In the field of plasmonics, noble metals such as Au or Ag have been frequently utilized due to their strong plasmon resonances arising from the Drude-like property of free electrons. On the other hand, transition metals such as platinum group metals (PGMs) are not considered as a plasmonic material because of their weak plasmon resonances damped by localized d-electrons. It is, however, known that transition metals exhibit various unique functionalities such as due to the d-electrons. For example, Pt can be a good electrocatalyst for various reactions. Pd can be a hydrogen storage material due to its ability to absorb and release large quantities of hydrogen gas. Therefore, if such functionalities are combined with plasmonic nano-systems, plasmonic applications may be extended to various fields. Surface enhanced Raman scattering (SERS) is recognized as a powerful vibrational spectroscopic method for studying molecular adsorbates on a metal surface despite the technical limitation for PGMs. Recently, we have reported that SERS spectra of molecular adsorbates can be obtained even on PGM surfaces using a sphere-plane type nanogap structure. Importantly, this technique enables us to observe SERS on atomically defined metal surfaces, meaning that atomic surface structure dependence of metal-molecule interactions can be studied using SERS. Pd can absorb hydrogen into the crystal lattice, resulting in formation of palladium hydride, PdH. Since optical constants of PdH are different from those of Pd, one can expect that plasmon resonance energy can be tuned by hydrogen uptake. Based on this system, we have demonstrated photo-induced variation of plasmon resonances. J. Hu, M. Tanabe, J. Sato, K. Uosaki, K. Ikeda, J. Am. Chem. Soc., 136, 10299 (2014)

Plasmonic spectroscopy and photochemistry on highly damping platinum group metals

249th National Meeting (2015)

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