title: Single-Molecule Surface-Enhanced Raman Scattering: Can STEM/EELS Image Electromagnetic Hot Spots?
abstract: 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.
authors: †Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States.
authors: Nasrin
authors: N
authors: Mirsaleh-Kohan
authors: †Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States.
authors: Vighter
authors: V
authors: Iberi
authors: †Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States.
authors: Philip D
authors: PD
authors: Simmons
authors: ‡Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
authors: Nicholas W
authors: NW
authors: Bigelow
authors: ‡Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
authors: Alex
authors: A
authors: Vaschillo
authors: †Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States.
authors: Meng M
authors: MM
authors: Rowland
authors: †Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States.
authors: Michael D
authors: MD
authors: Best
authors: §Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.|∥Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States.
authors: Stephen J
authors: SJ
authors: Pennycook
authors: ‡Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
authors: David J
authors: DJ
authors: Masiello
authors: §Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.|⊥Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, United States.
authors: Beth S
authors: BS
authors: Guiton
authors: †Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States.
authors: Jon P
authors: JP
authors: Camden
keywords: EELS; LSPR; SMSERS; STEM; electromagnetic hot spots; plasmonics