Probing Molecular Junctions Using Surface Plasmon Resonance Spectroscopy

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• 作者：Ken T. Shimizu ; Ragip A. Pala ; Jason D. Fabbri ; Mark L. Brongersma ; Nicholas A. Melosh
• 刊名：Nano Letters
• 出版年：2006
• 出版时间：December 2006
• 年：2006
• 卷：6
• 期：12
• 页码：2797 - 2803
• 全文大小：309K
• 年卷期：v.6,no.12(December 2006)
• ISSN：1530-6992

文摘

The optical absorption spectra of nanometer-thick organic films and molecular monolayers sandwiched between two metal contacts havebeen measured successfully using surface plasmon resonance spectroscopy (SPRS). The electric field within metal-insulator (organic)-metal(MIM) cross-bar junctions created by surface plasmon-polaritons excited on the metal surface allows sensitive measurement of molecularoptical properties. Specifically, this spectroscopic technique extracts the real and imaginary indices of the organic layer for each wavelengthof interest. The SPRS sensitivity was calculated for several device architectures, metals, and layer thicknesses to optimize the organic filmabsorptivity measurements. Distinct optical absorption features were clearly observed for R6G layers as thin as a single molecular monolayerbetween two metal electrodes. This method also enables dynamic measurement of molecular conformation inside metallic junctions, as shownby following the optical switching of a thin spiropyran/polymer film upon exposure to UV light. Finally, optical and electrical measurementscan be made simultaneously to study the effect of electrical bias and current on molecular conformation, which may have significant impactin areas such as molecular and organic electronics.