Alternative nano-lithographic tools for shell-isolated nanoparticle enhanced Raman spectroscopy substrates

Area of Science:

• Nanotechnology
• Surface Science
• Spectroscopy

Background:

• Metal nanoparticles (MNPs) are used as surface-enhanced Raman spectroscopy (SERS) substrates for reaction monitoring.
• Catalytically active MNPs can cause interference from side products.
• Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) uses insulating shells to prevent MNP catalysis, but achieving pin-hole-free shells with high enhancement is challenging.

Purpose of the Study:

• To explore alternative methods for fabricating shell-isolated plasmonic nanostructures for chemical sensing.
• To investigate combinations of chemical synthesis and lithographic techniques for SHINERS substrates.
• To evaluate the effectiveness of atomic layer deposition (ALD) for creating robust, pin-hole-free shells.

Main Methods:

• Comparison of three fabrication approaches: chemically synthesized MNPs with chemical shells, lithographic substrates with chemical shells, and lithographic substrates with ALD shells.
• Utilizing atomic layer deposition (ALD) for shell fabrication.
• Characterization of enhancement factors and verification of shell integrity using a gold etchant.

Main Results:

• Atomic layer deposition (ALD) enables the fabrication of controllable and reproducible pin-hole-free shells.
• Lithographic SHINER substrates coated with a 2.8 nm aluminum oxide shell achieved an enhancement factor of 7.5 × 10³ ± 17%.
• ALD-fabricated shells were confirmed to be pin-hole-free through etching experiments.

Conclusions:

• ALD is a superior method for creating pin-hole-free shells for SHINERS applications.
• Lithographically fabricated SHINER substrates offer a promising route for sensitive and selective chemical sensing.
• This work overcomes limitations in traditional SHINERS fabrication, enabling wider applications in catalysis and chemical analysis.