2014 Fiscal Year Annual Research Report
ハイブリッドプラズモンによる近接場ラマン顕微鏡の高感度高帯域化
| Project/Area Number |
25286008
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| Research Institution | Osaka University |
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Principal Investigator |
VERMA Prabhat 大阪大学, 工学(系)研究科(研究院), 教授 (60362662)
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| Co-Investigator(Kenkyū-buntansha) |
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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| Project Period (FY) |
2013-04-01 – 2016-03-31
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| Keywords | ナノプローブ / ナノマイクロ科学 / ナノ構造物理 / 近接場光学顕微鏡 |
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| Outline of Annual Research Achievements |
In this project, we proposed to develop an extremely sensitive near-field Raman microscope based on plasmon hybridization of two metallic nanostructures- a nano-tip and a nano-film. This research starts with theoretical optimization of the parameters involved in fabrication, followed by experimental fabrication and characterization. In the second year of this project, we have achieved the following:
1. Numerical simulation of metallic tip-film system:
In continuation with the simulation work done in the first year, we performed further 3D-FDTD simulations on the tip-film system to improve our results. This was particularly focused on understanding the effect of the type of metal used. In order to achieve results in the lower frequency reason, we focused on silver and aluminum metals. While the plasmon resonance for Au varies between about 600 to 1000 nm, it varies from 450 to 650 nm for Ag and from 300 nm to 450 for Al.
2. The effect of surface roughness:
In addition to the shape, size and the kind of metal, we found that the surface roughness of metal strongly affects the plasmon resonance. Usually, the simulations assume that the surfaces are atomically smooth, while this is not true in the real experiments. Very rough surfaces give bad results and very smooth surfaces are not possible to fabricate. Thus we optimize the surface roughness that is acceptable as well as possible to fabricate. We have realized through simulation that average roughness of 2 nm is acceptable, and we have also achieved this value in our experiments.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
In order to obtain the desired plasmon hybridization and to confirm the confinement and enhancement as well as the tuning of the plasmon resonance, a 3D-FDTD simulation is necessary to optimize various parameters of the tip-film system. Once we successfully optimize the parameters by numerical simulation, the next step is to fabricate the same structures and examine them practically, and finally utilize them for highly sensitive optical nanoimaging. In this year, we have been successful in optimizing various parameters, particularly the kind of metal and the surface roughness. We have theoretically obtained the tunability in plasmon resonance by calculating the absorption spectra for Ag and Al, and have obtained the effect of surface roughness. We have also developed techniques to obtain extremely smooth metal films with the average roughness under 2 nm. This is an important result, utilizing which we can take up the next step in research.
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| Strategy for Future Research Activity |
As the optimization through theoretical simulation is almost finished, we have started the fabrication process. In the coming year, we will fabricate the various plasmonic nano-tips by evaporating gold, silver and aluminum on commercially available AFM cantilever, which is made of silicon. First, the cantilever will be oxidized under high temperature water-vapor, so that the base material becomes silicon-dioxide. Then the metal will be evaporated on this oxidized cantilever tip in ultra-high vacuum. Similarly, metallic thin-films of various thickness will be fabricated. We are now working on optimizing the evaporation technique to obtain high quality surfaces with surface roughness under 1-2 nm. Both the tip and the film will be then coated with an ultra thin layer of SiO2, so that the gap between the tip and the film can be maintained at a value that was optimized numerically in the first part. After successful fabrication, we will confirm functioning of the tip-film system by measuring the white-light scattering spectra and finally apply this tip-film system in TERS measurements to study various samples and obtain nanoimaging, as planned.
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| Causes of Carryover |
プラズモンハイブリダイゼーションの実験には、平滑性の高い金属薄膜を用いる必要がある。薄膜作成のために既存のスパッタの電源部分を変更する必要があったが、この工事が遅延したために薄膜作成実験に遅れが生じた。ここで得られた実験経過を見て近接場光学顕微鏡システムの拡張を行う予定であったため、備品の選定に遅れが生じた。なお試料薄膜の作製にかわって、プローブの設計や観察を先行して行うことにしたため、実験全体に大きな遅れは生じていない。
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| Expenditure Plan for Carryover Budget |
近接場顕微鏡用プローブの設計と金属薄膜の作製がほぼ完了し、既存の近接場光学顕微鏡システムを用いて予備実験を行った。その結果、ラマン分光系の感度を高める必要があるということがわかった。特に、既存のシステムで用いているCW近赤外レーザーでは出力とクオリティともに不十分である。この問題を解決するために、既存の光源より出力が高くビームパターンの良いレーザーを購入することを予定している。
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