High-Quality Surface Plasmon Polaritons in Large-Area Sodium Nanostructures

Area of Science:

• Materials Science
• Nanotechnology
• Optics

Background:

• Sodium (Na) is theoretically an excellent plasmonic material due to minimal optical loss in the visible to near-infrared (NIR) spectrum.
• Research on sodium plasmonics has been limited, hindering its practical application.

Purpose of the Study:

• To develop a scalable fabrication method for sodium (Na) nanostructures.
• To investigate the plasmonic properties of Na nanostructures, particularly their surface plasmon polariton (SPP) modes.
• To address the instability of Na in ambient conditions and demonstrate a stabilization strategy.

Main Methods:

• Fabrication of Na nanostructures using a combination of phase-shift photolithography and thermo-assisted spin-coating.
• Characterization of Na nanopit arrays with varying periodicities (300-600 nm).
• Development of a simple encapsulation strategy for stabilizing Na nanostructures.

Main Results:

• Successfully fabricated Na nanopit arrays with tunable SPP modes across the visible to NIR spectrum.
• Achieved narrow SPP resonances as low as 9.3 nm.
• Observed line width narrowing of resonances from visible to NIR, indicating suitability for NIR applications.
• Demonstrated stabilization of Na nanostructures in ambient conditions for over two months.

Conclusions:

• The developed fabrication method is scalable for producing Na nanostructures.
• Sodium is a promising low-cost, low-loss plasmonic material for nanophotonics and plasmon-enhanced applications.
• The encapsulation strategy effectively enhances the stability of Na nanostructures.