Single-Molecule Surface-Enhanced Raman Scattering: Can STEM/EELS Image Electromagnetic Hot Spots?
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- 作者：Nasrin Mirsaleh-Kohan ; Vighter Iberi ; Philip D. Simmons ; Jr. ; Nicholas W. Bigelow ; Alex Vaschillo ; Meng M. Rowland ; Michael D. Best ; Stephen J. Pennycook ; David J. Masiello ; Beth S. Guiton ; Jon P. Camden
- 刊名：The Journal of Physical Chemistry Letters
- 出版年：2012
- 出版时间：August 16, 2012
- 年：2012
- 卷：3
- 期：16
- 页码：2303-2309
- 全文大小：435K
- 年卷期：v.3,no.16(August 16, 2012)
- ISSN：1948-7185
文摘
Since the observation of single-molecule surface-enhanced Raman scattering (SMSERS) in 1997, questions regarding the nature of the electromagnetic hot spots responsible for such observations still persist. For the first time, we employ electron-energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) to obtain maps of the localized surface plasmon modes of SMSERS-active nanostructures, which are resolved in both space and energy. Single-molecule character is confirmed by the bianalyte approach using two isotopologues of Rhodamine 6G. Surprisingly, the STEM/EELS plasmon maps do not show any direct signature of an electromagnetic hot spot in the gaps between the nanoparticles. The origins of this observation are explored using a fully three-dimensional electrodynamics simulation of both the electron-energy-loss probability and the near-electric field enhancements. The calculations suggest that electron beam excitation of the hot spot is possible, but only when the electron beam is located outside of the junction region.