A Closer Look at Monocrystalline Goldflakes for Plasmonic Applications

Thorsten Feichtner TDSU Photonic Nanostructures, MaxPlanck Institute for the Science of Light, Erlangen, Bavaria, Germany Materials for energy conversion, Helmholtz Centre Berlin for Materials and Energy, Berlin, Germany Muhammad Bashouti TDSU Photonic Nanostructures, MaxPlanck Institute for the Science of Light, Erlangen, Bavaria, Germany Björn Hoffmann TDSU Photonic Nanostructures, MaxPlanck Institute for the Science of Light, Erlangen, Bavaria, Germany Achmed Salaheldin Institute of Particle Technology, Friedrich-Alexander-University Erlangen-Nuernberg, Erlangen, Germany Mirza Mačković Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander-University Erlangen-Nuernberg, Erlangen, Germany Christel Dieker Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander-University Erlangen-Nuernberg, Erlangen, Germany Peter Richter Semiconductor Physics, Technische Universität Chemnitz, Chemnitz, Germany Ovidiu Gordan Semiconductor Physics, Technische Universität Chemnitz, Chemnitz, Germany Dietrich Zahn Semiconductor Physics, Technische Universität Chemnitz, Chemnitz, Germany Erdmann Spieker Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander-University Erlangen-Nuernberg, Erlangen, Germany Silke Christiansen TDSU Photonic Nanostructures, MaxPlanck Institute for the Science of Light, Erlangen, Bavaria, Germany Materials for energy conversion, Helmholtz Centre Berlin for Materials and Energy, Berlin, Germany

Wet-chemical synthesis of nm-thin gold flakes with large areas has become a viable method to realize flat, monocrystalline raw material for the fabrication of high quality plasmonic devices. Using transmission electron microscopy (TEM), self-synthesized flakes were proven to be defect-free and single crystalline except for twin boundary formation parallel to the flake surface. By means of micro-ellipsometry we determine their complex dielectric constant for the first time, showing their lower losses in comparision to evaporated gold or polished monocrystalline gold [1]. Focused ion beam (FIB) milling was used to thin down the flakes which were subsequently analyzed with electron backscatter diffraction (EBSD). The gold flakes remain monocrystalline down to a thickness of 10 nm allowing state of-the-art nanofabrication processing to obtain nano-antennas or other desired plasmonic structures at sizes and structure perfections impossible to be reached with evaporated, nano-crystalline gold thin films. Finally we show first tests in realizing "topographic" optical antennas, where flakes with several hundred nanometer thickness where used built optimized geometries with local variations in thickness.

[1] R. L. Olmon, B. Slovick, T. W. Johnson, D. Shelton, S.-H. Oh, G. D. Boreman, and M. B. Raschke, Phys. Rev. B 86, 235147 (2012).

thorsten.feichtner@mpl.mpg.de