Plasmonic Nanospectrocopy of Individual Nanoparticles - Studies of Metal-Hydrogen Interactions and Catalysis

Abstract: Localized surface plasmon resonance (LSPR) is the phenomenon of collective oscillation of conduction electrons in metal nanoparticles smaller than the wavelength of light used for the excitation. Plasmonic metal nanoparticles are able to confine light to extremely small volumes around them, i.e. below the diffraction limit. This gives rise to strongly localized and enhanced electromagnetic fields in so-called “hot spots” of the plasmonic nanoparticle. These hot spots are advantageous for sensing, as well as enhancing surface processes, since any object inserted in the hot spot will influence the optical resonance of the system via coupling to the local field. Placing a well-defined nanoobject in the hot spot of a plasmonic nanoantenna offers, thus, unique possibilities to obtain detailed information about the role of specific features (e.g. facets, size, shape or relative abundance of low-coordinated sites) of that particle for its functionality/activity at the single particle level. Consequently, there is an increasing interest to use plasmonic antennas as an in situ tool to investigate physical/chemical processes in/on single functional nanomaterials. Single particle measurements are possible with the use of dark-field scattering spectroscopy, since plasmonic nanoparticles efficiently scatter light and are easily observable in the dark-field microscope. In this context, this work was dedicated to: i) Development of fabrication methods for making plasmonic nanoantenna structures with the possibility to place a nanoparticle of interest (e.g. a hydride former or a catalyst) in the hot spot of the antenna, as well as fabrication methods for accommodation of protecting layers for the antenna via complete encapsulation in a core-shell scheme. ii) Investigation of the role of size, shape, defects and microstructure in hydride formation thermodynamics of single-crystalline and polycrystalline palladium (Pd) nanoparticles. iii) Application of the developed fabrication schemes and experimental strategies to the investigation of (photo)catalytic reactions at the single particle level.