Combining Electron Energy Loss Spectroscopy and Cathodoluminescence Spectroscopy for nanoplasmonics
The optical properties of metallic nanostructures are governed by surface plasmons, collective electron oscillations that localize the optical energy at nanometer spatial scales. Therefore, studying plasmons at the relevant length scales requires nanometer spatial resolution, which can be obtained with electron microscopy . In particular, Electron Energy Loss Spectroscopy (EELS) and CathodoLuminescence spectroscopy (CL) have become popular techniques to map plasmons .
EELS analyses the energy lost by a fast electron beam scattered by a sample, while CL analyses the light emitted following the scattering of a fast electron beam by a sample. Both of these techniques yield information about the plasmons locally excited by the fast electron beam. Thanks to the progress of instrumentation and theory over the last fifteen years, one can now analyze precisely and quantitatively EELS data from the near InfraRed to the UltraViolet . On the other hand, one can now characterize in depth the plasmon light emission through its radiation pattern and polarization using CL [4, 5]. However, despite their success, EELS alone and CL alone leave some critical questions about plasmons unanswered. Precisely, using one of these techniques brings limited information about the energy decay processes of plasmons, namely, absorption by the sample or light emission, or their coupling to light.
In this talk, I will discuss some new directions allowed when combining EELS and CL for nanoplasmonics. After introducing EELS and CL as separate tools, I will review recent combined experiments on single metallic nanoobjects. In particular, I will focus on experiments performed using a Scanning Transmission Electron Microscope (STEM) (Fig. 1) and supported by numerical simulations. I will discuss how the differences in the measured signals relate to the different natures of EELS and CL. I will discuss theoretically the quantities measured by EELS and CL. Finally, in the light of these first studies, I will mention the perspectives offered when using EELS and CL as complementary techniques.
Fig. 1. a. Sketch of a combined EELS and CL experiment using a Scanning Transmission Electron Microscope. b. EELS (blue) and CL (red) spectra measured at the tip of a 60 nm edge long nanoprism relying on graphene sheet. c. Spatial variations of the EELS and CL signals measured at the resonance energy of the spectra. Extracted from .
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I gratefully acknowledge my collaborators: Luiz F. Zagonel, Viktor Myroshnychenko, Benito Rodríguez-González, Marcel Tencé, Leonardo Scarabelli, Jens Förstner, Luis M. Liz-Marzán, F. Javier García de Abajo, Franz-Philip Schmidt, Ferdinand Hofer, Joachim Krenn and, last but not least, Odile Stéphan and Mathieu Kociak. The research leading to these results has received funding from the European Union Seventh Framework Programme [No. FP7/2007-2013] under Grant Agreement No. n312483 (ESTEEM2).