Second-harmonic spectroscopy of surface immobilized gold nanospheres above a gold surface supported by self-assembled monolayers

Kazuma Tsuboi, Shinya Abe, Shinya Fukuba, Masayuki Shimojo, Miyoko Tanaka, Kazuo Furuya, Katsuhiko Fujita, Kotaro Kajikawa

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We have investigated linear and nonlinear optical properties of surface immobilized gold nanospheres (SIGNs) above a gold surface with a gap distance of a few nanometers. The nanogap was supported by amine or merocyanine terminated self-assembled monolayers (SAMs) of alkanethiolates. A large second-harmonic generation (SHG) was observed from the SIGN systems at localized surface plasmon resonance condition. The maximum enhancement factor of SHG intensity was found to be 3× 105 for the SIGN system of nanospheres 100 nm in diameter with a gap distance of 0.8 nm. The corresponding susceptibility was estimated to be (2) =750 pmV (1.8× 10-6 esu). In the SIGN system supported with the merocyanine terminated SAMs, the SHG response was also resonant to the merocyanine in the nanogap. It was found that the SHG response of the SIGN systems is strongly frequency dependent. This leads us to conclude that the large (2) is caused by enhanced electric fields at the localized surface plasmon resonance condition and is not due to an increase of the surface susceptibility following from the presence of the gold nanospheres. The observed SHG was consistent with the theoretical calculations involving Fresnel correction factors, based on the quasistatic approximation.

Original languageEnglish
Article number174703
JournalJournal of Chemical Physics
Issue number17
Publication statusPublished - 2006
Externally publishedYes


ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

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