16:00-16:45

Monitoring Plasmon-Assisted Photochemical Reaction in Ultra-Small Space by Surface-Enhanced Raman Scattering

Localized electromagnetic field induced by photo-illumination at a vicinity of plasmon active metal nano-structure can be considered as the exotic perturbation to modify/change photo-excitation and/or polarization process of molecules locates close to the metal surface. The field may give us a chance for photo-chemical/physical manipulation of a single molecule at ultra-small space. In the present study, an isolated single-walled carbon nanotube with the diameter less than 1.5 nm was used as the target molecule. Carbon nanomaterials such as graphene sheet, nanohorns and carbon nanotube have been widely studying to develop wide variety of applications due to their unique structural, optical and electronic characteristics. Especially carbon nanotube has attracted attention, because introduction of structural defect and hetero-atom doping into the structure can control local electronic state resulting in the development of novel catalytic property such as oxygen reduction reaction. To create novel catalyst by the control of the structure in an atomic scale, plasmon-assisted photochemical reaction should be applied. We have succeeded in the fabrication of optimized metal nano-dimer arrays for obtaining intense local surface plasmon and consequently surface-enhanced Raman scattering (SERS). In the present study, SERS measurement was employed for investigating the electronic and defect characteristics of an individual single-walled carbon nanotube (SWNT) at metal nano-gap under electrochemical potential control.

We observed highly-intense SERS spectra showing single radial breathing mode (RBM) peak with narrow 3 ~ 5 cm^-1 FWHM, indicating successful measurements on a single SWNT positioned at the gap of the nano-metal dimer. We also found that certain intermediate frequency modes (IFMs) increases drastically with the increase of the local defect density of the structure characterized by D-band. Present result implies that observation on IFMs serves to identification of defects as well as catalytic activity monitoring. Electrochemical potential dependence of the RBM intensity was also observed, and the intensity peaked with certain potential. Based on the model of electron doping / undoping at SWNTs, absolute potential of the Fermi level of an individual SWNT can be evaluated. These results demonstrated that SERS measurement enable to prove and create the local defect and electronic properties of an individual SWNT at metal nano-gap.

• Nagasawa, F. et al., Chem. Commun., 2011, 47, 4514-4516
• Takase, M. et al., J. Photochem. Photobiol. A. 2011, 2-3, 169-174
• Nabika, H. et al., J. Phys. Chem. Lett. (Perspective; “Toward Plasmon-Induced Photoexcitation of Molecules”), 2010, 16, 2470–2487.

Speaker

Prof. Kei Murakoshi, Division of Chemistry, Graduate School of Science Hokkaido University, Japan

Chair

Dr. Kohei Uosaki, MANA Principal Investigator, NIMS