Optical Properties of Electron-Beam-Induced-Deposition-Based Metamaterial

Katja Hoeflich Leuchs Division, Max Planck Institute for the Science of Light, Erlangen, Germany Institute of Nanoarchitectures for Energy Conversion, Helmholtz Centre Berlin for Materials and Energy, Berlin, Germany Paweł Woźniak Leuchs Division, Max Planck Institute for the Science of Light, Erlangen, Germany Institute of Optics, Information and Photonics, Friedrich-Alexander-University Erlangen-Nuernberg, Erlangen, Germany Gerald Broenstrup Leuchs Division, Max Planck Institute for the Science of Light, Erlangen, Germany Peter Banzer Leuchs Division, Max Planck Institute for the Science of Light, Erlangen, Germany Institute of Optics, Information and Photonics, Friedrich-Alexander-University Erlangen-Nuernberg, Erlangen, Germany Silke Christiansen Leuchs Division, Max Planck Institute for the Science of Light, Erlangen, Germany Institute of Nanoarchitectures for Energy Conversion, Helmholtz Centre Berlin for Materials and Energy, Berlin, Germany Gerd Leuchs Leuchs Division, Max Planck Institute for the Science of Light, Erlangen, Germany Institute of Optics, Information and Photonics, Friedrich-Alexander-University Erlangen-Nuernberg, Erlangen, Germany Caspar Haverkamp Leuchs Division, Max Planck Institute for the Science of Light, Erlangen, Germany Institute of Nanoarchitectures for Energy Conversion, Helmholtz Centre Berlin for Materials and Energy, Berlin, Germany

Electron beam induced deposition (EBID) is a fabrication technique using electron beam impact for the decomposition of locally inserted gas molecules into a vacuum chamber. Using a focused electron beam for direct writing provides access to the highly flexible fabrication of three-dimensional nanostructures on any conductive substrate in a single step process.
Such 3D nanostructures with sub-wavelength dimensions in the visible range have the potential for realizing intriguing nano-optical effects via the controlled manipulation of light at the nanoscale [1]. However, a detailed understanding and, thus, the ability for optimization of possible optical applications [2] requires the knowledge about the optical material response, i.e. the complex permittivity of the utilized materials.
For the case of the commonly used metal-organic compounds, deposited EBID materials are of granular structure with single-crystalline metal particles embedded in a carbonaceous matrix. Due to the serial processing, EBID layers are strongly restricted in size. Thus, their optical properties are not accessible by conventional ellipsometry. To retrieve the dielectric function of an EBID-material (here based on dimethyl-gold(III)-acetyl-acetonate), micro-sized in lateral dimensions layers of different nm-ranged thicknesses onto transparent conductive substrates were optically investigated. The experimental data from microscopic transmission and reflection measurements were then carefully analyzed by using a rigorous algorithm [3].
The retrieved permittivity shows a systematic dependence on the EBID layer thickness and a maximum in the imaginary part related to the absorptive resonance of the embedded gold nanoparticles. Given the increase of the carbon content with increasing deposition time in the present diffusion-limited deposition regime, the permittivity of the thinnest investigated EBID layer represents a realistic estimation for the optical response of nanostructures from EBID-material. Such investigations of the optical properties of EBID materials allow for the numerical and experimental study of complex nanostructures fabricated from this heterogeneous composite.

References
[1] K. Höflich, R. B. Yang, A. Berger, G. Leuchs, and S. Christiansen, Adv. Mater. 23, 2657-61 (2011).
[2] K. Höflich, M. Becker, G. Leuchs, and S. Christiansen, Nanotechnology 23, 185303 (2012).
[3] M. G. Moharam, D. A. Pommet, E. B. Grann, and T. K.Gaylord, J. Opt. Soc. Am. A 12, 1077 (1995).

caspar.haverkamp@mpl.mpg.de