Surface-Enhanced Raman Spectroscopy on Hybrid Graphene/Gold Substrates near the Percolation Threshold

Area of Science:

• Materials Science
• Nanotechnology
• Spectroscopy

Background:

• Graphene's unique electronic properties make it suitable for advanced optical applications.
• Surface-enhanced Raman spectroscopy (SERS) requires substrates with high sensitivity and low background noise.
• Photoluminescence and fluorescence can interfere with SERS measurements, reducing signal quality.

Purpose of the Study:

• To investigate ultrathin gold films on graphene as SERS-active substrates.
• To compare the performance of hybrid graphene/gold substrates with conventional SERS substrates.
• To understand the role of the percolation threshold in SERS enhancement.

Main Methods:

• Fabrication of ultrathin gold films on monolayer CVD graphene via electron-beam deposition.
• Determination of the percolation threshold using sheet resistance and spectroscopic ellipsometry.
• Surface morphology analysis using scanning electron microscopy (SEM) and atomic force microscopy (AFM).
• SERS measurements using Crystal Violet dye.

Main Results:

• Maximum SERS signal enhancement observed near the percolation threshold of gold films.
• Figure of Merit (FOM) correlates with SERS enhancement, calculated from dielectric permittivity.
• Achieved SERS enhancement factor of approximately 10^5.
• Demonstrated graphene's ability to quench photoluminescence by ~60%.

Conclusions:

• Hybrid graphene/gold substrates offer superior SERS performance compared to conventional substrates.
• Optimizing gold film thickness near the percolation threshold is crucial for maximizing SERS enhancement.
• Graphene's photoluminescence quenching capability further improves the utility of these hybrid substrates for SERS.