmy plate method, Langmuir, 10.1021/la990624m, 16, 5, 2394-2397, 2000.03, The efficient use of the Wilhelmy plate method to measure dynamic contact angles with asymmetric Au-thiol self-assembled monolayer (SAM) plates is studied. To prepare a Au(111) surface for SAM formation, gold is deposited only on one side of substrates. The sessile drop method is applied to estimate wettability of SAMs, because of this asymmetric feature of Au-thiol SAM samples. A modified Wilhelmy plate method to analyze the wettability of SAMs is proposed. Using mica as substrates, this method provides sufficient precision. This will help future studies of Au-thiol SAM wetting in combination with other surface characterization techniques..
153. H. Takiguchi, K. Sato, T. Ishida, K. Abe, K. Yase, Kaoru Tamada, Delicate surface reaction of dialkyl sulfide self-assembled monolayers on Au(111), Langmuir, 10.1021/la981450w, 16, 4, 1703-1710, 2000.02, Self-assembly of n-dioctadecyl sulfide (ODS) on Au(111) has been closely investigated by using X-ray photoelectron spectroscopy (XPS), in which the binding condition of sulfur on Au(111) was determined by the S(2p) XPS peak position, and the surface density and chain conformation of adsorbed molecules were determined by the relative XPS peak intensity, C(1s)/S(2p). The surface reaction of ODS on Au(111) was unstable unlike ODT SAM, and it was changed drastically by small variation of adsorption condition. When adsorption was carried out in 1 mM CH2Cl2 solution at room temperature, ODS molecules mostly formed fully adsorbed SAMs, intact without C-S cleavage. This was evaluated by the C(1s)/S(2p) intensity, which was twice as strong as ODT SAM, and by the S(2p) peak which appeared as a doublet at the position of 'unbound' sulfur [S(2p3/2) at approx. 163 eV], suggesting 'physisorption' of ODS on Au(111). On the other hand, when a different condition for SAM formation was used (e.g., high temperature, long time immersion, or CHCl3 as a solvent), the C(1s)/S(2p) intensity decreased to a value smaller than ODT SAM, and the S(2p) peak was shifted to lower binding energies, the 'bound' (162 eV) and 'free' (161 eV) sulfur positions. In these SAMs, different surface reactions including carbon-sulfur (C-S) bond cleavage seem to occur rather than nondestructive adsorption. High-resolution atomic force microscope images revealed that ODS SAM, prepared by 24-h immersion in 1 mM CH2Cl2 solution at room temperature, formed a hexagonal lattice with the lattice constant, d = 0.46 nm, which is nearly equal to the close-packed distance between alkyl chains and totally incommensurate against gold adlattice. Our data suggest a unique self-assembling process of ODS SAM, in which the chain-chain interaction is expected to be more predominant rather than the molecule-substrate interaction unlike ODT SAM..
154. S. Frey, K. Heister, M. Zharnikov, M. Grunze, Kaoru Tamada, R. Colorado, M. Graupe, O. E. Shmakova, T. R. Lee, Structure of self-assembled monolayers of semifluorinated alkanethiols on gold and silver substrates, Israel Journal of Chemistry, 10.1560/0K18-2RLA-GAQD-NHRU, 40, 2, 81-97, 2000.01, Self-assembled monolayers (SAMs) formed from semifluorinated alkanethiols (SFATs) CF3(CF2)9(CH2)nSH (F10HnSH: n = 2, 11, and 17) on polycrystalline Au and Ag were characterized by X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and near edge X-ray absorption fine structure spectroscopy. SFATs were found to form highly ordered and densely packed SAMs on both substrates. The molecules are strongly bonded to the substrates via their sulfur head groups, in the same manner as conventional alkanethiol (AT) SAMs. The hydrocarbon (except for n = 2) and fluorocarbon parts of the adsorbed SFATs retain the expected planar zigzag and helical conformations of the respective bulk materials. The orientation of the fluorocarbon chains does not depend on the substrate. These entities are almost perpendicular to the substrate in F10H2S/Au and F10H2S/Ag and become slightly more tilted in SFAT SAMs with longer hydrocarbon moieties. However, the alkyl parts of the SFAT films exhibit tilt and twist angles that are similar to those of normal alkanethiol films on Ag and Au substrates despite the reduced packing density in the SFAT films as compared to normal AT SAMs. We suggest that the substrate-related differences in tilt and twist angles for both systems are associated with the different character of the head-group-substrate bonding on Au and Ag..
155. S. Ohnishi, M. Hato, Kaoru Tamada, H. K. Christenson, Presence of particles on melt-cut mica sheets, Langmuir, 10.1021/la981049+, 15, 9, 3312-3316, 1999.04, We show the presence of numerous particles on mica surfaces melt-cut for use in the surface force apparatus (SFA). The particles, as observed by atomic force microscopy, are typically 20-25 nm in diameter and 2-3 nm high, and cover up to 0.05% of the surface area. They consist of solidified droplets of molten mica, scattered across the surfaces during the cutting of cleaved mica with a white-hot platinum wire. The particles adhere strongly to the mica surfaces in inert atmospheres but become mobile and disappear upon scanning under water and polar liquids. They seem to remain attached to the surfaces in nonpolar liquids. The particles appear to affect to a noticeable extent only experiments involving capillary condensation of water between mica surfaces..
156. Masakatsu Hato, Hiroyuki Minamikawa, Kaoru Tamada, Teruhiko Baba, Yoshikazu Tanabe, Self-assembly of synthetic glycolipid/water systems, Advances in Colloid and Interface Science, 10.1016/S0001-8686(98)00085-2, 80, 3, 233-270, 1999.04, Glycolipids (amphiphiles that bear oligosaccharides as their hydrophilic headgroups) are of importance both scientifically and technically. This review describes recent advances in our understanding of the molecular correlations in phase behavior in aqueous glycolipids over the past several years. In the first part, we discuss how headgroup stereochemistry affects the phase behavior of glycolipids both in two- and three-dimensional systems. In the second part, we discuss the effects of alkyl chain structure and phase behavior of phytanyl-chained glycolipid/water systems. The physical properties of glycolipid/water systems depend strongly on the inter-headgroup interactions that are related to such factors as stereochemistry (conformation) and size of headgroups, type of sugar residues involved, alkyl chain structure, etc. Thus, apart from the conventional concept like `hydrophilic/lipophilic balance', explicit accounts of headgroup interactions are crucial to control the particular glycolipid/water system concerned. This is in marked contrast to the conventional amphiphile/water systems where the inter-headgroup interactions are in most cases simply repulsive..
157. J. Zhao, H. R. Hafiz, H. Akiyama, Kaoru Tamada, F. Nakanishi, Kinetics of photoreaction of p-phenylenediacrylic acid derivative in LB films
An infrared spectroscopic study, Molecular Crystals and Liquid Crystals, 322, 233-238, 1998.12, Photocycloaddition of LB multilayer system of a p-phenylenediacrylic acid derivative compound has been studied by infrared spectroscopy. A two-step kinetics are found. It is revealed that the reaction process results in changes in the molecular environment, which also affects the kinetics of the reaction..
158. Kaoru Tamada, J. Nagasawa, F. Nakanishi, K. Abe, T. Ishida, M. Hara, W. Knoll, Structure and growth of hexyl azobenzene thiol SAMs on Au(111), Langmuir, 14, 12, 3264-3271, 1998.06, The structure and growth of functionalized thiol self-assembled monolayers (SAMs) on Au(111) derived from a new compound, 12-(4-((4-hexylphenyl)azo)phenoxy)dodecane-1-thiol ("hexyl azobenzene thiol"), were examined by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), dynamic contact angles, Fourier transform infrared-reflection absorption spectroscopy (FTIR-RAS), and reflection UV-vis absorption spectroscopy. The hexyl azobenzene thiol SAM showed adsorption kinetics comparable to that of alkanethiols. At the initial stage of SAM growth, formation of nanosize domains resulting from the rearrangement of molecules on the surface was confirmed in a similar manner as for alkanethiol SAMs with long alkyl chains. The hexyl azobenzene thiol SAM exhibited a unique molecular ordering due to the intermolecular interaction between tail groups. Molecular resolution AFM images revealed an expanded lattice (nearest neighbor spacings, a = 5.3 ± 0.1 Å, b = 5.6 ± 0.1 Å; angle between the two axes, φ = 85 ± 1°) relative to that of simple azobenzene-terminated SAMs, due to the influence of the hexyl-terminal groups attached to the para-position of the azobenzene moieties. Average molecular tilt and twist angles (α = 14°, β = 42°) were determined by quantitative analysis of C-H stretching mode for FTIR-RAS data. The reflection UV-vis absorption spectra implied that the long axes of the trans-azobenzene moieties were aligned normal to the plane of surface in fully covered SAMs, while those were more tilted (aligned more parallel to the surface plane) in the submonolayers..
159. Fusae Nakanishi, Jun'ichi Nagasawa, Kaoru Tamada, Masaru Yoshida, Haruhisa Akiyama, Yong Kuan Gong, Koji Abe, Photoreactive poly(vinyl alcohol) bearing p-phenylenediacrylic acid moiety
Property and photoreaction of Langmuir-Blodgett film, American Chemical Society, Polymer Preprints, Division of Polymer Chemistry, 39, 1, 355-356, 1998.03, A novel photoreactive Langmuir-Blodgett film was prepared using poly(vinyl alcohol) with conjugate diolefin moiety as the side chain. The characteristics of LB film were evaluated and its high photoreactivity as a function of molecular arrangement were investigated using spectroscopic analysis. The photoreactivity of these polymers were enhanced due to the presence of excimers. The IR spectrum of irradiated LB film showed the decrease in double bonds absorption intensity. Cycloaddition of double bonds took place in the irradiated LB film forming cyclobutane rings..
160. Kaoru Tamada, J. Nagasswa, F. Nakanishi, K. Abe, M. Hara, W. Knoll, T. Ishida, H. Fukushima, S. Miyashita, T. Usui, T. Koini, T. R. Lee, Structure of SAMs generated from functionalized thiols on gold, Thin Solid Films, 10.1016/S0040-6090(98)00618-X, 327-329, 1-2, 150-155, 1998.01, The structure and growth of two classes of self-assembled monolayers (SAMs) on Au(111) derived from the adsorption of the functionalized thiol hexyl-azobenzenethiol (12-(4-(4-hexylphenylazo)phenoxy)dodecane-1-thiol) and the partially fluorinated alkanethiols (CF3(CF2)9(CH2)11SH and CF3(CF2)7(CH2)6SH were examined. The structural properties of the SAMs were strongly influenced by the interactions between the functional groups comprising the tails of the molecules. Molecular resolution atomic force microscopy (AFM) images of the hexyl-azobenzenethiol SAMs revealed an expanded lattice (nearest neighbor spacing, a · 0.53 nm, b · 0.56 nm, and angle between the two axes, φ · 85·) relative to those of simple azobenzene-terminated SAMs. The expanded lattice probably results from the presence of the hexyl tail groups. The structure of the SAMs formed from the fluorinated alkanethiols was also probed by AFM, Fourier transform infrared spectroscopy (FTIR-RAS) and dynamic contact angle measurements. The degree of molecular tilt of the fluorocarbon halix appears to be influenced by the length of the methyl enespacer moieties, which might result from the introduction of flexibility into the molecular chains..
161. H. R. Hafiz, Kaoru Tamada, F. Nakanishi, Thermodynamic standardization for highly photoreactive LB films made from amide derivative of p-phenylenediacrylic acid, Molecular Crystals and Liquid Crystals, 10.1080/10587259808030210, 322, 123-128, 1998.01, The thermodynamic concept was introduced in order to elucidate the dynamic flexibility of the amide derivative of p-phenylenediacrylic acid "1" for the formation of its monolayer. The phase transition region appeared in the surface pressure - area isotherms was interpreted in terms of molecular comformational changes between two extreme forms; bent comformation and erect comformation. The LB films prepared at higher temperatures possessed highly oriented and closely packed molecular assembly, as revealed by means of spectroscopy. Even though, the LB films prepared at lower temperatures exhibited a higher photoreactivity..
162. Wolfgang Knoll, Grit Pirwitz, Kaoru Tamada, Andreas Offenhäusser, Masahiko Hara, Supramolecular interfacial architectures for controlled electron transfer, Journal of Electroanalytical Chemistry, 10.1016/S0022-0728(97)00088-0, 438, 1-2, 199-205, 1997.11, We report on the structural principles and requirements for the controlled formation of supramolecular architectures of electron transfer protein layers at electrode surfaces functionalized by organic mediator layers, organized by self-assembly or Langmuir/Blodgett/Kuhn technique. STM and AFM are employed to elucidate at the molecular level details of the monolayer formation, in particular, at early stages of the nucleation and growth process of SAMs. Optical methods, in particular surface plasmon spectroscopy and mica waveguide spectroscopy are used to observe on-line the build-up of these multilayer assemblies. With a combined surface plasmon spectroscopy and cyclovoltammetry set-up it is possible to investigate the interfacial architecture and the electron transfer reactions of the proteins simultaneously..
163. Kaoru Tamada, Masahiko Hara, Hiroyuki Sasabe, Wolfgang Knoll, Surface phase behavior of n-alkanethiol self-assembled monolayers adsorbed on Au(111)
An atomic force microscope study, Langmuir, 13, 6, 1558-1566, 1997.03, n-Alkanethiol (CnH2n+1SH) self-assembled monolayers (SAMs) adsorbed on Au(111) were studied with an atomic force microscope (AFM) to confirm the influence of the lateral interaction between adsorbed thiols on the film morphology. Two experiments were performed: firstly, a study of the domain formation at the initial stage of SAM growth (single component) and, secondly, investigations of the coadsorption phenomenon in mixed SAMs composed of two alkanethiols having different chain lengths. For the kinetics study, Au(111) was immersed into the 10-2 mM ethanol solutions with the single component alkanethiol (C4H9SH, C12H25SH, or C18H37SH), for varying times (1 s to 10 min). In all cases, the film coverage increased as the immersion time became longer, and finally the surface was totally covered with thiols after an immersion time of 3 min or more. Clear island formations were observed in the partially covered C12H25SH and C18H37SH SAMs, while C4H9SH formed meshlike domains. The mixed SAMs were prepared by immersing Au(111) into 1 mM ethanol solutions with mixed alkanethiols (C4H9SH/C18H37SH) of various compositions, Rsoln = [C4H9SH]/[C18H37SH] = 1/1 to 100/1, for a time of 1 h. Clear phase separation was observed at Rsoln = 20/1 and 40/1. Above or below these compositions, the film surface appeared very flat, covered with a nearly single component, C4H9SH or C18H37SH, respectively. This is the first systematic study of the surface phase behavior of alkanethiol SAMs by AFM imaging. It reveals more direct information about the film morphology than previous studies with conventional surface analytical techniques such as X-ray photoelectron spectroscopy, ellipsometry, contact angles, etc..
164. Takashi Tamaki, Mutsuyoshi Matsumoto, Reiko Azumi, Kazuyuki Kasuga, Hideki Sugihara, Takuji Hirose, Jun Ichi Nagasawa, Hisakazu Nozoye, Kaoru Tamada, Yoshihiro Sugi, Takamasa Hanaoka, Current topics on harmonized molecular materials, Busshitu Kogaku Kogyo Gijutsu Kenkyusho Hokoku/Journal of the National Institute of Materials and Chemical Research, 4, 2, 49-52, 1996.12, The objective of this report is to survey current topics on what we call 'harmonized molecular materials', including organic/organic or organic/inorganic hybrid materials such as host-guest suprarmolecular materials, organometallic complexes, self-assembled monolayers, layered inorganic/organic compounds or films,liquid crystals, and microporous materials, which are fabricated with the aid of molecular synergism. Recently, much attention has been focused on these state-of-the-art materials, because they are not only basically interesting, but also promising for potential applications. They are expected to achieve high performance in chemical, electronic, or optical function and to make a breakthrough of related industrial technologies in near future. Since there are quite a lot of research activities in this field, it is impossible to cover all of them in this issue. This report deals with as many topics as possible to see the present status and the future prospect of the related materials..
165. Kaoru Tamada, Hiroyuki Minamikawa, Masakatsu Hato, Kenjiro Miyano, Phase transition in glycolipid monolayers induced by attractions between oligosaccharide head groups, Langmuir, 12, 6, 1666-1674, 1996.03, The surface property of two kinds of synthetic glyceroglycolipids was investigated to confirm the stereoeffect of sugar residues on the phase behavior in monolayers: one is the maltooligosaccharide-containing lipids [MalN(C12)2] and the other is cellooligosaccharide-containing lipids [CelN(C12)2]. The two kinds of glycolipids exhibit the opposite dependence of the surface pressure - area (II-A) isotherm on the number of glucose residues (N), in that MalN(C12)2 tends to be more expanded as N increases, while CelN(C12)2 tends to be more condensed. The liquid-expanded/liquid-condensed phase transition in Cel4(C12)2 was evaluated by the Brewster angle microscopy and the latent heat analysis with the Clausius - Clapeyron equation, as a model of film condensation induced by the attraction between oligosaccharide head groups. The film morphology of Cel4(C12)2 was unique in that it exhibits the optically isotropic and flexible fluid type of the LC phase, while Glc(C16)2 forms a two-dimensional tilted crystalline phase in the same way as fatty acids and phospholipids. The heat of transition (ΔH) of Cel4(C12)2 does not converge toward zero even at high temperature. In other words, the main transition of Cel4(C12)2 does not become second order in contrast to the behavior usually encountered in monolayers. The refractive index of the oligosaccharide head groups in water as well as the alkyl chains in air must be properly taken into account to interpret the reflectivity..
166. Masahiko Hara, Kaoru Tamada, Christian Hahn, Naoki Nishida, Wolfgang Knoll, Adsorption and desorption processes of self-assembled monolayers studied by surface-sensitive microscopy and spectroscopy, Supramolecular Science, 10.1016/0968-5677(96)00028-4, 3, 1-3, 103-109, 1996.01, Adsorption and desorption processes of self-assembled monolayers (SAMs) have been studied on an Au(111) surface by scanning tunnelling microscopy (STM), atomic force microscopy (AFM). X-ray photo-electron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). At the initial growth stage, the ordered nucleation of SAM located at the herringbone turns of the Au(111)-(22×√3) surface reconstruction and diffusion-controlled domain formation have been imaged by STM and AFM. Details of the oxidation process in UV desorption were also investigated by XPS. In addition, the dimerization reaction during desorption was confirmed by TDS for the first time in the alkanethiol SAM system..
167. Kaoru Tamada, Kenjiro Mlyano, Capillary wave propagation on water covered with polyamic acid monolayer films, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.1143/JJAP.33.5012, 33, 9 R, 5012-5018, 1994.01, Externally generated capillary wave propagation has been studied on water covered with poly(amic acid) alkylammonium salts. In addition, fluorescence microscope observation was performed with a poly(amic acid) containing a fluorophore dye. The octadecylammonium salt of this polymer exhibits condensed liquid/gas coexistence films when the pressure is very low (pressure Π ≃ 0), where the liquid phase is highly viscoelastic. Such domain structures were not found in the hexadecylammonium salts of other polymers. However, all films used here can be compressed homogeneously and isotropically at higher pressures, independent of the chain length of alkyl amines. These observations suggest that the mechanical character in the highly condensed state is determined mainly by the flexibility of polymer chains, while the degree of condensation in the dilute state is more influenced by the alkyl amines..
168. Kaoru Tamada, Sanghoon Kim, Hyuk Yu, Lateral Diffusion of a Probe Lipid in Biphasic Phospholipid Monolayers
Liquid/Gas Coexistence Films, Langmuir, 10.1021/la00030a020, 9, 6, 1545-1550, 1993.01, The method of fluorescence recovery after photobleaching has been used to determine the lateral diffusion coefficient (D) of a fluorescent lipid probe in L-α-dilauroylphosphatidylcholine monolayers. The surface mass density was varied over a wide range from the liquid expanded/gas coexistence phase (LE/G) to the homogeneous liquid phase. The lateral diffusion coefficient reached a maximum value at the “liftoff” point on the surface pressure-area curve (D ≈ 1.2 × 1(10−10 m2/s, A = 1.1−1.3 nm2/molecule, T = 22−24 °C), corresponding to the onset of the uniphasic LE state, and decreased from this maximum as the mass density was varied to both higher and lower values of area per molecule (A). The results were analyzed according to the effective-medium theory and the free area model, respectively. The D values in the LE/G biphasic monolayers were evaluated as a function of the area fraction of the LE phase, whereby it was shown that the gas bubbles in the LE/G can be regarded as semipermeable obstacles for the lipid probes, with a relative permeability of the gas bubbles with respect to the LE phase of 0.2–0.3..
169. Kenjiro Miyano, Kaoru Tamada, Capillary wave propagation on water nonuniformly covered with a solid film, Langmuir, 9, 2, 508-514, 1993, Capillary wave propagation has been studied on water nonuniformly covered with a solid film. The wave propagation characteristics have been correlated with the morphology of the film which was observed with a fluorescence microscope. The propagation characteristics were found to be determined by the connectivity of the solid islands rather than by their coverage. When the film consists of solid islands much smaller than the wavelength, the islands are practically invisible to the wave even when they cover half of the water surface; the film made of larger islands shows the properties of a solid sheet at the same coverage. This is because the connectivity is easily established in a film composed of larger islands. When the capillary wave traverses an isolated island much larger than the wavelength, the wave is characterized as the one on a solid film of an infinite extent. When the size of the island is not much larger than the wavelength, however, the apparent amplitude of the wave can increase on coming out of the island. This is the first direct evidence that the capillary wave characteristics depend on the detailed yet macroscopic structure of the film..
170. Kenjiro Miyano, Kaoru Tamada, Capillary waves
a new monolayer characterization technique using an old method, Thin Solid Films, 10.1016/0040-6090(92)90178-E, 210-211, PART 1, 96-97, 1992.04, The capillary wave (surface wave) on water is shown to be a sensitive probe to characterize the monolayers spread on it. The principle of the capillary-wave probe, the unique features of the technique, and its use as an integral part of an LB-deposition trough are briefly described..
171. Kenjiro Miyano, Kaoru Tamada, Capillary wave propagation on water covered with inhomogeneous monolayers. Liquid/gas coexistence films, Langmuir, 8, 1, 160-163, 1992.01, Externally generated capillary wave propagation has been studied on water whose surface was covered with a monolayer in the liquid/gas coexistence phase up to 1 kHz. A simultaneous morphology observation with a fluorescence microscope enabled us to make a one-to-one correspondence between the fraction of the liquid film and the propagation characteristics. It was found that the liquid film does not affect the capillary wave significantly until it covers more than 90% of the water surface, which indicates that the dynamic elasticity of the liquid monolayer below 1 kHz is extremely low. It was also noted that the bubbles (the gas phase) were very stable against coalescence, implying that the line tension of the liquid phase is quite low. These findings suggest that the liquid phase in equilibrium with the gas phase is in a very shallow intermolecular potential. It was confirmed that the surface waves do not affect the morphology of the monolayer..