Hyperbolic metamaterials (HMMs) consisting of alternating dielectric and metal layers are playing a key role in the field of nanophotonics due to their wide range of potential applications including thermal emission engineering, photonic density states engineering, super resolution imaging and sensing. Gold is a practical plasmonic material to fabricate HMMs in the visible to near- infrared range due to its high chemical stability. As a noble metal, Au needs an adhesion promoter and recently amino-propyl-trimethoxy-silane (APTMS) was used instead of metallic adhesion layers. We showed that these latter ones, classically Ti or Cr, increase the losses of the propagating plasmons as compared with APTMS. In this work, we have successfully fabricated and characterized HMMs with various number of periods . The gold layer was 10 nm and the dielectric 12 nm thick, thus allowing for hyperbolic dispersion in the near-infrared range. We have used APTMS adhesion layer on each interface between Au and alumina to provide a better adhesion and also to obtain high quality smooth layers. The Au and alumina layers were fabricated using sputtering and atomic layer deposition techniques, respectively. The use of these techniques helps to obtain a high HMM quality, having a final roughness of 0.80 nm RMS, even after the tenth period. Using these structures, we show that the effective medium approach (EMA) may be used even for a structures with as little as 3 periods. The optical characterization shows very good agreement with the theoretically predicted ones, both rigorous approach, as well as EMA ones.

Date Published: 17 September 2018
PDF
Proc. SPIE 10719, Metamaterials, Metadevices, and Metasystems 2018, 107192J (17 September 2018); doi: 10.1117/12.2319955

Published in SPIE Proceedings Vol. 10719:
Metamaterials, Metadevices, and Metasystems 2018
Nader Engheta; Mikhail A. Noginov; Nikolay I. Zheludev, Editor(s)