Nanoplasmonics and nanophotonics with electrons
Mathieu Kociak
Laboratoire de Physique des Solides (UMR CNRS 8502), Bâtiment 510, Université Paris-Sud, 91405, Orsay, France
17:15 - 18:15 Tuesday 23 March 2010 TUG P2 How light behaves and interacts with matter the nanometer scale is a fascinating subject. Indeed, at the nanometer scale both the electromagnetic field and the electron wave functions may be subject to confinement. This is why the optical properties of nano-objects will in general depend drastically on their shape, size and local environment. This the case for surface plasmons on metallic nanoparticles, which can be viewed as classical electromagnetic standing waves, or for the excitons in quantum emitters (such as Quantum Dots), where the confinement now affects the electron wavefunction.
Obtaining spectroscopic information at the scale of a nanoparticle, or within the nanoparticle itself is not straightforward because the required spatial resolution can be one or two order of magnitude smaller than the equivalent wavelength of light in the vacuum. Such information is however crucial in many applications (for example biosensors for surface plasmons or photodetectors for excitons). The techniques using photons alone to probe optical properties of nanoparticles thus tend to be very difficult to use. An alternative is to use electrons, taking advantage that the Electron Energy Loss Spectroscopy (EELS) and the Cathodoluminescence (CL) spectroscopy can be roughly viewed as the nanometric analog to the optical absorption and the photoluminescence respectively.
In this talk, I will review few results obtained in a Scanning Transmission Electron Microscope (STEM) on the nanometer-scale optical properties of metallic nanoparticles and quantum emitters.
In a first part, I will describe how EELS in a STEM can be experimentally used to obtained spatially resolved spectral imaging on metallic nano-objects [1]. I will start from simple, highly crystalline nanoparticles (silver triangles and cubes) to top-down, highly unperfect structures (Split Ring Resonators), and put a special emphasis on the spatial coherence of plasmons in such nanoparticles [2,3]. I will draw the link between the EELS signal and the optical quantity of interest in near-field optical experiments, namely the Electromagnetic Local Density of States [4].
In a second part, I will present a new CL set-up we have developed and show how it can be used to probe optical properties of quantum emitters at the scale of quantum confinement – typically few nanometers. This will be exemplified on recent results on GaN/AlN composite nanowires [5].
[1] J. Nelayah, M. Kociak et al., Nature Physics, 3, 348 (2007)
[2] J. Nelayah, M. Kociak et al., Nano Letters, in press (2010)
[3] S. Mazzucco, M. Kociak et al., submited (2010)
[4] J. Garcia de Abajo and M. Kociak, Phys. Rev. Lett., 100, 106804 (2008)
[5] L. Zagonel et M. Kociak, in preparation (2010)
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