Template-stripped asymmetric metallic pyramids for tunable plasmonic nanofocusing

Area of Science:

• Plasmonics
• Nanophotonics
• Optical Engineering

Background:

• Plasmonic nanofocusing is crucial for nanoscale optical manipulation.
• Existing methods often face limitations in efficiency and scalability.
• Achieving controlled plasmon generation and interference is key.

Purpose of the Study:

• To demonstrate a novel scheme for plasmonic nanofocusing using internally illuminated asymmetric metallic pyramidal tips.
• To enable the generation of nanoscale optical hotspots with high efficiency.
• To explore applications in near-field optical microscopy and optical trapping.

Main Methods:

• Fabrication of wafer-scale arrays of sharp metallic pyramids via template stripping.
• One-step angled metal deposition to create structural asymmetry.
• Internal illumination with linearly polarized light for Kretschmann-like coupling.

Main Results:

• Asymmetric pyramids enable plasmon convergence at the apex, creating nanoscale hotspots.
• Symmetric pyramids exhibit destructive plasmon interference, hindering focusing.
• Computer simulations and far-field experiments confirm efficient optical energy focusing into nanoscale volumes.
• Demonstrated large field enhancements and angle-dependent spectral tuning.

Conclusions:

• The demonstrated asymmetric pyramidal tips provide an effective method for plasmonic nanofocusing.
• The technique offers low background light, wafer-scale fabrication, and a straightforward excitation scheme.
• These asymmetric tips are promising for near-field optical microscopy and array-based optical trapping.