Seminars

2012-10-02

Applications of STEM/EELS to Plasmon-related Effects in Optical Spectroscopy

Asst. Prof. Jon P. Camden, University of Tennessee, Knoxville - Dept. of Chemistry
Speaker's Website
Asst.Prof. David J. Masiello, Dept. of Chemistry

A large number of optical phenomena rely on the unique ability of metallic nanostructures to concentrate light on length scales that are smaller than the diffraction limit of visible light. Noble metal nanoparticles such as silver and gold have optical properties that make them suitable for various applications including imaging beyond the diffraction limit, solar energy harvesting, and surface-enhanced spectroscopy. These special properties result from an excitation of the localized surface plasmon resonance (LSPR), which is a collective oscillation of the conduction band electrons. LSPRs are known to depend strongly on the size and shape of the nanostructure and can be excited by both electrons and photons. Recently, electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) has emerged as a technique capable of mapping plasmonic properties on a scale 100 times smaller than optical wavelengths. While this technique has great potential, the connection between electron-driven plasmons, encountered in EELS, and optically driven plasmons, encountered in plasmonic devices, is not well understood. Our research focuses on correlating optical spectroscopy and electron microscopy from the exact same nanostructures. Our approach is twofold. (1) We are imaging plasmon modes in single nanoparticle structures as well as nanoparticle aggregates and correlating these measurements with optical scattering measurements and fully 3D electrodynamics simulations of the exact same structures. (2) We seek to image directly the molecules that give rise to surface enhanced spectroscopies and establish their location relative to the plasmons which underlie these optical scattering spectroscopies.