Browsing by Author "Nagao, Tadaaki"

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Graphene-Loaded Plasmonic Zirconium Nitride and Gold Nanogroove Arrays for Surface-Charge Modifications
(2020-06-26)
Yu, Min-Wen
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Ishii, Satoshi
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Ku, Ji-Ren
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Yang, Jhen-Hong
;
Huang, Chih-Hsiang
Graphene-on-metal (G/M) heterostructures have gained considerable attention in recent years owing to their outstanding optical and electrical properties. In this study, the polarity of graphene doping to different metallic materials underneath graphene is analyzed for applications in surface-charge modifications. Kelvin probe force microscopy clearly reveals the charge-transfer effects of plasmonic zirconium nitride (ZrN) and gold (Au) on the formation of G/M heterostructures. In addition, both ZrN and Au nanogroove arrays are fabricated by focused ion beam to generate surface plasmon resonances. The charge-transfer effects influence the effective permittivities of ZrN and Au surfaces such that opposite plasmonic resonance shifts are demonstrated for the ZrN and Au nanogroove arrays. Our results show that the choice of metallic material is important for achieving a desired charge transfer in the loading of graphene onto metallic materials.
Marimo-Bead-Supported Core-Shell Nanocomposites of Titanium Nitride and Chromium-Doped Titanium Dioxide as a Highly Efficient Water-Floatable Green Photocatalyst
(2020-07-15)
Kaur, Manpreet
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Shinde, Satish Laxman
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Ishii, Satoshi
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Jevasuwan, Wipakorn
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Fukata, Naoki
The release of untreated industrial wastewater creates a hazardous impact on the environment. In this regard, the development of an environmentally friendly catalyst is of paramount importance. Here, we report a highly efficient and reusable core-shell TiN/SiO2/Cr-TiO2 (TSCT) photocatalyst that is composed of SiO2-cladded titanium nitride (TiN) nanoparticles (NPs) decorated with Cr-doped TiO2 NPs for the removal of organic contaminants from water. The TiN NPs serve as the main light absorber component with excellent visible-light absorption along with Cr-TiO2 NPs. The TSCT shows remarkable improvement in the photodecomposition of methylene blue (MB) over Cr-TiO2 and TiO2 NPs. An efficient structural design is proposed by adopting calcium alginate beads (P-Marimo beads) as a transparent scaffold for supporting our TSCT, which floats nature on the water surface and realizes easy handling as well as excellent reusability for multipurpose water purification. Surprisingly, our TSCT is found to keep its catalytic activity even after the illumination is turned off. Our proposed P-Marimo-encapsulated TSCT can be utilized as an excellent green photocatalyst with high photocatalytic performance, good recyclability, and easy handling.
Narrow-Band Thermal Emitter with Titanium Nitride Thin Film Demonstrating High Temperature Stability
(1970-01-01)
Yang, Zih-Ying
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Ishii, Satoshi
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Doan, Anh Tung
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Shinde, Satish Laxman
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Dao, Thang Duy
A refractory wavelength selective thermal emitter is experimentally realized by the excitation of Tamm plasmon polaritons (TPPs) between a titanium nitride (TiN) thin film and a distributed Bragg reflector (DBR). The absorptance reaches nearly unity at approximate to 3.73 mu m with the bandwidth of 0.36 mu m in the experiment. High temperature stabilities are confirmed up to 500 and 1000 degrees C in ambient and in vacuum, respectively. When the TiN TPP structure is compared to the TiN-insulator-TiN (TiN-metal-insulator-metal (MIM)) structure, the former shows higher Q-factor, which indicates the advantage of choosing the TiN TTP structure against the MIM structure. The proposed refractory TiN TPP structure is lithography-free and scalable, which paves a way for large scale thermal emitters in practical usage.
Narrowband Wavelength Selective Thermal Emitters by Confined Tamm Plasmon Polaritons
(2017-09-01)
Yang, Zih-Ying
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Ishii, Satoshi
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Yokoyama, Takahiro
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Thang Duy Dao
;
Sun, Mao-Guo
This study experimentally demonstrates infrared wavelength selective thermal emission based on Tamm plasmon polaritons (TPPs). Unlike conventional TPP structures, which have a thin metal layer on a distributed Bragg reflector (DBR), the proposed structure has a thick metal under a DBR that is more robust for thermal radiation. The number of DBR pairs is a critical factor in maximizing the narrowband emission needed to satisfy the impedance matching condition, which varies with the choice of metal film. Optimum designs for four different metals, aluminum, gold, molybdenum, and tungsten, are presented. The temporal coupled-mode theory was introduced to explain the origin of the high Q-factor of the proposed structure, which can achieve a twice higher Q factor for the measured emissivity compared to typical plasmonic thermal emitters. The structure is one-dimensional, consisting of only multilayers and free from nanopatterning, offering a practical design in applications such as gas sensing, narrowband IR sources, and thermophotovoltaics.
Optical microresonator arrays of fluorescence-switchable diarylethenes with unreplicable spectral fingerprints
(2020-07-01)
Okada, Daichi
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Lin, Zhan-Hong
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Huang, Jer-Shing
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Oki, Osamu
;
Morimoto, Masakazu
High-security identification requires authentication that is hard to counterfeit and replicate. For anti-counterfeiting data storage and rewritable memory devices, chromic materials are adoptable, where the dichromatic colours can be switched by external stimuli. If further individual information is embedded in each pixel, a much higher-level security system beyond the zero/one data array will be realized. For this purpose, a fine whispering gallery mode (WGM) fingerprint pattern from a microresonator is applicable. Here we propose that photoswitchable optical microresonators made of a fluorescent photochromic organic material function as anti-counterfeiting, rewritable optical memories. The WGM photoluminescence of the resultant microspheres can be switched on and off repeatedly by irradiation with ultraviolet and visible light. The shape of the micro-resonator varies from a sphere to an oblate ellipsoid and hemisphere, depending on the self-assembly process, and the WGM spectral pattern depends sensitively on the morphology of the resonators. Furthermore, surface self-assembly on a hydrophobic/hydrophilic micropatterned substrate affords a highly integrated array of microresonators as dense as millions of pixels per square centimetre. The spectral fingerprints of all pixels are different from one another; therefore, the photoswitchable microarrays are applicable as an ultimate anti-counterfeiting system which is hard to replicate.
Tamm plasmon selective thermal emitters
(2016-10-01)
Yang, Zih-ying
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Ishii, Satoshi
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Yokoyama, Takahiro
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Dao, Thang Duy
;
Sun, Mao-guo
Selective thermal emissions from the excitation of Tamm plasmon polaritons (TPPs) are demonstrated. A TPP structure is composed of a distributed Bragg reflector (DBR) and a thin metal film on top. The tunability of the thermal emission was experimentally achieved only by changing the DBR\'s photonic bandgap. Low cost and large area selective thermal emitters can be realized by TPP-based structures. (C) 2016 Optical Society of America