Probing plasmon modes in metallic nanostructures by optics and fast electron excitations
The aim of this project is to study experimentally and theoretically metallic nanoparticles by optical extinction of set of particles and STEM-EELS spectroscopies of single particles to show differences and similarities in the spectral response of plasmon modes and, additionally, to propose applications in photovoltaics and energy saving windows.
Plasmonic nanostructures can be used in applications such as photovoltaic and energy saving windows. Recently, emerging solar cells are of great interest due to low fabrication costs, however they suffer of low efficiencies. Anisotropic scattering properties of plasmonic structures on a substrate offers a solution by creating antireflective coatings which generate the light trapping effect inside the substrate. Energy saving windows consists in the reduction of solar infrared radiation passing through a window. Several low-emissivity coatings exist in the industry like tin oxide thin films or metal thin films. These materials show high performance in the mid-infrared but allow to pass the near infrared. The use of nanoparticles with spectral signal in the near infrared are beneficial to bring an additional protection in the near infrared. Metallic nanoparticles manifest localized surface plasmon resonances which are collective oscillations of electron cloud and depend on size, shape and surrounding medium. In anisotropic plasmonic structures, two families of modes generally exist, transverse and longitudinal, and their spectral responses can be identified by optical measurements and easily interpretated in terms of light polarization. On the other hand, the spectral and spatial overlaps impede their separate measurement in conventional EELS. In this project, by exploiting the novel techniques and concepts introduced in electron spectroscopy, we propose two strategies enabling to overcome this difficulty and selective probe longitudinal and transverse modes. The first strategy is numeric and relies on morphing of nanostructure, rooted in the geometrical nature of localized surface plasmons. By changing the aspect ratio of nanostructures, the relative weight of plasmon modes is modified. The other strategy exploits the phase-matching between the electron beam and the plasmon excitation to enhance their coupling. This is achieved by rotating the nanostructure with respect to electron beam. The comparison of EELS data with optical measurements and theoretical simulations will allows to understand the plasmonic properties from a fundamental point of view.
- Alfredo Campos Otero - Investigador Principal (IP)
- Franck Antonio Aguilar Gómez (Estudiante)