Abstract
We demonstrate high resonant absorption of visible light with a plasmonic nanocavity chain structure fabricated through resistless nanoimprinting in metal (RNIM). The RNIM approach provides a simple, reproducible, and accurate means to fabricate metallic nanopatterns with high fidelity. The nanocavities are shown to be efficiently excited using normally incident light, and the resonant wavelength can be controlled by either the width or the depth of the cavity. Numerical simulations confirm the experimental observations, and illustrate the behavior of the nanocavity chain waveguide and insensitivity to incident angle. The resonant absorption is due to the excitation of a localized metal-insulator-metal cavity mode. The interacting surface waves allow cavity lengths on the order of ten nanometers for light having a free space wavelength of about four hundred nanometers. Coupling of the cavities with an intervening surface plasmon wave results in a collective excitation and a chain waveguide mode that should prove valuable for more sensitive detection based on surface enhanced Raman scattering.
Highlights
Noble metals are good plasmonic materials, and they offer a complex dielectric constant at visible wavelengths with a relatively small imaginary component and a negative real part that provides for transverse magnetic surface waves
We demonstrate a plasmonic nanocavity chain structure using resistless nanoimprinting in metal (RNIM) [14]
When transverse magnetic (TM) light illuminates the structure, surface charges on the two opposite metal walls allow the narrow gap to excite the MIM waveguide mode [19], and this coupled surface waveguide mode resonates within the cavity, reflecting from the top and bottom of the cavity
Summary
Noble metals are good plasmonic materials, and they offer a complex dielectric constant at visible wavelengths with a relatively small imaginary component and a negative real part that provides for transverse magnetic surface waves. The use of extreme conditions is undesirable and not suitable for wafer-based processing An alternative to this is nanoimprint lithography, where a mold is used to mechanically deform a soft material by applying low pressure and low temperature [10]. While this has normally been used to pattern polymer resists, it has been used to directly pattern colloidal Au nanoparticles, allowing feature sizes down to about 100 nm to be achieved [11, 12]. It is important to use a low pressure and low temperature process that forms patterns on high quality metal films without any intermediate layers. The structure shows polarization sensitive and angular insensitive absorption, and has high field enhancement within the nanometer-scale cavity dimensionsshows the RNIM process flow
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