Abstract
Series of co-sputtered silver-indium tin oxide (Ag-ITO) films are systematically fabricated. By tuning the atomic ratio of silver, composite films are manifested to have different microstructures with limited silver amount (<3 at.%). Two stages for film morphology changing are proposed to describe different status and growth mechanisms. The introduction of silver improves the preferred orientations of In2O3 component significantly. Remarkably, dielectric permittivity of Ag-ITO films is highly adjustable, allowing the cross-over wavelengths λc to be changed by more than 300 nm through rapid post-annealing, and thus resulting in tunable epsilon-near-zero and plasmonic properties in the near-infrared region. Lower imaginary permittivity compared with pure metal films, as well as larger tunability in λc than pure ITO films suggest the potentiality of Ag-ITO films as substituted near-infrared plasmonic materials. Extended Maxwell-Garnett model is applied for effective medium approximation and the red-shifting of epsilon-near-zero region with the increase of silver content is well-fitted. Angle-variable prism coupling is carried out to reveal the surface plasmon polariton features of our films at optical communication wavelength. Broad dips in reflectance curves around 52–56° correspond to the SPP in Ag-ITO films.
Highlights
Lower imaginary permittivity compared with pure metal films, as well as larger tunability in λc than pure ITO films suggest the potentiality of Ag-ITO films as substituted near-infrared plasmonic materials
Alternative plasmonic materials to conventional noble metals have been the forefront of intense study during the last decades, since feasible devices based on metallic building elements are impeded by their inherent bottlenecks, such as dissipative ohmic losses, non-tunable optical properties, and incompatibility with standard nanofabrication processes [1,2,3]
The above results demonstrate a plasmonic material that can be controlled through composition and rapid post-annealing with extreme tunability of ENZ region and reasonable loss for applications
Summary
Alternative plasmonic materials to conventional noble metals have been the forefront of intense study during the last decades, since feasible devices based on metallic building elements are impeded by their inherent bottlenecks, such as dissipative ohmic losses, non-tunable optical properties, and incompatibility with standard nanofabrication processes [1,2,3]. Reports about composite films and their potential applications have attracted attentions in the past few years, such as tunable plasmonic metamaterials, nonlinear devices and mostly, modulated electrode component [25,26,27,28,29,30,31] Those theoretical and experimental results focused on visible [28,29], deep infrared [30], and terahertz [31] ranges. A comprehensive investigation of composite films operating around the telecommunication wavelength needs to be conducted, including structural analysis, growth mechanisms, optical analysis (permittivity, ENZ region, etc.), effective approximation for specific permittivity and ENZ-shifting simulation, as well as the verification of surface plasmons activated by 1550 nm light
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