Near-Normal Incidence Dark-Field Microscopy: Applications to Nanoplasmonic Spectroscopy

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• 作者：Jonathan A. Fan ; Kui Bao ; J. Britt Lassiter ; Jiming Bao ; Naomi J. Halas ; Peter Nordlander ; Federico Capasso
• 刊名：Nano Letters
• 出版年：2012
• 出版时间：June 13, 2012
• 年：2012
• 卷：12
• 期：6
• 页码：2817-2821
• 全文大小：271K
• 年卷期：v.12,no.6(June 13, 2012)
• ISSN：1530-6992

文摘

The spectroscopic characterization of individual nanostructures is of fundamental importance to understanding a broad range of physical and chemical processes. One general and powerful technique that addresses this aim is dark-field microscopy, with which the scattered light from an individual structure can be analyzed with minimal background noise. We present the spectroscopic analysis of individual plasmonic nanostructures using dark-field illumination with incidence nearly normal to the substrate. We show that, compared to large incidence angle approaches, the near-normal incidence approach provides significantly higher signal-to-background ratios and reduced retardation field effects. To demonstrate the utility of this technique, we characterize an individual chemically synthesized gold nanoshell and a lithographically defined heptamer exhibiting a pronounced Fano-like resonance. We show that the line shape of the latter strongly depends on the incidence angle. Near-normal incidence dark-field microscopy can be used to characterize a broad range of molecules and nanostructures and can be adapted to most microscopy setups.

Keywords:

Dark field; nanoplasmonics; spectroscopy; polarization; Fano resonance; nanoshell