Au-Si plasmonic platforms: synthesis, structure and FDTD simulations.

Beilstein J Nanotechnol. 2018; 9: 2599–2608. Published online 2018 Sep 28. doi: 10.3762/bjnano.9.241 PMCID: PMC6176829 PMID: 30345219 Au–Si plasmonic platforms: synthesis, structure and FDTD simulations Anna Gapska,1 Marcin Łapiński,1 Paweł Syty,2 Wojciech Sadowski,1 Józef Eugeniusz Sienkiewicz,2 and Barbara Kościelska1 Anna Gapska 1Faculty of Applied Physics and Mathematics, Department of Solid State Physics, Gdansk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdansk, Poland Find articles by Anna Gapska Marcin Łapiński 1Faculty of Applied Physics and Mathematics, Department of Solid State Physics, Gdansk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdansk, Poland Find articles by Marcin Łapiński Paweł Syty 2Faculty of Applied Physics and Mathematics, Department of Theoretical Physics and Quantum Information, Gdansk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdansk, Poland Find articles by Paweł Syty Wojciech Sadowski 1Faculty of Applied Physics and Mathematics, Department of Solid State Physics, Gdansk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdansk, Poland Find articles by Wojciech Sadowski Józef Eugeniusz Sienkiewicz 2Faculty of Applied Physics and Mathematics, Department of Theoretical Physics and Quantum Information, Gdansk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdansk, Poland Find articles by Józef Eugeniusz Sienkiewicz Barbara Kościelska 1Faculty of Applied Physics and Mathematics, Department of Solid State Physics, Gdansk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdansk, Poland Find articles by Barbara Kościelska Ernst Meyer, Associate Editor Author information Article notes Copyright and License information Disclaimer 1Faculty of Applied Physics and Mathematics, Department of Solid State Physics, Gdansk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdansk, Poland 2Faculty of Applied Physics and Mathematics, Department of Theoretical Physics and Quantum Information, Gdansk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdansk, Poland Corresponding author. Barbara Kościelska: Received 2018 Jun 12; Accepted 2018 Sep 12. Copyright © 2018, Gapska et al.; licensee Beilstein-Institut. This is an Open Access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0). Please note that the reuse, redistribution and reproduction in particular requires that the authors and source are credited. The license is subject to the Beilstein Journal of Nanotechnology terms and conditions: (https://www.beilstein-journals.org/bjnano) Abstract Plasmonic platforms based on Au nanostructures have been successfully synthesized by directional solidification of a eutectic from Au and the substrate. In order to determine homogeneous shape and space distribution, the influence of annealing conditions and the initial thickness of the Au film on the nanostructures was analyzed. For the surface morphology studies, SEM and AFM measurements were performed. The structure of platforms was investigated using XRD and XPS methods. Structural investigations confirmed, that nanostructures consist of metallic Au, growing along the [111] direction. The most homogeneous seems to be the platform obtained by solidification of a 2.8 nm Au film, annealed at 550 °C for 15 min. This sample was subsequently chosen for theoretical calculations. Simulations of electromagnetic field propagation through the produced samples were performed using the finite-difference time domain (FDTD) method. The calculated absorbance, as a result of the FDTD simulation shows a quite good agreement with experimental data obtained in the UV–vis range. Keywords: Au plasmonic platforms, dewetting, eutectic, finite-difference time domain (FDTD) Introduction The evolution of metal thin films into nanostructures under various thermal conditions has been repeatedly studied for many years. However, the number of works on this subject has increased significantly over the last ten years. This is mainly due to technological needs related to the development of optoelectronics, photonics, electronics and energy conversion systems, fields in which metallic nanostructures found their application. Of course, this increase was closely related to the development of novel manufacturing technologies. One of the most interesting fields based on metal nanostructures is plasmonics. The use of plasmonic effects opens up many interesting possibilities, as for example photoluminescence intensification or subwavelength propagation. There are a lot of methods for the manufacturing of plasmonic platforms. Some of them are relatively simple and cost-effective, but sizes and shapes of the obtained metallic nanoparticles are not homogeneous. On the other hand, there are also methods that can yield more homogeneous distributions of nanostructures, but are far more complex and expensive, such as electron beam lithography. One promising technique that could be used to fabrication of plasmonic platforms is the method based on the directional solidification of eutectics. In this process, two or more phases can grow, depending on the phase equilibrium system. The formation of various geometries during eutectic solidification is also possible. In addition, the existence of a eutectic between the substrate, to which a metal in the form of a thin layer is applied, and the metal, significantly reduces the melting point of the metal. This is clearly visible in the case of the Au–Si eutectic, which has a melting temperature of ca. 363 °C [1–4]. It seems that in the case of directional solidification of eutectics as a method of manufacturing of nanostructures, the platforms are homogeneous. Unfortunately, as it can be found in literature, that eutectic-based growth may lead to an increase of inclusions of another phase in metallic structures [2,4–6]. When nanostructures are formed from thin metal films, directional eutectic growth is not the only process that needs to be considered. As-deposited thin films are most often metastable and can dewet or agglomerate with increase of temperature. During annealing of thin films, small fluctuations of the film thickness appear leading to the creation of voids in the film and their subsequent growth. This can happen well below melting temperature of the film so dewetting occurs while the film remains in the solid state. When the temperature of the system is increased up to the eutectic temperature, the solid–liquid transition takes place and liquid droplets remain on the support surface [2]. In plasmonics, one of the most commonly used metal is Au, characterized by a large number of free electrons, which leads to a high plasma frequency and a negative real permittivity over a wide range of frequencies. Taking into account the existence of a eutectic from Au and Si, wh (...truncated)