Resonant Raman scattering on graphene: SERS and gap-mode TERS

Area of Science:

• Materials Science
• Nanotechnology
• Spectroscopy

Background:

• Nanoscale deformations in 2D materials impact electronic properties, necessitating high-resolution characterization techniques.
• Surface-enhanced Raman scattering (SERS) sensors are sensitive to structural variations in graphene.
• Existing methods struggle to resolve local defects and mechanical states in 2D materials.

Purpose of the Study:

• To demonstrate gap-mode tip-enhanced Raman Scattering (gm-TERS) for nanoscale probing of 2D material structure and mechanical state.
• To optimize gm-TERS parameters using SERS for enhanced signal and resolution.
• To characterize local strain and defects in graphene films.

Main Methods:

• Utilized gap-mode tip-enhanced Raman Scattering (gm-TERS) on a monolayer graphene film atop a plasmonic gold nanodisk array.
• Employed SERS to determine optimal gold nanodisk diameter and excitation wavelength for gm-TERS.
• Analyzed vibrational modes (G mode splitting) in gm-TERS spectra to detect and quantify local strain.

Main Results:

• Achieved a local plasmonic enhancement factor of 100 for graphene vibrational modes.
• Demonstrated a spatial resolution of 10 nm, enabling nanoscale chemical mapping.
• Detected local tensile mechanical strain in graphene, evidenced by G mode splitting (G+ and G-), estimating stress up to 1.5%.

Conclusions:

• Gap-mode TERS is a powerful tool for rapid and precise nanoscale characterization of local structural defects in 2D materials.
• The technique allows for the detection and quantification of mechanical strain in graphene.
• gm-TERS mapping holds significant potential for advancing the development of 2D material-based devices, such as SERS sensors.