Electron energy loss spectroscopy and cathodoluminescence as powerful tools for studying surface-plasmon modes in metal nanostructures

Myroshnychenko, Viktor, Nelayah, Jaysen, Stéphan, Odile, Kociak, Mathieu, Colliex, Christian, Adamo, Giorgio, MacDonald, Kevin F., Zheludev, Nikolay I., Carbó-Argibay, Enrique, Rodríguez-Fernández, Jessica, Liz-Marzán, Luis M. and García de Abajo, F.Javier (2010) Electron energy loss spectroscopy and cathodoluminescence as powerful tools for studying surface-plasmon modes in metal nanostructures. SPIE Photonics Europe, Brussels, Belgium. 11 - 15 Apr 2010.

Abstract

Metallic nanoparticles can interact strongly with external sources such as light or electron beam due to resonant excitation of surface plasmon modes which leads to strong electric field enhancements, particularly near edges and in gaps between metallic parts. The geometrical sensitivity of plasmon resonance allows one to play with size and shape of the particles in order to tune plasmon resonances to wavelengths of interest. This has given rise to an active research in finding new techniques for controlling size and shape of metallic nanoparticles.
The study of the near field associated with particle plasmons by optical means is limited by the low resolution. In contrast, the methods that are based on interaction of fast electrons with nanostructures allow one getting local information on plasmons with nanometer resolution. In particular, electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) provide powerful tools for studying plasmons in metal nanostructures. The maxima in the energy loss spectra of transmitted electrons and maxima in the emission of light reflect the energies of the particle-plasmon excitations to which they couple.
In the present work we provide the experimental and theoretical analysis of energy loss suffered by fast electrons passing through or near system of metallic nanoparticles of different shapes as well as the resulting CL emission spectra. The theoretical results are calculated using the boundary element method based upon rigorous solution of Maxwell's equations. Plasmon modes in the metallic nanoparticles are observed. The dependence of the loss and emission spectra on a particle morphology is explored. We also analyze the dependence of the spectral features on an electron-spot position for different particles morphologies. Our work demonstrates that the combination of the high spatial resolution of the transmission electron microscope and the high-energy resolution of a light detection system gives relevant information on optical modes.

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Contributors

Author: Kevin F. MacDonald

Author: Nikolay I. Zheludev

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