|Tuesday, July 19
Synthesis, characterization and optical properties of plasmonic supercrystals
* Florian Schulz, University of Hamburg, Germany
Felix Lehmkühler, Deutsches Elektronen-Synchrotron (DESY), Germany
Niclas S. Mueller, Freie Universität Berlin, Germany
Francesco Dallari, Deutsches Elektronen-Synchrotron (DESY), Germany
Sabrina Juergensen, Freie Universität Berlin, Germany
Eduardo B. Barros, Universidade Federal do Ceará, Brazil
Gerhard Grübel, Deutsches Elektronen-Synchrotron (DESY), Germany
Holger Lange, University of Hamburg, Germany
Wolfgang J. Parak, University of Hamburg, Germany
Stephanie Reich, Freie Universität Berlin, Germany
Superlattices of gold nanoparticles (AuNP) with diameters > 20 nm exhibit interesting optical properties. The periodic arrangement of the AuNP within the superlattices leads to new well-defined collective plasmon-polariton modes and with tailored geometries even deep strong light-matter coupling at room temperature is possible. To observe and study these phenomena a precise control of superlattice geometry is crucial. The robust synthesis of such quasicrystalline superlattices with large domain sizes will be presented. The supercrystals with a well-defined layered structure are studied with transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and X-ray cross-correlation analysis (XCCA). Their optical properties are characterized by micro-absorbance spectroscopy. The light-matter interaction of the supercrystals depends on their geometry: interparticle spacing, particle size, crystal structure and thickness. Controlling the geometry of the supercrystals therefore allows to tailor the light-matter interactions. The plasmonic coupling within the supercrystals results in a high density of “hot spots”, small volumes between the AuNP with strongly enhanced electric fields. This can be utilized for surface-enhanced spectroscopies and to tune absorbance and emission of intercalated materials. Future directions therefore include the incorporation of molecules and small nanoparticles into the supercrystals, the assembly of more complex structures like bimetallic nanoparticles and the synthesis of supercrystals with different crystal structures.
Templated Self-Assembly of Gold Nanoparticles onto Substrates: Periodic Arrays and Helical Structures
* David Vila-Liarte, CIC biomaGUNE, Spain
Dorota Grzelak, University of Warsaw, Poland
Agustín Mihi, Institut de Ciència de Materials de Barcelona (ICMAB), Spain
Wiktor Lewandowski, University of Warsaw, Poland
Luis M. Liz-Marzán, CIC biomaGUNE, Spain
Two different types of self-assembly of gold nanoparticles onto substrates have been achieved using either nanostructured PDMS or liquid crystal molecules as templates. In the first case, a periodic array of clusters made of assembled nanoparticles is obtained, giving access to near- and far-field plasmonic interactions. In the second example, helical nanofilaments drive the organization of gold nanoparticles into chiral structures with plasmonic circular dichroism.
Gold-platinum synergy for the plasmonic reduction of CO2 with water into methane
* Leila Hammoud, ICPEES (CNRS UMR 7515 / University of Strasbourg), France
Claire Strebler, ICPEES (CNRS UMR 7515 / University of Strasbourg), France
Valérie Keller, ICPEES (CNRS UMR 7515 / University of Strasbourg), France
Valérie Caps, ICPEES (CNRS UMR 7515 / University of Strasbourg), France
The gas phase photoreduction of CO2 with water can be achieved over wide gap semi-conductors. It can also be achieved by plasmonic excitation of gold nanoparticles (NPs), however leading to 100 times lower methane production rates. In this presentation, a systematic study of the effect of the Pt/Au ratio on the plasmonic performance of bimetallic AuPt/TiO2 composites will be described. It will be shown how a synergy between platinum and gold improves methane production rates by one order of magnitude.
Chiral nonlinear optical properties of ligated noble metal nanoclusters
* Joanna Olesiak-Banska, Wroclaw University of Science and Technology, Poland
Anna Pniakowska, Wroclaw University of Science and Technology, Poland
Marek Samoc, Wroclaw University of Science and Technology, Poland
Noble metal nanoclusters (NCs) are nanoparticles of the size <2nm, exhibiting a combination of molecule-like and nanocrystal properties. NCs present unique optical properties, also in nonlinear regime, where they offer enhanced multiphoton absorption cross-sections in comparison to organic and organometallic molecules. Here, the studies on chiral linear and nonlinear optical properties of gold nanoclusters are presented. In order to quantitatively describe chiral nonlinear optical properties, two-photon circular dichroism (TPCD) was determined with two-photon excited luminescence measurements with circularly-polarized light, in a wide range of wavelengths. Comparison of the concentration-independent values of one-photon anisotropy factor and TPCD reveals that TPCD is ~320 times stronger than one-photon anisotropy factor. Thus, two-photon excitation provides higher contrast mechanism in perspective applications such as chiral biomolecules imaging with nonlinear microscopy.
Searching for an Universal Standard to Evaluate Surface-Enhanced Raman Scattering (SERS) substrates
Arash Azarakhshi, University of Victoria, Canada
Tay Li-Lin, National Research Council Canada, Canada
* Alexandre Brolo, University of Victoria, Canada
This presentation will describe attempts to develop metrics for the evaluation of metallic nanostructured surfaces used as substrates for surface-enhanced Raman scattering. Measurements of SERS data at high and low concentrations of analytes were studied. Statistical approaches and computational methods were applied to generate a set of metrics used to compare two commercial SERS substrates.