| 研究課題/領域番号 |
25286008
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| 研究機関 | 大阪大学 |
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研究代表者 |
VERMA Prabhat 大阪大学, 工学(系)研究科(研究院), 教授 (60362662)
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| 研究分担者 |
齊藤 結花 大阪大学, 工学(系)研究科(研究院), 准教授 (90373307)
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| 研究期間 (年度) |
2013-04-01 – 2017-03-31
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| キーワード | ナノプローブ / ナノマイクロ科学 / ナノ構造物理 / 近接場顕微鏡 |
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| 研究実績の概要 |
1. Numerical simulation of metallic tip-film system:We continued further 3D-FDTD simulations on the tip-film system to improve our results. We mostly focused on silver and aluminum metals as the plasmonic material, which shows plasmonic resonances in the wavelengths smaller than 500 nm. We confirmed about the maximum acceptable value of surface roughness. The results obtained from simulations were used in the fabrication process.
2. Fabrication of tip-film system for silver:We confirmed from simulation that a roughness below 2 nm is acceptable. Therefore, in this term, we spent our effort in making extremely flat silver surface will surface roughness between 1 and 2 nm. This was very tricky, but at the end, we succeeded in optimizing the deposition parameters. Under this condition, we fabricated both the tip and the film of various thicknesses with roughness under 2 nm. In order to keep a constant small gap between the tip and the film, we coated the tip with a transparent layer of 2-nm-thick SiO2.
3. Measurement of scattering spectrum:After fabrication of both tip and film, we proceeded for the measurements of scattering spectrum of various combinations. First, we fixed the diameter of the tip apex to 40 nm, and varied the silver film thickness from 4 to 24 nm, which were coated with a 2-nm-thick SiO2 layers. Scattering spectra for each film was measured and we observed the shift in scattering peak, which indicates the hybridized plasmon resonance of the tip-film system. This set of experiment was repeated for tips with apex diameter of 30 and 20 nm.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
As of now, we have successfully completed most of the work we proposed in this project. We had certain unforeseen problems, particularly about obtaining extremely smooth silver surfaces with an average surface roughness below 2 nm. While obtaining an extremely smooth surface was easy in the case of gold metal, it was not the same for silver. After optimizing various parameters and incorporating new ideas, we were finally successful in preparing silver films with surface roughness of less than 2 nm. Further, we also coated these films with about 2-3 nm thick SiO2 layer, which guarantees a constant gap between the tip and the film. After completing this task, we successfully measured the scattering spectrum to see how hybridized plasmon resonance shifts with respect to the tip size and the film thickness. In the current situation, we have successfully optimized the parameters for a tip-film system that shown tunable plasmon resonance in the wavelength range of about 450 nm to 650 nm by utilizing silver metal. We have successfully fabricated the optimized system, and have experimentally measured the scattering spectra, which correspond to the hybridized plasmon resonance. As predicted from the simulation, our experiments showed that silver coated nano-tip and silver nano-film shows a tunable hybridized plasmonic system, where the plasmon resonance can be well controlled by changing the film thickness at nanometer scale. For film thicknesses for 4 to 24 nm, we obtained a plasmon resonance tenability from about 450 to 650 nm.
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| 今後の研究の推進方策 |
We have already achieved the expected goal of tuning in plasmon resonance with silver metal down to about 450 nm. Now one of the most important work that still remains incomplete is to apply this fabricated tip-film system for tip-enhanced Raman scattering (TERS) measurements, where we have tune the enhancement by selecting proper film thickness. In order to achieve maximum enhancement in TERS, it is necessary to tune the laser wavelength to match the resonance of Raman scattering from the sample, and at the same time design a plasmonic system that can enhance the same laser wavelength efficiently. In this sense, our hybridized plasmonic system will be very useful, because we can tune the enhancement for any given laser wavelength by adjusting the film thickness in the tip-film system. Further, we also wish to extent the plasmon tunability below 450 nm, which is possible by using aluminum metal as the plasmonic material. Therefore, we also plan to repeat the whole fabrication and measurement process for aluminum in the next year. After successful fabrication of aluminum tip-film system, we will measure the white-light scattering spectra and finally apply this tip-film system in TERS measurements to study various samples and obtain nanoimaging.
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| 次年度使用額が生じた理由 |
Our research was a bit delayed as we unexpectedly spent longer time on the experimentally obtaining the required surface quality of the film. Since the plasmonic hybridization is a process where localized plasmons interact with delocalized plasmons, the metallic thin film, which provides the delocalized plasmons, must have very low surface roughness, with an average surface roughness below 2 nm. In the case of gold metal, it was comparatively easy to obtain average surface roughness even better than 1 nm. However, it was extremely difficult in the case of silver. We spent very long time in exploring all the possibilities and in optimizing the deposition parameters. Finally, we were able to obtain low surface roughness, but the next steps were delayed because of this.
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| 次年度使用額の使用計画 |
We also planned to extend this work for aluminum metal, where the range of tunable resonance can be extended to below 450 nm. We hope and plan to perform this by repeating the entire work for aluminum metal. In order to finish all this work, we need one more year, and would like to extend this project for one more year and carry forward the remaining money of this project to next year.
The remaining grant of this project for the last year will be utilized for three purposes-1.For purchasing consumable items required for the research planned for this year.2.For publications related to this project.3.For attending domestic and international conferences to present the research achievements under this project.
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