Tips versus Holes: ×10 Higher Scattering in FIB-made Plasmonic Nanoscale Arrays for Spectral Imaging

Area of Science:

• Nanotechnology
• Plasmonics
• Surface-Enhanced Raman Spectroscopy (SERS)

Background:

• Plasmonic nanostructures are key components for advanced SERS imaging devices.
• Fabrication of desired nanostructures, particularly protrusions, using focused ion beam (FIB) presents challenges.

Purpose of the Study:

• To develop and demonstrate a FIB methodology for sculpting positive plasmonic nanostructures (protrusions).
• To experimentally compare the optical properties of FIB-generated nanoprotrusions and nanoholes.
• To evaluate the utility of hyperspectral microscopy for plasmonic imaging.

Main Methods:

• Gallium FIB was used to sculpt nanoprotrusions by removing surrounding material.
• Nanoprotrusions and nanoholes with varying aspect ratios were fabricated by controlling FIB dwell time.
• Optical absorption and scattering spectra were measured using a hyperspectral camera and analyzed.

Main Results:

• Scattered light intensity from nanoprotrusions was an order of magnitude higher than from nanoholes.
• Optical absorption and scattering spectra showed broad peaks similar to gold nanospheroids.
• Plasmonic resonance intensified and red-shifted with increasing nanostructure height.

Conclusions:

• FIB sculpting is an effective method for fabricating plasmonic nanoprotrusions for SERS imaging.
• Hyperspectral microscopy is a powerful tool for characterizing plasmonic nanostructures.
• Nanostructure geometry significantly influences plasmonic response, with implications for device design.