29 research outputs found

    Photothermally controlled Marangoni flow around a micro bubble

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    We have experimentally investigated the control of Marangoni flow around a micro bubble using photothermal conversion. Using a focused laser spot acting as a highly localized heat source on Au nanoparticles/dielectric/Ag mirror thin film enables us to create a micro bubble and to control the temperature gradient around the bubble at a micrometer scale. When we irradiate the laser next to the bubble, a strong main flow towards the bubble and two symmetric rotation flows on either side of it develop. The shape of this rotation flow shows a significant transformation depending on the relative position of the bubble and the laser spot. Using this controllable rotation flow, we have demonstrated sorting of the polystyrene spheres with diameters of 2 μm and 0.75 μm according to their size

    Photoacoustic emission from Au nanoparticles arrayed on thermal insulation layer

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    Efficient photoacoustic emission from Au nanoparticles on a porous SiO2 layer was investigated experimentally and theoretically. The Au nanoparticle arrays/porous SiO2/SiO2/Ag mirror sandwiches, namely, local plasmon resonators, were prepared by dynamic oblique deposition (DOD). Photoacoustic measurements were performed on the local plasmon resonators, whose optical absorption was varied from 0.03 (3%) to 0.95 by varying the thickness of the dielectric SiO2 layer. The sample with high absorption (0.95) emitted a sound that was eight times stronger than that emitted by graphite (0.94) and three times stronger than that emitted by the sample without the porous SiO2 layer (0.93). The contribution of the porous SiO2 layer to the efficient photoacoustic emission was analyzed by means of a numerical method based on a one-dimensional heat transfer model. The result suggested that the low thermal conductivity of the underlying porous layer reduces the amount of heat escaping from the substrate and contributes to the efficient photoacoustic emission from Au nanoparticle arrays. Because both the thermal conductivity and the spatial distribution of the heat generation can be controlled by DOD, the local plasmon resonators produced by DOD are suitable for the spatio-temporal modulation of the local temperature

    Water Droplet Bouncing on a non-Superhydrophobic Si Nanosprings

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    Self-cleaning surfaces often make use of superhydrophobic coatings that repel water. Here, we report a hydrophobic Si nanospring surface, that effectively suppresses wetting by repelling water droplets. We investigated the dynamic response of Si nanospring arrays fabricated by glancing angle deposition. The vertical standing nanospring arrays were approximately 250 nm tall and 60 nm apart, which allowed the droplets to rebound within a few milliseconds after contact. Amazingly, the morphology of the nanostructures influences the impact dynamics. The rebound time and coefficient of restitution were also found to be higher for Si nanosprings than vertical SI columns. It has been proposed that the restoring force of the Si nanosprings may be responsible for the water droplet rebound and can be explained by considering the droplet/nanospring surface as a coupled spring system. These nanospring surfaces may find applications in self-cleaning windows, liquid-repellent exteriors, glass panels of solar cells, and antifouling agents for roof tiling.Comment: 19 pages, 5 figures, 2 table

    Experimental Evidence of a Twofold Electromagnetic Enhancement Mechanism of Surface-Enhanced Raman Scattering

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    The electromagnetic enhancement mechanism is a major contributor to surface-enhanced Raman scattering enhancements, which are a direct consequence of the roughness present on noble metal surfaces. The electromagnetic enhancement mechanism is a twofold phenomenon that involves the enhancement of both the incident excitation and scattered Raman fields. In this paper, we report a direct observation of the double-enhancement mechanism using a Ag nanorod array/SiO₂ dielectric layer/Ag mirror multilayer thin-film “local plasmon resonator”. The effect of light interference was controlled by adjusting the film thickness of the SiO₂ phase control layer (PCL), and the absorption rate in the Raman scattering wavelength range was tuned from 90 to 0%. In addition to the characteristic Raman peak of an aqueous solution of 4, 4-bipyridine, the background of the Raman scattering spectrum was also enhanced. By examining the relationship between the background Raman emission and the absorption spectrum, we demonstrated that the intensity of the background emission is closely related to the surface-enhanced Raman scattering (SERS) enhancement. We further illustrated that the Raman scattered field and background were enhanced when the absorption was high in the wavelength range of the scattering field. The present results not only suggest that the PCL layer may increase the intensity of plasmon-mediated broadband emission but also provide us with sufficient evidence for a twofold SERS enhancement mechanism

    貴金属ナノ粒子による光熱変換に関する研究

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    京都大学0048新制・課程博士博士(工学)甲第18979号工博第4021号新制||工||1619(附属図書館)31930京都大学大学院工学研究科マイクロエンジニアリング専攻(主査)教授 鈴木 基史, 教授 木村 健二, 教授 蓮尾 昌裕学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDFA
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