2004 Fiscal Year Final Research Report Summary
Local non-linear spectroscopy using electromagnetic enhancement effect of a metal tip apex
| Project/Area Number |
15204026
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics I
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| Research Institution | Japan Advanced Institute of Science and Technology (2004)
Tohoku University (2003) |
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Principal Investigator |
USHIODA Sukekatsu Japan Advanced Institute of Science and Technology, President, 学長 (90176652)
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| Co-Investigator(Kenkyū-buntansha) |
SAKAMOTO Kenji National Institute for Materials Science, Nanomaterials Laboratory, Senior Researcher, ナノマテリアル研究所, 主任研究員 (00222000)
MEGURO Kazuyuki RIKEN, Laboratory for Surface Photodynamics, Researcher, 表面フォトダイナミックス研究チーム, フロンティア研究員 (00360652)
MIZUTANI Goro Japan Advanced Institute of Science and Technology, School of Materials Science, Associate Professor, 材料科学研究科, 助教授 (30183958)
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| Project Period (FY) |
2003 – 2004
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| Keywords | Scanning tunneling microscope (STM) / Raman scattering / Surface plasmons / Tip-enhanced Raman scattering (TERS) / Optical second harmonic generation / Carbon nanotubes / Single molecule detection / Metal nanowires |
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| Research Abstract |
When a laser beam is shined at the tip-sample gap of a scanning funneling microscope (STM), the electromagnetic field is strongly enhanced immediately below the sharp tip apex. Using this phenomenon one can realize optical spectroscopy with very high special resolution beyond the optical diffraction limit. In this study we have constructed a tip-enhanced nonlinear spectroscopy system that consists of an ultra-high-vacuum low-temperature STM, a highly sensitive photon detection system, and a tunable laser system. As a first experiment, we have measured the tip-enhanced Raman spectra of single wall carbon nanotubes (SWNT) deposited on the Au(111) surface with excitation light of 785 nm. In this experiment we used Au tips, which are expected to show large electromagnetic enhancement. The Au tips were fabricated by electrochemical etching in a saturated aqueous solution of NaCl. By adjusting the temperature and pH of the electrolyte, we have succeeded in producing Au tips with the radii of curvature less than 50 nm. Using an Au tip we observed STM images of the sample until an individual SWNT bundle was found. Then the STM tip was fixed over the target SWNT bundle, and subsequently the Raman spectra were measured as a function of the tip-sample distance. The Raman intensity of the G-band (〜1590 cm^<-1>) of SWNT decreases rapidly as the tip-sample distance increases up to 〜10 nm. This result clearly shows the tip-enhanced scattering effect. Furthermore, we have observed optical second harmonic generation from Au nanowire arrays on faceted NaCl(110) substrates with wire widths from 40 to 60nm, in order to investigate the general local field near Au nanostructures. We have found that the amplitude of the incident field polarized perpendicular to the nanowire axes is considerably reduced by the de polarization field induced in the nanowires.
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